EU STRESS TESTS: SPANISH RESULTS ON SEISMIC EVENTS IAEA, International Experts Meeting on External Events

Transcription

1 IAEA (Vienna) 4-7 September, 2012 EU STRESS TESTS: IAEA, International Experts Meeting on External Events

2 INDEX 1. NUCLEAR FLEET IN SPAIN UNDER STRESS TESTS 2. PURPOSE AND SCOPE OF EU STRESS TESTS 3. SPECIFIC SCOPE ON EXTERNAL EVENTS 4. SPANISH RESULTS ON PLANT SEISMIC SAFETY: MAIN ISSUES 5. IMPROVEMENTS ADOPTED OR TO BE IMPLEMENTED 6. CONCLUSIONS

3 01 NUCLEAR FLEET IN SPAIN UNDER STRESS TESTS NPPs & FUEL FACTORY FACILITIES: 8 REACTORS IN OPERATION (6 SITES) - 2 TECHNOLOGIES (PWR & BWR) - 3 SUPPLIERS (W, GE, KWU) 1 REACTOR BEING DECOMMISSIONED 1 REACTOR DISMANTLED 1 FUEL FABRICATION PLANT PWR NPP (W) PWR NPP (KWU) BWR NPP (GE) NPP (IN DECOM.) NPP DISMANTLED FUEL FACTORY

4 02 PURPOSE AND SCOPE OF EU STRESS TESTS PURPOSE AND SCOPE OF EU STRESS TESTS

5 02 PURPOSE AND SCOPE OF EU STRESS TESTS Making full use of available expertise (WENRA), ENSREG group has developed the EU Stress Tests Specifications, on the basis of a comprehensive and transparent risk assessment. DEFINITION AND TARGETS. EU STRESS TESTS SPECIFICATIONS: (May/2011): Reassessment of the safety margins of every NPP in the light of the events occurred at Fukushima: extreme natural events challenging the plant safety functions and leading to a severe accident. Evaluation of the response of a NPP when facing a set of extreme natural events beyond its design basis. Verification of the preventive and mitigative measures adopted (defense in depth): protect from initiating events; avoid loss of safety functions; reinforce severe accident management.

6 02 PURPOSE AND SCOPE OF EU STRESS TESTS EU STRESS TESTS GENERAL SPECIFICATIONS The technical scope of the stress tests must consider essentially a deterministic approach when analyzing an extreme scenario, irrespective of its occurrence probability. Initiating external events considered must be credible at the site: earthquake, flooding, or other natural external events Combination of initiating external events and failures must be considered too (credible scenarios). Key safety functions: reactor core protection, containment isolation and integrity, nuclear spent fuel integrity (reactor, pools, containers).

7 02 PURPOSE AND SCOPE OF EU STRESS TESTS EU STRESS TESTS DEVELOPMENT PROCESS Plant review report by the licensees (Oct, 2011). Independent review by each national regulator (Dec. 2011). EU Peer Review (Jan-March, 2012) or Integrated European Review by multidisciplinary teams: Review of national reports, Supplementary questions, Country visits (one plant/country). All along the process the CSN closely interacted with the licensees, to focus some of their proposed approaches and improvements.

8 03 SPECIFIC SCOPE ON EXTERNAL EVENTS SPECIFIC SCOPE ON EXTERNAL EVENTS

9 03 SPECIFIC SCOPE ON EXTERNAL EVENTS EARTHQUAKES DESIGN BASIS: Identify for every plant the Design Basis Earthquake (DBE) as PGA, reasons for the choice, margins added, so as the methodology applied. Validity of data in time; current adequacy of design basis. Provisions to protect the plant against the DBE: key SSCs which are needed to safe shutdown and remain available after the earthquake; how to prevent reactor core or spent fuel damage; consideration of indirect effects (as failure of non seismic SSCs or internal pipework, loss of external power supply, situation outside the plant ). Plant compliance with its current licensing basis: maintenance tasks, inspections, periodic safety reviews.

10 03 SPECIFIC SCOPE ON EXTERNAL EVENTS EARTHQUAKES EVALUATION OF SEISMIC MARGINS (SM): Range of earthquake severity above which loss of key safety functions or severe damage to the fuel could be possible (beyond design basis). Range of earthquake severity for which the plant can withstand without losing confinement integrity (core and spent fuel storage). Specify which are the possible weak points and any cliff edge effects. Indicate if any provisions can be envisaged to prevent these cliff edge effects or to increase robustness of the plant (modifications of hardware, new procedures, organizational provisions). Consider, if physically possible at the site, the combination of an earthquake exceeding DBE and consequent flooding exceeding DBF (as dams or dikes induced failure).

