Experiments and Analysis for Measurements of Decay Heat Related Induced Activities in Simulated Line Source Driven D-T Neutron Fields of Phase IIIA: USDOE/JAERI Collaborative Program on Fusion Neutronics

The recently concluded phase IIIA experiments of the USDOE/JAERI collaborative program mark a watershed in that a D-T line source was simulated by moving detectors/annular Li₂O blanket-assembly with respect to a stationary point source. Three experiments were conducted in three stages during this phase: (i) source characterization (step-mode, 10 cm step, 9h47m duration, 3 sample locations), (ii) in-situ short irradiation (stationary assembly, 30m duration, 2 sample locations), (iii) in-situ long irradiation (continuous-mode, 9h51m duration, 3 sample locations). The sample-materials included: Fe, Ni, Mo, SS316, W, Ta, Zr, Al, Sn, Ag, Pb, Zn, Nb, Ti, V, Co and In. The sample locations inside the phase IIIA assembly were so chosen as to monitor (a) the impact of lack of line source simulation on decay γ-radioactivity, (b) the influence of SS304 first wall, (c) the role of neutron spectral degradation in the annular Li₂O fusion blanket assembly. The experimental results demonstrate that: (1) continuous-mode operation provides better simulation of line source even for radioactive products of half lives as low as ∼10 min, (2) the decay γ-emission rates generally drop as one moves away from the center of simulated line source (length=2 meters), (3) the presence of surrounding annular blanket leads to larger enhancements in the γ-emission rates ascribable to reactions induced by energy-degraded neutrons. The analysis of these measurements shows up discrepancies for most of the materials. DKRICF lacks decay data for many isotopes. For example, decay data is absent for Y, ¹⁸⁶Ta, ¹⁸⁷W, and ¹⁸¹W. For Zr, ^91mY contribution is severely underestimated. Severe underestimation hits Zn and Sn (especially ^117mSn and ¹¹¹In). REAC2 related more important observations can be summarized as follows: For Mo, ⁹¹Mo is strongly overestimated and ¹⁰¹Mo, ⁹⁹Mo, ^98mNb, ⁹⁷Nb, ^93mNb are underestimated. For Zr, ^89m+gZr, ^90mY and ^91mY are strongly overestimated. For W, ^179mW yields abnormally large contribution for both short and long cooling times. The data base for Zn needs complete overhaul as for some isotopes there is strong overestimation (⁶⁵Ni, ⁶⁷Cu and ⁶⁹Zn), while yet for others, there is severe underestimation (^69mZn, ⁶⁵Zn and ⁶⁴Cu).