Effect of seawater intrusion on radioactive strontium (90Sr) sorption and transport at nuclear power plants

Abstract

Batch sorption and column experiments were conducted to investigate and compare sorption and transport behavior of Sr-90 on the assumption of seawater intrusion at nuclear power plants. Batch sorption experiments were carried out on fractured rocks and bedrocks using synthetic groundwater and seawater both spiked with Sr-90. In general, higher Sr-90 sorption occurred on fractured rock samples than on bedrocks, because of the presence of weathered secondary minerals (iron oxide and clay) on fractured rock surfaces. However, one particular bedrock sample (WSP-B) which has higher porosity and carbon amount than fractured rock samples also showed the higher Sr-90 sorption than its comparable fractured rocks. For all batch sorption studies, Sr-90 sorption distribution coefficient, K d decreased from groundwater to seawater environment due to the higher ionic strength of seawater (6.4 x 10(-1)-7.7 x 10(-1) M) compared to groundwater (4.0 x 10(-3)-6.0 x 10(-3) M). The three different ionic strength solutions were used in column experiments, and the results showed that transport behavior of Sr through a fractured rock had similar sorption trend to batch sorption results. The highest mobility (or least retardation) for Sr was found for 100 % seawater solution compared to the highest retardation (or least mobility) for 100 % groundwater solution. These sorption and transport data of Sr on solid materials contacted with various ionic strength solutions corroborate empirically defensible information for assessment of radioactive contamination in groundwater below the NPP sites located nearby shores. In addition, the experimental data will be incorporated to improve transport models of Sr-90 in the subsurface environment for severe nuclear accidents.