“Nuclear oversight is based on the principle of continuous improvement”

For several months now, no steam has been escaping from the cooling tower of the Gösgen nuclear power plant. "It had been a decade since any photographer had come here, to this fabulous round arena. It has a diameter of 114 meters, with circular walls that rise and narrow before opening up again at the top, 150 meters above the ground," described Richard Etienne, a journalist for the daily newspaper Le Temps, during a visit to the site.

However, the opportunity to access the heart of the plant was the result of a chance discovery made in July. “Risks of overload in the water supply pipe network, which could occur in the event of a pipe rupture in the non-nuclear area of the plant, have been identified,” said the plant operator.

There was another upheaval at the end of November when the Energy Foundation (SES) presented an expert report claiming that the Gösgen nuclear power plant had been affected by this fault since it began operating in 1979. According to Manfred Mertins, a nuclear safety expert at the Brandenburg University of Applied Sciences, while this problem has long been resolved in comparable power plants, it continues to pose major risks for Gösgen, which could even cause damage to the reactor core in the event of an earthquake.

Naturally, both the operator of Gösgen and the Swiss Federal Nuclear Safety Inspectorate (IFSN) refute these accusations. "The problem of undamped check valves was addressed in 1998 and improvements were ordered. At the time, the focus was on reinforcing the pipe supports rather than dampening the valves. In 2003, this measure was deemed sufficient and the case was closed," according to the Tages-Anzeiger.

In this battle between pro- and anti-nuclear advocates, it is the ideal opportunity to revisit this issue and address the sensitive question of safety. Interview with Professor Andreas Pautz and researcher Mathieu Hursin, both affiliated with the EPFL's Laboratory of Reactor Physics and System Behavior.

How do you respond to the accusations made against the Gösgen power plant? Could the security flaw reported by SES really have been present since 1979?

At this stage, it is still too early to determine with certainty how long this vulnerability has existed. The facilities commissioned in the late 1970s complied with safety standards that have since evolved considerably. It is therefore possible that a technical element that was considered compliant at the time may now be problematic in light of current requirements. This requires an in-depth analysis that only the supervisory authority (IFSN) is in a position to carry out.

If this flaw had existed for a long time, why did the IFSN only identify it in 2025?

Once again, it should be remembered that nuclear oversight is based on the principle of continuous improvement. Analysis methods evolve, new tools emerge, and scientific knowledge becomes more refined. It is therefore not uncommon for certain vulnerabilities to be identified after several decades of operation—not because of negligence, but because evaluation criteria and control technologies are constantly becoming more precise. The important thing is that the IFSN identified this problem and immediately took the necessary measures.

The late discovery of a flaw does not mean that the plant was dangerous, but rather reflects the constant evolution of safety standards.

How dangerous could this problem be for a power plant like Gösgen?

To date, there is no evidence that this vulnerability has endangered the power plant or the population. Swiss nuclear power plants are designed according to the principle of defense in depth, with multiple protective barriers and redundant systems. Even if a weakness appears in a particular area, this does not mean that there is an acute risk to the entire site. The full assessment will determine the actual extent of the problem and define the appropriate corrective measures.

Is it common for flaws to still be discovered in second-generation power plants?

Yes, it can happen. Second-generation power plants were designed based on the knowledge available between the 1960s and 1980s. Since then, international standards have been significantly strengthened and, thanks to global feedback and major advances in nuclear safety research, scenarios that had previously been little studied have been identified.

The late discovery of a flaw does not mean that the plant was dangerous, but rather reflects the constant evolution of safety standards. These lessons are incorporated directly into the design of third-generation facilities, where the lessons learned from such events are implemented.

The future of nuclear power lies precisely in third-generation power plants. Will they be safer?

Third-generation power plants do indeed incorporate “passive” safety features that are capable of operating largely autonomously, as well as significantly higher safety margins. They are designed to withstand extreme events and minimize the need for human intervention in the event of an incident. This represents a considerable advance in nuclear safety.

The transition to a more modern fleet of power plants will inevitably take place gradually.

But are they completely safe, and isn't the main problem their exorbitant cost?

Nuclear energy relies on extremely rigorous risk management, which must be kept to a minimum. Third-generation power plants offer a higher level of safety, but this performance comes at the cost of greater technological complexity and, consequently, higher costs. These costs are now one of the main challenges to their deployment, along with project duration and the issue of societal acceptance.

There is even talk of fourth-generation nuclear power...

Fourth-generation power plants aim to make better use of nuclear fuels in order to reduce the volume of waste produced or shorten its radioactive lifespan. Several concepts are based on the use of recycled fuels or systems capable of “burning” some of the most problematic elements in current waste.

However, these technologies are still under development and are not yet ready for large-scale application. Their potential is real, but caution remains necessary regarding the time frame for their introduction and their technical maturity.
In terms of safety, fourth-generation plants must at least meet the standards offered by third-generation plants; some Generation IV technologies could even exceed them significantly.

Ultimately, isn't the main concern with nuclear power that we will remain dependent on risky and, moreover, aging power plants for a long time to come?

Existing power plants were designed to operate for several decades, but their long-term operation requires rigorous maintenance and modernization programs, as well as, in some cases, difficult decisions such as early shutdown. Until their successors—whether new nuclear power plants or renewable energy sources—are available, it remains essential to ensure enhanced monitoring and maintain an impeccable safety culture. The transition to a more modern fleet of power plants will inevitably be a gradual one.