Chemical Species from Tritium-Breeding Compacts by Raman Spectroscopy

Abstract

The retention of tritium in reactor breeding compacts has been studied in these experiments at conditions simulating nuclear reactor accidents, and the experimental results have been used to determine New Production Reactor safety envelopes. The tritium-breeding compacts tested contain thousands of spherical particles within a carbonaceous matrix; each particle is fabricated as a kernel of lithium aluminate, enriched in 6Li for breeding tritium by (n,α) reaction, surrounded by consecutive shells of porous carbon, pyrolytic carbon, silicon carbide, and pyrolytic carbon to retain the tritium during breeding. The experiments demonstrated that in an accident with a sudden reactor temperature jump to 1300°C, more than 99% of the tritium would be retained within the compact for over 50 hours, which is ample time to bring such an accident under control. In these experiments, chemical species released from the compacts were measured by laser-Raman spectroscopy to enable design of chemical safety systems. Chemical species that were observed at intermediate temperatures, including H2O, H2, CO, and hydrocarbons, resulted from compact exposure to air, whereas species released at high temperatures, including HT and CO, originated within the particles. The Raman data identified the dominant tritiated species to be HT, at concentrations commensurate with measurements of total tritium using ion chambers and scintillation counter. These tests attained Raman detectability as low as 6.4 parts-per-million (ppm) for HT.