Radiation Damage in Reactors

Fuel, cladding, and structural materials, moderators, coolants, pressure vessels, and other components of nuclear reactors are bombarded by fast and thermal neutrons (with fluxes up to and above 10¹⁵ cm⁻² sec⁻¹) at elevated temperatures. Fuel elements are also exposed to fission fragments; all components are exposed to high fluxes of gamma rays. As a result the physical properties of materials are modified, usually in undesirable ways. Brittleness, altered creep, and swelling which leads to complex deformations and induced stress are common problems. A broad understanding of these effects in terms of displaced atoms, point defects, dislocations, disordered regions, voids, and transmutation‐induced impurities has been developed. Much empirical information has become available, and means for lessening certain effects have been found. Knowledge of the details of atomic mechanisms, particularly their quantitative aspects, in the broad range of materials of interest is still inadequate, and the body of empirical data, particularly at the higher levels of exposure, needs to be extended. Bombardment of thin specimens with charged particles from accelerators has been a useful tool for simulating high neutron exposure, but the degree to which the simulation is adequate needs further investigation.