DECAY RADIOACTIVITY INDUCED IN PLASMA-FACING MATERIALS BY DEUTERIUM-TRITIUM NEUTRONS

Deuterium-tritium (D-T) neutron-induced radioactivity constitutes one of the foremost issues in fusion reactor design. Designers have been u sing radioactivity codes and associated nuclear data libraries for nuc leonic designs effusion reactors. However, in the past, there was hard ly any experimental validation of these codes/libraries. An elaborate, experimental program was initiated in 1988 under a U.S. Department of Energy/Japan Atomic Energy Research Institute collaborative program t o validate the radioactivity codes/libraries. Measurements of decay ga mma spectra from irradiated, high-purity samples of Al, Si, Ti, V, Cr, Mn-Cu alloy, Fe, Co, Ni, Cu, SS316/AISI316, Zn, Zr, Nb, Mo, In, Sn, T a, W, and Pb, among others, have been carried out under D-T neutron fl uences ranging from 1.6 x 10(10) to 6.1 x 10(13) n/cm(2) and cooling t imes ranging from similar to 10 min to similar to 3 weeks. As many as 14 neutron energy spectra were covered for a number of materials. The analyses of the isotopic activities of the irradiated materials using the activation cross-section libraries of four leading radioactivity c odes, i.e., ACT4/THIDA-2, REAC-3, DKR-ICF, and RACC, have shown large discrepancies among the calculations on one hand and between the calcu lations and the measurements, on the other. Vanadium, Co, Ni, Zn, Zr, Mo, In, Sn, and W each count the largest number of discrepant isotopic activities. It is strongly recommended to continue additional radioac tivity experiments under additional neutron energy spectra and large n eutron fluence on one hand and to Improve activation cross sections re lated to the problematic isotopic activities on the other. A unique ac tivation cross-section library and associated radioactivity code are a lso recommended for the best results. In addition to providing detaile d results of the status of predictability of individual isotopic activ ities using the ACT4, REAC-3, DKR-ICF: and RACC activation cross-secti on libraries, safety factors cum quality factors characterizing each l ibrary are presented and discussed. The related issues of confidence l evel and associated uncertainty are also highlighted. These considerat ions are of direct practical importance to reactor designers.