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 facilitys 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 DOEs 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. governments largest capital construction project (Figure 1).
Figure 1. The U.S. governments biggest construction project: $5.7 billion for Hanfords waste treatment project.
When completed, it also will be the worlds 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, Flowserves 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 didnt allow for remote repair and therefore did not meet the requirements of the WTP project.