SEVERE ACCIDENT FEATURES OF THE ALTERNATIVE PLANT DESIGNS FOR NEW NUCLEAR POWER PLANTS IN FINLAND

Transcription

1 SEVERE ACCIDENT FEATURES OF THE ALTERNATIVE PLANT DESIGNS FOR NEW NUCLEAR POWER PLANTS IN FINLAND Risto Sairanen Radiation and Nuclear Safety Authority (STUK) Nuclear Reactor Regulation P.O.Box 14, FI Helsinki, Finland ERMSAR 2010, Bologna May 2010

2 Licensing Steps in Finland Operating License Construction Construction License nuclear safety Bidding & site preparation energy policy Decision in Principle Siting including EIA Feasibility studies ERMSAR 2010, Bologna May,

3 Nuclear power plants in Finland Olkiluoto NPP (TVO) 2 operating units - ABB BWRs EPR under construction EIA done for Olkiluoto 4 Loviisa NPP (Fortum) 2 operating units - VVERs EIA done for Loviisa 3 Fennovoima Ltd EIA done for 3 alternative sites for a new plant ERMSAR 2010, Bologna May,

4 Plants listed in current decision in principle applications: Plant type Supplier Power TVO Fenno voima ABWR Toshiba-Westinghouse 1600 MW Fortum ESBWR KERENA AES2006 APR1400 APWR EPR GE Hitachi Areva NP Atomstroyexport KHNP, Korea Mitsubishi Areva NP 1650 MW 1260 MW 1200 MW 1450 MW 1650 MW 1700 MW ERMSAR 2010, Bologna May,

5 Key Finnish requirements for severe accidents 100 TBq release limit for Cs-137 (probability must be smaller than /a) Independence of severe accident systems designed for normal operation or design basis accidents Severe accident systems must be single failure tolerant Severe accident systems are classified to Safety Class 3 100% of easily oxidising reactor core materials must be assumed to react with water. limits the containment volume of some BWRs Containment filtered venting ERMSAR 2010, Bologna May,

6 STUK review of Applications for Decision in Principle STUK has sent in 2009 to the Ministry of Employment and the Economy preliminary safety assessments of the three new applications The safety assessments have two appendixes feasibility assessment of plant alternatives assessment of the suitability of the plant site The assessments are available in English on STUK web page: ERMSAR 2010, Bologna May,

7 STUK Feasibility assessment of the plant alternatives: severe accidents All plant alternatives were reviewed using the same structure focusing only on the main aspects of severe accident management: primary system depressurisation melt stabilisation containment heat removal hydrogen containment filtered venting severe accident instrumentation and control ERMSAR 2010, Bologna May,

8 ABWR, Toshiba Specific features: Isolation condensers (4x33%) Passive containment cooling system (4x33%) ERMSAR 2010, Bologna May,

9 ABWR severe accident systems Primary system depressurization: 8 pneumatic valves, 4 motor operated valves Heat removal from containment PCCS, 4x33%.Transfers decay heat into the IC/PCCS pool located in the reactor (aux) building. No need to refill the pool for 24 h Melt stabilisation Core catcher. Steam produced in the core catcher is condensed via PCCS. Experimental program to validate core catcher design is under way Hydrogen Inerted containment Containment is dimensioned for hydrogen produced due 100% Zr oxidation Containment filtered venting Will be installed if the plant is build in Finland ERMSAR 2010, Bologna May,

10 ESBWR Specific features: No main coolant pumps (nat. circulation) Isolation condensers (4x33%) Passive containment cooling system (6 x 11MW) ERMSAR 2010, Bologna May,

11 ESBWR Severe accidents Primary system depressurization: 8 squib valves for depressurization (DPV) Heat removal from containment PCCS, 6x11MW. Transfers decay heat into the PCCS pool located in the reactor (aux) building. No need to refill until 72 h melt stabilisation Core catcher (BiMAC). Bimac is flooded from gravity driven cooling system (GDCS) pools. Steam produced in BiMAC is condensed in PCCS. Experimental verification is required for construction permit, if the plant is selected Hydrogen Inerted containment 100% Zr oxidation has not been assumed for the US ESBWR (containment size). Vendor is investigating possibilities to fulfil the Finnish requirement Containment filtered venting Not in the US ESBWR. Will be installed, if the plant is built in Finland ERMSAR 2010, Bologna May,

