High-power neutron sources

Abstract

Introduction. The most advanced countries of the world --the USA, Japan, the countries of the European Union, and Russia --have approached the solution of the controlled fusion (CF) problem and continue to develop the International Experimental Reactor (ITER). Although the science is familiar with many fusion reactions that are perfect from the ecological viewpoint, i.e., without neutron emission (p + B, ~He + 3He, and 3He + D; in the latter case, neutrons are created only in the side channel of the low-intensity reaction D+D), in the forthcoming decades the level of engineering will allow one to use only the D-T reaction: D + T = 4He(3.5 MeV) + n(14.1 MeV), in which most of the energy is released with neutrons. The development of fusion energetics in the near future is associated precisely with this reaction because it proceeds at the lowest temperatures (100-200 million degrees) [1].Since the density of the neutron flux which acts on the wall of a thermonuclear DT reactor should be of the order of a few MW/m 2, one of the key problems of fusion energetics is the creation of new radiationstable structural materials and low activated materials. This complicated physicotechnical problem can be solved by the joint efforts of materials science researchers in many countries. It is impossible to go ahead in this field of research without the creation of a high-power source of thermonuclear nefitrons. The Fusion Programme Evaluation Board headed by H. Colombo concluded that such a source should be created within the framework of the ITER program for the shortest period [2].At present, reliable data on the behavior of structural materials exposed to long-term high-energy neutron irradiation are absent, because low-energy neutron tests in nuclear reactors cannot answer most of the questions. Thus, there is uncertainty the in evaluation of the radiation stability and durability of the basic structural materials. The ITER itself will not solve the problems encountered, since the totM fluence for the period of its operation will amount to as little as 1 MW. yr/m 2 (1.5-1021 neutrons/cm 2) [3], and this fluence will be accumulated only at the end of the reactor run, so that the data obtained will not offer the possibility of making a correct choice of structural materials for an experimental thermonuclear power plant. Despite the fairly moderate density of the thermonuclear power released per unit volume in the case of a tokamak reactor (,--3 MW/m 3) [1], the neutron load at the first wall of a thermonuclear reactor should be 2-3 MW/m 2 (or ~1014-1.5 -1014 neutrons/cm 2 9 sec). The time of action of the neutron flux at the wall should be equal to 10-20 yr. Thus, the total fluence experienced by the first wall for the period of the campaign is estimated to be 3. 1022-9 9 1022 neutrons/cm 2.Clearly, however successful the operation of the ITER, an experimental fusion power plant cannot be created if a large program of fusion materials development (durability, decrease in the conductivity upon irradiation damage, variations in ...