Gidropress presentation

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2006 Effect of HA-2 and SPOT systems on severe accident prevention in WWER-1000/392 design Presented by N.Fil OKB GIDROPRESS 3rd CRM of IAEA CRP on NC, Cadarache, September 11-15, 2006

1. Introduction: 

1. Introduction WWER-1000/V-392 design is developed on the basis of operating WWER-1000 (most are of V-320 model). WWER-1000 are in commercial operation in Russia, Ukraine, Czech Republic and Bulgaria (26 units, 400 r-y). Last commissioned are: 2000 – Temelin-1; 2001 – Volgodon-1; 2002 – Temelin-2; 2004 – Kalinin-3, Khmelnitsky-2, Rovno-4. Nearest years - 4 WWER-1000 at Tianwan and Kudankulam NPPs (configuration of the last one is very close to WWER-1000/392). Now AES-2006 design on the basis of WWER-1000 is under development for near future of nuclear power in Russia and bidding abroad. In Russia it is planned to introduce 2 GWt per year after 2010.

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Application of passive safety systems in WWER-1000/392 is directed to achievement of higher safety level, in particular in terms of CDF and LER.   Key systems for CDF decrease are: - SPOT - core decay heat removal system to prevent severe accidents resulting from station blackout, - HA-2 - core flooding system to prevent severe accidents resulting from LOCA with active ECCS failed. These BDBA sequences essentially contribute to core melt frequency for existing WWER-1000/320 plants.

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HA-2 – 4 trains, 8 tanks of 1000 m3 water with 16 g/kg boric acid. Long term core cooling in case of a LOCA with active ECCS failed. SPOT – 4 trains, air-cooled HXs, capacity about 3% of reactor rated power. Long term removal of decay heat via SG in case of station blackout. 2. HA-2 and SPOT systems HA-2 SPOT

Flow rate from HA-2: 

Flow rate from HA-2 Flow rate assumed for safety analysis SPOT capacity against air temperature

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To demonstrate effect of HA-2 and SPOT, analysis of SBO and LBLOCA sequences with and without operation of HA-2 and SPOT systems was performed. Analysis is of realistic type, e.g.: -initial plant conditions correspond to the normal operation at rated power without account for possible uncertainties in plant parameters; -core characteristics are assumed in accordance to design without account for the calculation uncertainties and errors; -failures of equipment (other than assumed in scenarios) and operator errors are not taken into account.   Analysis was performed by TRAP-97 code package (developed by OKB “Gidropress”, certified by Russian regulatory body). Its main codes are DINAMIKA-97 and TECH-M-97 codes. Some supporting calculations – by KORSAR-V1, RELAP5/Mod3.2 and ATHLET-1.2A. 3. Methodology

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EVENTS PREDICTION ( * - TRAP) PRE-TEST POST-TEST TRAP validation: ISP-27, SBLOCA, BETHSY

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PCT prediction (x – test, red – TRAP) TRAP validation: ISP-27, SBLOCA, BETHSY PRE-TEST POST-TEST PCT “prediction”

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TRAP validation: re-analysis of ISP-13, LBLOCA, LOFT Red solid squares – TRAP PCT “prediction” Calculation: 1-PCT; 2-time of PCT Experiment: 3-PCT; 4-time of PCT Event’s “prediction” (BEMUSE program of OECD/NEA)

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4. Effect of SPOT for SBO sequence Without SPOT With SPOT Reactor outlet temperature Peak cladding temperature 1 – ATHLET, 2 – RELAP, 3 – DINAMIKA, 4 - KORSAR

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5. Effect of HA-2 for LBLOCA sequence Coolant inventory in RPV Peak cladding temperature TECH-M RELAP5 Without HA-2 With HA-2

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6. Conclusions Station blackout accident without operation of SPOT system results in exceeding of maximum design limit of fuel rod damage already in 2-2.5 h after initiation of accident. Operation of SPOT system prevents any core damage during this BDBA.   LBLOCA with active ECCS failed without operation of HA-2 system results in exceeding of maximum design limit of fuel rod damage in a few minutes after initiation of accident. Operation of HA-2 system prevents core damage above DBA acceptance criteria during this BDBA.   New passive safety systems HA-2 and SPOT allowed significant improvement of plant safety. In particular, core melt frequency for WWER-1000/392 design is about three orders of magnitude less than for operating WWER-1000/320.