EMBALSE NGS PLEX OVERVIEW

Transcription

1 EMBALSE NGS PLEX OVERVIEW G. Díaz, R. Sainz, P. Luna, C. Shiersmann, O. Monsech Central Nuclear Embalse, Nucleoeléctrica Argentina Sociedad Anónima, Argentina address of main autor: ABSTRACT Embalse Nuclear Generating Station (ENGS), a CANDU 6 type with 648 MWe output, started operation in In the last 10 years it has shown an excellent performance with an average capacity factor of %. An effective plant operation and management of the effects of aging on equipment, piping, accessories, components and structures that constitute plant principal systems by means of a continuos inspection program; is required. The end of the design life is foreseen for However, a political decision about the intention for an Embalse PLEX has been taken. In this paper an analysis of the Embalse-NGS Program for a possible Plant Life Extension (PLEx) is presented. A typical program for a CANDU PLEX has three main phases: Phase 1: Pre-project definition. Phase 2: Project Engineering and preparation. Phase 3: Project Implementation. However, there are also other programs, for example, In Service Inspection (ISI), Preventive / Predictive Maintenance (call-up cards), Routine Testing, Operating Routine, which focus on maintaining a high reliability of safety and process systems, as well. These are not included herein but their contributions to the Aging Assessment (AA) as well as to the performance of the plant are very important. 1- GENERAL CONSIDERATIONS ABOUT EMBALSE-NGS Embalse NGS is located on the shore of the Embalse Lake, in the province of Córdoba, Argentina and is operated by NUCLEOELECTRICA ARG. S.A., which also operates Atucha I (a PV-HWR designed by SIEMENS-KWU). Embalse NGS has the following features: - CANDU 6 type with 648 MWe output, - First criticality in 1983, and Commercial Start up in January Load Factor (LF) in the last 10 years %. - Designed for 30 years of operation with a LF of 80%. End of design life is estimated to be in Period between planned outages: originally 12 months. Since 1992: 18 months. The safety impact of this period change between outages was assessed as very small with the PSA and agreed with the regulatory body. Nucleoeléctrica Argentina S.A. (NA.SA) -Embalse NGS s operator- has initiated the first Phase of a PLEx program. A specific Working Team has been implemented to this effect and has received training from AECL in PLiM methodologies. This work is under development.

2 The team is an integration of Embalse plant personnel and CNEA (Comisión Nacional de Energía Atómica - nuclear R&D governmental institution) staff. The group constitution is still in progress and is now incorporating some additional experienced personnel from the plant. Argentina currently has two operating NGS s: Embalse and Atucha I. Another one is under construction: Atucha II. Atucha I NGS started its commercial operation in 1974 and has a design life of 32 FPY (Full Power Years). With an average capacity factor of 68,32% the end of the design life is foreseen for the year NA.SA has not yet considered the Life Extension of Atucha I NGS. The official decision for the completion of Atucha II gives additional reasons for the Embalse PLEx, providing continuity to the Argentinean nuclear program and keeping alive the knowledge gained in nuclear industry. Besides, the continued economic growing after the 2001 national crisis makes all the possible sources of electricity important. This, along with the world trend of re-licensing of plants, which are reaching the end of their design life, is making the refurbishment methodology more standardized and less expensive. 2- EMBALSE PLEX PHASES There are different approaches to the phases involved in a PLEx program. Embalse is following a methodology developed by AECL, which is in agreement with the IAEA guidelines for this issue and is currently used with minor differences by the Canadian Utilities. A typical program for CANDU PLEx has three main successive phases: - Phase 1: Pre-project definition, - Phase 2: Project Engineering and preparation - Phase 3: Project Implementation. Phase 1 consists of all preparatory activities that are required to define the refurbishment scope and costs. The main elements of Phase 1 are: i. Systematic and rigorous condition assessments / life assessments (including recommendations); ii. Safety Assessment and analysis of features at Embalse related to current technology obsolescence and licensing practices (including recommendations); iii. Preparation of Preliminary Design Packages ( PDPs ) for design changes resulting from step ii mentioned above (note that PDPs include Cost-Benefit Analyses) and an overall economic analysis of alternatives to refurbishment; iv. Based on the conclusions reached in the PDPs, NA.SA s Utility Change Control Board (CCB) will make final decisions on which design changes are to be implemented. Then Phase 2 starts Phase 1 can be dived in two areas:

3 Aging Assessments (AA) of Critical Systems Structures and Components (CSSC). They are focused on determining the ability to perform their functions safely and economically. The AAs also include recommendations regarding the best way to handle the aging effects of the CSSC Safety Assessments (SA): They are aimed at complying with regulatory requirements as well as with safety concerns. Once these AAs and SAs are complete, a required design change package will result and must be evaluated in order to determine the feasibility of PLEx. Once this is done, it will be possible to make the Economical assessment in order to justify the PLEx, and to go on with Phases 2 and 3. Phase 2 includes the determination of the main outage date and duration, the engineering (basic engineering and detailed engineering) of the modifications to be performed, and the provision of spare / new equipment. Some of the key activities in this phase are: - Establish outage date and duration - Design modifications and specifications for service and supply provisions - Develop invitations to bid - Sign contracts with suppliers (for the engineering and / or construction of the suggested modifications and spares) - Complete detailed engineering and equipment supply, including site preparation, training, etc. Phase 3 is referred to as the extended outage that will be needed for retubing the reactor (Fuel Channel - and feeder - replacement also known as the refurbishment outage). In order to optimize this outage it is necessary to systematically identify which SSCs are candidates for repair / replacement during that outage, which is done in the previous phase 1. Also, as aging processes continue, current walk-downs, inspections, and maintenance or monitoring programs could not detect all degradation: additional inspections may be needed. Figure 1 shows the current schedule followed for the implementation of the three phases of the PLEx program at Embalse NGS.

4 Figure 1: Embalse NGS PLEx program 3- CURRENT ACTIVITIES Although activities are currently centered in the execution of Ageing Assessments and Safety Assessments, many other activities are taking place. For important Components for which there is a certainty of replacement and that are critical from the point of view of cost and time for supply and engineering development, Embalse NGS has started the Phase 2 in a separate way. This are: - Retubing, which consist on pressure and calandria tubes and feeders pipes replacement - Steam Generator replacement That is represented in Figure 1 with the overlapping of Phases 1 and 2. There are many other modifications / corrective actions that have been focused in a PLEx program for example the condenser retubing, the coating of circulating water main pipe with a protective paint, moderator heat exchanger modifications, enhancement of the In-service Inspection Program, etc.

5 3.1. Aging Assessment of CSSC Because of normal aging of materials during plant operation, a risk situation could be induced from the economic or safety point of view. This risk should be mitigated or at least minimized, predicting early failures and taking the proper and opportune corrective actions to prevent the material deterioration or failure. The Aging Assessment constitutes an important part in the PLEx feasibility determination. As it can be seen in the Schedule above, the initial step in the aging evaluation is a prioritization at the system and main components level in order to determine whether or not an Aging Assessment should be applied. This step was done with the support of AECL and using the experience of others CANDU 6 refurbishments. It starts with an extended list of 173 elements (systems, components and commodities) which constitute all the systems of the plant. Then with the help of external experience and very knowledgeable people from the plant the need for an Aging Assessment was determined. Two (2) main techniques are the used: Condition assessment (CA) and life assessment (LA). The splitting in CA, LA is done in order to save resources. The CA is basically less deep than the LA and is done using the information available at the plant or with information external to the plant that is easily available (not very costly information). Figure 2 shows a general scheme of the LA procedure. That scheme is basically the same as that used by the IAEA guidelines, but with some customization for Embalse. The decision whether to apply CA, LA or nothing is based on the criticality of the SSC, which is determined by means of a prioritization (screening) method. The criticality is based on: - The impact of the SSC failure on Plant Safety - The impact of the SSC failure on Plant Availability - The SSC cost including the replacement difficulties/issues. In the following Table is shown a scheme with the CA / LA application criteria. Table 1: Criteria for selecting the assessment methodology between LA and CA Critical Non-Critical but Relevant Non-Critical Active Components CA CA - Not analyzed - Not analyzed Passive Components LA CA - Not analyzed - Not analyzed Systems CA - Not analyzed - Not analyzed 99 CA and 19 LA were identified to be performed. Each analysis was divided into relevant parts and it was discussed who should do what. Also it was determined which organization has the lead responsibility: NASA or AECL. The result of the Screening of the Critical Systems Structures and Components, along with the responsible for each part of the required

