Validation of induced radioactivity calculations for candidate fusion materials through measurements in a graphite-centered assembly

Induced radioactivity measurements were carried out jointly by the USA and Japan in a graphite-centered assembly, in the framework of ITER Task T-218 entitled ‘Shielding Blanket Neutronics Experiments’. An intense, accelerator-based D-T rotating target neutron source at JAERI, with a nominal intensity of 5 × 1012 s–1, was used. Two locations, providing different neutron energy spectra, were chosen for irradiating samples of a range of materials of interest to ITER. Three independent experimental campaigns were conducted so as to accommodate a large number of samples, on one hand, and as many short and long half-life products as possible, on the other. The total neutron fluence ranged from 4.7 × 1011 to 1.5 × 1014 ncm–2. Altogether, samples of Mg, Al, SiO2, Ti, V, Cr, Mn, Fe, Co, Ni, FH82 steel, SS316LN steel (ITER grade), Cu, Zn, KCl, Zr, Nb, Mo, Ag, In, Sn, Dy, Ta, Hf, Re, Au, Ir, and Pb were irradiated. The irradiated samples were cooled for variable periods ranging from 30 s to 250 days before their decay gamma-ray spectra were counted on high purity intrinsic germanium detectors. The half lives of the observed radioisotopes have ranged from 18.7 s (46mSc from Ti) to 5.3 years (60Co from Ni). The neutron energy spectra for the two locations were calculated using Monte Carlo code MCNP with FENDL-1 and ENDF/B-VI data libraries. The analysis of isotopic activities, expressed in Bq cc–1, of the irradiated materials has been carried out using REAC-3 radioactivity code, with FENDL-2A and FENDL-1A activation cross-section and decay data libraries. Typically, C/E lies in a band of 0.5–1.5 for the results being reported.