Measures for Ensuring Hydrogen Fire and Explosion Safety for VVER-440/230 BEZLEPKIN V., SEMASHKO S., SVETLOV S., SIDOROV V., IVKOV I., KRYLOV Y., KUHTEVICH V

Measures for ensuring hydrogen fire and explosion safety for VVER-440/230 BEZLEPKIN V., SEMASHKO S., SVETLOV S., SIDOROV V., IVKOV I., KRYLOV Y., KUHTEVICH V. St-Petersburg Institute “ATOMENERGOPROEKT” (SPAEP), Russia

Abstract

This paper deals with the findings of calculation analysis as regards the release of mass, energy and hydrogen during BDBA at Kola NPP equipped with VVER-440 reactor (B-230 design) and in respect of distribution of hydrogen throughout NPP tight compartments. The analysis figures out the number and locations of passive catalytic hydrogen recombiners and of the sensors of the hydrogen concentration monitoring system. In order to prove the hydrogen safety of the design, it has been necessary to review accidents accompanied by maximum emissions (both peak and integral ones) of hydrogen into the tight area. During DBA, no steam/zirconium reactions occur in the reactor core. Out of BDBA, the severe accidents with damage to the core accompanied oxidative reactions between zirconium and steel with emission of hydrogen are regarded as the most dangerous ones. Assessment of additional hydrogen sources shows that the contribution of such sources to the total amount of hydrogen that may emit during a severe accident is insignificant. Calculations have been made for the following scenarios of severe accidents, which seem to be the most important in terms of hydrogen safety analysis: − 20 mm leak from the primary circuit in combination with a failure of the emergency makeup system; − 500 mm PCP rupture in the vicinity of reactor inlet branch with bi-lateral leakage of coolant. Releases of mass and energy during the aforesaid scenarios, changes of medium parameters within the tight compartments and analysis of possible fire conditions have been analyzed by means of Russian computer codes RATEG/SVECHA/HEFEST, KUPOL-М and LIMITS. The said analysis shows that the large break accident (500 mm), i.e. PCP rupture in the vicinity of the reactor branch with bi-lateral leakage of coolant is of the keen interest in terms of hydrogen safety. This accident typifies powerful short-term release of hydrogen at a significantly lesser integral release (as compared to a small leak accident). In the course of propagating the said accident, dangerous local concentrations of hydrogen may occur (with a possibility of rapid deflagration combustion) in the places which are closely located to the leakage. In this case, maximum volume of the boxes, where fast deflagration combustion may occur is commensurate with the volumes of main rooms. In case of 20 mm small primary leak and of a failure of the emergency makeup system, maximum emissions of hydrogen would be significantly lower than peak emissions during 500 mm large break accident, anyhow an integral release into the tight rooms would be drastically higher. Capacity of the hydrogen removal system has therefore been selected based on possible peak emissions of hydrogen, on the one hand, and a necessity of removing of huge amount of hydrogen within a long period of time, on the other. Avoidance of such combustion conditions whose loads may lead to a destruction of civil structures and of localizing safety systems has been the key criterion for selecting the locations and capacity of the recombiners. Analysis of various arrangements of recombiners allows to design the hydrogen removal system in such a way that the concentration of hydrogen in combination with aqueous steam and air would turn out to be lower than the concentration limits of fire propagation throughout the entire calculation range of changing the parameters of medium within the rooms during the accidents under review. The concentration monitoring system is built up so that operator would have representative information on the changes in the concentration of hydrogen within the tight rooms. Sensors are located in the places where hydrogen may very probably occur and such places have been determined based on the findings of calculation analysis. Thus, the measures aimed at removal and monitoring of hydrogen recommended on the basis of the presented calculation analyses are in full compliance with the requirements set out in relevant regulatory documents and maintain concentrations of hydrogen at the levels satisfying the hydrogen safety criteria.

