The Department of Energy is preparing to restart demolition of the Plutonium Finishing Plant at the Hanford Site in Washington state, after most work was halted after a spread of radioactive contamination in December.
A contractor-led, DOE-overseen management assessment evaluating preparations to resume work is expected to start Aug. 13. It could clear the way to resume removal in September of certain demolition debris left from last year and for the start of actual demolition in October, according to a tentative DOE schedule.
The highly contaminated facility could be torn down to slab on grade and demolition debris removed from the plant’s campus by June 2019, under the schedule. The Tri-Party Agreement, which sets legal deadlines for cleanup at Hanford required the plant to be reduced to slab on grade by September 2017, which was a one-year extension granted in 2016. However, the focus now is on ensuring work is finished without harming workers or the environment.
The plant was used during the Cold War to process Hanford-generated plutonium in a liquid solution into oxide powder or metal pucks for shipment to a nuclear weapons production plant. After two decades of cleanout, demolition began in late 2016.
Last December, discovery of a contamination spread halted work even as demolition of the plant’s Plutonium Reclamation Facility neared completion. The reclamation facility was expected to be the most contaminated part of the Plutonium Finishing Plant.
Subsequent bioassays found 11 workers with internal radioactive contamination. That was in addition to 31 workers found with internal contamination after an airborne spread of contamination during demolition of the plant in June 2017. In addition, personal and government vehicles were contaminated, and some were driven out of Hanford. Very small amounts of airborne contamination were detected in 2017 several miles away from the plant, including at the Rattlesnake Barricade near public Highway 240 and the Columbia River.
A new plan, developed with assistance from an expert panel assembled by DOE, calls for continued open-air demolition of the remainder of the plant. Tenting or another type of cover for parts of the plant being demolished were considered, but the effort would take too long, said Karen Wiemelt, a senior vice president at Jacobs Engineering Group, which owns the DOE contractor doing the work, CH2M Hill Plateau Remediation Co. Designing, procuring, and constructing a tent or other structure could take a couple years, leaving the contaminated building partially demolished and vulnerable to animal intrusions. “It makes far more sense to proceed very deliberately and with enhanced controls,” she said.
The new demolition plan has been divided into lower-risk work, which would be done first, followed by higher-risk work. Work would restart with load out of demolition debris now on the ground around the plant’s main processing segment. Demolition would begin on less contaminated parts of the main plant and a vault used to hold plutonium. The estimated radioactive material at risk, or radioactive material, in the lower-risk work would be 10 grams total.
The Washing state Department of Ecology, a regulator on the project, agreed last month to lift its January stop-work order for lower-risk work after all concerns of the expert panel and any additional concerns raised in the August management review were addressed. However, it will not lift the stop-work order for the higher-risk work until lower-risk work is completed and the effectiveness of controls for that work is evaluated.
The higher-risk work could start as soon as early 2019, beginning with demolition of the A and C lines in the main processing plant and infrastructure in utility tunnels beneath the lines. Lines of glove boxes were used for plutonium processing. Although most of the glove boxes were removed during preparations for demolition, that area of the plant remains contaminated from spills that were sometimes painted over or covered with tile. Ventilation will be used to help contain contamination and keep it from spreading during demolition.
Once the remainder of the main plant is down, work will advance in the spring to load out the rubble left at the Plutonium Reclamation Facility. The rubble is covered with several inches of soil and gravel to contain contamination. Before it is removed, the rubble pile will be soaked with water to turn it into a muddy slurry to prevent radioactive contamination from becoming airborne. The rubble pile contains most of the remaining radioactive material at risk, an estimated 238 grams, and the A and C lines and utility tunnels contain 64 grams.
Other changes to work will include monitoring for the spread of radioactive material in more locations and more frequently, Wiemelt said. Demolition will be done sequentially rather than at more than one area at a time, a strategy used earlier to try to catch up to the schedule. Debris piles will be allowed to accumulate for no more than one day before being loaded out. In addition, fixative will be applied to contain radioactive particles to manufacturer recommendations. In the past some fixative was diluted to make it easier to apply.
