Incorporating delayed neutrons into the point-model equations routinely used for neutron coincidence counting in nuclear safeguards

Abstract

We extend the familiar Bӧ hnel point-model equations, which are routinely used to interpret neutron coincidence counting rates, by including the contribution of delayed neutrons. After developing the necessary equations we use them to show, by providing some numerical results, what the quantitative impact of neglecting delayed neutrons is across the full range of practical nuclear safeguards applications. The influence of delayed neutrons is predicted to be small for the types of deeply sub-critical assay problems which concern the nuclear safeguards community, smaller than uncertainties arising from other factors. This is most clearly demonstrated by considering the change in the effective (α,n)-to-spontaneous fission prompt-neutron ratio that the inclusion of delayed neutrons gives rise to. That the influence of delayed neutrons is small is fortunate, and our results justify the long standing practice of simply neglecting them in the analysis of field measurements.

An evidential evaluation of nuclear safeguards

“…Hence, the aggregations of three kinds of indicators will be computed, respectively, according to the combination rule of Dempster-Shafer theory of evidence, noted as M s , M m , and M w , shown in Table 6. Chlorine trifluoride Medium I 10 Nickel powder, high purity Medium I 11 Gasket, large Weak I 12 Feed system/product and tails withdrawal Weak I 13 Expansion bellows Weak I 14…”

“…Since improper use of nuclear energy may cause mass destruction, it is necessary to evaluate nuclear safeguards and limit the development of nuclear detonations. Nuclear safeguards evaluations [9][10][11][12][13][14] are invoked to test and verify that states meet with the international treaty, which put forward by International Atomic Energy Agency (IAEA) and make sure that those nuclear materials will not be used to manufacture nuclear weapons. In order to make the evaluation of indicators and then make the final assessment of the States' declarations to the institution concerning any activity which are related to nuclear power, the IAEA experts collect relevant information from some main sources: information provided by the State itself, Internet and newspapers, and nonsafeguards IAEA databases.…”

The calculation of light element impurity (α, n) yield curves in a PuO2 matrix and associated specific yield coefficients: Influence of the reaction cross sections

“…In the present work, we focus on just one practical aspect: prediction of neutron production via (α,n) reactions in PuO2 arising from interactions with light element impurities. It is important to understand the method and its accuracy in relation to the widely used Pu assay technique of passive neutron correlation counting [6,7,8] in which the total neutron counting rate and various orders of correlated-neutron counting rate are determined. However, in the usual one-speed prompt-fission point-item model, the measurement item is described by three model parameters: the spontaneous fission rate, SF; the leakage self-multiplication factor, ML; and the (α,n)-to-(SF,n) ratio, α.…”