Analyses of transients for 400MWth-class EFIT accelerator driven transmuter with the SIMMER-III code

European R&D for ADS development is driven in the 6th FP of the EU by the EUROTRANS Programme. In EUROTRANS, two ADS design routes are followed, the XT-ADS and the EFIT. The EUROTRANS Design Domain has developed a conceptual reference design of the EFIT, a 400 MWth ADT, loaded with a CERCER U-free fuel with an MgO matrix. For the clad, 9Cr1MoVNb T91 steel has been chosen. The core coolant is pure lead with inlet and outlet temperatures of 400 and 480 °C. EFIT design is to be optimized towards: a good transmutation efficiency, high burn-up, low reactivity swing, low power peaking, adequate subcriticality, reasonable beam requirements and a high level of safety. In the current paper, safety analyses performed with SIMMER-III are reported and discussed. Basically two different safety areas have been analyzed. Firstly, protected and unprotected transients which are initiated by a mismatch of power-to-flow or resulting from a beam disturbance or overpower situation. Secondly a steam generator tube rupture (SGTR) accident has been investigated with its potential impact on the active core. From the safety point of view all ADTs with a high load of Minor Actinides are characterized with a 'zero' Doppler fuel feedback, a high void worth for lead and a very small beta-effective. In addition the massive Helium production from the transmutation process leads to high pressure potentials in the plena. Although the boiling point of Pb is high, voiding may take place via two routes: gas release from the plena after pin failure or steam entering into the core after a SGTR accident. Severe of the transient scenarios analyzed are unprotected with beam-on: unprotected transient overpower, unprotected loss of flow and unprotected blockage accident (UBA). Beam trip scenarios are also analyzed. As the transient behavior of the MgO based fuel and the T91 clad has large uncertainties, the unprotected accidents with the potential of fuel failure and gas release deserve special attention. Extensive investigations have been performed for UBA as it represents a route into pin failure. A summary of all transient cases will be presented while more details reported concerning ULOF.