VALVES FOR handling radioactive waste must sometimes include unconventional solutions. That’s what happened when Flowserve Corp. recently designed and implemented innovative valve and automation solutions for control, isolation, and treatment of radioactive waste slurries at the Hanford Waste Treatment Project (WTP) in southeast Washington State.
Hanford has one of the world’s largest concentrations of radioactive waste, which is the legacy of 45 years of plutonium production for nuclear weapons. The site contains 53 million gallons of high-level radioactive waste, 60% by volume of the nation's total, stored in 177 old, deteriorating underground tanks, located 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, and 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 downstream.
To remediate this hazard, the U.S. Department of Energy (DOE) commissioned a project for treating and converting the high-level radioactive waste to glass logs. “Vitrification” is considered the most effective treatment process for this type of contamination because it produces a durable, stable form that incorporates and immobilizes radioactive waste. Once immobilized, the high-level radioactive portion of the WTP’s waste will be temporarily stored at Hanford 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.
DOE’s Office of River Protection contracted with Bechtel National Inc. in December 2000 to build the WTP, which it’s estimated will cost $5.7 billion and take up to 10 years to complete. It will be the world’s largest vitrification facility, and will include three nuclear facilities: one for pretreatment, a second for low-activity waste vitrification, and a third for high-level waste vitrification. Much of the project focuses on waste handling, so worker safety is never breached, and isolating and treating the waste is achieved.
In the initial treatment process, specialized valves were needed in WTP’s “bulges” containment vessels. 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 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 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.
|FIGURE 1: BIG WASTE TREATMENT|
To treat its 53 million gallons of high-level radioactive waste, the Hanford Waste Treatment Project (WTP) will feature the world’s largest vitrification and pretreatment facilities, including Flowserve’s plug valves and valve automation systems.
When it learned that Bechtel was favoring top-entry style ball valves for the bulges, Flowserve’s team advocated for high-performance plug valves instead. “Plug valves work better in slurries than ball valves,” says Mark Shaw, Flowserve Flow Control’s western regional manager. “Plug valves have adjustable positive sealing upstream and downstream and 360º around the top of the plug. By design, plug valves have no cavities where material can collect and/or solidify. Plug valves handle slurry more effectively because they have more than double the sealing area of a typical ball valve. We worked closely with Bechtel, and focused on designing and building a solution to give Bechtel what it needed,” says Shaw. “At that time, that solution didn’t exist in our product line.”
Based on its Durco G4 plug valve’s 35-year history tough-slurry and nuclear-power applications, Flowserve recommended its soon-to-be-released Durco Mach 1 top-entry plug valve, which could be modified for the remote operation and repair that Bechtel required. Flowserve also designed Mach 1 to allow a variety of valve seating materials, including the ultra-high molecular weight polyethylene (UHMWPE) needed to stand up to WTP’s radioactive slurries. “Mach 1 gave us the flexibility to build a solution for Bechtel,” says Fred Shanks, Flowserve Flow Control’s senior product engineer. “It was a remotely repairable valve that could have an UHMWPE seat that could be easily removed.”
In addition, Mach 1 required some added modifications at Flowserve’s facility in Cookesville, Tenn., to make it remotely repairable and fully radiation resistant. “UHMWPE is highly wear and radiation resistant, but 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.”