International Standard Problem ISP 42 Simulation Exercise on PANDA Tests

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International Standard Problem (ISP- 42)
Simulation Exercise on PANDA Tests
4th RCM on the IAEA CRP on Natural Circulation
Phenomena, Modelling and Reliability of Passive
Safety Systems that Utilize Natural Circulation

• A.K. Nayak, P.P. Kulkarni, V. Jain and P.K.
  Vijayan
• Reactor Engineering Division,
• Bhabha Atomic Research Centre,
• Trombay, Mumbai, INDIA - 400 085

Vienna, Austria, Sept. 10-13, 2007
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ISP-42

• The ISP-42 exercise was carried out in the PANDA
  facility located at PSI, Switzerland under the
  auspices of the OECD NEA committee for the safety
  of nuclear installations (CSNI), financed by the
  research foundation of Swiss Utilities.
• The ISP-42 tests consists of six phases (Phase A
  through Phase F) for the simulation and study of
  various passive safety systems of the ESBWR,
  particularly in the containment during a
  postulated LOCA situation.
• The test Phases A to F are presently being
  simulated using the codes ASTEC and RELAP5
  

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Description of the PANDA Facility

• PANDA is a large-scale facility constructed at
  PSI, mainly to investigate containment phenomena.
  Also, the facility is used for the investigation
  of both overall system response and key phenomena
  of PCCS during the long term decay heat removal
  for Advanced Light Water Reactors (ALWRs).
• It is scaled 140 with respect to the power and
  volume, and 11 with respect to height of the
  ESBWR.
• The decay heat in the core of the Reactor
  Pressure Vessel (RPV) is simulated by
  electrically heated rods.
• Besides the RPV, the facility simulates the
  Drywells (DWs), Wetwells (WWs), Gravity Driven
  Cooling System (GDCS) tank, Passive Containment
  Coolers (PCCs) along with the pool and the
  associated piping.

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Schematic of PANDA
PCC3FEEDL
PCC2FEEDL
PCC1FEEDL
PCC1
PCC3
19800
PC1FEEDL
PEL
PCC2VNTL
PCCDRNL
PCC3VNTL
GDCS
PCC1VNTL
GDCSDRNL
DW1
DW2
MSL1
11700
VB2
MSL2
R P V
MVL1
MVL2
VB1
WW1
WW2
WETLINE2
WETLINE1
000
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PANDA component geometry details
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Summary of Phases
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Computer Code ASTEC

• ASTEC (Accident Source Term Evaluation Code)
• Main capabilities
• Applications to PSA2, including uncertainty
  analysis,
• Accident management studies,
• Investigations of NPP behaviour in Severe
  Accident condition, including source term
  evaluation,
• Support and interpretation of experiments,
• Basis for a better understanding of Severe
  Accident physical phenomena.

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ASTEC Main Modules

• CESAR module for RCS thermal hydraulics
• Water and gas (steam, H2 is the only
  non-condensable gas in this version),
• 5-equation approach
• DIVA module for core degradation
• RUPUICUV module for Simulation of Direct
  Containment Heating effects in cavity through a
  semi-empirical approach (correlations).
• CORIUM module for Simulation of the behaviour of
  corium droplets transported by DCH hot gases into
  the containment atmosphere and sump.
• MCCI modules for concrete ablation and release of
  noncondensable gases
• CPA module lumped-parameter approach in a
  multi-comp. containment

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RELAP5/MOD3.2 Code

• RELAP5/MOD3.2 is a best estimate code used mostly
  for nuclear reactor thermal hydraulic analysis
• It is based on one-dimensional two-fluid model
  (six-equation model).
• The code has been extensively validated with
  several test data for integral as well as
  separate effect tests.
• The code is capable of simulation of condensation
  phenomena in presence of non-condensables.
• There is evidence of assessment of
  non-condensable test data for passive cooling
  systems and ability to capture degradation of
  heat transfer coefficient in presence of
  non-condensables.

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Simulation Results

• Simulation of Phase A and B has been completed
• Phase C is currently being simulated
• Simplifications
• Heat losses are neglected
• The CESAR module of ASTEC Considers only hydrogen
  as the noncondensable gas in place of air

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ASTEC nodalization of PANDA facility
PCCS
GDCS
DW-2
DW-1
RPV
WW-2
WW-1
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RELAP5 Nodalization of PANDA facility
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Phase A Simulation

• Start-up of PCCS
• To study the start-up of passive cooling system
  when steam is injected into a cold Drywell filled
  with air and to observe the resulting gas mixing
  and system behavior.
• The specific phenomena observed during the phase
  were
• Steam jet injection into Drywell
• Air/Steam venting into suppression chamber
• Gas mixing and stratification in Drywell and
  Wetwell gas space
• Steam condensation on walls of drywell and in
  tubes of PCC
• System pressurization

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Phase A Configuration

• All vessels are connected.
• GDCS drain line is closed
• Vacuum Breaker (VBL) and Main vent lines (MVL)
  are closed.

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Phase A initial and boundary conditions
Initial conditions

• Boundary condition
• The test was carried out at constant 1 MW power
  throughout

• Simulation procedure
• All systems including PCCS are valved-in at time
  t0 s
• Test initiation Switching on RPV heater and
  raising it to 1 MW at time t 0
• Test termination Pair or 6000 s test duration
• Transient calculations were continued till 5000 s

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Phase A Sample results
RPV Pressure
RPV Temperature
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Phase A Sample results
Steam Flow Rate From RPV to DW1
Gas Partial Pressure
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Phase B Simulation

• GDCS Discharge
• To investigate the discharge of cold water from
  the GDCS tank into the Reactor Pressure Vessel
  (RPV) and to observe induced phenomena such as
• Discharge of cold water into saturated RPV
• Void collapse in RPV,
• Vacuum breaker opening,
• Non-condensable gas entrainment from the SC to
  DW,
• Resumption of boiling in RPV,
• PCCS start-up.

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Phase B Configuration

• GDCS Drain opened
• Vacuum breaker lines are opened
• Vacuum Breaker Valve opens if ?p 3.2 kPa and
  closes if ?p
• Remaining configuration same as phase A.

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Phase B initial and boundary conditions
Boundary Condition
Initial Condition

• This phase was carried out with 1.4 MW power for
  initial 300 s and then reducing it linearly to22
  800 kW in next 1800 s, then keeping it constant
  till the end
• The GDCS Discharge starts at 48 s and continues
  till the GDCS tank is empty (till 1271 s)

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Phase B Sample results
RPV inventory
GDCS inventory
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Phase B Sample results
Steam Flow Rate through MSL1
Drywell Pressure
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Conclusions

• Simulation of ISP-42 test phases A and B has been
  carried out using the codes ASTEC and RELAP5.
• Predictions are compared with the experimental
  data
• The deviation in ASTEC simulation of gas partial
  pressure can be attributed to the fact that the
  CESAR module of ASTEC can model only hydrogen as
  non-condensable gas.