France's Underwater Nuclear Reactor

Mehran Nazir
March 19, 2011

Submitted as coursework for Physics 241, Stanford University, Winter 2011

Fig. 1: Cutaway of DCNS's underwater nuclear reactor, powered by Flexblue technology. Source: Wikimedia Commons

French naval defense company, DCNS, is spearheading a validation study on an underwater nuclear reactor design off the coast of France, announced on January 20, 2011. Nearly 80% of France's electricity demand is fulfilled by its nuclear energy facilities, the highest percentage in the world. [1] Given France's proven expertise in small- and medium-sized reactor design, construction, system integration, and fuel R&D, France is positioning themselves to be a leader in a technology that has potential to change the energy landscape for many resource-constrained nations around the world.


DCNS's Flexblue technology will be at the center of the nuclear reactor's operation. Flexblue integrates models of boilers that have been used in submarines with nuclear propulsion. These small nuclear boilers, along with a turbine generator, a power plant, and auxiliary systems, will create energy to be transmitted through submarine cables to land. The current designs of the technology (see Figure 1) would include cylindrical hulls that measure about 100 meters long and about 12 to 15 meters in diameter. These nuclear reactors will be anchored anywhere between 60 to 100 meters underwater and several kilometers off the coast. These reactors are designed to provide 50 to 250 MWe, far smaller than large nuclear reactors of today. However, this level of energy production could suffice for anywhere between 100,000 to 1 million people. [2] Engineers intend to demonstrate a level of safety comparable to that of today's Generation-III reactors.

DCNS will be combining its expertise in nuclear technologies (40+ years) and its history of work in submarines (100 years) to develop this technology. DCNS is uniquely positioned in systems and naval nuclear propulsion, and would leverage these skills to advance this technology. DCNS will be working in conjunction with French companies Areva, EDF, and the French Atomic Energy Commission to build these reactors. A prototype will be built and tested by 2013, and is targeted to be implemented in the three to four years following the initial testing. [3]

Advantages and Risks

Proponents of this technology point out that these submarines would be much lesser prone to terrorist attacks that terrestrial-based nuclear reactors must face. Although attacks from the sky are virtually eliminated, the challenge of defending these facilities from underwater attacks remain. At the moment, plans include a naval force to be guarding the reactor at all times.

Nuclear reactor leaks would be much more difficult and costly to resolve for the underwater reactor. In the event of a nuclear reactor failure, the hazards that radioactive fallout would pose would be mitigated in water as opposed to open air. On the other hand, having diffused throughout the water, controlling radioactive fallout in a higher pressure region increases the technical difficulty of the project. Operating a nuclear reactor underwater will raise the surrounding waters by several degrees, heavily affecting the marine biology that exists in these deep waters. This has caused major debate between proponents of the technology and environmentalists. [4]

It is surprising that the underwater nuclear reactor project has taken off in the aftermath of the British Petroleum disaster that occurred this past year. The BP oil spill highlighted the difficulties inherent in catastrophe prevention for deep water operations. Regardless, these technologies are of enormous interest to island nations that are resource-constrained as it is. Japan would be a likely customer of the technology, along with Hawaii. DCNS predicts it will sell around 200 reactors over the next twenty years [2]. There is also a significant cost advantage to building these reactors versus the large nuclear plants, which range in the billions of dollars. Once the technology has been developed, estimates of these plants range in the hundreds of millions of dollars.

In the following years, DCNS will be conducting further research on technical and production options, market potential, competitiveness analyses, proliferation studies, safety and security studies.

© Mehran Nazir. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] "France: Nuclear Electricity Net Generation," U.S. Energy Information Administration.

[2] T. Madelin, "DCNS Veut Développer un Réacteur Nucléaire Sous-Marin de Petite Puissance," Les Echos, 11 Jan 11.

[3] I. Landauro, "DCNS Plans to Develop Underwater Civilian Nuclear Reactor," Wall Street Journal, 20 Jan 11.

[4] J. van der Made, "Is French Underwater Nuclear Reactor Design Safe?," Radio France International, 20 Jan 11.