PRODUCTION OF VOID AND PRESSURE BY FISSION TRACK NUCLEATION OF RADIOLYTIC GAS BUBBLES DURING POWER BURSTS IN A SOLUTION REACTOR

The Kinetic Experiment on Water Boiler (KEWB) reactor is a 50-kw aqueous homogeneous research reactor which was designed to study the safety characteristics and dynamic behavior of this class of reactors. When the reactor is placed on a short-period power transient, its aqueous uranyl sulfate fuel solution becomes rapidly supersaturated with H/sub 2/ gas produced by the radiolysis of water. At a critical gas concentration, fission track nucleation of H/sub 2/ bubbles occurs. The rapid formation and growth of these bubbles creates a pressure field, the so-called inential pressure, which causes an increase in solution volume. This increase in solution volume, referred to as void, causes a loss of reactivity and constitutes an important shutdown mechanism. The conditions under which fission track nucleation of gas bubbles occurs are described. It is shown that the void volume and void compensated reactivity can be calculated from a knowledge of the pressure field. Simple models for the pressure field are presented which satisfactorily describe the observed pressures. The inpile capsule and KEWB experiments which confirm the validity of the mechanisms for these processes are described. The equations and more » data presented make it possible to predict with accuracy the onset and magnitude of the inential pressure and the dynamic reactivity for a large class of aqueous homogeneous reactors. (auth) « less