MELCOR model development for ARIES Safety Analysis

1. MELCOR model development for ARIES Safety Analysis Paul Humrickhouse Brad Merrill INL Fusion Safety Program ARIES Meeting UCSD San Diego, CA January 23rd-24th, 2012

2. Status of MELCOR modeling for ARIES-ACT SiC DCLL Follow up on VV permeation result from last meeting Plans and action items for next meeting Presentation Outline

3. An item from the last meeting was to start the update of existing MELCOR ARIES-AT models to perform accident analyses, primarily loss-of-coolant-accidents (LOCAs) Two models exist, one with the advanced SiC/SiC blanket and one with the DCLL blanket Both models lacked vacuum vessel, cryostat, and bioshield thermal models, need for decay heat removal and/or VV pressure relief accidents, and to answer the question of whether or not the VV can be cooled by helium Since the last meeting, we have modified and added the ARIES-CS VV to the ARIES-AT models, plus a cryostat based on ARIES-AT drawings. This required switching the VV cooling system to helium from water We are testing these models on a long-term-station-blackout (LTSBO) accident, with decay heat removal by gas injection into the cryostat volume Status of ARIES-ACT MELCOR Models

4. MELCOR Model Elevations Based on ARIES-AT Heat transfer vault Circ. HXs Pump Header PbLi drain tank

5. Vacuum Vessel/Cryostat/Divertor Model CV15 HS7102 Bioshield HS6102 CV10 Cryostat HS7023 +7021 HS10126 HS7101 HS10299 CV460 HS10128 HS6101 HS450 HS340 HS7011 +7013 CV450 CV310 HS10026 CV20 CV700 HS10028 HS7001 +7003 CV300 HS7031 +7033 HS10298 HS6103 HS7103

6. HS431 CV410 Schematic of Radial Blanket Thermal Segments HS441 HS401 HS411 CV440 CV420 HS440 CV340 HS332 CV430 HS410 HS430 HS322 CV400 HS400 HS330 CV320 HS320 CV330

7. Advanced SiC Blanket Model HS7023 • Convection, and radial/axial radiation and/or conduction accounted for in model • ITER-like thermal cryo-shields on outer surface of vacuum vessel (VV) CV700 CV465 HS7021 CV310 HS10126 HS10128 UD HS10299 U-IBHTS 260 240 275 To VV HTS 280 OBB I IBB OBB II OBVV OBHTS 245 IBHTS 250 265 IBVV 270 HS7001 HS7003 CV700 HS7013 HS7011 HS340 HS330 HS320 HS322 HS332 HS400 HS410 HS411 HS401 HS430 HS440 HS441 HS431 HS450 CV700 CV310 CV330 CV320 CV340 CV400 CV420 CV410 CV430 CV440 CV430 CV450 CV460 CV480 CV300 CV470 300 290 290 295 285 210 205 From VV HTS LD HS10026 HS10028 220 230 To PbLi HTS OTHDR HS10298 235 225 CV310 200 L-IBHTS HS7031 215 ITHDR CV700 HS7033 From PbLi HTS

8. Super-insulation or Thermal-Shield? • Super-insulations relies on thermal radiation heat transfer across gaps between multi-layered metal foils of high emissivity. For a vacuum in the gaps, the heat flux, q (W/m2-K), across N foils of emissivity “” is: • Super-insulation used for LHC VV and cryostat* • ITER’s Thermal-Shield is constructed is a shell around the VV coated with silver for low surface emissivity. The low temperature shell is cooled by helium at 80 K. Air injected into the cryostat during a long term station blackout (LTSBO) will add air heat convection in the gap between the shell and the VV. • LHC employs both a super-insulation blankets and Thermal-shields. Which option will be used for ARIES-AT? *A. Poncet, “Series-Produced Helium II Cryostats for the LHC Magnets: Technical Choices, Industrialization, Costs,” Adv. Cryo. Engr., Vol. 53

9. MELCOR DCLL Model Schematic PbLi heat exchanger IB Shield IB blanket OB blanket OB Shield FW FW VV VV Zone 1 Zone 2 He toroidal header He heat exchanger PbLi concentric pipe PbLi toroidal header He concentric pipe

10. SiC Results for a LTSBO with Air Injection in the Cryostat The inboard side of the VV is being cooled by the helium interior to VV, suggesting that internal natural convection from the inboard to the outboard of the VV may be important. However, because the VV model only has a single fluid volume, additional modeling will have to be performed to verify this possibility. Model overstates inboard cooling

11. DCLL Results for a LTSBO with Air Injection in the Cryostat Calculation has not progressed as far as SiC case. Steady state FW temperatures do not include enhancement for helium cooling. Need guidance on this.

12. Summary • ARIES-AT MELCOR models have been modified and expanded to model ARIES-ACT, including both SiC and DCLL cases • Preliminary LTSBO analysis verifies model is “wired” correctly • Future work will focus on refinement of the model to reflect ARIES-ACT parameters • Many model details are still for ARIES-AT • Helium vs. Water cooled VV • Thermal Shield vs. Super-insulation • Divide VV into multiple control volumes • Natural convection may occur within the VV from the inboard to the outboard side of the VV; present model doesn’t capture this correctly

13. Simple equilibrium permeation model used for scoping Surface concentrations u – upstream d - downstream Coolant Fick’s law of diffusion Follow up - Vacuum Vessel Permeation • Parameters used for the VV permeation analysis: • Upstream T2 pressure 5 Pa and downstream pressure of zero • Question from last time on the validity of 5 Pa • Detailed ITER divertor analysis* gives similar neutral pressures: *A. S. Kukushkin et. al, “Effect of neutral transport on ITER divertor performance”, Nuclear Fusion 45 (2005) 608-616.