Transient analyses of the 400MWth-class EFIT accelerator driven transmuter with the multi-physics code: SIMMER-III

Abstract

In the EUROTRANS Programme of the 6th FP of the EC, EFIT, the European Facility for Industrial Transmutation, a generic conceptual design of a 400MWth ADS transmuter loaded with a CERCER U-free fuel with an MgO matrix, is developed. The safety objectives for the EFIT are achieved on the basis of the defense-in-depth concept. For the safety assessment various protected and unprotected design basis conditions (DBC) and design extension conditions (DEC) transients have been analyzed as e.g. the protected and unprotected loss of flow (PLOF/ULOF), beam trip transients, over power transients and especially the unprotected blockage accidents (UBAs). Key safety analyses of the EFIT core have been performed with the SIMMER-III code, currently the only code which can handle core disruptive conditions for heavy liquid metal cooled reactors. Unprotected transients set upper safety limits and play an important role in the overall safety assessment and transient behaviors of an ADS with MgO based fuel and T91 cladding. The high temperature range is still affected by significant uncertainties, therefore, unprotected accidents with a potential of fuel failure and fission gas release deserve special attention. In this paper, analyses of important and challenging transient cases will be presented. The SIMMER-III simulated results indicate that under the current conditions, the EFIT core can survive in most of the transient cases without pin failure except in the UBA cases. The analyses thus demonstrate the general high safety potential of an ADS like EFIT. Results of the UBA cases show that pin failure happens in the core center and propagation of the pin failure could be possible, while the core will finally arrive at a lower power condition because of the sweeping out of the fuel from the active core.