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									                                   BARC




  Application of Computer Code ASTEC for
         Severe Accident Studies in
          IPHWRs and VVER-1000

    Sunil Ganju, B. Chatterjee, D. Mukhopadhyay,
       R. K. Singh, H. G. Lele and A. K. Ghosh


                    Reactor Safety Division,
         Bhabha Atomic Research Center, Mumbai (INDIA)

The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
     Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       1
BARC
           Application of Computer Code ASTEC for Severe
           Accident Studies in IPHWRs and VVER-1000

   OVERVIEW OF IRSN-BARC COOPERATION STUDIES

   BRIEF DESCRIPTION OF IPHWRs (Indian Pressurised
   Heavy Water Reactors)

   IPHWR SAFETY STUDIES WITH ASTEC
        Thermal-hydraulic and hydrogen distribution behaviour in the
        containment.
        Simulation of aerosol behaviour experiments in NATF facility
        at BARC.
        Aerosol and FP transport in the primary heat transport (PHT)
        system and containment.

   VVER SAFETY STUDIES WITH ASTEC

   CONCLUSIONS AND FUTURE PLANS


 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       2
BARC
             IRSN-BARC COOPERATION IN THE FIELD OF
                    NUCLEAR REACTOR SAFETY
   COOPERATION ON CONTAINMENT SAFETY(STC-1, May 2000)
     Area of Cooperation: Development and Validation of code ASTEC (jointly
       developed by IRSN, France, and GRS, Germany) for containment and
       PHT thermal hydraulics and aerosol behaviour.


    • ASTEC applications for                                                 CPA            IODE           SYSINT
                                                                      Thermalhydraulics &  Iodine in     Safety system
                                                                       Aerosol behaviour containment     management
                                                                        In containment

         Containment thermal hydraulics                                                                   ISODOP
                                                                                                    Isotope treatment
                                                                                  SOPHAEROS Isotope treatment

          and aerosol behaviour studies in
                                                                                                         & activity
                                                                                Aerosol & FP vapour    & Activity
                                                                                 behaviour in RCS          CESAR


          IPHWRs
                                                                                                      Thermal. in RCS
                                                                                                           DIVA
                                                                                                           DIVA
                                                                                                       Core degradation

         PHT system aerosol                      behaviour                                                ELSA
                                                                                                         FP release


          studies in IPHWRs                                                                              CORIUM
                                                                                                         Corium in
                                                                                                        containment

         PHT     system     thermal-hydraulic                          MEDICIS
                                                                       Corium/Concrete
                                                                         Interaction
                                                                                                     RUPUICUV
                                                                                                 Corium ejection &

          studies in IPHWRs
                                                                                                 Entrainment in cont.




         Safety studies for VVER-1000
                                                                              ASTEC V1 CONSTITUTIVE MODULES



    The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
         Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                                                 3
BARC
            Salient Features of 220 MWe INDIAN PHWRs

       Pressurised Heavy Water Reactor system                      Figure

       ‘Figure-of-Eight’ layout used in PHT permits coolant in each circuit
       to make two passes through the core. Figure

       Calandria penetrated by 306 horizontal fuel channels (220 MWe)                   Figure

       Zircaloy pressure tube with stainless steel end fittings              Figure

    Twelve fuel bundles in each channel with heavy water coolant                      Figure

       Pressure tube surrounded by a concentric calandria tube, which keeps
       the low-temperature heavy water moderator in the calandria thermally
       isolated from the hot fuel channels Figure
       Presence of large heat sink provided by cold mass of moderator gives
       high assurance of fuel channel integrity and helps prevent fuel melting
       in case of accidents
       No large pressure vessel in the coolant loop. Largest rupture limited to
       the size of the reactor headers or a break in the main steam line

 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                           4
BARC
            Salient Features of 220 MWe INDIAN PHWRs


         CONTAINMENT SYSTEM
DOUBLE CONTAINMENT PRINCIPLE

Primary Containment
   Pre-stressed concrete shell (42 m. diam.)
   Design pressure = 270.98 KPa

Secondary Containment
   Reinforced concrete shell
   Design pressure = 108.483 KPa

