Optimization of Maintenance Programmes at NPPs

Transcription

1 Optimization of Maintenance Programmes at NPPs Benchmarking study on implemented organizational Schemes, Advanced Methods and Strategies for Maintenance Optimization Summary Report Paolo CONTRI, Giustino MANNA, Vesselina RANGUELOVA, Claude RIEG & Michel BIETH DG JRC Institute for Energy Safety of Eastern European Type Nuclear Facilities EUR EN

2 Mission of the Institute for Energy The Institute for Energy provides scientific and technical support for the conception, development, implementation and monitoring of community policies related to energy. Special emphasis is given to the security of energy supply and to sustainable and safe energy production. European Commission Directorate-General Joint Research Centre (DG JRC) Institute for Energy, Petten (the Netherlands) Contact details: Michel Bièth Tel.: +31 (0) Legal Notice Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use which might be made of this publication. The use of trademarks in this publication does not constitute an endorsement by the European Commission. The views expressed in this publication are the sole responsibility of the author and do not necessarily reflect the views of the European Commission. European Communities, 2006 Reproduction is authorised provided the source is acknowledged. Printed in the Netherlands, DG JRC, Institute for Energy, PR & Communication

3 Maintenance Optimization of NPPs BENCHMARKING STUDY ON IMPLEMENTED ORGANIZATION SCHEMES, ADVANCED METHODS AND STRATEGIES FOR MAINTENANCE OPTIMIZATION Summary Report Paolo CONTRI, Guistino MANNA, Vesselina RANGUELOVA, Claude RIEG & Michel BIETH DG JRC Institute for Energy 1

4 Executive Sumary This report summarizes the results of Task 1 (Summary of maintenance optimization programmes in SENUF Member Countries) of the SENUF (Safety of eastern European type NUclear Facilities) network, carried out in It is focused on the analysis of a Questionnaire on the Optimisation of the Maintenance Programs for Nuclear Power Plants. Other sources of information from other Countries with advanced experience in maintenance programmes are also analysed, in order to develop a proposal for further R&D in the SENUF framework. State-of-the-art practice in maintenance optimization, i.e. predictive maintenance based on monitoring component condition, reliability centred maintenance, and risk-informed maintenance in the NPPs of the collaborating parties are discussed to identify differences and commonalities in the Western and Eastern European practice, and based on this evaluation, to identify areas for further collaboration with the EC/JRC. The report shows that improved maintenance programmes could effectively meet the challenges posed by the new socio-economical framework where the nuclear plants have to operate, i.e. market liberalization and long term operation of the plants. All Countries facing the above mentioned scenarios are spending their best efforts in the improvement of the maintenance programmes in the following areas: a) human factors, b) reliability centred programmes and c) trend analysis of degradation mechanisms in the long term, which could definitely support the evolution of the actual maintenance programmes in the direction required by the new challenges. However, many practical issues still have to be solved before a broad application of the proposed techniques is completed. Therefore an extra effort is needed, particularly in relation to the WWER plants, to make the predictive maintenance approach (risk centred) fully applicable to these installations. The effort should comprise R&D on material degradation mechanisms and applicability of probabilistic tools, but also organizational actions and improved consideration of human factors. In conclusion, the report proposes that the next R&D effort of the SENUF initiative should be spent at two different levels: 1. At the organizational level, covering the integration among existing programmes, management of human factors, definition of feedback loops and interactions between programmes, decision-making process (either risk informed or not). 2

5 2. At the technical level, improving the applicability of existing pioneering techniques to other existing plants, especially WWERs, where many practical issues appear to provide even additional challenges on their implementation. It is the case of the investigation of ageing and degradation mechanisms for WWER components, of the simplified use of probabilistic tools for condition based maintenance and risk informed inspections (when PSA is not available at the plant), of the use of reliability concepts for performance goal setting and monitoring, and of their trending in time. 3. At the communication level, providing a suitable forum for experience exchange on the daily maintenance issues, even in the currently applied framework of a generic preventive maintenance system. The report proposes follow-up actions in relation to these levels, and suggests exercises and case studies which could be built in a concrete action plan for R&D in the specified areas. 3

6 Table of Content 1 Introduction Background Objectives Document structure The SENUF questionnaire on advanced strategies to optimize NPP maintenance General Analysis of the questionnaires Conclusions on the questionnaire and preliminary identification of the R&D needs Organizational challenges in optimized maintenance of Nuclear Power Plants Background Proposals for R&D Reliability Centered Maintenance Background Use of Probabilistic Safety Assessment in support of maintenance optimization PSA applications PSA technical and quality attributes needed to support riskinformed maintenance optimization Country experience with RCM US NRC framework for risk informed decision making East and Central European Countries experience with risk informed maintenance optimization Spanish Experience with RCM The maintenance programme in long term operation perspective Background Experience at the IAEA Experience in Spain Experience in Finland Experience in the USA Conclusions and proposals for R&D tasks in SENUF...40 References...44 List of Abbreviations

7 1 Introduction 1.1 Background The SENUF (Safety of eastern European type NUclear Facilities) network, as a new European initiative integrated into the JRC/IE s existing nuclear safety related SAFELIFE action, was established in 2003 [1,2] to facilitate the harmonization of safety cultures between the Candidate Countries (CCs) and the European Union (EU), the understanding of needs to improve the nuclear safety in CCs, and the dissemination of JRC-IE nuclear safety institutional activities to CCs. SENUF is integrated into SAFELIFE. SAFELIFE provides an integrated approach to R&D activities on critical issues for plant life management of ageing nuclear power installations. The focus is on establishing European best-practices for deterministic and risk-informed structural integrity assessment of key components considering all nuclear power plant (NPP) designs both western and Russian-type. It exploits the Institute of Energy (IE) existing competence in characterization of materials degradation, defect assessment, non-destructive testing, neutron methods and advanced modelling techniques for residual stress analysis, as well as developing appropriate new areas expertise. The activity is organized as a series of major work packages addressing the key primary circuit components: Reactor Pressure Vessel and Internals. A special series of work packages cover specific topics, namely: weld characterization, maintenance methods; development of risk-informed methods, ND methods and testing, human factor influence, development of novel facilities. In particular, the work package 5 addresses the optimization of the maintenance methods and relies on the activities of the network SENUF. The SENUF activities started in 2003 [2], after an organizational meeting of the interested parties held in Petten on July 3-4, 2003 [1]. The Working Group on ''Safety of Nuclear Facilities in Eastern Europe dedicated to Nuclear Power Plant Maintenance, hereinafter referred to as SENUF-WG-NPPM, was founded with the following objectives: a) Review and identification of the remaining open (generic/specific) maintenance related issues, b) Promotion of well designed and prepared maintenance plans for systems, structures and components, c) Support for the implementation of advanced maintenance approaches, including implementation of preventive (condition based) maintenance as well as preventive mitigation measures, d) Evaluation of the advanced risk informed maintenance approach and provision of assistance in its implementation. 5

8 The following Countries/Organizations showed interest in the group activity: Belgium (Tractebel), Bulgaria (Kozloduy NPP), Czech Rep. (Dukovany and Temelin NPP), Finland (Loviisa NPP), France (EDF), Hungary (Paks NPP), Lithuania (Ignalina NPP), Romania (Citon), Russian Federation (Rosenergoatom), Slovakia (Bohunice and Mochovce NPP), Slovenia (Krsko NPP), Spain (Endesa), Ukraine (Energoatom). The first Steering Committee meeting was held on September 27-28, 2003 in Petten [3]. Before the first Steering Committee meeting in 2003, nine Institutes/Organisations signed the SENUF Collaboration Agreement. In the period between the first and second Steering Committee meeting the Bulgarian NPP Kozloduy and RAAN/SITON (Subsidiary of Technology and Engineering for Nuclear Projects - Romania) joined the network. Energoatom (Ukraine) also joined the network in The current composition of the network is shown in the table below. Organisations Country Date of signature 1 Kozloduy NPP Bulgaria 12/11/ Framatome ANP Germany 22/12/ Paks NPP Hungary 22/12/ Ignalina NPP Lithuania 28/10/ RAAN/SITON Romania 22/12/ VNIIAES Russian 22/12/2003 Federation 7 Bohunice NPP Slovakia 22/12/ Mochovce NPP Slovakia 22/12/ Krsko NPP Slovenia 22/12/ Endesa Genercion Spain 22/12/ Energoatom Ukraine 27/09/2005 A background report was developed in 2004 on Nuclear power plant maintenance in the CIS and CEEC [5]. The report collected and evaluated the available and applied maintenance methods at NPPs of acceding and candidate countries to the European Union (ACCs) as well as of the wider Europe (covering Russian Federation and Ukraine), and based on this evaluation, preliminary identified areas for further collaboration with them. The second Steering Committee Meeting was held on October 28-29, 2004 in Madrid [4]. The activity of the network in relation to maintenance optimization was planned in three tasks, as explained below. This summary Report on Benchmarking study on implemented organizational Schemes, Advanced Methods and Strategies for Optimization of the Maintenance Activities represents the main deliverable of Task 1; it is preliminary to the implementation of more advanced tasks on the Development 6

