Identification of research areas in response to the Fukushima accident

Transcription

1 ÚJV Řež, a. s. Identification of research areas in response to the Fukushima accident Jozef Mišák International conference SES September 2012, Bratislava Panel III: World after Fukushima and stress tests. Should the Slovak energy policy be reassessed? Challenges for research and innovations

2 Content of the presentation Background R&D relevant lessons learned from the Fukushima accident Identification of areas for research and development Concluding remarks Acknowledgment: This presentation is based on the results of the work by the SNETP Fukushima Task Group composed of Elena Paffumi and Karl- Fredrik Nilsson, JRC Petten, Mike Smith, AMEC, Gaudenzio Mariotti and Paolo Contri, ENEL, Giovanni Bruna, IRSN, Benedikt Martens, SCK/CEN, Hans-Georg Willschuetz, EON and Jozef Misak, NRI Rez (Chair) Giovanni Bruna, IRSN 1

3 SNETP scope of the work SNETP stakeholders (at present more than organizations): nuclear industry, research centres, technical safety organisations, universities, etc. SNETP overall goal is to enhance the sustainability of nuclear fission by supporting technological development. Actions for ensuring sustainability of nuclear power: 1.Ensure long term safe operation of current Generation II reactors 2.Built and ensure safety and competitiveness of evolutionary Gen III reactors 3.Develop Gen IV fast breeders with closed fuel cycle 4.Enlarge the nuclear fission portfolio beyond electricity production: H 2, synthetic fuels, H 2 O desalination, paper, cement industry 2

4 3

5 Objectives of the Fukushima Task Group Tasks of the Group specified by the Governing Board at Meeting n 7 held in Rome, 31 March 2011 Assess the lessons learned from the accident, Assess the results of the stress tests, Assess their implications for SNETP, on Gen II/III, as well as on other components of the Platform, Make proposals to SNETP (and possibly in turn, by the Board to the European Commission), Link with ENEF Risks WG on the topic R&D should be the main focus of the Task Group: a framework document to be developed, later on to be detailed by other working groups 4

6 Causes of the accident and plant damages 5

7 Main accident sequence 6

8 Radiactivity release and radiation levels Cs release rate: from Bq/hr to 10 7 Bq/hr Site boundary: between 10 and 100 msv/hr Inside buildings up to 1 Sv/hr 7

9 Overview of recovery actions (by Tepco) 8

10 Temporary covering 9

11 Next activities Final damage state of RPV, CV, debris repartition not exactly known; available in some years Dismantling under preparation; fuel removal from SPF is expected to start within 2 years and from the RPV in 10 years. Hot cells will be built on the site to treat the non-transportable debris. R&D actions expected to be necessary to support the future recovery actions (developing monitoring tools, updated process for waste treatment, etc.)

12 Background In spite of Fukushima, majority of countries decided to rely on nuclear energy in their energy mix The accident should not stop the development, rather should form the basis for the improvements Nuclear safety should be science based in order to benefit from the state of the art knowledge and practices Actions needed nationally and internationally All stakeholders should learn from the accident: regulators, governments, operators, utilities, vendors, nuclear industry in large, engineering organizations, research and development Nuclear safety R&D constitutes an important base for safety improvements and accident prevention Accumulated experience should be reflected in international safety standards/rules/guidance for methodologies and computer codes for safety assessment 11

13 R&D relevant lessons learned from the Fukushima accident (1 of 4) Although existing NPPs are very safe, the accidents caused by certain hazards leading to common cause failures can not be completely eliminated Low likelihood of occurrence of any hazards only shall not be used as sufficient justification for elimination of the hazard from design considerations In particular, external hazards including their secondary effects must be given high attention as likely initiators of the common cause failures Quantified assessment of safety margins beyond the design basis should become an important component of the assessment Margins for protection against external hazards needs reconsideration using advanced methods based on historical data and latest hazard analysis including future projections 12

14 R&D relevant lessons learned from the Fukushima accident (2 of 4) Due to common cause failures several units on the same site can be affected at the same time and in such situation the interconnection between units does not represent a reliable back-up All NPP states (including shutdown regimes) and all sources of radioactive materials (including spent fuel pools) must be considered in the safety assessment The capabilities to predict the cause and consequences of severe accidents are still limited: there are areas where level of knowledge require further improvements Hydrogen production, transport, accumulation, flammability, explosions should be given high attention as a potential source of the safety barriers damage Accident management measures shall consider conditions of severely damaged infrastructure 13

15 R&D relevant lessons learned from the Fukushima accident (3 of 4) There is a need of advanced analytical resources capable to assist the crisis management Under station blackout conditions the timeliness in availability of recovery capability to ensure continued core cooling, spent fuel pool cooling and containment integrity is important Protection of containment integrity under post accident conditions including elevated pressure and hydrogen concentration is the issue of highest importance Certain natural external impacts and combination of such impacts can lead to a failure of all levels of defence in depth (CCF) and possibilities to increase robustness should be looked for Behaviour of various structural materials under severe accident conditions requires further attention 14

