The UK’s nuclear regulator is considering further regulatory action against Sellafield following a mishandling of plutonium oxide earlier this year.

According to the Office for Nuclear Regulation’s (ONR) latest incidents report, Sellafield had incorrectly transported a residual quantity of plutonium oxide to the wrong site.

The waste was expected to be sent to the National Nuclear Laboratory (NNL) in Workington, Cumbria, rather than to the Sellafield site. This was further exacerbated by the waste being unsuitably packaged.

NNL had accepted the package before recovering and returning it to Sellafield, with the former notifying the ONR three days afterwards on 2 March.

To maintain security and safety, Sellafield suspended all plutonium oxide movements in the facility in response to the error, introduced enhanced interim transport controls and initiated its own investigation.

Sellafield's weaknesses

Despite these measures, the ONR identified shortcomings in Sellafield’s internal investigation, specifically in its assessments of risk and corrective actions. The regulator also highlighted Sellafield’s “weaknesses” in organisational learning from previous events.

Sellafield has had similar instances of waste mishandling in the past, including a major case in 2013 where it paid a fine of £700,000 ($936,000) for sending several bags of radioactive waste to a landfill site in Cumbria instead of a specialised disposal facility. The error was put down to a technical issue with the site’s then new monitoring software.

Plutonium disposal

The UK is home to the largest plutonium dioxide stockpile in the world, amounting to 140t, which is stored and managed at Sellafield.

Due to the plutonium materials radioactivity and chemical activity, the government has moved away from reusing the material and is looking at permanent disposal.

Despite this recent mishandling error, Sellafield remains one of the largest and most complex nuclear sites in the world with dozens of safety checks carried out on the site throughout the year, both internally and by the ONR.