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

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Safety studies for MYRRHA

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

  4. Reminder (PDS-XADS) : TH analysis results for unprotected accidents (I)

  5. Reminder (PDS-XADS): TH analysis results for unprotected accidents (II)

  6. 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

  7. 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:

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

  9. 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

  10. Enhancement of free convection:effect of DpF reduction max. fuel temperature - ULOF max. clad temperature - ULOF EHX PHX

  11. 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

  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 2: boiling water Option 1: pressurized water lead-bismuth water

  14. 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)

  15. 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

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

  17. 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

  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 rate Difference 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 • …

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