A target accuracy assessment using new available covariance data, the AFCI 1.2 covariance data, has been carried out. At the same time, the more theoretical issue of taking into account correlation terms in target accuracy assessment studies has been deeply investigated. The impact of correlation terms is very significant in target accuracy assessment evaluation and can produce very stringent requirements on nuclear data. For this type of study a broader energy group structure should be used, in order to smooth out requirements and provide better feedback information to evaluators and cross section measurement experts. The main difference in results between using BOLNA or AFCI 1.2 covariance data are related to minor actinides, minor Pu isotopes, structural materials (in particular Fe56), and coolant isotopes (Na23) accuracy requirements.
A major challenge for future fast reactors could be the recycling of minor actinides (MAs) in the core fuel in order to minimize waste and to meet both the sustainability objective and the reduction in the burden of geological disposal. Although the prevailing issues will be found in the development and validation of the appropriate fuels, the presence of MAs in the core can deteriorate the core reactivity coefficients. However, in this paper, we will show that there is no well-defined physical limit to the amount of MAs in the core fuel, and that a careful physics analysis can indicate the most appropriate measures that reduce the MA impact on the reactivity coefficients, and in particular, for Na-cooled reactors, on the Na void reactivity coefficient.
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