Valve innovation assists Hanford nuclear waste cleanup
The liquid wastes being stored at the DOE's Hanford Nuclear Site are mostly water with radioactive solids deliberately mixed into a slurry for treatment. Flowserve is supplying two styles of valves and valve automation packages to assist ongoing remediation efforts at the facility in Washington state. The overall project is expected to take 10 years and cost $5.7 billion, currently the federal government's largest single domestic capital construction project...
• The liquid wastes being stored at Hanford are mostly water with radioactive solids deliberately mixed into a slurry for treatment. Flowserve is supplying two styles of valves and valve automation packages. The "bulge valves" are all stainless steel Mach 1 plug valves that have ultra high molecular weight polyethylene seals and will be located inside a double containment vessel called a "bulge." Each bulge valve will have a stainless steel stem extension connecting it with either a manual operator or a standard aluminum actuator located outside the bulge containment vessel. The jumper valves are made of the same materials with stainless steel actuators mounted directly to the valves. The Jumper valve assemblies will be located inside the high radiation "Canyon" areas of the waste treatment building. Each component has been modified with special materials selected to resist erosion, corrosion and/or radioactive degradation for the working life of the Hanford Waste Treatment Plant. Additional design modifications were also made to permit robotic servicing and repair of each component.
Valves and valve automation products designed for handling radioactive waste are carefully specified and manufactured to meet strict government requirements. This ensures standards conform to critical demands in severe services associated with nuclear applications. To meet these stringent requirements, valve solutions in this field must sometimes rely on devices used outside of convention and history to become ideal solutions. Such was the case when product engineers and specialists at Flowserve Corp. designed innovative valve and automation solutions for the control, isolation and treatment of radioactive waste slurries at the Hanford Waste Treatment Project (WTP) in Washington State.
A Radioactive Situation
The Hanford site in southeastern Washington State has one of the largest concentrations of radioactive waste in the world. The waste is the legacy of 45 years of plutonium production for nuclear weapons, which began with the Manhattan Project in the 1940s and continued throughout the Cold War.
At Hanford, 53 million gallons of high-level radioactive waste, 60% by volume of the nation's total, is stored in 177 old and deteriorating underground tanks just seven miles away from the environmentally sensitive Columbia River. An estimated one million gallons of waste have already leaked from 67 of the facility's oldest tanks. Radioactive waste has been detected in the groundwater that flows to the Columbia, endangering the river habitat and the health of millions of Washington and Oregon residents who live downstream.
To remediate the hazard, the Department of Energy (DOE) commissioned a project in which the high-level radioactive waste is treated and converted to glass logs in a process known as vitrification. Vitrification is currently considered the most effective treatment process for this type of contamination, as it produces a durable and stable form that fully incorporates and immobilizes radioactive waste. Similar projects have been successfully employed in the United States, France and England.
Once immobilized, the high-level radioactive portion of the WTP waste will be temporarily stored at the Hanford site in stainless steel canisters until it can be shipped to a federal geologic repository for permanent disposal. The low-level radioactive portion of the waste will be stored on-site.
The Massive Cleanup
The DOE's Office of River Protection awarded a contract to Bechtel National Inc. in December 2000 to design, construct and commission the Hanford Waste Treatment Plant. It's estimated the build-out of the WTP will cost the government $5.7 billion and take up to 10 years to complete.
The WTP project currently under construction is a massive undertaking that is now the U.S. government's largest capital construction project. When completed, it will also be the world's largest vitrification facility. The project includes three major nuclear facilities – the first one for pretreatment, a second for the low-activity waste vitrification, and a third for high-level waste vitrification.
From construction to final vitrification, the WTP project is a major feat of modern engineering. A significant portion of the project focuses on how the waste is handled so that worker safety is never breached while the overall goal of isolating and treating the waste is achieved.
In the first part of the waste treatment process, specialized valves were needed for installation in containment vessels called "bulges." Each bulge is roughly the size of a small swimming pool and is designed to contain all the pumps, valves and piping required to transfer the radioactive liquid waste slurry from the existing underground storage tanks to the waste pretreatment building for processing.
