Fuel performance simulations of ESNII prototypes: Results on the MYRRHA case study

Nominal and transient conditions of the ESNII prototypes were investigated in the INSPYRE Project using the European fuel performance codes GERMINAL, MACROS and TRANSURANUS. This Deliverable presents the results of the simulations of the MYRRHA case study: MYRRHA nominal irradiation conditions and the occurrence of a beam power jump (over‐power) transient at the beginning and end of life of the fuel pin in reactor. Besides the application of the reference (“pre‐INSPYRE”) code versions, the activity involves the evaluation of the impact of the improved models of MOX fuel properties developed in INSPYRE and implemented in the three fuel performance codes. These modelling advances concern the thermal properties (thermal conductivity, melting temperature), mechanical properties (thermal expansion, Young’s modulus) and the mechanistic treatment of fission gas behaviour and release from MOX fuels. The results yielded by the pre‐INSPYRE and post‐INSPYRE versions of the codes involved are presented and assessed in terms of evolution in time, as well as axial and radial profiles of significant quantities, both integral and local. Then, the code results are compared with the design limits set for the MYRRHA fuel pins, in particular the maximal fuel temperature admitted, which prevents fuel melting, and the maximal allowed cladding plasticity that ensures the cladding integrity. The outcome is a complete compliance of the pin behaviour with the design limits, respecting adequate margins even in the case of the hottest fuel pin and in the case of beam power jump transients.