Uranium loss from BISO-coated weak-acid-resin HTGR fuel

Recycle fuel for the High-Temperature Gas-Cooled Reactor (HTGR) contains a weak-acid-resin (WAR) kernel, which consists of a mixture of UC2, UO2, and free carbon. At 19000C, BISO-coated WAR UC2 or UC2-UO2 kernels lose a significant portion of their uranium in several hundred hours. The UC2 decomposes and uranium diffuses through the pyrolytic coating. The rate of escape of the uranium is dependent on the temperature and the surface area of the UC2, but not on a temperature gradient. The apparent activation energy for uranium loss, ΔH, is approximately 90 kcal/mole. Calculations indicate that uranium loss from the kernel would be insignificant under conditions to be expected in an HTGR