The pretreatment system combines a filtration process that removes the solids from the waste slurry and an ion-exchange process that then removes the soluble high-level waste from the remaining liquid. Guidelines for this part of the project required manual and automated valves that could be operated and repaired from outside the containment bulges to ensure worker safety and radioactive containment. All bulge valves were subject to NQA-1 inspection and documentation to meet strict DOE specifications. Bulge valve actuators and positioners were also specified to be mounted outside the containment barrier of each bulge.
Innovative Valve Solution
Flowserve learned that Bechtel was favoring top-entry style ball valves for the bulges. The Flowserve team instead believed that Flowserve high-performance plug valves would be a more effective solution.
"Plug valves work better in slurries than ball valves," says Mark Shaw, western regional manager, Flowserve Flow Control. "Plug valves have adjustable positive sealing upstream and downstream and 360° around the top of the plug. By design, plug valves have no cavities where material can collect and/or solidify. Because plug valves also have more than double the sealing area of a typical ball valve, they are a more effective solution for slurry handling."
At the time, Flowserve's only in-house candidate for the WTP bulge valves was the Flowserve Durco G4 plug valve. While the G4 had a successful 35-year history of service in tough slurry applications and had been used in nuclear power applications with nuclear N-stamp requirements, its older design did not allow for remote repair and therefore did not meet the requirements of the WTP project.
"We worked very closely with Bechtel, and were focused entirely on designing and building a solution that would give Bechtel what they needed," says Shaw. "At that time, that solution did not yet exist in our product line."
Design Meets Opportunity
The Flowserve team would soon have a solution – the new Durco Mach 1 high-performance plug valve. Though the Mach 1 had not yet been released, this new plug valve had been designed with flexibility that the G4 did not offer. This gave Flowserve the chance to pursue the Hanford project with a top-entry plug valve that could be modified for remote operation and repair.
Bechtel also needed the valve's seat to be constructed of wear- and radiation-resistant Ultra-High Molecular Weight Polyethylene (UHMWPE), to stand up to the radioactive slurries at Hanford. Fortunately, Flowserve had already designed the Mach 1 to allow a variety of seat materials, including UHMWPE.
"The Mach 1 gave us the flexibility to build a solution for Bechtel," says Fred Shanks, senior product engineer, Flowserve Flow Control, who worked on the Hanford project. "It was a remotely repairable valve that could have an UHMWPE seat that could be easily removed."
Still, the Mach 1 would require modifications to enable its remote repair and make it fully radiation-resistant. A team of Flowserve engineers at the company's Cookeville, Tenn., engineering and manufacturing site began working with the Flowserve sales team in Washington to modify the Mach 1 for Bechtel.
Proving the Concept
The modification process wasn't without hitches along the way. "While UHMWPE is highly wear- and radiation-resistant, it also requires higher torque levels," adds Shanks. "Adjusting for space constraints Bechtel gave us to work with and torque requirements of the Mach 1 with an UHMWPE seat was a delicate balancing act. It forced us to keep innovating with the valve's design and what actuators we could use for it."
In early September 2001, Larry Shields, a Flowserve Flow Control senior sales engineer, arranged for a presentation to the Bechtel WTP design team. Shaw and Shields presented a prototype Mach 1 valve with modifications for cartridge repair and a remotely operable stem extension to demonstrate the removal and replacement of the repair cartridge.
Bechtel engineers were very receptive to the modified design, and seemed to be convinced that it would work for the application. Due to stringent DOE requirements, however, Bechtel required Flowserve to prove the Mach 1 valve design and materials capabilities with a working demonstration in a slurry service that would closely replicate the WTP site conditions.
Bechtel gave Flowserve worst-case specifications for the radioactive slurry and required a twenty-year equivalent cycle test. Flowserve developed a recipe for the test media to match the size of the solids and their viscosity and weight per Bechtel's specifications.
Shaw drew from his previous work in pumps and well-drilling to come up with a combination of commercially available drilling fluids and bentonite clay additives matching the test media specifications. During a visit to Cookeville two weeks before the demonstration, Shaw helped a team of Flowserve engineers and technicians, led by Shanks, to design and build a recirculating test rig to keep media solids in suspension as required during valve testing. The test demonstration satisfied Bechtel's requirements, and the modified Mach 1 plug valve was added to the list of acceptable valves for the Bechtel WTP bulge applications.
