Electronuclear breeding of nuclear fuel in thorium targets

Abstract

621.039Electronuclear breeding of nuclear fuel can be done not only in uranium but also in thorium targets. In comparing these two systems it should be kept in mind that the average number of particles produced when a high-energy nucleon interacts with a thorium nucleus is virtually identical to the number of particles produced in a nucleon-uranium collision (about 25 particles per inelastic nucleon-nucleus collision at energy T = 1 GeV and about 20 particles at 0.5 GeV [1]).In the reactor-energy range r < 10.5 MeV,* however, the fission cross section and therefore the number of neutrons produced are considerably smaller for thorium than for uranium. For this reason, it can be expected in advance that the rate of breeding of nuclear fuel will be lower in the thorium medium. Nonetheless, it is still significant. Moreover, the thorium target is also interesting from the standpoint of being an efficient method for producing a large amount of 233U, which has unique technical applications.** Targets with metallic uranium and thorium also differ substantially from one another in that the thorium density is 1.7 times lower than the uranium density, as a result of which the thorium target, utilizing all neutrons which are produced, should be 1.5-2 times larger in size. Correspondingly, in this case the position of the maxima in the spatial distribution of the breeding characteristics will be shifted by a factor of approximately 1.7 compared to uranium. At the same time, uranium and thorium oxide have approximately the same density Lo(ThO2)/p(UO2) = 9.69/10.96 = 0.88], and for this reason the spatial distribution of the characteristics of the process occurring in oxide targets will be close. The objective of the present work is to perform statistical modeling of the interaction of a beam of high-energy protons with different types of thorium targets and to compare the results with similar data for uranium targets.The computational method is similar to that used in the preceding works [2][3][4][5][6]. The geometry of the target remains unchanged: a cylinder with a thin channel along the axis for introducing the primary proton beam to a depth z0. Since we are mainly interested in estimating the maximum neutron flux and the highest yield of 233U, the target must be large in order that neutron leakage from the target be negligibly small. The calculations were performed for a target whose dimensions were twice those of the uranium target considered in [3][4][5][6]: the length L = 180 cm, the diameter D = 240 cm, and z0 = 52 cm. Neutron leakage from such a target is small even if sodium coolant is used, when the mean free path of the particles in the target matter increases substantially. Such a target can be regarded as "practically infinite," and its specific geometric parameters are no longer important. The kinetic energy of the primary proton beam is assumed to be T = 1 GeV.Metallic 232Th Target. Such a target determines the maximum parameters for electronuclear breeding of fuel that can be achieved without additional enric...