On Leakage from the Near-surface Radioactive Waste Storage Facility

Maisiagala RADON type radioactive waste storage facility was commissioned in 1963 in a marshy, ecologically sensitive locality, where soluble radionuclides easily can penetrate and migrate with groundwater. To assure the requirements of radiation safety, the analysis of radionuclide leakage from the radioactive waste storage facility is performed continuously. H (tritium, T1/2=12.33 years) is of greatest interest in the storage facility reservoir or its surroundings. Liquid scintillation counting (LSC) involving ultra-low level device Quantulus (Wallac) was utilized for quantitative determination of tritium. Elevated H concentration (reached 23900 Bq l) is observed continuously in the borehole, which is nearest to the radioactive waste reservoir. The average prevailing groundwater flow direction is close to the northern direction. This is the direction of waterlogged lowland, the head of the river, where radionuclides can penetrate. H concentration in the borehole located 12 m further in the prevailing groundwater flow direction, varies from minimum detectable values to 7500 Bq l. MOC3D software was used for modelling H transport in groundwater. For field measurements a portable gamma-spectrometer Inspector-2000 (Canberra) with 20% relative efficiency HPGe detector (GC2018) was used. The measurements in-situ revealed both qualitative and quantitative variation of gamma-ray intensity at the facility’s territory and outside.The remaining contamination by Ra was confirmed at the spot at the distance of ~20 m from the radioactive waste reservoir, Ra concentration at the spot reached 106 Bq kg in 2004. Cs concentration in soil does not exceed that in Lithuanian soils after Chernobyl NPP accident. H concentration in soil moisture, both on the territory of facility and outside, increases with depth and reached 187±10 Bq l. H concentration in lupine (Lupinus polyphyllus) reached 150±9 Bq l. It exceeds H concentration in grass outside the facility territory by 20-30 times. The fact that elevated H concentration was found not only in groundwater of boreholes on the territory of the storage facility, but in soil moisture and vegetation samples shows that radionuclide leakage from the reservoir occurs and the possibility of leakage can increase over time. The storage facility requires continuous monitoring and management strategy in the nearest future.