St-Petersburg Institute “ATOMENERGOPROEKT” (SPAEP) Measures for ensuring hydrogen fire and explosion safety for VVER-440/230 z

V. Bezlepkin, S. Semashko, S. Svetlov, V.Sidorov, I.Ivkov, Y.Krylov, V.Kuhtevich (SPAEP)

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Computer analysis as the basis of hydrogen mitigation system for power unit 2 at Kola NPP

z improved analysis of mass, energy and hydrogen releases during beyond design basis accidents

z analysis of hydrogenz distribution in the confinement

z substantiation for amount and locations of hydrogen passive autocatalytic recombiners (PAR)

z substantiation for amount and locations of monitoring system detectors

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Severe Accident code RATEG/SVECHA/GEFEST (reactor plant analysis)

RATEG — best-estimate thermal-hydraulic code (comparable with RELAP5 class codes) Two-fluid 1D thermal-hydraulic flow 1D and 2D heat conductionz SVECHA — advanced set of severe core damage models Material interactions Flowing materials models GEFEST— lower plenum models Vessel-corium interaction Vessel deformations and failure

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Nodalization scheme of reactor V-230 (Kola NPP, power unit 2) Code RATEG/SVECHA/GEFEST

VESSEL_VKS-U RPV_WALL_U KTB20_VESSEL KTB20_P 2.68 VESSEL_VKS-U-OUTET HOT_WALL_VESSEL VESSEL_VKS-M-U Total calculation framework VESSEL_VKS-M- OUTLET 2.32 includs the following elements: VESSEL_VKS-M VESSEL_OUTLET BARREL- U RPV_WALL_M 155 hydrodynamic volumes 1.82 VESSEL_BYPASS_0 Условные обозначения: (channels and mixing chambers); VESSEL_BYPASS_1 канал VESSEL_VKS-L-M 0.92

камера BARREL-M 3 reactor coolant pumps (RCP) BZT_PERF_SHROUD

BZT_TUBES_LOW (37) BZT_TUBES_LOW VESSEL_INLET граничное условие

канал нулевой длины 15 boundary conditions of different

VESSEL_VKS-L тепловой элемент z

CORE_BAFFLE types (fixed wall, coolant outflow from break at given outlet pressure, BARREL-L RPV_WALL_L D_FA216 (216) VESSEL_DOWN1 input of coolant with given flow rate SHROUD_FA48 (48) ROUD_ARK_CUZ (37) CORE_FA48 (48x126) SH CORE_48

ARK_CUZ CORE_228 _FA12 (12) + SHROU EAT_SHIELD (36) CORE_BYPASS ORE_BYPASS_1 H

C and properties) SHROUD CORE_FA12 (12x126) + CORE_FA216 (216x126) 42 valves of different types -3.49 33 heat elements VESSEL_NKS 21 tabulated functions (material K (37) ARK

TUBES_ARK (37) VESSEL_LP-NKS2 VESSEL_DOWN2 properties, energy release, pump SHROUD_FA_AR CORE_FA_ARK (37x126) REL_ARK BAR run-out and others) VESSEL_LP-NKS VESSEL_LP-NKS1 -6.90 more than 350 controlling variables

VESSEL_LP

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Nodalization scheme of power unit 2 at Kola NPP. Loop with PRZ and steam generator

KTB20_PRZ TURB_1 KTB20_P

IPU1_PRZ KTB20_P

KTB20_P PRZ_U SG_OUT_TU RB_1

IPU2_PRZ SG_OUT_BR UA_1 KBT20_HC_1 KBT20_CC_1 KTB20_P KTB20_P KTB20_P Условные обозначения: PRZ_M PRZ_WALL_ канал SG_H C-U _1 SG_TUBES-U_1 (2544) SG_CC-U_1 SG_STEAM_1 PRZ_H EA TE (400) R PRZ_I SG_TUBE-U_1 (2544) SG_HC-M-U_1 SG_CC-M-U_1 камера 5. 38

SURGE_LINE_3 SG_HC-M_1 SG_TUBES- M_1 (1722) SG_CC-M_1 граничное условие

SG_TUBE-M_1 ( 1722) SG_TOP_1 (3) SG_HC-L-M_1 SG_CC-L-M_1 SURGE_LINE_2 канал нулевой длины

SG_HC-L_1 SG_TUBES-L_1 ( 1270) SG_C C-L_1 SURGE_LINE_1 MF_PRIM_A_1 SG_TUBE-L_1 (1270) тепловой элемент SG_UP_1 SAP_1_1 SG_IN_1 z SG_OUT_1 PR Z_SL_1 2.32 1.8 VESSEL_ OUTLET HOT1_1 HOT1_SAP HOT1_1_IN DUMMY_PRZ HOT4_1 H O SG_DC-U_1 T2 _ 1 0.92 HOT3_1 HOT3_1 HOT_ГЗЗ_1 SG_SEP_1 SG_efw HOT_WALL_1 (2) SG_FW_1 SG_EFWP_1

