My previous post touched on geologic disposal of radioactive wastes and substances. Continuing from there, I will touch on disposal in repository sites, where not only natural but man-made barriers are utilised in ensuring the isolation of these substances. Additionally, I will also introduce one consideration – water – that is crucial in ensuring the safety of these repository sites against leakages into the surrounding environment.
Science and Technology Review‘s publication (March 1996) explains how a system of geological and man-made barriers can be used to isolate nuclear waste and prevent the leakage of radioactivity:
The figure shows a cross section of an underground repository with the waste in the center. Moving outwards, the waste package may contain various metal and alloy disposal containers. The engineered repository system also involves diffusion barriers by packing materials around the waste. However, I would like to draw your attention to the outer two layers of this repository: the near-field environment, which can extend several hundred meters into the surrounding rock, involves natural barriers that can slow the migration of radionuclides. The far-field environment, is also crucial – preferably an arid climate with low precipitation, high evaporation and no ground saturation to minimise the transport of radionuclides by water.
This leads me to the next point, the important consideration of water in safe nuclear waste isolation. Science and Technology Review also states that water can dissolve and transport radionuclides. Possible corrosion of waste packages may leach radionuclides into groundwater, hence it is important that a repository is located well above the water table.
Buschek, Nitao and Ramspott (1995) also studies the feasibility a nuclear waste repository at Yucca Mountain. In their study, they focus on the importance to substantially reduce relative humidity and liquid flow near waste packages, to limit waste package degradation and radionuclide dissolution and release. Similar to Science and Technology Review, it highlights how water may adversely affect waste isolation.
As such, the presence of water may dissolve and mobilise radionuclides. Leaching into groundwater may also render them available for transportation. This is a possible risk pertaining to underground waste depositories that may threaten to pollute larger water bodies.
In my next post, I will provide a related case study of a nuclear waste facility that is currently in negotiations to be built in the Great Lakes basin of Canada.
Thanks for reading!
Clarke, W. L. (1996). The Safe Disposal of Nuclear Waste. Science & Technology Review
Thomas Buscheck, et al., Localized Dry-Out: An Approach for Managing the Thermal–Hydrological Effects of Decay Heat at Yucca Mountain, Lawrence Livermore National Laboratory, Livermore, CA, UCRL-JC-121332 (1995)