Influence of Reactivity Insertion Rate on Evolution of Core Disruptive Accident in Heavy Liquid Metal Fast Reactor: Case Study: MYRRHA

The sensitivity of the reactivity of a fast reactor core to changes in its geometry and/or fuel relocation calls for a particular attention with regard to criticality events. Core Disruptive Accidents (CDAs) are therefore intensively studied in the safety assessment of fast-spectrum systems. This paper aims to present a summary of the physics and phenomena relevant for a CDA in the core of a Heavy Liquid Metal Fast Reactor (HLMFR), as well as to provide an overview of the multi-scale multi-physics model developed to describe the involved physics. The developed model is employed to better understand the evolution of a CDA and its termination mechanisms in the core of MYRRHA. The considered CDA is assumed to be induced by the compaction of the degraded core. This work demonstrates that in the range of the achievable Reactivity Insertion Rates (RIRs), the compaction-induced reactivity increase is countered by the Doppler effect and the expansion of core materials, and that the type of the expansion and the contribution of each material to the expansion depend on the rate at which the reactivity is inserted in the system. Obtained results are further confirmed with an equivalent model in the severe accidents code SIMMER-III.