11 03 SPECIFIC SCOPE ON EXTERNAL EVENTS FLOODING (and similarly Extreme Weather Conditions ) DESIGN BASIS: Flooding against which the plant is designed: Identify the design basis flooding (DBF) and methodology applied to define it. Sources of flooding, validity of data in time, current adequacy of design basis. Provisions to protect the plant against the DBF: water intake, power supply, situation outside the plant, effects linked to the flooding or to the origin phenomena (very bad weather conditions). Plant compliance with its current licensing basis. EVALUATION OF MARGINS: Level of flooding that the plant can withstand without severe damage to the fuel (core or spent fuel storage). Time between warning and flooding. Weak points, cliff edge effects; provisions to prevent them.

12 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY SPANISH RESULTS ON PLANTS SEISMIC SAFETY

13 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY SPANISH NPPs SEISMIC DESIGN BASES The DBE of Spanish NPPs ranges from PGA 0.1 g to 0.2 g (0.25 g in case of José Cabrera Spent Fuel Storage Facility, ATI). The Iberian Peninsula has showed low to moderate seismicity. SSC seismic classifications according to: NRC-RG 1.29; ANSI-N Licensees have verified the fulfillment of these design bases and their appropriateness (according to the original standards).

14 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY SEISMICITY MAP (IBERIA & MAGRHEB) FROM 1320 TO NOW Green dots are earthquakes happened before XX Century Red ones are shocks instrumentally located Brown ones means roughly located Big size dots represent Intensity MSK VIII Garoña Trillo J. Cabrera Almaraz, I - II Ascó, I - II Cofrentes Vandellós, II

15 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY SEISMIC MARGIN ANALYSIS Seismic margin beyond DBE was analyzed for all Spanish plants in the nineties and according with USA SM methodologies (EPRI and NRC). It was obtained by comparing the seismic margin of each SSC needed for safe plant shutdown, against RLE spectra anchored by 0.3 g. HCLPF values correspond to the mean seismic capacity of each plant, to reactor shutdown by two independent paths and maintaining the plant 72 h in a safe condition. Results and procces details were presented in past meetings: OECD - NEA Workshops on Seismic Risk (Tokyo, August 1999) and Seismic Re-evaluation of NPPs (Ispra, March 2001). IAEA, International Symposium on Seismic Evaluation of Existing Nuclear Facilities; Vienna, August 2003.

16 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY SEISMIC MARGIN ANALYSIS From the nineties the HCLPF of two plants has been upgraded. As specify in the EU Stress Tests, the HCLPF has been required for: SSC needed to reach a safe shutdown condition Containment integrity (including isolation devices) SFP structural integrity, including racks in the Spanish case SFP cooling and make-up systems Systems to cope with loss of electricity supply scenarios In Spain too, relevant systems to face a severe accident (used in SAM guides)

17 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY SEISMIC MARGIN ANALYSIS SITE DBE (SSE) SAFE SHUTDOWN SAFETY FUNCTIONS CONTAINMENT ISOLATION AND INTEGRITY SPENT FUEL POOL INTEGRITY (SFP) PGA HCLPF PGA VALUE OF PLANT SEISMC CAPACITY Trillo 0.12 g 0.20 g 0.30 g 0.24 g Temp. Stor. Buildg. 0.30g Vandellós g 0.30 g 0.30 g Cofrentes 0.17 g 0.28 g 0.50 g 0.30 g Ascó I-II 0.13 g 0.30 g 0.30 g 0.30 g Almaraz I-II 0.10 g 0.21 g Unit I 0.24 g Unit II 0.30 g 0.30 g Garoña 0.10 g 0.17 g 0.30 g 0.30 g

18 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY Regulatory Requirements followed: GL SUP. 4 -> NUREG > GL SUP. 5 Major Steps: RLE Selection: NUREG/CR-0098, EPRI 6041 (Red. Factor). Screening of plant systems: NUREG/CR-4482 (NRC Method.), EPRI NP-6041, NUREG 1407 (EPRI Method.). Screening of components: NUREG/CR-4482, NUREG/CR-4334 (NRC Method.), EPRI 6041, EPRI 5228 (EPRI Method.). Plant walkdowns: EPRI NP Capacities of components: CDFM (Conservative Deterministic Failure Margin), EPRI NP-6041, NUREG/CR Plants seismic capacity and associated probabilities of exceedance from the Spanish PSHA level 2 (1994).

19 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY EARTHQUAKES INDIRECT EFFECTS Internal Flooding. Enhancing robustness beyond design basis: Assessment of the seismic resistance of SSC identified (in PSA) as potentially generating initiating events or affecting mitigation systems. Barriers against flooding effects (drains, check valves, etc.) and instrumentation for their detection must be seismically qualified. New analysis required for piping seismically non-qualified. Identification of flooding scenarios caused by SSC with large masses of water that might give effects not analyzed, to identify protective barriers. New analysis & design modifications to be finished in short term (Dec. 2012).