16 R&D relevant lessons learned from the Fukushima accident (4 of 4) Although the reactors should not necessitate filtered venting under certain conditions it may become an efficient way for protection against overpressurization under severe accident conditions Qualification/survivability of instrumentation under harsh conditions is an important precondition for accident management Some aspects of operational processes favourite for standard operation (top-down decision making) has turned into inefficient feature for the accident management Human/organizational factors under high stress and harmful conditions play essential role 15

17 Structure of the document developed by the Task Group 1. Introduction 2. Overview of challenges identified during Fukushima accident 3. Lessons learned from the Fukushima accident 4. Identification of research areas associated with the lessons learned 13 research areas addressed Lessons learned from the Fukushima accident Objectives of the activities in this area Examples of specific tasks in the given area 5. Basic insights related to research needs for Gen II and III reactors 6. Conclusions 7. References 16

18 Sources of information SNETP documents The IAEA expert mission report The Japan government report The Near Term U S Nuclear Regulatory Commission report The OECD/NEA Forum on Fukushima accident; this was actually a meeting of the NEA Committee on Nuclear Regulatory Activities (CNRA) The ETSON position paper on research needs for GEN 2 and GEN 3 NNPs The IRSN Special report on Fukushima The IAEA International Experts Meeting on Reactor and Spent Fuel Safety in the Light of the Accident at the Fukushima Daiichi Nuclear Power Plant, March 19-22, 2012 The report of the Fukushima Nuclear Accident Independent Investigation Commission (NAIIC), established by the National Diet of Japan 17

19 Identified areas for research and development 1. Systematic assessment of vulnerabilities to defence-in-depth and safety margins for beyond design basis loads 2. Human/organizational factors under high stress and harmful conditions 3. Improved methods for external event hazard evaluation 4. Use of the probabilistic methods to assess plant safety in relation to extreme events 5. Advanced deterministic methods to assess plant safety in relation to extreme events 6. Advanced safety systems for nuclear power plants 7. Advanced materials for nuclear power 8. Advanced methods for the analysis of severe accidents 9. Improved procedures for management of severe accidents 10. Assessment of the radiological effects of the severe accidents 11. Improved modelling of fuel degradation in the spent fuel pool 12. Methods for minimization of contamination in the NPP surroundings and for treatment of large volume of radioactive waste 13. Accident management in the framework of the integrated rescue system. 18

20 Systematic assessment of vulnerabilities to defence-in-depth and safety margins for beyond design basis loads Development a systematic methodology for the determination of safety margins and the risk of occurrence of cliff-edge effects for extreme events beyond the design basis. development and validation of methods for comprehensive evaluation of defence in depth measures, in particular for the third and fourth level of defence determination of the possible effects of extreme events with respect to interrelation between the plant system operation and personnel intervention development of acknowledged procedures for the assessment of the ultimate resistance of the barriers against releases of radioactive materials to the extreme loads development of suitable methodology for the identification of threshold phenomena (cliff edges) determination of the sensitivity of the main safety functions to extreme loads development of comprehensive models for assessing the behaviour of NPPs under the conditions of the beyond design basis extreme loads

21 Human/organizational factors under high stress and harmful conditions The analysis of the importance of the human and organisational factors for managing emergencies in the conditions of high stress and harsh working conditions, with the objective of identifying possibilities for improvement and to develop efficient assessment tools and procedures. assessment of the importance of human factors in the efficiency of accident management evaluation of the applicability of standard management methods on the capability of personnel to respond in emergency conditions analysis of the functionality of the various means of communication under conditions of heavily damaged infrastructure analysis of habitability of working places needed for management of emergencies development and updating of training materials for the preparation of emergency response teams, especially for the workers of the technical support centre evaluation of the effectiveness of interventions under extraordinary conditions assessment of needs of redundant technical means and emergency teams for individual units assessment of the conditions transfer of the responsibility for accident management from operational staff to higher levels of management, assessment of safety culture issues in accident management

22 Improved methods for external event hazard evaluation Development of methodologies for hazard evaluation for low probability events of both natural and man induced (accidental) scenarios. The research will aim at the minimisation of the uncertainties affecting the hazard and to the identification of suitable levels for the design basis values to be used for the design/reevaluation. identification of very rare, extreme internal and external events, potentially leading to common cause failures simultaneously arising on several units at the same site implementation of suitable methodologies for determining the frequency of occurrence of extreme phenomena with very long period of return, including the combination of extreme events, even in case of limited availability of historic data development of methods for hazard evaluation in the case of rare events (i.e. tsunami), with insufficient historic records available updating of methodologies for site selection in relation to the likelihood of extreme external events development of methods for expert elicitation of rare events

