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| Fig. 1: 2005 view of Sellafield, Cumbria. (Source: Wikimedia Commons) |
Radioactive waste disposal has long been a contentious issue in the UK. The UK government defines radioactive waste as material that is radioactive itself or was contaminated by radioactivity. [1] The UK's main sources of nuclear waste are the nuclear power industry, defense activities, research establishment, and medical and industrial uses of radioactivity. [2] Radioactive waste is categorized based on the level of activity it contains and the heat that this activity produces. [2] Here we will focus on the disposal of High Level Waste (HLW), which has high enough activity levels that it needs shielding in handling operations and creates high levels of radiogenic heat. [3]
According to the UK Department for Business, Energy and Industrial Strategy (BEIS) and the Nuclear Decommissioning Authority (NDA), the total volume of radioactive waste from all sources in stock as of April 1, 2022, was 137,000 m3, of which almost 99% was low-activity waste. The reported volume of HLW up to that date is 1,990 m3. [4]
The mass of HWL generated each year is directly proportional to the nuclear energy generated and can thus be calculated as the mass of fuel rod consumed each year (assuming no reprocessing). The HWL generated in 2021 can be calculated in the following way. The fission energy potentially present per kilogram of fresh fuel rod (at 5% enrichment) is [5]
| 0.05 × | 230 × 105 eV/atom ×
1.602 × 10-19 J/eV ×
6.022 × 1023 atoms/mole 0.238 kg/mole |
|
| = | 4.66 × 1012 J kg-1 = 4.66 × 10-6 EJ kg-1 | |
The mass of HWL generated per year is then the mass of 5% enriched fuel consumed per year, or [6]
| 0.41 EJ y-1 4.66 × 10-6 EJ kg-1 |
= | 8.80 × 104 kg y-1 |
As with most nuclear waste in the UK, HLW is currently handled in the Sellafield reprocessing plant in Cumbria, England. [7] The reprocessing of HLW creates nitric acid based Highly Active Liquor (HAL), which contains fission products and process additives. HAL is then concentrated in an evaporator and stored in Highly Active Storage Tanks (HASTs) before vitrification. The concentration of HAL is often measured as a storage volume. The additives in HAL can account for the difference in the mass of HLW generated as computed above (pre-processing) and the numbers reported by the NDA (post-processing). [8] As the liquid high level waste emits large amounts of heat produced by radioactive decay, HASTs require continuous cooling to ensure it does not evaporate. [9] However, some of the silo structures holding Sellafield's nuclear waste have become intolerable, requiring new construction on-site and a process that will cost at least £121 bn. [9]
The size of the Sellafield site can be seen in Fig. 1.
However, storing especially HWL at sites like Sellafield, is not sustainable in the long run, as HLW can have a lifetime of up to hundreds of thousands of years. [3] Thus, to protect the public for longer periods of time, the UK has moved towards Geological Disposal Facilities (GDFs). These underground structures are designed to safely contain and isolate HLW from the biosphere by leveraging both geological and engineered barriers. The GDF will be located at a depth of 200 and 1000 m to avoid effects from surface erosion and glaciation, ensuring that waste can safely decay for thousands of years. [10] While GDFs could offer a safe storage place for HWL, their construction is highly complex and very costly, and GDFs are not expected to accommodate nuclear waste before 2040 and it might take even longer until they can accommodate HLW. [11]
High-level nuclear waste, despite constituting only a small fraction of Britain's radioactive waste, requires careful management due to its high levels of radioactivity. The current disposal site at Sellafield is not sustainable in the long run because of the long lifetime of HWL and the risk of environmental contamination due to leaks. GDFs present a safer alternative to current nuclear waste disposal options. However, the siting and construction of GDFs take decades, requiring the government to find safe alternatives to store HLW in the meantime.
© Cosima Paul. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Basic Principles of Radioactive Waste Management," U.K. Office for Nuclear Regulation, February 2015.
[2] "UK Radioactive Waste Inventory 2022," UK Nuclear Decommissioning Authority, 2022.
[3] M. I Ojovan and H. J. Steinmetz, "Approaches to Disposal of Nuclear Waste," Energies 15, 7804 (2022).
[4] "2022 UK Radioactive Waste Detailed Data," UK Nuclear Decommissioning Authority, 2022.
[5] T. Chen, "China Nuclear Power," Physics 241, Stanford University, Winter 2024.
[6] "BP Statistical Review of World Energy 2022," British Petroleum, June 2022.
[7] F. J. Turvey and C. Hone, "Storage of Liquid High-Level Radioactive Waste at Sellafield" Radiological Protection Institute of Ireland, December 2000..
[8] B. Dunnett et al., "Physical Properties of Highly Active Liquor Containing Molybdate Solids," Procedia Chem. 21, 24 (2016).
[9] S. Subramanian, "Dismantling Sellafield: The Epic Task of Shutting Down a Nuclear Site," The Guardian, 15 Dec 22.
[10] A. I. Marsh, L. G. Williams, and J. A. Lawrence, "The Important Role and Performance of Engineered Barriers in a UK Geological Disposal Facility for Higher Activity Radioactive Waste," Prog. Nucl. Energy 137, 103736 (2021).
[11] T. Greene, "Nuclear Storage Plans For North of England Stir up Local Opposition," The Guardian, 23Aug 21.
