A BENCHMARK EXERCISE FOR THE QUALIFICATION OF PWR PRESSURIZER MODELS

Abstract Detailed mathematical models of PWR pressurizers have been developed independ-ently by the CEGB, EOF, ENEL and EPRI, amongst others. The models form part of complete PWR station models which are used for operational or fault studies. Most of the main physical processes which occur within a pressurizer are represented in Che models but they differ in both the formulation of the equations and the numerical methods used for their solution. In the absence of plant test data for a PWR pressurizer it was agreed, as part of an existing collaborative work programme, that some measure of qualification of the four models could be achieved by comparing predictions obtained from them when used to independently simulate a series of specified transients. The ‘benchmark’ transients were selected in such a way as to be representative of fault or severe operational - transients and to excite all of the physical phenomena that are represented in the models, leading to the detailed specification of the forcing functions for seven transients. Identical dimensional data and initial conditions corresponding to those for a typical 3-loop PWR pressurizer together with heat transfer related coefficients dervied from published scale rig measurements were used in each of the models. The predictions of pressure and mixture level obtained from each of the models are illustrated for some of the benchmark transients and the agreement between the model predictions is good, any significant discrepancies being readily explained by differences in the representation of specific physical or fluid properties within the models.