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 The issues emerged in Nuclear Leaks, a year-long Guardian investigation into problems spanning cyber hacking and toxic workplace culture at Sellafield, which also revealed the site has a worsening leak from a huge silo of radioactive waste. GMB, which represents tens of thousands of workers across the energy industry, said it was “deeply concerned” by the reports of leaks and cybersecurity failings at the site. GMB national secretary Andy Prendergast said that its members at Sellafield had been raising concerns over a string of problems for years. These included a “lack of training and competence among staff, inadequate safety procedures and a culture of fear and intimidation”. “GMB has repeatedly raised concerns over safety and staffing levels, which are mainly due to turnover and the age and demographic of the workforce,” Prendergast wrote. A senior industry source has said that a hardcore of longstanding Sellafield employees who are resistant to change have been nicknamed “We Bees” – short for “we be here when you be gone”. Several sources have cited the area’s insular community and reliance on Sellafield for well-paid employment as a barrier to change. In his letter to Claire Coutinho, secretary of state for energy security and net zero, which was also sent to Sellafield’s chief executive, Euan Hutton, and the NDA chief, David Peattie, Prendergast called for the trio to take “urgent action to address these concerns”. In response to the Guardian’s reports, Coutinho wrote to Peattie this month saying allegations about failings in cybersecurity, site safety and workplace culture at Sellafield were “serious and concerning” and needed “urgent attention”. Her intervention followed the revelation that Sellafield was hacked by groups linked to China and Russia and that the industry regulator, the Office for Nuclear Regulation, had put the site into “significantly enhanced attention” for cybersecurity. In his response, Peattie told Coutinho: “I can assure you that there is no compromise to public safety, and no complacency when it comes to addressing requisite improvements to cyber security and site safety and ensuring a zero-tolerance approach toward bullying and harassment of staff.” He said Sellafield had “no record or evidence of any such cyber-attack which resulted in malware on Sellafield systems”. Peattie said Sellafield would have a new head of cybersecurity in place from January. A Sellafield spokesperson said: “Safety is our overriding priority at Sellafield. We are proud of our safety record and we are always striving to improve. “Our chief executive officer Euan Hutton has worked closely and collaboratively with our site-based trades unions, including GMB, throughout his tenure. “None of the issues detailed in this letter have been raised during this engagement in the terms described. “It’s also important to note that our independent regulator has confirmed historic cultural issues have not led to unsafe activities at Sellafield.” The spokesperson said the number of “safety professionals” on site had grown in recent years. They disputed statistics included in the GMB’s letter, and said Sellafield had an “open door policy” with its trade unions, GMB, Prospect and Unite. It has previously said employees are “empowered to raise issues and challenge when things aren’t right”. A spokesperson for the Department for Energy Security and Net Zero said: “The energy security secretary wrote to the Nuclear Decommissioning Authority and spoke with both their CEO and the regulator, who provided assurances there have been no successful cyber-attacks at Sellafield. She has also requested regular updates on work to improve cyber-security and tackle workplace culture concerns.”