An investigation of the activation of water by D-T fusion neutrons and some implications for fusion reactor technology

Several fundamental aspects of the activation of water by neutrons in D-T fusion systems have been investigated in this work. The basic physical principles involved and the status of pertinent nuclear cross-section and radioactivity data were reviewed. The integral response of the dominant 16O(n,p)16N reaction was calculated using several evaluated differential cross-section representations and characteristic D-T fusion neutron spectra. The impact of cross-section uncertainties was also assessed in this context. Two integral experiments were carried out at a D-T neutron generator facility to investigate the production and transport of 16N radioactivity in a D-T fusion neutron environment. Radioactivity yield data were acquired in one of these integral experiments (IE-1) and the measured results were compared with values obtained from calculations which employed both analytical and Monte-Carlo techniques. Measurements on the shielding of high-energy gamma rays from 16N decay by stainless steel (SS-304) and copper were performed in an additional integral experiment (IE-2) and these data were interpreted by a combination of analytical calculations and Monte-Carlo simulation. Some consequences of neutron-induced 16N radioactivity in the cooling water of a fusion reactor were examined for two contemporary conceptual designs of the International Thermonuclear Experimental Reactor (ITER). This analysis benefitted from insight acquired through the present integral studies. It was found that this radioactivity generating process would lead to significant biological doses outside the reactor containment vessel and could also deliver potentially damaging radiation doses to superconducting magnet insulators unless care is taken to provide adequate shielding when designing a fusion reactor.