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Afterheat removal from a helium reactor under accident conditions: CFD calculations for the code-to-code benchmark analyses on the thermal behaviour for the gas turbine modular helium reactor
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ECN-RX--97-066 Article (scientific)
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Published in: To be published in the proceedings of the NEA workshop on 'High temperature engineering research facilities and experiments' (12 (), , , Vol., p.-.

The International Atomic Energy Agency (IAEA) Co-ordinated ResearchProgramme (CRP) on 'Heat Transport and Afterheat Removal for Gas Cooled Reactors under Accident Conditions' has organised benchmark analyses to support verification and validation of analytical tools used by the participants to predict the thermal behaviour of advanced gas cooled reactors during accidents. One of thew benchmark analyses concerns the code-to-code analysis of the Gas Turbine Modular Helium Reactor (GT-MHR) plutonium burner accidents. The GT-MHR is a passive safe, helium cooled, graphite moderated, advanced reactor system with a thermal power of 600 MW that is based on existing technology. The GT-MHR can also be fuelled with plutonium. If the main helium cooling and the auxiliary shut-down cooling systems fail or become unavailable, the core afterheat is removed by radiation and convection inside the reactor vessel and the reactor cavity to the Reactor Cavity Cooling System (RCCS). The objective of the RCCS is to serve as an ultimate heat sink, ensuring the thermal integrity of the core, vessel and critical equipment within the reactor cavity for the entire spectrum of postulated accident sequences. This paper describes the heat transport inside the reactor core to the RCCS. For this purpose, the heat transfer mechanisms as well as the flow patterns inside the core, the reactor pressure vessel, and the cavity have been calculated by the Computational Fluid Dynamics (CFD) code CFX-F3D). The behaviour of the RCCS itself is not described. One calculation considers the full power operation, while two calculations consider Loss Of Forced Convection (LOFC) accidents, one at pressurised conditions and the other depressurised conditions. The heat transfer from the reactor vessel to the environment under normal operation conditions is 2.64 MW. The highest temperature in the core is 1222K, and the average core temperature is 1075K. The highest reactor vessel temperature is 679K. The highest temperatures are reached during a depres- surised LOFC accident the highest core temperature is 1644K, and the highest vessel wall temperature is 736K. The highest vessel wall temperatures occur near the mid plane of the core for the depressurised LOFC, and in the upper part of the reactor vessel for the pressurised LOFC. The heat loss of the reactor vessel during accidents is about 2.2 MW. A comparison between results of the calculations performed by other benchmark participants cannot be made yet, because these calculations are still in progress. 7 refs.

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