The GMB trade union has called on the government and nuclear authorities to take “urgent action” to address concerns over safety at Sellafield.

The union has written to the energy minister, the Nuclear Decommissioning Authority (NDA) and Sellafield’s chief executive to demand greater investment into keeping the 11,000 employees at the vast nuclear rubbish dump in Cumbria safe.

Earlier this month, the Guardian revealed a catalogue of concerns over safety at the sprawling 6 sq km (2 sq mile) site in north-west England.

Sources familiar with risk reports at the site have said they showed that more than 100 safety problems are a matter of serious regulatory concern. They include fire safety deficiencies such as a lack of functioning alarms in parts of the site that contain radioactive material. There have been work stoppages due to a lack of suitably qualified staff trained in nuclear safety and increasing numbers of contamination and radiation protection incidents