The Impact of Pulsed Irradiation Upon Neutron Activation Calculations for Inertial and Magnetic Fusion Energy Power Plants

Abstract

Inertial fusion energy (IFE) will operate and magnetic fusion energy (MFE) power plants may operate in pulsed modes. The two confinement schemes, however, will have quite different time periods. Typical repetition rates for IFE power plants will be 1-5 Hz. MFE power plants will likely ramp up in current for about 1 hour, shut down for several minutes, and repeat the process. Traditionally, activation calculations for IFE and MFE power plants have assumed continuous operation and used either the “steady-state” (SS) or “equivalent steady-state” (ESS) approximations.^1-5 It has been shown, however, that the SS and ESS methods may not yield accurate results for all radionuclides of interest.⁶ The present work expands that of Sisolak, et al. by applying their formulae to conditions which might be experienced in typical IFE and MFE power plants. In addition, complicated, multi-step reaction/decay chains are analyzed using an upgraded version of the ACAB radionuclide generation/depletion code.⁷ Our results support previous work in the conclusion that the SS method is suitable for application to MFE power plant conditions.⁶ We also find that the ESS method generates acceptable results for radionuclides with half-lives more than a factor of three greater than the time between pulses. For components that are subject to 0.05 Hz (or more frequent) irradiation (such as the first wall and coolant), use of the ESS method is recommended. For components or materials that are subject to less frequent irradiation (such as high-Z target materials), pulsed irradiation calculations should be used.