Simulation of helium and residue production in the Megapie target

Abstract

This work is aimed at characterizing the Megapie target in terms of main contributors to the activity, modification of the chemical composition as well as residue and volatile gas production. Calculations are performed with the nuclear transport code MNCPX2.5.0 coupled to the evolution code CINDER'90. In this work, we provide results for the lead-bismuth and its container. A sensitivity analysis with regards to the different models available in MCNPX2.5.0 as well as the effect of impurities is discussed. Spallation neutron sources have various applications, among which Accelerator Driven systems (ADS) considered as a possible option for the incineration of minor actinides. These systems couple a high intensity proton accelerator to a sub critical reactor through a spallation target. The subsequent multiplication of neutrons in the sub-critical nuclear reactor will then start the transmutation reactions. The advantage of such devices is that one can use nuclear fuels with high level of minor actinides, thus allowing high efficiency transmutation, which is not possible in current reactors because of safety concerns (delayed neutrons, temperature...). Megapie (Megawatt Pilot Target Experiment) is a joint ini- tiative by six European research institutes and JAERI (Japan), to design, build and demonstrate the feasibility of a liquid lead bismuth target for spallation facilities at a beam power level of 1MW at PSI (Switzerland). The target has been irradiated successfully during 4 months. The analysis of the results collected during the experiment is currently under progress. The comparison of these results with simulations will bring interesting lessons for future designs of spallation targets in terms of performances, resistance to damages, radioprotection of the target and evolution with time of the target characteris- tics. To simulate such spallation target, generally, nuclear trans- port code packages are used and coupled to evolution codes. Transport codes usually consist of the coupling of a high energy part relying on spallation models and a low energy part utilizing nuclear data tables. The HINDAS program (1) contributed in providing simulation tools for ADS as reliable as possible or, at least, with a known uncertainty. In particu- lar, improved models were delivered, namely INCL4 (2) for the intranuclear cascade and ABLA (3) for the evaporation- fission, and implemented into the high energy transport code LAHET3 (4) and MCNPX (5). In this work, we have performed calculations with the transport code MCNPX2.5.0 using the detailed geometry of the Megapie target (6), in order to estimate the main