Pulse irradiation tests of special oxide fuel designed for plutonium dispos
al, 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,)O-2-MgAl2O4-PuO2, is proposed for once-through use of Pu in light wate
r reactors. However, because of smaller negative Doppler and void reactivit
y coefficients in the ROX fuel, higher peak fuel enthalpies are expected un
der RIAs than for UO2 fuel. Thus, the tests of simulated ROX, in which Pu w
as replaced by U for easier realization, were conducted to a peak fuel enth
alpy of 0.96 kJ g(-1) (230 cal g(-1)): which is above current Japanese safe
ty limits for UO2. The transient behavior of the simulated ROX fuel was qui
te different from that of UO2, because of its different thermo-physical pro
perties. Fuel failure was associated with fuel melting at peak fuel enthalp
ies of 1.63 kJ g(-1) (390 cal g(-1)) to 2.22 kJ g(-1) (530 cal g(-1)). Sign
ificant mechanical energy generation, the reason for the limit, however, wa
s not observed. (C) 1999 Elsevier Science B.V. All rights reserved.