KENNEWICK — Three radioactively contaminated underground structures at high risk of collapse on the Hanford nuclear reservation could be filled with concrete-like grout within a year.
The Department of Energy has concluded they could fail and release radioactive contamination.
“A number of structures are overstressed and at risk of age-related failure, which could result in a release of contamination with impacts to human health and the environment,” DOE said in a letter last week to the Environmental Protection Agency, a Hanford regulator.
Two of the structures, a trench and a tank at the center of the site, are estimated to be contaminated with a combined 170 to 255 pounds of plutonium.
DOE could award a contract for grouting as soon as March, according to the letter.
It has not declared an emergency, but is calling the grouting a “time-critical” action, which allows work to proceed during a public comment period that could begin in late March.
The trenches and settling tank were all used at the Plutonium Finishing Plant in central Hanford, where plutonium from fuel irradiated in Hanford reactors arrived in a liquid solution into buttons the size of hockey pucks for shipment to weapons plans.
Earlier this month workers finished demolishing the Plutonium Finishing Plant down to the ground, but below-ground structures still need to be addressed.
Highest risk of collapse
After a partial collapse of a waste storage tunnel at Hanford’s PUREX plant in May 2017, DOE and its contractor CH2M Hill Plateau Remediation Co. analyzed other old and contaminated structures to determine if they were at risk of collapsing.
They determined that the three below-ground structures at the Plutonium Finishing Plant presented the highest risk, requiring stabilization to prevent a collapse and the potential to spread contamination.
The structures include a settling tank and two cribs, sometimes called trenches, where liquid waste from the Plutonium Finishing Plant were poured into the ground.
A Governmental Accountability Office report released last week also looked at the larger of the two cribs and the settling tank, saying that the Z-9 crib might not be cleaned up until 2034 and the settling tank might not be cleaned up until 2028.
The Z-9 crib is contaminated with an estimated 105 pounds of plutonium and the nearly 100 cubic yards of radioactive sludge in the settling tank contains an estimated 65-150 pounds of plutonium.
The PUREX tunnel that collapsed and the second waste storage tunnel at the plant have both been filled with grout, in a process similar to what’s proposed for the Plutonium Finishing Plant underground structures.
According to preliminary information posted by DOE at Hanford.gov, grouting the three structures most at risk now would not preclude more cleanup in the future.
Support for grouting
Hanford Communities, a coalition of Hanford-area-local governments, supports the grouting plan.
“Injecting engineered grout into the void space of all three structures will insure that the roofs will not collapse and provide a pathway for contamination to be released into the environment,” Hanford Communities said in a statement Monday.
The structures pose a greater risk even than the second Hanford PUREX tunnel, which was filled with grout to prevent a collapse, it said.
Hanford Challenge, a Seattle-based Hanford watchdog group, does not object to the grouting as a short-term solution, but it should not be a substitute for complete cleanup, said Tom Carpenter, executive director.
Here’s what DOE plans:
• The Z-9 crib, which operated from 1955 to 1962, would be filled with about 4,000 cubic yards of grout, making it by far the largest of the three proposed grouting projects.
The crib is a 20-foot deep hole sloping to a 60-by-30-foot floor, where about 1 million gallons of waste from the plant was poured. It has a concrete roof, supported with six concrete columns.
The grouting could be completed in the fall or early winter of 2020.
• The Z-361 Settling Tank, which was used from 1949 to 1973, would be filled with 400 cubic yards of grout.
It is a reinforced concrete structure that is 28 feet long, 15 feet wide and up to 18 feet deep. Contaminated liquids were sent to the tank to allow solid waste to settle out.
A video inspection in 1999 showed cracking in the interior roof of the tank, dissolving of the interior steel liner and deterioration of the concrete sidewall of the tank.
Grouting could be completed this summer.
• The Z-2 Crib, which was used from 1949 to 1969, would be filled with 140 cubic yards of grout.
No estimate of plutonium in the crib was immediately available, but waste with about 15 pounds of plutonium was discharged to the Z-2 Crib and its companion Z-1 Crib. Overflow from the Z-2 Crib went to the Z-1 Crib.
The soil on top of the Z-1 Crib has sunk and extra soil was added there earlier.
Both cribs are open-bottomed boxes about 12-feet square and 14-feet tall.
DOE would like to have the Z-2 Crib grouted by summer 2020.
Tank, cribs cleanup plans
A final cleanup decision has already been approved for the three structures, and DOE believes the grouting will not interfere with those plans.
The structures of the two cribs are planned to be removed and the contaminated soil beneath them removed and treated for permanent disposal.
The plan for the settling tank is to remove the remaining sludge from the tank and grout it in place.
DOE’s proposed schedule to begin work starts with a contract award for grouting in March and testing of grouting equipment in April and May.
A video inspection of the underground structures could be done in May, with grouting beginning in July for the smallest structures.
That would likely but the start of grouting after the end of a 30-day public comment period. DOE also is expected to announce a public meeting in March to explain the project.
