Safety studies for MYRRHA

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Safety studies for MYRRHA

• B. Arien, S. Heusdains, H. Aït Abderrahim
• on behalf of the MYRRHA Team and Support

IP-Eurotrans Workshop DM1-WP1.5
Brussels, March 17, 2006
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Contents

• 3 topics
• Enhancement of free convection
• LBE freezing in heat exchangers
• TH modelling of the spallation loop with RELAP
• Future work

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Enhancement of free convection

• Unprotected total LOF and LOH accidents are
  beyond MYRRHA Draft_2 design
• 2 possible ways to improve natural circulation
• by increasing the DH between core and HXs
• by reducing the pressure losses
• First investigations with a simplified model
• loop model simulating the pool type system
• SITHER code provided with a free convection
  module (SITHER-FC)
• results are indicative

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Reminder (PDS-XADS) TH analysis results
for unprotected accidents (I)
Transient Fuel Clad LBE Water
LOF Partial (1 EHX check valve failed) OK OK OK OK ?
LOF Partial (1 pump trip) OK OK OK OK ?
LOF Total (4 pumps trip) OK T gt 700C after 7 s OK OK ?
TOP (410 pcm) OK OK OK OK ?
LOH Partial (1 SCS failed) OK OK OK OK ?
LOH Total (2 SCS failed) OK T gt 700C after 9 min OK Boiling after 20 min ?
Partial LOF Partial LOH OK OK OK OK ?
Total LOF Total LOH Melting after 20 min T gt 700C after 5 s OK Boiling after 1 min ?
Overcooling OK OK Freezing after 14 min in PHX 5 min in EHX OK ?
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Reminder (PDS-XADS) TH
analysis results for
unprotected accidents (II)
Transient Fuel Clad LBE Water
SA blockage (2.5) OK Failure OK ?
Spurious beam start-up OK OK OK ?
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Enhancement of free convection strategy of
computation

• Start from SITHER-FC as originally developed for
  preliminary studies in the MYRRHA project ? free
  parameters
• Calibrate SITHER-FC (free parameters) from
  Draft_2 design and results obtained with RELAP
• 2 possible options for the HXs in emergency
• Emergency HXs (draft_2 design) EHX
• Primary HXs PHX
• Effect of DH increase (DH difference of
  elevation between core and HXs)
• Effect of pressure loss reduction over the core
• Note spallation loop behaviour in transient
  conditions not taken into account in the present
  study (very conservative)

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Enhancement of free convection simplified loop
model

• mass conservation
• momentum conservation
• energy conservation (core , HXs, pipes)

Momentum equation in the loop model

• G mass flow rate
• C inertial coefficient
• DpF friction pressure losses (f(G))
• DpP pump pressure head ? 0 in fc mode
• DpB buoyancy pressure

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Enhancement of free convection
SITHER calibration unprotected LOF case
core mass flow rate
temperatures in EHX
max. fuel temperature
max. clad temperature
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Enhancement of free convection
effect of DH increase
max. fuel temperature - PLOF
max. clad temperature - PLOF
DH (m)
PHX EHX
high core 0.81 1.67
low core 3.0 4.0
max. fuel temperature - ULOF
max. clad temperature - ULOF
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Enhancement of free convection
effect of DpF reduction
max. fuel temperature - ULOF
max. clad temperature - ULOF
EHX
PHX
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Enhancement of free convection conclusions

• Effect of DH increase
• Even with large DH emergency EHXs are not able to
  keep core integrity in case of unprotected LOF
  accident (EHXs are not designed to evacuate
  nominal power)
• Use of PHXs in emergency situations allows to
  mitigate strongly the unprotected LOF effects
• Effect of Dpcore reductionrelatively small
  benefit
• Behaviour of spallation loop should be taken into
  account

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LBE freezing in heat exchangers

• LBE freezing in HXs can occur with overcooling in
  secondary circuit
• In extreme conditions plugging could occur
• If total plugging ? possibility of LOF LOH
• Difficulty to recover the normal operation in
  case of plugging

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LBE freezing in heat exchangers HX types
Option 2 boiling water
Option 1 pressurized water
lead-bismuth
water
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LBE freezing in heat exchangers model (I)

• Code WALEBI (LBE/water HX) updated for freezing
• Purely thermal model
• Mechanical effects are not taken into account
  (conservative)

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LBE freezing in heat exchangers model (II)
Option 2
Option 1
r solution of
liquid LBE temperature
r frozen layer position (normalized to the
inner/outer tube radius)
water temperature
f(r) function depending on geometry and
thermophysical properties of the materials
freezing temperature
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LBE freezing in heat exchangers results (I)
Option 1
LBE
water
liquid LBE
frozen LBE
water
LBE
Option 2
water
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LBE freezing in heat exchangers results (II)
Frozen layer thickness
Total freezing
Total freezing
Option 1
Option 2
s frozen layer thickness normalized to the
inner/outer clad radius
Tw water inlet temperature
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LBE freezing in heat exchangers conclusions

• Risk of tube plugging seems negligible
• Freezing is less important with option 2

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TH modelling of the spallation loop general
sketch
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TH modelling of the spallation loop RELAP model
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TH modelling of the spallation loop results
Mass flow rate
Difference of free surface levels
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Future work

• Input from and interaction with designers (WP1.1,
  WP1.2, WP1.4) are imperative
• TH modelling of XT-ADS with RELAP
• CFD simulation of XT-ADS primary system with
  FINE\HEXA (SCK?CEN) and CFX (NRG) forced
  convection and free convection
• Optimization of the emergency cooling system