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The 2022 French nuclear outages: Lessons for nuclear energy in Europe 

July 24, 2023 Work Area: Advanced Nuclear

Beginning in the mid-1970s, France began deploying dozens of large light water nuclear power reactors. Over the course of just 15 years, the investment in nuclear energy led to the most rapid decarbonization of an industrialized economy power grid in history, moving France from about 70% fossil fuel on the grid to about 10% by 1990 — representing hundreds of millions of tonnes of CO2 avoided. Nuclear energy operated at high capacity in France for nearly five decades, providing on average about 75% of grid power (with wind and solar providing about 12% in 2022). France’s nuclear power plants, along with 47 reactors in 12 other EU member states, have played a substantial role in meeting Europe’s climate goals and ensuring its energy security, supplying about a quarter of its total electricity and about a third of its low-carbon electricity.  

However, France’s nuclear contributions were interrupted in 2022 due to extended maintenance shutdowns and curtailments due to weather-related river conditions, which resulted in record-low nuclear availability in France. At its lowest point, France’s nuclear availability sat at around 40% of maximum capacity for about a month. This dip led some critics to question the reliability of nuclear energy and its potential role in Europe’s decarbonization strategy.  

But are the issues with the French fleet in 2022 a sign of unavoidable issues with large-scale nuclear deployment? Or a case of situational neglect and lost opportunity that can be remedied with better policy, some technical fixes, and more attention by regulators and industry? These are important questions to answer to objectively assess what role nuclear can play in Europe’s zero-carbon future.  

Clean firm power

This is a particularly critical question because the weight of studies has concluded that decarbonizing the electricity sector, even one dominated by renewable energy like wind and solar, is likely to be less expensive and faster, if we have a substantial amount of “clean firm,” always-available, non-weather dependent power sources in the mix. Nuclear is one of these clean firm options globally (along with geothermal energy, hydrogen combustion, biomass, and fossil gas with carbon capture), and it is already well established in the European grid, with operational plants in 13 of 27 member states. And, as mentioned, nuclear already supplies around quarter of the Europe’s total electricity, and about a third of its low-carbon electricity.

Aside from its carbon benefits, nuclear energy can reduce the total spatial footprint of a clean electricity generation system in a land-scarce region such as Europe, reduce the need for new long-distance transmission lines, and reduce strain on critical mineral and material requirements. As a result, with binding targets and increasingly robust climate policy taking root in the EU, we are seeing renewed interest in nuclear power generation far beyond France: Spain, Finland, and Sweden have all announced plans to increase capacity of their existing plants, while Romania, Poland, and the Netherlands have announced plans to build new nuclear plants.  

There is no question that nuclear energy could play a valuable, possibly even pivotal role in a low-carbon European future. Does the 2022 experience in France negate this possibility? 

To answer this question, lets first examine the facts. 

France’s nuclear energy in 2022

France’s nuclear energy industry encountered a series of overlapping issues in 2022. 

  1. Tiny corrosion and heat-stress induced cracks in a set of reactor pipes that the French nuclear company, EDF, “Frenchified” from the original Westinghouse design modified by EDF using a new geometry; these pipes, in the safety injection and residual heat removal system, were identified over the course of routine maintenance checks. The cracks, if not corrected, would likely have eventually led to leaks of water inside the reactor containment building. 
  1. Scheduled maintenance of some plants that could neither be deferred nor executed quickly as a result of workforce and resource limitations.  
  1. High river temperatures which prompted a reduction in output from France’s remaining operating reactors. 

Let us examine these issues in turn. 


First, it is important to recognize that the pipe corrosion issues were identified and are being fixed in consultation between EDF and the French Regulator, with 70% nuclear availability achieved earlier this year with complete inspection and repair to be completed by the end of 2025, according to the proposed inspection and maintenance strategy. It is also important to recognize that while the defective piping zones are located in a safety-relevant area, redundant safety systems would have ensured reactor cooling even if the defective piping had failed. No doubt it was unlucky timing, but the outages can also be viewed as evidence that the nuclear energy maintenance and safety regime in France is working. While it would have been ideal if the corrosion mechanism had been identified as part of the design change to the safety injection and residual heat removal system prior to the reactors being certified (or better yet, if EDF had adhered to the original standard design) what matters is that such issues were identified and managed appropriately before they became major problems.  

Second, and at the same time, this incident highlights the need for an important improvement in the way future nuclear energy plants are delivered. True, the slow remediation of the corrosion issue is ultimately a quality control issue for which EDF bears responsibility. It indeed may point to some underlying issues within EDF itself, considering that the company endured a similar equipment-defect situation in 2016. But it also points to the need for more thorough commoditization and standardization in the nuclear industry. Current nuclear plants, like those owned by EDF, resemble large complex infrastructure projects rather than mass-produced products. That means when equipment needs updating, it is done through bespoke customization — as was done here — on sometimes complex and large components — instead of swapping out whole pieces of off-the-rack equipment. Smaller, simpler, standardized reactors that are largely manufactured in factories rather than stick built on site will not only avoid problems associated with local departures from tested designs but also allow for more timely and cost-effective repairs. Such changes to the nuclear deployment business model are also critical to allowing it to scale to the level needed to address climate change.  

Workforce limitations resulting from mixed political signals 

Another cause that has been suggested by EDF and French unions for the length of the ensuing maintenance outages following identification of the corrosion issues is the declining capacity of the nuclear workforce in France, brought on by wavering government support and lack of policy clarity for the sector. The initial shutdowns were already a big burden for a single operator (EDF) to handle, but the subsequent planned maintenance activities — many of which had been delayed or reduced in scope in 2021 due to the Covid-19 pandemic — proved too much for a nuclear industry that had seen its investment undermined by years of unsupportive government support.  

