Hunterston nuclear power station in North Ayrshire, Scotland, has breached radiation safety rules and suffered five other problems with its safety systems, officials said.

The latest report from the UK government watchdog, the Office for Nuclear Regulation (ONR), found Hunterston “failed to adequately account for” radioactive materials last October.

One of the nuclear plant’s cooling systems – needed to prevent overheating when a reactor is shut down – developed a fault because of confusion over valves. There were other issues with cooling systems, a fueling machine and the graphite core.

After a series of other health and safety incidents ONR said Hunterston’s operators, EDF Energy, showed “a lack of sensitivity to industrial safety events”. The company’s emergency arrangements for coping with a nuclear accident also needed improving, ONR said in its report.

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Critics have attacked EDF’s safety record, and called for Hunterston’s two aging and cracked reactors to be permanently shut down. The reactors are “well past their sell-by date,” they argued, according to a published report in The Ferret, an independent non-profit media cooperative in Scotland.

No One at Risk
EDF, however, said none of the incidents had put workers or the public at risk and that “stringent safety levels were maintained at all times”. ONR said the shortfalls were “relatively low level” but it took “appropriate regulatory action where necessary,” according to The Ferret report.

Reactor three at Hunterston has an estimated 377 cracks in its graphite core and has been shut down since March 9, 2018. Reactor four, which operated for less than four months in 2019, has been shut since December 10 while its core cracks are further assessed.

EDF is aiming to restart both reactors in April but it cannot do so until ONR has said they are safe. Planned restart dates for the reactors have been repeatedly postponed over the last two years.

ONR posted online its quarterly site report on Hunterston B covering October 1 to December 31, 2019. It criticizes EDF for six incidents that occurred over the three months.

On October 22, ONR served an “enforcement letter” on EDF because of a breach of the regulations covering radioactive sources. These are materials emitting radiation used by industry as gauges and for inspections.

“The station had failed to adequately account for and label radioactive sources, which resulted in some sources not being subject to the required leak testing,” ONR said.

Plan in Place
“The station has recognized these non-compliances and has provided an appropriate plan of action,” ONR said. “The radioactive sources were sealed instrument check sources and did not present a hazard to workers or the public. ONR will carry out an inspection to confirm that the enforcement actions have been carried out satisfactorily.”

While reactor four was running at full power in the last three months of 2019 one of its four cooling systems developed a fault. This “post trip cooling system” was “one of the means by which cooling is provided to the reactor when it is shut down”, explained ONR in The Ferret report.

EDF had to fix the problem within 31 days otherwise the reactor would have to be switched off. “The investigation established that the isolation of a faulty valve position indicator for the coolant feed system had also isolated the valve actuator control,” ONR said.

“It had previously been understood that the valve position indicator and actuator were supplied from separate electrical supplies,” ONR said in the report.

The faulty indicator was repaired and it was confirmed there was “sufficient redundancy” as three of the four post trip cooling systems remained operational, ONR added.

“This event did not compromise nuclear safety. Corrective action is being taken to ensure subsequent configuration control.”

Other Issues
ONR also raised “two regulatory issues of low significance” with EDF about cooling systems, but required no formal action to be taken. One concerned an “incomplete maintenance record card” and the other was because the potential for radioactive tritium in cooling water had not been fully described.

There were also issues with “unauthorized settings” on fueling equipment and modelling of the mechanical strength of parts of the graphite core. In both cases ONR said that nuclear safety was maintained, The Ferret report said.

“From the evidence sampled, the inspector was satisfied that the events reported during the period, had been adequately investigated and appropriate event recovery actions identified,” ONR said

ONR also stressed the need for improvements in EDF’s approach to conventional health and safety. “A number of industrial safety events highlighted where continued focus on safety is required,” ONR said.

“The station reflected on the causes, which included a lack of sensitivity to industrial safety events, personal accountancy and fuller application of the organizational learning process. A continued commitment to existing improvement plans was expressed by the station.”

In addition ONR required EDF to re-run an emergency exercise conducted on October 17. This was meant to test responses to a nuclear accident “under security lockdown conditions” with the Civil Nuclear Constabulary (CNC), which polices nuclear power stations.

“The exercise was challenging and showed that there is a need to enhance the operability of the EDF corporate emergency arrangements in conjunction with the CNC response procedures,” ONR said.

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