9 of a database on Advanced and special tools, equipment, materials and processes (Task 2) and the development of a State-of-the-art Report on Reliability Centred Maintenance (Task 3). This report summarizes the results of the Task 1 of SENUF and merges them with other sources of information on the experience in Countries with advanced experience in maintenance programmes in order to develop a proposal for further R&D in the SENUF framework. 1.2 Objectives The objectives of the current report are the following: To analyze and summarize the existing strategies on NPP maintenance optimization, i.e. predictive maintenance based on monitoring component condition, reliability centred maintenance, and risk-informed maintenance in the NPPs of the collaborating parties; To identify differences and commonalities in the Western and Eastern European practice, and based on this evaluation, to identify areas for further collaboration with the EC/JRC. This document was written for the SENUF Members, to drive the next R&D tasks of the network. However, the report is also open to the engineering Community, with the aim of triggering a broader debate on these issues and on the need for support actions at the EC level. 1.3 Document structure The first part of this report (Chapter 2) deals with the analysis and synthesis of the questionnaires received by the SENUF members. Chapters 3 to 6 discuss areas of potential further activity of the network, providing some background information for the state-of-art in the engineering community. 1.4 Acknowledgments This report is mainly based on the analysis of the result of a questionnaire on Advanced strategies to optimise maintenance, which was filled in by nine SENUF partners. Their contribution to this research is deeply acknowledged, as it provides a solid basis from the daily operation life to the R&D in the maintenance field. 7

10 2 The SENUF questionnaire on advanced strategies to optimize NPP maintenance 2.1 General A questionnaire on Advanced Strategies to optimize maintenance was developed at the IE, with the cooperation of some SENUF partners, and it was delivered to all the SENUF partners in February The objective of the questionnaire was to explore the methods in use in the plant operating community to develop, implement, support, and justify various maintenance processes. The intention of the study was not to rate the relevant plant management or their maintenance concepts and practices, but rather to establish an overall impression of the character of the maintenance approach and organization. The questions covered the following 13 areas. Their selection was carried out on the basis of common approaches in the plant operating community, codified for example in the document [27]: 1. Background information on the plant; 2. Maintenance management; 3. Types of maintenance; 4. Maintenance optimization process; 5. Intolerance for equipment problems; 6. Long-range focus; 7. Maintenance personnel knowledge and skills; 8. Efficient and effective work management processes; 9. Maintenance procedures; 10. Maintenance facilities, tools and equipment; 11. Procurement of parts, material and services; 12. Maintenance history; 13. Area for improvement. Nine Organizations / Plants (Paks NPP, Bohunice NPP, Mochovce NPP, Ignalina NPP, Krsko NPP, Biblis NPP, CITON, Endesa PWR, Endesa BWR) filled the questionnaire. In total, it can be said that the experience of a broad range of nuclear plant types was transferred to the questionnaires, with few representatives each, namely: PWRs (incl. WWERs) LWGRs (incl. RBMK) BWRs PHWR (inc. Candu). It has to be noted that, unfortunately, neither Russian nor Ukrainian operating organizations sent the questionnaire. Therefore, the conclusions described in the next sections may not be fully applicable to any single family 8

11 of reactors, either WWERs or others, but they have to be considered as representative of a broad population of European reactor types. The following chapter shows an analysis of the questionnaires, preliminary to the final evaluation and the identification of priorities and future actions. 2.2 Analysis of the questionnaires The aim of Chapter 1 was twofold: trending the plant performance in the last five years as a result of the recent generalized effort in maintenance optimization, and providing some information on the organization at the maintenance department. The participants provided only few indicators. The load factors are shown in Fig. 1. The Organization in the maintenance departments ended out very diversified. The most common organizational structures are the following: Maintenance Manager (MM) reports to the plant manager (PM); MM reports to Technical Deputy of PM; MM reports to Operations Manager; Divisions of Reactor, Turbine, Electrical, etc. own both operation and maintenance (REA, Ignalina NPP). Also the role of the Component / System Engineer was very diversified among the represented plants. The aim of Chapter 2 was to investigate the management structure and procedures, through analysis of the following issues: 1. Maintenance objectives and goals; 2. Lines of communication; 3. Procedures; 4. Monitoring, indicators of programme effectiveness and selfassessment tasks; 5. Regulatory control. In general, the following can be said on the questionnaire answers: All plants have clearly defined plant policy / strategies under which high quality maintenance is required; General Goals and Objectives are related to smooth plant operation, or in some cases (three plants) to lower level maintenance activities; Communication lines are both vertical and/or horizontal; Long-range planning and monitoring of the maintenance programme is considered essential for all plants; All plants make a distinction between actual work monitoring and long-term effectiveness of the programme. Self 9

12 Assessment, Root-cause analysis, Trend analysis, are the most used techniques to monitor long term effectiveness of maintenance activities, while performance indicators are generally used in the short term work monitoring; Regulatory body monitoring is related to control of the Maintenance Rule implementation (plants following NRC approaches), for others just general regulatory oversight process is applied. No examples of master lists were provided and therefore it was difficult to appreciate the priorities given to the components in relation to their safety significance. However, from many qualitative statements it can be concluded that all plants do apply the safety classification in the development of the master list. As a generic evaluation of the answers, it can be noted that the criteria for maintenance activities prioritization are still very different, with a potential different impact on the plant safety. Also the maintenance effectiveness indicators/ parameters are still very different: only few attempts are in place towards a risk-informed approach. At last, the human performance reliability in relation to the maintenance programme is also very differentiated and could be improved, as in some plants it is at a very basic level. The aim of Chapter 3 was to understand the most common approach to maintenance in place at the plants: in particular preventive (time or condition based) versus corrective, and to evaluate the relevant implementation techniques. In general, it can be observed that the time based preventive approach is still dominant. The few cases of predictive (condition based) procedures are considered part of preventive approaches. The ratio between preventive and corrective procedures is rather uneven, ranging between twenty and one. The basis for the preventive maintenance procedures was declared as in the following: Manufacturers recommendations (design document); Component history (failure rate analysis); Engineering judgment; Regulatory requirements; Owner s group information; ALARA principle. The aim of Chapter 4 was to investigate approaches and techniques for maintenance optimization. In few cases, Reliability Centred Maintenance (RCM) is applied. However, it is usually in the framework of pilot projects and in relaxed form. The most widely used goals for the optimization process are the following: 10

13 Maximizing safety; Maximizing component reliability (plant availability); Reducing maintenance costs; Guarantee long-term operation; Dose control. The aim of Chapter 5 was to understand the common practice in the analysis of the failure of critical components, the data recording systems, the re-qualification procedures, the on-line maintenance criteria, and the definition of the component failure data (for probabilistic assessment, etc.). According to the questionnaires, root cause analysis, and trend analysis are in place everywhere. Databases on equipment failure are maintained at each plant; however differences appear to be significant in the amount, form and usability of the data stored. No information is available on the collection of the so-called near miss events that receive more and more attention as operational safety indicators. Concerning the tools used to monitor the plant operational parameters, almost all plants declare real time signals connected to monitoring. No information is provided in the questionnaires on the quality of the available failure data; data of insufficient quality cannot be used for both trend analysis and even probabilistic assessment of the system vulnerability. Actually the equipment failure criteria are based on combination of manufacturer s information, engineering analyses, operational experience and generic PSA evaluations. Few teams developed a systematic collection of component reliability data; among them Cernavoda NPP, which uses those data for updating the Plant PSA. Most of the plants showed preference for interchangeable spare components, which guarantee cost and time optimization. On-line preventive maintenance is implemented in different ways among the analyzed plants, as in the following: In few equipment out of the scope of TS ( 3 plants); To all equipment, in accordance with TS (2 plants); To equipment out of the scope of safeguard systems (but what is the definition of safeguard systems?), in all possible circumstances (1 plant); To all equipment, in accordance with operating limits and conditions (OLC) and PSA (2 plants); To all the safety systems, in accordance with the TS (1 plant). However, the interpretation of the questionnaires was sometimes difficult, as it was not clear whether they address only preventive or both preventive and corrective activities (for example carried out during the outage time). The aim of Chapter 6 was to investigate the long-term framework of the maintenance activities performed at the various plants. The long-term objective is a generic feature of all the maintenance programmes. In particular component reliability is a generic issue to 11

14 guarantee investment protection and increase of electricity output. All of the plants (6 out of 9) that have answered the question on LTO are considering possible years of extension of the original plant lifetime. The long term outage planning is very different and it varies from 1 to 12 years, but most of the plants adopt a 10-year cycle. All plants are in favour of strong long-lasting partnership with the original manufacturers in order to provide a reliable supply of original spare parts. The common percent rate of return workers from outage to outage is 50-70%. The aim of Chapter 7 was to investigate the procedures for personnel training. All plants declared that the training tasks represent an essential part of the entire training programme. It is composed of both initial and periodical refreshing training sessions and covers all relevant areas. The type of training provided can be: On-the-job (OJT); In the simulator (mock-up); In classroom; At vendor facilities. Contractors training is carried out in most cases. As a result, a strong sense of ownership among the maintenance responsible people was highlighted as important (7 out of 9); however no much experience is available to assess the actual impact (3 out of 7). The aim of Chapter 8 was to investigate the management of the maintenance: responsibilities, coordination, sequences, and approval. The maintenance work is triggered by different mechanisms in the various plants. At some plants, a very integrated system keeps under control many sources, such as: record-keeping of component failures, results of investigations required by the safety authority, results of generic inspections, result of pressure tests, results from the analysis of emergency actions, material tests and other surveillance programs, analysis of the operational history, works postponed from the previous outage maintenance periods, work-requests from fellow-organizations, lessons learned during the previous outage maintenance works. Conversely, the coordination mechanisms between the different division/units involved in the implementation is quite similar and it foresees periodic meetings under the supervision of the maintenance department specialists. In some cases the proposed work packages are assessed by an Integrated Assessment Group. In some cases the level of planning is defined by the estimated relevance and impact on safety of the planned work. This assessment is carried out on the basis of a detailed analysis of the work scope, risk analysis and 12