6 assessment, was summarized in a Division of Responsibility Matrix (DOR matrix). See a part of the DOR matrix in Annex 1. This matrix was originally developed to identify the assistance required from AECL. It was further expanded later to 204 elements. This was done in order to include others suppliers (as for instance ANSALDO for the most of the BOP) and to break down and consider some components from the BOP not included or included in a single group. This matrix was originally developed to identify the assistance required from AECL. It was further expanded later to 201 elements. The new assessment arise as a result of include others suppliers (as for instance ANSALDO for the most of the BOP) breaking down the previously identified assessment and considering some components from the BOP not included or included in a single group. The final DOR matrix gives the following distribution of assessments and responsibility: Table 2: Resume of the DOR matrix Assessments under AECL responsibility 21 Assessments under ANSALDO responsibility 61 Assessments under NASA responsibility 79 Commodities Condition Assessments COMM 50 Components Condition Assessments CCA 19 System Condition Assessments SCA 75 Components Life Assessments CLA 16 Commodities Life Assessments COMMLA 3 Required Assessments SCC that not require any assessment Total

7 Assessments Aging Assesments AECL ANSALDO NASA Commodities LA Components LA System CA Components CA Commodities CA Responsible A Pilot Aging Assessment of a group of four important components was conducted, in order to validate CNE procedures for the project. The following types of documents have been developed: Table 3: Documents generated in PLEX Qty Type Code Comments 8 Procedures GPEV-CNE-P-XX some of them still under preparation 7 Task instruction GPEV-CNE-IT- XX Are instruction for specific task, at a lower level than the procedures. 7 Aging Assessment GPEV-CNE- include Life Assessment and EE/EV-XX Condition Assessments 23 Reports GPEV-CNE-I-XX which constitute the support for the Aging Assessments, e.g. Walkdown reports, Chemistry reports, etc. Table 4: List of System / Components for the pilot study BSI Name B01a04 Steam Generators LA Feeders LA P102 A, SG s Feed Water pumps LA B y C 3331-P1, P2 PHT Feed pumps CA This pilot study also involves the elaboration of the Embalse s specific procedures for the CA & LA mentioned above. The group was selected taking into account

8 - A proposed list from AECL, - The knowledge about the critical components in the plant - Both active and passive components in order to validate the procedures. IAEA-CN A review of the results and the use of the methodology have been done by experts from AECL. The work performed by NASA PLEx team was found to be satisfactory. Several points were discussed and as a result of the revision, a change to the procedure was introduced, concentrating the effort in the aging-related issues. In addition to the pilot study others components have already been assessed those are: Large Nuclear Heat Exchangers (Which includes Heat Exchangers for the following systems: Shutdown Cooling, Moderator, PHTS Purification, ECC) DCC (AECL responsibility). The rest of the required assessments are in progress. Its finalization is expected to be done accordingly with the above schedule for what a detailed and careful planning and tracking is necessary. In that sense, the commodities are of special interest as this have to finish before the systems CA conclusions. It is worth noticing that many recommendations will arise from assessments and it is important to have a way to manage them properly. A database is under development at Embalse NGS, aimed at managing the execution of the proposed recommendations and modifications. To achieve this, criteria are being determined to prioritize recommendations and to schedule and follow their execution. In the same way a lot of documentation will be generated in electronic format and its handling is also a NA.SA concern. The current challenge will be to make the best use of the computer technologies changing the staff habits of working with papers Walkdowns Walkdowns are a powerful tool for aging assessment. It is very important to see in the field what is found (or not found) in the documentation. Inspections, maintenance activities and system / component configuration review can give extra information if they are performed searchingly, using an Aging-Thinking criterion. Interviews with SSC s responsible staff are also performed in order to get the feeling and experience from the people who daily deal with the SSC s. During planned outage 2005, several walkdowns were performed. Planned outages are an excellent opportunity to see those SSCs that are inaccessible, during on power. In 2005 walkdowns were performed checking general equipment and those SSC s that had been previously assessed (i.e. steam generators, steam generators feed pumps, feeders and PIC feed pumps). Besides, specific walkdowns were performed with AECL specialists. Nuclear piping, civil structures and main cables were checked and many useful recommendations emerged from these walkdowns. In the March-April 2007 planned outage, again general and specific walkdowns were performed with designers in order to gather information from both the BOP (along with ANSALDO) and NSP (along with AECL) systems. Also the implementation of some of the recommendations emerged from the aging assessments were initiated. Seismic walkdown has also been performed during the 2007 outage in order to support the SA s.

