Subcritical accelerator-controlled medium-power nuclear reactor

Abstract

A new generation of nuclear power plants is now being intensively developed worldwide. The current plan is to increase the nuclear power plant capacity in the world from 20 to 30% over the 1990 capacity by 2010 [1]. Different ideas on increasing the degree of safety of power plants (see, for example, [2]) are being put forth at the same time. A large fraction of these works is directed toward producing designs of powerful (-103 MW) subcritical nuclear power reactors in which the chain reaction is initiated by neutrons produced in a target consisting of a heavy element (W, Pb or U) by protons accelerated in a high-current accelerator (with an average current of several hundreds of mA) in the energy range (T) from several hundreds of MeV up to 1.6 GeV [3, 4].The objective of these designs is to solve the three basic problems facing mankind: Elimination of Chernobyl-Type Accidents. Since the reactor operates in the subcritical regime (Keff < 1), an explosive reaction is impossible.Burning Up Long-Lived Nuclear Wastes. In the reactors currently being planned the neutron flux density reaches _ 1016 cm-2.sec-1, which makes possible transmutation of long-lived wastes over a comparatively short period of time and therefore elimination of the need for storing them;Fuel. It is well known that at the current rates of development of nuclear power worldwide the reserves of the traditional energy resources (oil, gas, uranium) will last for approximately 50-100 years. In the nuclear reactors being developed, it is proposed that thorium be used in a 232Th-233U cycle. The thorium reserves are several orders of magnitude larger than uranium..This makes it possible to push the energy crisis forward beyond the foreseeable future.Our objective in the present paper is to give a justification for using a reactor with standard parameters (specifically, VVI~R-440 reactors, which are widely used in the Union of Independent States) in a subcritical regime combined with a proton accelerator with a relatively low current and energy.The functional diagram of such a nuclear power plant with an accelerator is displayed in Fig. 1. A 50 cm in diameter and I00 cm high cylindrical volume is freed at the center of the reactor by removing a corresponding number of uranium rods (which constitutes about 7 % of the total fuel mass) in order to insert there a target of the same size (the size is determined by the necessity of absorbing accelerated protons).In a VVI~R reactor (including heavy-water reactors) the neutron-flux density reaches ~o -2.1014 cm-a'sec -1. Therefore to compensate for the missing neutrons the intensity of the proton beam must be high enough to provide a neutron flux with the same density from the surface of the target.In [3][4][5][6] the neutron yield per proton in the region of the energy of accelerated protons from 250 MeV up to 2-3 GeV was estimated for two different targets; the results agreed to within the limits of error. For purposes of estimation, in the present work we used the results of [5] in the case of a uranium targ...