15 experiences review. In case of especially complex works, which are not covered by existing procedures, a safety evaluation is preliminarily carried out, followed by a full scope risk analysis and complete pre-job briefing in accordance with the procedure for Important Occasional Activities. Equipment which underwent a maintenance activity are generally tested before operation, at all plants. However, there is a different coverage of such post maintenance testing procedures and also the testing methods look different. This appears to be a field where further experience exchange may be beneficial, particularly when lack of spare parts compels to rework some components, or when the acceptance criteria have been changed. The aim of Chapter 9 was to investigate the framework, development, validation and enforcement of the maintenance procedures. Most of the plants have a preventive type maintenance system. Procedures are periodically reviewed (common periodicity is 3-5 years) and the vendors manual are integral part of them, almost always, and therefore are also periodically reviewed. Acceptance criteria are periodically reviewed by third parties; however, not many details are provided in the questionnaire on how such a review is carried out. The aim of Chapter 10 was to investigate the availability and use of tools and facilities for maintenance at the various sites. Most of the Utilities have centralised training centres. Many plants have very well equipped centres, even with full scale simulators. The aim of Chapter 11 was to investigate the procedures for procurement of spare parts and services. In general, the procurement is managed by dedicated units. In most cases the acceptance criteria are typical commercial criteria, not plant specific. There are no mentioned cases of shared spare parts among NPPs in different Organisations. All plants developed acceptance criteria and testing procedures for components reworked, sometimes even with different materials from the original. The issue of the partnership with the suppliers was very well addressed in the document [5]; the questionnaire did not add anything relevant to this concern. The aim of Chapter 12 was to investigate the procedures for recording the maintenance history. It is almost general practice to have computerised systems for the maintenance archive, where in some cases very detailed information is stored. Sometimes it is not clear if such amount of data is really used for the improvement of the procedures and for the optimisation of the maintenance planning. There is no mention of the use of maintenance indicators evaluated on the basis of such large data bases. 13

16 The aim of Chapter 13 was to identify both the areas of good practice and the areas for improvement of the maintenance programmes. Concerning the best practice, the following can be recorded: On-line maintenance (Spanish BWRs); Creative maintenance staff (Paks NPP); Field inspection, Metrology Lab (Cernavoda NPP); ISI, thermography, prophylactic measurement, sealing programme (Bohunice NPP); Work co-ordination & management system, personnel training & qualification, in-house technical capability (Mochovce NPP); Maintenance optimization programme (Krsko NPP); Special training, self-assessment of plant departments and contractors (Ignalina NPP). Concerning the areas of improvement, the following can be recorded: Introducing condition monitoring; Focusing on long-term operation. Reducing human factor impact. Analysing and improving post maintenance testing procedures. Developing network for spare parts sharing. Utilizing/extending maintenance performance indicators. Improving maintenance history record. Establishing partnership with contractors. Eliminating over/under-maintenance. Installing maintenance training centre; Improving procedure quality; Reducing collective dose. The next chapters provide further analysis of the data presented here, with additional information on the practice in other Countries not participating to SENUF, in order to identify the R&D needs to be addressed in the next SENUF actions. 3 Conclusions on the questionnaire and preliminary identification of the R&D needs The questionnaires clearly indicated the trend for the optimization of the maintenance programmes. The analysis of the identified areas for improvements and where R&D is needed leads to two main groups of issues: organizational issues (quality of the procedures, training centres, outage optimization, partnerships with the contractors, etc.) and methodological/conceptual issues (human factors, reliability centred maintenance, long term operation). These are the issues to be addressed in future R&D programmes; background and state-ofthe-art studies should trigger specific research actions aimed at providing reliable tools and methods for application to real cases. The above-mentioned need is connected to two fast developing scenarios: 14

17 1. The open electricity market, which is going to be a reality in most of the European Countries in few years. Such economical and financial framework demands for significant reduction of the generation costs, very strict investment planning, controlled reliability of the equipment and components and therefore for reliable indicators of the effectiveness of the maintenance programmes; 2. The generic trend towards the extension of the operating life of the existing plants. Such life extension requires a detailed review of the original design assumptions, also reflected into current maintenance practice, and the continuous monitoring of the component reliability (performance goals) in order to support a suitable trend of the safety evaluation beyond the design life. To cope with these scenarios, it is highlighted in many questionnaires how this effort on maintenance optimization should be carried out by the power generating organizations at large and should not be confined to few technical and maintenance departments at a plant. The change in the maintenance approach that is required by the new socioeconomical framework requires also a more global view of the traditionally restricted maintenance issues. New programmes are launched in many countries, which are transversal programmes, cross cutting existing programmes. It is the case of the Ageing Management Programme (AMP) that very often is reduced to coordination among existing programmes such as maintenance, ISI, operation, etc. [6,13]. In some Countries even broader umbrella programmes are launched, such as the Configuration Management programme (CMP), which aims at the consistency between the following three elements [12]:? 1. The design intent and detailed design documentation? 2. The operating and maintenance procedures 3. The plant configuration The interesting contribution of this model to the plant safety is the coordination among design maintenance and operation, supported by a robust analysis of the safety margins, as shown in Fig.3. The crucial issue identified by the CM is the control of the safety margin assumed by design and its fluctuation during the plant life, as a consequence of construction issues, design changes, operation, ageing and maintenance [64]. In conclusion, it appears that state-of-the-art maintenance programmes should both include a more explicit control of the safety performance of the SSCs and address organisational issues, which proved to be crucial in the reliability of the whole programmes. The following areas represent recurrent areas where Utilities and Regulatory Bodies spent considerable efforts in recent years in the attempt to improve the approach to the maintenance issues, namely: 1. Organizational factors, in order to improve the character of crosscutting issue of the maintenance programme, where all the available 15

18 information on SSCs have to concur to the overall control of the plant safety; 2. Reliability centred maintenance, where risk related information support the control of the overall plant safety; 3. Long term operation, where improved control of material and component ageing needs close interfaces with the maintenance programme to support the safe plant performance in time. In this sense, the questionnaire confirmed the new trend already followed in many Countries in the world. Some regulatory and utility frameworks have been already modified in this direction in the world; it is the case of the last US Regulatory documents [17-23], Hungarian procedures, Spanish regulations, Finnish PLIM models, just to mention the most widely known. The generic name of maintenance rules was given to these new approaches, in order to differentiate them from the traditional, time-based preventive maintenance. More in detail, the following items are generally identified as the areas where more research and development are needed for the improvement of the existing maintenance practice; they are also the discriminating features of the maintenance rules : 1. The precise identification of the scope of the condition based maintenance rules, clearly linked to the safety classification of the SSCs: typically the Countries choose the safety related SSCs, SSCs which mitigates accidents or transients, SSCs interacting with safety related SSCs, and SSCs that could cause scram or actuation of safety related systems. Therefore, many non safety-related SSCs may see the application of such maintenance rules, with augmented efforts in monitoring their performance and planning their reparation; 2. The setting of the performance goals for every component in the scope of the maintenance rules, ranking them according to their risk significance for the plant safety. This task may end up very challenging as, when industry experience is not available, either dedicated PSA tasks have to be developed (with special requirements on PSA quality) or special qualification programmes for the evaluation of the component reliability; 3. The performance monitoring techniques for the very broad categories of structures systems and components in the scope of the rules; 4. The assessment of the safety during implementation of maintenance actions; 5. The feedback from the result of the monitoring of the component reliability back into the inspection, surveillance and maintenance procedures. Root cause analysis, equipment performance trend analysis and corrective actions have to be developed on a case-bycase basis. 16

19 In addition to the result from the questionnaire, the mentioned subjects are shortly addressed in the following chapters, aiming at a better definition of the R&D needs, with additional details from other experience in countries, which did not participate to the questionnaire. The objective is to provide both a state of the art of the initiatives implemented in some leading Countries and a more detailed background for further research activities in the SENUF environment. To this aim, the following experiences have been selected, as particularly representative of the new trend in the maintenance rules: The US experience, because of its systematic approach to the preventive maintenance, also used by other Countries as a reference The Spanish experience, because of its integration between US technical requirements with European regulatory frameworks, also oriented to plant long term operation; The Finnish experience, because of its strong integration between maintenance, ageing control and investment protection in a long term perspective; The Hungarian experience, because of one of the first attempts to implement maintenance rules at a WWER plant. The next chapters provide a description of the above-mentioned issues, embedded in the country practice. Some Country experience is mentioned more than once, due to the different emphasis and perspective of the relevant chapter they are in. However, all the quotations support the final discussion in Chapter 7 on the R&D needs, without contradictions and therefore they were not grouped in a single paragraph. 4 Organizational challenges in optimized maintenance of Nuclear Power Plants 4.1 Background The answers to the 13 Chapters of the SENUF questionnaire, if read vertically and compared, allow the benchmarking of the maintenance strategies in the referred NPPs; if read horizontally, show how the different NPPs are tackling issues of horizontal nature, mainly related to the organizational and human side of NPPs. It is never enough to recall that high-risk and high-reliability organizations, as NPPs, are key elements of the modern societies, and that their importance will be even greater in the future. These organizations are not machines, which always respond to given inputs by producing the foreseeable outputs, and obey to a system of controls. They are complex socio-technical systems whose social or human facet, although long neglected, received increasing attention in the last decades, especially after some major accidents. 17

