The general theory of radiation damage in solids is outlined briefly. Those aspects of the damage which are important in altering the mechanical properties of reactor structural metals and alloys are considered in greater detail. Procedures by which estimates can be made of the numbers of displaced atoms and of their spatial distribution, as well as of the stability of various damage configurations, are described.
Three basic processes occur under irradiation which can influence the metallurgical state of a material. Transmutations, mainly due to neutron capture, can change alloy compositions. Displacement of atoms from their original sites tend to homogenize the distribution of components of alloys on a microscopic scale. Excess defects introduced by radiation accelerate diffusion and, consequently, diffusion-controlled processes. The latter two effects will oppose each other in a number of cases, and the resulting balance will be determined mainly by temperature and radiation flux. High-temperature creep, being diffusion controlled, will be enhanced under irradiation. Spike effects may also cause creep.
The intent of the present paper is not to provide specific and quantitative estimates concerning the magnitude of the phenomena described, but rather to outline the mechanistic concepts presently believed responsible for their occurrence and to indicate the manner in which order of magnitude calculations can be performed for any specific situation.