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Radioactive waste products are generally classified into two broad categories – low-level waste (LLW) and high-level waste (HLW) , such as uranium till minings and spent nuclear reactor fuel respectively (Energy Information Administration, 2022). While the disposal of LLW is often deemed to be “straightforward and can be undertaken safely almost anywhere” (World Nuclear Association, 2023), HLW is usually first stored away for a certain period of time to allow the decay of radioactivity and heat before disposal (World Nuclear Association, 2023). As the management of HLW is significantly more challenging, this blog article will focus on the current measures used to store and dispose HLW, and the risks of pollution arising from the (mis)management of HLW.

Storage and disposal of high-level nuclear waste

High-level radioactive waste, such as spent nuclear fuel, is first stored temporarily in underground or surface storage tanks, large concrete bays, or water pools. For such radioactive waste materials to be permanently stored away, HLW must be completely isolated from the environment for at least 10 half-lives, which can range from centuries to hundreds of thousands of years (Saeb & Patchet, 2003).

The final disposal of HLW through storing it in a Deep Geological Repository (DGR) has been deemed as an internationally accepted method for managing high-level nuclear waste (Lopez-Fernandez et al., 2015). Additionally, DGR is also among the preferred options when handling the high-energy contents of HLW such as spent nuclear fuel. This first involves storing the HLW in special dry storage casks which consist of several barriers, each with a specific purpose (Kurniawan et al., 2022):

These containers are then stored deep within a stable geologic environment, usually around an average of 500m underground. The surrounding bedrock, or host rock—which acts as the fifth barrier—has to be of low permeability to ensure that the nuclear fuel remains isolated for prolonged periods (Nuclear Waste Management Organisation [NWMO], n.d.).

Figure 1: Storage of spent nuclear fuel in a deep geological repository (Source: Bruno et al., 2020)

So… what’s the problem with nuclear waste disposal?

The amount of nuclear waste stemming from spent nuclear fuel is predicted to increase exponentially within the next 50 years, as shown in this graph below:

Figure 2: Growing quantities of spent nuclear fuel over the next 50 years (Source: Yano et al., 2018)

This then brings forth the issue of not just space constraints to store large quantities of spent nuclear fuel, but also the need to assess if current waste disposal methods are sufficient. While nuclear waste disposal is relatively well-established for LLW, Ojovan and Steinmetz (2022) argue that HLW disposal, even with the utilisation of DGRs, still remains challenging. These challenges often pertain to three main reasons: the need for constant safety monitoring, that the operation of DGRs is still relatively understudied, and that these repository sites require prolonged periods of geological stability:

Figure 3: Limitations of several HLW disposal methods (Source: Ojovan & Steinmetz, 2022)

Furthermore, while dry storage casks and DGRs appear to have multiple safeguards to ensure that HLW is properly stored away, trace amounts of more mobile radionuclides can still end up dispersed in rock-groundwater systems (Chapman & McCombie, 2003). This is due to the fact that as HLW containers are not completely resistant to corrosion (Kurniawan et al., 2022), radioactive waste leakages can still occur.

A notable example of a HLW leakage is the radioactive contamination at the Hanford Nuclear Reservation – the result of 67 out of 149 single shell tanks leaking a total of 1.9 million litres of radioactive waste. HLW at this site has been argued to have already migrated through the vadose zone, resulting in groundwater contamination (Ma et al., 2018). This is especially concerning given the many potential repercussions, such as the contamination of drinking water sources and the bioaccumulation of radionuclides within crops planted in contaminated soils. Furthermore, this leakage has also been projected to eventually reach the Columbia River (Washington State Department, n.d.), which would then magnify the extent of contamination significantly.

References

Bruno, J., Duro, L., & Diaz-Maurin, F. (2020). 13—Spent nuclear fuel and disposal. In M. H. A. Piro (Ed.), Advances in Nuclear Fuel Chemistry (pp. 527–553). Woodhead Publishing. https://doi.org/10.1016/B978-0-08-102571-0.00014-8

Chapman, N., & McCombie, C. (2003). Chapter 2 Safety and security issues in deep geological disposal. In Waste Management Series (Vol. 3, pp. 21–44). Elsevier. https://doi.org/10.1016/S0713-2743(03)80004-1

Department for Business, Energy & Industrial Strategy. (2014, July 24). Geological disposal of radioactive waste: A guide for communities. GOV.UK. https://www.gov.uk/guidance/managing-radioactive-waste-safely-a-guide-for-communities

Kurniawan, T. A., Othman, M. H. D., Singh, D., Avtar, R., Hwang, G. H., Setiadi, T., & Lo, W. (2022). Technological solutions for long-term storage of partially used nuclear waste: A critical review. Annals of Nuclear Energy, 166, 108736. https://doi.org/10.1016/j.anucene.2021.108736

Leaking tanks—Washington State Department of Ecology. (n.d.). Retrieved February 7, 2023, from https://ecology.wa.gov/Waste-Toxics/Nuclear-waste/Hanford-cleanup/Leaking-tanks

Lopez-Fernandez, M., Cherkouk, A., Vilchez-Vargas, R., Jauregui, R., Pieper, D., Boon, N., Sanchez-Castro, I., & Merroun, M. L. (2015). Bacterial Diversity in Bentonites, Engineered Barrier for Deep Geological Disposal of Radioactive Wastes. Microbial Ecology, 70(4), 922–935. https://doi.org/10.1007/s00248-015-0630-7

Ma, R., Zheng, C., & Liu, C. (2018). Groundwater Impacts of Radioactive Wastes and Associated Environmental Modeling Assessment. In R. A. Meyers (Ed.), Encyclopedia of Sustainability Science and Technology (pp. 1–12). Springer. https://doi.org/10.1007/978-1-4939-2493-6_203-3

Multiple-Barrier System. (n.d.). Retrieved February 6, 2023, from https://www.nwmo.ca/en/A-Safe-Approach/Facilities/Deep-Geological-Repository/Multiple-Barrier-System

Nuclear power and the environment—U.S. Energy Information Administration (EIA). (n.d.). Retrieved February 6, 2023, from https://www.eia.gov/energyexplained/nuclear/nuclear-power-and-the-environment.php

Ojovan, M. I., & Steinmetz, H. J. (2022). Approaches to Disposal of Nuclear Waste. Energies, 15(20), Article 20. https://doi.org/10.3390/en15207804

Powell, T. (2021, April 30). An underground tank in Washington is leaking gallons of radioactive chemical waste. https://www.cbsnews.com/news/hanford-nuclear-site-leaking-radioactive-chemical-waste/

Saeb, S., & Patchet, S. J. (2003). Radioactive Waste Disposal (Geology). In R. A. Meyers (Ed.), Encyclopedia of Physical Science and Technology (Third Edition) (pp. 633–641). Academic Press. https://doi.org/10.1016/B0-12-227410-5/00641-4

Yano, K. H., Mao, K. S., Wharry, J. P., & Porterfield, D. M. (2018). Investing in a permanent and sustainable nuclear waste disposal solution. Progress in Nuclear Energy, 108, 474–479. https://doi.org/10.1016/j.pnucene.2018.07.003