20 Organizational accidents became the subject of a specialist discipline, called accidentology, whose scholars suggest that the organizational accidents have multiple causes, and are difficult to understand and control, then difficult to predict [1]. Such accidents can have devastating effects on populations, assets, environment, and it is difficult that an organization can survive under the burden of the heavy human and economic losses caused by them. All technological organizations produce something and, as a consequence, expose people and assets to danger [36]. It is necessary that these organizations adopt protective measures, whilst running productive activities. It is necessary, if they want to develop sustainably, that they are committed to safety, whilst pursuing their productive objectives. It is a general problem that, whilst the productive aspects of organizations are well understood and the associated processes, in general, transparent, the safety functions are of a different and subtle nature. Furthermore, because underpinning Safety consumes productive resources, it is also necessary for organizations to find out the optimal balance among these two synergical and competing factors: Production and Safety. Because the world where organizations like NPPs operate is continuously changing, such balance cannot be a fixed ratio, but should be continually assessed and adjusted, adapted to the needs of the time, on the basis of the most up-to-date scientific and technical knowledge. The changes registered in the nuclear industry are mainly due to the structural changes in the electricity supply industry, which are a result of the deregulation, privatization and the need to increase the competitiveness of the nuclear industry [37]. The deregulation of the electricity market implies that competition, market reforms, as well as environmental constraints and access to finance will be main issues for the power sector in the short, medium and long-term future [38]. As stressed by INSAG-18 [37], the pressures exerted by the acting changes can lead to organizational modifications, such as mergers, downsizing and consequent outsourcing of the lost expertise, which may negatively affect the approach to safety and the safety culture of NPPs and individuals. It is already a reality that maintenance services are increasingly contracted to external companies. The over reliance on external sources and expertise, which cannot be guaranteed in the long term, make it difficult to maintain the availability of the required expertise and is not exempt from organizational problems among the operating organization and the Contractors. To address these issues, appropriate actions need to be taken to ensure that: Contractors conform to the technical standards and the safety culture of the operating organization; The activities carried out by personnel who are not permanent employee of the plant be controlled by well-established management systems covering, among others, the training and qualification of contractor personnel, as well as radiation protection, familiarity with plant systems and adherence to the 18

21 plant procedures, during both normal operation and emergency conditions [39]. And these are only few examples of measures needed for guaranteeing the smoothly running of the maintenance interventions. Maintenance, especially during shutdown, is complex and characterized by many coupled activities and tasks, with interacting effects and involving several organizations (e.g. operating organization, regulatory body, contractors). Good co-ordination among these activities and among the personnel of the different involved organizations should be guaranteed. Good co-ordination is achieved if good communication is established among the different parties, and, more deeply, if all parties are aware of their purposes, their goals and their respective contribution to the common objectives. These ingredients are necessary for performing effectively and efficiently maintenance interventions, and for meeting the goal of knocking down maintenance expenses. For these reasons, the involved managers and staff face the challenges posed by complex socio-technical systems: it is not only the interaction man-machine, focus topic of part of the Human-Factors literature, that matters. It is the diversity of the maintenance activities, and its organizational challenges that need attention, considering that carrying out maintenance requires the coordination of expertise in numerous technical fields, and in a strategic way. Moreover, because the maintenance services increasingly involve external companies, the organizational challenges become even bigger. All these aspects are familiar to the SENUF partners, who communicated through their answers to the benchmarking study, the need for 1. Cutting maintenance expenses; 2. Coping with the complex organization development work ; this is indicated by some of them as a potential cause of accidents incubation; 3. Definition of a strong basis for long term partnership with highly qualified and technically skilled contractors; 4. Reduction of the human factors impact during maintenance activities. Surely, a questionnaire is a practical but limited tool for getting information from the nuclear-power sector reality. It is foreseeable that direct interviews and workshops would bring much additional information on the improvement areas that SENUF partners are willing to tackle, hopefully together, exchanging experiences and creating synergies. It is not the purpose of this work, neither of its follow-up proposals, to speculate on the meaning of expressions such as Safety Culture, Organizational Culture, Learning Organizations, already investigated by authoritative scholars [40-43], and, in some cases abused. It is its aim to join those representatives of the industrial and scientific communities, who are converging their efforts towards the setting up of applicable quantitative tools 19

22 and methodologies for enhancing the safe and the economic performance of Nuclear Power Plants [44-46]. 4.2 Proposals for R&D Maintenance is surely a key activity for NPPs, especially in view of their LTO. And the maintenance teams, and divisions, and their management have to meet the challenge of preparing the NPPs of yesterday for the world of tomorrow. In the framework of SENUF, a possible way ahead might be: 1. To prepare a State-of-the-Art Report on the up-to-date methodologies and assessment tools concerning organizational and human factors; 2. To run dedicated seminars or workshops, for SENUF partners or at SENUF sites, where the most up-to-date knowledge in the field is made available to the participants and confronted with the field knowledge and experience available within SENUF; 3. To assess and benchmark the available tools and methodologies using the maintenance data available or retrievable within SENUF; 4. To analyze the results and formulate suggestions, in view of the LTO of NPPs. If achievable, an improved assessment tool or methodology might be proposed, as spin-off, to the scientific community. 5 Reliability Centered Maintenance 5.1 Background Over past several years substantial achievements have been accomplished by the nuclear power plants, worldwide and in the Central and East European region in particular, to improve plants safety and enhance plant operation performance. Following the leading international experience, many of the plants have used probabilistic methods to complement the deterministic safety assessments and developed plant specific Probabilistic Safety Assessment (PSA) models. The results from these PSA analyses have been further centrally used to support implementation of risk informed decision making to optimize plant operation. PSA results have also been extensively used to justify modifications to the traditional plant operational and maintenance practices and procedures, e.g. known as different PSA applications to support risk-informed operational practices. Matters related to the implementation of risk informed strategies to the optimization of maintenance practices in relation to the SENUF activities are discussed in more details in this chapter. 20

23 Several approaches such as: Reliability Centred Maintenance (RCM), Total Productive Maintenance (TPM), Reviewing Existing Maintenance (REM), Risk Based Inspection (RBI), Reliability Engineering and Safety Integrity Levels (SIL) have been considered and implemented to partially enhance different aspects of maintenance practices. However the experience shows that the highest impact is yielded when an integral approach is taken to maintenance optimization, which is based on the complementary use of deterministic and probabilistic considerations. So called Risk-informed approach can be used for maintenance optimization where the consequential impact is considered against the principle objectives of safe, reliable and cost effective operation. A riskinformed approach to maintenance optimization decision-making represents a philosophy whereby risk insights are considered together with other factors to establish requirements that better focus the maintenance organization s attention on maintenance issues commensurate with their importance to safety and generation. The main objective of risk-informed maintenance practices is to implement optimized maintenance schedule and programmemes which allow: To improve plant performance and enhance safety level by ensuring higher reliability and availability of plant equipment implementing latest industry and technology development in the filed of maintenance; To optimize the maintenance cost by focusing maintenance activities on NPP items and equipment in a manner commensurate with their safety significance. 5.2 Use of Probabilistic Safety Assessment in support of maintenance optimization PSA applications PSA modelling techniques for assessing plant safety and measuring risk are effective tools for evaluating the effectiveness of the maintenance activities to assure that the safety significant systems and equipment are being adequately maintained and their reliability and availability correspond to the assumptions made on this subject in the NPP Safety Analysis Report. PSAs tools help also to assure that maintenance activities do not reduce plant safety and increase risk by, for example, extensive maintenance resulting in increased equipment unavailability [8-10, 47-50]. PSA can be used to prioritize the system maintenance related activities, which can have the greatest impact on risk and plant safety. Maintenance can be planned and scheduled accordingly. The results of maintenance activities and the performance of the equipment can be compared against the modelling performance assumptions used for the 21

24 reliability and availability of the equipment. Decisions can then be reached on the adequacy of the performance of the system, the need for revised maintenance activities, or the need for system redesign or modifications. This process of identifying risk significant systems and equipment can also be used to plan and schedule all maintenance activities on a risk informed basis. PSA can be used to identify systems for which detailed study of maintenance activities is appropriate. This detailed study can then be carried out using other techniques. PSA can subsequently be used to monitor the risk impact of changes in maintenance and testing strategies, provided adequate data on the change in system or component reliability is available. If there is a risk monitor model, the PSA can also be used to examine the risk impacts over the set of activities from the proposed maintenance schedule. This will include the specific combinations of equipment that are removed from service, the frequency and duration of planned maintenance, and the plant operating mode for each activity. This will provide a risk profile for the duration of the schedule, the mean risk over the duration, and the integrated core damage probability for the complete set of activities. The use of PSA should help maintenance staff to optimize the maintenance programme, i.e.: To identify equipment requiring somewhat upgraded preventive maintenance, (as an increase in its reliability results in a substantial gain in safety); To identify equipment requiring sustained or slightly reduced preventive maintenance (as a decrease in its reliability does not affect the level of safety); To identify equipment requiring only corrective maintenance (as its unavailability does not result in a major increase in risk). Furthermore, some items in the maintenance programme or maintenance requirements set up by engineering judgement may not lead to an increment in the safety level. PSA based methods provide tools to balance the safety, operational/technical and economical requirements. The development and management of an effective maintenance programme involves complex, multidiscipline and multidimensional analyses. PSA provides quantitative information about the potential risk benefits from improved equipment availability and the risk consequences when equipment is removed from service for maintenance. This information should then be compared with other factors, such as costbenefits, adequate safety margins, deterministic maintenance requirements, etc. which influence the maintenance optimization decisions making. Usually the decisions on implementation or not of a 22

