ranium was discovered in 1789 by Martin Heinrich Klaproth, a German chemist, in the mineral pitchblende. Radioactivity was first discovered in 1896 when Antoine Henri Becquerel, a French physicist, detected it from a sample of uranium. Since there is little demand for uranium metal, uranium is usually sold in the form of sodium diuranate, also known as yellow cake, or triuranium octoxide. Naturally occurring uranium consists of three isotopes: uranium-234, uranium-235 and uranium-238. Although all three isotopes are radioactive, only uranium-235 is a fissionable material that can be used for nuclear power and bomb production.
Naturally occurring uranium consists of three isotopes: uranium-234, uranium-235 and uranium-238. Although all three isotopes are radioactive, only uranium-235 is a fissionable material that can be used for nuclear power. It makes up 0.72% of the naturally occurring element. When struck by a neutron, its nucleus can release energy by splitting into smaller nuclei such as strontium, xenon, krypton, barium, etc. Some of the fragments are other neutrons which can strike other U-235 nuclei and cause them to split as well. Fissionable U-235 capable of producing enough free neutrons to sustain a nuclear chain reaction. This rapid release of energy is the desired outcome for a bomb. In power reactors, the number of free neutrons is decreased with absorbing material so the energy release is large but controlled and steady.
Research is ongoing to be able to enrich the percentage of U-235 to higher levels economically and quickly. It has historically been done by using large numbers of high speed spinning centrifuges. But, there is another way that seems to be gaining ground using lasers. The technology promises to use a smaller installation and produce enriched U-235 in much larger amounts at less cost. Good news for the nuclear power industry. Bad news for those worried about the spread of the technology to agents of terrorism.
More below the squiggle about this technology. ⤵
How Big Will Sites Be?
The New York Times published this article Sunday August 21st about the laser technology advances. The following graphic compares the Pentagon outlined in the left image to the Iranian centrifuge site at Natanz. The right image is the proposed site and size near Wilmington, NC, for the laser facility. It is much smaller and would be very hard to detect relative to the other huge sites. And, it is proposed to make tons of U-235.
General Electric says its initial success began in July 2009 at a facility just north of Wilmington, N.C., that is jointly owned with Hitachi. It is impossible to independently verify that claim because the federal government has classified the laser technology as top secret. But G.E. officials say that the achievement is genuine and that they are accelerating plans for a larger complex at the Wilmington site.
Donald M. Kerr, a former director of the Los Alamos weapons lab who was recently briefed on G.E.’s advance, said in an interview that it looked like a breakthrough after decades of exaggerated claims. Laser enrichment, he said, has gone from “an oversold, overpromised set of technologies” to what “appears to be close to a real industrial process.”
For now, the big uncertainty centers on whether federal regulators will grant the planned complex a commercial license. The Nuclear Regulatory Commission is weighing that issue and has promised G.E. to make a decision by next year.
Some History of the Technique
In the early 1970s, Lawrence Livermore Laboratory put growing effort in laser technology research. Livermore scientists began experiments using lasers to enrich uranium. By the end of the 70s, scientists were reporting important progress.
Science, technology, and hardware development were so impressive that in 1985, the Department of Energy selected LIS - Laser Isotope Separation as having the best potential to provide a low-cost, environmentally sound method to enrich uranium for the U.S. and its partners. DOE's goal was to replace the aging and energy-inefficient gaseous diffusion plants in Ohio and Kentucky.
Plant-scale laser and separator hardware began operation in 1986, while researchers were continually improving their performance and reliability. The early 1990s marked the first tests with full-sized components in integrated systems producing enriched uranium over many tens of hours. The Energy Policy Act of 1992 transferred the U.S. government's uranium enrichment activities to USEC, which at that time was a government corporation charged with supplying the nuclear fuel industry with enrichment services through gaseous diffusion technology.
In July 1994, after a two-year period during which Livermore's LIS activities were on a standby status, USEC gave the green light for advanced development. The technology was then transferred from DOE to USEC for commercialization, representing the largest technology transfer in the Laboratory's history.
