In any nuclear power plant, heavy metal atoms are consumed as the fuel “burns.” Even though the plants begin with fuel that has had its uranium 235 content enriched, most of that easily fissioned uranium is gone after about three years. When technicians remove the depleted fuel, only about one twentieth of the potentially fissionable atoms in it (uranium 235, plutonium and uranium 238) have been used up, so the so-called spent fuel still contains about 95 percent of its original energy. In addition, only about one tenth of the mined uranium ore is converted into fuel in the enrichment process (during which the concentration of uranium 235 is increased considerably), so less than a hundredth of the ore’s total energy content is used to generate power in today’s plants.
This fact means that the used fuel from current thermal reactors still has the potential to stoke many a nuclear fire. Because the world’s uranium supply is finite and the continued growth in the numbers of thermal reactors could exhaust the available low-cost uranium reserves in a few decades, it makes little sense to discard this spent fuel or the “tailings” left over from the enrichment process.
The spent fuel consists of three classes of materials. The fission products, which make up about 5 percent of the used fuel, are the true wastes—the ashes, if you will, of the fission fire. They comprise a mélange of lighter elements created when the heavy atoms split. The mix is highly radioactive for its first several years. After a decade or so, the activity is dominated by two isotopes, cesium 137 and strontium 90. Both are soluble in water, so they must be contained very securely. In around three centuries, those isotopes’ radioactivity declines by a factor of 1,000, by which point they have become virtually harmless.
Uranium makes up the bulk of the spent nuclear fuel (around 94 percent); this is unfissioned uranium that has lost most of its uranium 235 and resembles natural uranium (which is just 0.71 percent fissile uranium 235). This component is only mildly radioactive and, if separated from the fission products and the rest of the material in the spent fuel, could readily be stored safely for future use in lightly protected facilities.
The balance of the material—the truly troubling part—is the transuranic component, elements heavier than uranium. This part of the fuel is mainly a blend of plutonium isotopes, with a significant presence of americium. Although the transuranic elements make up only about 1 percent of the spent fuel, they constitute the main source of today’s nuclear waste problem. The half-lives (the period in which radioactivity halves) of these atoms range up to tens of thousands of years, a feature that led U.S. government regulators to require that the planned high-level nuclear waste repository at Yucca Mountain in Nevada isolate spent fuel for over 10,000 years.
An Outdated Strategy
Early nuclear engineers expected that the plutonium in the spent fuel of thermal reactors would be removed and then used in fast-neutron reactors, called fast breeders because they were designed to produce more plutonium than they consume. Nuclear power pioneers also envisioned an energy economy that would involve open commerce in plutonium. Plutonium can be used to make bombs, however. As nuclear technology spread beyond the major superpowers, this potential application led to worries over uncontrolled proliferation of atomic weapons to other states or even to terrorist groups.
The Nuclear Non-Proliferation Treaty partially addressed that problem in 1968. States that desired the benefits of nuclear power technology could sign the treaty and promise not to acquire nuclear weapons, whereupon the weapons- holding nations agreed to assist the others with peaceful applications. Although a cadre of international inspectors has since monitored member adherence to the treaty, the effectiveness of that international agreement has been spotty because it lacks effective authority and enforcement means.
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