23 Use of the probabilistic methods to assess plant safety in relation to extreme events Improvement of the methodologies, harmonisation of the criteria and extended range of applicability of the methods with emphasis on a more comprehensive consideration of extreme external hazards, their combinations and the consequences of these hazards with prolonged duration and simultaneous occurrence on several units enhanced probabilistic approach for external events (flooding, climatic events) rules for practical elimination of mechanisms, leading to large damage to fuel and to large releases methods for evaluation of component failure modes in extreme unlikely scenarios analysis of the reliability of human factors, common cause failures, behaviour of the SFP, prolonged loss of UHS, long term SBO, non-availability off-site help quantification of PSA: extended periods of the accident, interactions between interventions of operators and systems, several units on the same site, reliability of recovery actions under harsh conditions consideration of the status and availability of reliable information on the infrastructure actual status assessment of the reliability of innovative design solutions (passive systems) methodology for probabilistic assessment of security threats to NPPs

24 Advanced deterministic methods to assess plant safety in relation to extreme events Improvement of methods for the assessment of the extent of the damage to structures, components and systems of NPP under various extreme loads beyond the design basis analysis of operating experience from the events initiated by unpredicted external events updating of methods for the assessment of effects of geophysical factors and extreme weather conditions, methodology for determination of the secondary effects of earthquakes, including the loss of the ultimate heat sink, floods, fires, loss of coolant, destruction of infrastructure, disruption of the access of personnel to the site, the dynamic effects of the destruction of the civil structures, hydrogen explosions modelling the effects of individual extreme events and their combinations, the identification and prevention of threshold phenomena (cliff edges) reassessment of e criteria for the design and evaluation of the effectiveness of protection against external hazards analysis of the operability of safety important equipment at the beyond design basis extreme events analysis of extreme events initiated by potential terrorist attacks

25 Advanced safety systems for NPPs Acquisition of the necessary knowledge and methods, demonstration of the reliability and functional capabilities of the innovative safety systems and components, in particular systems based on passive features Modelling the behaviour and assessing the efficiency and reliability of passive equipment and components, e.g. oimproved battery autonomy, opre-pressurized core flooding tanks (accumulators), oelevated tank, natural circulation loops (core make-up tanks), ogravity drain tanks, opassive coolers for secondary side of steam generators based on natural circulation, opassive cooling circuits for containment heat removal, opassively cooled core isolation condensers, opassive filtered containment venting systems, osump natural circulation, opassive hydrogen recombiners

26 Advanced materials for nuclear power Development of new structural materials for nuclear components with increased resistance to harsh operating conditions (corrosion, high radiation doses, high-frequency thermal and mechanical fatigue) further assessment of existing fuel and cladding materials in conditions of severe accidents and development of new fuel and cladding materials with increased resistance and improved coolability during severe accidents, assessment of existing and development of new structural materials for spent fuel storage (including dry storage) aimed at increasing their resistance to hazards, further assessing the degradation mechanism and ageing of materials, developing simulation and monitoring of degradation, including non-metallic materials, cables and civil structures, modelling and testing of the behaviour of components under severe accident conditions, execution of test programmes to determine material properties under severe accident conditions (e.g. irradiation, strain rate, high temperature) and development of data base to support analysis, evaluation of how the use of non-standard cooling media (e.g. polluted water) affect the integrity and functioning of components (e.g. blocking of valves, dampers, creation of deposits on cladding, effects on material of the reactor vessel, etc)

27 Advanced methods for the analysis of severe accidents Critical assessment of the state of the art, improvement and validation of robust computational tools for the comprehensive evaluation of the course of accidents in the reactor cooling system and in the containment, with a view of reducing the uncertainty in the results critical assessment of current knowledge (state of the art) modelling of severe accidents development and validation of models/simulation platforms for analysis of severe accidents validation of computer codes and assessment of uncertainties for severe accidents modelling of core heating, chemical reactions, degradation of the core, postaccident heat removal, coolability of overheated and partially destroyed core examination of interaction of materials under conditions of severe accidents possibilities of stabilisation of molten corium in the reactor vessel or in the containment efficiency of filtered containment venting progression of core melting in the reactor vessel or corium in the containment production, distribution and accumulation of hydrogen, the mechanisms of flame acceleration and the transition from deflagration to detonation issues of recriticality in complex geometries

