IMPROVEMENTS TO THE MODELLING OF TWO-PHASE FLOW IN A TRANSIENT REACTOR ANALYSIS CODE

摘要

Accurate prediction of transient two-phase flow is crucial to the safety cases for Light Water Reactors. Effort has been made to base such cases on "Best Estimate" (BE) codes which attempt to model what is actually happening. TRAC-PF1 is a BE code and it uses a two-fluid model: this enables it to predict non-equilibrium situations, but multiplies the number of effects which must be represented. An obvious test for a BE code is that it should reproduce relatively simple experiments on two-phase flows: if it fails to do this, there can be little confidence in its predictions of the far more complex events associated with reactor transients. The main aim of this project is to improve the representation in two areas in which the standard form of the code is obviously weak, namely annular flow and interfacial friction An improved code, which combines the strongest parts of the best available correlations, has been developed and used to model a number of simple "single effect" experiments. It is found mat in every case the predictions from the improved code agree better with the experimental values than those from the standard TRAC code.