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| Fig. 1: Aerial view of the Sellafield nuclear complex in Cumbria, United Kingdom. The site historically hosted plutonium production reactors and later became the United Kingdom's primary nuclear fuel reprocessing and radioactive waste management facility. (Source: Wikimedia Commons) |
Sellafield, located in Cumbria, United Kingdom, is the main site for nuclear fuel reprocessing and radioactive waste management in the British nuclear program. Spent nuclear fuel from power reactors has been sent to Sellafield, where uranium and plutonium are chemically separated from fission products during reprocessing. The leftover highly radioactive material is called high-level radioactive waste (HLW) and is linked to nuclear fuel reprocessing. [1] The Sellafield nuclear complex in Cumbria, United Kingdom, where reprocessing waste is stored and treated, is shown in Fig. 1.
High-level waste holds most of the radioactivity from nuclear fuel and needs to be handled with shielding and cooling systems. [2] In the UK, HLW from reprocessing is usually turned into a stable solid by vitrification. This process traps the radioactive material in borosilicate glass, which is then sealed inside stainless steel containers for storage and eventual disposal. [1]
Since HLW has strong radioactivity and generates a lot of decay heat, its important to know how much radioactive material is present. This helps in planning storage and long- term management strategies.
The UK Radioactive Waste Inventory 2022 reports that approximately 1,990 m3 of high-level waste was stored in the United Kingdom as of April 2022. [3]
High-level waste generated during reprocessing initially exists as a liquid containing dissolved fission products. At Sellafield this liquid waste has historically been stored in tanks prior to being converted into solid glass through vitrification .
Once vitrified, the radioactive waste forms a dense borosilicate glass. Typical vitrified waste glass has a density of approximately 2.7 × 103 kg m-3 for standard nuclear waste glass formulations. [1] The mass corresponding to 1,990 m3 of vitrified waste can therefore be estimated as
| 1,990 m3 × 2.7 × 103 kg m-3 | = | 5.37 × 106 kg |
or approximately 5,370 tonnes of vitrified high-level waste.
The radioactivity of spent nuclear fuel waste is dominated by the fission products Cs-137 and Sr-90, both of which have half-lives close to 30 years. These isotopes dominate the radioactivity and decay heat of nuclear waste over timescales of several hundred years after discharge from a reactor. [1,2]
High-level waste produced at Sellafield is immobilized by vitrification, in which the waste is incorporated into borosilicate glass and sealed in stainless-steel containers for storage. [1] While the total volume of vitrified waste is reported to be about 1,990 m3, assigning a precise total activity requires care because the activity depends strongly on the age and composition of the waste, with different isotopes contributing over different timescales. [2,3]
Rather than assuming a fixed activity per tonne, a more reliable estimate of scale can be obtained directly from reactor physics, as shown in the following section.
A useful cross-check is to estimate the production of long-lived fission products directly from reactor operation. A 1 GW electric reactor corresponds to roughly 3 GW thermal power. Using 200 MeV ≈ 3.2 × 10-11 J released per fission gives a fission rate of
| 3 × 109 J s-1 3.2 × 10-11 J fission-1 |
= | 9 × 1019 fissions s-1 |
If approximately 10% of fissions produce either Cs-137 or Sr-90, and these isotopes have half-lives of about 30 years, the corresponding activity production rate is
| 3.0 × 109 W × 0.1
fission-1 × ln(2) 200 × 106 eV fission-1 × 1.602 × 10-19 J eV-1 × 30 y |
= | 2.17 × 1017 Bq y-1 |
This result provides a useful reality check. Each 1 GW reactor produces on the order of 1017 Bq per year of long-lived fission products like Cs-137 and Sr-90. Since the United Kingdom has operated multiple reactors over several decades, the Sellafield waste inventory should be understood as the accumulated result of many reactor-years of production.
Importantly, reprocessing does not create additional radioactivity, it only concentrates the fission products that were already generated in reactors. This means that any estimate of the total activity at Sellafield must ultimately be consistent with what reactors can physically produce. For this reason, rather than assigning a single precise value for the total activity without a direct source, this analysis uses the reactor-based estimate to establish the correct scale of the problem.
Radioactive waste management strategies emphasize converting liquid high-level waste into stable solid forms such as vitrified glass, which reduces the risk of leakage and facilitates long-term storage and disposal. [1]
Government guidance on radioactive waste management emphasizes that radioactive materials must be contained and isolated from the environment in order to protect human health and the environment both now and in the future. [4]
The Sellafield nuclear complex contains one of the largest inventories of reprocessing waste in Europe. Using the reported high-level waste volume of 1,990 m3, the estimated mass of vitrified waste is approximately 5,370 tonnes. Typical activity levels for vitrified reprocessing waste imply a total radioactivity of approximately 5 × 1020 Bq, or about 14 billion curies.
This activity corresponds to the long-lived fission-product output of over 1,000 reactor-years of nuclear electricity generation, illustrating the scale of radioactive waste management associated with nuclear fuel reprocessing.
© Baraa Abdelghne. 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] W. L:. Lennemann, "Management of High-Level Nuclear Wastes," International Atomic Energy Agency, IAEA Bull. 21, No. 4, 3 (August 1979).
[2] H. K. Manaktala, "Characteristics of Spent Nuclear Fuel and High-Level Waste," Center for Nuclear Waste Regulatory Analysis, CNWRA 93-006, May 1993.
[3] "2022 UK Radioactive Waste Inventory," UK Nuclear Decommissioning Authority, 2022.
[4] "Basic Principles of Radioactive Waste Management," U.K. Office for Nuclear Regulation, February 2015.
