Work Underway on Vit Plant Test Facility
In about three weeks the control tower outside the Full Scale Vessel Test Facility at Washington State University Tri-Cities will grow to 90 feet tall, as part of an effort to geometrically mimic conditions at the Hanford Waste Treatment Plant’s Pretreatment Facility. The test facility, also called the EnergySolutions Engineering Laboratory, was built by EnergySolutions to test mixing of high-level waste within the vessels in the Pretreatment Facility. EnergySolutions, which has a Bechtel National subcontract for the testing, donated the new lab to the university in August 2012 and is leasing it back until most testing is completed.
The control tower now is 75 feet tall but will be topped with a control hut in the coming weeks that will be used by operators to monitor and control pulse jet mixers in a tank within the lab. Pulse jet mixers will work like turkey basters in the tanks, sucking up waste and then shooting it back out to disperse the solids as they start to settle in the tank. The control hut, with valves and electronic equipment, will be higher than the tanks inside the test lab, just as the controls at the Pretreatment Facility will sit above the tanks there. “We wanted to emulate all aspects of the design—pipeline length, elevation, diameters,” said Langdon Holton, the Department of Energy’s senior technical authority for the vitrification plant, as some members of the Hanford Advisory Board toured the lab this week. Compressed air will be piped from the tower to pulse jet mixers in a 13-foot diameter, 16-foot-tall tank within the lab’s high bay.
In the first of three phases of testing to be done over about three years, the control system of the pulse jet mixers will be tested. The testing is expected to begin in a few months using a nonradioactive waste simulant and will continue with simulants that become progressively more difficult to keep mixed. To test the limits of the system, the lab has some air piping that includes bends, and some of the piping from the control hut to the tank in the lab is nearly horizontal. As the first phase of testing is mostly completed, the piping and tank will be used to demonstrate the effectiveness of equipment being considered for periodic inspection at the vitrification plant to evaluate metal components. Concerns have been raised that over 40 years of operation of the plant, metal could erode or corrode.
DOE Considering Use of Smaller Tanks
At the same time work is being done at the WSU lab, work also will be done at Mid-Columbia Engineering in Richland, Wash. The commercial facility will be used to make decisions on a new tank design after DOE announced a plan to replace eight planned tanks at the Pretreatment Facility with up to 16 smaller, uniform tanks that could keep waste mixed better. Not all of the tanks would be used when the Pretreatment Facility begins operating, giving it some redundancy in case of problems with tanks in black cells. After a final tank design is selected and a tank manufactured, the third phase of testing would resume at the WSU lab. Former Energy Secretary Steven Chu committed to mixing tests using a full-scale tank to resolve technical issues and give confidence in the design. The lab has a skylight to allow the tank that will be used initially for testing to be lifted out and replaced with the new tank.
Late Built DSTs Had Only Minor Issues
The last eight double-shell waste tanks built at Hanford had only minor construction issues, according to the final construction review report released by the Department of Energy this week. The review concluded that double-shell tanks in the AP Tank Farm were in better condition overall following construction than Tank AY-102, which is leaking waste between its shells. It was the first tank to be built. The interior leak is suspected to be due in part to difficulties with the tank’s construction, prompting a look at the construction history of the other double-shell tanks. The AP Tank Farm was the sixth group of tanks and was built from 1982-86. Some 5 to 12 percent of welds in those tanks required rework during construction, compared to 34 percent in the bottom of the inner shell of Tank AY-102, according to the review done by Washington River Protection Solutions.
The construction reviews became an issue when Sen. Ron Wyden (D-Ore.) obtained the reviews that had been finished by early March and said they contradicted DOE’s statements that construction difficulties on Tank AY-102 were an isolated problem. He concluded that six tanks in addition to Tank AY-102 have construction problems that could increase the risk of leaks and 13 more tanks may have construction problems that will shorten their life span. He has asked Energy Secretary Ernest Moniz to provide a plan to address tank construction issues, including considering building more waste storage tanks. DOE said the interior leak in Tank AY-102 likely was the result of construction difficulties and a combination of high heat waste that is sitting above waste without an added corrosion inhibitor at the bottom of the tank. None of the other double-shell tanks have that combination of waste, according to DOE.
The construction review on Tank AY-102 concluded that “construction difficulties and trial-and-error repairs left the primary tank bottom with residual stresses that could not be foreseen by the designers. These provided a fertile incubator for sustained corrosion to take place.” The Washington State Department of Ecology has ordered DOE to start removing waste from the tank by Sept. 1. Other construction reviews concluded that enhanced inspection was needed on the next three tanks built after Tank AY-102, which included the second tank in the AY Tank Farm and the two tanks in the AZ Tank Farm. Some problems also were found that were similar to those in Tank AY-102 in the next three tanks constructed, those in the SY Tank Farm built from 1974-77. The 13 tanks in the AW and AN Tank Farms, built from 1976-80, also had some issues that leave room for uncertainty in long-term tank integrity, the reviews said.
