Trend of tritium concentration in air in the Kyoto University Research Reactor Containment

This paper describes the history of tritium concentration in condensate in the containment building air of the Kyoto University Research Reactor (KURR) which supports two major sources of tritium: a D2O (heavy water) facility and a Cold Neutron Source (CNS) facility (liquid deuterium). Mathematical models were developed to predict both the changes in HTO concentrations in water pools and the emission of HTO soaked in the concrete material during the leakage incident from the D2O facility in late 1980's. After the renewal of distribution pipes and a tank for the D2O facility in 1997 the cause in growth of HTO concentration in the building air has appeared during venting cessation as before the renewal. This may be attributable to the fact that the higher HTO concentration in exhaust condensate than 2x105 Bq/mL was detected from not only the CNS but also the D2O facility. This suggests that the increases in the HTO concentration in air are due not to the leak from tritium source in theses facilities, but to the production of tritium caused by the irradiation of nitrogen in air by the fast neutrons near the reactor core. (author)