Most of us don’t spend a lot of time worrying over radioactive waste. We just hope it’s being stored safely and as far away from our communities as possible.
The government, on the other hand, is well aware of the 53 million gallons of radioactive and chemical waste currently stored in 177 underground tanks a few miles west of the Columbia River in Richland, WA. To manage this waste on a long-term scale, the government is funding the massive Hanford Waste Treatment and Immobilization Plant Project (Hanford WTP). The waste there is by volume 60% of the nation’s total inventory of high-level radioactive waste, and it’s the result of over 50 years of plutonium production for bombs.
The massive amount of waste involved is a little unnerving on its own, but the story gets more daunting when you learn that an estimated 1,000,000 gallons have leaked from 67 of the tanks. If the waste reaches the river, it could possibly affect the people who live downstream as well as the river wildlife. That’s why managing it is such a priority.
“Radioactive materials have been detected outside the tanks’ shells,” elaborates John Eschenberg, the Department of Energy’s project manager for the Hanford project. “Hanford is 9 to 13 kilometers from the river. But we do know that the leaked waste has not reached the river or the groundwater.”
For decades, the government has been considering different strategies for dealing with the Hanford waste to make it less toxic and more stable in terms of containing it. But it wasn’t until the past few years, after the leaks were detected, that decisive and lasting action was taken. Congress has mandated an active cleanup of the Hanford waste. The result is the multi-billion-dollar Hanford WTP, scheduled to be operational in 2011.
A Little Background
Back in 1943, Hanford was chosen as a site for weapons-grade plutonium and uranium production because of its remote location and proximity to the Columbia River and the recently built Grand Coulee Dam, both of which could help cool the reactors. The mission was to create a new weapon that promised to bring a swift end to World War II. This weapon was the atomic bomb. And it was Hanford plutonium, in the form of the Nagasaki bomb, that did ultimately end WWII.
The first Hanford nuclear reactor was up and running by 1944, and by 1964 there were eight more. The reactors, which have been inactive now for over 15 years, facilitated the irradiation of aluminum-clad uranium fuel. The irradiated fuel rods went to processing facilities. These facilities used strong nitric acid to dissolve fuel-rod cladding, followed by a chemical process to separate the undesirable constituents from the uranium and plutonium. Because that process used acid, it created a great deal of chemical waste products. Highly toxic waste, that is.
The millions of gallons of liquid and solid waste at Hanford were stored in carbon steel tanks. “To put acid waste into a carbon-steel tank,” begins Eschenberg, “you have to add a lot of caustic material so that it doesn’t degrade the tanks.” So the waste was made more alkaline by adding sodium hydroxide. That converted the pH level from 1 to 14, all the way to the other end of the scale. When it’s in this form, it’s compatible with the carbon-steel tanks.
With the fall of the Iron Curtain in 1989, plutonium production halted. That means much of the waste at Hanford has been stored for at least 20 years. Smaller amounts of radioactive waste would’ve done OK being stored there, but the amount of waste Hanford produced was so massive and toxic that another solution had to be applied.
Time For Cleanup
In 1989, a tri-party agreement was signed by the Washington Department of Ecology, the USEPA, and the Department of Energy (DOE) to set environmental milestones. One of the main priorities was to empty the contents of the 177 waste tanks at Hanford and vitrify that waste. Vitrification is a chemical process through which a substance may be converted into a stable form of glass.
To achieve vitrification on this level, a new waste-treatment site needed to be built at Hanford. “The parties involved knew that the tank waste was dangerous in its current form,” says Eschenberg, “and in accordance with the law, when you contaminate the environment you now have a responsibility to clean it up.” From 1989 to 2001, there were two attempts to build a vitrification plant at Hanford, but both of them got cancelled.
“There was a 10-year period where we knew vitrification was the proper technique, but due to design and funding difficulties the project was never fully funded. Today we have a commitment from Congress to fund this plant, and now we have the right design for all the waste.”
In December 2001, the DOE awarded Bechtel the contract for the Hanford WTP. The goal is to have all the waste vitrified by 2028.
Vitrification Overview
The type of vitrification conducted at Hanford is a chemical process producing a durable and stable form of radioactive waste by blending tank waste with molten glass. The molten byproduct is then placed in stainless steel canisters, where the waste becomes stable and impervious to the environment. Over time, the radioactivity level slowly dissipates.
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| Electricians install cable trays in the low-activity waste facility. |
Vitrification uses a solid form of glass called borosilicate glass, a raw material known as glass frit. “The glass frit is mixed with concentrated waste and then transferred into a melter,” begins Eschenberg. “This is all a closed-loop process. The melter operates at about 1,000 centigrade. Then, as the frit and waste are melted, it forms into molten glass. The molten mixture is poured into heavy-walled, stainless steel canisters and cooled into a solid waste form.”
Vitrification is the first choice for storing highly toxic wastes because the glass produced is the most robust waste form known to man. “The radionuclides that are glassified create a molecularly bonded glass matrix. This is a highly desirable characteristic because it means these radioactive elements are entrained in the glass, can’t get out, and can’t readily seep into the groundwater or the environment.”
