Management relied too heavily on near real-time continuous air monitors (CAMs) to check for airborne radioactive particles during demolition of the Hanford Site’s Plutonium Finishing Plant, according to the root cause evaluation for the December spread of radioactive contamination from the project. Hanford cleanup contractor CH2M Hill Plateau Remediation Co. on Thursday submitted its evaluation report for review by an expert panel assembled by the Department of Energy and released it to the public.
Confidence in the CAMs contributed to decisions on the pace and methods of demolition, according to the report. The CAMs issued an alarm in June, after which Hanford workers were ordered to take cover indoors, when airborne radioactive particles were detected. But the system did not alarm during the contamination spread from Dec. 14 to 18, possibly because heavy particles quickly settled out of the air.
The December contamination spread resulted in at least 11 workers testing positive for inhaled or ingested radioactive particles. About 36 vehicles were contaminated, including some cars driven off Washington state complex including to worker homes. The contamination spread beyond the plant and across a road in central Hanford. Testing by the Washington state Department of Health that combines air samples collected over a number of months found very low levels of contamination near the Columbia River, not far from where the public is allowed.
“The cumulative impact and significance of the events leading up to the December 2017 event were not recognized,” the report said. “Some amount of contamination is anticipated during open-air demolition, and each event was treated as a discrete event, individually discussed and actions taken.”
Response to individual events became routine, and the events began to seem normal over time. As a result, risk was not fully analyzed, documented, or controlled, according to CH2M.
The contractor in November 2016 began demolition of the facility used during the Cold War to convert liquid plutonium into plutonium “buttons” and oxide powder for use in the U.S. nuclear arsenal.
Fixative sprayed on the higher elevations of the most contaminated part of the plant, the Plutonium Reclamation Facility, was diluted, which was not recommended by the fixative manufacturer, the report said. It was too thick to be pumped if not diluted. A 25-75 dilution had been common before the June contamination incident. After that incident policy was changed to dilute the fixative by only 50 percent, but no technical basis or analysis was done to confirm the diluted fixative would be durable, the report said.
During initial demolition, building rubble was cut into smaller pieces and loaded out before much of it could accumulate. But plans changed as demolition of the Plutonium Reclamation Facility progressed. Exhausters were placed inside the building to create negative air pressure to help contain contamination, but the exhausters became less effective as more of the building was demolished.
A decision was made that it would be easier to control rubble on the ground than on the partially demolished structure, and the speed of demolition increased to a faster pace than rubble could be loaded out. The plan was to cover the rubble with fixative initially and eventually with a layer of soil.
Hanford officials overestimated how well the fixative and soil would contain radioactive particles, the report said. In one example, fixative sprayed on the rubble might hit the front side of a piece of debris, but not the back side. CH2m also said a scientific dispersion model used for the project did not cover the possibility of large amounts of debris accumulating.
“The project was in the challenging position of achieving safe and controlled demolition while attempting to maintain schedule progress, which included completion of the TPA (Tri-Party Agreement) milestones and contractual commitment dates,” the report said.
Management did not adequately address all employee concerns and suggestions, and opportunities may have been missed for better oversight of the project, the report said. Some workers shared their experiences on other Hanford demolition projects or raised issues about the fixative, it noted.
The report lists 42 corrective actions. They include developing models that account for larger radioactive particles being swept up on windy days; completing a documented evaluation of the appropriate use of fixative; developing training on reliance on CAMs; and establishing requirements that using tracking of radiological data to support decisions related to demolition.
CH2M missed the September 2017 to have the Plutonium Finishing Plant down to slab on grade, but Hanford regulators have emphasized safety over accelerating the pace of work. The milestone had previously been pushed back from September 2016.
Demolition is currently halted at the plant and will not restart until a new demolition strategy is approved. The work will be led by Jacobs Engineering, which acquired CH2M in December.
The corrective actions, if agreed upon by the DOE expert panel, will be implemented for the remainder of demolition. They also are expected to be used by CH2M as it works on other high-hazard projects, including cleanup of the highly radioactive spill under the Hanford 324 Building.
