DIRECT DISPOSAL OF HTR FUEL-ELEMENTS - CONCEPT AND STATE OF DEVELOPMENT

In the early years of development of the high temperature reactor (HTR), uranium-thorium fuel plus reprocessing was considered to be the logical fuel cycle permitting optimum utilization of the uranium resources. The non-proliferation of nuclear weapon grade nuclear fuels as a political necessity, but also economic reasons, enforced the shift in the late seventies to fuel elements with low enriched uranium (LEU) as UO2 also in the advancing HTR development. Accordingly, work on the Thorex process of reprocessing thorium bearing HTR fuel elements was discontinued and, instead, studies were begun of the usability, after graphite separation, in reprocessing HTR LEU fuel elements of the PUREX technology existing at that time. However, the high burnup of 80,000 to 100,000 MWd/t specific of the HTR, and the associated low residual content of U-235 and of fissile plutonium bred, of which 80 to 90% are used already in situ, limits the economics of fuel reprocessing. For these reasons, direct disposal is sought for HTR fuel elements, also above and beyond the early types of fuel for which there is no longer any reprocessing capability.