On the choice of delayed neutron parameters for the analysis of kinetics experiments in 235U systems

The six-group, delayed-neutron parameters which have been incorporated into the ENDFIB-VI and JEF-2.2 evaluations represent a significant departure from the, until recently, almost universally adopted Keepin experimental data. This note quantifies the influence of the new data on the analyses of kinetics experiments in a reflected 23SU system and uses the results to make some preliminary recommendations as to the best choice of data to be used in such analyses. In particular, it is shown that the choice of parameters in the JEF-2.2 library appears to be inconsistent and leads to the prediction of non-physical behaviour in models employing this data.