The Behavior of Tritium in Concrete During the Decommissioning Stage of Heavy Water Research Reactors

During the operation of the heavy water research reactor, tritium is generated through ternary fission in fuel elements and the activation of trace elements in the primary coolant by neutrons. Tritium exhibits strong permeability and a relatively long half-life. During the decommissioning phase of the reactor, residual tritium remains in concrete and related facilities or equipment. As decommissioning progresses, the originally enclosed system is gradually opened, leading to the release of tritium. Although the beta particles emitted by tritium have weak penetration ability, once tritiated water (HTO) enters the human body via inhalation, ingestion, or skin absorption, its biological half-life is prolonged. It distributes uniformly throughout the body and participates in metabolic processes, resulting in non-negligible internal exposure hazards. This poses long-term potential risks to both occupational workers and public health. The behavior of tritium in concrete was examined through a comprehensive literature review to support the safe decommissioning of nuclear reactors and to mitigate associated radiological and environmental risks. This study focuses on the key forms of tritium in concrete, which are identified as: 1) adsorption and diffusion of HTO/HT, 2) isotope exchange of HTO with concrete's structural water, and 3) tritium capture by defects in cementitious phases (e.g., 3CaO·2SiO₂·4H₂O) or exchange with hydrogen in Ca(OH)₂. The findings herein offer vital guidance for the tritium management strategy and worker protection during the decommissioning of China's first heavy water research reactor.