The Elimination of High-Dose-Rate Neutron Activation Products Within Nuclear Power Plant Structural Materials

Under the Safe Storage (SAFSTOR) decommissioning option, a nuclear power plant under U.S. Nuclear Regulatory Commission jurisdiction is allowed to remain dormant following spent fuel removal to allow for the decay of residual radiation as long as decommissioning is completed within 60 years of shutdown [10 CFR 50.82(a)(3)]. This residual radioactivity is due to the neutron activation of structural materials surrounding the core during its operational period. In this paper, we will use a simple MCNP model of a small molten salt reactor to identify which elements produce high-dose activation products (APs), rank them to identify which must be totally excluded and which are acceptable in small concentrations, and discuss possible next steps to eliminate the most problematic APs. We will show that only a few elements generate the high-dose APs responsible for the dormancy period and that if these few can be eliminated, or at least severely reduced, the need for much of the dormancy period can be eliminated, greatly simplifying decommissioning efforts, thus reducing both the time and monetary resources necessary to complete decommissioning.