25 certain change to plant maintenance practices is taken after careful consideration of all factors influencing the decision to ensure that resources are used most efficiently to support a high level of plant safety and availability. The framework for such an integrated decision making process is outlined in several publications [51-56] and is briefly discussed below at the example of US NRC regulations PSA technical and quality attributes needed to support riskinformed maintenance optimization The American Society of Mechanical Engineers has published Standards for Probabilistic Safety Assessment for Nuclear Power Plants applications [57]. The PSA attributes needed for different applications are also addressed in various IAEA publications [58], which give advices also on how to modify an original/general PSA model in order to use it for different application. As concerns the use of PSA models to support maintenance optimization, all these publications require as minimum modelling requirements the availability of a detailed plant specific Level 1 PSA. To most effectively evaluate the importance of each component and each planned maintenance activity on overall plant risk, the PSA should include both internal and external initiating events. In general, proposed maintenance plans will include containment or confinement systems and their support systems. Therefore, the analyses should also include at least a limited scope Level 2 PSA. Also, it should be recognized that maintenance induced failures of the containment systems can introduce containment by-pass situations, which may go undetected for some time. At many plants PSA is used to optimize the combinations of planned maintenance that are performed during plant power operation ( on-line maintenance ) and during shutdown. To most effectively determine the net risk impact from each proposal, the scope of analysis should include PSA models for shutdown conditions. These models are necessary for a detailed comparison of the risk from performing each activity during shutdown and during power operation. Shutdown PSA models are required to evaluate trade-offs and to minimize total plant risk during all operating modes. Many plants schedule planned maintenance for coordinated groups of equipment at the same time (e.g. one complete train of safety systems, electrical inspections, etc.). The relative risk from this type of maintenance, compared with individual component outages, depends on the specific plant design and its normal operating configuration. If this type of correlated maintenance is proposed, the PSA models must include appropriate logic to account for the fact that all affected components are out of service simultaneously. The PSA must also account for changes to the plant-operating configuration when this type 23

26 of maintenance is performed. For example, it is necessary to revise assumptions and models for normally running and stand-by equipment when each train is out of service. This may require substantial changes to the original PSA models if they are based on a specific assumed plant configuration. The need to have an adequate PSA model suitable to quantify correctly risk of different plant configurations is essential prerequisite which must be ensure before any modifications to the actual plant maintenance practices are introduced. 5.3 Country experience with RCM US NRC framework for risk informed decision making The US NRC PRA (PSA) Policy Statement [51] encourages greater use of PRA to improve safety decision-making and regulatory efficiency, including the use of PRA to support decisions to modify an individual plant's licensing basis. To meet the requirements of the US NRC Maintenance rule ([17] - Section 65 in Part 50, Requirements for monitoring the effectiveness of maintenance at nuclear power plants) many US plants have developed their plant specific Probabilistic Safety Assessment (PSA) models/ studies. These PSA studies are further utilized/ applied for optimization of In-service Testing, In-service Inspections, Technical Specification, Graded Quality Assurance and others plant activities. To regulate the performance, assessment and evaluation of such PSA applications the US NRC has issued a number of Regulations: RG on licensing basis; RG on in service testing; RG on graded quality assurance; RG on technical specifications; RG on in service inspection. Guide establishes the framework for risk informed decisionmaking process (see Fig.4) and determines the probabilistic safety criteria (see Fig.5) to be used in this process. This guide and the other supportive ones on different applications are widely used by the utilities in the USA to justify to NRC and modify their operational practices, including implementation of on-line maintenance, Reliability Centred Maintenance, Maintenance Planning using Risk Monitoring tools, etc. 24

27 5.3.2 East and Central European Countries experience with risk informed maintenance optimization In order to analyze the current practices related to the optimization of maintenance activities in SENUF members countries, it was decided to hold a joint IAEA/ IE Technical Meeting on Use of PSA Tools to support NPP Maintenance Activities, The meeting took place at Petten, 31 May-3 June, 2005, and was attended by 30 participants from 13 countries [60]. The main objective of this meeting was be to provide a forum for professional staff from utilities and regulatory authorities from the Central and Eastern European countries and SENUF members to discuss PSA applications related to the optimization of plant maintenance activities. Discussions were held on two major subjects: Reliability Centred Maintenance (RCM); Risk Monitors as a tool to support on-line maintenance practices; Risk informed maintenance optimization. The meeting identified the most common practices, areas where major difficulties are experienced and formed a view on the future perspectives for applying risk informed approaches for optimization of NPP maintenance for SENUF members plants. The following conclusions were derived at the end of the meeting: All SENUF members have clearly defined their intention to continue with activities aiming at plant operation s and in particular maintenance s optimization; Well established methods for risk informed maintenance optimization exists and many of the plants in Eastern and Central Europe are embarking on their use; Plants in Spain and Slovenia indicated that they closely follow the relevant developments in US NRC regulations and guides and respective practices in US Plants maintenance optimization. Several pilot studies on RCM are in progress in Czech Republic, Romania, Slovakia, Bulgaria; Spanish NPPs have successfully implemented several projects for implementation of RCM (see chapter 5.3.3) and their experience shared under the umbrella of SENUF network will be very much appreciated; All countries were interested to compare results from the implementation of pilot projects on RCM and in particular on equipment categorization. It was suggested to benchmark the implementation of RCM for a single safety system in a same WWER type of reactor plants. 25

28 5.3.3 Spanish Experience with RCM The Spanish experience with the implementation of the Reliability Centred Maintenance is highlighted below, as further support to the conclusions of this report [61,62]. As of June 2005, 9 units of PWR or BWR type of reactor NPPs, with 7896 MWe installed capacity, were in operation in Spain. The general scheme of Spanish maintenance optimization programme is presented in Fig. 6. The Reliability Centred Maintenance is a methodology based on systematic, objective and documented analysis, which can be applied to any industrial facility to establish an efficient preventive maintenance plan. US EPRI first applied RCM methodology [63] in the nuclear industry in The following main principles regulated the development and implementation of RCM at Spanish plants: 1. The maintenance tasks are focused on the failure modes that can affect the component function within the facility: The main objective of the maintenance tasks is to maintain the system functionality, If the consequence of a failure does not have an adverse effect on safety; operations, environment or cost, then there is no need to carry out scheduled maintenance, For instance, an open valve that remains open doesn t need maintenance addressed to its operation; 2. Priority is given to tasks of predictive maintenance instead of preventive ones: Predictive maintenance is less intrusive and more effective than the time-directed overhaul tasks, Predictive Maintenance includes vibration analysis, ultrasound, oil analysis, wear-particle analysis and thermography; 3. The frequency is concordant with the equipment performance: The vendors recommendations can lead to an excessive or inefficient maintenance plan, The RCM evaluation will consider the historical maintenance, the operative conditions and the plant design; 4. The results of maintenance actions and past tests, within a 5 years period at least, are considered for the design of the new Maintenance Plan: For those components with a good performance, should be reviewed the preventive maintenance tasks, getting a special importance the associated unavailabilities, For those components with an abnormal performance, should be analyzed the detected problems and failures; 26

29 5. RCM considers all the maintenance tasks in a global way, independently of the issuing or executing department: Maintenance, Operation, Engineering, Others, which allow to identify possible redundancies or duplicities with a great saving potential implied. The process for development and implementation of RCM consists of five major steps: 1. Definition of the scope of the NPP equipment subject to RCM; 2. Analysis of Components Criticality/ Safety significance/ Failure modes (with possible use of PSA models); 3. RCMaintenance Plan Definition; 4. Maintenance Plan Implementation; 5. Maintenance Plan Monitoring and updating process (feedback). Two different type of methodologies have been applied for the analyses of component criticality: The Simplified Methodology analyses the component criticality for the whole of the failure modes; The Detailed (Traditional) Methodology analyses the component criticality for each one of the failure modes. The later one is more time and resource consuming, however the results obtained allow better tailoring of the maintenance programmes and addressing only critical failure modes for each type of equipment, thus allowing more effective use of maintenance resources. The Implementation of RCM in Spain resulted in the following benefits: Increased in Equipments Availability; Reduction in Programmed Unavailabilities; Plant Risk Minimization; Human Error Probability Minimization; Evidence of Design deficiencies; Better control over the Components Life Cycle; Continuing adjustments to Maintenance Tasks; Best Knowledge of the Facility; Implementation of a Continuing Improvement new Culture. The following plants in Spain have developed and implemented RCM: Cofrentes NPP, BWR-GE (traditional and simplified methodologies); Trillo NPP, PWR-Siemens (traditional and simplified methodologies); 27

