1. Summary of the Neutronics Analysis of Blankets for the Hybrid Fusion Neutron Source A.V.Zhirkin, B.V.Kuteev, M.I.Gurevich, B.K.Chukbar, NRC “Kurchatov Institute”, Moscow, Russia FNS/P7-25
The best result in reprocessing of spent nuclear fuel and a nuclear fuel production is obtained in molten salt blankets using natural lead and FLiBe. In these blankets it is possible to install an operating mode with keff ~ 0.95 if thermal neutron spectrum is prevailed. However due to high sensitivity of lead to influence of an electromagnetic field, FLiBe blankets can be used only.
Use of a fast neutron spectrum for reprocessing of spent fuel and production of fissile elements in lead blanket does not take an advantage over use of thermal neutron spectrum because fission reaction rate is essentially decreased. The relation of (n, g) reaction rate to the sum of (n, f), (n, 2n) and (n, g) reaction rates almost is not varied and is equal 29 % for a thermal spectrum and 30 % for a fast one.
The natural lithium which is a part of FLiBe must be cleared of 6Li isotope which is a strong absorber of thermal neutrons. In use of natural lithium fission reaction rate has considerable decrease (by a factor of more than 10).
For (n, f), (n, 2n) and (n, g) reactions in 239Pu neutrons are totally absorbed per 1 D-T neutron. It is accepted, that (n, 2n) reaction in mix of F7LiBe with 239Pu occurs only in 239Pu. For (n, g) reaction, 7.06 neutrons are absorbed. It is possible to reprocess kg of 239Pu per year in the assumption that 239Pu reprocessing is a result of (n, f), (n, 2n) and (n, g) reactions.
In 239Pu for an energy spectrum of thermal, intermediate and resonant neutrons, (n, g) reaction rate is 30 % with respect to the sum rate of reactions (n, f), (n, 2n) and (n, g). For a fast spectrum this value is 50 %.
The (n, g) reaction rate for 238U is equal The generation 239Pu from 238U which weight is kg in the result of (n, g) reaction is equal kg/year.
In a 6Li shell around of the FNS external contour, it is absorbed 1.94 particles per D-T neutron. The mass of shell is kg. In 6Li2O shell, 6.26 particles are absorbed. The mass of 6Li2O shell is kg. The abundance of 6Li is mas. %. In salt F7LiBe which is a part of a blanket layer, 4.20 neutrons are absorbed. Total absorption for an isotope 6Li is 8.20 particles. The tritium generation is equal kg/year.
In solid-state blanket, absorption in 232Th which mass is kg for 240 pipes placed in D2O moderator is equal particles. The production of 233U is kg/year. 233U burning out for a year does not exceed 30 %. In an isotope 6Li which mass is kg particles are absorbed. In lithium oxide 6Li2O which mass is kg particles are absorbed. Total absorption in an isotope 6Li is particles. The tritium generation is equal kg/year.
In blanket with use of heavy water solutions of salts and oxides of uranium and thorium reaction rates of nuclear fuel production are approximately equal to the same reaction rates in solid-state blankets.
The key problem for solid-state blankets is extraction of a considerable quantity of fission products, and for blankets using heavy water solutions of salts or oxides of uranium and thorium is radiolysis and sedimentation of radio toxic elements on walls of vessels.
Fig. 1. FNS model vertical section view.
Fig. 2. FNS model horizontal section view.