Neutron Activation of Structural Materials of a Dry Storage System for Spent Nuclear Fuel and Implications for Radioactive Waste Management

Abstract

In order to estimate the radiological characteristics of disused dry storage systems for spent nuclear fuel, a stepwise framework to calculate neutron sources (ORIGEN-ARP), incident neutron flux and reaction rate (MCNPX), effective cross-section (hand calculation), and residual activity (ORIGEN-2) was established. Applicability of the framework was demonstrated by comparing the residual activity of a commercialized storage system, HI-STORM 100, listed in the safety analysis report and calculated in this study. For a reference case assuming an impurity-free storage system, the modified effective cross-sections were theoretically interpreted and the need for managing disused components as a radioactive waste for at least four years was demonstrated. Sensitivity analyses showed that the higher burnup induces the higher residual radioactivity, and the impurity 59Co may extend the minimum decay-in-storage period up to 51 years within the reported range of 59Co content in stainless steel. The extended long-term storage over 100 years, however, caused no significant increase in residual radioactivity. Impurity control together with appropriate decay-in-storage was proposed as an effective approach to minimize the secondary radioactive waste arising from disused dry storage systems. The results of this study could be used to optimize the decommissioning and waste management plan regarding interim storage of spent fuel.