Prompt multiplication factor measurements in subcritical systems: From MUSE experiment to a demonstration ADS

In the context of the world energy demand growing and of greenhouse effect concern, new nuclear power options are extensively studied, especially systems dedicated to high activity waste incineration. It is the case of fast accelerator driven subcritical systems which are the subject of several projects among which the recently completed MUSE programme. From the coupling of a fast subcritical mock-up to a pulsed neutron source, various methods leading to the measurement of the reactivity level and kinetic parameters, which are of prime interest for safety, were investigated. An analysis of pulsed neutron source time spectra taking into account the full distribution of the time intervals between two consecutive fission events – the kp method – was developed and is recalled in this paper. Complete results obtained during the MUSE experiment with this method are given and compared to reference measurements as well as to PNS measurement analysis like exponential fitting or area methods. The quality of the results led to the investigation of the applicability of the method in the case of a continuous source interruption and then in the case of a power ADS. In both cases, on the basis of simulations, no obstacles are found to get the prompt multiplication factor from this method. The aim of this paper is to give a complete overview of the kp method applications and limits.