12 ESBWR Passive Containment Cooling System (PCCS) ERMSAR 2010, Bologna May,

13 Areva KERENA BWR Large number of passive safety systems emergency condensers passive containment cooling passive pressure pulse transmitters ERMSAR 2010, Bologna May,

14 KERENA Severe accidents Primary system depressurization: forcing the safety valves open, 4+4 valves operated by pilots heat removal from containment containment cooling condensers (CCC), 4x5 MW. Transfers decay heat into a pool in the reactor building Melt stabilisation Melt retention within RPV by external cooling of the vessel. Large vessel improves margins Hydrogen Containment inerted during normal operation 100% Zr oxidation taken into account in containment design Containment filtered venting No ERMSAR 2010, Bologna May,

15 Korean KHNP APR1400 PWR Specific features: two loop plant new type of safety injection tanks (accumulators) which eliminate need of LPSI double containment for the Finnish alternative IVR-ERVC ERMSAR 2010, Bologna May,

16 APR1400 Severe accidents Primary system depressurization: two independent motor operated depressurization valves (2x100%) Heat removal from containment Containment spray system reserved for severe accidents (SACCS). Active components are 2x100%. Some modification may be needed to fulfil the Finnish N+1 requirement Melt stabilisation Melt retention within the pressure vessel by external cooling. Coolant injection 2x100% (active components) Small margin to critical heat flux! Vendor investigates alternative solutions Hydrogen ~40 recombiners, large containment Containment filtered venting Will be installed if the plant is build in Finland ERMSAR 2010, Bologna May,

17 Mitsubishi APWR Specific features: single containment (dome area) new type of accumulators eliminate need of LPSI ERMSAR 2010, Bologna May,

18 APWR Severe accidents Primary system depressurization two motor operated depressurization valves 2x100% Heat removal from containment Containment spray/rhr (DBA-system) a new system utilising the passive parts of containment ventilation system (2x100%?). Experimental verification is needed Melt stabilisation melt discharge into a wet cavity. Top cooling of a debris bed = Olkiluoto 1/2 concept. MHI is investigating other possibilities (core catcher?) Hydrogen Recombiners, large containment Containment filtered venting Will be installed if the plant is build in Finland ERMSAR 2010, Bologna May,

19 Russian AES2006 VVER. Severe accidents Primary system depressurization: pilot operated pressurizer relief valves does not fulfil the Finnish requirement for independent severe accident systems heat removal from containment passive containment cooling system (4x33%). water inventory sufficient for 24h, after that can be refilled from external reservoir Experimental justification is required at the construction permit phase melt stabilisation core catcher below the RPV. Experimental justification is required at the construction permit Hydrogen Recombiners, large containment Containment filtered venting not planned. Justification needed for construction permit ERMSAR 2010, Bologna May,

20 AES 2006 passive heat removal systems: PHRS/SG & PHRS/C (containment) external heat removal tanks on top of containment PHRS/C condensers steam and condensate lines ERMSAR 2010, Bologna May,

21 EPR is licensed in Finland according to Finnish requirements EPR (Olkiluoto 3) Severe accidents EPR Main features: Primary system is depressurized < 20 bar prior pressure vessel failure (2x100%) spray nozzles Core melt cooling in a separate compartment. Passive flooding (2x100%) x x passive flooding device Containment heat removal by sprays (2x100%) Hydrogen removal by autocatalytic recombiners (47) Containment filtered venting (1x) CHRS (2x) spreading compartment melt flooding via cooling device and lateral gap in-containment refueling water storage tank x x water level in case of water injection into spreading compartment FL flow limiter ERMSAR 2010, Bologna May,

22 Review summary All plant alternatives can be modified to fulfill the Finnish severe accident requirements Some of them need new development ESBWR containment volume to accommodate 100% Zr oxidation APWR melt stabilisation APR1400 melt stabilisation and status (May 2010) The Finnish Government has proposed favourable decision-in principle for two of the three applications (Fennovoima, TVO) The Parliament must ratify the decision. The vote is expected later this year ERMSAR 2010, Bologna May,