Characteristics of electronuclear targets containing water

Abstract

The effect of liquid-metal coolants on the characteristics of electronuclear systems was studied in [1, 2]. Our objective in the present paper is to investigate the effects associated with the use of water as a coolant. This is of special interest in connection with the fundamental possibility of using electronuclear setups for breeding nuclear fuel directly in the fuel elements of thermal reactors for secondary utilization of these reactors.Since an accelerator that would make possible industrial operation of setups of this type has not yet been developed and in view of the fact that there is no generally accepted concept for utilization of such setups in the current system of nuclear power production, we shall not investigate in the present paper the systems aspects of the electronuclear method; we shall confine our attention to the analysis of the physical characteristics of an electronuclear reactor. In the present work we investigated the change of the parameters of such a reactor when the liquid metal coolant is replaced with water. For this, a computer was used to model two targets of an electronuclear reactor with the same geometric size, differing only in the fact that in one case the coolant is 2~and in the other the coolant is water. The outer diameter of the cylindrical blanket is 120 cm, the blanket is 90 cm long, and the channel for introducing a beam of 1 GeV primary protons is 26 cm long. The diameter of the lead core, onto which this beam is aimed, is 64 cm. It is assumed that the composition of the blanket is the same as that of the VVI~R-1000 core [3]: The volume fraction of 238U + 235U, 56Fe, H20 (207pb) is 34.2, 12, and 53.8%, respectively. The volume fraction of metallic uranium in the blanket e(238U + 235U) = e(UO2), where e(UO2) is the volume fraction of UO 2 in the fuel of the VVI~R-1000 core.The calculations were performed using the same statistical Monte Carlo program methods as in [1, 2]. Changes were introduced only in the specific nature of the water-containing coolant. Three groups of effects were examined. First, the effect of an admixture of hydrogen atoms on the properties of an electronuclear reactor were analyzed. In this case, the neutron spectrum shifts in the direction of low energies up to the thermal region, and the anisotropy of the low-energy neutron-proton scattering must be taken into account (at temperatures T < 10.5 MeV). At this stage the calculations were performed assuming that the components of the blanket are uniformly mixed and the hydrogen-oxygen chemical bond in the water molecule was neglected. The cross sections of the elements in the thermal region were assumed to be constants: a(0.0215 eV) ---ao, where a o are taken from reference data. The thermal motion of the nuclei in the medium was taken into account in accordance with the Maxwell-Boltzmann spectrum.The next group of effects concerned taking into account the chemical bond of the hydrogen atoms in a water molecule and the energy dependence of the cross sections in the thermal region. The chemical bond...