Malfunctioning electrical equipment installed in a number of nuclear power plants across France present a worst-scenario risk of causing a catastrophic meltdown of their reactor cores, according to France’s nuclear safety watchdog, the Autorité de Sûreté Nucléaire (ASN).
The problem concerns a specific model of electric circuit breakers found in 18 reactors present in seven nuclear plants spread around the country, including one less than 100 kilometres from Paris, three on the Channel coast and one close to the border with Germany (see map below).
In a written report warning of the danger, dated last September, experts from the ASN’s technical arm, the Institut de radioprotection et de sûreté nucléaire (IRSN), described the flaw as “a not insignificant heightening of the risk of meltdown of the core”.
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In an investigation into the problem in 2011, the operator of the plants, French utilities giant EDF, found that the problem affected all but one of its reactors with an output of 1300 megawatts (MW). The exception is its plant at Saint-Alban, in south-east France.
The circuit breakers notably serve in the case when a nuclear plant is affected by a power cut from the main grid, when they switch electricity supply over to the site’s internal back-up system. This procedure is not uncommon, and was successfully put into operation at the Flamanville nuclear power plant – which has two of the 1300 MW reactors - during the weekend of February 8th-9th, when the local power grid went down during severe storms.
But if the circuit breakers fail to work, this can lead to a loss of the electric switchboards relaying a large amount of a plant’s equipment, and notably including the emergency water pumps that, in the event of a problem, cool a reactor’s core. The core of a reactor is where its nuclear fuel is contained and where the nuclear reactions take place.
When the first incidents were recorded four years ago, EDF initially identified the problem as being caused by the greasing of a component of the circuit breakers. However, after this was remedied on all the reactors concerned, several were still blighted by the problem. The IRSN experts recorded 11 further incidents of circuit breakers failing to work during the first half of 2013. “The total causes that lead to the non-closure of the circuit breakers are not known and the degreasing alone is not of a nature to resolve the anomaly,” wrote the IRSN, stressing “the importance for safety” that the problem presents.
Manufactured by French corporation Schneider Electric, the faulty circuit breakers were first installed in 2010 to replace an ageing model. Between August and September that same year, EDF recorded three significant incidents affecting safety which were caused by the malfunctioning new circuit breakers.
In August 2011, following yet more incidents of the circuit breakers failing to work, EDF concluded that the problem was potentially common to all its 1300MW plants, excepting Saint-Alban. The average age of these plants is 25 years (that of reactors producing 900MW is 31 years while France’s oldest plant, Fessenheim, is 37 years-old).
A background of under-investment in maintenance
In December last year, the ASN’s head of nuclear plant surveillance, Thomas Houdré, issued a stern summons to EDF after “taking into account the difficulties until now to identify and address the causes of the recurrent closing down failures [of the circuit breakers] witnessed over four years”. He gave the utility giant two months in which to report back to him with a clear plan of action to find the reasons why the circuit breakers were not working, and to detail what measures were in place to limit the damage caused by such incidents – and in the case of a resulting accident.
He also ordered EDF to begin “as of now” looking for new equipment to replace the faulty circuit breakers. Whether or not coincidentally, EDF reported back to Houdré on February 12th, one week after his deadline and while Mediapart had begun investigating the issue.
Mediapart has learnt that in its reply, EDF said there was no common cause for the malfunctioning of the circuit breakers but rather several different reasons. Its response to the question of what measures were in place to deal with the incidents included repeating the remote procedure commanding the circuit breakers and, if this did not eventually work, performing the action manually.
Contacted by Mediapart, EDF said in a statement saying that its studies of the problem “were able to demonstrate that the faults of some circuit breakers are isolated cases”, adding: “The circuit breakers concerned by this fault return to operation when re-started manually.”
Also contacted by Mediapart, Houdré’s deputy, Philippe Dupuy, adopted a quite different tone to that of his superior and that of the IRSN experts’ report. “We’re not worried, we are mobilised and vigilant,” he said, adding that the problem of the non-functioning circuit breakers was classified at the lowest level of significance on the IRSN table of incidents. “It is not serious, the risk is not enormous,” he added. Contrary to what his superior wrote to EDF in December, Dupuy argued that the non-functioning of the circuit breakers was a question of unreliability rather than a failing.
Asked what guarantee there was that the same problem could not occur at any of all of France’s 58 nuclear reactors, and not only those with a 1300 MW capacity, Dupuy replied: “None, which is why there are regular trials of this equipment.”
However, Thierry Charles, the deputy general director for safety at the IRSN, the ASN’s technical arm, was less reassuring. “It is an important issue,” he said. “On the other hand, there are ways of getting round it, recommencing the command procedure or doing to it manually.”
“A piece of equipment must fulfill its functions as of the first time it’s required to,” he added. “It might be that it functions after several attempts, but that does not mean it’s functioning properly.”
Meanwhile, the newly-appointed president of the ASN, Pierre-Franck Chevet, earlier this week testified before a parliamentary commission of enquiry set up to examine the costs of France’s nuclear industry. During the February hearing on 13th, Chevet raised his concerns over EDF’s management of maintenance work on its nuclear power stations.
“In five years, the volume of work carried out during unit shutdowns has more than doubled,” he said (see video of the hearing here).
“I think there has been, globally, an under-investment in maintenance work over the preceding ten years, five years, which had to be caught up with,” Chevet told the commission. “By definition, when you catch up with maintenance that should have been done before there is necessarily a volume of work, now, that is significantly higher.”
“We have observed that, between the initial planning forecast, established by EDF, for the unit shutdowns and the time it took [for work] to be carried out, there is a difference of 50%. That’s to say that between the length of time forecast for the unit shutdown and the time they took, there is more than 50%. So, there is very visibly a problem of organization of work, knowing that as soon as you go beyond the planning forecast you obviously create problems regarding the quality of work that is carried out, and even which could cause problems for safety, because you have to manage a planning, an organisation, that you hadn’t allowed for.”
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English version by Graham Tearse