20 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY EARTHQUAKES INDIRECT EFFECTS (Cont.) Fires and Explosions: Identification of combustible/explosive materials in the plant. Safe shutdown SSC should not be affected by that issue. Sloshing in Spent Fuel Pools & UHS: Loss of water inventory analysis for earthquakes of 0.3 g. Two fold potential impact: loss of pool inventory & internal flooding. All the plants have demonstrated no relevant impact. Earthquake Effects on Nearby Industries: Previous analysis have been revisited and their results considered appropriate for the Stress Tests context.

21 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY DAMS RUPTURE ANALYSIS Five plants have great dams upstream with a priory potentiality to affect corresponding sites. Dam structural resistance analysis: All the dams are able to withstand the DBE of affected plants. Different margins has been verified for each case. Dam break analysis have been performed (extreme worst case) Break conditions assumptions (dam type specific) Flooding analysis based on specific models: flooding timing & level The CSN will afford actions to try to harmonize the assumptions made in the licensees analysis and the ones considered for dam emergency plans.

22 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY DAMS RUPTURE ANALYSIS (Cont.) TRILLO (Dry Site) VANDELLÓS II (Dry Site) COFRENTES (DBE: 0.17 g) SM: Alarcón dam (0.26 g) and Contreras dam (0.44 g) Grading level/flooding level: 372 m / m ASCÓ (DBE: 0.13 g) SM: Mequinenza dam (0.16 g) and Ribarroja dam (0.14 g) Grading level/flooding level: 50 m / m

23 04 SPANISH RESULTS ON PLANTS SEISMIC SAFETY DAMS RUPTURE ANALYSIS (Cont.) ALMARAZ (DBE: 0.10 g) Seismic margin: Valdecañas dam (> 0.3 g) Grading level/flooding level: m / m GAROÑA (DBE: 0.10 g) Seismic margin: Arroyo (Ebro) dam (0.378 g) Grading level/flooding level: 518 m / 516 m JOSÉ CABRERA, ATI (Spent Fuel Temporary Storage Facility) (DBE: 0.25 g) Grading level/flooding level: 628 m / 626 m

24 05 ADOPTED IMPROVEMENTS OR TO BE IMPLEMENTED ADOPTED IMPROVEMENTS OR TO BE IMPLEMENTED

25 05 ADOPTED IMPROVEMENTS OR TO BE IMPLEMENTED SHORT TERM (up to Dec. 2012) UPGRADING THE SPANISH PSHA A new PSHA Level 2 not yet validated, has been considered (July 2012) by using specific tools from a CSN project (OPPEL), with considering two alternative seismotectonic zonations and adopting maximum magnitudes values from current faults palaeosismic data. Preliminary results matching with 10-4 /yr, as mean probability of exceedance value, show a discrete increasing above the DBE values in all plant sites, except in the Cofrentes site.

26 05 ADOPTED IMPROVEMENTS OR TO BE IMPLEMENTED MEDIUM TERM (Dec. 2014) MANDATORY BY THE CSN: All spanish NPPs under operation with a seismic margin lower than 0.3 g, must be upgraded up to reach a HCLPF mean seismic capacity of 0.3 g, and strengthen their seismic design in compliance with additional CSN requirements. VERY LONG TERM (farther than Dec. 2016) DECISION ADOPTED BY CSN: The CSN is developing a programme to develop a new Spanish PSHA according with the most recent IAEA standards and international experience.

27 06 CONCLUSIONS CONCLUSIONS

28 06 CONCLUSIONS CONCLUSIONS CSN s evaluation has not identified any aspect that involves a safety-relevant weakness which could require the urgent adoption of measures. Relevant improvements have been identified as: Increase the seismic capacity of relevant SSCs up to 0.3g. Increase the plant capacities to withstand internal events, such as internal floods, which could been produced by earthquakes. Implementation of appropriate measures to cope with extreme external events as flooding or weather conditions. All the identified improvements will be implemented in several stages from now to the end of 2016 (long term).

29 06 CONCLUSIONS ON-GOING ACTIVITIES IN SPAIN The Spanish National Report is not the end of our activities relating to the EU Stress Tests reassessment. The CSN still continues working on certain issues and performing the deemed necessary verifications. The CSN has requested licensees to conduct additional studies and to proceed with the detailed specification of the design modifications. Improvements implementation schedule based on a triple scheme: short (Dec.12), medium (Dec.14) and long-term (Dec.16). Any new information about what happened in Fukushima, or coming from other international experience, may give rise to new safety requirements.

30 THANK YOU FOR YOUR ATTENTION! Muchas gracias