Nuclear-weapons designers require plutonium with a very high plutonium 239 isotopic content, whereas plutonium from commercial power plants usually contains substantial quantities of the other isotopes of plutonium, making it difficult to use in a bomb. Nevertheless, use of plutonium from spent fuel in weapons is not inconceivable. Hence, President Jimmy Carter banned civilian reprocessing of nuclear fuel in the U.S. in 1977. He reasoned that if plutonium were not recovered from spent fuel it could not be used to make bombs. Carter also wanted America to set an example for the rest of the world. France, Japan, Russia and the U.K. have not, however, followed suit, so plutonium reprocessing for use in power plants continues in a number of nations.
An Alternative Approach
When the ban was issued, “reprocessing” was synonymous with the PUREX (for plutonium uranium extraction) method, a technique developed to meet the need for chemically pure plutonium for atomic weapons. Advanced fast-neutron reactor technology, however, permits an alternative recycling strategy that does not involve pure plutonium at any stage. Fast reactors can thus minimize the risk that spent fuel from energy production would be used for weapons production, while providing a unique ability to squeeze the maximum energy out of nuclear fuel. Several such reactors have been built and used for power generation—in France, Japan, Russia, the U.K. and the U.S.—two of which are still operating [see “Next-Generation Nuclear Power,” by James A. Lake, Ralph G. Bennett and John F. Kotek; Scientific American, January 2002].
Fast reactors can extract more energy from nuclear fuel than thermal reactors do because their rapidly moving (higherenergy) neutrons cause atomic fi ssions more effi ciently than the slow thermal neutrons do. This effectiveness stems from two phenomena. At slower speeds, many more neutrons are absorbed in nonfi ssion reactions and are lost. Second, the higher energy of a fast neutron makes it much more likely that a fertile heavymetal atom like uranium 238 will fi ssion when struck. Because of this fact, not only are uranium 235 and plutonium 239 likely to fi ssion in a fast reactor, but an appreciable fraction of the heavier transuranic atoms will do so as well.
Water cannot be employed in a fast reactor to carry the heat from the core— it would slow the fast neutrons. Hence, engineers typically use a liquid metal such as sodium as a coolant and heat transporter. Liquid metal has one big advantage over water. Water-cooled systems run at very high pressure, so that a small leak can quickly develop into a large release of steam and perhaps a serious pipe break, with rapid loss of reactor coolant. Liquid-metal systems, however, operate at atmospheric pressure, so they present vastly less potential for a major release. Nevertheless, sodium catches fire if exposed to water, so it must be managed carefully. Considerable industrial experience with handling the substance has been amassed over the years, and management methods are well developed. But sodium fi res have occurred, and undoubtedly there will be more. One sodium fire began in 1995 at the Monju fast reactor in Japan. It made a mess in the reactor building but never posed a threat to the integrity of the reactor, and no one was injured or irradiated. Engineers do not consider sodium’s flammability to be a major problem.
Researchers at Argonne National Laboratory began developing fast-reactor technology in the 1950s. In the 1980s this research was directed toward a fast reactor (dubbed the advanced liquidmetal reactor, or ALMR), with metallic fuel cooled by a liquid metal, that was to be integrated with a high-temperature pyrometallurgical processing unit for recycling and replenishing the fuel. Nuclear engineers have also investigated several other fast-reactor concepts, some burning metallic uranium or plutonium fuels, others using oxide fuels. Coolants of liquid lead or a lead-bismuth solution have been used. Metallic fuel, as used in the ALMR, is preferable to oxide for several reasons: it has some safety advantages, it will permit faster breeding of new fuel, and it can more easily be paired with pyrometallurgical recycling.
See what we're tweeting about
7 Comments
Add CommentPerhaps the "smartest" thing that we could do is to stop calling it nuclear "waste".
Reply | Report Abuse | Link to thisAs this article makes clear, the byproducts of nuclear fission are potentially valuable in and of themselves. Instead of elaborate schemes to bury this stuff for thousands of years, we should "mine" its possible uses.
