Abstract
Nuclear power plants 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 a number of minerals, which are common constituents of aggregates, in concrete it was shown that ~95% of the dpa is generated by neutrons with energies above 0.1 MeV. Neutrons with energies above 1 MeV contribute only ~20 to 25% to the dpa. Therefore, if neutron fluence is used as correlation parameter for the concrete degradation, the neutron fluence energy cut-off of 0.1 MeV should be used. Based on the projected neutron fluence values (E > 0.1 MeV) in the concrete biological shields of the US 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.
