KENNEWICK, Wash. — Two methods could be developed to treat some of Hanford’s radioactive tank waste that would cost significantly less than vitrifying it, or turning it into a stable glass form at the Hanford vitrification plant, according to a draft report by a panel of experts.
The Washington state Department of Ecology says it is keeping an open mind on the proposed technologies, but has many questions about the determination that they would be “as good as glass.”
Ecology, a Hanford regulator, gave its opinion on the proposed options Thursday in Kennewick as a committee of the National Academies of Sciences met to discuss supplemental treatment of low-activity radioactive waste.
Congress in 2016 ordered the analysis of options for treating some of Hanford’s 56 million gallons of radioactive waste held in underground tanks, which is being done by a panel of experts from Department of Energy national laboratories.
The waste is left at the site from the past production of plutonium for the nation’s nuclear weapons project.
Congress also directed the National Academies to review the analysis, including a draft report released in April.
The $17 billion vitrification plant was planned to treat all of the high level radioactive waste in Hanford’s underground tanks, but not all of the low activity radioactive waste, which makes up an estimated 90% of the waste.
The April draft report looked at supplemental treatment methods for low activity radioactive waste.
Vitrifying the waste, which could be done by expanding the nuclear reservation’s vitrification plant, would have the highest cost at $20 billion to $36 billion, it found.
Encasing the waste in a concrete-like grout would have the lowest cost at $2 billion to $8 billion. The other possibility is steam reforming, which would blend the waste with dry materials at high temperatures to produce ceramiclike particles at a cost of $6 billion to $17 billion.
Steam reforming is the least technically mature of the three processes, and grouting would create large amounts of treated waste for disposal, the preliminary report said.
The Washington state Department of Ecology, a Hanford regulator, has long said it wanted a final waste form that “is as good as glass,” or as protective of the environment, if it is buried in Hanford landfill. Any radionuclides that could escape from the treated waste form — whether grout, ceramiclike pellets or glass logs — over hundreds or thousands of years could contaminate groundwater.
New evaluations described in the preliminary report on supplemental treatment options show that high performance grout and steam reforming might keep radionuclides from escaping better than glass.
The results are contrary to 30 years of previous results, said Suzanne Dahl, Ecology section manager of tank waste treatment. Ecology would need to complete a significant evaluation to concur with results showing grout could be better than glass, she said.
The performance evaluation appears to be based on limited studies, and it is not clear how the grout proposed now would be different than grout previously studied and found to be not as protective of the environment as glass, she said.
It’s also a big step from treating waste in 55 gallon drums to treating it in containers the size of shipping boxes, she said. Thoroughly mixing the waste and grouting materials would be more challenging, and the grout might not set evenly.
Dahl also said she was concerned about the issues that might be encountered as steam reforming technology is further studied and processes are scaled up to the size needed to be used at Hanford.
Ecology’s current priorities include preparing to start treating low activity waste at the vitrification plant by 2023 and completing construction of the plant’s facility to treat high level waste, she said.
Ecology also is watching as DOE investigates ways to prepare high level waste for treatment, Dahl said. New options could be proposed rather than using the 120-foot-tall Pretreatment Facility being built at the plant to separate out a high level waste stream for treatment.
The National Academies committee plans to issue its capstone report as soon as late July on the draft report released last month by national lab scientists. It has already released reports advising scientists on what to include in their study.