9 The fact of having a team on site doing the assessment is an advantage from a point of view of the walkdown as well as the close relation with the engineering, maintenance and operating staff of the utility Team Development / Management reorganization A new managing body has been created to achieve the Plant Life Extension of Embalse NGS. This is the Life Extension Project Office. Organization charts attending the requirements of each of the phase have been done. A new group of forty-five people, have enlarged the original group. All of them are working together for the new head office, which have its head at the Embalse site. Activities done to date have contributed to the team consolidation and to the interaction of the team with the rest of the plant staff. Besides, a selection of new staff is still in progress both for Plant Operating and for the PLEX projects including the resources for the next phase Safety Assessments The SAs are mainly focused on providing answers and information to the expected Licensing Requirements, the need for updating Deterministic and Probabilistic Analyses and the comparison of Embalse with newer CANDU 6 design plants and other CANDU 6 plants in order to determine the areas for potential improvements. Since they involve many decisions related to the definition and compliance with the safety goals for the extended life, NA.SA s preference is that AECL, or other supplier, provide assistance while NASA keeps the leadership in the document production. There are two groups of SA s. For the first one, NA.SA s intention is to ask for assistance from AECL. The second one is going to be addressed only by NA.SA. The first group includes the following aspects: 1- Review of all accident analyses included in the Final Safety Analysis Report, using current analysis tools and methodologies, and taking into account the design changes that will be introduced to the plant during the refurbishment. 2- PSA-Related Tasks for Seismic Events and Flooding Events. NASA has already produced a very detailed level 1 PSA for full power and Shutdown States, and a PSA for internal Fires is currently in progress. A seismic re-evaluation of the plant is being carried out, with the methodology of the Seismic Margin. Work is performed with the assistance of AECL and of national universities. A first seismic walkdown has already been performed during the 2007 outage. Many recommendations for improvement arised from this walkdown. 3- Inventory of CANDU 6 Safety Design Changes: a thorough listing of safety related design changes relevant to CANDU 6 plants has been compiled, and these design changes have been categorized according to their potential applicability to Embalse. The applicable changes will be analysed by senior NA.SA staff to select those that will be implemented at Embalse.

10 4- Review of Trip Coverage: AECL has supplied NASA an Input Document related to Trip Coverage that includes a list of shutdown systems trip parameters and set points at today's Canadian CANDU 6 plants, together with the design basis for each trip (accident scenarios that require the trip coverage and the acceptance criteria). Also proposed parameters to be added during the refurbishment of Canadian plants are included in the document. A comparison with the trip coverage at Embalse is performed, and recommendations for improvement are made. These recommendations will be analyzed taking into account regulatory requirements in Argentina. The second group of SAs, which will be addressed only by NA.SA, are: 1- Review of the Embalse level 1 PSA study including the shutdown PSA. This was done for Embalse and was not reviewed by any external organization, other than the regulatory authority but with a limited scope. 2- Review of the safety of the plant against modern standards and practices, based on IAEA's Periodic Safety Review methodology. This is expected to become a requirement of the National Regulatory Authority. 3- Review of safety system reliability. This is going to be done with the current PSA models, by using the appropriate requirements for minimum unavailability. 4- Determination of the best way for doing the Benefit-Cost Analyses that will support the refurbishment and life extension decision. 5- Human factor Engineering program. Even when there has not been a systematic plan for the execution of the SA, some work has been already accomplished. For instance, the PSA, which has been done in a very good level of detail according to the ARN s (Argentinean Nuclear Regulator) requirements, is now very useful. The review of system reliability is also based on the PSA models, and having good Fault trees models is an important advantage. Many other tasks are partially performed in the day-by-day operation. For instance, the analysis of the applicability of the design changes incorporated in other CANDU utilities. This comes to the plant through the Nuclear Associations such as WANO, COG, IAEA, or through the designer AECL- who is always looking for safety improvement in the CANDU plants. Issues like the trip coverage have been analyzed in the Safety Report but have not been updated. In addition, NASA has some analysis and thermal-hydraulic codes and models for this. 4-AGING ASSESSMENTS RESULTS This section, briefly explain how the main results are summarized. The results emerging from the aging assessments are documented in the Assessment report as conclusions, judgments of health prognosis, and recommendations. Conclusions include conclusions with respect to life attainment (to January 2011), and separate conclusions with respect to life extension.

