Thermal hydraulics behavior of a rod bundle with partially blocked area during the reflooding phase of the Loss Of Cooling Accident
Résumé
During an accident causing the loss of the coolant of the primary circuit (LOCA), partial or even complete drying of the fuel assemblies may occur. In these conditions, of the fuel temperature increase and the coolant pressure drop in the reactor core may lead to significant deformation or rupture of the fuel rod cladding. Depending on the burnup of the fuel rod, extensive fuel fragmentation may occur, leading to fuel relocation within the ballooned area and the core coolability might be impaired. "Institut de Radioprotection et de Sureté Nucléaire" has launched, with the support of EDF and more recently with the US-NRC, the COAL experiments focusing on the outstanding issue of the coolability of a partially deformed fuel assembly. The influences due to the presence of a blockage will be evaluated through a semi-integral experiment using a 7x7 bundle geometry at the full length scale. The flow bypass of the blocked region, due to the reduction of the section between the deformed fuel rods will lead to a reduction of mass flow in the sub channels of the blockage and then the heat transfers. This paper presents the test section with the instrumentation, the thermal hydraulics parameters and pre-calculations using the DRACCAR code developed by IRSN. The results of these experiments will help to improve and validate the heat exchange models implemented in the DRACCAR code studying the 3D thermal mechanical processes coupled with a thermal hydraulics tool to deal with the complex reflooding processes.
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