The first three technical issues that have prevented construction on key parts of the Hanford Site’s Waste Treatment Plant since 2012 have been resolved, according to the Department of Energy. Work continues on five additional technical issues identified after then-Energy Secretary Steven Chu directed an in-depth look that year at possible problems at the plant. But the three resolved matters “are certainly the three toughest technical issues,” said Bill Hamel, DOE assistant manager for the Hanford vitrification plant project.
Resolution means that engineering work may resume on the Pretreatment Facility for the vit plant, which contractor Bechtel National is building to process up to 56 million gallons of chemical and radioactive waste stored at the DOE site in Washington state. However, construction will not resume until issues are considered closed at the conclusion of the design and engineering work.
The five remaining technical issues are expected to be resolved by the end of 2018, but DOE has not released an estimated date for resumption of construction. Construction halted on the Pretreatment Facility and part of the High-Level Waste Facility due to issues related to high-level radioactive waste. Design and engineering on the High-Level Waste Facility resumed in 2014.
Issues resolved at the Pretreatment Facility are the potential accumulation of hydrogen in the building’s process tanks; the potential for hydrogen accumulation in pipes and nonprocess tanks; and the potential for a nuclear criticality in process tanks. Criticalities could occur if a sufficient number of large, heavy particles of plutonium settled out of waste in processing tanks.
The proposed solution would involve blending or diluting the waste feed to reduce the amount of large plutonium particles in each process batch. The means for accomplishing that will be determined in the engineering phase of the work, but could involve a possible new tank farm facility being called the Tank Waste Characterization and Staging Facility that DOE has been discussing publicly since 2014. A majority of Hanford’s storage tanks do not hold waste with large plutonium particles.
DOE proposes to use periodic ventilation to clear hydrogen accumulation in the head space of Pretreatment Facility process tanks. A revised process-tank design would have a smaller head space so less hydrogen could accumulate and the air volume could be turned over more quickly. Hydrogen accumulation in tanks would be addressed by eliminating some high points in piping where hydrogen might accumulate, along with adding vents to piping where needed.
Engineering studies and nuclear safety evaluations were performed to analyze the three issues, according to DOE. Technical and nuclear safety teams proposed and confirmed the design features, process changes, and safety controls to address the issues, it said. DOE has notified the Defense Nuclear Facilities Safety Board of progress on the three issues. “DOE and the Waste Treatment Plant contractor have performed a comprehensive set of work activities, which now provides us with sufficient confidence to direct the resumption of design activities affected by these technical issues,” DOE said in a letter to the board.
The remaining five issues include determining whether the plant’s pulse jet mixers can keep waste well mixed and that the mixers can be adequately controlled. A full-scale test of the mixers is underway at the Atkins Engineering Laboratory at Washington State University Tri-Cities, was built for Waste Treatment Plant testing. The other remaining issues involve questions about whether corrosion or erosion of metal equipment could shorten the plant’s operating life; making sure adequate equipment is in place to continue operations in the event of equipment failure; performing additional structural analysis of planned tanks within the Pretreatment Facility; and ensuring the ventilation system is adequate.
