Rachel Reeves has been urged not to carry out mooted funding cuts for nuclear sites including Sellafield amid safety concerns, as it emerged that the number of incidents where workers narrowly avoided harm had increased at the Cumbrian site. The GMB union has written to Reeves, the chancellor, before Wednesday’s budget to raise safety concerns after rumours emerged that the budget for the taxpayer-owned Nuclear Decommissioning Authority (NDA) could be reduced, which could result in cuts at nuclear sites including Sellafield and Dounreay in Scotland. In the letter to Reeves, seen by the Guardian, union leaders warned that a safety incident at Sellafield, Europe’s most hazardous industrial site, would “have devastating consequences far beyond the immediate community”. The NDA had a budget of £4bn in the last financial year. The warning came as recently released annual accounts for the NDA showed “near misses” at Sellafield had risen in the last financial year, and an “international nuclear event-scale” incident had occurred at the site, which is a vast dump for nuclear waste and also the world’s largest store of plutonium. The NDA said there was an “inadequate response” during an incident in 2023 as some staff did not follow procedures when an emergency alarm unexpectedly sounded inside the site’s hazardous chemical separation area. The report also said Sellafield, which employs 12,000 people, had received six enforcement letters from its regulator, the Office for Nuclear Regulation, and that in studying its safety record the “rate of significant near misses is higher across 2023-24”. It found that the impact on employees from work injuries had “often been significant” even if many of the incidents had appeared innocuous. In the letter, Denise Walker and Roger Denwood, of the GMB, wrote: “While operators and regulators work tirelessly to ensure safety, the inherent risks of the site mean that any lapse in safety standards could result in serious and far-reaching economic and ecological consequences.” They said radioactive “materials must be safely managed to prevent leaks or accidental releases of radiation. The health risks of radiation exposure, including cancer and other serious illnesses, are well documented.” They added: “Any reduction in funding would inevitably result in fewer resources for maintenance, monitoring, and emergency preparedness-heightening the risk of a serious incident.” The Guardian’s Nuclear Leaks investigation in late 2023 revealed a string of cybersecurity problems at Sellafield, as well as issues with its safety and workplace culture. Last week the National Audit Office said the cost of decommissioning the site had risen to £136bn, with major projects running years behind schedule. A spokesperson for the NDA and Sellafield said: “We have been engaging closely with the Department for Energy Security and Net Zero and the Treasury on our plans and requirements. We will always prioritise the safety and security of our employees, sites and communities while delivering our nationally important mission.” An NDA spokesperson said: “The increase in near misses does not relate to nuclear safety, it relates to conventional events, predominantly slips and trips in the workplace.” They added that its “group health and safety incident rate is in line with the wider industry” and work continued to improve safety performance. A government spokesperson said: “We are committed to the nuclear sector and will continue to support the NDA in its important mission to manage our nuclear legacy and clean up sites safely.”