6. Irradiation- and temperature-induced phenomena

6.1 Concrete activation

Neutron irradiation of concrete produces secondary gamma radiation as a result of nuclear reactions on the constituent atoms. The emission of γ photons may occur concomitantly with neutron absorption ("n, γ" radiative capture), or deferred, by deactivation of the new nuclei formed if the latter are unstable. Depending on the nature of the nuclei involved, radioactive decay can take place over short periods (s, min, h), which can hinder operations, or over long periods ( $⩾$ months), which can lead to long-term closure of facilities.

In the case of fission power reactors, most of the ambient gamma radiation comes from neutron capture in...