Delayed Neutron Detection with an Integrated Differential Die-Away and a Delayed Neutron Instrument

摘要

The Next Generation Safeguards Initiative (NGSI) of the U.S. Department of Energy (DOE) has funded a multilaboratory/university collaboration to quantify the plutonium (Pu) mass in, and to detect the diversion of pinsfrom, spent nuclear fuel assemblies. The first half of this NGSI effort is focused on quantifying the capability ofa range of nondestructive assay (NDA) techniques with Monte Carlo modeling and the second half involvesmeasuring spent fuel. The focus of this paper is on the performance of the detection of delayed neutrons. Adelayed neutron counting instrument using 36 fission chambers and a 14 MeV pulsed DT neutron generator wasstudied previously as part of the NGSI effort. The present paper will quantify the capability of a new delayedneutron instrument using an array of four ~3He gas filled proportional counters to detect the delayed neutrons anda DT generator as the source of interrogating neutrons. This new design was selected in order to minimize thefission of ~(238)U, to use a more realistic neutron generator design in the model, to reduce the cost and to facilitatethe integration of a delayed neutron with a differential die-away instrument. Since this paper will focus ondelayed neutron detection, the goal is to quantify the signal from ~(235)U, ~(239)Pu and ~(241)Pu, which are the isotopespresent in spent fuel that respond most significantly to a slow neutron interrogation. This report will quantify thecapability of this new delayed neutron design to measure the combined mass of ~(235)U, ~(239)Pu and ~(241)Pu for 16 of the64 assemblies of the NGSI Spent Fuel Library in water.