San Diego, California, 17-19 June 2002

Elementary Tritium Contribution to the Doses by Ingestion and Re-Emission from Releases in Inertial Fusion Reactors:

comparison of HT and HTO

M. Velarde, J.M. Perlado

Instituto de Fusión Nuclear (DENIM) / Universidad Polité cnica Madrid (UPM)

J. Gutierrez Abascal, 2; E.T.S.I.I., 28006 Madrid (Spain)

Tel: +34 91 336 3108/09/10 — Fax: +34 91 336 3002 — martadenim.upm.es

The evaluation of the radiological environmental impact of elementary tritium emission to the atmosphere on IFE reactors has different phases. The factors influencing the Primary phase (atmospheric releases) are boundary conditions such as atmospheric and geometric grid from the emission point. The Second phase occurs when the tritium is deposited in the ground, and it suffers the transformation rapidly to tritiated water (less than one week). This process depends on the kind of soils (clay, loam or sand), relative humidity and microporosity of soil. This phase is decisive in the dosimetric effects in elementary tritium and in the chronic and collective doses to population. This Second phase is the goal of this work for selected inventories from IFE reactors by using MACCS2, UFOTRI and HOTSPOT8 codes for severe accidents and NORMTRI for normal operational conditions..

Contributions from chemical forms, HT and HTO, depend on boundary conditions near the source of emissions. The atmospheric conditions are a key issue in the contribution levels from the tritium to the effective and equivalent dose. In the primary phase the wet and dry depositions, as well as the stability class, the intensity rains factor and wind speed increase or diminish the values of the doses. The contribution by ingestion of food in both cases is closely 80-90% of the total dose for each chemical form in the secondary phase. However, the HTO has a larger contribution to the term of internal radiation by inhalation and absorption for the skin than that of HT, which has the rest of its contribution by reemission to the atmosphere in form of HTO. These values increase when going away the plume of the emission point.

This work will conclude that the two chemical forms (HT and HTO) contribute in a different way to the effective and equivalent individual dose (MEI-EDE), and to the chronic doses. Elementary tritium contributes as large as 90-98% to the total dose from ingestion of foods/natural agriculture and meat (HTO only 40 %) and the rest of doses are from inhalation generated by the re-emission to the atmosphere. For comparison, HTO contributes 20-25% from inhalation and skin absorption to the total dose. We conclude that the elementary tritium is incorporated to the plants in a very efficient way and penetrates deeper in the soil when the porosity is large. The work also presents conclusions on the period in which the release is produced, indicating than the maximum toxicity appears when the accident happens in the growth season of the vegetables.