Analysis of Induced Activities Measurements Related to Decay Heat in Phase IIC Experimental Assembly: USDOE/JAERI Collaborative Program on Fusion Neutronics Experiments

Abstract

The selection of materials and design options for fusion device components depends crucially on the level of radioactivity and decayheat induced in the components subject to D-T neutron irradiation. An experimental program was carried out to obtain decay γ emission spectra from samples of Fe, Ni, Cr, MnCu alloy, Ti, Mo, Zr, Ta, W, Si, Mg, Al, V, Nb, SS316, YBa₂Cu₃O₇ and ErBa₂Cu₃O₇, which were subjected to simulated fusion neutron environment. Cooling times obtained ranged from 10 min to 7 days. The experimental results have been analyzed using four leading radioactivity codes: DKRICF, REAC, RACC and THIDA. The integrated decay γ emission rates (over 100 KeV to 3 MeV) have been compared in addition to decay γ emission spectra. It is observed that : (i) generally, much better agreement is found between computed (C) and experimentally measured (E) values for integrated γ emission rates as against the detailed γ spectra, (ii) C/E ratios for integrated γ emission rates are found to range from 0.001 to 300, though most of the ratios cluster between 1 to 2. Significant discrepancies are obtained on C/E ratios for a number of cases for the four codes used above. Most of the observed discrepancies are due to (a) missing or wrong fundamental decay γ-ray data, e.g., (1) missing decay data in DKRICF for ¹⁸⁶Ta, ¹⁸⁷W, ¹⁸¹W, ^90mY, ⁸⁶Rb, ⁸⁸Y, etc., (2) wrong decay γ-intensities for W products in THIDA, (b) inaccurate activation cross sections, e.g., for V, Zr, Mo in DKRICF, RACC, REAC, (c) errors on computed neutron energy spectra, (d) various experiment related factors, essentially poor counting statistics for weak neutron induced reactions.