Sequential Charged-Particle and Neutron Activation of Flibe in the Hylife-II Inertial Fusion Energy Power Plant Design

The majority of radionuclide generation/depletion codes consider only neutron reactions and assume that charged particles, which may be generated in these reactions, deposit their energy locally without undergoing further nuclear interactions. Neglect of sequential charged-particle (x,n) reactions can lead to a large underestimation in the inventories of radionuclides that make a significant impact upon various radiological indices.¹ We have adopted the PCROSS code for use with the ACAB activation code to enable calculation of the effects of (x,n) reactions upon radionuclide inventories and inventory-related indices.^2,3 The present work builds upon our previous work and the work completed by R. A. Forrest for magnetic fusion energy devices.^4,5 Using this capability we have performed activation calculations for Flibe (2LiF + BeF₂) coolant in the HYLIFE-II inertial fusion energy (IFE) power plant design. For pure Flibe coolant, we find that (x,n) reactions dominate the residual contact dose rate at times of interest for maintenance and decommissioning. For impure Flibe, however, radionuclides produced directly in neutron reactions dominate the contact dose rate, and (x,n) reactions do not make a significant contribution. Our results demonstrate the potential importance of (x,n) reactions and that the relative importance of (x,n) reactions varies strongly with the composition of the material considered. Future activation studies should include (x,n) reactions in all calculations until a method for screening their importance in a particular situation has been established.