Estimation of cooling water activation in high-energy heavy ion medical accelerator

Abstract

The estimation of air, material, and cooling water activation is essential for designing a robust nuclear safety protocol for high-energy heavy ion medical accelerators. Demineralized cooling water activation is simulated for the C-12 ion beam medical accelerator (synchrotron) with a maximum energy of 430 MeV/u. Three conservative scenarios are proposed for the estimation of demineralized cooling water activation. Simulations were performed by using a combination of MCNPX2.7.0 and VCINDER codes. Simulation parameters were optimized to match the volume of the cooling water in the accelerator system. The sums of the ratios of specific activities to unrestricted release limits were calculated for the three scenarios as a function of decay time. All activity concentrations are far less than the corresponding unrestricted release limits after a 1-day decay time because the sums of the ratios are all less than 1.0. Noticeable hazardous radioactive elements were found to be H-3, Be-7, and C-11 which have relatively long half-life times. Although hazardous radioactive elements with relatively short half-life times (within 10 min), such as N-13, O-14, and O-15, are also produced in large concentrations, there are no unrestricted release limits specified in the table issued by the National and International Radiation Protection Ordinances. The estimation of cooling water activation is useful for designing a nuclear safety protocol for high-energy heavy ion medical accelerator facilities. Specifically, the results suggest that the direct discharge of the cooling water waste into the environment (in case of an accident or the end of the life cycle of cooling water) must not be permitted. A separate reservoir for cooling water waste collection is recommended with a dedicated real-time measuring equipment to measure the concentrations of H-3, Be-7, C-11, N-13, O-14, and O-15 separately.