Threats to French PWR's Ultimate Heat Sinks

1. “Nuclear power for the people” Nesebar, 26-29 September, 2010 Véronique BERTRAND IRSN, France Système de management de la qualité IRSN certifié FRENCH PWR’S ULTIMATE HEAT SINKS THREATENED BY THEIR ENVIRONMENT

2. SUMMARY • Heat sink: generalities • Total loss of heat sink at Cruas unit 4 in December 2009 • Total loss of heat sink management from the initial design • EPR Flamanville 3 pumping station’s design • Conclusion

3. Heat sink - generalities FRENCH NPPs IMPLANTATION 58 reactors in operation (+1 under construction–EPR at Flamanville) 19 sites :  4 coastal • Flamanville (2×1300 MWe) • Paluel (4×1300 MWe) • Penly (2×1300 MWe) • Gravelines (6×900 MWe)  1 estuarine • Blayais (4×900 MWe)  14 riverside (including 11 with cooling towers)

4. Heat sink - generalities • Pre-filtration and filtration in the pumping station • 2 circuits supplied ensuring the reactor’s cooling • Cooling circuit of the nuclear island including safety systems called Essential Service Water System (ESWS) • Cooling circuit of the conventional island • Conventional island • Role of the cooling circuit • The cooling circuit of the conventional island isn’t a system important to safety

5. Heat sink - generalities CONVENTIONAL ISLAND NUCLEAR ISLAND Reactorcoolantsystem MSS TURBINE AFS ALTERNATOR HEATER FFCS RHRS CONDENSER SIS CSS CCWS ESWS Safetyheat sink Conventional heat sink COOLING TOWER REACTORS COOLING: CASE WITH COOLING TOWER

6. Heat sink - generalities REACTORS COOLING: A SAFETY FUNCTION • ESWS: cooling of an intermediate cooling system, the Component Cooling Water System (CCWS) • ESWS and CCWS are systems important to safety • ESWS: two redundant trains • CCWS responsible for cooling of safety equipment

7. Heat sink - generalities PROTECTION AGAINST EXTERNAL HAZARDS • External hazards considered from the initial design • earthquakes • external flooding • cold weather • snow • extreme wind • other phenomena • External hazards underestimated • freezing • frazil ice • high air temperatures • seaweed • vegetable matter • external flooding with or without extreme wind

8. Expérience feedback in 2009 TOTAL LOSS OF HEAT SINK AT CRUAS 4 IN DECEMBER 2009 • CRUAS NPP (900 MWe): 4 units • Date of the incident: 1st December, 2009 • Rated level 2 on the INES scale

9. Total loss of heat sink at Cruas 4 in December 2009

10. Total loss of heat sink at Cruas 4 in December 2009 CCWS Building CCWS Building ESWS Galleries ESWS Galleries Unit 1 Unit 1 Unit 2 Unit 2 Unit 3 Unit 3 Unit 4 Unit 4 ESWS Galleries ESWS Galleries trains A & B of unit 1 trains A & B of unit 1 B1 B1 A1 A1 A2 A2 B2 B2 B3 B3 A3 A3 A4 A4 B4 B4 trains A & B of unit trains A & B of unit 4 4 Intake coarse filtration Intake coarse filtration Intake coarse filtration Intake coarse filtration & trash removal system & trash removal system & trash removal system & trash removal system (1 grid/train) (1 grid/train) – – units 1&2 units 1&2 (1 grid/train) (1 grid/train) – units 3&4 B1 B1 B2 B2 A1 A1 A2 A2 A3 A3 A4 A4 B3 B3 B4 B4 Discharge basin Discharge basin Discharge basin Discharge basin Train B Train B Train Train A A Train Train A A Train Train B B Discharge ducts Discharge ducts Discharge ducts Discharge ducts Intake channel Intake channel Rhône river bed Rhône river bed Floating Floating dyke dyke River Rhône River Rhône Navigation Channel Navigation Channel

11. Total loss of heat sink at Cruas 4 in December 2009

12. Total loss of heat sink at Cruas 4 in December 2009 WHAT HAPPENED ? • 01/12/2009 : massive unprecedented blockage • ESWS train A unavailable • Reactor 4 shutdown • ESWS train B unavailable • Unit 4: total loss of heat sink  the first time in France concerning a PWR • National Crisis Organization activated • French public authorities (ASN) • Technical support (IRSN) • French utility (EDF)

