Point kinetic model for fluid fuel systems

Abstract

Pulse irradiation tests of special oxide fuel designed for plutonium disposal, called rock-like oxide (ROX), have been conducted in the Nuclear Safety Research Reactor (NSRR) to investigate the transient behavior of ROX fuel under reactivity initiated accident (RIA) conditions. An uranium free ROX, (Zr,Y)O2–MgAl2O4–PuO2, is proposed for once-through use of Pu in light water reactors. However, because of smaller negative Doppler and void reactivity coefficients in the ROX fuel, higher peak fuel enthalpies are expected under RIAs than for UO2 fuel. Thus, the tests of simulated ROX, in which Pu was replaced by U for easier realization, were conducted to a peak fuel enthalpy of 0.96 kJ g−1 (230 cal g−1), which is above current Japanese safety limits for UO2. The transient behavior of the simulated ROX fuel was quite different from that of UO2, because of its different thermo-physical properties. Fuel failure was associated with fuel melting at peak fuel enthalpies of 1.63 kJ g−1 (390 cal g−1) to 2.22 kJ g−1 (530 cal g−1). Significant mechanical energy generation, the reason for the limit, however, was not observed.