Once the waste is in its vitrified form, the toxicity level is low enough that you could touch the glass without any major side effects (but don’t try this at home!). However, if you were exposed to high-level waste before it’s vitrified, you could get a lethal dose in a matter of minutes.
The United States has been using vitrification very successfully for some time now. It’s been used for years at the Savannah River Site in South Carolina, which had been, like Hanford, a production site for bombs. West Valley, NY, which used to be a commercial nuclear fuel-processing plant, has already completed the chore of putting its liquid waste into glass. Europe and Australia also use vitrification for nuclear waste.
So is vitrification completely reliable in protecting from leaks? Unfortunately, it’s difficult to guarantee that anything will be 100% leak-free, but vitrification is as good as it gets. The goal of vitrification is to create a stable waste form that will last tens of thousands of years. To ensure that it does, the vitrified glass used at waste-treatment plants is first tested for stability by exposing samples of it to accelerated aging.
Once vitrified, even if some high-level waste were to somehow leak, the way it’s stored creates a further level of security. It’s put in two steel canisters, one inside the other, and stored hundreds of feet underground. So even if there were any instability, the chance of toxicity reaching any humans—or even animals—is reassuringly slim. (So, yeah, you can exhale now.)
The Scope of It All
The Hanford WTP is a federally funded project. The customer is the DOE Office of River Protection, and the project is funded on an annual basis by the US Congress. The DOE selected Bechtel Corp. to construct the new vitrification plant at Hanford because of the firm’s superb reputation and record. “Bechtel was selected primarily because of their history of delivering on big, complex construction projects and their nuclear expertise,” says Eschenberg. “They’ve been involved with the construction of over 40 nuclear power plants, and that was one of the things that made them very appealing to us.”
Site prep began in October 2001, and the first concrete was placed in July 2002. But the actual vitrification will not begin until the project is completed. The original estimated cost was $5.8 billion, but of course, the final cost is yet to be determined. The spending to date is around $3 billion.
When completed, the Hanford WTP will be not only the world’s largest nuclear-waste processing facility, but also the nation’s biggest industrial construction project ever. It’s truly a one-of-a-kind project of massive proportions breaking new ground in terms of nuclear-waste management and construction. To give you an idea of the size of this undertaking, below are some numbers:
- Building volume: 13,900,000 cubic feet
- Concrete: 110,000 cubic yards
- Structural steel: 16,000 tons
- Heating and ventilation ductwork: 880 tons
- Piping: 98.5 miles
- Tanks: 512 major vessels, approximately 4 million gallons total capacity
- Workers: approximately 2,000 engineers and other professionals, and 600 people on the construction site itself
The entire Hanford site is 560 square miles, and the construction covers about 65 acres. It will include three major facilities: a pretreatment plant, a low-activity-waste vitrification plant, and a high-level-waste vitrification plant. It will also contain a large analytical lab, operations and maintenance buildings, utilities, and office space.
Although the main focus of the construction is to create the vitrification facilities, the Hanford WTP also includes other cleanup activities, such as decontaminating and decommissioning all of the old processing buildings and exhuming some contaminated soil and replacing it with new soil. Currently, the construction is about one-third of the way toward completion.
Treating the Waste
The first stop in the waste-treatment process is pretreatment. This happens in a pretreatment facility, and that’s where the low-activity waste is separated from the high-level waste. These wastes are separated because federal law requires that high-level waste be buried in a national repository.
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| A massive tank cover is moved into position. |
Low-activity waste is the liquid portion of the tank waste, and it contains a relatively small amount of radioactivity in a large volume of material. High-level waste is mainly the solids of the tank waste. This is the really bad stuff. It contains most of the radioactivity in a relatively small volume of materials. “In the 177 underground storage tanks, 10% of that waste contains approximately 90% of the radioactivity,” offers Eschenberg.
The pretreatment facility is huge. It covers an area the size of four football fields and is approximately 12 stories in height. To separate the two wastes, there are several steps involved. First is leaching the radioactive components, which are really just a small portion of the main gallons. Next is filtration, in which the solids are filtered out. The next step is ion exchange, which removes the soluble high-level waste from the remaining liquid.
Once the high-level waste is separated from the low-activity waste, each waste form goes to its respective vitrification plant. After it’s vitrified, the low-level waste is stored in stainless steel containers that are 4 feet in diameter, 7 feet in height, and weigh more than 7 tons. These containers will have a relatively low toxicity level, so they will be stored on the Hanford site itself in permitted trenches covered with soil.
Once the high-level waste is vitrified, it’s initially contained in stainless steel canisters that are 30 inches in diameter and approximately 15 feet high. Once filled, these canisters will weigh more than 3 tons, and they’ll be temporarily stored at Hanford. However, because their radioactivity level will be relatively high after vitrification, they will have a final destination, that of Yucca Mountain in Nevada. Yucca Mountain is not yet licensed to receive the waste, but it is the government’s elected facility and should be ready by the time the vitrification begins at Hanford. Once at Yucca Mountain, the canisters will be buried hundreds of feet underground.
