Since the oil shocks of the 1970’s the French government has invested heavily in nuclear power. At that time, most of the electricity in France came from oil fired power stations, and the oil was imported mostly from the Middle East. With no oil or gas fields of its own and coal fields almost exhausted, it began a large-scale nuclear energy programme.

There are now 58 nuclear reactors in France, which provide nearly 80 per cent of the country’s electricity supply. Now, in a bid to bring dependable energy to remote coastal communities, the French government has decided to give the green light to a different kind of nuclear power programme - smaller nuclear reactors to be based on the ocean floor.

In January, France's naval construction firm DCNS agreed on a joint two-year study of a concept for submerged nuclear power plants together with French company Areva, Electricité de France and the French Atomic Energy Commission (CEA). Promoters say these could provide energy for millions of people in coastal locations worldwide.

The concept for the nuclear submarine, known as FlexBlue, involves a cylindrical vessel about 100 meters long and 15 meters in diameter that would encase a complete nuclear power plant with an electrical capacity of between 50 MW and 250 MW. By comparison Sizewell B power station in Suffolk has an output of almost 1200MW.

Flexblue would comprise a small nuclear reactor, a steam turbine-alternator set, an electrical plant and associated electrical equipment. Submarine power cables would carry electricity from the Flexblue plant to the coast.

With costs significantly cheaper than traditional onshore reactors - estimated at several hundred million Euros compared to about 5 billion Euros for a full-sized reactor - French engineers believe it could lead to a boom in the uptake of nuclear power.

Russian plans



The French are not the only ones interested in offshore nuclear power. The Russians have already developed the design for a floating nuclear power plant which uses two 70-MW reactors derived from those used in Russian submarines and icebreakers and launched a prototype last year.

The French's flexblue plants would be designed to be moored on a stable seafloor at a depth of 60 to 100 metres a few kilometres off shore. A system of ballast tanks would be used to raise or lower the plant during installation and for major maintenance, refuelling or dismantling.

The reactors would be adapted for continuous power generation. Flexblue would use power plants of a standard design requiring very limited site-specific tailoring. This makes these plants fundamentally different from land-based nuclear power plants, which must be tailored in terms of civil engineering to accommodate local site constraints.

Flexblue nuclear plants would be stationary subsea installations with no independent means of propulsion. They would be transported by purpose-built vessels similar to those currently used to install offshore platforms. These same vessels would carry Flexblue plants to approved shipyards for refuelling, major maintenance and eventual dismantling.

DCNS aims to design Flexblue plants so that they can be remotely controlled from a shore-based facility. Each plant would, however, include an onboard control room giving operators local control over critical operations, including startup and some maintenance phases. The plant would also be directly accessible at all times by mini-submersibles. Maintenance would be based on proven procedures similar to those used by DCNS for many years to maintain, update and extend the life of naval vessels.

The cost of the reactors is estimated to be in the region of several hundred million Euros, compared to about 5 billion Euros for a full-sized reactor. DCNS Chairman and CEO Patrick Boissier said, ‘preliminary studies show that we should be compatible with the cost of renewable energies, and better than solar power.’

Waste disposal and accidents

Long-term storage plans for highly radioactive waste are still to be decided but DCNS confirmed all dismantling and decommissioning would be done onshore.

The company claims that Flexblue plants would be designed from the outset to prevent any contact between nuclear materials and the marine environment. Underwater submersion would also provide a natural means of cooling the reactor, they say, as well as enhancing security, and the only substance released into the environment would be the seawater used for cooling.

Cores would be protected by three barriers: fuel cladding, reactor vessel and hull. The designers argue that immersion in sea water would ensure an infinite natural means of passive cooling and permit inherent safety and security. In addition, each plant would also be protected against potential intruders. The French argue that a submerged power plant would be less vulnerable to earthquakes, tsunamis, or floods, and would be far less vulnerable to terrorist attack.

Sceptics are concerned that warmer water released from the reactors could be dangerous for local ecosystem. And, should there be a nuclear accident ‘the sea will be destroyed,’ according to the President of Anti-nuclear organisation Crilan, based in Cherbourg. ‘The fierce warming-up of the water will cause a massive thermal shock that will destroy sea life.’

However, supporters of Flexblue have attempted to downplay concerns suggesting the undersea reactors would be based entirely on proven technologies, simply combined in a new way. They say with two-thirds of the world’s population currently living within 80 kilometres of the sea the new technology could make nuclear power more attractive to countries. For more remote locations, the nuclear reactors could allow for a fast and efficient way to add electrical supply to the region without needing any surface-based infrastructure, including the kind of supply systems needed for coal or oil-powered stations.

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