Assessment study of the Relap5/3.2 code against low pressure onset of flow instability in parallel heated channels

Best Estimate computer codes have been, so far, deveioped for safety analysis of nuclear power plants and were extensively validated against a large set of separate effects and integrai test facilities experimental data reievant to such kind cf reactors. Their application to research reactors is not fully straightforward. Modelling problems generally emerge wheii applying existing nìodels to 10w pressure and more particularly to subcooled mw boiling situations. The objective of the prent work is to investigate the RELAP5/3.2 system code capabilities in predicting phenoniena that could be encountered t.sdcr abnonnal research reactor’s operating conditions. For this purpose, the separate effect related (o the static onset of flow instability is investigated. The cases considered herein are the flow excursion tests performed at the Oak Ridge National Laboratory Thermal Hydraulic Test Loop (THTL) as well as some representative Whittle and Forgan (W&F) experiments. The simulation results are presented and the capabilities ofRELAP5/Mod 3.2 in predicting this critical phenomenon are discussed.