On the determination of the fraction of fissioned plutonium nuclei during low-grade fuel burnup

A method is proposed for determining the proportion of fissioned 239Pu nuclei in total fuel burn-up, by measuring the ratio of concentration of 106Ru and 137Cs by γ spectroscopy. The paper discusses the question of the monitoring of burned up and disintegrated nuclei of fission products during irradiation and gives a formula for determining the corresponding adjustments. The proportion of fissioned 239Pu nuclei for a water-cooled reactor of the Novovoronevsk atomic power station type, with an average rated burn-up of 14.8 kg/t, is determined experimentally. The conclusion is drawn that a change in the spectrum of the neutron field in the fuel container, depending on its height and varying from one fuel element to another, considerably influences burn-up and thus also the accumulation of 239Pu in water-cooled low-enrichment reactors. (author)