Enhancements along with application of the Asymptotic Progressing nuclear data Incremental Adjustment (APIA) methodology by individual assimilations of fast reactor data

Abstract In view of precise fast reactor analyses, we find that the Asymptotic Progressing Incremental nuclear data Adjustment (APIA) methodology described in previous papers is able providing particularly useful, consistent adjustments by assimilating the integral experimental data in an individual manner. The outcome of dedicated APIA simulations, largely resulting independent of experimental and postulated analytical modeling uncertainties including cross-correlations, supports this conclusion. Clearly, the fully decoupled approach allows identifying and thus best separating effects coming from the different integral experiments considered in the assimilation process; we thus propose a criterion for considering or rejecting additional, individual experiments to enlarge an existing database. We may advise considering further a new experiment under the condition that after completion of the corresponding incremental step the posterior ratios of computed to experimental values for all experiments whose assimilation has occurred in the preceding steps remain unchanged, coinciding with one. Only in this case, the reduced χ 2 of a larger number of representative target experiments covering the database may decrease, improving the quality of the data; otherwise, we recommend rejecting the experiment. We illustrate this general result based on representative APIA sequences involving assimilations of central spectral indices measured in the critical configurations Godiva, ZPPR-9, Big Ten, Pu239 Jezebel and SNEAK 7A.