An ageing storage silo at the Sellafield nuclear site - just over 30 nautical miles from Manx coast - is leaking 2,100 litres of contaminated water into the ground each day.

The radioactive leak from the Magnox swarf storage silo could continue until at least the late 2040s, a report by the UK National Audit Office reveals.

However, Sellafield and its regulators believe that current leakage rates pose a low risk to workers and the public.

The report, which was published this week, says that the silo has been leaking contaminated water into the ground since 2019 and Sellafield has been unable to fix it - and it could continue until this part of the silo is emptied in the late 2040s or early 2050s.

Sellafield is the UK’s most complex and challenging nuclear site with highly hazardous materials stored there from across the UK’s nuclear industry. It also holds a legacy of contaminated buildings, untreated waste and ageing facilities.

Some of these pose an ‘intolerable’ risk, the NAO report notes. These buildings and their contents will remain highly hazardous for years.

The Nuclear Decommissioning Agency, which took over direct control of the Cumbrian complex eight years ago, now expects it will take until 2125 to clean up the site and safely store the waste in modern facilities.

Work began in December last year on removing waste from all four of Sellafield’s legacy ponds and silos.

However, it has made less progress than it expected to, in part because of the impact of the Covid pandemic, the report states.

It says: ‘The slow pace of retrievals has significant safety and financial consequences. For example, the Magnox swarf storage silo has been leaking contaminated water into the ground since 2019; the rate is currently estimated at around 2,100 litres per day.’

Sellafield is exploring options to further reduce the consequences of the leak, overseen by its regulators. Its target for substantially emptying three of the legacy ponds and silos are now six to 13 years behind those estimated in 2018.

Sellafield has plans to increase the pace of over the decommissioning over the next decade.

But the report notes: ‘There is a risk that facilities to treat the waste will reach the end of their useful lives before all the waste is retrieved.

‘In the worst case scenario, new facilities would be needed to treat a relatively small quantity of waste at a cost of hundreds of millions of pounds, causing further delays.’

Sellafield has made better progress addressing the risks associated with the plutonium it stores and believes these risks will continue to decline until 2060, the report adds.

It concludes: ‘In spite of improvements, we cannot yet say that the NDA and Sellafield are achieving value for money. Large projects are still being delivered later than planned and at higher cost.’