Treat it like garbage and it's a problem - treat it like gold and it won't end up dumped in a stream.
In retrospect it’s too bad our environmental friends gave the “man made global warming” treatment to nuclear power in the 60’s by using superstition and scare tactics to intimidate people with bad information. I’m sure they thought they we’re justified in their views at the time but now we realize the extreme damage of their ignorance. If we had gone nuclear 40 years ago we could have averted spewing gigatons of tons of carbon into our atmosphere and averted the “tipping” point we find our climate in today. Not to mention we could have spent the last 40 years making nuclear power safer and more efficient and the United States less reliant on fossil fuels. This is just one example of how environmentalist can do incalculable damage to our nation and to our climate when they start screaming before they know what they’re talking about.
Reply | Report Abuse | Link to thisNuclear power's problems were and are primarily financial; the plants are simply not cost effective relative to the alternatives. We can build a 750 mW(e) combined-cycle plant for around $750 million or a 1200 mW(e) nuclear unit for 6 or 7 billion dollars.
Reply | Report Abuse | Link to thisThe fast reactor concept, while technically intriguing, is likely to be even more of an economic problem.
http://en.wikipedia.org/wiki/Generation_IV_reactors
Reply | Report Abuse | Link to thisLiquid Metal Fast Reactors (LMFRs), of which the authors are touting, have a terrible operational record. The USA has built 3, of which 2 have had unintentional core melts. In 1996, the Japanese Monju LMFR leaked 5 tons of its highly radioactive liquid sodium coolant which caught fire, and has been shut down for 10 years. The French Super Phoenix had power oscillations which caused them to shut it down too.
Reply | Report Abuse | Link to thisIn 1972, President Nixon fired ORNL's Director, Dr. Weinberg for advocating the meltdown proof Molten Salt Reactor (MSR) because the GOP had selected the LMFRs instead. MSRs can and have operated on all 3 fissiles (U235, U233, & Pu239) and can best utilize thorium. Why not restart this Generation IV reactor instead?
REFs: http://en.wikipedia.org/wiki/Alvin_M._Weinberg
http://en.wikipedia.org/wiki/Molten_salt_reactor
http://en.wikipedia.org/wiki/Generation_IV_reactors
The leak at Monju was not radioactive.
Reply | Report Abuse | Link to thisChap, you are correct, the sodium leak was not radioactive as it was in Monju's Secondary Coolant circuit. I apologize for the mistake I posted above.
Reply | Report Abuse | Link to thisHowever, had the leak been in the Primary Coolant circuit while the reactor was operating, the leak would have been highly radioactive due to the 15 hr halflife of Na-24, which emits energetic 1.4 MeV & 2.8 MeV gamma rays. Large amounts of Na-24 are created by neutron absorption within the LMFR's core.
Furthermore, sodium fires, even without complicating radioactivity, are difficult to contain because hot sodium reacts with air, water, carbon dioxide (CO2), and even concrete! It's ash is sodium oxide (Na2O), which will combine with any water to make highly caustic sodium hydroxide (NaOH), which is lye, or Draino (drain cleaner)!
Molten Salt Reactors (MSRs), coolant and fuel is melted LiF-BeF2 into which sufficient fissile (U-235, U233, &/or Pu-239) are dissolved. Molten salts do not react with air or water and freeze below 500 C, thereby encapsulating the radioactive materials (e.g., Fission Products). Furthermore, they do not require pressure vessels as they operate at atmospheric pressure. The USA has built and successfully operated 2 MSRs at Oak Ridge National Laboratory: ARE (1954) & the MSRE (1960s).
REFs:
http://www.gen-4.org/Technology/systems/msr.htm
http://nuclear.inl.gov/deliverables/docs/msr_deliverable_doe-global_07_paper.pdf
http://www.ornl.gov/~webworks/cppr/y2001/pres/119930.pdf