ASSESSMENTS OF SWEDISH NUCLEAR POWER PLANT IN THE AFTERMATH OF THE FUKUSHIMA DAIICHI ACCIDENT

Transcription

1 ASSESSMENTS OF SWEDISH NUCLEAR POWER PLANT IN THE AFTERMATH OF THE FUKUSHIMA DAIICHI ACCIDENT Lovisa Wallin-Caldwell

2 Outline Introduction Swedish nuclear power plants Swedish nuclear power regulation Back-fitting and modernisation Severe accident mitigation systems PSR Outcome of EU stress stests Results and future work (National Action Plan) Thoughts and reflexions

3 Swedish nuclear power plants and installations 7 ASEA BWRs (5 different designs) 3 Westinghouse PWRs (2 different designs) BWR ASEA Atom PWR Westinghouse Forsmark NPP Other Fuel manufacturing Westinghouse SE Ringhals NPP Final Low/interm. Waste storage Studsvik Research center and waste treatment Oskarshamn NPP Barsebäck NPP Permanently shutdown Central intermediate Spent fuel storage CLAB

4 The Swedish nuclear power regulations The Swedish nuclear power regulations Goal oriented requirements and non prescriptive Developed based on the US GDC with extended requirements regarding e.g. grace periods, diversification, separation, natural phenomena, severe accidents SSM is currently revising regulations for nuclear power plants. This review will consider The outcome from EU stress test and 2 nd extraordinary CNS as well as WENRA RLs and IAEA safety standards The IRRS mission in 2012 International requirements for new reactors

5 Back-fitting and modernisation Continuous back-fitting and modernizations Mainly driven as a result of experience from events, issues identified during operation and new knowledge (research) Safety modernisation programs were introduced following the new requirements issued in 2005 Requirements concerning Natural phenomena and external events earthquakes, flooding, winds, ice, LOOP, Loss of UHS, etc Common Cause Failures Separation and Independence SAM (long term cooling, etc) Examples Replaced reactor protection systems Additional redundant safety trains are introduced Installation of hydrogen re-combiners

6 Severe accident mitigation measures

7 Schematic view of the severe accident mitigation features installed in Swedish NPPs BWR PWR

8 PSR (every 10 year) Introduced in the 80 s (regulated since1999) Have not been the driving force for back-fitting or modernisation in Sweden, because these measures have been separately and continues introduced (e.g. following new requirements and experience from events)

9 The outcome of the EU stress test SSM issued a National Action Plan (NAcP) covering all identified issues and potential measures that would be further evaluated and implemented Covers recommendations from the Licensees stress test reports National stress test report Peer review national report Compilation of Recommendations and Suggestions report CNS Categorized based on urgency and complexity with deadlines 2013, 2014 and 2015 Technical and administrative measures based on the results from assessments and evaluations (2020)

10 The outcome of the EU stress test, cont. The Swedish NAcP defined essential safety goals Extreme natural events 10-5 /yr Electrical AC power lost for 72 hours UHS lost for 72 hours Multi-unit events Containment filtered venting system available for 7 days Results and experience will be used as an input to regulations SSM introduced recurrent meetings with NGO

11 Significant issues and actions in the Swedish NAcP Updated seismic analyses secondary effects Paleoseismological data Further assessments of : extreme weather conditions incl. flooding, ice storm, etc. electrical power supplies and distribution system instrumentation and monitoring spent fuel pools hydrogen management Independent core cooling system A decision draft was prepared before Fukushima accident in 2011 and was put on hold after the accident. The purpose of the system is to increase Diversification Robustness (external events) Separation Multi-unit events

12 Actions taken Inspections, testing and verification Incl. SOER WANO Additional mobile equipment, lights, battery chargers and air compressors Updates to analyses, procedures, routines and training programs Reinforced firefighting services SAM systems improvements

13 Challenges when implementation the Swedish NAcP Seven different designs Ongoing modernization program Coordination with security Ongoing development and future integration of new regulations

14 Thoughts and reflexions Useful exercise that identified and highlighted important weaknesses Needs to be integrated in the overall supervision (could for example be introduced as part of the PSR) Public interest differed significantly between countries The EU stress tests were to a large extent a screening analysis. Potential areas of improvements were identified. Further evaluations or more detailed analyses were needed before specific measures could be specified.

15 Thoughts and reflexions, cont. The EU stress tests were limited in scope and did not consider plant and site specific risk profiles. Also, the timeframe did not allow for indepth evaluations The EU stress test specification allowed for interpretations Important differences between countries Differences between designs PWR respectively BWR Generations of designs Standards and guidance related to extreme external hazards (incl. extreme weather) were limited in scope Methods and methodology differed

16 Thoughts and reflexions, cont. Results are not trivial to read Similar plats could have significant differences in results Location of the plant are of great importance Seismic/low seismic regions External hazards are site specific Core damage and end state could be subject to interpretations Loss of safety functions RPV level Core heat-up Core melt Methodology and methods used varied Deterministic respective realistic and probabilistic Expert and engineering judgments Responsibilities within countries varies Emergency preparedness External support

17 Thank you for your attention!