Impact of Steel Equipment on Cyclotron Activation and Its Implications for Radioactive Waste Management

This study expands and enhances an activation assessment framework based on MCNP6.2® and FISPACT-II.4.0 to systematically evaluate the impact of steel equipment on neutron activation within a positron emission tomography cyclotron vault. The neutron flux submodel was experimentally validated at a cyclotron facility in operation, and the assessment framework was applied to a reference cyclotron in Korea to analyze how steel equipment characteristics affect neutron activation. The results showed that the presence of steel equipment reduces the activation of concrete walls by up to 50%. However, the steel itself may become significantly activated, surpassing the clearance level and potentially generating new low-level radioactive waste. This is primarily due to the cobalt impurity concentration in steel being up to 100 times higher than in concrete. Furthermore, the presence of steel equipment could increase the total radioactive waste volume by 120% to 1600% depending on the duration of decay storage.

Based on these findings, it is recommended that steel equipment be located in a separate room outside the cyclotron vault to minimize activation and radioactive waste volume. For cases where the equipment must be housed within the vault, design provisions are proposed to reduce both equipment and concrete activation. These include (1) positioning steel equipment opposite the proton beam’s direction and as far as possible from the irradiated target and (2) considering cobalt-free nickel alloys to minimize activation. This study contributes valuable insights into optimizing cyclotron facility design and radioactive waste management to facilitate safe and efficient decommissioning.