1. 10 0.92 SG_MF _1 PUM P1 VESSEL_INLET COLD6_1 COLD5_1 COLD5_00 BR EAK_R U BREAK_PUMP COLD5_1 COLD4

COLD1_1 SG_FW_IN_1

C OLD _W AL L_1 COLD_WALL_4 COLD_WALL_3 SG_RISER_1

BREAK CO LD 3_1

BR EAK_2 KTB20_P KTB20_P SG_TUBES-U (2544) -0.6 COLD2_1 1 Условные обозначения: _

COLD_WALL_2 A K_2

WALL_7 SG_TUBES-M (1722) W канал _

G SG_DC_1

камера SG_TUBES-L (1270)

граничное условие

канал нулевой длины

тепловой эл емент SG_BOTTOM_1

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Nodalization scheme of reactor V-230 (Kola NPP, power unit 2) Code RATEG/SVECHA/GEFEST

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Measures of severe accident management

Condition of use Control action

Difference between the coolant Opening of RPV depressurization temperature in circulation loops and system valves the saturation temperature gets less than 10 degree. Steam temperature above the corez Opening of PRZ safety valves, gets higher than 355 оС cooldown of the reactor plant through the secondary circuit by opening of BRU-K, BRU-SN and BRU-A valves Steam temperature above the core Opening of PRZ safety valves gets higher than 355 оС, and pressure in the primary circuit exceeds 12,74 MPa

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Determinative severe accident scenarios

z Leak from the primary circuit Dnom 20 mm with coolant make-up system failure z

z «LB LOCA» – double-ended break of PCP Dnom 500 mm near the reactor inlet

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Calculation results for in-vessel stage of severe accidents

Parameter Dnom 20 Dnom 500 Initial event, s 0 0 Actuation of emergency protection, s 447 3 Switching-off of turbo-generators, s 457 3 Opening of valves of emergency gas blowdown system, s 715 - Beginning of core drainage, s 1600 0,1 Beginning of core heating-up, s 9450 50 Beginning of hydrogen generation 14500 330 z Complete drainage of the core 15000 50 Temperature of fuel element cladding gets higher than 16683 689 design limit (1473 К), s Beginning of materials release and in-vessel elements 43420 990 output of from damaged part of the core into the reactor bottom chamber, s Exceeding of melting temperature in damaged part of the 42970 - core (T>2850K) Beginning of make-up water supply into the core and - 1900 increase of coolant level, s Stabilization of thermo-hydraulic parameters, s - 5000

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Calculation results for accident «Leak from the

primary circuit Dnom 20 mm with coolant make-up system failure» 14000000 20

12000000 16 10000000

8000000 12

6000000 z 8 àâëåí èå (Ï à) Ä 4000000

Ì àññî âû é ðàñõî4 ä (êã/ñ) 2000000 0 0

0 20000 40000 60000 0 20000 40000 60000 Âðåì ÿ (ñ) Âðåì ÿ (ñ)

Pressure in the primary circuit Coolant flow rate into the breach

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Calculation results for accident «Leak from the

primary circuit Dnom 20 mm with coolant make-up system failure» 3 3000

2 ) 2000 Ê z âåí (ì ü ) î ð Ó

1 åì ï ( åðàòóðà 1000 Ò

0 0

0 20000 40000 60000 0 40000 80000 120000 160000 Âðåì ÿ (ñ) Âðåì ÿ (ñ) Coolant level in the core Inlet and outlet temperature in the core

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Calculation results for accident «Leak from the primary circuit Dnom 20 mm with coolant make-up system failure»

1.0

0.8

0.6

% z 0.4

0.2

0.0

0 40000 80000 120000 160000 Âðåì ÿ (ñ)

Integral hydrogen release

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Calculation results for accident LB LOCA «Double- ended break of PCP Dnom 500 mm near the reactor inlet» 3 14000000

12000000

10000000 2

8000000 z 6000000 àâëåí èå(Ï à)

Óðî âåí (ì ü 1 ) Ä 4000000

2000000

0 0

0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 Âðåì ÿ (ñ) Âðåì ÿ (ñ)

Pressure in the primary circuit Coolant level in the core

2500 160000

) 2000 120000 Ê z 1500

àññà (êã) 80000 Ì

åì ï ( åðàòóðà 1000 Ò 40000 500

0 0

0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 Âðåì ÿ (ñ) Âðåì ÿ (ñ)

