Simulation of loss-of-flow transients in research reactors

The course of loss-of-flow transients in pool-type research reactors, with scram disabled, is investigated. The analysis is performed with a customized version of the code PARET. The focus is on determining the two-phase flow-stability boundaries as function of initial reactor conditions, recognizing that flow instability is the basic mechanism responsible for core damage in such type of transients. A useful chart is provided, which describes the stability region in terms of initial reactor power, initial pool temperature, peaking factor, and flow-decay time constant.