TWO ACCIDENT BASED VOLUMES

ENGINEERED SAFETY FEATURES
Containment Isolation, RB Coolers, PCFPB,
PCCD, SCFRP



  The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
       Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       5
BARC
           Salient Features of 220 MWe INDIAN PHWRs




 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       6
BARC
           Salient Features of 220 MWe INDIAN PHWRs




 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       7
BARC
                    IPHWR SAFETY STUDIES WITH ASTEC

   Thermal-hydraulic and hydrogen distribution behaviour in
    the containment
         Accident Sequence

         Hypothetical dual failure: LOCA in RIH with unavailability or loss of ECCS
       46 kg H2 released over a period of about 8.5 hours in the transient
       63,000 kg steam released within a period of 120 seconds

         CPA (containment module) application: Base Case
       11 non-equilibrium zones for the various compartments and one DRASYS
         zone for suppression pool

         Variants: Influence of Safety Options on H2 Distribution Behaviour in
          containment:
                  - Passive Ducting between the two Fuelling Machine Vaults
                  - Forced Circulation of air at a defined flow rate from the break
                            compartment into the Pump Room Vaults

    The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
         Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007             8
BARC
                   IPHWR SAFETY STUDIES WITH ASTEC
           Thermal-hydraulic and hydrogen distribution behaviour in containment




 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007        9
BARC
                   IPHWR SAFETY STUDIES WITH ASTEC
           Thermal-hydraulic and hydrogen distribution behaviour in containment

 FURTHER STUDIES COMPLETED

 Progressive refinement in the nodalisation scheme to achieve
    Grid-insensitive nodalisation
    31-volume nodalisation study completed

  Cases Studied
       Case 1: Total 14 zones, zone ZFMV1 divided into 2 sub zones.
       Case 2: Total 11 zones. The Dome and Boiler Room considered as one zone
               and the zone ZFMV1 divided in to 4 sub volumes as in Case 1.
       Case 3: Total 13 zones. ZFMV1 divided in 4 sub-compartments and only one
               zone considered for the Dome and Boiler Room.
       Case 4: Total 15 zones. ZFMV1 divided in 4 sub-compartments, three
               zones considered for the Dome and Boiler Room.
           4 sub-cases considered by changing the inter-
            compartment junction definitions.
       Case5: Total 31 zones. All zones defined in the base case split into 4 sub-
              volumes except the Suppression Pool (ZSPOOL), Vent Shaft (ZSHFT)
              and the V2 volumes

 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007               10
BARC
                   IPHWR SAFETY STUDIES WITH ASTEC
           Thermal-hydraulic and hydrogen distribution behaviour in containment

RESULTS, DISCUSSION
• Results highly dependent on
  nodalisation refinement:
  - Affects peak H2 conc. in a
   volume.
  - Affects time required to
    homogenise hydrogen across
    various volumes.

• More detailed nodalisation
studies is imperative.
  100-volume nodalisation
  scheme being developed for
  analysis.




 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       11
BARC
                    IPHWR SAFETY STUDIES WITH ASTEC
                            Simulation of aerosol experiments conducted in
                               the ‘Nuclear Aerosol Test Facility’ (NATF).
                     NATF
• Objectives
  - Investigation of spatial and temporal              Air Discharge
    behavior of metallic or oxide aerosols                                                                                       Sketch of NATF Test
    under simulated post-accident contt.                                              TBG                                               Vessel
    atmospheres.                                                 Filter
                                                     To atmospheric                       PT                                              TGS

  - Study of aerosol scrubbing in a water            dispersion
                                                                                                                                              S
                                                                                                                                                     PRV
                                                     studies
    pool simulating the suppression                                         TC   C
                                                                                                                                     PS
    pool of nuclear power plants.                                                W
                                                       Aerosol                                      Test
                                                       Injection                                                                  Steam
  - Validation of existing computer codes              (PTAG)
                                                                                                   Vessel
    for aerosol behavior studies in the                                                                                            TBL    L
    containment of NPPs.                                                  TWI / TWO
                                                                                     C
                                                                                                                                     Filling water
  - Estimation of source term for                                                    CD
                                                                                                                                          Drain
    atmosphere dispersion models.                         6/5/2007                             Compiled by N. V. Gole for NATF                             5




