AS THE Bush administration pushes plans for a new generation of nuclear plants, America鈥檚 existing reactors are being plagued by cracks and corrosion. One plant came close to a catastrophic meltdown before the problem was discovered.
鈥淲e鈥檙e facing reactors deteriorating, cracking and leaking as they get older,鈥� says David Lochbaum, who was a safety engineer in the US nuclear industry for 17 years but now works for the anti-nuclear Union of Concerned Scientists. 鈥淚f we are lucky we will avoid a disaster. But don鈥檛 count on it.鈥�
The first hint of a problem came from France in 1991, when cracks were found in nozzles in the lid of a reactor near Lyon. That prompted the US Nuclear Regulatory Commission (NRC) to assess the risk in reactors in the US. It concluded in 1993 that cracks along the nozzles鈥� length would not significantly affect safety, and that cracks around the circumference, though potentially more worrying, were 鈥渋mprobable鈥�.
Advertisement
But in October 2000 a crack leaking boric acid was discovered along a nozzle at a reactor in South Carolina. In the following months, cracks were found at three reactors at nearby Oconee, some around the nozzles鈥� circumference.
The NRC ordered the operators of 69 reactors across the US to check their nozzles. At the Davis-Besse reactor in Ohio, in March 2002, investigators discovered that boric acid leaking through a cracked nozzle had eaten a hole about the size of a football in the lid of the reactor pressure vessel. Over several years, carbon steel designed to contain the reactor鈥檚 cooling water at a pressure of more than 138 atmospheres had been completely eaten away (see Graphic).
All that was stopping the radioactive water from exploding out of the reactor was a 1-centimetre skin of corrosion-resistant stainless steel, which had already begun to balloon outwards. 鈥淚t was close to yielding, I must admit,鈥� says Alex Marion, director of engineering for the industry鈥檚 Nuclear Energy Institute. If the water had been lost, the uranium fuel could have overheated and caused the reactor to melt down. This is what happened in 1979 during the US鈥檚 worst nuclear accident at Three Mile Island in Pennsylvania.
The discovery sent shock waves through the nuclear industry. Cracks have now been found in 14 reactors. Power companies plan to replace the lids on 29 reactors, for $25 million each. 鈥淓veryone has the disease,鈥� says Marion. 鈥淚t鈥檚 just a matter of time before the symptoms appear.鈥�
The aftermath has been almost as traumatic for the NRC. Its 100-page post-mortem is fiercely critical of its own inability to prevent the corrosion. It failed to adequately assess the risk and to check assurances by the company operating Davis-Besse, it concluded.
Some of the NRC鈥檚 own experts believe the failures stem from a deeper malaise within the organisation. In a memo to commissioners in February, Steven Long, a senior NRC risk analyst, argued that its risk assessment procedure is inadequate. 鈥淚 am concerned that eventually we will fail to protect the public,鈥� he said.
Lochbaum believes the problem will get worse as the reactors age. Virtually all the reactors operating in the US are expected to have their working lives extended from 40 to 60 years.
But Brian Sheron, the NRC鈥檚 deputy chief of reactor regulation, insists existing procedures are reliable. He argues that an inspection that discovers a flaw is a success. 鈥淚t鈥檚 fine as long as you don鈥檛 get a failure that jeopardises public safety. I think we will get more cracks in unexpected places, but we鈥檒l handle it.鈥�
At a reactor 150 kilometres south-west of Houston, Texas, his prediction has already come true. In April, two nozzles at the bottom of the pressure vessel were discovered to be seeping boric acid. Leaks at the bottom of a vessel had not been discovered before and are much harder to fix than leaks in the lid.
