Numerical study on tritium dispersion in coastal waters: The case of Hangzhou Bay, China

Abstract

Identification of tritium dispersion characteristics is critically important to recognize the environmental impact due to discharge of radioactive liquid effluents from nuclear industry. For the first time, this study simulated the dispersion behavior in the coastal waters of tritium discharged from Qinshan nuclear power base, where the sole heavy water reactor is located and the largest tritium amount was discharged in China. Both the flow field and tritium concentration distribution in Hangzhou Bay were displayed under normal and accidental discharge conditions considering the realistic water dynamic characteristics. Effects of river and tidal flow on tritium dispersion, effects of tritium evaporation factor, as well as public radiation dose were specially discussed. The results show that tidal flow is the major factor in deciding tritium dispersion for the Hangzhou Bay case. River flow could also affect tritium dispersion, particularly in the southwest region of the discharge point. Under normal discharge condition, the maximum tritium concentration in the vicinity of Qinshan nuclear power base is at 104 Bq/m3 level, which is an order of magnitude higher than the natural background tritium. Under accidental discharge condition, maximum tritium concentration decreases along with an increasing tritium dispersion time. Results furthermore indicate that a considerable tritium evaporation fraction appears for the Hangzhou Bay case. In spite of this, radiation dose involving ingestion and inhalation pathways associated with liquid tritium discharge is still much lower than the regulatory dose limit. This study is expected to recall attentions to tritium dispersion characteristics apart from providing fundamental simulation data for tritium distribution in the waters of Hangzhou Bay.