Modelling the dose to man from exposure to tritiated water vapour

Peaceful Nuclear Explosives (PNE) usually result in the release of tritium as tritiated water vapour (HTO) to the atmosphere. Dose calculations using the deposition velocity-dose conversion constant approach, although valid for most nuclides, have been shown by measurements during flaring of the Rulison gas stimulation experiment to grossly over-estimate tritium doses. This paper presents new, improved methods of calculating the dose to man from the release of HTO. One model is appropriate for the food-chain transfer of HTO under conditions of no or very light precipitation. The primary parameters are the surface air concentration, absolute humidity, and appropriate experimentally-derived constants associated with specific pathways. A key feature of this model is a more realistic treatment of the uptake of HTO by vegetation. The second model is used with light, moderate, or heavy precipitation. The basic equation used for this model expresses wet deposition versus time as a function of cloud thickness, HTO concentration, rain rate and absolute humidity. Both models appear to give reasonable HTO dose calculations, the first model for United States gas stimulation experiments and the second for proposed nuclear excavation projects. (author)