A multi-region computer model for predicting nuclear excursions in aqueous homogeneous solution assemblies.

Abstract

Fissile materials in the form of aqueous homogeneous solutions are used during the chemical processing of nuclear fuel. In this form there exists the possibility of an accidental criticality of the solution. To determine the consequences of such accidents, computer models have been developed to simulate nuclear excursions. A one-region model and a multi-region model have been developed to simulate both power and pressure pulses. These models include a new radiolytic gas production model that tracks the number of radiolytic gas bubbles produced during an excursion. Also, an equation of state, which accounts for the production of inertial pressure due to a "lag" in thermal expansion and the creation of radiolytic gas bubbles, has been developed for both models. The multi-region model can account for the spatial distribution of the nuclear energy deposited in the solution and both axial and radial acceleration of the fuel material caused by the production of inertial pressure. Predicted power and pressure pulses have been compared with experimental data from the KEWB, CRAC, and SILENE experiments. The computer models have been very successful in predicting the magnitude of both power and pressure pulses. Also, the multi-region model has provided new information on the spatial distribution of solution parameters during an excursion.