The alarms jumped in the middle of last January. EDF (Electricity of France), which is the French public company that produces the most electricity in Europe, confirmed that it had been forced to revise down its production of electricity of nuclear origin by 2022 due to the need to undertake unforeseen maintenance tasks in several of its nuclear reactors.
For the umpteenth time, this news led to a heated debate among opponents of nuclear energy, who claimed to glimpse in EDF’s decision an unequivocal symptom of aging of the French nuclear fleetand its supporters, who made an effort to temper and normalize an event that was somewhat unpredictable.
Placing so many eggs in the same basket has advantages, but also risks
France’s commitment to nuclear energy is very solid. In fact, it is the second country in the world with the most nuclear reactors, only behind the United States, and this energy resource is fundamental in its electrical mix because it has traditionally generated around 70% of total electricity. Putting so many eggs in the basket of nuclear energy has advantages, but also drawbacks such as those that are currently facing us.
Its most obvious asset is that, thanks to its resounding commitment to nuclear energy, France has the electric mix with fewer emissions of greenhouse gases from the nineteen largest economies on the planet. In addition, this infrastructure allows this country to export electricity to some of its neighbors (especially Italy and Great Britain), which has consolidated it as the largest exporter of energy from all over Europe.
France has the electricity mix with the lowest greenhouse gas emissions of the nineteen largest economies on the planet
However, this strategy is not foolproof. The challenges that French nuclear energy is currently facing demonstrate its vulnerability and how sensitive it is to the possibility that several nuclear reactors are affected simultaneously for the same problem. Given the current war situation and France’s dependence on this source of energy, this is its biggest Achilles’ heel.
This is precisely what is happening right now, but some of the criticism that nuclear power is facing due to preventive and corrective maintenance that is being carried out in some French reactors do not have a solid basis. Especially those who defend that the French nuclear park is old and overlook the fact that most of its nuclear reactors are still far from reaching the 40-year stipulated design life, which is usually less than their useful life.
In fact, it is possible that when it overcomes the challenge that lies ahead of the French energy model come out reinforced, although to understand why it is necessary to know what has caused the affected nuclear reactors to be stopped longer than initially planned. The safety of these facilities is at the heart of the decisions that are being made, and there is no doubt that this is objectively good news for everyone.
In any case, France’s resounding commitment to nuclear energy has not contributed to reducing the cost of electricity. In fact, just a few days ago we witnessed how the pool French was close to 3000 euros/MWha record figure caused, precisely, by having placed most of the eggs in the same basket: that of nuclear energy.
What is the SCC and why has it put French nuclear energy in check
Nuclear power plants produce electricity constantly, but, of course, they require carrying out preventive and corrective maintenance tasks periodicals, as Alfredo García, better known on Twitter as nuclear operatorduring the conversation we had with him several months ago:
“A nuclear power plant operates for eighteen months on average non-stop, and during this period of time maintenance is also carried out. Most of the equipment is duplicated, tripled or quadrupled, so while one of them is working we carry out the review and preventive or corrective maintenance of one of its reserves».
During 2020 and 2021, the two bloodiest years of the pandemic caused by the spread of the SARS-CoV-2 virus, some of the non-urgent maintenance tasks that were planned in several French nuclear reactors were delayed. When the health situation improved these works of routine maintenance resumedand, according to EDF, in one of the reactors of the Civaux nuclear power plant, the technicians identified the problem that has triggered the debate in which we are immersed.
Using ultrasonic analysis equipment, they found in some welds of the security injection system, known as SIS, a few tiny cracks of less than 0.5 mm in length that in the long term could degrade them. The SIS is a piping circuit designed to inject water into the vessel with the purpose of acting as an emergency coolant and neutron absorber. If you are curious, in this article we explain in detail what the vessel is and what elements make up the primary circuit of a nuclear reactor.
This form of material corrosion is known as SCC (Stress Corrosion Cracking), an acronym in English that indicates the possibility that corrosion can cause the breakage of a material when it is subjected to a certain level of stress or tension. Those responsible for the Twitter account Nuclear Youth They explain this mechanism very well. in a thread that they have recently published, and to which we suggest you spend a few minutes if you are interested in this topic.
SCC is a process in which micrometer-scale cracks appear and expand through the thickness of the weld. It is a very bloody process, since it is only detectable after an incubation period (not measurable) that can last several decades pic.twitter.com/x1pca1xfn5
– Nuclear Youth (@jjnucleares) April 19, 2022
According to the French Institute of Radioprotection and Nuclear Safety, the technicians who analyzed the welding of the reactors of the Civaux nuclear power plant concluded that in the short term this degradation there was no risk involved. The SIS pipes are 3 cm thick and the penetration of the SCC is less than 1 mm.
Even so, prudence in the context of nuclear energy must be maximized, which is why they decided preemptively stop all the nuclear reactors that could be affected to review and repair all the welds affected by this degradation of the material.
The inactivity of these reactors while these and other preventive or corrective maintenance tasks are being carried out has meant that, as we have seen in the first lines of this article, EDF has been forced to revise its energy production forecast downwards electrical of nuclear origin.
Corrosion can cause a material to break when it is subjected to a certain level of stress or tension.
It is disturbing that a tiny damage, although with the potential to go further, has put the French nuclear park in check, but it is also impressive the level of demand that the nuclear industry and the agencies that oversee it have imposed themselves so that the safety of these facilities prevails.
Identifying the minute cracks produced by SCC in SIS welds requires the use of highly sophisticated ultrasonic analysis equipment, and this procedure also requires technicians be very thorough. And the information we handle reflects that they are being.
Ignacio Araluce, the president of Foro Nuclear, explained to us in the conversation that we had with him at the end of 2019 how the strategy of multi-level security that the nuclear industry has implemented:
“There is an internal supervision in the nuclear power plants that is responsible for carefully examining the work of the operators. And beyond this there is additional supervision, at the company level, that examines not only the performance of the workers, but also that of the organization. And above this there are other external monitoring teams made up of international experts who examine whether the security methods used by companies are adequate.
In addition to the latter, there are international organizations, such as WANO, that supervise everything with a certain frequency, relying on the best experts. Finally, controlling everything is the regulatory body, which is elected by parliament by qualified majority and has sufficient independence and rank to supervise the operation of nuclear facilities. Perhaps more can be done, but it is clear that the top priority of a nuclear power plant is safety.”
The SCC does not reflect that the French nuclear park is aged
If we bear in mind everything that we have investigated in this article so far, it seems reasonable to conclude that the degradation that has triggered the appearance of SCC is the natural result of the aging of nuclear facilities. However, some of the reactors that have been affected by this problem, such as those at the Civaux or Chooz nuclear power plants, they are the most modern of the French nuclear park.
SCC is a very sensitive problem that also affects other critical industries
In fact, they are less than 25 years old, so they still have plenty of operating time left to complete their design life, and possibly even longer to exceed their useful life. SCC is a very delicate problem that also affects other critical industriessuch as the construction of bridges or the pipelines of gas pipelines, so the companies and agencies involved are developing increasingly sophisticated analysis technologies to identify it and keep it under control.
We are all concerned about the safety of nuclear facilities, and it is natural and beneficial that this should be so. In the end the pressure they receive from outside the companies that manage them, and also the stress they impose on themselves, are the fundamental ingredients of the strategy that seeks to prevent an accident as serious as that of the Chernobyl nuclear power plant from happening again. All the effort that is carried out in this area is welcome.
Pictures | Civaux nuclear plant (E48616) | Nuclear Forum
George is Digismak’s reported cum editor with 13 years of experience in Journalism