High ~(36)Cl/Cl ratios in Chernobyl groundwater

摘要

After the explosion of the Chernobyl Nuclear Power Plant in April 1986, contaminated material was buried in shallow trenches within the exclusion zone. A ~(90)Sr plume was evidenced downgradient of one of these trenches, trench T22. Due to its conservative properties, ~(36)Cl is investigated here as a potential tracer to determine the maximal extent of the contamination plume from the trench in groundwater. ~(36)Cl/Cl ratios measured in groundwater, trench soil water and leaf leachates are 1 -5 orders of magnitude higher than the theoretical natural ~(36)Cl/Cl ratio. This contamination occurred after the Chernobyl explosion and currently persists. Trench T22 acts as an obvious modern point source of ~(36)Cl, however other sources have to be involved to explain such contamination. ~(36)Cl contamination of groundwater can be explained by dilution of trench soil water by uncontaminated water (rainwater or deep groundwater). With a plume extending further than that of ~(90)Sr, radionuclide which is impacted by retention and decay processes, ~(36)Cl can be considered as a suitable tracer of contamination from the trench in groundwater provided that modern release processes of ~(36)Cl from trench soil are better characterized.