Numerical simulation of evaporation and dispersion of tritium released in Hangzhou Bay

The secondary source term (SST)-tritium re-released into the atmosphere from liquid effluents-is a pathway that has received limited attention in nuclear facility risk assessments. This study provides the first quantitative investigation of the SST at Qinshan Nuclear Power Plant (NPP), using a coupled hydrodynamic-atmospheric model to evaluate the environmental behavior of tritium under normal and accidental scenarios. The model quantifies the dual marine-atmosphere pathways, revealing that while marine dispersion is governed by seasonal hydrodynamics, atmospheric dispersion is governed by multi-scale meteorology, where seasonal monsoons determine primary transport corridors and short-term calm conditions trigger high-concentration events. The SST accounts for 0.99 % of the liquid effluent under normal operations, rising to 1.1 % in an accident scenario. While the public dose from the SST is negligible under normal coastal operations, it poses a critical risk to future inland facilities where enclosed hydrology can amplify its effect. This risk is further underscored in an accident scenario, where a short-term release is comparable in magnitude to the entire annual gaseous emission from a 3000 MW pressurized water reactor. This framework provides an essential tool for more complete risk assessments and for informing policy on events like the Fukushima water discharge.