An engineer trained to distrust extraordinary claims has spent the past decade working in a field built on them. Low-energy nuclear reactions (LENR) remain controversial, with many physicists unconvinced by claims of excess heat or transmutation. Jacques Ruer approaches the field differently: not as a theorist, but as a builder.

Jacques Ruer was a quiet child, more interested in how things worked than in the games around him. He describes himself as introspective, someone who found his fun in science. The turning point came one Christmas morning: a microscope he had asked for. “For me, it was an opening—a completely new world.” Besides the microscopic world he was also passionate about rocket technology and the conquest of space.

That curiosity carried him through École Centrale de Paris, one of France's most prestigious engineering schools, and into a career that would take him across continents, industries, and decades, from the white heat of molten steel to the invisible promise of a reaction most scientists say is impossible.

"As an engineer, I am always skeptical, and every time there is a new result, my first reaction is to look for... mundane phenomena that may explain this result, before talking about LENR."

Ruer's first professional chapter was in the steel industry. As a research engineer, he helped develop electromagnetic stirring of liquid steel, a process for guiding molten metal with magnetic fields. The technology worked so well that he became a technical manager for a company commercializing it, a role that took him around the world commissioning installations in steel plants. 

This was the kind of work that taught him to think in systems: heat flow, energy transfer, the physics of extreme environments. That knowledge would prove to be very useful in other contexts. In the early 2000s, his activities shifted toward pollution control and energy management, domains he found to be deeply intertwined. "When you see pollution control, it's always connected to energy management, one way or the other." 

From there, the path led to renewable energy, more or less by accident. Ruer's company was taken over by an Italian firm while he was on vacation. When the new director asked what he was working on, Ruer mentioned he had just started looking at wind turbines. "Excellent," came the reply. "We have a European project and nobody to take care of it." Overnight, Ruer was reassigned. It was 2004. The field was just beginning—and it was still possible to become an expert by moving faster than the market.

He went on to contribute to floating offshore wind turbines and tidal stream turbines, one of which still operates off an island on the west coast of France. He also invented a large-scale energy storage process using pumped heat, sometimes called a Carnot-type battery. But there was no market for it yet. "If there is no wind and no sun, the answer iss easy, just switch on your gas turbine." But things are changing now.

He was used to being early. "When you are in research, you are always ahead of your time. You have to be." And he was also used to being misunderstood at home. He was better known in French government ministries than in his own company. "Inside the company, I was almost a stranger, but I was very well known in Paris, in different ministries."

"When you are in research, you are always ahead of your time. You have to be."

The pivotal conversation came just before Ruer’s retirement. He was involved in a European project for high-temperature nuclear reactors when a British colleague posed a simple question at a meeting in Brussels: had he heard what Andrea Rossi, a controversial figure associated with LENR claims, was up to? Ruer was skeptical, but curiosity won.. "I decided to have a look at it."

That decision pulled him into LENR before he retired. “It’s good… because when you retire, you have to know what to do.” He attended his first LENR conference in 2012 and began publishing almost immediately, applying heat-transfer modeling to unexplained experimental results, particularly microscopic craters on electrode surfaces. “How is it possible to melt metal in such tiny spots?” His simulations suggested the hotspots lasted only nanoseconds.

By 2016, he was elected president of the French LENR association, SFSNMC—a role he never sought. “All of a sudden… I was nominated.” He also serves as vice president of the International Society for Condensed Matter Nuclear Science.

"In our case, it's easy to make it work, even if it is difficult to explain why it works...I think we are at the doorstep of something that really works."

"As an engineer, I am always skeptical, and every time there is a new result, my first reaction is to look for normal reactions, mundane phenomena that may explain this result, before talking about LENR." That instinct defines his role in the field. Ruer is not trying to prove that something extraordinary is happening. He is trying to rule out everything ordinary first.

It was tested directly when an explosion occurred in Jean-Paul Biberian’s laboratory. Some in the community speculated that the blast might have been nuclear in origin.Ruer disagreed.

He went and studied the physics of explosions, learned the critical distinction between deflagration and detonation, and conducted his own small-scale experiments, filming them for good measure. A gentle deflagration produces a mild bump. But under certain conditions, when a flame travels through a narrow tube, it can transition into a supersonic detonation, generating enormous pressure from very small quantities of gas. "I'm quite convinced that this 'nuclear explosion'… was not a nuclear explosion, but a hydrogen oxygen explosion."

His most sustained contribution has been in calorimetry, the precise measurement of heat, which constitutes the central methodological challenge in any LENR experiment claiming to produce excess energy. He designed a high-temperature calorimeter for hydrogen experiments, performing the calculations and heat-flow simulations himself. When he reviewed existing setups, he found problems. So he redesigned them.

