Status report : guard containment CFD analysis.
Under the auspices of the CEA Cadarache/ANL-US I-NERI project a comprehensive investigation has been made of improvements to the Gen-IV GFR safety case over that of the GCFR safety case twenty five years ago. In particular, it has been concluded and agreed upon [1] that the GFR safety approach for the passive removal of decay heat in a protected depressurization accident with total loss of electric power needs to be different from that taken for the HTRs. The HTR conduction cooldown to the vessel wall boundary mode for an economically attractive core is not feasible in the case of the GFR because the high power densities (100kW/1 compared to 5 kW/1 for pebble bed thermal reactor) require decay heat fluxes well beyond those achievable by the heat conduction and radiation heat transfer mode. A set of alternative novel design options has been evaluated for potential passive safety mechanisms unique to the GFR. In summary, from a technological risk viewpoint and R&D planning, the option which has been identified is the block/plate-based or a pin-based reactor with a secondary guard containment/vessel around the primary vessel to maintain the primary system pressure at a high enough level which would allow primary system natural convection removal of core generated decay heat to be effective. Dedicated emergency decay heat exchangers would have to be connected in a 'failure-proof' configuration to the primary system and have natural convection capability all the way to the ultimate heat sink. What has been collaboratively agreed upon and selected for further development is the natural convection option with a block/plate or pin type derated core and a hybrid passive/active approach.[2] The guard containment will be utilized but it will be sized for an LWR containment range backup pressure (5-7 bars) with an initial pressure of 1 bar. The assessment has shown that a significantly higher back pressure is required for total natural convection driven removal of significant decay heat levels at GFR target power densities. The lower back-up pressure, plus whatever natural convection is available at this pressure, will be utilized to significantly reduce the blower power of the active DHR system sized to remove 2-3% decay power. The objective is to be able to have such low power requirements so that power supplies such as batteries without the need for startup, can be utilized. This lower back-up pressure should be sufficient to support natural convection removal of 0.5% decay heat which occurs at {approx}24 hrs. So there should be no more need for active systems/power supply after the initial period of one day. Furthermore, since there will be a decay of the after-heat from 2-3% to 0.5% in this time period, credit should be taken in probability space for loss of active systems during the 24 hours. The safety approach will then be a probabilistic one. In the future discussions with the regulatory authorities the approach which will then be taken is that this class of decay heat removal accidents should be treated in combination with the PRA rather than solely through deterministic calculations. Work is now ongoing in the U.S.-France I-NERI GFR project to further evaluate this hybrid passive/active approach to heat removal for depressurized decay heat accidents. The objective of the analysis documented in this report is to provide information on local and global temperature, pressure and flow distributions in the guard containment , during steady state, and reactor vessel depressurization conditions due to a small break in the reactor vessel bottom control rod drive system. This is for the 2400 MWt plant option. The results should lead to improved guard containment designs and enhanced margin for safety criteria.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 924681
- Report Number(s):
- ANL-GENIV-054; TRN: US0802980
- Country of Publication:
- United States
- Language:
- ENGLISH
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