Comparison of MCB and FISPACT burn-up performances using the HELIOS experiment technical specifications

The objective of the HELIOS experiment was to test innovative, uranium-free nuclear fuel containing americium and to study helium release and fuel swelling behaviour during irradiation. The experiment consisted of irradiation of five fuel samples, each containing various initial concentrations of Pu and Am in different inert matrices. The irradiation was performed in the High Flux Reactor (HFR) at Petten during nine cycles (i.e. about nine months) for a total duration of 240 equivalent full-power days. The neutronic calculations play an important role in preparation and analysis of the irradiation experiments. Therefore, this paper presents an explicit burn-up analysis of the HELIOS samples using two numerical tools, the MCB and FISPACT codes. The focus of this calculation is on the concentrations of Pu, minor actinides (MAs) and He during irradiation time and on total sample power due to nuclear reactions and decay. Particular attention was paid to Am242m, the fission cross-section of which is significant in the thermal neutron spectrum. The MCB code incorporates an improved method of producing this, which was subsequently tested and qualified. The sensitivity of the nuclide evolution to the choice of JEF2.2 and JEFF3.1 transport cross-section libraries was also investigated.