Activity Measurement of Iodine Fission Products in 2LiF-BeF 2 Salt and Its Application in Redox Potential Surveillance for a Thorium Molten Salt Reactor.

The activities of 131 I, 132 I, 133 I, and 135 I produced by neutron-induced fission of 235 U in 2LiF-BeF 2 (FLiBe) eutectic salt and their dependence on the redox potential were studied. The dependence observed experimentally suggested that the activity ratio for 131 I to 132 I could be used as an indicator of the redox potential for FLiBe salt. Relying on the selective adsorption of iodine ions on the activated silver probe by ion exchange, a novel method for activity distribution measurement of the iodine isotopes in FLiBe salt was founded. The method is simple, fast, and easy to operate and would be suitable particularly to in situ monitor the redox potential of a thorium molten salt reactor, where the redox potential should keep at a high level to avoid possible safety risk induced by 233 Pa deposition in the reactor.