[Decoding] Analysis of Greenpeace’s Report on Flood Risks for Gravelines EPR2

Greenpeace has released a report questioning the safety of the Gravelines nuclear power plant in light of climate change risks. The nuclear industry has already implemented robust measures to anticipate these challenges. EDF, which already operates six reactors on the site, is planning to build two new EPR2 reactors, addressing long-term challenges. This topic, widely studied, is already well-established in the public debate.

On Thursday, October 3rd, Greenpeace published a report titled “Gravelines Nuclear Power Plant: A Sandcastle by the Sea.” Unsurprisingly, as an organisation that campaigns for nuclear phase-out, the report recommends not constructing new nuclear reactors at Gravelines (Nord). Since September 17th, EDF’s project to build two EPR2 reactors has been the subject of a public debate led by the National Commission for Public Debate (CNDP). These new reactors will ensure long-term security of electricity supply and decarbonisation of industry in the region.

Climate Change Adaptation: A Priority

One of Greenpeace’s main criticisms focuses on the alleged lack of anticipation and consideration of climate change risks, particularly flooding risks for seaside facilities. However, industry players, as well as safety authorities, have demonstrated that this issue is a priority today, as it should be for all energy sectors. The RTE report, Futurs énergétiques 2050, highlights that heatwaves, floods, and storms will affect the entire energy system, making it imperative that every energy production sector, as well as transmission and distribution, prepares for these challenges.

The Gravelines site (with six reactors) has benefited from specific upgrades, and even more extensive work is planned for the EPR2 reactors. The French Nuclear Safety Authority (ASN) has already stated that climate change adaptation would be one of the two priorities in the review process for extending reactor operations beyond 50, or even 60, years. Greenpeace’s report acknowledges these works without questioning their seriousness.

The French Nuclear Society (Sfen), in its 2021 issue of the Revue Générale Nucléaire (RGN), titled Climate Hazards: Anticipating and Protecting, covers several aspects of adapting nuclear facilities. This dossier addresses phenomena such as flooding, heatwaves, and strong winds, and it discusses the measures put in place to protect facilities from extreme weather events, which are likely to become more frequent due to climate change. Beyond the initial design, which today incorporates all the knowledge accumulated over half a century about natural phenomena and climate change, the nuclear industry’s practice is to re-evaluate the specifics of each site every ten years and adapt the facilities. For Sfen, this represents a sign of humility and seriousness in the ongoing process of climate adaptation, where industrial societies will continue to learn over time.

Greenpeace’s report also mentions the Adapt programme, a major climate change adaptation project led by EDF at its facilities. As the Cour des Comptes (French Court of Auditors) highlighted in a dedicated report, “the uniqueness of the Adapt project lies in its ‘site-by-site’ approach and its systemic vision. For each site, the project follows a methodology by selecting climate scenarios (high, low, medium) and conducting climate, hydrological, and thermal projections adapted to each.” To support Adapt, EDF’s R&D teams have historical expertise in meteorology, hydrology, hydraulics, and climate change. This climate expertise, developed since the publication of the first Intergovernmental Panel on Climate Change (IPCC) report in 1990, is shared across the nuclear and hydroelectric sectors and benefits from collaborations with external experts. Moreover, when validating design assumptions or safety periodic reviews, an independent analysis is carried out by the IRSN (French Institute for Radiological Protection and Nuclear Safety) and ASN.

Safety Margins and Measures Taken at Gravelines

The Gravelines power plant has reinforced protections to address climate risks, particularly flooding caused by rising sea levels. Following the Complementary Safety Assessments (ECS) conducted after the Fukushima accident, significant investments were made between 2020 and 2022 to adapt the site to extreme climate events. These measures include reinforcing the anti-flood peripheral protection, designed to withstand events of much greater magnitude than those observed so far.

In addition, a diversified cold source, independent of the primary natural source (the sea), has been installed to ensure redundancy in the event of a failure. The platform height chosen for the EPR2 reactors at 11 metres of the General Levelling of France (niveau général de la France or NGF) provides increased protection against “extreme” flooding.

In its report, Greenpeace calls for the publication of an analysis of “the risks of submersion for the new seaside reactors, up to the end of their decommissioning in 2130-2150.” It is impossible to predict with certainty the state of climate change over such long time horizons. Designing a facility based on assumptions beyond a century could lead to inadequate or even counterproductive measures.

EDF has already included significant safety margins, exceeding the most catastrophic climate change and sea-level rise scenarios, with assumptions accounting for up to 8°C of warming. EDF’s hypotheses take into account the highest sea level, including a tide with a coefficient of 120. An additional margin is added to account for millennial events, and an evaluation of sea-level rise is included, based on various models, using the most challenging assumptions. These margins allow for adaptation to evolving environmental risks.

