The Department of Energy has resolved three key technical issues that have delayed construction on part of the Hanford vitrification plant since 2012, it announced Friday.
DOE still has five more technical issues to resolve at the plant, “but these are certainly the three toughest technical issues,” said Bill Hamel, DOE assistant manager for the project.
Some design and engineering work now can resume at the plant’s largest building, the Pretreatment Facility.
The plant is being built to turn up to 56 million gallons of radioactive and hazardous waste into a stable glass form for disposal. The waste is left from the past production of plutonium for the nation’s nuclear weapons program.
The plant’s most recent estimated cost of $16.8 billion does not include any changes that could be required by resolving technical issues.
Former Energy Secretary Steven Chu halted work on parts of the plant that would handle high-level radioactive waste in 2012 until technical issues were addressed. Construction has continued on other parts of the plant, which could begin treating low-activity radioactive waste as soon as 2022.
“Since that time, DOE and the (vit 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 recent letter to the Defense Nuclear Facilities Safety Board, which shared Chu’s concerns.
The first three issues are resolved, but not closed. DOE has proposed a path forward that will be addressed in design and engineering of the facility before issues are considered closed and construction resumes.
No date has been released for the restart of construction on both the Pretreatment Facility and part of the High Level Waste Facility at the plant, but the five remaining technical issues are expected to be resolved by the end of 2018.
Design and engineering work resumed on the limited areas of the High Level Waste Facility that were affected in 2014.
DOE now is confident it has a plan to make sure that large, heavy particles of plutonium do not settle out in processing tanks within the Pretreatment Plant, causing the potential for an unplanned nuclear reaction.
It will address the issue by adjusting the waste feed from tanks that may have the particles. It could blend waste with the particles with waste from other tanks that do not have the issue.
The blending would limit the amount of plutonium particles in each batch to prevent enough plutonium from accumulating to trigger an unplanned reaction.
The work might be done in a separate facility yet to be built, but no decision has been made.
The other two issues that have been resolved are related to the buildup of hydrogen generated by waste in the Pretreatment Facility, which could potentially lead to an explosion.
It could build up in tanks in the facility or piping. They would be in areas of the plant, called black cells, where people are not planned to enter once the plant starts treating high-level radioactive waste.
The main risk for a hydrogen buildup in Pretreatment Facility tanks would be during a shutdown with waste left sitting in a tank.
DOE proposes a new tank design with a smaller head space so less hydrogen accumulates and the volume of the air in the head space could be cleared quickly. Periodic venting is planned.
An evaluation of piping will be done. In places where hydrogen accumulates a vent could be installed to flush it out. Since hydrogen is lighter than air, high points in piping might be eliminated.
DOE’s plan is to make as few changes as possible to construction already done at the facility.
Remaining technical issues include determining whether pulse jet mixer can keep all high-level radioactive waste well mixed and the control system is adequate. Full-scale testing of the pulse jet mixers began in December at the Atkins Engineering Laboratory at WSU Tri-Cities.
The pulse jet mixers are designed to have no moving parts that would require maintenance after they start mixing radioactive waste and become contaminated. They work like a turkey baster, sucking up mostly liquid waste within the tank and then expelling it, mixing the waste in the process.
The other four remaining issues include preventing corrosion and erosion of equipment that could shorten the plant's planned 40-year life; making sure adequate equipment is in place in case of equipment failure; performing more structural analysis of the planned tanks within the Pretreatment Facility; and ensuring the ventilation system meets requirements.
The Pretreatment Facility, which will stand 120 feet tall and have a footprint of 540 by 215 feet, is planned to separate waste into low-activity and high-level radioactive waste streams for separate treatment.
The waste will be vitrified, or turned into glass, at the plant’s High Level Waste Facility and the Low Activity Waste Facility.
All parts of the plant are not expected to be operating together until 2036, but a new facility is planned outside the vit plant campus to prepare some low-activity waste for treatment at the Low Activity Waste Facility before the Pretreatment Facility is finished.