Summation Calculation of Delayed Neutron Emission and its Application to Reactor Kinetics

The kinetics of a point reactor is solved directly form buildup and decay of fission-product (FP) nuclei for the first time. The purpose of this paper is to identify possible sources of the peculiar behavior of in-hour equations calculated from delayed neutron temporal data in ENDF/B-VI, that were obtained from FP fission yields decay data. Specifically, the in-hour equation is calculated in the summation method directly from FP data in ENDF/B-VI. For ²³⁵U, ²³⁸U and ²³⁹Pu, the present calculation of the in-hour equation show similar behavior to those obtained from the temporal data. To identify FP data responsible for this peculiarity, the asymptotic form of the in-hour equation at infinitely long periods is examined. It is found that the most important precursors for long reactor periods are found ¹³⁷I, ⁸⁸Br and ⁸⁷Br. They cover more than 60 % of the reactivity. Among them, ¹³⁷I alone covers 30- 50 %. Moreover, ¹³⁶Te is found a possible candidate for the peculiarity from the time dependence of the delayed neutron emission. It is recommended that the precision of their Pn values should be improved experimentally. For ¹³⁷I, ⁸⁸Br, and ⁸⁷Br, the precision, dPn/Pn, should be decreased down to 2 % and for ¹³⁶Te to 5%. Except for the Pn and fission yield data of these precursors, the presently available FP data seem to provide reasonable time dependence of DN emission having almost comparable precision (≤ 10%) with empirical evaluations. (author)