Activities of OECD/NEA in the Regulatory Aspects of Plant Life Management

Transcription

1 Activities of OECD/NEA in the Regulatory Aspects of Plant Life Management Andrei Blahoianu NEA / CSNI / IAGE Chairman Andrei.Blahoianu@cnsc-ccsn.gc.ca ccsn.gc.ca Alejandro Huerta OECD/NEA Nuclear Safety Division Alejandro.Huerta@oecd.org Second International Symposium on NPP Life Management, October 15-18, 2007 Shanghai, China

2 Overview Background on the OECD/NEA OECD/NEA s activities related to the regulatory aspects of long term operation and plant life management

3 What is the OECD? 30 Member countries < 20% World s population > 3/5 world s exports produce > 2/3 goods & services provides > 4/5 economic aid to developing countries generates > 4/5 nuclear power in world. 346 reactors units in 17 OECD countries. 10 more units under construction: 4 Korea, 3 Japan, 2 Slovak Rep., 1 Finland.

4 What is the NEA? Semi-autonomous body within the OECD. Established February 1958 as European Nuclear Energy Agency. NEA today comprises 28 Member countries and represents ~ 85% of world s installed nuclear capacity. Contributes to the development of nuclear energy as a safe, environmentally-acceptable and economical energy source through co-operation among its participating countries. Closely co-operates with IAEA as well as other international agencies.

5 NEA Strategic Arenas 1. Nuclear safety and regulation 2. Radioactive waste management 3. Radiation protection and public health 4. Nuclear science 5. Economics, resources and technology 6. Legal affairs

6

7 Joint CNRA/CSNI Strategic Plan - Main Challenges declining nuclear infrastructure increased public expectation on the safety in the use of nuclear energy industry initiatives to improve plant economics and safety performance in the production of nuclear power necessity to ensure safety over plant lifecycle new reactors and new technology

8 What are CSNI/CNRA contributions to regulatory aspects of plant life management?

9 Importance of structural integrity/ageing Materials degradation has been experienced worldwide since the inception of nuclear power plant operation Degradation is expected to continue as plants age and operating licenses are extended Unanticipated and unmanaged structural degradation could result in significant loss of safety margins and undermine public confidence. Resource burden on both regulators and operators

10 Historical Issues with Materials Degradation Radiation embrittlement of RPVs IGSCC in BWR piping BWR internals cracking Steam generator tube degradation IGSCC and low temperature creep cracking in CANDU feeder piping PWSCC in PWRs Boric acid corrosion IASCC in PWRs Vibratory fatigue Thermal fatigue Erosion/corrosion Concrete containment creep

11 Ageing management programs A: Environmental effects B: RPV PTS C: Fatigue, piping failures D: RI-ISI - NDE E: Containments and long term behavior of concrete F: Wire system ageing External hazard Seismic design, codes and standards Seismic input motions and damaging capacities

12 Environmental effects PWSCC in thick sections of nickel based alloys used in the reactor vessel head penetrations and other components, in particular Alloy 600 and its associated welds. Questionnaire Experience, Status of existing data and research, Regulatory practices in the various member countries.

13 RPV / PTS Reactor Pressure Vessel lifetime PROSIR (Probabilistic Structural Integrity of a PWR Reactor Pressure Vessel) Issue some recommendations on best practices in probabilistic determination of the PTS screening criterion to assure an understanding of the key parameters of this type of approach, like transient description and frequency, material properties, defect type and distribution, fracture mechanic methodology Complement to FALSIRE and ICAS program on RPV integrity. Final results in late 2007 Phase 3 has been approved on June 2007 to estimate the probability of crack arrest in order to have a complete round robin exercise on RPV integrity

14 Passive component failures in risk assessment PRA challenges -Models -Time dependent aging and degradation effects -Consideration of inspection monitoring -Passive failures: as initiators, as affecting failures of mitigation systems -Common cause and dependencies -Screening and simplified approach Structural integrity challenges -Operational history not sufficient alone -Analysis of precursors event important to infer probabilities -Understanding of physical behavior and models -Realistic, best estimate analysis -Explicit consideration and characterization of uncertainties -Synthesis of service history experience, physical models and expert judgment OECD/NEA Piping Failure Data Exchange project (OPDE)