• Set-Up
  - Cylindrical test vessel, 2.25 m. diam., 2 m. height (Vol.= 10 m3).
  - Plasma Torch Aerosol Generator.
  - Instrumentation for aerosol characterisation and thermo-hydraulic parameters.
  The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
       Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                                                                                        12
BARC
                      IPHWR SAFETY STUDIES WITH ASTEC
                              Simulation of aerosol experiments conducted in
                                 the ‘Nuclear Aerosol Test Facility’ (NATF).

                             NATF
•       CPA simulation of aerosol
        experiments in NATF
    - Nodalisation of the single-volume geometry
      into 1, 6, or 12 ‘zones’ and study of the
      spatial and temporal aerosol behaviour.

    - Reasonable agreement on peak average
       aerosol concentration. Good agreement
       on decay of aerosol concentration in
       the vessel with time.

    - Parametric studies on influence of various
      aerosol parameters viz. aerosol density,
      particle size range, and aerosol phenomena
       (thermophoresis, diffusiophoresis, etc.).
    - Total of about 15 cases analysed using
      various nodalisation schemes and varying
       the aerosol parameters.

    The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
         Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       13
BARC
                   IPHWR SAFETY STUDIES WITH ASTEC
                           Aerosol and FP transport in IPHWR PHT system

                           Accident Sequence, Nodalisation
      Hypothetical dual failure: LOCA in RIH with unavailability / loss of ECCS

      Limited core uncovery and release of a small amount of fission products
       besides the evolution and transport of steam (Cs is the predominant FP
       released)

     T/H and FP data for the various volumes of the PHT system used as boundary
     conditions for ASTEC V1.3-SOPHAEROS calculations

      PHT modelled using 76 volumes               Figure
        Core region simulated using 4 parallel channels
        One pair represents maximum rated power channel of the core and the other pair
                  represents a channel with average power corresponding to the
                  remaining 152 pairs of channels
        Each of the 4 channels divided into ten volumes of equal length
        Large break in RIH
        78 junctions to connect the various volumes



 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                   14
BARC
                            IPHWR SAFETY STUDIES WITH ASTEC
                                                   Aerosol and FP transport in IPHWR PHT system




                                                    118(4)




                                                                                                                                                       108(4)
                                      319 117(1) 119(1) 320                                                                       307             107(1) 109(1) 308


                                        318                   321                                                                   306                          309



                                                                                 121(1)
                                                                                                                                                                          111(1)
                                                                                                                                                                                                          Break
                                                             120(2)                                                                                             110(2)




                                                                                                                                        106 (2)
                                         116 (2)




                                                                                 122(1)                                                                                            112(1)


                                                                                 322                                                                                               312
                                317                                                                                         305

                 400(1)                                                 100(1)                               200(1)                                                       300(1)
                                                                                                                                                                                              201
                                                                                                                                                                                         Break Junction
                                                                 323                                                  326
                                                                                 301                 304

                                                                                 102(1)             104(1)            204(1)
         316              330                                                                                                                                       327              313
                                                               202(1)            302                   303

                                                                                          103(10)
        115(1)                                                                                                                                                  213(1)               113(1)
                          215(1)                               324                        203(10)                     325


                                                                                                                                                                    328
                          329
         315                                                                              214(10)                                                                                    314


                                                                                          114(10)




 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                                                                                                                                            15
BARC
                    IPHWR SAFETY STUDIES WITH ASTEC
                                  Aerosol and FP transport in IPHWR PHT system




                                                                     SOPHAEROS results



   Deposited Aerosols Mass Ratio (%) by Mechanism                        Retention Factors
                                                                       SPECIES   % RETAINED
             MECHANISM              RATIO                                Cs          81
                 Settling            2.82                                    I       88.7

