Half of the reactor fleet off the grid – the causes of the standstills in France

As at 15 August 2022, 27 reactors in France are connected to the grid, 22 of which are operating at full capacity. That is less than half of the 56 reactor units that could be operated in our neighbouring country.

In France, which wants to expand nuclear power even further under President Macron, nuclear power thus has a record global share of approx. 67 % (2020) of the total electricity mix.

This value is expected to be significantly lower for 2022. The country, which traditionally exports a lot of electricity, is also dependent on large amounts of imports from neighbouring European countries - there is currently no sign that this will change in the winter, even if the situation should have improved somewhat by then. But why are so many reactors out of service at the moment? What are the causes? And can we assume that such scenarios will repeat themselves in the next few years?

The standstills and output reductions can basically be divided into three categories by their causes:

Safety-relevant damage
heat and/or drought
planned standstills.

However, not every standstill can be clearly assigned to one of these causes. This is because, for example, reactors that have to be checked for safety-relevant damage are already undergoing a planned overhaul.

Safety-relevant damage to the safety injection system

At the end of 2021, during the safety inspections that take place every ten years (visite décennale), so-called stress corrosion cracking was detected for the first time in Unit 1 of the Civaux NPP in the vicinity of welds of the safety injection system lines. After the damage at the Civaux-1 plant became known, the operator EDF also took reactor Unit 2 in Civaux off the grid for investigations; corresponding damage was also confirmed at the identically designed reactor units Chooz B-1 and B-2. This means that all reactor units of type N4, the most powerful French reactors with a gross capacity of 1,560 MW, are off the grid.

The twelve 1,300-MW units of the P'4 reactor type have also proven to be susceptible to this corrosion phenomenon. These are located at the Belleville, Cattenom, Golfech, Nogent-sur-Seine and Penly sites. These reactors of the two types N4 and P'4 are to be examined as soon as possible with the help of a new test method. EDF also plans to examine the entire reactor fleet for possible damage by 2025.

Heat and drought

Another reason for the unavailability of electrical power is the persistent heat and drought. The problem does not only affect French reactors: this year, for example, reactors in Switzerland or Belgium have already had to be run at reduced power; in Germany, too, there have been output reductions in recent years due to heat and drought.

The reason for this is that cooling water is needed to operate a nuclear power plant. This cooling water is taken from bodies of water and then returned to them. For reasons of water protection, corresponding national regulations stipulate that either the flow rate of the water that is returned to the body of water or the temperature of the respective body of water must not exceed site-specific limit values when the cooling water is reintroduced. In order to comply with these limits, it may be necessary to reduce the plant output accordingly or to shut the plant down.

In order to ensure the stability of the electricity grid, the French nuclear supervisory authority ASN, at the request of the grid operator RTE, has temporarily approved the application of increased limits for water protection applicable in France during prolonged heat waves for the plants Blayais, Bugey, Golfech, Saint-Alban and Tricastin. The plants may continue to operate for the time being until 11 September, subject to a close monitoring programme for the water body.

Planned outages

The third reason for unavailability is the scheduled overall maintenance and refuelling outages, during which fuel assemblies are replaced as well as a large number of routine inspections, maintenance and servicing work is carried out in order to maintain the safe operation of the power plant fleet. Depending on the length of the fuel assembly cycle, these take place approximately every 12 to 18 months and correspond roughly to the annual overall maintenance and refuelling outages known in Germany. In France, they are called visites partielles and normally last about one to two months.

In addition, a visite décennale, which usually lasts about five months, takes place about every ten years. In this context, a réexamen périodique de sûreté, which is equivalent to a German periodic safety review (PSR), is carried out beforehand during operation. During the five months, more in-depth tests and analyses are carried out and any improvements deemed useful are implemented. After a successful visite décennale, a reactor receives approval from the supervisory authority for continued operation for ten years. Since the reactors of the 900 MW series in particular are currently reaching their planned age of 40 years, this is automatically equivalent to an extension of their operating lives to 50 years.

What will the situation be like during the winter and in the coming year?

As the demand for electricity in France is higher in the winter than in the summer, the two regular inspections described are usually carried out more in the summer so that the plants can generate electricity in the winter. However, due to the current additional problems with stress corrosion cracking, the standstills lead to considerable restrictions in electricity generation - to the point that France, as mentioned at the beginning, currently has to buy electricity from other European countries in order to guarantee the supply.

The extent to which these problems will continue cannot be predicted at this point in time. At least there will be fewer inspections in the winter, and difficulties caused by heat can also be ruled out then. What will be important for the generation capacities available then will be what findings emerge from the current investigations into possible stress corrosion cracking and how many other reactors are affected by cracks. If these are limited to the above-mentioned reactor types and can be repaired promptly, the situation should ease again. The only thing that is certain is that the six new EPR reactors announced by President Macron (plus a possible eight in prospect) will not go online this decade.