Fusion Science and Technology / Volume 4 / Number 2P2 / September 1983 / Pages 681-686
Tritium / dx.doi.org/10.13182/FST83-A22938
Experimental evidence collected by several researchers suggests that gamma radiation may enhance the release of tritium from structural materials in fusion reactors. If so, this may reduce inventories and, in first walls, it may reduce permeation rates. The release process is not well understood, but it appears to involve Compton scattering of photons by electrons of the host material. The excited electrons then interact with binding potential fields to effect the release of bound tritium atoms. This process seems to be fairly efficient in nonmetals where it may result in enhanced diffusion, but it should be less important than thermal processes in metals. Experiments were conducted in the gamma irradiation facility of the Advanced Test Reactor at the Idaho National Engineering Laboratory to determine whether gamma radiation has an appreciable effect on the normal permeation of tritium through stainless steel. Low concentrations of HT were allowed to diffuse through a 0.071-cm-thick tube of 316 stainless steel, heated between 590 and 733 K. Gamma irradiation intensities were varied from 1.3 to 155 C/kgh (5 × 103 to 6 × 105 R/h). Ion chamber detectors were used to measure tritium concentrations on both sides of the tube. It was found that in the presence of excess H2, the higher gamma irradiation intensity exhibited slightly higher permeation rates of tritium. When the walls of the permeation tube and the HT were highly oxidized, the permeation rates were much more scattered, and the gamma irradiation seemed to have no observable effect. It was concluded that the effect of gamma radiation on tritium permeation through stainless steel in a fusion reactor environment should be small. However, the relative ease with which tritium from HTO was seen to permeate the material raises questions regarding tritium management in breeder blankets.