Valve innovation helps with nuclear waste

Dec. 5, 2006
Valves and actuators designed for handling radioactive waste must meet strict government requirements. This sometimes requires unconventional solutions. Such was the case at the Hanford Waste Treatment Project (WTP), Hanford, Wash.

Valves and actuators designed for handling radioactive waste are carefully specified and manufactured to meet strict government requirements. This ensures that standards conform to the critical demands in severe services associated with nuclear applications. To meet these stringent requirements, sometimes unconventional solutions are required. 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), Hanford, Wash.

A radioactive situation

The Hanford site in southeastern Washington 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  from the environmentally sensitive Columbia River. An estimated 1 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 U.S. Department of Energy (DOE) commissioned a project in which the high-level radioactive waste is treated and converted to glass logs using 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 South Carolina, New York, 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 is estimated that 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 (Figure 1).

Figure 1. The U.S. government’s biggest construction project: $5.7 billion for Hanford’s waste treatment project.

When completed, it also will be the world’s largest vitrification facility. The project includes three major nuclear facilities — the first one for pre-treatment, 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 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 also were specified to be mounted outside the containment barrier of each bulge.

Plugging for a 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 doubled 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 (Figure 2).

Figure 2. Plug valves have more sealing area than ball valves, making them superior in slurry service.

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 didn’t 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 hadn’t yet been released, this new plug valve had been designed with flexibility that the G4 didn’t 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 was not without some hitches along the way. “While UHMWPE is highly wear- and radiation-resistant, it also requires higher torque levels,” adds Shanks. “Adjusting for the space constraints that Bechtel gave us to work with and the 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, senior sales engineer, Flowserve Flow Control, 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. However, due to stringent DOE requirements, 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 (Figure 3).

Figure 3. The space constraints were an important factor in valve selection.

Bechtel gave Flowserve worst-case specifications for the radioactive slurry and required a 20-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.

Unleashing creativity

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 that exactly matched the test media specifications. During a visit to Cookeville only two weeks before the scheduled demonstration, Shaw helped a team of Flowserve engineers and technicians, led by Shanks, to design and build a recirculating test rig to keep the 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.

“A big part of the process was brainstorming ideas,” says Shields. “We would throw out ideas and try to figure out what would work. We were really trying to innovate to get Bechtel what they needed. Our engineering and manufacturing teams worked together to see how we could implement the ideas.”

“We didn’t just present a concept to Bechtel,” notes Shaw. “We took the time and the initiative to prove to Bechtel that our concept would work.”

“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.”
“Flowserve did quite well under the circumstances,” adds Sutton. “They were very cooperative and very sensitive to our requirements.”

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 5° angle to promote drainage. The universal joints at the top and at the bottom of the extension were required to eliminate any side-loading that the 5° operating angle would create.

Shaw and Shields worked with Vince Rohrig, automation product manager, and Stan Piela, special projects engineer, Flowserve Flow Control, to successfully design field-adjustable hardware for manual and automated operation of the bulge valves regardless of their 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 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 also 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, Flowserve 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 had been received for the bulge valves, Flowserve began receiving inquiries from Bechtel about its capabilities for the “jumper valve” portion of the project. The Flowserve team presented Bechtel with another modified Mach 1 valve featuring Automax stainless steel rack-and-pinion valve automation packages to meet the requirements of this application (Figure 4).

The 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 the intense radioactive levels inside the pretreatment building, the jumper valves were to be operated and repaired remotely by robotic devices. These valves also were specified with radiation-resistant pneumatic actuators, switches and accessories, which were to be mounted directly on the valve bodies.

Unlike the 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 that would enable the 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 that the actuation packages could be removed for access to the top of the valve for cartridge replacement.

Although Bechtel didn’t require another upfront demonstration, several design modifications were required. Space constraints forced Flowserve to propose smaller stainless steel Flowserve Worcester Controls 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 that 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 that the actuators would meet NQA-1 inspection requirements and that Flowserve could guarantee Bechtel 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.”

Roy Johnson is NW regional manager in Cookville, Tenn.; e-mail him at [email protected].

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