In-Line Tritium Monitoring in the GCFR Vented Irradiation Capsule GB-10

摘要

An in-line tritium monitoring system was designed, tested, and operated on the sweep gas from the Gas-Cooled Fast Reactor irradiation capsule GB-10. Cooled charcoal traps removed fission and activation products and the HTO form of tritium from the gas stream but allowed the HT form to pass through. The tritium-bearing gas stream then passed through an ionization chamber containing a vibrating-reed electrometer which recorded the tritium response on a strip-chart recorder. Total tritium (HT + HTO) determination was attempted by passing the sweep gas through an HTO converter (magnesium at 500 exp 0 C) that quantitatively converted HTO to HT when the gas stream contained hydrogen carrier. An alternate and independent tritium detection system was included downstream from the ionization chamber. The gas stream could be valved through an HT converter (CuO at 500 exp 0 C), which quantitatively converted HT to HTO, and then valved through heated lines to molecular-sieve traps. Laboratory procedures were necessary to release the tritium and to determine the amount adsorbed by the molecular-sieve traps. Fifteen tritium monitoring experiments were completed with this system. Data obtained from the electrometer and molecular -sieve samples were in excellent agreement. Molecular-sieve samples were necessary on some experiments due to low tritium levels and the unexpected presence of exp 24 Ne in the gas stream.The low-level exp 24 Ne was apparently produced in the fuel region of the capsule and was not retained by the charcoal traps. Monitored tritium was significantly lower than the calculated birth rate. Areas exposed to fission product deposition retained tritium from high-purity helium and released tritium when the gas stream contained hydrogen carrier. Temperature-dependent tritium release was observed while sweeping the heated charcoal trap region of the GB-10 fuel rod. (ERA citation 04:003338)