A Validation of RELAP on Predicting Nuclear Power Plant Phenomena

Abstract

In this study, RELAP5’s capability to simulate thermal stratification under different conditions is assessed. In nuclear power plants (NPPs), thermal stratification can occur in the following locations: pressurizer, piping systems such as hot legs, cold legs, surge lines, and cooling tanks if available. In general, thermal stratification in a horizontal pipe could not be simulated by RELAP5 due to the inherent one-dimensional setting. Moreover, RELAP5 failed to simulate turbulent penetration which was often a pre-requisite prior to thermal stratification in a pipe. This type of situation could arise in connection between hot leg and surge line, spray lines, feed water lines, etc. It is recommended that for this type of problem CFD be used. In the literature, it was found that RELAP5 was capable of simulating thermal stratification in a pool or a tank-like component if multiple channels and crossflow junctions were used. However, due to uncertainties associated with the input model, the current RELAP5 model failed to reproduce experimental data and therefore further investigation would be required to identify the sources of error.

Investigation on RELAP5-3D© capability to predict thermal stratification in liquid metal pool-type system and comparison with experimental data

“…Based on the experimental campaign carried out by Saedi (1983) and Kim (1984), simulation activities performed by Shumway et al (2002) and Bayless et al (2015) assessed the capability of RELAP5 to reproduce thermal stratification phenomenon in the pressurizer, modelling the component with a single vertical pipe and adopting the stratification model. The computational activity has been repeated by Ahn et al (2018) investigating the influence of the number of nodes on the evaluation of the thermal stratification. The simulations highlighted good agreement with the experiment when the nodalization scheme is sufficiently fine, 10 nodes in this case.…”

“…About the pool, Ahn et al (2018) highlighted that the effect of the axial discretization on the accuracy of solution is minimal and a sufficiently fine meshing permits a good evaluation of the thermal stratification. For this purpose, CIRCE-ICE model presents a very fine nodalization along the axial coordinate, following the primary flow path discretization, according with the sliced modelling approach.…”