The Technology
Science and Technology Review published an article in May 2000 issue supplied by Livermore scientist Stephen Hargrove. The article described the importance of the tunable laser to this process.
In LIS enrichment, uranium metal is first vaporized in a separator unit contained in a vacuum chamber. The uranium vapor stream is then illuminated with laser light tuned precisely to a color at which U-235 absorbs energy.
The generation of laser light starts with diode-pumped, solid-state lasers providing short, high-intensity pulses at high repetition rates. This green light from the solid-state lasers travels via fiber-optic cable to energize high-power dye lasers. The dye laser absorbs green light and re-emits it at a color that can be tuned to the isotope of interest. In uranium enrichment, the light converts to three wavelengths of red-orange light, which is absorbed only by U-235.
Each color selectively adds enough energy to ionize or remove an electron from U-235 atoms, leaving other isotopes unaffected. "The uranium atoms are subjected to a razor-sharp beam," notes Livermore physicist Steve Hargrove. "Given the several kilowatts of high average power of the dye laser beam, it's a significant achievement that the wavelengths are stable to better than 1 part in 10 million and that the beam's ability to travel long distances is nearly perfectly preserved."
Because the ionized U-235 atoms are now "tagged" with a positive charge, they are easily collected on negatively charged surfaces inside the separator unit. The product material is condensed as liquid on these surfaces and then flows to a caster where it solidifies as metal nuggets. The unwanted isotopes, which are unaffected by the laser beam, pass through the product collector, condense on the tailings collector, and are removed.
The green light diode laser feeds pulses into the dye laser. The dye laser absorbs green and re-emits colors of that are able to be adjusted, or tuned. The red-orange colors are tuned to be absorbed by the U-235 isotope. The energy absorbed by the electron ejects it from the isotope leaving behind a positively charged U-235. They are attracted to a negatively charged plate and harvested.
Spinoff Technologies
Livermore scientists estimated more than 60 potential spinoffs from this LIS technology from medical isotopes and diagnostics to astronomy. For astronomy, the spinoff has indeed born fruit. Laser guide star, has been of immense use to astronomers because it removes the effects of atmospheric turbulence that blurs the images taken by Earth-bound telescopes. It is commonly used by many world class observatories.
The laser guide star uses technology originally developed for the LIS effort. The guide star begins with green light from flashlamp-pumped, solid-state lasers beneath the main floor of the telescope dome. The light travels through fiber-optic lines to a compact dye laser similar to that used in uranium enrichment. The dye laser converts the light from green to yellow, and a beam projector mounted on the telescope directs the yellow light up through the upper atmosphere.
At an altitude of about 95 kilometers, the laser beam hits the layer of sodium atoms that are continuously produced by burning micrometeorites. The light excites the sodium atoms, causing them to emit yellow light in all directions and create a sharply defined guide star. An adaptive optics system at the telescope corrects the guide star image for atmospheric distortions. The corrections made to the guide star's light sharpen the image of all of the celestial objects in the same patch of sky under the telescope's view.
What About the Dangers?
Iran began its laser program in the 1970s. But it kept the results secret. The silence violated Iran’s agreement with the International Atomic Energy Agency. The I.A.E.A. learned of contracts, enrichment runs and even a prototype plant. Iran insisted that it dismantled the facility in May 2003 and dropped laser enrichment. In February 2010, Iranian scientists were praised by Mahmoud Ahmadinejad for their “relentless efforts” to build lasers for uranium enrichment. Ever since, the I.A.E.A. has sought unsuccessfully to learn more.
When experts cite possible harm from the commercialization of laser enrichment, they often point to Iran. The danger, they say, lies not only in pilfered secrets, but also in the public revelation that a half-century of laser failure seems to be ending. Their concern goes to the nature of invention. The demonstration of a new technology often begets a burst of emulation because the advance opens a new window on what is possible.
Arms controllers fear that laser enrichment is now poised for that kind of activity. News of its feasibility could spur wide reinvestigation. Dr. Slakey of the American Physical Society noted that the State Department a dozen years ago warned that the success of Silex could “renew interest” in laser enrichment for good or ill — to light cities or destroy them.
That moment, he said, now seems close at hand.