Subcriticality determination in accelerator driven systems (ADS)

Different current and planned experiments (MUSE, YALINA, Guinevere) are designed to study the zero power neutron physical behavior of accelerator driven systems (ADS). The detailed analysis of the kinetic space-time behavior of the neutron flux is important for the evaluation of these ADS experiments. Current analysis for all these experiments is based on the standard methods - Sjöstrand method and Slope method – both based on the point kinetics equations. The point kinetics equations are developed from different approximations to the transport equation. Nevertheless, all these partial differential equations of the transport equation are solved by the separation of space and time to derive the point kinetics equations. The separation of space and time does not provide useful results for cases with strongly space-time dependent external source like it appears during the shutdown of the external neutron source. In recent years, two big projects have been launched to solve the problem of sub-criticality determination in ADS experiments and for the future during ADS operation. In the 6th European Framework program in the integrated project EUROTRANS, the domain 2, ECATS has been dedicated to ADS experiments and the analysis methods for the experiments. In the same time frame, the IAEA has launched the coordinated research project: ”Analytical and Experimental Benchmark Analyses of Accelerator Driven Systems (ADS)”. Different correction methods based on Monte Carlo Results for the YALINA-Booster system have been derived for the Sjöstrand method as well as for the Slope method in EUROTRANS/ ECATS. Good results have been achieved with this correction method for the analysis of the detectors in the thermal zone. Nevertheless, there is still a problem existing in the fast zone which is the really important zone, since the follow up experiment GUINEVERE and the foreseen facility MHYRRA will be a pure fast system. The results for the analysis of the fast zone of YALINA-Booser are still not convincing, even with the use of correction factors. Good results, but once more only for the thermal and the reflector positions, have been shown in the IAEA CRP by the US American group, especially. These results rely on the use of correction factors form deterministic calculations. The conclusion of the IAEA meeting suggests for further activities, maybe a further CRP among others, the following two topics: “Online Reactivity Monitoring and Control of Sub-critical System”; and “Determination of Sub-criticality Level and Uncertainties Analyses”.