Valvification
When dealing with radioactive waste, a major concern is how to protect the safety of those working at the plant. Therefore, all equipment specified for a new plant must meet strict NQA and DOE nuclear standards specifications. In short, when dealing with equipment used for radioactive applications, there are three basic types of safety rules: distance (how far one will be from the radioactivity), time (how long one will be even remotely near the radioactivity), and shielding (how much radiation is blocked). Bechtel and the DOE are working together to find the best way to design equipment to balance these three elements. They then give their equipment specifications to equipment manufacturers who bid their projects.
For the Hanford WTP, this process has often required the creation of new versions of existing equipment. A perfect example of this is with the valves. One of Bechtel’s valve suppliers for this project is Flowserve Corp. Initially, Bechtel was favoring a top-entry–style ball valve for the bulges. Flowserve, however, believed that plug valves would provide a better solution.
Bulges are the containment vessels through which the waste liquids are transferred from the underground storage tanks to the pretreatment building. Bulge valves are used to control or isolate the amount of liquid being transferred. “Plug valves work better in slurries than ball valves,” says Mark Shaw, western regional manager at Flowserve Flow Control. “Plug valves have adjustable positive sealing upstream and downstream and 360 degrees around the top of the plug. By design, plug valves have no cavities where slurry particles can collect. Because plug valves also have more than double the sealing of a typical ball valve, they are a more effective solution for slurry handling.”
Bechtel agreed. “Bechtel specified bulge valves for both manual and automated valve packages for this project,” continues Shaw. “All of the bulge valves require special stem extensions to permit operation from outside the double-walled containment of each bulge vessel for worker safety. The manual valves were specified to be operated by personnel outside the bulge vessel with levers or hand-wheel operators. For the automated valves, standard pneumatic actuators were specified to be mounted outside the bulge vessels.”
The only existing valve candidate at the time was Flowserve’s Durco G4 plug valve. However, the requirements for the Hanford WTP were such that the valves needed to allow for remote robotic repair, which the existing G4 plug valves could not do. So Bechtel and Flowserve put their heads together to create a new solution.
After much innovative designing and stringent testing, the new Mach 1 high-performance plug valve was modified to meet the nuclear and remote-repair requirements for use in the bulges. In addition to allowing for remote operation, this valve met other qualifications as well, such as having a seat that was made of wear- and radiation-resistant ultra-high-molecular-weight polyethylene so it could hold its own in the abrasive radioactive slurries at Hanford.
The Hanford WTP jumper valves also had special requirements that resulted in further modifications of the Mach 1 valve. The automated jumper valves will be used to control or isolate liquids within the waste-treatment buildings. These automated-valve packages needed to be supplied with radiation-resistant materials, along with special fasteners and mounting hardware to permit the robotic removal of the automation package.
The modification of the jumper valves proved to be a little more difficult than modification of the bulge valves, but in the end it all worked out. “We had to have Flowserve help us design larger bolts,” begins Paul Miller, engineering group supervisor for mechanical handling jumpers at Bechtel. “The bolts needed to be made for use with a manipulator arm. Then Flowserve had to build a steel box on top of the valve so they could mount an actuator with its bolts located so that the actuator could be taken off separately as well.” Flowserve will soon be testing this new valve.
The Challenges Abound
In many ways—and not just in terms of size—the Hanford WTP has been without precedent. Those working on it have needed to develop innovative and original solutions as the construction unfolds. In addition, because of the high cost (at least $6 billion) and important purpose of the plant, there is a very high level of state and public involvement. Interfacing the various needs of all the stakeholders and dealing with the technical and legal aspects of the construction have made this project extremely challenging for all parties involved.
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| An aerial view of the pretreatment facility. |
Bechtel’s Miller says that designing the hot cell, the area where radiation levels are too high for workers to enter, has been one of the most challenging engineering aspects of the project. That’s because the equipment used in the hot cell needs to be designed to operate remotely, and some of the existing equipment required was not already designed to that end.
Case in point: The jumpers they’re now building, called “large-build jumpers.” “They’ve never been built before anywhere on the planet,” starts Miller. “They’re huge. We’ve designed the jumper, and another vendor is working with us to develop it. We’ve tested it, and it’s working. But it’s a big challenge when you’re doing something that’s never been done before.”
Because the Hanford WTP is so massive in size, the design and building and permitting aspects of it are being done simultaneously. “Managing those three elements is proving to be one of the most difficult challenges this project has faced,” says Eschenberg. “Normally, you design a plant completely, then bid the work to a contractor. Then you have to license the plant. Because it’s a hazardous-waste plant, you have to permit it with the state. Then you construct it. But because of the challenging regulatory deadline of 2011, we had to do each of these stages at the same time.”
“This has been one of the most challenging projects in my 20-plus-year career with Flowserve,” begins Shaw. “It’s been a very long process. First we took a new product and modified it to meet the various requirements of some very demanding applications. Then we proved it would work, got the technical specifications changed, and re-bid the entire package to win two contracts. We are now in our fourth year and still working on further WTP revisions. Although this project has been very challenging, it has provided me with great satisfaction in playing a small role in the cleanup of some of the most toxic contamination on the planet.”
Journalist AMY SORKIN KURLAND specializes in marketing communications.
OW - May/June 2006 |