30 Santa María de Garoña NPP, BWR-GE (traditional methodology); Almaraz 1&2 NPPs, PWR-W (simplified methodology); Ascó 1&2 NPPs, PWR-W (traditional and simplified methodologies); Vandellós 2 NPP, PWR-W (traditional and simplified methodologies). 6 The maintenance programme in long term operation perspective 6.1 Background Long Term Operation (LTO) is a growing interest process in most of the nuclear Countries due to the ageing of the plant fleets and the need to secure important energy sources combined with investment protection. It appears that suitable maintenance programmes are one of the few pillars of the LTO programmes; many Countries decided to modify their maintenance programmes as a precondition for LTO. All Countries implementing an LTO programme applied extensive modifications to their requirements on maintenance at first step, setting up mechanisms to monitor the effectiveness of the maintenance activities. In general the engineering community believes that the maintenance programme should have specific attributes in order to support a long-term operation (LTO) programme for the plant. More specifically, the maintenance programmes based on standard preventive maintenance (time based), not oriented to the monitoring of its effectiveness, are not considered suitable to support the LTO programmes. Crucial attributes for maintenance programmes in order to support LTO are considered: the verification of the performance goals, the root cause analysis of failures, the feedback from maintenance to the ISI programme, the feedback on the OLC, etc. In particular, the following features are believed to be indispensable for a state-of-the-art maintenance programme, even if the LTO process is not urgent in the Country: 1. Monitor the performance of the SSCs which may have impact on safety during all operational statuses of the plants; 2. Assess and manage the risk that may result from the proposed maintenance activities in terms of planning, prioritisation, and scheduling. Therefore, systematic approach to the improvement of the maintenance effectiveness is a generic tendency in Countries where LTO programmes are in place; however, the progress in this field depends on both the maturity of LTO project and on the specific regulatory framework. 28

31 In some countries requirements exist on the evaluation of efficiency of the maintenance with respect to safety criteria (Maintenance Rule, MR). In these countries the utilities have to develop and implement systematic approach to the planning, performing and evaluation of the maintenance in response to the MR. A common example of the proof of efficiency of the repair work is for example the containment leak-test. The key aspect is the integration of existing programmes such as: ISI and monitoring, trending, maintenance, replacement, to ensure a long term plant operation. In this sense the experience of the USA, Spain, Hungary, Finland and other countries with an LTO programme in place are a confirmation of this generic statement: all these countries modified their regulatory requirements on maintenance, in the direction mentioned above, as one of the preconditions for the LTO of their plants. Therefore the analysis of these LTO programmes becomes essential to understand the requirements on the state of the art maintenance programmes posed by the International Community. More details are provided in the following on the position developed at the IAEA, in Spain, Finland and in the USA, for reference. 6.2 Experience at the IAEA The IAEA has not yet developed specific documents on the detailed procedure to be followed for the extension of the operational lifetime, as the approach in the countries is very differentiated and in many cases not yet mature. However, a large number of IAEA documents are available on basic safety concepts that could be relevant to life extension programmes [6-16], and in particular on the requirements of the maintenance programmes in view of LTO programmes. A clear position is common to all the IAEA documents: LTO is a programme that can be implemented only when the plant can demonstrate a suitable safety level in all its statuses; The LTO programme are crucially based upon a strong integration of many existing programmes at the plants, such as ageing management, configuration control, predictive maintenance, etc. The Regulatory frameworks for long-term operation (LTO) differ from country to country in accordance with the licensing system. In countries where the operational license is granted for a well-defined operational lifetime, a formal license renewal is practiced. In some countries the utilities have a license renewal for 20 years. Some other Member States have just started the development of regulations for license renewal and project planning. In the countries where the operational lifetime is not limited by license, the Periodic Safety Review (PSR) is frequently chosen as the regulatory tool for an LTO, but in a ten-year framework only. However, despite of the differences that affect the regulatory strategy in the countries and the consequent differences in the application/approval process 29

32 for LTO, the main technical components of the LTO programmes and their basic technical tasks are shared among most of the countries. A general approach to LTO, independent of the regulatory framework, can be based upon the following assumptions: 1. Separation of pre-conditions to LTO and LTO specific tasks; 2. Separation between regulatory issues (PLEX, PSR, PLIM, etc.), technological issues (degradation) and economical issues; 3. Clarification of the LTO scope and objectives, and therefore of the interfaces between maintenance, ISI, AMP, etc.; 4. Analysis of the differences between active and passive SSCs, replaceable and non-replaceable components. This approach leads to the following definitions: 1. Preconditions for LTO: tasks needed to reach the required level of plant safety and to prove it. Required also for current operation during design life (see for example the safety factors of the PSR). They may include the following actions/programmes: Keeping the SAR updated; Keeping the EQ updated; Keeping the design basis updated; Update the EE hazard; Update the safety analysis; Appropriate maintenance programme, with monitoring of its effectiveness and trending features in time; etc. 2. LTO specific tasks: tasks needed to maintain the required level of plant safety in the long term in relation to material ageing, technological obsolescence and staff knowledge, beyond the plant life defined at the design phase by the technological limits. They are affected by the extension of the beyond design basis lifetime. They may include the following actions/programmes: Trend analysis of material and component degradation; Management of the staff ageing; Management of the long term technological obsolescence of SSCs; Public acceptance; Environmental issues (population, installations, emergency planning); etc. Prior to giving consideration to long-term operation, it is essential to check that the plant has been maintaining an acceptable safety level of the operation ( preconditions ). In particular the review of the maintenance programme (MS&I) and of the ageing management programme (AMP), which in many countries includes maintenance, should be conducted, in order to check if the 30

33 trend analysis is adequate to support a decision on the long term. An essential element of the LTO programme is the extrapolation of the detected degradation on the planned operational lifespan. The licensee should demonstrate that for the extended operational lifetime: 1. The safety and ageing analysis remain valid and could be projected to the end of intended operational lifetime; 2. The effects of ageing on the intended function(s) will be adequately managed; 3. There is a mechanism to deal with unexpected ageing mechanisms that can surface. In many cases, the plant existing maintenance and ageing management programmes can be credited as acceptable programmes for the long-term operation. For the remaining cases, either the plant existing programme can be augmented to satisfy the listed above attributes or new programmes should be initiated. The results of the trend analysis should be evaluated considering the following: The entity of life time extension; Time required to implement corrective actions; Probabilistic Safety Assessment (PSA) application; Expert judgment (risk is often subjective). One of the following strategies can be implemented in case of noncompliant items: Replacing or restoring the component; Changing the operational conditions and/or improving ISI; Developing additional analyses (eliminating initial conservatism with more refined methods); Performing a re-evaluation test (with improved qualification methodologies). In fact beyond design life the design safety margin can be maintained through accommodation of the new issues into the design conservatism, sometimes built up with rough design methods, conservative environmental conditions and conservative operation assumptions. In general, ageing is addressed in procedures for maintenance, surveillance, in service inspection programme, etc. as one of the physical processes, which could lead to failure. The operating experience shows that active and short-lived SSC are in general addressed by existing maintenance programmes. Conversely, the performance and safety margins of the passive long-lived SSC are assumed to be guaranteed by design. However, the analysis of the operating experience showed that unforeseen ageing phenomena may occur either because of shortcomings in design, manufacturing or by operating errors. Therefore the implementation of an AMP and a predictive MS&I programme is definitely a condition for the operation within the limits of design or licensed lifetime and is a pre-condition for an LTO 31

34 as well. Moreover, the ageing management is intended to provide a crosscutting connection among all maintenance and inspection activities carried out on active components also, to provide a unified understanding and treatment of the degradation phenomena. In conclusion, both the AMP and MS&I programmes could be accepted if the following actions are completed: Programme scope is defined; Preventive actions are developed; Parameters to be monitored or inspected are detected; Detection of ageing effects is ensured; Monitoring and trending is performed; Acceptance criteria are defined; Corrective actions confirmation process are defined; Administrative control is fixed; Operating experience of the programme is considered. Some of these attributes are inter-related. Particularly the frequency, the trending and the number of locations to be monitored may reflect the operating experience from past operation. A task preliminary to the trend analysis is the identification of SSC that have a limited lifetime as per design, such as limits defined by fatigue, or metal embrittlement due to temperature and radiation, etc. The ageing analyses defining time limits and the relevant maintenance programme have to be reviewed. Generally, the scope of this review would focus on those systems, structures, and components that have an intended safety function or the failure of which could have an adverse effect on the plant safety during the long-term operation. The scope of this AMP review can therefore be grouped into the following two categories: 1. All safety-related systems, structures and components relied upon to ensure the following functions: The integrity of the reactor coolant pressure boundary, The capability to shut down the reactor and maintain it in a safe shutdown condition, The capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposure; 2. All non-safety-related systems, structures and components whose failure could prevent satisfactory accomplishment of any of the functions identified above. Some SSCs are dedicated to a specific function that may be essential to the safe operation of the plant, such as fire protection, severe accident management, etc. These SSCs may or may not fall into either of the above two categories, but they should be included in the scope of the assessment of long-term operability. 32

