Thermal Analysis for a Heterogeneous VHTR Transmutation Fuel Block as a Function of Burnup

The VHTR is one of the Generation IV Reactor concepts utilizing TRISO fuel, which enables it to have a higher burnup. Thus, giving higher fuel utilization which is capitalized upon in this work, where one third of the uranium carrying fuel compacts are replaced with transuranic burning fuel for light water reactor waste transmutation. The single fuel block burnup calculation of the transuranic fuel yielded disproportionate power sharing between transuranic and uranium fuel. Therefore, a finite difference code was prepared to assess the maximum temperature and temperature gradient that can be expected in a heterogeneous fuel block intended for waste transmutation. Power reduction by a factor of 1.4 was observed by coolant channels neighboring both Pu/MA TRISO and UO2 compacts from beginning of fuel life to the end of life. This power reduction allowed for a corresponding reduction in the end of life UO2 centerline temperature even though the UO2 power density was four times that of Pu/MA TRISO. (authors)