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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. Contents. 3 topics Enhancement of free convection LBE freezing in heat exchangers

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safety studies for myrrha

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

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

Enhancement of free convection
reminder pds xads th analysis results for unprotected accidents i
Reminder (PDS-XADS) : TH analysis results for unprotected accidents (I)
reminder pds xads th analysis results for unprotected accidents ii
Reminder (PDS-XADS): TH analysis results for unprotected accidents (II)
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)

Enhancement of free convection: strategy of computation
enhancement of free convection simplified loop model
Enhancement of free convection: simplified loop model
  • mass conservation
  • momentum conservation
  • energy conservation (core , HXs, pipes)

G: mass flow rate

C: inertial coefficient

DpF: friction pressure losses (=f(G))

DpP: pump pressure head  0 in fc mode

DpB: “buoyancy” pressure

Momentum equation in the loop model:

enhancement of free convection sither calibration unprotected lof case
Enhancement of free convection: SITHER calibration – unprotected LOF case

core mass flow rate

temperatures in EHX

max. fuel temperature

max. clad temperature

enhancement of free convection effect of d h increase
Enhancement of free convection:effect of DH increase

max. clad temperature - PLOF

max. fuel temperature - PLOF

DH (m)

max. fuel temperature - ULOF

max. clad temperature - ULOF

enhancement of free convection effect of d p f reduction
Enhancement of free convection:effect of DpF reduction

max. fuel temperature - ULOF

max. clad temperature - ULOF

EHX

PHX

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 reduction:relatively small benefit

Behaviour of spallation loop should be taken into account

Enhancement of free convection: conclusions
lbe freezing in heat exchangers
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
lbe freezing in heat exchangers hx types
LBE freezing in heat exchangers: HX types

Option 2: boiling water

Option 1: pressurized water

lead-bismuth

water

lbe freezing in heat exchangers model i

l

iquid

s

olid

tube

water

LBE

LBE

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)
lbe freezing in heat exchangers model ii
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

lbe freezing in heat exchangers results i
LBE freezing in heat exchangers: results (I)

Option 1

LBE

water

liquid LBE

frozen LBE

water

LBE

Option 2

water

lbe freezing in heat exchangers results ii
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

lbe freezing in heat exchangers conclusions
LBE freezing in heat exchangers: conclusions
  • Risk of tube plugging seems negligible
  • Freezing is less important with option 2
th modelling of the spallation loop results
TH modelling of the spallation loop : results

Mass flow rate

Difference of free surface levels

future work
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
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