The threat of ice sheet melting, also mentioned by Greenpeace, would be gradual rather than sudden. This sea-level rise is anticipated, and measures could be implemented well in advance to maintain the safety of the installations. In the worst case, it would always be possible to unload the fuel and shut down the reactors before safety is compromised. Moreover, the Nuclear Safety Authority (ASN) will always have the power to shut down a plant if it no longer meets safety standards.

Scenarios and Provisions for Future EPR2 Reactors

Greenpeace’s report claims that protection relies solely “on the robustness and proper sizing of the surrounding walls and dikes.” This demonstrates a lack of understanding of nuclear safety principles, one of which is defence-in-depth. Introduced in nuclear safety in the early 1970s, defence-in-depth involves several layers of protection within nuclear facilities.

These layers include not only technical features intrinsic to the facility but also material devices, organisational measures, and predefined procedures. The goal is to prevent accidents and, if prevention fails, to limit potential consequences. Initially structured into three levels during the design of the currently operational reactors, defence-in-depth now comprises five levels, as defined by IRSN: the prevention of operating anomalies, the management of accidents, the limitation of severe accident consequences, and finally, the limitation of radiological consequences in the event of releases. Emergency measures, such as evacuation and the distribution of potassium iodide tablets, are planned to protect the population.

In the case of future EPR2 reactors, the safety objective is to maintain a dry platform (where the reactor is located). Hence, its elevation to 11 metres of the General Levelling of France. Even if water were to reach the platform, the defence-in-depth concept would protect the facility, particularly the reactor building’s advanced watertightness and emergency systems (such as backup diesel generators). If these measures are insufficient, the Nuclear Rapid Action Force (FARN) can be deployed, capable of regaining control of a facility within a few hours.

Lessons from Experience

Greenpeace’s report asks, “How long can the safety of the Gravelines plant be guaranteed if it becomes surrounded by water and isolated like an island?” On the North Sea, the English Channel, or the Atlantic coast, such a situation would only be temporary, as it would require the combination of a high tide with a very high coefficient and a very violent storm, both inherently temporary phenomena.

The report states: “The isolation of the Gravelines plant, surrounded by water, would affect the entire infrastructure. This situation would lead to degraded operations, posing access challenges for workers, particularly for team rotations. Vital functions would be endangered, such as evacuating the electricity produced by the plant, its power supply, and the operation of pumps for reactor cooling.” While electricity evacuation is desirable for powering the region, it is not a vital function of the reactor and is not classified as a safety function. The goal, in such a case, is to protect safety functions, including reactor cooling, by ensuring the protection of the platform or buildings against rising water.

When a plant is disconnected from the grid, for example, due to damage to the transmission infrastructure, it can operate in “islanding” mode. This is what happened during Storm Ciaran in 2023. The electric grid in the Cotentin region was damaged, cutting off the Flamanville plant’s evacuation line. EDF successfully executed the plant’s islanding operation, quickly reducing the reactor’s power to around 25% of its nominal value. About 5% of this power was used to operate the plant’s essential equipment.

Although this situation is serious, it is a scenario the nuclear industry has already faced, particularly in the United States. For example, the Waterford 3 plant in Louisiana was preemptively shut down before Hurricane Katrina made access difficult. It was the first plant to restart and produce electricity after the hurricane, demonstrating the nuclear sector’s ability to manage extreme conditions while ensuring safety. A similar situation occurred at Fort Calhoun in Nebraska, where the plant was protected and kept safe following flooding from the Missouri River, with the reactor literally becoming a “nuclear island.”

The Need for Early Public Engagement

Greenpeace regrets not having access to a vulnerability study document. This document will be presented as part of a public consultation during the Creation Authorisation Request (DAC) to the ASN in 2026. Greenpeace seeks to anticipate a debate whose primary objective is to draw lessons from ongoing public discussions. It is important to note that the CNDP (National Commission for Public Debate) aims to hold the public debate as early as possible in a project’s development. This allows citizen contributions and concerns to be considered from the outset, influencing the design and direction of the project more effectively. This is even a legal requirement for major projects and a constitutional right (Article 7 of the Environmental Charter). ■

By the Sfen with Technical Section 4 (Safety and Environmental Protection)

Sfen thanks Technical Section 4 (Safety and Environment) for their swift availability in helping to produce this analysis.

Image: Gravelines Power Plant – ©ContyBruno/EDF