             Laminar diffusion       0.02                                Xe          0.0
                                                                         Kr          0.0
            Turbulent diffusion      0.00
                                                                         Sn          82.0
              Eddy impaction         2.06
                                                                         Ag          65.4
              Bend impaction         0.71                                Ba          20.2
             Thermophoresis          94.38                               Te          89.8
             Diffusiophoresis        0.00                                Sr          9.2
                                                                         Sb          16.7


 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                        16
BARC
                   IPHWR SAFETY STUDIES WITH ASTEC
                                Aerosol Behavior in IPHWR Containment


                                                                                                        C s A IR B O R N E M A S S            SMFMV1
                                                                                                                                              SMFMV2
                                                                                    1.8
                                                                                    1.6                                                       SMBR1

Stand-alone CPA calculation performed with                                          1.4
                                                                                                                                              SMBR2




                                                                   MASS (KG)
                                                                                    1.2


the assumption that the entire FP inventory                                         1.0                                                       SMBR3
                                                                                0.8                                                           SMPRV1
released from the core directly released                                        0.6
                                                                                0.4
                                                                                                                                              SMPRV2

into the containment.                                                           0.2
                                                                                0.0
                                                                                                                                              SMSGV1

                                                                                          0.0         2000.0         4000.0        6000.0
                                                                                                                                              SMSGV2
                                                                                                                                              SMSHFT
Fuelling Machine Vault 1 (ZFMV1) in the                                                                TIME (SEC)
                                                                                                                                              SMV2
containment defined as break compartment
and the steam and FP releases assumed to                                                                       TOTAL Cs MASS

be injected into this compartment only.                                              4,50

                                                                                     4,00

                                                                                     3,50




                                                                        MASS (KG)
FP calculations performed for two pre-                                                                                                        TOT-SM
                                                                                     3,00

                                                                                     2,50
                                                                                                                                              TOT-DM
dominant species Cs and I                                                            2,00

                                                                                     1,50                                                     TOT-mass
                                                                                     1,00

                                                                                     0,50

                                                                                     0,00
                                                                                            0,0   1000,0 2000,0 3000,0 4000,0 5000,0 6000,0


                                                                                                         TIME (SEC)




 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                                                                                   17
BARC
               SEVERE ACCIDENT ANALYSIS FOR VVER 1000
                             VVER 1000 ASTEC V1 plant model improvement

 ASTEC V1.2 calculation of the
     SBO scenario with PRZ valves
     stuck open.
 New Plant Model :
 1. Added components
 • Grid Spacers
 • Lower Core Plate
 • Guide Tubes with and without B4C
 2. Physical models                                       Prediction of final core state: former plant model
 • Heat transfer in new components
 • Gap heat transfer between baffle-
     barrel-vessel
 • B4C oxidation
 • B4C-SS reaction
 3. Observations
 • Heat-up of barrel and vessel wall
 • Higher H2 & corium production
 • Vessel failure by one hour earlier
     than with former plant model.                          Prediction of final core state: new plant model

 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                                         18
BARC
               SEVERE ACCIDENT ANALYSIS FOR VVER 1000
                           Influence of oxidation environment


                                                                                           LOCA+SBO : Poor
 Scenarios considered with                                                                 Oxidation

 ASTEC V1.2 calculations

 SBO with PRZ Stuck Open
   (steam rich)

 Large LOCA with SBO                                                        8
                                                                       1.8x10
    (steam starved)                                                         8
                                                                       1.6x10
                                                                                               Qfp(Decay Power)
                                                                            8
                                                                       1.4x10                  Qzro2(Zr Oxidation Power)
                                                                            8
                                                                       1.2x10        SBO +PRZ open : Strong




                                                           Power (W)
                                                                            8
                                                                       1.0x10
                                                                                     Oxidation
                                                                            7
                                                                       8.0x10
                                                                            7
                                                                       6.0x10

 Hydrogen generation is 15.6
                                                                            7
                                                                       4.0x10
                                                                            7
                                                                       2.0x10
 times more for SBO+PRZ open                                              0.0
                                                                                0   5000    10000    15000    20000    25000


 as compared to LBLOCA                                                                        Time (s)




