Impact of tritium discharged from a research reactor on concentrations in environmental water samples

¹ Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
² Osaka University of Pharmaceutical Sciences, Nasahara, Takatsuki-city, Osaka 569-1094, Japan

Abstract

The distribution of environmental tritium concentrations in several samples taken near the Kyoto University Research Reactor (KURR) was studied. The KURR Institute (KURRI) supports three major sources of tritium: a D₂0 (heavy water) facility and a Cold Neutron Source (CNS) facility in the KURR containment, and a tritium target fabricated in an accelerator in the critical assembly building. This report focuses on estimating the rate of release of tritium from these sources into the environment, and grasping the relation between the rate and the concentrations in samples of water such as precipitation, air moisture and surface water taken near the release point. The concentrations of tritiated water (HTO) in the stack exhaust condensate were in the range 0.8-3 kBq dm^-3 though those in air in the buildings that support the HTO sources ranged from 5 Bq dm^-3 to 2 kBq dm^-3. The HTO concentrations in the air decreased by ca. 1/500 within 300m of the KURR stack, which is five times the current global level about 5 km off-site. Assessing the degree of attenuation of HTO concentrations in the field is informative for estimating the chronic impact of contaminants in the environment.