Mass of primary circuit coolant Inlet and outlet temperature in the core

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Calculation results for accident LB LOCA «Double- ended break of PCP Dnom 500 mm near the reactor inlet»

5000 0.4

4000 0.3 ) Ê 3000 z % 0.2 2000 åì ï åðàòóðà ( Ò 0.1 1000

0 0.0

0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 Âðåì ÿ (ñ) Âðåì ÿ (ñ) Temperature of fuel element cladding Integral hydrogen release in 216 FA for different height: 1 -Tw1,2-Tw4,3-Tw7,4-Tw10

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Stages of core damage and hydrogen generation 2830 oC Melting of UO2

2710 oC Melting of ZrO2 o 2450 C Melting of B4C 1975 - 2830 oC Formation of corium (U-Zr-O) with ceramic inclusions 1975 oC Melting of oxide-stabilized α-ZR(O), beginning of UO2 dissolution in melted zirconium 1730 oC Melting of Zr-1%Nbz 1550 oC Intensification of zirconium oxidation by steam associated with formation of ZrO2 cubic 1230 oC Eutectic interaction between zirconium alloys and stainless steel, losing of pile capacity by steel constructions

1000 oC Beginning of zirconium intensive oxidation, formation of liquid U as a result of Zry/UO2 interaction 600 - 2710 oC Possible ballooning, damage of fuel element cladding as a result of embitterment 380 oC Beginning of steel constructions oxidation

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Core degradation stage of accident «Leak from the primary circuit Dnom 20 mm with coolant make-up system failure»

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Core degradation stage of accident «Leak from the

primary circuit Dnom 20 mm with coolant make-up system failure»

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Leak Dnom 20 mm

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Minor hydrogen sources under conditions of BDBA at VVER-440/230 z Water radiolysis in reactor and confinement z Steam radiolysis in zthe atmosphere of confinement z Decomposition of hydrazine and ammonia z Corrosion of metal surfaces z Decomposition of organic covering z Generation for 30 days — less than 200 kg, maximum release rate — less than 0,002 kg/s.

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Estimation of hydrogen generation under conditions of BDBA, minor sources, 1 day 50

Коррозия алюминия 30 Разложение покрытий кг , Коррозия стали 25 z Разложение N2H4 Радиолиз воды в ГП водорода

20 Радиолиз пара Радиолиз в АЗ Выход 15 Теплоноситель

0 0123456789101112131415161718192021222324 Вр е мя, часо в

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Results of hydrogen sources calculation for BDBA

Minor Parameter In-vessel stage sources Accident Accident D 20 D 500 znom nom Integral hydrogen Less than 200 kg 659 kg 293 kg release for 30 days

Peak rate of Less than 0,002 hydrogen 0,04 kg/s 5 kg/s kg/s generation

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Stages of confinement hydrogen safety analysis

z Development of confinement geometrical model

z Analysis of hydrogen sources(code RATEG/SVECHA/GEFEST, IBRAE, RFNC VNIIEF, SPAEP)

z Confinement hydrogen distribution analysis (code KUPOL-M, RSSC IPPE) z z Determination of possible combustion modes and ignition events (code LIMITS, RRC KI)

z Analysis of equipment and structures loads (code DANCO, RFNC VNIIEF)

z Development of variants remove hydrogen system on base PARs and hydrogen control system

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Primary criteria of hydrogen safety

z Exclusion of fast flame in large volumes (comparable to the sizes of containment main compartments) and therefore, exclusion zof impermissible loads on equipment and structures z Allowing of hydrogen concentration exceeding the detonation limits only within the limited space with the characteric size L, satisfying the criterion L < 7⋅λ (λ - is the size of mixing detonation cell)

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Passive hydrogen autocatalytic recombiners (PARs) development of VTI and INPK RET (Russia)

PAR type RVK-65 RVK-500

Height, mm 730 850 Dimension in scheme, mm 125x155z 170x330 Frame cross-section, mm 70x100 170x330 Mass, kg 4.5 23 Performance *, g/s 0.009 0.068

* Performance of recombinators is given for pressure 0,1 MPa and hydrogen concentration 5 % Vol.

