ASSESSMENT OF LATEST DEVELOPMENTS IN SODIUM VOID REACTIVITY WORTH CALCULATIONS

A renewed assessment of the sodium void reactivity worth is being presented in this paper after new cross-section evaluations (JEFZ)l and computational methods (ECCO/ERANOS)2,3 have been established. The CIRAN04 experimental programme, which provides the experimental data base for Plutonium Burning cores5 (CAPRA design) is also a reason for such a renewed study. A detailed analysis of the experiments requires the use of transport theory with an accurate representation of anisotropic streaming and the use of perturbation theory for transport methods. This allows the separation of the global effect into a leakage term and a non-leakage term and the application of known method corrections (the anisotropy of streaming not yet implemented) to the determination of the leakage components. The discrepancies observed for the negative leakage term are important using the current computational scheme but it has been shown that it is caused by the existence of a strong anisotropy of streaming due to existing leakage corridors in the MASURCA lattice. The positive non-leakage term is sensitive to nuclear data and its prediction presents some small discrepancies in comparison with the experimental results. The sodium void reactivity worth in plutonium burning cores has a different sensitivity to nuclear data and the analysis of the CIRANO programme has shown that this can be correctly predicted