Wylfa will renew fears over the safety of a privatised nuclear industry and set back the Government's plans to sell it off. The nightmare scenario is of the uranium metal fuel rods in the core of the reactor overheating and beginning to melt. If the operators could not regain control, tons of white-hot uranium would melt their way through the concrete and steel at the bottom of the reactor and into the ground, resulting in an uncontrollable release of intensely radioactive fission products fatal to all who went near.
To ensure that such a thing does not happen, reactors are provided with a whole series of protective measures to ensure "defence in depth". But the British system places as much emphasis on the "safety culture" of the company - that is, on making sure that safety is properly considered at every level of management - as it does on the physical and engineering devices.
The philosophy is simply that engineered systems are only as good and reliable as the people who run them. What was at issue in Mold Crown Court was not that anyone had actually been harmed, but that the management of safety at the plant had broken down just as much as the physical equipment and that the managerial breakdown was more worrying than the failure of the equipment.
Wylfa is one of the first- generation Magnox power stations which are reaching the end of their working lives but which are lucrative cash-earners because their capital costs have long since been paid off.
The reactors, which contain uranium metal fuel stacked in 6,150 vertical channels, are designed to be refuelled while operating so as to avoid loss of income from generating electricity. Reactor number one of the twin-reactor station was refuelling on-line during the night of 31 July when part of the "grab" used to pull fuel elements up fell out of the machine and into the open channel.
The station managers should have shut the reactor at once, because the grab was blocking the channel and obstructing the flow of coolant gas. Instead, they continued to operate the station for nine hours. The risk was that the fuel in the blocked channel might over-heat and start to melt, releasing highly radioactive fission products into the circulating gas. Even had that happened, no radioactivity would have got out into the environment, because the gas is hermetically sealed inside the reactor pressure vessel and its associated pipework.
The other channels would not have been affected because the flow of gas through them was unobstructed so there was no possibility of a 1986 Chernobyl-style melt-down of the entire reactor core. Fortunately for Nuclear Electric, the fuel in the blocked channel had not begun to overheat by the time managers finally switched the reactor off.
More than 20 years ago, several fuel channels did overheat and fuel partially melted in a similar Magnox reactor, operated by British Nuclear Fuels, at Chapelcross in Scotland. However, the design of these reactors is so robust that not only was there no serious radioactive release, but also the company was able to refurbish the reactor and return it to service.
But major worries remain. From the moment they were told of the Wylfa incident, the Government's nuclear safety inspectors feared that Nuclear Electric had been more concerned about money than about public safety. Nuclear Electric stoked their worries by its aggressive response to inquiries.
The company broke the industry tradition of not contesting charges brought by the Nuclear Installations Inspectorate. Instead, Nuclear Electric fought every inch of the way. The result has been not just a waste of public money on lawyers' fees, but continuing concern about whether safety retains primacy of place in the new, commercialised nuclear industry.Reuse content