13. Total loss of heat sink at Cruas 4 in December 2009 • Application of the Emergency Operating Procedures (EOPs) • Difficulties in the procedure • Unit 4 in a safe state 3 hours later • Use of the thermal inertia of the refuelling water storage tank (RWST) reserve • Efficient cleaning of filtration device and ESWS/CCWS exchangers • Total loss of heat sink lasted 10 hours • Units 2&3 partially lost heat sink

14. Total loss of heat sink at Cruas 4 in December 2009 Canadian pondweed plants

15. Total loss of heat sink at Cruas 4 in December 2009 LESSONS LEARNT • First ever occurrence on a PWR in France • Partial loss of heat sink on units 2 and 3 together with the total loss on unit 4 • Efficient management needs quick and reliable diagnosis of the situation and mitigation means • Need to improve the emergency procedure • Use of thermal inertia of RWST water proved to be effective • On-site trash rack pre-filtration cleaning devices proved to be insufficient  IRSN started an in-depth analysis of this incident

16. Experience feedback in 2009 OTHER EVENTS • Frazil ice event at Chooz B NPP in January • Vegetable matter ingress in Le Blayais NPP, February and March • Drum screens clogging at Fessenheim NPP in December

17. Experience feedback in 2009 CONSEQUENCES • Action plan from the utility EDF • Heat sink operating conditions and design • Operating procedures • Criteria for emergency organization activation • IRSN analysis • Characterisation of hazards • Monitoring and protection of the pumping station • Existing means, procedures, organization

18. TOTAL LOSS OF HEAT SINK MANAGEMENT FROM THE INITIAL DESIGN • Incident procedure evolution • Probabilistic safety assessment (PSA) contribution • Loss of heat sink on all units of a NPP

19. Total loss of heat sink management from the initial design of French NPPs INCIDENT PROCEDURE EVOLUTION • Use of the thermal inertia of the refuelling water storage tank (RWST) reserve • Emergency heat sink for cooling temporarily the component cooling water system (CCWS) • Throughout a containment spray system (CSS) heat exchanger • Foreseen enhancement: operation of one reactor cooling pump and one charging pump

20. Total loss of heat sink management from the initial design of French NPPs PROBABILISTIC SAFETY ASSESSMENT (PSA) CONTRIBUTION • PSA for PWR 900 MWe developed at IRSN • Potential scenarios resulting from a total loss of ultimate heat sink with a high frequency • Beyond the initial design • Implementation of modifications • Automatic disconnection of the reactor coolant letdown line

21. Total loss of heat sink management from the initial design of French NPPs LOSS OF HEAT SINK ON ALL UNITS OF A NPP • Recently subject to particular attention in France • Wide study following the partial flooding of Le Blayais NPP • Analysis of the guaranteed available on-site resources • Modifications: sufficient required capacities of steam generator water supply • Equivalent program for next safety reviews of other series

22. EPR Flamanville 3 pumping station’s design

23. EPR Flamanville 3 pumping station’s design • Improvement of the pumping station’s initial design • Four independent water trains • Two diversified types of filtration devices with screens and chain filters • Strengthening of the cleaning means of pre-filtration and filtration devices • Enhanced reliability of head loss measurements to pre-filtration trash racks and filters • New system: the ultimate cooling water system (UCWS) • Foreseen for cooling an intermediate cooling system, which in turn cools • The containment heat removal system (CHRS) • The fuel pool cooling system (FPCS) third train • Normal supply for ESWS and UCWS: pumping station • Diversified cooling source: connexion to the outfall structure

24. CONCLUSION • Environmental conditions can impact the safety of nuclear reactors  Come back to the initial design • 3 lines of defence • Prevention: identification and knowledge of hazards  Appropriate design equipment • Pumping station: monitoring, detection and protection means  To ensure a permanent ESWS flow rate • Management of a total loss of heat sink  To cool the reactor until the heat sink recovery • Expectation for EPR Flamanville 3 pumping station: to cope with external hazards

25. THANK YOUFOR YOUR ATTENTION