Modelling Environmental Impacts of Cesium-137 Under a Hypothetical Release of Radioactive Waste

Waste tanks at the nuclear facility located at Sellafield, UK, represent a nuclear source which could release radionuclides to the atmosphere. A model chain which combines atmospheric transport, deposition as well as riverine transport to sea has been developed to predict the riverine activity concentrations of ¹³⁷Cs. The source term was estimated to be 9 × 10⁴ TBq of ¹³⁷Cs, or 1% of the assumed total ¹³⁷Cs inventory of the HAL (Highly Active Liquid) storage tanks. Air dispersion modelling predicted ¹³⁷Cs deposition reaching 127 kBq m^-2 at the Vikedal catchment in Western Norway. Thus, the riverine transport model predicted that the activity concentration of ¹³⁷Cs in water at the river outlet could reach 9000 Bq m^-3 in the aqueous phase and 1000 Bq kg^-1 in solid phase at peak level. The lake and river reaches showed different transport patterns due to the buffering effects caused by dilution and slowing down of water velocity.