Radioactive waste includes the radioisotope carbon-14, which upon underground long-term storage is expected to be transformed to radioactive methane. For risk assessment modelling accounting for possible leakage to the surface, it is therefore important to assess the fates of methane that enter streams and lakes with the groundwater.
Methane can be transported with groundwater to discharge areas and thereby enter e.g. streams and lakes. There the groundwater methane can be diluted with sediment-produced methane and/or transformed to carbon dioxide by microbial methane oxidation. The balance between these processes is poorly understood but important for the risk assessment of potential leakage of radioactive methane from radioactive waste.
To support improved risk assessments, several projects in collaboration with SKB AB have focused on assessing ground water input and the relative proportions of the groundwater methane that is emitted to the atmosphere or oxidised to carbon dioxide.