Multiphysics CATHARE2 modeling and experimental validation methodology against CABRI transients

Abstract CABRI is an experimental pulse reactor, funded by the french Institute for Radiological protection and Nuclear Safety (IRSN) and operated by CEA at the Cadarache nuclear center, France. Its aim is to study and thus to better understand RIA (Reactivity-Initiated Accident) effects on nuclear fuels. The restart of the CABRI reactor in 2015 offers the opportunity to validate tools involving multiphysic calculation schemes on reactivity insertions (RI) transients at a system scale. Physics of the in-pile CABRI tests is complex and implies various physical fields (solid and fluid thermics, thermal-hydraulics, mechanics and neutronics) and their coupled effects. The reactivity insertion in CABRI is mastered by the depressurization of a neutron absorber ( 3 He), contained into transient rods. The increase of the neutron flux inside the core induces the neutronic power increase inside the core and a multiphysic effect, called “TOP” effect, inside the in-core transient rods that causes an acceleration of the gas depressurization. The challenge is thus to manage the simulation of these RIA complex transients catching the governing multiphysical phenomena to be identified. In order to achieve this objective, a model for the CABRI transients and a scientific calculation tool have been developed and should be validated. This paper proposes a modeling of governing multiphysic phenomena of RIA transients in CABRI reactor based on a Quantified Phenomena Identification and Ranking Table (QPIRT). These models are introduced in the CATHARE2 tool in a dedicated version named PALANTIR and Best-Estimate simulation results are compared with experimental data obtained on CABRI commission tests: core power and 3 He pressure evolution.