Ageing nuclear submarines could put sailors and public at risk, report warns HMS Tireless, a Trafalgar-class nuclear submarine, at Devonport naval base. Photograph: David Levene Britain's ageing hunter-killer nuclear submarines are suffering mounting technical problems that could endanger the safety of sailors and the public, a report from the Ministry of Defence (MoD) has warned. Five Trafalgar-class submarines, between 22 and 29 years old, are running into reliability issues with the reactors that power them, increasing the risk of cracks, pipe failures and radiation leaks. The oldest, HMS Tireless, leaked radioactive coolant from its reactor for eight days in February. At the moment the problems are being effectively managed, says the report from the MoD's internal safety watchdog, the Defence Nuclear Safety Regulator (DNSR). But it has issued a new amber warning that "attention is required to ensure maintenance of adequate safety performance." The problems have arisen because the operational lives of Trafalgar submarines have had to be extended to cope with prolonged delays in bringing Astute-class submarines into service to replace them. After billion-pound budget overruns and repeated construction and teething difficulties, only two of seven proposed new submarines are currently in the water. The Royal Navy's five Trafalgar boats, launched between 1984 and 1991, are now all expected to function for up to 33 years, with the last one not being mothballed until 2022. "As a result, the Trafalgar class are operating at the right hand end of their 'bathtub' reliability curves," says the DNSR report. This means that the number of problems being encountered by the boats is increasing steeply as they reach the ends of graphs shaped like baths. "The effect has been seen in a number of emergent technical issues over the last few years" which "can be directly attributed to the effects of plant ageing," the report says. The report, which covers 2012-13 and was put online by the MoD without any announcement, does not say what any of the technical issues are. But critics point out that they must include the reactor coolant leak sprung by HMS Tireless during operations off the west coast of Scotland on 4 February. The MoD has since said that the leak lasted for 192 hours, including six days at the Devonport naval dockyard in Plymouth. Permission was also given for Tireless to vent radioactive air to the atmosphere, which the MoD said was "well within the normal permitted limits for discharges to the environment." According to John Large, an independent expert on nuclear submarine safety, the main risk from ageing was the "catastrophic failure" of components in the pressurised reactor system, including circuit pipework and the reactor vessel. Steel becomes more brittle, particularly if it is irradiated, making it more likely to crack, he said. The DNSR report says that the problems facing Trafalgar-class submarines are "analogous" to those experienced by Britain's first generation of Magnox nuclear power stations, all but one of which are now shut down. This "strongly suggests" that it was cracks in increasingly brittle metal that DNSR was concerned about, Large argued. DNSR had admitted that the Trafalgar submarines posed an increased risk of nuclear accidents, he said. It seems as if admirals in Whitehall have overruled nuclear safety by demanding that the remaining elderly boats are held in service as a string-and-sticky-tape stopgap measure. Peter Burt, from the Nuclear Information Service in Reading, warned that the longer the submarines remained in service, the greater the risk of mishaps. "The MoD should not be putting its operational requirements before the safety of submarine crews and members of the public," he said. The DNSR report also predicts that the four newer Vanguard-class submarines that carry Trident nuclear warheads are "likely to exhibit plant ageing effects" because their lives have been extended to the late 2020s and early 2030s. It repeats earlier concerns about shortage of skilled nuclear staff and the impact of increased privatisation. The MoD stressed that safety was paramount in its activities. "We would not operate any submarine unless it was safe to do so," said an MoD spokesman. The report acknowledges that we are taking the necessary action to effectively manage the technical issues raised by the regulator.