Radiation-induced degradation of concrete in NPPs

Nuclear power plant life extensions to 60 and potentially 80 years of operation have renewed interest in long-term material degradation. One material being considered is concrete. Swelling of aggregates driven by radiation-induced displacements of atoms is currently considered to be the most probable leading contributor to the radiation-induced degradation of concrete mechanical properties. In the biological shields of nuclear plants, atom displacements are dominated by neutron contributions while gamma-ray contributions are negligible. For several minerals that are common constituents of aggregates in concrete, it was shown that approximately 95 % of the displacement per atom is generated by neutrons with energies above 0.1 MeV. Neutrons with energies above 1 MeV contribute only approximately 20 % to 25 % to the displacement per atom. Therefore, if neutron fluence is used as the correlation parameter for the concrete degradation, the 0.1 MeV neutron energy cutoff should be used for the fluence. Based on the projected neutron fluence values (E > 0.1 MeV) in the concrete biological shields of the U.S. pressurized water reactor fleet and the available data on radiation effects on concrete, some decrease in mechanical properties of concrete cannot be ruled out during extended operation beyond 60 years.