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Dealing with nuclear waste?
Got this in my inbox this morning. Sounds like an interesting approach to containing nuclear waste/radioactive material by turning it into glass. Discuss.
| quote: | A solution for N-waste
CLEANUP I Amec has a plan to turn the waste into glass
Derrick Penner
Vancouver Sun
CREDIT: Associated Press files
The Hanford nuclear reservation near Richland, Wash.
A nasty legacy of the Cold War lurks beneath the arid plains of south central Washington state: millions of gallons of nuclear waste that the U.S. Department of Energy needs to clean up before it finds its way into the nearby Columbia River.
The engineering firm Amec is proposing a method to help in the cleanup that sounds so simple it is elegant.
Take the waste -- cake-like chunks of uranium- and plutonium-laced salts contained in underground tanks -- and turn it into blocks of glass using a technique the company calls GeoMelt.
There are 177 of the tanks around the vast, 586-square-mile Hanford nuclear reservation that contain some 53-million gallons of the waste -- some of it dating back to the 1940s and the Manhattan Project that built the world's first atomic bombs.
Leo Thompson, technology director for Amec's 50-person GeoMelt unit in nearby Richland, Wash., said the Columbia River meanders past the Hanford site, and the big fear is that the waste-filled tanks will leach their radioactive cargo through the soil, into the ground water and eventually the river.
"You can't just leave [the waste] as it is," Thompson said. "It's in these tanks in the ground, and some of the tanks have leaked. So it has to be dealt with."
Thompson said the waste was created in the production of weapons-grade uranium and plutonium from spent fuel rods of nuclear reactors.
As many as nine reactors operated on the Hanford site over its history.
He added that plutonium and uranium were chemically separated out of the spent fuel, and the left over waste was neutralized using caustic sodium hydroxide, which was then stored in underground tanks. What is left over is cake-like sodium nitrate and sodium nitrite that is tainted with traces of plutonium, uranium, cesium, heavy metals and other toxic compounds.
Some of the tanks were built in the 1950s with only single walls and were "designed with a limited lifespan. . . . Waste has been in them longer than it was designed to be," Thompson said.
The U.S. Department of Energy has taken one step to reduce the risk of leaks by removing all liquid from the tanks.
And the department is in the midst of a $2-billion US-per-year cleanup effort to remove all nuclear waste on the site by 2035.
Thompson said the department has given itself until 2028 to treat all the waste in the storage tanks, but the treatment plant it has commissioned to handle the job is over budget, behind schedule and won't have the capacity to do the entire job by the deadline.
So the department has embarked on a program to test supplementary treatment methods, including Amec's GeoMelt technology.
The GeoMelt test was commissioned by the Department of Energy's Office of River Protection and its prime contractor at Hanford, CH2M-Hill Hanford Group Inc.
Thompson said Amec has a $90-million US contract to test GeoMelt on the tank waste using a version of the technology called In Container Vitrification.
It involves taking the waste from the tanks, mixing it with soil and oxide compounds that encourage the formation of glass and then putting it into an insulated metal container the size of a standard shipping container where it is superheated to temperatures of 2,000 degrees celsius using a 5,000-amp jolt of electricity delivered by a pair of electrodes that are poked into the mixture.
The high temperature causes the soil, oxide and waste to melt, and the molten material cools into a 42-tonne block of glass that, while radioactive, won't leak or leach and will resist deterioration for thousands of years, Thompson said.
He added that cesium is the most dangerous compound in the tank waste, which will leave the resulting glass blocks with dangerous levels of radiation for about 300 years. However, some of its other radioactive particles will remain hazardous for thousands of years.
Amec is also testing GeoMelt on radioactive soil from Hanford that is buried in some 142 vertical shafts made from open-ended steel drums that were welded together.
Thompson said they use the same process, but the radioactive soil cannot be dug out of the ground without the risk of spreading radioactive dust into the environment, and it cannot be safely removed using conventional methods.
So electrodes are stuck into the ground "in situ" around the 24-inch-diametre shafts, and the resulting jolt of power creates a 15-foot pillar of glass that isolates the contaminated dirt and can be safely dug up for storage.
To date, Thompson said Amec has conducted several tests of the In Container Vitrification process, including a full-scale demonstration on simulated, non-radioactive material, and smaller tests on actual waste.
He added that engineers from the company's Vancouver and Trail offices have been involved in designing some elements of the project since about 2003, and Thompson anticipates they will remain involved as the firm builds a full-scale pilot plant to continue testing the method on waste material.
Thompson said Amec has also run a successful test of the in-situ method on a simulated shaft, again using only non-radioactive material.
"I think it's going well," Thompson said. "It's a challenging project, but what we're doing is trying to build a first-of-a-kind nuclear processing plant [by] taking GeoMelt and trying to adapt it to treat this particular waste stream."
He added that the waste plant that the Department of Energy has already commissioned is using a different method of turning the waste into glass, but he believes Amec's method is simpler, cheaper and the leading candidate to become the alternative treatment plant.
Thompson said Amec has already used GeoMelt in both its in-container and in-situ variations on radioactive waste elsewhere in the U.S. and Australia. It has also GeoMelt to isolate chemical waste at projects in Australia, Japan and in the U.S.
"It's satisfying," Thompson said about the work. "It's nice to actually treat something that results in a permanent solution. A lot of times waste is dealt with by taking it and putting it in special landfills . . . and just storing it for the next generation."
"With this process, it's a permanent treatment and that in itself is satisfying."
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AMEC'S RECIPE FOR N-WASTE
The GeoMelt process turns radioactive waste into stable, leak-proof blocks of glass.
1. Plutonium, uranium and cesium-tainted waste is liquefied into a slurry that is pumped into a dryer.
2. Plain dry soil and oxidizers, such as boron oxide and zirconium oxide, are mixed in to promote the formation of glass.
3. The mixture is pumped into a sand-lined, insulated container the size of a shipping container in which the process, called In Container Vitrification, will take place. Electrodes are inserted into the mixture.
4. The atomic-waste mixture is superheated using a 5,000-amp current of electricity that heats it to temperatures up to 2,000 degrees Celsius.
5. As the waste mixture melts and shrinks, more waste mixture is poured on top during the eight-stage process, which takes eight days to complete.
6.The melted material is allowed to cool into a 42-tonne glass brick that cannot leak or leach out of its metal container.
7. The electrodes are cut and the metal container is sealed so that it can be more safely stored for the thousands of years it will take for the material's radiation to dissipate.
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