Evaluation of Long Term Environmental Tritium Reemissions Following Reactor Shut-Down

Abstract

More than 60 years of heavy water-moderated reactor operations at Canadian Nuclear Laboratories’ (CNL) Chalk River site, have led to low level, persistent airborne tritium releases and tritium contamination in near surface geophysical strata (atmosphere, vadose zone, shallow groundwater and vegetation). Decades ago, the long-term-average flux of tritium from the National Research Universal (NRU) reactor to the surrounding area approached a steady state marked by slightly but clearly elevated local tritium levels in all geophysical strata at the Chalk River site. This study considers these near-surface geophysical compartments as a future source of tritium releases (reemission) following planned NRU decommissioning in 2018. The reemission phase ecological half-life (or conversely transfer coefficient) has been derived from elevated tritium concentrations which persisted in plants collected at the experimental garden plot near the NRU stack at the Chalk River site during the 15 month-long NRU shutdown in 2009-2010.