35 6.3 Experience in Spain During the last years, Spanish utilities that own nuclear power plants (NPP) are increasingly concerned with optimising plant life management [31]. As a result of this interest, Life Management Programmes have been set up with the strategic objective to operate the NPPs as long as they are considered safe. In parallel with this initiative, both utilities and the Spanish Nuclear Regulatory Body (CSN) are working to identify specific aspects of the licensing process that could be necessary for long-term operation of NPP. In order to facilitate the application of CSN Safety Guide 1.10 Periodic Safety Reviews of Nuclear Power Plants, the Spanish utilities association (UNESA) has developed a specific guide, titled Guideline for the development of Periodic Safety Review. The areas considered within the UNESA guide are the following: Operating experience; Experience related to the radiological impact; Changes in the regulations and laws; Equipment behaviour; Installations modifications; Probabilistic safety assessment; Updating of safety evaluation and improvement programmes. The two areas related to ageing and life management are equipment behaviour and updating of safety evaluation and improvement programmes. The approach to Life Management has also been standardised by UNESA by the development of a common methodology. This methodology has the following phases: 1. Selection of systems, structures and components; 2. Identification and study of ageing mechanisms; 3. Maintenance evaluation; 4. Review of operation and maintenance programmes. Selection of systems, structures and components: Life Management Programmes will mainly address components having the greatest sensitivity to ageing and higher operating and maintenance (O&M) costs. These components will be the object of further investigations and research to identify the parameters that affect their life cycle. The steps for selection of important components are the following: Selection of systems and components; Grouping of similar components. The selection of systems is done considering safety, availability and cost criteria. The selection of components within these systems is performed based on a wide range of criteria such as: Significant impact on safety level of component failure; 33

36 Component is safety-related or required for safe shut-down; Important component in licensing process; More aggressive than design operating and environmental conditions; Component maintenance is not effective for ageing control and mitigation; High cost or long period needed for component replacement. Finally the establishment of grouping criteria allows inclusion in the same class of components with similar surveillance parameters and techniques. This allows for a more effective and efficient ageing surveillance and management of these grouped components, as they require similar parameters and techniques. Identification and study of ageing mechanisms: The Programme begins with an initial condition evaluation, which serves as the basis for establishing the main preventive/corrective maintenance and monitoring actions, and for preparing the first cost/benefit analyses for Life Management. The Programme continues to progress with periodic reevaluation of condition to confirm the corrective measures are the right ones and to adopt new measures, if necessary, as a result of the monitoring established. The initial conditional evaluation of each component is performed considering the following information: Component (or group of components) design, manufacturing and operational data, including process and service conditions, stress values, etc; Potential degradation mechanisms and of the level of harshness of selected components is determined based on previous collected data; The degradation mechanisms analysis is complemented by history of the operation and maintenance, and the results of diagnosis and monitoring, to detect incidents that might have affected the condition of the plant, or for evidence of degradations; Uncertainty about the severity of some of these ageing effects may require extra inspections or tests, to provide more precise data. Condition evaluation requires collection and ordering of the documentation and records of manufacturer, operation and maintenance that contain information needed for the analysis. This collection requires application of procedures that establish the data and records, with the periodicity of their acquisition clearly identified for successive re-evaluations, and the screening requirements for easier collection and analysis. The result of this analysis is an Evaluation Report for each component or group of similar components. In addition, each evaluation report includes 34

37 information about the following age related matters for the target component(s): Component detailed description, including design and service information, potential degradation mechanisms and main variables controlling ageing process. Techniques allowing to detecting, surveying and monitoring the component ageing mechanisms, including inspection, surveillance and periodic testing; Lifetime prediction methodology, including life consumption assessment algorithms, degradation status determination and evolution calculations and acceptance criteria for ageing prediction; Recommendation for ageing mitigation: different theoretical approach to mitigate ageing effects are proposed in Evaluation reports, including new research and development activities to solve existing problems in mitigation techniques. Maintenance evaluation: In addition to the improvements in operation and service conditions, a substantial part of the causes and effects of ageing mechanisms have to be mitigated by maintenance work. The nature of these long-term ageing mechanisms has meant that, in certain cases, current maintenance practices do not prevent them. This requires these practices to be evaluated and modified where necessary to improve their efficiency in conservation and the mitigation of degradation. The maintenance evaluation methodology requires the following activities: Detection of the component-degradation mechanisms pairs to evaluate; Determination of the programmes, practices and procedures that affect each component/degradation mechanism pair; Evaluation of the possible deficiencies in control of ageing of the maintenance of each components and propose, when necessary maintenance improvements. These activities are materialised in the following process: Production of Component Degradation Data Sheets (CDDS). The data to be filled out on the CDDS are component description; functions; design parameters; operating experience; degradation mechanisms; and the part of the component affected by ageing; Generation of Maintenance Practices Data Sheets (MPDS): For each programme, practice and procedure that affect each component degradation mechanism pair, a MPDS is prepared with: practice limitations; time when corrective action is taken; data needs; mitigation, detection and monitoring actions; and 35

38 criteria, as well as any other experience or comments from practices application experience; Creation of Maintenance Evaluation Checklist (MEC). Each component CDDS and all the MPDS that affect the component are compared to obtain the MEC of the component. MEC shows the possibly deficiencies in ageing control of each component maintenance. When required, maintenance improvements are proposed. The most extended actions are changes in service condition, fluid chemistry control and environmental conditions, as well as, improvement or recovery of material characteristics and modification in operation modes. Review of Operation and Maintenance Programmes Based on the conclusions of the previous activity, several actions can be taken in order to review the operation and maintenance programmes. These actions could be the following: Repairs, replacement or modifications of the components most severely affected, if availability or performance improvement justify the investment; Modification of operating procedures and in service conditions to make them less harsh; Improve maintenance practices to achieve full efficiency for safe and economically viable life extension; Implement additional monitoring to improve condition evaluation and trends, especially for component degradation mechanism combinations with more uncertainties. This will reduce the effort required for collection and analysis of information, and allow the use of realistic criteria for ageing parameters in the life management decision-making process. Examples of maintenance programmes optimisation are the extensive effort in older plants to replace old cable and instrumentation, which were considered age-sensitive. An example of the mitigation activities is the core optimization, which reduces reactor pressure vessel neutron embrittlement. In conclusions, Spanish utilities consider a strategic objective to operate their NPP on the long term, and so have set up a common plant life management methodology that is developed through specific Life Management Programmes. The common plant life management methodology adopted is divided into four main activities: Definition of the priorities and scope of the Life Management Programme. Plant systems, structures and components important for lifetime management are selected and prioritised using a methodology based on screening criteria; Evaluation of the initial condition as the basis for identifying ageing mechanisms and establishing the main 36

39 preventive/corrective maintenance and monitoring actions. Periodic re-evaluation of condition confirm the corrective measures are the right ones or lead to adopt new measures, if necessary, as a result of the monitoring established; In addition to the improvements in operation and service conditions, effects of ageing mechanisms have to be mitigated by maintenance work. The nature of these long-term ageing mechanisms is such that, in certain cases, current maintenance practices do not prevent them. This requires these practices to be evaluated and modified when necessary; Based on results of previous activities, it is possible to propose measures to review the Operation and Maintenance programmes to optimise the lifetime management; Finally, software tools to facilitate ageing assessment and condition evaluation for main important component for lifetime management have been developed and are available for NPPs. 6.4 Experience in Finland The ageing management at the Loviisa NPP [16] is based on both the operational and maintenance feedback and the continuous safety improvement programme guided by the PSA. The original construction specification indicates a 30-year lifetime for the Loviisa plant. However, single main components were given higher lifetimes. The plant lifetime estimation was based on the predicted lifetimes for the critical components, e.g. RPV. However, there was some conservatism in assumptions and calculations. An annealing of the RPV of Loviisa unit 1 was performed in year A successful power upgrading and re-licensing project was performed at the Loviisa NPP in These major modifications made it possible to select the ageing management strategy more freely. New predictions based on the analyzed operating experiences and more accurate calculations gave a longer and more accurate lifetime prediction. According to present analyses, the predicted economical lifetime for Loviisa units is more than 45 years. Decision levels: Yearly level: Preventive maintenance during operation and annual outages, Definition of scope and time for changes in the operational procedure; Licensing period [5-10 years] (these are usually the most important decision targets for the economy): Investigation and research programmes on degradation mechanisms for active and passive components, 37

40 Assessment of the optimal scope for the preventive maintenance, Development of a long-term modification programme with practical safety improvements; Plant lifetime level [>10 years]: Optimization of the time schedule for large modifications (e.g. improvements to the safety automation), Implementation for comprehensive inspection, research and data collection programme for economically unchangeable components. The AMP at the Loviisa NPP is based on three decision levels that are applied to different time spans. These three levels can be named as the yearly level, the licensing period level and the plant lifetime level. The actions at each level are the following: Limits of preventive maintenance: The preventive maintenance programme at Loviisa is based on the Safety Related Operational Limits and Conditions (Tech. Spec.) of the plant. The Safety Related Operational Limits and Conditions gives the practical limits which should be taken into account in the design and scheduling of the preventive maintenance actions. Plant computers support the scheduling during operation and annual outages. The scope of the preventive maintenance programme are audited yearly by the QA and the safety engineers of the plant together with various specialists. One important fact is that an NPP operating license is issued in Finland for a limited time, and can be renewed only after a thorough safety review. The safety review also includes the assessment of ageing. The current 10-year operating license of both Loviisa units will expire at the end of New integrated AMP and maintenance systems Another part of the ageing management strategy at the Loviisa NPP is represented by the definition of the responsibilities at the "system group" level. In the year 2002 a special group of 16 persons called "ageing engineers" was chosen at the Loviisa plant for co-ordinating necessary ageing analyses. More than 100 of the most important SSC's are divided into system groups, and one ageing engineer is responsible for each system group. The person in charge (system group owner) updates the ageing information of his system group into the ageing specific database and makes the proposals for modification or repair work as well as changes to the preventive maintenance programme. The person in charge has also a supporting group of 5 to 8 persons, which provides technical support for his decisions. 38

