Investigation of tritium and 233U breeding in a fission-fusion hybrid reactor fuelling with ThO2

Abstract

In the world, thorium reserves are three times more than natural Uranium reserves. It is planned in the near future that nuclear reactors will use thorium as a fuel. Thorium is not a fissile isotope because it doesn't make fission with thermal neutrons so it could be converted to 233U isotope which has very high quality fission cross-section with thermal neutrons. 233U isotope can be used in present LWRs as an enrichment fuel. In the fusion reactors, tritium is the most important fusil fuel. Because tritium is not natural isotope, it has to be produced in the reactor. The purpose of this work is to investigate the tritium and 233U breeding in a fission-fusion hybrid reactor fuelling with TI1O2 for At=10 days during a reactor operation period in five years. The neutronic analysis is performed on an experimental hybrid blanket geometry. In the center of the hybrid blanket, there is a line neutron source in a cylindrical cavity, which simulates the fusion plasma chamber where high energy neutrons.(14.1 MeV) are produced. The conventional fusion reaction delivers the external neutron source for blankets following, 2D + 3T -* 4He (3.5 MeV) + n (14.1 MeV) The fuel zone made up of natural-ThO2 fuel and it is cooled with different coolants. In this work, five different moderator materials, which are Li2BeF4 , LiF-NaF-BeF2 , Li2oSngO , natural Lithium and \A\i?b^, are used as coolants. The radial reflector, called tritium breeding zones, is made of different Lithium compounds and graphite in sandwich structure. In the work, eight different Lithium compounds were used as tritium breeders in the tritium breeding zones, which are Lİ3N, Li2O, Li2O2 , Li2Ti03, Lİ4SİO3, Li2ZrO3, LiBr and LiH. Neutron transport calculations are conducted in spherical geometry with the help of SCALE4.4A SYSTEM by solving the Boltzmann transport equation with code CSAS and XSDRNPM, under consideration of unresolved and resolved resonances, in S8-P3 approximation with Gaussian quadratures using the 238 groups library, derived from ENDF/B-V. For a self sustained fusion fuel supply, a tritium breeding rate (TBR) > 1.05 is required. At the beginning of the reactor period (BOL) and at the end of the reactor period (EOL), LinPbs3 moderated blanket has well results compared to other moderators for TBR. According to Lithium compounds used tritium breeding zone, at the BOL and at the EOL, LiH, L13N, Li2O, Li2O2 and Lİ4SİO4 have well results. In the fuel zone of the fission-fusion hybrid reactor, 233U isotopes are produced with 232Th (n,y) 233U reactions. At the BOL and at the EOL, Lii7Pb83 moderated and Li2Zr03 tritium breeder blanket has well results compared to other moderators and tritium breeders for U breeding rate (UBR).

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