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“Fast nuclear reactors” not the solution to plutonium wastes


Ultimately, however, the core problem may be that such new reactors don’t eliminate the nuclear waste that has piled up so much as transmute it. Even with a fleet of such fast reactors, nations would nonetheless require an ultimate home for radioactive waste, one reason that a 2010 M.I.T. report on spent nuclear fuel dismissed such fast reactors.  

Can Fast Reactors Speedily Solve Plutonium Problems? The U.K. is grappling with how to get rid of weapons-grade plutonium and may employ a novel reactor design to consume it Scientific American By David Biello  | March 21, 2012 The U.K. has nearly 100 metric tons of plutonium—dubbed “the element from hell” by some—that it doesn’t know what to do with. The island nation does not need the potent powder to construct more nuclear weapons, and spends billions of British pounds to ensure that others don’t steal it for that purpose. The unstable element, which will remain radioactive for millennia, is the residue of ill-fated efforts to recycle used nuclear fuel.

One solution under consideration is to recycle the plutonium yet further—by using it as fuel in a pair of new, so-called “fast” reactors. Such nuclear reactors can actually “consume” plutonium via fission (transforming it into other forms of nuclear waste that are not as useful for weapons). The U.K. is considering a plan to build two of General Electric’s PRISM fast reactors, the latest in a series of fast-reactor designs that for several decades have attempted with mixed success to handle plutonium and other radioactive waste from nuclear power. The idea remains that fast reactors, which get their name because the neutrons that initiate fission in the reactor are zipping about faster than those in a conventional reactor, could offer a speedy solution to cleaning some nasty nuclear waste, which fissions better with fast neutrons, while also providing electricity as a by-product.

The U.K. is hardly alone in struggling to cope with nuclear waste, whether plutonium or otherwise. The U.S. remains a nation in search of a solution for what to do with its nearly 70,000 metric tons of spent nuclear fuel, which has a small fraction of plutonium mixed in it. A recent blue ribbon commission impaneled by President Obama suggested looking for communities that would volunteer to take the waste, for a fee.

Nor is the U.K. alone in considering fast reactors as a solution for eliminating plutonium. Japan’s has built a fast reactor known as Monju to recycle its used nuclear fuel. France had one for awhile, too, but it has since been shut down due to difficulty operating the plant as designed. In fact, most such fast reactors have proved difficult to run reliably. “At one time or another, [fast reactors] were a priority program in the U.S., Japan, France, Germany, Italy and Russia,” notes physicist Thomas Cochran of the Natural Resources Defense Council, an environmental group. “They were largely failures in all those places and in two nuclear navies, so one should think twice before trying it again.”

Novel design
The trouble with fast reactors has largely been related to what’s used to cool them—liquid sodium in the case of GE’s PRISM and many others. The better half of table salt, this element cools a fast reactor nicely and also ensures there is no perpetual chain reaction. And, thanks to a more than 800-degree Celsius boiling point, it can operate at low pressures, unlike conventional reactors. But sodium also reacts explosively with either air or water, necessitating elaborate safety controls in places where it must get close to water in order to create steam to turn a turbine to make electricity, such as steam generators. As a result of numerous fires from leaking systems, operating sodium-cooled fast reactors to date have been shut down more than they have run. “You can’t take the top off and look down in the reactor and correct any problems,” Cochran notes. “You have heroic maintenance issues any time you need to go into the reactor.”

And that’s why GE has decided that the solution is to keep such reactors small, to minimize safety concerns as well as the size of systems, among other design changes. …….  The challenge is that the metal fuel gets hot—and unlike oxide-based fuels, when it heats, it swells. If the fuel expands too much, it can crack the surrounding cladding, and that presents a big problem. GE’s solution is to put in less fuel….

Fit for purpose

Of course, there is a simpler solution to the U.K.’s plutonium problem: bury it…… Such fast reactors are more expensive than even traditional reactors, such asWestinghouse’s new AP-1000 under construction in China and the U.S., which are estimated to cost roughly $7 billion apiece. Conventional light-water reactors can also “consume” plutonium, if need be. …. Ultimately, however, the core problem may be that such new reactors don’t eliminate the nuclear waste that has piled up so much as transmute it. Even with a fleet of such fast reactors, nations would nonetheless require an ultimate home for radioactive waste, one reason that a 2010 M.I.T. report on spent nuclear fuel dismissed such fast reactors.  http://www.scientificamerican.com/article.cfm?id=fast-reactors-to-consume-plutonium-and-nuclear-waste

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June 30, 2012 - Posted by | Reference, reprocessing, UK

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