Analyses of transients for an IAEA benchmark on accelerator driven transmuters with fertile-free fuels

In the framework of the IAEA project on 'Studies of Advanced Reactor Technology Options for Effective Incineration of Radioactive Waste', a series of benchmarks is performed to investigate the transient behaviors of various transmuters. One benchmark analysis concerns the transients in Accelerator Driven Transmuters (ADTs) using several types of dedicated fertile-free fuels, such as CERCER fuels with a ZrO2 matrix or with an MgO matrix. For this benchmark, a mid-size 580 MWth ADT with a large fraction of minor actinides (MAs) and Pb/Bi cooling has been proposed and investigated using the SIMMER-III code. As a first step, the relevant safety parameters have been determined, e.g., Doppler constants, coolant worth and cladding worth. Several transient classes have been analyzed, mostly focusing on reactivity-driven perturbations with time-scales in the ms and s range: unprotected transient overpower (UTOP), unprotected loss of flow (ULOF) and the unprotected blockage accident (UBA). In the area of UBAs a case has been simulated which leads to local pin failure and fuel redistribution in the flowing PB/Bi. For completeness, a beam trip (BT) and an unprotected transient over current (UTOC) have also been calculated. (author)