By Peter Fairley
Fast reactors, whose high-speed neutrons
can break down nuclear waste, are on the road to commercialization. That
message has been advanced forcefully by Russia, China, and India.
At a global conference sponsored by the
International Atomic Energy Agency last week in Paris, Russia and India
described large demonstration plants that will start operating next year and
further deployments that are still in the design phase. China, meanwhile,
described a broad R&D effort to make fast reactors comprise at least
one-fifth of its nuclear capacity by 2030.
By breaking down the longest-lasting and
hottest components of spent fuel from light-water reactors, fast reactors would
need only 2 percent of the space required by a conventional reactor to store
spent fuel. Fast reactors would also reduce the time that the waste must remain
in storage from roughly 300,000 years to just 300. “Are they going to eliminate
the need for geological repositories? No. But it will reduce the burden,” says
Thierry Dujardin, acting deputy director general for the Organization for
Economic Cooperation and Development’s Paris-based Nuclear Energy Agency.
Despite that enticing promise, however,
the inherent hazards of today’s state-of-the-art fast reactors also loomed
large at the Paris confab, which concluded a few days before Monday’s two-year
anniversary of the Fukushima accident in Japan. At the conference, Dujardin
said that fuel safety and prevention of severe accidents need to be “high
priorities” for fast reactor research.
The problem with most fast reactors in
construction or development is the molten sodium that cools their cores. Molten
sodium is highly corrosive and explodes on contact with water and oxygen. Most
dangerous, however, is that the sodium-cooled fast reactor, or SFR, exhibits
what physicists call positive reactivity. Unlike conventional reactors, which
experience their fastest possible chain reaction when operating at full power,
the SFR’s chain reaction is capable of further acceleration than its equipment
is designed to handle. This puts such reactors at greater risk of a runaway
reaction that could cause a core meltdown or breach its steel containment
vessel.
Many technical presentations at last
week’s meeting focused on improved materials and designs intended to protect
SFRs from the most extreme accidents imaginable. But alternative core designs
were also well represented, and some countries are hedging their bets by
testing the alternatives. A U.S. company, Transatomic Power, recently revealed designs for a new kind of molten salt reactor, which
has different safety characteristics than a reactor cooled by molten sodium
metal and should be compact and cheap to manufacture (see “Safer Nuclear Power at Half the
Price”).