Due initially to political pressure following the tsunami-caused nuclear accident at Fukushima, French leadership withdrew from nuclear energy over two successive administrations. France’s previous president Francois Hollande, ahead of the 2012 presidential elections, negotiated with one of the French opposition parties, promising to shutdown certain French reactors and significantly cut nuclear’s share of the energy mix. President Macron committed to the same at the outset of his first term, though on a less aggressive timeline. President Macron has recently changed course, but such prolonged negative government signaling to an industry not only hampers public and private investment in said industry, it also signals to incipient engineers, scientists, and others not to pursue a career in the industry. Indeed, recruitment agencies for the industry have suggested these factors have contributed to nuclear workforce shortages across several disciplines. Who wants to join a dying field, after all?  

Though the increasing turn to renewables over the past decade may have contributed to France’s recent difficulty in efficiently building new reactors, EDF’s former CEO has also pointed to the workforce factors above as detriment to France to getting through this maintenance episode quickly. Had the necessary long-term investments been made, and had sufficient specialized workforce been available, they may have. EDF did, after all, bring in hundreds of additional workers from Canada and the U.S. to assist with the maintenance.

As unfortunate as it has been, this period is just a brief snapshot in time and not representative of the industry’s decades of reliable service. While it is near the bottom of the pack amongst other countries in terms of unplanned nuclear power outages, France’s nuclear energy availability the three years prior to 2022 was still nearly 70%. and reached that level again by January 2023. 

High river temperatures and curtailment 

As for the output curtailments due to river conditions, such weather-related incidents are an increasing reality for all energy industries amidst the changing climate. But they are a manageable issue. Importantly, they did not represent a binary “available/unavailable” reliability issue either — the plants were able to keep running safely but were forced as a matter of regulation to reduce output for the sake of river ecosystems downstream (French law requires such reductions when water temperatures reach certain thresholds, or when river levels and flow rates are low). River-sited fossil fuel and hydroelectric plants sometimes reduce output for similar environmental reasons.  

No generation source, including renewable energy, is immune from seasonal weather variations. Wind power in the EU, for example, generated less than half its yearly high over the summer of 2022, and there are sometimes multiple days and weeks where wind output is negligible throughout the region. Dramatic variations in seasonal availability also exist for solar energy. While energy storage can address daily fluctuations for wind and solar, multi-week and seasonal wind and solar droughts are not practically addressable with current storage technology.  

In contrast, several technical options exist today to reduce or prevent curtailments of nuclear energy plants during heat waves, such as recirculating or indirect wet cooling, as is used at 42 U.S. reactors, including Palo Verde in the desert of Arizona. Even dry cooling is possible though not yet used commercially (Nuscale’s Carbon Free Power Project in Idaho plans to employ dry cooling). Several French reactors were eventually granted waivers to continue unabated operation during the summer heat, but other options exist as well. 

A recent analysis studied the impact of past European heat waves on nuclear power output and the technical means to address them. The conclusions are summarized below: 

  • Curtailment of nuclear power due to periods of extreme heat has had the effect of reducing European nuclear power output by approximately 0.1% since the year 2000. For France specifically, which with its many inland river-sited plants has been the worst hit country, the corresponding figure is approximately 0.15% 
  • At peak times, less than 5% of European nuclear power capacity has been unavailable specifically due to curtailment during recent heat waves. Even at times of peak curtailment, the availability of nuclear power exceeded that of any other low-carbon electricity generating technology in Europe, including solar PV, wind, and hydroelectricity. 
  • To address this problem in the near to mid-term, technical fixes are not necessarily required. For example, the French nuclear fleet runs at 60% capacity factor during the summer, heat wave or not, since it is typically deployed to vary with load, and load is lowest in summer, so scheduled outages are common. Electricity prices have remained modest during curtailment periods (€40-60/MWh) and France covers its own demand during the summer. To compensate for lost output at its most vulnerable river-sited plants during heat-wave curtailments, France could increase output at the remainder of its fleet if economic incentives were provided. 
  • Over the longer term, there are technical options readily available for all types of power plants, including nuclear, to increase both rates of utilization as well as availability. These will be driven by economics, not engineering limits. The cost increases associated with these options are relatively modest. 

Nuclear may not be entirely unaffected by seasonal changes, but it remains a highly reliable clean firm option. 

The big picture 

In short, the evidence suggests that France’s experience over the past year and a half is an isolated episode, an unfortunately timed confluence of challenges, rather than indication of a chronic problem with nuclear energy. French nuclear availability was back up to 73% in January 2023 from a low of 40% the previous August, and the fleet is expected to generate about 76-84% of its average by the end of 2023. In the end, the difficulties experienced can be attributed to mistakes by EDF, flaws in the current nuclear delivery model, underinvestment in French nuclear, and very unfortunate timing.  

The French nuclear sector must learn from these events and improve, and the proactive responses from EDF and the French regulator suggest it is doing so. For Europe, the lessons are equally clear. Longer term, standardized, commoditized nuclear plant delivery will avoid the problems of local customization and labor-intensive remediation in favor of modular replacement, as with airline maintenance.  And a variety of operational and technical fixes are available to address nuclear cooling challenges in heat waves. 

No zero-carbon energy option is without its challenges, and nuclear energy is no exception. But the French nuclear experience illustrates far more success than failure. The events of 2022 do not change that. Decarbonization of a European electric grid that may need to double or triple in size by midcentury will require a portfolio of options. Nuclear energy remains a highly reliable, and likely indispensable, component of that mix. 

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