28 Improved procedures for management of severe accidents Verification of effectiveness and extension of the scope of severe accident management strategies, development of alternative ways for obtaining information regarding the status and expected development of the accident update of possible accident management strategies optimisation and validation of strategies and guidelines for accident management, including simple but robust and effective passive measures investigation of new options for improved strategies for accident management and their prioritisation, ensuring the functional ability of instrumentation in conditions of severe accidents, development of alternative ways of obtaining information in loss of DC power development of prediction models needed for management of accidents, including on line ICT tools operating in real time use of advanced simulators to improve operators preparedness analysis of the possibilities for prevention of containment bypass, analysis of the possibilities of orevention of containment over-pressurization accurate monitoring and classifying all possible on-site and off-site intervention means

29 Assessment of the radiological effects of severe accidents Enhanced modelling of radiological consequences, with higher flexibility in considering links to the processes and activities in the plant, more accurate description of transport of radioactive materials in the vicinity of the plant determination of the release of individual radioisotopes from heavily damaged fuel, their physical and chemical forms improved modelling of chemical and physical forms of released radioactive materials from heavily damaged fuel improvement and validation of models for dissemination of radioactive materials in the atmosphere and in aquatic systems, including possible effects of explosions and fires development of probabilistic methods for contamination simulation (PSA level 3), use of high-quality meteorological data and weather forecasts in the analysis of radiological consequences harmonisation of transfer of data suitable for prediction of radiological consequences prediction of the effects of radioactive releases to the environment health effects of low doses of radiation

30 Improved modelling of fuel degradation in the spent fuel pool Improvement of knowledge, development and verification of adequate computational means for the assessment of processes in spent fuel pools including transition into a severe accident, systematic reassessment of development of accidents in SFPs re-assessment of accidents in SFPs caused by loss of cooling identification of potential pathways leading to severe accidents with fuel melting mechanisms of fuel degradation in SFP, focusing on late phase phenomena and 3D effects creation of chemical forms of the substances produced in heavily damaged fuel in the pool, taking into account the presence of an highly oxidizing atmosphere evaluation of the possibility of the re-criticality in SFP (including situations without fuel damage) possibility of production of hydrogen and the consequences of deflagration and detonation of hydrogen specific conditions for the source term and for dissemination of radioactive materials measures for the prevention of the degradation of nuclear fuel measures for mitigating the consequences of severe accidents methodology of analysis of the integrity of barriers in relation to SFP

31 Methods for minimization of contamination and for treatment of large volume of radioactive waste Evaluation of the effectiveness of existing methods of radiological environmental monitoring as well as the effectiveness and availability of the technical means for the rehabilitation of potentially contaminated territory evaluation of the potential extent of the contamination of the environment and its impact in case of a radiation accident methods of identification and assessment of the effects of the released radioactive materials methods of fixation of radioactive substances on the contaminated territory evaluation of methods and means of radiological environmental monitoring, assessment of the resistance of the off-site monitoring network against extreme external hazards the availability and efficiency of technical means for the elimination of the consequences of accidents and the rehabilitation of the territory

32 Accident management in the framework of the integrated rescue system Evaluation of the current status and proposal for improvements of the integrated rescue systems at the national level, with emphasis on the management of accidents of NPPs effectiveness of current rescue system for management of accidents, including assessment of its applicability for other hazards improvement of methods of risk assessment depending on the source term for various types of hazardous substances assessment of needs and feasibility of external support to the NPP at corporate, national and international level development of methodologies and instructions for radiation protection in emergencies development of training programmes and scenarios for emergency drills assessment of the size of evacuation zones in case of natural disasters improvements of the system for informing the public review of the suitability of the INES scale as a tool of communication with the public harmonisation of criteria of acceptability and intervention levels for radiation accidents technical and organisational measures for integrated rescue systems

33 Concluding remarks (1) The Fukushima accident did not change the reasons for maintaining/enhancing the role of nuclear energy in energy mix as sustainable, low carbon source reducing import dependence of EU R&D should be considered as essential tool for better understanding the phenomena, allowing better prevention and mitigation of severe accidents, and also a source of qualified manpower No completely new phenomena revealed from the Fukushima accident However the specific research tasks in identified areas shall be considered with the appropriate priority given to them in the update of the SNETP Strategic Research Agenda In particular, the issues related to rare extreme events and severe accidents should be considered in a more comprehensive approach to safety in order to better understand the design margins as well as the behaviour of NPPs under design extension conditions 32

34 Concluding remarks (2) Basic directions of the research programs, as defined in the key SNETP documents, remain valid. However, a modification and rearrangement of ranking and priorities among the research areas seems appropriate and should be considered for future revisions In particular, more central position should be attributed to the safety problems in a whole, so that the safety-oriented R&D could become the actual driving force and engine for any future program at the heart of the nuclear research agenda Issues associated with the plant life time extension remain valid tasks, but they should be associated with comprehensive safety assessment using modern safety standards The implementation of generation III reactors and the transition to 4th generation reactors remain important tasks, keeping high safety level as utmost priority 33