15 Fatigue and thermal fatigue Vibration is still the main cause of fatigue failure of components in NPPs for non fatigue design components. Thermal fatigue mechanism is understood BUT predictability still remains an issue Consideration of environmental factors? As to current Codes, other mechanisms should be considered both at the design level and for component replacement Questionnaire: - Regulatory requirements and codes - Practical experience and incidents - Countermeasures related to stratification - Countermeasures related to mixing - Research on thermal fatigue - High cycle fatigue curve EPRI/NRC/CSNI Conference - (every other year) aiming to review the status - Load determination in thermal fatigue - Laboratory experiments for thermal fatigue - Environmental effects - Codes rules and guidelines - Engineering Consideration/Industrial applications CEA Benchmark 3D thermal load, simple enough to be reproduced by numerical simulations, in order to allow accurate mechanical studies and then validate or modify the assessment methodologies

16 Risk-informed ISI - Non destructive examination Risk based/risk informed in-service inspections developments, Qualification of NDT system to be used for the inspections. SOAR report on RI-ISI and NDT qualifications based on Questionnaire Workshop held in April 2004 in Stockholm Recommendations to CSNI/CNRA for a better use of RI-ISI and NDE qualification RISMET is a unique comparative study of various approaches to set up an ISI programme. Different approaches exist to screen components/structures WOG EPRI ENIQ Nordic countries approach US and Spain are using both quantitative and qualitative RI- ISI Sweden is using qualitative RI- ISI Others are either considering it or did pilot studies NDT qualifications is ongoing in several countries

17 Containment / Long term behavior of concrete 1. Assessment of containment integrity 2. Long-term behaviour of concrete in fuel cycle facilities

18 Assessment of containment integrity Loss of prestress force in tendons of post-tensioned concrete structures In-service inspection techniques for reinforced concrete structures having thick sections and areas not directly accessible for inspection Response of degraded structures (including finite-element analysis techniques) Instrumentation and monitoring Repair methods and Criteria for condition assessment Workshop on aging management of thick walled concrete structures including ISI, maintenance and repair in 2008 ISP 48 on containment capacity

19 External hazard: seismic hazards Seismic load affects all components and structures and can impact redundant protection systems 1.Safety Margin Evaluation of SSCs and Input Ground Motion etc. 2.Improvement of Regulation & Guidance on Seismic Design 3.Effect of Aging of SSCs on Seismic Safety 4.New Seismic Engineering Technology

20 3. Effect of Aging of SSCs on Seismic Safety Affect more components than structures Supports and anchorages have to be studied Seismic effects are reduced if an effective aging management program is in place

21 OECD OPDE Project Participants: Belgium, Canada, Czech Rep, Finland, France, Germany, Japan, Korea, Spain, Sweden, Switzerland, USA Co-operation efforts gathering Reg bodies and utilities. Piping failures or severances (>10% thickness) for all class of pipings 4000 events validated - 50 fields covering geometry, root causes, failure causes, etc The database contains enough information for deterministic and PSA uses. Second term Discussion on the third term

22 OECD/NEA SCAP Project Establish a complete database with regard to major ageing phenomena for SCC and degradation of cable insulation through collective efforts by OECD/NEA members, Establish a knowledge-base by compiling and evaluating collected data and information systematically, and Perform an assessment of the data and identify the basis for commendable practices which would help regulators and operators to enhance ageing management

23 OECD NEA ZIRP Project on Ex-Plant Materials from Zorita NPP Extract core internals materials from Zorita NPP to perform laboratories test The current proposal of this research project is limited to Core Internals Core internals components Core shroud (~ 4 cm thickness) Baffle plate (~ 2.85 cm thickness) Formers (~ 4 cm and 6 cm thickness) Bolts Some important features of these internals are: 26,5 EFPY High fluence: as much as 50/52 dpa in a real commercial reactor Thick sections in some plates: allows testing of specimens of sizes 1CT, to assess real through thickness property variation

24 OECD NEA ZIRP Project on Ex-Plant Materials from Zorita NPP Project include the following task: Task 1. Material Documentation, Fluence and Thermal Evaluation Task 2.Examination of Baffle-Former Barrel Assembly before Extraction Task 3. Crack Growth Rate Tests Task 4. Susceptibility to IASCC and Deformation Mode Task 5. Fracture Toughness Determination Task 6. Micro-structural and Micro-chemical Studies Task 7. Compilation of results and analysis The project will have two phases: Phase 1, including: Harvesting, task 1 and task 2 Phase 2: all other tasks

25 Concluding remarks CSNI and CNRA have identified the necessity to ensure safety over plant life cycle as one of the main challenges for nuclear safety that Reg. Authorities and research community will face. Actions are underway to address this challenge Effective ageing management involves taking informed actions to mitigate degradation of SCCs Based on understanding of the types of material and environments The OECD/NEA/IAGE currently contribute to LTO and Ageing Management in the area of structural integrity of components and structures Through technical tasks developing common understandings and approaches Direct link to regulatory concerns No guidelines per se but technical consensus and best practices reports