Accounting for Uranium-234 During the Analysis of Experiments at the Research Fast Reactor with High Enrichment

Abstract

Paper is an attempt to consider the influence of U-234 presence through the comparison of the calculated assessments of the temperature reactivity effect (TRE) and the sodium void reactivity effect (SVRE) of the fast research reactor CEFR with 64.4% enrichment on U-235 isotope and measured values of the temperature reactivity effect and sodium void reactivity effect. Additional investigation was performed to account for U-234 in the first criticality experiment. Experimental data are provided in frames of IAEA Coordinated Research Project “Neutronics Benchmark of CEFR Start-Up Tests”. The content of U-234 was calculated by us using mathematical model of the quasi-ideal enrichment cascade. Due to the high enrichment, the content of U-234, although still small, has ceased to be vanishingly small. The effect caused by this isotope is appeared not only through the presence of new isotope in the fuel load, but also in a decrease in the mass of the U-238 isotope in the fuel load. It is shown, that accounting for U-234 slightly increases the agreement of the calculated assessments of TRE among themselves (values of deviation shifted toward each other)/Also accounting for the U-234 isotope leads to a small but systematic increase in the values of the effective multiplication factor by 120-150 pcm.