1 Safety studies for MYRRHA B. Arien, S. Heusdains, H. Aït Abderrahim on behalf of the MYRRHA Team and Support IP-Eurotrans Workshop DM1-WP1.5Brussels, March 17, 2006

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

3 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 H 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

4 Reminder ( PDS-XADS) : TH analysis results for unprotected accidents (I) TransientFuelCladLBEWater LOF Partial (1 EHX check valve failed) OK LOF Partial (1 pump trip): OK LOF Total (4 pumps trip): OKT > 700°C after 7 s OK  TOP (410 pcm)OK LOH Partial (1 SCS failed): OK LOH Total (2 SCS failed): OKT > 700°C after 9 min OKBoiling after 20 min  Partial LOF + Partial LOH OK Total LOF + Total LOH Melting after 20 min T > 700°C after 5 s OKBoiling after 1 min  OvercoolingOK Freezing after 14 min in PHX 5 min in EHX OK 

5 Reminder (PDS-XADS): TH analysis results for unprotected accidents (II) TransientFuelCladLBEWater SA blockage (2.5%)OKFailureOK  Spurious beam start-upOK

6 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 H increase (H: 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)

7 G: mass flow rate C: inertial coefficient p F : friction pressure losses (=f(G)) p P : pump pressure head  0 in fc mode p B : “buoyancy” pressure Momentum equation in the loop model: mass conservation momentum conservation energy conservation (core, HXs, pipes) Enhancement of free convection: simplified loop model

8 Enhancement of free convection: SITHER calibration – unprotected LOF case max. fuel temperaturemax. clad temperature core mass flow ratetemperatures in EHX

9 Enhancement of free convection: effect of H increase max. fuel temperature - PLOF max. clad temperature - PLOF max. fuel temperature - ULOFmax. clad temperature - ULOF PHXEHX high core low core H (m)

10 Enhancement of free convection: effect of p F reduction max. fuel temperature - ULOFmax. clad temperature - ULOF EHX PHX

11 Enhancement of free convection: conclusions Effect of H increase:  Even with large H 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 p core reduction: relatively small benefit Behaviour of spallation loop should be taken into account

12 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

13 LBE freezing in heat exchangers: HX types Option 1: pressurized water Option 2: boiling water lead-bismuth water

14 LBE freezing in heat exchangers: model (I) liquid LBE solid LBE water tube Code WALEBI (LBE/water HX) updated for freezing Purely thermal model Mechanical effects are not taken into account (conservative)

15 LBE freezing in heat exchangers: model (II) Option 1 Option 2 f() : function depending on geometry and thermophysical properties of the materials liquid LBE temperature water temperature freezing temperature  : frozen layer position (normalized to the inner/outer tube radius)  solution of

16 LBE freezing in heat exchangers: results (I) liquid LBE frozen LBE LBE water LBE Option 1 Option 2

17 LBE freezing in heat exchangers: results (II) Frozen layer thickness Option 1Option 2  : frozen layer thickness normalized to the inner/outer clad radius T w : water inlet temperature Total freezing

18 LBE freezing in heat exchangers: conclusions Risk of tube plugging seems negligible Freezing is less important with option 2

19 TH modelling of the spallation loop: general sketch

20 TH modelling of the spallation loop: RELAP model

21 TH modelling of the spallation loop : results Mass flow rateDifference of free surface levels

22 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 …