Following initiation of D-T neutron shots in TFTR in late 1993, measurements of radioactivity have been conducted at various locations surrounding the fusioning plasma. Before the last discharge in April 1997, a large number of capsules of materials of direct relevance to fusion power development were irradiated for various neutron fluences in mixed D-T and D-D neutron fields. Irradiated materials include aluminum, silicon, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, indium, silver, europium, terbium, hafnium, tungsten, rhenium, lead, bismuth, gold, 316 stainless steel, a vanadium-chromium-titanium alloy, a manganese-copper alloy, inconel 625, and inconel 718. In addition, samples of uranium, thorium, thoriated tungsten, boron, polytetrafluoride, and strontium were irradiated. The underlying aim of the latter experiments was to get experimental radioactivity data related to practical applications of D-T neutron driven fusion reactors, i.e., transmutation of actinides and fission product nuclides, on one hand, and production of isotopes of medical and industrial applications, on the other.

Intermediate measurements of decay radioactivity of various samples have led to a database of saturation activities for radioactive products resulting from a large number of neutron-induced reactions for various neutron energy spectra. Five orders of magnitude variation in D-T neutron fluence is observed. For example, the D-T neutron fluence is largest at the reentrant irradiation end (closest to plasma), being ~10^-6 n/cm² per D-T neutron emitted, and is lowest at test cell wall (farthest from plasma), being ~10^-11 n/cm². Contrarily, the thermal neutron flux undergoes only three orders of magnitude change. This difference is directly reflected in measured saturation activities from high threshold and capture reactions.

The counting of decay gamma-ray activity of irradiated samples is in progress. So far, cooling periods have ranged from few minutes to few months during the ongoing first round. After completion of this round, the samples will be cooled for periods ranging from six months to one year so as to allow shorter term radioactivity to disappear. The thrust will then be on longer lived radioactivity. All the measurements are valuable for experimentally characterizing the activation properties of the irradiated materials, on one hand, and providing an invaluable resource for realistic benchmarking of ITER and DEMO calculational models, on the other. Understandably, the focus thus far has been on creating the database of experimentally measured saturation activities driven largely by early shutdown of TFTR. However, it is important to utilize this database to validate calculational methodologies and data libraries applied to nuclear analysis of ITER via a solely dedicated project. In addition, it is strongly recommended to continue measurements of neutron-induced radioactivity at D-IIID and Alcator C-Mod tokamaks to reinforce the existing experimental database from TFTR.

* Work supported by US DOE Contract No.'s DE-AC02-76CH03073 and DE-FG03-86ER52124.