"This has been a very challenging project in a lot of respects," says Jerry Sutton, senior piping materials engineer with Bechtel and a responsible engineer on the WTP project. "One aspect was the way the project was scheduled, which made everything extremely urgent. Everything we did was trying to catch up, because the project started construction about the same time we started engineering."
Automating the Valves
The next challenge in the process was to qualify Flowserve Automax valve automation systems with Bechtel, and to design and build adjustable stainless steel extensions with double universal joints to enable remote operation and repair of the valves from outside the bulge containment vessels. Bechtel required the valves to be welded into the bulge piping at a five-degree angle to promote drainage. Universal joints at the top and bottom of the extension were required to eliminate any side-loading the five-degree operating angle would create.
Shaw and Shields worked with Vince Rohrig, automation product manager, and Stan Piela, a Flowserve Flow Control special projects engineer, to design field-adjustable hardware for manual and automated operation of the bulge valves regardless of orientation or distance from the top of the bulge vessels.
"Bechtel wanted stem extensions that could adjust to any length they needed, so we had to innovate again," says Flowserve's Shaw. "We came up with a design for the extensions that could work for any valve in any position in the bulge. Vince's design allowed the extensions to be manufactured as a standard unit that was adjustable to any length during final installation."
Overcoming an Engineering Challenge
"This project was definitely a challenge," says Rohrig. "We've done a lot of stem extensions but nothing like these. Not only did the extensions have to telescope, they had to be designed to take the weight of the stem extension off of the valves. Bechtel also had a variety of torque requirements for these valves, from 500 to 20,000 inch-pounds."
Bechtel liked the stem extension concept Flowserve presented. As a result, Automax pneumatic actuators with Foundation Fieldbus switches were also qualified by Bechtel after meeting additional Bechtel and DOE requirements. A contract for the bulge valves and automation valued in excess of $1 million was signed in August 2002, with Flowserve as the exclusive source for bulge valves. So far, the company has worked with one of several bulge manufacturers to complete the first bulge containing 22 valves. Other bulge valve orders are in process.
The Jumper Valves
After the first order was received for the bulge valves, Flowserve began getting inquiries from Bechtel about its capabilities for the "jumper valve" portion of the project. Its team presented Bechtel with another modified Mach 1 valve featuring Automax stainless steel, rack-and-pinion valve automation packages to meet requirements of this application.
Specification for the jumper valves called for fully automated valves to be used within the pretreatment building with the same requirements for radioactive slurry handling as the bulge valves. Due to intense radioactive levels inside this building, the valves were to be operated and repaired remotely by robotic devices. These valves were also specified with radiation-resistant pneumatic actuators, switches and accessories, which were to be mounted directly on the valve bodies.
Unlike bulge valves, the jumper valves couldn't be built with stem extensions used to pull the plug and sleeve out of the valve body for repair. The challenge was to develop a "jack nut" feature to enable remote release and replacement of the plug and sleeve cartridge assembly by a robot. Additional design changes were required to modify the actuators and mounting kits so actuation packages could be removed for access to the valve's top for cartridge replacement.
Although Bechtel didn't require another upfront demonstration, several design modifications were required. Space constraints forced Flowserve to propose smaller Flowserve Worcester Controls stainless steel, rack-and-pinion actuator units not previously manufactured with stainless steel materials in place of the larger standard Automax stainless steel actuators originally proposed.
"The pretreatment building is a huge facility with lots and lots of equipment," says Shaw. "Everything is installed very closely together. It became apparent we had to build a very compact automation package. Bechtel gave us specific space dimensions that we had to meet. So we had to be flexible in what we were offering to Bechtel to meet their requirements."
Bechtel next wanted proof the actuators would meet NQA-1 inspection requirements and Flowserve could guarantee it would meet promised delivery schedules. After satisfying Bechtel's requirements, Flowserve received another multi-million dollar order for the automated jumper valves in August 2004.
"We worked very hard to gain Bechtel's confidence so we could design valve and automation packages that would meet the needs of their applications and facilities," says Shields. "We came up with two plug valve designs that were unique. That's what put us ahead of the competition."
Flowserve Flow Control is part of Flowserve Corp. (www.flowserve.com), which is based in Irving Texas. For more information, contact Mark Shaw, Flowserve Flow Control western regional manager, at email@example.com.