Hanford workers started pumping waste from the nuclear reservation’s oldest double-shell tank Thursday afternoon, beating a state of Washington deadline by one day.
The state Department of Ecology had ordered DOE and its contractor, Washington River Protection Solutions, to start emptying waste from Tank AY-102 by March 4 and finish the work within a year. The tank is leaking radioactive waste from its inner shell into the space between its inner and outer shells.
“Several thousand gallons of supernate waste already have been retrieved,” said Mark Lindholm, the contractor president, in an afternoon message to employees.
Supernate is the liquid waste within the tank, which makes up the majority of the tank’s contents. An estimated 650,000 gallons of liquid sits above an estimated 150,000 gallons of radioactive sludge at the bottom of the tank.
Removing the liquid is expected to be the comparatively easy part of the waste retrieval work. It could be completed early next week if work goes smoothly.
The liquid would have been removed before now, but was needed to help cool the sludge, which generates heat as it radioactively decays at the bottom of the tank. Heat can increase corrosion rates in the tank and contribute to generating potentially flammable hydrogen gas.
Washington River Protection Solutions will start the retrieval of sludge with sluicing technology that’s been used for more than a decade to empty waste from Hanford’s single-shell tanks and then move to a newer extended-reach sluicing system by late spring or summer.
The work in the double-shell tanks is complicated by a system of 22 pipes extending from the head space within the top of the underground tank down to the bottom of the tank. They were intended to help cool the tank by allowing heat to rise.
As work starts to retrieve the sludge sometime this month, precautions will be taken to protect workers from chemical vapors from the waste.
The liquid waste is being transferred through underground piping to a double-shell tank near the Hanford evaporation facility, which is used to reduce liquids to free up space in the 27 double-shell tanks that continue to be used to store waste.
The sludge will be moved in an above-ground line to a double shell tank near the vitrification plant, which is being built to glassify tank waste for disposal. Concrete shield blocks have been placed around the transfer line.
Barricades will be set up to restrict access to active work areas where the possibility of vapors may be increased, and industrial hygienists will be monitoring for vapors. Exclusion zones will be set up around exhauster stacks and workers must used supplied air respirators to enter those areas.
“The state is pleased with the efforts of DOE and Washington River Protection Solutions to meet the terms of the settlement agreement, even starting waste removal a day before the deadline,” said Tom Tebb, acting manager for the Washington Department of Ecology’s Nuclear Waste Program, in a statement. “The resources committed to removing waste from AY-102 highlights the priority DOE and its contractor put on keeping this project on track.”