More recently, he developed what he calls a “no-loss airflow calorimeter.” Airflow calorimeters appear simple: measure air temperature in and out, calculate heat. But in practice, losses distort the result. “What you measure is not really representative…” His design aims to eliminate that. “With this calorimeter, there is absolutely no heat losses… What you measure is everything coming out.” He defines his role carefully: “I am not a researcher… my skill is in engineering.”

“Tell me how it works,” he said, “and I will make it work on an industrial basis.” 
It’s both a promise - and a division of labor.

“What happens to us almost every day?” Ruer said. “It works—but we don’t know why.” That tension defines the field.

Some experiments produce measurable excess heat, but only under conditions that don’t align with earlier expectations. Instead of operating at 300 to 400 degrees Celsius, as in earlier Japanese work, some of the most promising results now appear at far higher temperatures—700, 800, even 900 degrees.Why temperature matters so much remains unclear.

For Ruer, that uncertainty is not evidence—it is a warning.“You have to make sure that because of this high temperature, you don’t have other phenomena that would explain the results,” he said. The risk is not that something new is happening, but that something familiar is being misread under extreme conditions.

That caution carries through to the field’s most persistent problem: reproducibility. “At times some researchers claim to get 14 watts, 20 watts,” he said. “And I become skeptical again, because others obtained only a few watts with a similar setup. It’s strange . You don’t know why.” Run the same experiment again, with a new sample, and it yields a few watts.” The field has signals—but not control.

Ruer also identifies what might be called a structural problem in the organization of LENR research. Too many groups, he argues, are working in isolation on bespoke apparatus. "Maybe there are too many experimental setups these days, and everybody is convinced that he wants to make his own system… and when you develop an experimental thing, it takes a lot of energy from you to make this thing work. And you don't do anything else. So… you are a prisoner to your own device." The contrast with his experience in industry is sharp. "In the industry… when you develop a project, there is one project manager, and the program is very well defined. But with universities and research laboratories, it does not work like that. Freedom of research is a major word, and if you start to explain to people you don't have freedom, you have to do this and that… it doesn't work."

What the field needs, in his view, is something closer to a Manhattan Project, with a goal and a real manager, not merely a coordinator. The European CleanHME project offered a glimpse of what coordinated effort can achieve: one team developed nanoparticle materials, another tested them using Ruer's calorimeter, and the results were genuine. "To work in isolation, it would never have been done," he said. But the project's funding is ending, and renewal is uncertain. "We ask for it, but now, we don't have the money, and others decide if we are funded or not… I am not very optimistic, simply because there is a lack of public money in Europe."

What the field needs, in his view, is something closer to a Manhattan Project, with a goal and a real manager.

The European CleanHME project offered a glimpse of what coordinated effort can achieve: one team developed nanoparticle materials, another tested them using Ruer's calorimeter, and the results were genuine.

Despite all of this, Ruer remains driven. "I think we are at the doorstep of something that really works," he said.

His focus is practical: build a demonstrator, a device that produces sustained, kilowatt-scale excess heat, enough to be unmistakable. "If you have 10 watts of heat excess, but you need to heat it up with 200 watts to keep it hot, well, it's not very exciting. But if you have a larger reactor giving you 200 watts of excess heat, and you only need 100 watts to keep it hot, it tends to be the proof of something important."

He is pushing for a kilowatt-scale system. “Exactly what Clean Planet is doing now.”The lesson comes from his own past. The breakthrough in tidal turbines wasn’t theory; it was a working prototype in the ocean. “You invite the politicians… to take pictures.” Without something to show, no chance. The same principle, he believes, applies to LENR. Theories can wait. When the interviewer compared LENR to the steam engine (used before thermodynamics was understood) Ruer agreed: “Thermodynamics was a baby born from the steam engine.”

But he is not without concern. Apparent transmutations—nickel becoming other elements—raise questions about sustainability. “If we start to destroy nickel… we will need to check if it is sustainable.”

Ruer frames the broader predicament with a comparison to the field's better-funded rival. In hot fusion, he observes, "we know why it works, but it's difficult to make it work. In our case, it's easy to make it work, even if it is difficult to explain why it works." Neither situation is perfect. But one of them, he believes, could produce results sooner, if it gets the chance.

“Tell me how it works,” he said, “and I will make it work on an industrial basis.” It’s both a promise - and a division of labor.

Photo of the CleanHME European Project group. Ruer is the 3rd from the left, next to the project coordinator Prof. Konrad Czerski