THE IMPACT AND STATUS OF NEUTRON-ACTIVATION CROSS-SECTIONS FOR SHORT-LIVED REACTION-PRODUCTS OF INTEREST IN FUSION-REACTOR DESIGN

The impact and status of the cross sections for production of short-li ved radioactivities in the intense high-energy neutron fields associat ed with deuterium-tritium fusion reactors is investigated. The main co ncern relative to these very radioactive species is that they may repr esent enhanced radiation sources not accounted for in typical transpor t calculations. These enhanced radiation sources may affect heat remov al and shielding requirements. The status of nuclear data required to assess these issues is surveyed Among the factors considered in defini ng the relevant reactions and setting priorities are quantities of the elemental materials in a fusion reactor isotopic abundances within el emental categories, the decay properties of the induced radioactive by -products, the reaction cross sections, and the nature of the decay ra diations. Attention has been focused on radioactive species with half- dives in the range from similar to 1 s to 15 min. Available cross-sect ion and reaction-product decay information from the literature are com piled and examined. The evaluated data sets are collapsed using neutro n spectra from three fusion reactor designs-ARIES I and If and the Int ernational Thermonuclear Experimental Reactor (ITER). The group-averag ed cross-section sets are then used to produce neutron-spectrum-averag ed one-group cross sections, which are, in hem, used to produce decay heating reaction rates for each of the reactions. The decay heating ra te is used as a measure of the radiation source strength associated wi th a given reaction. The decay hearing reaction rates are compared aga inst neutron on hearing reaction rates. Calculated decay heat to neurm n heating ratios are required to be >10% in order for the reaction to be considered of importance for further study. The reactions of import ance are identified as Si-28(n,p)Al-28, with a ratio Of similar to 10% , and Pb-207(n,n')(207m) Pb, with a ratio >50%. The Si-28(n,p)Al-28 re action could affect heat removal requirements for reactors employing s ilicon carbide as a structural material. The Pb-207(n,n')(207m) Pb rea ction could affect heat removal and shielding requirements for shieEd designs employing lead. Identified reactions of slightly less importan ce are Al-27(n,p)Mg-27, Be-9(n,alpha)He-6, Cr-52(n,p)V-52, O-16(n,p)N- 16, and Ph-204(n,2n)(203m) Pb-all of which have ratios between I and 4 %.