Tritium speciation in nuclear reactor bioshield concrete and its impact on accurate analysis

Kim, Dae Ji, Warwick, Phillip E. and Croudace, Ian W. (2008) Tritium speciation in nuclear reactor bioshield concrete and its impact on accurate analysis. Analytical Chemistry, 80 (14), 5476-5480. (doi:10.1021/ac8002787).

Abstract

Tritium (3H) is produced in nuclear reactors via several neutron-induced reactions [2H(n,?)3H, 6Li(n,?)3H, 10B(n, 2?)3H, 14N(n, 3H)12C, and ternary fission (fission yield <0.01%)]. Typically, 3H is present as tritiated water (HTO) and can become adsorbed into structural concrete from the surface inward where it will be held in a weakly bound form. However, a systematic analysis of a sequence of subsamples taken from a reactor bioshield using combustion and liquid scintillation analysis has identified two forms of 3H, one weakly bound and one strongly bound. The strongly bound tritium, which originates from neutron capture on trace lithium (6Li) within mineral phases, requires temperatures in excess of 350 °C to achieve quantitative recovery. The weakly bound form of tritium can be liberated at significantly lower temperatures (100 °C) as HTO and is associated with dehydration of hydrous mineral components. Without an appreciation that two forms of tritium can exist in reactor bioshields, the 3H content of samples may be severely underestimated using conventional analytical approaches. These findings exemplify the need to develop robust radioactive waste characterization procedures in support of nuclear decommissioning programs.

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Contributors

Author: Phillip E. Warwick

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