Transfer parameters for routine release of HTO - consideration of OBT

Knowledge of the transfer parameters for tritium is a key requirement to assess the public dose or to establish Derived Release Limits (DRL) appropriate for a heavy-water reactor. This report revises the transfer parameters used to assess tritium doses via the ingestion pathway. First, the procedure used in Canadian standard CSA-N288.1 to assess the DRL for tritium is revised, clearing up some misunderstandings about the derivation of transfer parameters for air to forage and animal products. Second, we rederive the transfer parameters, applying conditions of full equilibrium to dynamic equations that describe the transfer of tritiated water in food. The new transfer parameters for tritiated water in food are more plant- and site-specific than the generic transfer parameters. The most important improvement is the introduction of organically bound tritium (OBT) production in plants or animal products. Bulk transfer parameters are introduced, which include OBT as well as HTO. Based on a standard Canadian diet, the dose increase considering OBT is almost 50%. Recent experimental data obtained under equilibrium conditions are discussed, and the appropriateness of the revised transfer parameters for assessment purposes is demonstrated. (author). 26 refs., 7 tabs