Reactor Kinetics Calculated in the Summation Method

Abstract

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 causes of the peculiar inhour equations calculated from delayed neutron temporal data in ENDF/B-VI, that were obtained from FP fission yields decay data. In this paper, the inhour equation is calculated in the summation method directly from FP data in ENDF/B-VI. For ²³⁵U, ²³⁸U and ²³⁹Pu, the inhour equation in the present method shows similar behavior. To identify FP data responsible for this peculiarity, the asymptotic form of the inhour 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 candidate precursor 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 ^l37I, ⁸⁸Br, and ⁸⁷Br, the precision, dPn/Pn, should be decreased down to 2% and for ^l36Te to 5%.

Keywords:

• delayed neutrons
• reactor kinetics
• fission products
• fission yields
• decay data
• summation method