The dependence of the nuclide composition of the fuel core loading on multiplying and breeding properties of the KLT-40S nuclear facility

Abstract

The paper describes a method for determining the effective neutron multiplication factor and the breeding ratio for the KLT-40S at operating conditions. The main reactor design features are presented which are necessary for calculations. It is shown that the type of fertile nuclides has no virtual effect on the formation of the neutron flux density spectrum. The contribution of each neutron group to the fission reaction rate at the design fissile nuclide content of 18.6% is determined. The dependences of average values of macroscopic fission cross-sections, absorption of fissile nuclides and radiation capture of fertile nuclides on the fissile nuclide content in nuclear fuel are obtained. Averaging of cross-sections was carried out over neutron flux density spectra.As a result, dependences were obtained of the effective neutron multiplication factor and breeding ratio on the fissile isotope content for various fuel compositions of uranium and thorium cycles at the KLT-40S campaign start-up. In terms of the effective multiplication factor, the best result is obtained in the 232Th+233U composition when the fissile isotope content is more than 5%, and in the 238U+239Pu composition when the the fissile isotope content is less than 5%. In terms of the breeding ratio, the best result is obtained in the 232Th+235U composition when the fissile isotope content is up to 10%; if it exceeds 10%, its values are relatively the same for the 232Th+233U and 232Th+235U and 238U+235U compositions.Thus, the most efficient composition at the nuclear fuel campaign start-up is 232Th+233U with the 233U nuclide content more than 5% due to very high values of the effective neutron multiplication factor.