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Geometrical model of confinement for NPP with VVER-440/230

Geometrical model components Amount Internal control 21 volumes Control volumes External control 73 z volumes Total 94 Air flow paths for control volumes 33 Concrete walls 73 Equivalent heat Concrete floors 42 structures Metal structures 9 Total 124

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Nodalization scheme for KUPOL-M code analysis

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Dnom 500 LB LOCA Hydrogen, oxygen and steam concentrations in PRZ room

6 ) ) é é å å )

ë 0.25 ë é î 1 î 0.1 å ë . ä . ä î á á î î 0.2 . ä ( ( á

à 0.8 à î ä ä (

0.12 î î à ð ð ð î à î 0.15 ë

ä 0.6 ñ ï î è z ÿ â ê 0.08 è ö ÿ ÿ à è è 0.1 ð ö

ö 0.4 ò à à

í ð ð å ò ò ö í í í å

0.04 å

0.05 î ö ö 0.2 í í Ê î î Ê Ê 0 0 0

0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 Âðåì ÿ (ñ) Âðåì ÿ (ñ) Âðåì ÿ (ñ)

Hydrogen Oxygen Steam

1 – calculation without PARs 2 – calculation with PARs

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Dnom 500 LB LOCA Hydrogen, oxygen and steam concentrations in SG room above grade 9.6 m

6 ) ) é é å å ) ë

ë 0.25 é î 0.8 î 0.1 å ë . ä . ä î á á î î . ä ( ( 0.2 á

à à î ä 0.6 ä (

0.12 î î à ð ð ð î à î

ë 0.15 ä ñ z ï î è ÿ â ê è 0.4

0.08 ö ÿ ÿ à è è

0.1 ð ö ö

ò à à í ð ð å ò ò ö í í

í 0.2 å

0.04 å î

ö 0.05 ö í í Ê î î Ê Ê 0 0 0

0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 0 10002000300040005000 Âðåì ÿ (ñ) Âðåì ÿ (ñ) Âðåì ÿ (ñ)

Hydrogen Oxygen Steam 1 – calculation without PARs 2 – calculation with PARs

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Dnom 500 LB LOCA Analysis of possible combustion modes in PRZ room

Without PARs With PARs

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Dnom 500 LB LOCA Analysis of possible combustion modes in SG room above grade 9.6 m

Without PARs With PARs

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Fast flame for LB LOCA, no PARs(above +0.5 m)

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) H2 PARs locations option

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Monitoring system for hydrogen and oxyden concentrations Development of RSSC IPPE (Russia)

Hydrogen gas-analyzer

Oxygen gas-analyzer

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Hydrogen gas-analyzer detector

Possible temperatures range at meter location, С: - from 0 to 200 С - no restrictions; - from 200 to 250 С - during 1 hour; - from 250 to 700 С - during 250 s. z

Permissible compartment atmosphere composition, % Vol.: air - from 10 to 100; steam - up to 100; H2 - up to 25.

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Location of gas analyzers

Marking of Location № Name of equipment equipment (marking of compartment) System of hydrogen concentration control (1-st channel) 1 Hydrogen gas analyzer CQ001-B01 SG-MCP box (compartment А002) 2 Hydrogen gas analyzer CQ002-B01 Pressurizer box (compartment А101) Valve chamber of SG-MCP box 3 Hydrogen gas analyzer CQ003-B01 z (compartment А013) Hydrogen – oxygen gas 4 GH211 SG-MCP box (compartment А002) analyzer System of hydrogen concentration control (2-nd channel) 1 Hydrogen gas analyzer CQ006-B01 SG-MCP box (compartment А002) Compartment of MCP drives and main 2 Hydrogen gas analyzer CQ007-B01 closing valves (compartment А102) 3 Hydrogen gas analyzer CQ008-B01 SG-MCP box (compartment А002) Hydrogen – oxygen gas Valve chamber of SG-MCP box 4 GH212 analyzer (compartment А013)

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) H2 control locations at confinement rooms below +2.70

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) H2 control locations at confinement rooms below +9.60

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) H2 control locations at confinement rooms above +10.50

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Conclusions:

– We performed the reactor plant behavior analysis for BDBA to evaluate mass, energy and hydrogen sources to the confinement. – Minor ex-vessel hydrogen sources have been evaluated. z – Hydrogen distribution and accumulation analysis for confinement rooms et ex-vessel stage of severe accident have been carried out.

– Based on the analysis results the locations for H2 PARs and hydrogen control devices have been proposed.

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic) Thank you ! z

International Topic Meeting “VVER-2004”. (Oct. 19-22, 2004, Prague, Czech Republic)