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ACT1 LOFA model updates and LOCA analyses

ACT1 LOFA model updates and LOCA analyses. Paul Humrickhouse Brad Merrill INL Fusion Safety Program. January 22, 2013. General updates to MELCOR model since May. Some artifacts of the original ARIES-AT MELCOR model (which was the starting point for the ARIES-ACT1 model) have been corrected.

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ACT1 LOFA model updates and LOCA analyses

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  1. ACT1 LOFA model updates and LOCA analyses Paul Humrickhouse Brad Merrill INL Fusion Safety Program January 22, 2013

  2. General updates to MELCOR model since May • Some artifacts of the original ARIES-AT MELCOR model (which was the starting point for the ARIES-ACT1 model) have been corrected. • Some reconfiguration of coolant loops was necessary (Steel ring and divertors cooled by helium loops separate from VV He loop) • Water pressures in the low temperature shield were reduced • Still need to be at least ~6 bar because of height of roof heat exchanger • Some corrections to the steel ring model have been made • Nuclear heats were too high

  3. HS7023 CV715 Vacuum Vessel (VV) top HS7021 CV465 High Temp. Shield (HTS) (OB) HS10126 HTS (IB) HS10128 Upper Divertor VV (IB) Outboard (OB) Blanket I HS7011 CV705 HS7013 HS10229 CV310 Inboard (IB) Blanket OB Blanket II VV (OB) HS7001 HS7003 CV720 HS440 HS441 CV440 CV430 CV430 HS330 HS320 HS322 HS400 HS410 HS430 HS431 HS450 CV320 CV340 CV400 CV420 CV450 HS411 CV410 CV330 HS332 HS401 HS340 HS10228 LiPb Header CV300 HS10026 HS10028 Lower Divertor He Header HS7031 CV700 HS7033 Vacuum Vessel (VV) bottom He Header

  4. LOFA analysis update • Recall that decay heat removal is accomplished in this accident by natural convection in the water-cooled shield loop (to a HX on the roof) • Analysis presented at TOFE revealed no problems with structure temperatures, but water did boil • This was compounded when the pressure was subsequently reduced • The roof HX has been modified to remove more heat • The existing model was designed for ITER • Has been increased by a factor of 10 • Boiling still occurs. Not a structure temperature issue but need to accommodate pressures up to 8 bar.

  5. Structure temperatures during LOFA

  6. He LOCA Analysis • A Helium (Divertor/steel ring loop) ex-vessel LOCA has been modeled • Double guillotine break in outlet pipe • Primary concern: overpressure in cryostat leading to release of radioactive material • ARIES-CS guidance: 3x105 Pa is pressure limit for the cryostat • Pressure increased to ~6.5x105 Pa after break • Existing model had a factor of ~6.2 more He ex-vessel than in-vessel • 3 to 1 is a better rule of thumb; ex-vessel volumes have been reduced accordingly

  7. He LOCA Analysis

  8. Water LOCA Analysis is planned • Loss of He/LiPb flow and water LOCA leaves no mechanism for decay heat removal • Gas injection is probably required to mitigate such an accident • Use of multi-layer insulation (MLI), which provides a series of barriers to radiative AND conductive heat transfer, may complicate heat removal • Many models available for heat transfer across MLI that include: • Radiation between metal layers • Conduction through metal and plastic spacers • Conduction in gas spaces when the pressure rises

  9. Conclusions and (near) future work • 3 accident cases to wrap up: • Long-term station blackout/LOFA • Ex-vessel break in high temperature He loop. Need to: • Increase size of cryostat; or • Use more (4) He loops; or • Design cryostat to withstand higher pressure • Water LOCA/LOFA • Add MLI heat transfer model and investigate gas injection • Structure volumes and surface areas need to be revised to reflect new radial build

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