11 Using all the inputs into the condition assessment process, a judgment is made of the health or life prognosis in relation to life attainment (to January 2011), and life extension (by 30 years beyond 2011). A health prognosis (excellent/good/fair/poor) should be assigned to each SCC covered by the aging evaluation, and also an overall prognosis should be assigned to the SSC. Suggested definitions applicable to both life attainment and for life extension for each of the categories are provided in the procedures. Recommendations include: special inspections to disposition an ARDM/address uncertainties in the evaluation an ARDM, improvements to existing plant programs, design changes, repairs, replacements, control of operating conditions (chemistry for example), etc. This are organized into one of the following 5 categories: 1. Repair or replacement that requires an extended maintenance outage (i.e. refurbishment outage) 2. Repair or replacement during normal maintenance outages 3. Plant program support activities to condition assessment 4. Plant program enhancements 5. Economic opportunities 5- ECONOMIC & FINANCIAL EVALUATION With all the modifications arising from the SA and the AA, it will be necessary to make decisions on the investments to enhance plant reliability and predictability. The analysis must consider the current and future conditions of the plant (for instance the possible increased cost of maintenance of an aged plant). Embalse is now in the process of establishing the best procedures for the economic analysis. Even when there are many guidelines for the Cost-Benefit Analyses for the modifications, there are some parameters that depend upon the national context (e.g. energy prices, the value of the repair and national provisions, etc). Another consideration is the possibility for up rating which could be convenient to be implemented during the refurbishment outage. The SA and AA have not addressed this possibility yet, but it is intended to be done once the pilot studies end and the AA s of the complete CSSC are started. 6- FUTURE CHALLENGES The main objective is to achieve safe and economical Long-Term Operation (LTO). Therefore, it is necessary to meet each of the target dates indicated in the schedule shown above. For all the activities and mainly for the refurbishment outage, NA.SA s intention is to maximize the local participation in the engineering and in the provision of materials. Besides the new staff already hired is necessary to take some plant staff from their current position to work on PLEx activities and replace them with new people. This will also assure the human resources for the operation of the utility during the extended life. A contact with the regulator has recently been established. It is interested in involving itself in this subject, in order to be able to set requirements and follow the process.

12 The use of modern technologies for data handling is also a challenge we are facing at. It will be very important to change the staff habits of working with papers making the information easily available to every body in the plant. Finally, it is our intention to work closely with IAEA - with whom NASA has a Technical Cooperation Project - as well as the designer, other plants and any other organization related with the nuclear technology, in order to take advantage of the new methodologies and the experience gained in this field.

13 Annex 1 Table 5: Division of Responsibility (DOR) Matrix Component / System Nº serie BSI CONDITION AS- SESSMENT LIFE ASSESSMENT include in each assessment, within the scope boundary. AECL information sources and from NASA. c) Perform Interviews with the Plant site staff. d) Perform site walkdowns. data gathered for use in this assessment, including mechanisms a chemistry (Age review. Related Degradation Mechanisms Assessment). Prognosis of components, including associated recommendations. h) Complete Draft report. and disposition comments. j)perform external review ments and issue final report. l) Lead responsibility SCC Supports (raceways, trays, etc) X N N N N N N/O N/O N N A N N Reactor Building Containment Penetrations X N N N N N N/A N/A N N A N N Reactor Building (RB) X N N N N/A N/O/A N/A N/A A A N A A Main Moderator System X N N N N/A N/A N/A N/A A A N A A Large Nuclear Pumps X N N N N/O N/O N/O N/O N N Large Nuclear Heat Exchangers X N N N N N N N N N A N N Large Nuclear Vessels X N N N N/A N/A N/A N/A A A N A A Moderator Purification System X N N N N N N N N N A N N Main Heat Transport System X N N N N/A N/A N/A N/A A A N A A Steam Generators X N N N N/O/A N/O/A N/O/A N/O/A N N A/O N N Feeders X N N N N/A N N/A N/A N N A N N Motors X N N N N/O N/O N/O N/O N N N N Isolated Phase Bus and Accessories X N N N N/O N/O N/O N/O N N N N

14 Figure 2: Flow diagram of a Life Assessment process PRIORITIZATION Determination of Critical Structures Systems and Components (CSSC) Information about: Obsolescence Programs Inspection areas Information gathering about the CSSC Subcomponentes Selection Probabilistic Safety Assessment (PSA) Plant availability Impact PLEX PHASE 1 LIFE ASSESSMENT Internal and external operating experience To provide understanding about the degradation mechanisms Additional R&D and inspection requirements Detailed Walk down Review of history and interview Chemical Review Analysis of Degradation Mechanisms Identify Aging Related Degradation Mechanisms Identify stressors To analyze effectivity or operation, maintenance and other plant programs Operating history Design of the plant Current Maintenance program (related with the aging management) Questions to the manufacturer. Review of design criteria Conclusions: Life Prognosis Requirements of maintenance, Inspection Upgrades or replacements IMPLEMENTATION Business case PLIM / PLEX. To implement changes in the assets management (plant programs) R&D and services area Engineering Utility