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Conference Article: Thermal Response of a High Temperature Reactor during Passive Cooldown under Pressurized and Depressurized Conditions

Abstract

HTR design is characterized by its inherent safety features with respect to passive decay heat removal through conduction, radiation and natural convection. This passive concept was first introduced in the German HTR-Module (pebble fuel) design and subsequently extended to other modular HTR design in recent years e.g. MHTGR (prismatic fuel), PBMR (pebble fuel), GT-MHR (prismatic fuel) and the new generation reactor V/HTR (prismatic fuel). In the past numerical simulations of the HTR-Module have been performed using the thermalhydraulic code THERMIX which was developed for the analysis of HTRs with pebble fuels and verified by experiments. Following modifications in the code it has been applied recently for the calculation of GT-HTR with prismatic fuels. These calculations have been checked against the results of CRP-3 benchmark problem analyzed by various countries with diverse codes. Based on the promising results of the benchmark calculation, the code has now been extended to the thermal analysis of the V/HTR which is conceived primarily for the production of hydrogen requiring very high temperatures (> 850 C) for the electrolysis or thermo-chemical processes. In this paper, the thermal response of the V/HTR (operating inlet/outlet temperatures 490/1000 C) during post shutdown passive cooling under pressurized and depressurized primary system conditions has been investigated. Additional investigations have also been carried out to determine the influence of other inlet/outlet operating temperatures (e. g. 490/850, 350/850 or 350/1000 C) on the maximum fuel and pressure vessel temperature during depressurized cooldown condition. In addition, some sensitivity analyses have also been performed to evaluate the effect of varying the parameters i.e. decay heat, graphite conductivity, surface emissivity etc on the maximum fuel and pressure vessel temperature. The results show that the nominal peak fuel temperatures remain below 1600 C for all these cases, which is the limiting temperature relating to radioactivity release from the fuel. The analyses presented in this paper demonstrate that the code THERMIX can be successfully applied for the thermal calculation of HTRs with prismatic fuel. The results also provide some fundamental information for the design optimization of V/HTR with respect to its maximum thermal power, operating temperatures etc.

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Reference:

Proceedings of the Conference on High Temperature Reactors, Beijing, China, September, 22-24, 2004

International Atomic Energy Agency, Vienna (Austria)

HTR-2004, pp:1-17