Impact of Ad Hoc Improvement of Decay and Cross-Section Data on the Prediction of Fusion-Neutron-Induced Radioactivity in Zirconium and Tungsten

Abstract

Measured decay rates resulting from neutron irradiation of zirconium and tungsten samples in a typical fusion environment have been compared with the computed values, and the sources of errors in the data and the calculational method have been identified. Comparison of four codes showed large differences that arise mainly from differences in the data libraries provided with these codes. The following reactions were found to be most important in terms of their contribution to the decay photon emission rate: [sup 90]Zr(n,2n)[sup 89m+g]Zr, [sup 90]Zr(n,p)[sup 90m]Y, [sup 90]Zr(n,[alpha])[sup 87m]Sr, [sup 91]Zr(n,p)[sup 91m]Y, [sup 186]W(n,[gamma])[sup 187]W, [sup 186]W(n,p)[sup 186]Ta, [sup 186]W(n,np)(n,d)[sup 185]Ta, [sup 184]W(n,p)[sup 184]Ta, [sup 183]W(n,p)[sup 183]Ta, [sup 182]W(n,p)[sup 182]Ta, and [sup 186]W(n,[alpha])[sup 183]Hf. However, decay data and cross sections for these reactions are not adequate in currently available libraries. An effort was made to improve the decay data by using the values from the most recent Table of Radioactive Isotopes and to improve the cross sections by using a simple curve-fitting procedure. Modified or improved decay data and cross sections were implemented in a representative code, and the computation was performed again. A great improvement in the computed results was observed for both sample cases. This work can easily bemore » extended to other fusion-relevant materials by utilizing the methodology presented here. The improved decay and cross-section data were applied to an International Thermonuclear Experimental Reactor (ITER) blanket using tungsten as a first-wall coating material and Li[sub 2]ZrO[sub 3] as a breeding material. The specific photon yield in each zone was computed, and as much as three orders of magnitude difference in the photon yield in the tungsten zone and [approximately] 10 to 15% difference in the zirconium-containing breeding zone was observed. 72 refs., 38 figs., 6 tabs.« less