41 During the past few years, critical components and systems of the plant were selected and their attributes concerning ageing were recorded using new methods. The general data are stored into a special ageing database of structures, systems and components (SSC). The database is linked together with the various archives and databases of the utility. The basic structure of the new integrated system with AMP and maintenance at the Loviisa NPP is presented in Fig Experience in the USA The NRC has developed a license renewal process that establishes the technical and administrative requirements for renewal of operating power plant licenses and that can be completed in a reasonable period of time with clear guidance to assure safe nuclear plant operation for up to an additional 20 years of plant life. During the review process, the applicant must demonstrate that programmes are in place to manage those aging effects applicable to the passive, long-lived structures and components of the plant. The review also verifies that the analyses that are based on the current operation term have been evaluated for the 20-year extended operation. The license renewal requirements are provided in the licensee renewal rule, 10 CFR Part 54, Requirements for Renewal of Operating Licenses for Nuclear Power Plants. The rule was first published in Based on lessons learned from the demonstration programme and to allow sufficient credit for existing programmes, particularly the maintenance rule (10 CFR 50.65), the rule was revised in The amended rule established a regulatory process that is more efficient, more stable and more predictable than the previous license renewal rule. In particular, Part 54 was clarified to focus on managing the adverse effects of aging. The NRC staff in 2001 issued several license renewal guidance documents to aid in the development and review of license renewal applications. As an example, the Generic Aging Lessons Learned (GALL) Report classifies plant structures and components; lists the materials, environments, aging affects and mechanisms; and documents how existing commonly used plant programmes can be used or modified to mitigate or manage these aging effects. Other guidance documents issued in 2001 included the standard review plan for review of license renewal applications for nuclear power plants (SRP-LP) and the Regulatory Guide (RG) 1.188, Standard Format and Content for Applications to Renew Nuclear Power Plant Operating Licenses, which endorses the Nuclear Energy Institute (NEI) guidance in NEI 95-10, Revision 3, Industry Guideline for Implementing the Requirements of 10 CFR Part 54- The License Renewal Rule. All these documents are currently being revised to reflect the lessons learned from reviewing the license renewal applications. In addition, the NRC has also issued inspection procedures (IP and IP 71003) on the scope and content of the NRC inspections at the plant sites. 39

42 7 Conclusions and proposals for R&D tasks in SENUF The analysis of the questionnaire and of other Countries experience described in the previous chapters suggests that improved maintenance programmes could effectively meet the challenges posed by the new socioeconomical framework where the nuclear plants have to operate: market liberalization and long term operation of the plants, respectively. All Countries facing the above mentioned scenarios are spending their best efforts in the improvement of the maintenance programmes in the following areas: a) human factors, b) reliability centred programmes and c) trend analysis of degradation mechanisms in the long term, which could definitely support the evolution of the actual maintenance programmes in the direction required by the new challenges. Therefore these areas do deserve additional R&D in order to reach the full applicability to real cases. In fact, in the specific case of the SENUF Countries, all members shared the theoretical conclusions of the need to optimize the maintenance programmes in the mentioned directions. However, many practical issues still have to be solved before a broad application of the proposed techniques is completed, particularly at some WWER plants, as highlighted for example by [7] as a result of many safety reviews carried out in WWER plants, and summarized in the following: 1. Consideration should be given to strengthening the predictive maintenance programme. The plant should consider focusing on the quantity of controls, quality of results and the usage of techniques to improve safety equipment reliability and availability and to correct preventive maintenance or address anticipated or immediate corrective maintenance; 2. The management of temporary modifications to plant equipment should be better evaluated, approved, installed and controlled. The quality of such modifications should be made consistent with the international practices; 3. Moreover, large modernization programmes have been implemented in many WWER plants that request strong configuration management tools; 4. Plant surveillance practices should always assure early detection of failures, deficiencies or leaks. In particular, it has been observed that many plants performs analyses of the tests results, but prognosis methods for possible degradation of the SSCs status should be applied after that. In addition to that, response times (for example stroke times for valves, I&C equipment delay times, etc.) should be always monitored to guarantee that they do not change during plant operation. At last, analyses of surveillance results of systems, structures and components are regularly performed, but trending analyses should be performed on these results; 40

43 5. Many departments (a common number is 4-7) are involved in surveillance activities: this structure requires control of activities in several levels to assure that the testing schedule is accomplished and that the overall plant safety is guaranteed; 6. The availability of advanced safety assessment tools, such as living PSA of adequate quality, should become a daily practice in many plants. In conclusion, probabilistic assessment methods should be more widely used to support decision making; 7. The availability of human resources with adequate experience, knowledge management in time, and management oversight on maintenance operation are three generic issues in many plants; 8. The availability of spare parts is a generic issue which compels to requalify new components; 9. The ageing mechanisms for some components should be fully investigated for some WWER plants, as the generic lessons learnt recorded for western plants are not always applicable; 10. The evaluation of the risk associated to the maintenance implementation is not always carried out (see the Paks NPP accident during fuel cleaning) in advance; 11. The self-assessment of the maintenance programmes should be extensively applied. Effectiveness indicators should be widely applied and the feedback from maintenance to S&I programmes should be always considered. The above-mentioned issues suggest that an extra effort is needed, particularly in relation to the WWER plants, to make the predictive maintenance approach (risk centred) fully applicable to these installations. The effort should comprise R&D on material degradation mechanisms and applicability of probabilistic tools, but also organizational actions and improved consideration of human factors. In the questionnaires many plants claim the broad application of ageing control, control of the modifications and other apparently isolated programmes. Therefore there is the feeling that the improvement of the maintenance rules should also represent the chance for a better integration of many existing programmes, currently run by different departments and with not much interaction under the objective of the overall plant safety. In conclusion, the next effort of the SENUF initiative should be spent at three different levels: 1. At the organizational level, covering the integration among existing programmes, management of human factors, definition of feedback loops and interactions between programmes, decision-making process (either risk informed or not). One model that seems to cover these aspects is, for example, the Life Management Programme (PLIM), which aims at keeping the plant in good condition in the long-term, usually with a time target of years. This includes careful operation and maintenance, development 41

44 of a replacement strategy (particularly when lack of spare parts is a reality), and mitigation of ageing effects. This kind of PLIM programme needs continuous and effective links from the operating experience to the long-term decision-making. The regulatory tool for approving the long-term operability might be the PSR. However, the use of the PLIM to ensure the LTO can be misunderstood: the scope of the PLIM may not cover all ageing relevant issues up to the end of the extended lifetime of the plant. The advantage of a mixed system PLIM + PSR is that the identification and the resolution of the safety issues are not only completed in the frame of the PSR, but it is continuously addressed during the operation. 2. At the technical level, improving the applicability of existing pioneering techniques to other existing plants, especially WWERs, where many practical issues appear to provide even additional challenges on their implementation. It is the case of the investigation of ageing and degradation mechanisms for WWER components, of the simplified use of probabilistic tools for condition based maintenance and risk informed inspections (when PSA is not available at the plant), of the use of reliability concepts for performance goal setting and monitoring, and of their trending in time. Two sub-actions may be taken at this level: i. Develop a data base on degradation mechanism for WWER components and relevant monitoring techniques in all environmental conditions (including harsh and standard ), ii. Develop suitable risk informed techniques for the safety assessment (also when specific PSA studies are not available at the plant) and reliability evaluation of systems and components (performance goal settings, monitoring and trending), for the risk based monitoring of the maintenance programme, and for the evaluation of the plant risk profile, optimization of inspection techniques and assessment of the risk associated to the maintenance actions. As most of the mentioned issues appear to be specific to some types of plants, it is suggested to choose one or two candidate plants and to run pilot projects on few selected systems and components of different nature (I&C, structures, mechanical components, etc.). Two candidate systems may be the Primary Heat Transport System and the High pressure, emergency core cooling system. These systems are common to all types of reactors involved in the SENUF program. This exercise may provide a concrete answer to a real, generic demand for improved maintenance programmes, seen as part of the overall plant effort for safer plant operation. 3. At the communication level, providing a suitable forum for experience exchange on the daily maintenance issues, even in the currently 42

45 applied framework of a generic preventive maintenance system. In fact, the questionnaire identified some areas where a significant improvement could be achieved in the daily maintenance (see Chapter 2), even in the currently applied framework of a generic preventive maintenance system. In particular, a forum could be open for exchange of experience addressing some daily maintenance issues, independent from the general framework of the maintenance program, such as: Post maintenance testing procedures. Networks for spare parts sharing. Use of maintenance performance indicators. Collection and use of maintenance history records. Partnership between plants and contractors. Control of the collective dose during maintenance activities. The background provided in this report should be used to develop a concrete action plan for R&D in the specified areas. 43

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50 Figure 1: Load factors all plants excl. 3 plants Figure 2 PLIM at Loviisa NPP 48