TR10: Traveling-Wave ReactorA new reactor design could make nuclear power safer and cheaper, says John Gilleland. By Matt Wald
Enriching the uranium for reactor fuel and opening the reactor periodically to refuel it are among the most cumbersome and expensive steps in running a nuclear plant. And after spent fuel is removed from the reactor, reprocessing it to recover usable materials has the same drawbacks, plus two more: the risks of nuclear-weapons proliferation and environmental pollution.
These problems are mostly accepted as a given, but not by a group of researchers at Intellectual Ventures, an invention and investment company in Bellevue, WA. The scientists there have come up with a preliminary design for a reactor that requires only a small amount of enriched fuel--that is, the kind whose atoms can easily be split in a chain reaction. It's called a traveling-wave reactor. And while government researchers intermittently bring out new reactor designs, the traveling-wave reactor is noteworthy for having come from something that barely exists in the nuclear industry: a privately funded research company. As it runs, the core in a traveling-wave reactor gradually converts nonfissile material into the fuel it needs. Nuclear reactors based on such designs "theoretically could run for a couple of hundred years" without refueling, says John Gilleland, manager of nuclear programs at Intellectual Ventures. Gilleland's aim is to run a nuclear reactor on what is now waste. Conventional reactors use uranium-235, which splits easily to carry on a chain reaction but is scarce and expensive; it must be separated from the more common, nonfissile uranium-238 in special enrichment plants. Every 18 to 24 months, the reactor must be opened, hundreds of fuel bundles removed, hundreds added, and the remainder reshuffled to supply all the fissile uranium needed for the next run. This raises proliferation concerns, since an enrichment plant designed to make low-enriched uranium for a power reactor differs trivially from one that makes highly enriched material for a bomb. But the traveling-wave reactor needs only a thin layer of enriched U-235. Most of the core is U-238, millions of pounds of which are stockpiled around the world as leftovers from natural uranium after the U-235 has been scavenged. The design provides "the simplest possible fuel cycle," says Charles W. Forsberg, executive director of the Nuclear Fuel Cycle Project at MIT, "and it requires only one uranium enrichment plant per planet." |
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A Preassembled Nuclear Reactor
06/16/2009
Massachusetts Institute of Technology
Comments
How much will there be?
How radioactive will it be?
What is its effective half-life?
How much shielding will it require?
What is its potential for mischief?
hsfrey
02/25/2009
Posts:13
Also, what will be the volume of waste and what are the costs of dealing with the waste?
JonPaul
02/25/2009
Posts:1
What are the end product?
The end products are residual (unburned) U-238, fission products, and transuranic elements (Np, Pu, Am, and Cm)
How much will there be?
The fuel in this reactor is Pu-239. The energy content in 1 lb of Pu-239 is equivalent to more than 2,000,000 lbs of coal, so nuclear power produces an enormous amount of energy and an extremely small amount of waste.
Currently we have 104 nuclear reactors in operation in the US, which generate about 20% of our electricity. The total amount of spent fuel discharged is about 2,000 tons per year. Of this, 95% is U-238 (which could be used as fuel in the Wave reactor), 4% is fission products (waste), 1% is transuranics (TRU). Of the 1% TRU, 90% is Pu, which can be recycled as fuel. The remaining 10% (0.1% of the total) is Np, Am, and Cm, which is considered waste, but can be recycled in a fast reactor like the Wave. The amount of fission products (waste) generated each year is 4% of 2,000 tons or 160,000 lbs. There are 300 million people in the US, so the average share of the nuclear waste is 160,000 lbs / 300 million = 0.0005 lbs, or 0.2 grams per person per year. If you received 100% of your electricity from nuclear power for your entire lifetime, all of the nuclear waste generated from your use would fit in a coffee cup. Compare this to the average person's carbon footprint of 20 tons of CO2 per year.
How radioactive will it be?
The radioactivity of the end products from the Wave reactor would be essentially the same as from the current generation of reactors.
What is its effective half-life?
The half-lives of the numerous fission products vary from a fraction of a second to many years. It takes about 500 years for the fission products to decay to same level of radioactivity as the natural uranium we started with.
How much shielding will it require?
Spent fuel is stored under water for at least 5 years to allow the fuel to cool (water is also an excellent shielding material). After that the fuel can be transferred to dry storage casks, which use steel and concrete for shielding. Six inches of concrete will stop more than 90% of the radiation from the spent fuel. A typical cask has about 3 inches of steel (for gamma shielding) and almost 3 feet of heavily reinforced concrete (for both gamma and neutron shielding).
What is its potential for mischief?
None. The combination of physical security, the huge mass of the storage systems, and self-protecting nature of radioactive materials make spent fuel extremely unattractive for mischief or misuse.
pronuke
03/07/2009
Posts:4
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