 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007                                                         19
BARC
                SEVERE ACCIDENT ANALYSIS FOR VVER 1000
                     Influence of quenching (through hydro-accumulators)

•SBO with PRZ Stuck Open with Hydro accumulators

•Large LOCA with SBO with Hydro accumulators
•Prolonged core heat-up
•Higher hydrogen production
•Delayed failure of vessel bottom




   Case : SBO+HA                        Case :LOCA+HA

  The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
       Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       20
BARC
               SEVERE ACCIDENT ANALYSIS FOR VVER 1000
                                  Sensitivity studies with ASTEC V1.2



    Parameters Selected
    •Candling velocity at grid
    •Clad candling velocity
    •UO2 and ZrO2 solidus/liquidus temperatures
    •Clad dislocation criteria

    Basis of Selection
    •FPT0,1,2 Analysis

    Results:
    Low candling velocity and multiple dislocation criteria show influence
    on
    • hydrogen production, corium composition (debris, metal and pool)
    • vessel failure time




 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       21
BARC
           Application of Computer Code ASTEC for Severe
           Accident Studies in IPHWRs and VVER-1000

 CONCLUDING REMARKS
 IPHWRs
 Applicability of ASTEC for thermal hydraulic, hydrogen distribution and aerosol
 behaviour studies in the containment was demonstrated.
 Applicability for aerosol behaviour studies in the PHT system of IPHWRs was
 demonstrated.
 ASTEC proposed to be used for a detailed integral accident analysis for IPHWRs.
 Studies performed being continued further:

       Modelling of thermal hydraulic behaviour of the PHT of IPHWRs using CESAR
           Comparison against available results from other codes at BARC (RELAP)

       Performing coupled CESAR-SOPHAEROS calculation for a severe accident
       sequence for IPHWRs
       Performing a coupled CESAR-SOPHAEROS-CPA calculation for the accident
       sequence analysed in the above –mentioned studies
 Efforts underway to simulate hydrogen distribution and aerosol tests in an
 upcoming multi-compartment experimental BARC facility ‘Containment Studies
 Facility’ (CSF). (Figure)

 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007             22
BARC
           Application of Computer Code ASTEC for Severe
           Accident Studies in IPHWRs and VVER-1000
CONCLUDING REMARKS
VVER-1000
Phase-wise severe core damage study for VVER-1000 with ASTEC.
Improvements of the former plant model:
    Heat-up of barrel and vessel wall predicted,
    Higher hydrogen and corium production,
    Vessel failure occurs an hour earlier.

Higher steam availability in the reactor core during the SBO with PRZ valve stuck
open leads to higher hydrogen generation than the case for LBLOCA in the cold
leg along with SBO.
Prolonged core heat-up evident for accumulator injection cases leads to higher
hydrogen production and delayed failure of vessel bottom.
Sensitivity studies for SBP with PRZ valve stuck open show influence of low
candling velocity and multiple dislocation criteria on hydrogen production, corium
composition (debris, metal and pool) and vessel failure time.
All these calculations gave reliable and consistent results. Work being continued
for benchmark exercises with codes RELAP5/SCDAP, MELCOR and
ICARE/CATHARE.
Uncertainty analysis should be performed.

 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007               23
BARC
                  Application of Computer Code ASTEC for Severe
                  Accident Studies in IPHWRs and VVER-1000




PHT System
Model Enclosure




Control &
Instrumentation Room


                   Containment Model




    The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
         Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       24
BARC
           Application of Computer Code ASTEC for Severe
           Accident Studies in IPHWRs and VVER-1000


                                      ACKNOWLEDGEMENTS
                  IRSN
                  BARC
                  FZK
                  Mr. J. P. Van Dorsselaere, ASTEC Coordinator, IRSN
                  Dr. T. Albiol, SARNET Coordinator
                  Dr. Walter Tromm, FZK
                  Dr. P. Grudev, INRNE, BAS




                                      THANK YOU


 The 2nd European Review Meeting on Severe Accident Research (ERMSAR-2007)
      Forschungszentrum Karlsruhe GmbH (FZK), Germany, 12-14 June 2007       25

								
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