Another issue has come under scrutiny at Stack 110, a significant emissions point in the 9212 uranium-processing complex at the Y-12 nuclear weapons plant in Oak Ridge, Tenn.
According to a March 25 report by staff of the Defense Nuclear Facilities Safety Board, a monitoring team with Y-12 contractor Consolidated Nuclear Security noted that enriched uranium dust was collecting at a faster-than-expected rate in the filters associated with Stack 110.
Non-destructive measurements of the filters identified the accelerated buildup of uranium.
“These filters collect dust from the ventilation of the vacuum induction melt furnaces and other E-wing operations and were part of the upgrades that replaced the bag filter house in December 2013,” according to the weekly activity report, the latest from Y-12.
The staff report said the system has “backflow and internal air-pulse features” that are designed to remove any loading of uranium dust on the filters. However, it was also noted that the feature has not yet provided the expected reduction of uranium dust on the filters.
Checks and measurements are conducted at the stack filters on a periodic basis to “ensure nuclear criticality safety and security loading limits are not exceeded,” the DNFSB report stated.
The report said the engineering team at Consolidated Nuclear Security has started measuring the uranium buildup more frequently. In addition, CNS has ordered some replacement filters “in anticipation of the need to replace the filters in a few months.”
Besides that, the Y-12 contractor is working with the ventilation manufacturer to come up with filters that will improve the “backflow feature” to keep fissile material from collecting on filters at Stack 110.
A Y-12 spokeswoman did not immediately respond to questions about whether new filters have since been installed at the site.
There have been other issues of concern at Stack 110, where a couple of stacks were consolidated a few years ago as part of a program to reduce nuclear risks at Y-12. The 9212 complex is Y-12’s oldest production facility and is targeted for replacement by 2025.
Earlier this year, uranium casting operations were temporarily halted at Building 9212 after it was discovered that a couple of feet of water had collected in a “discharge tube” below Stack 110’s dust collector.
That finding in January raised questions about nuclear criticality safety.
CNS spokeswoman Ellen Boatner said the casting operations later resumed after that situation was investigated. She said it was determined that the water did not pose a nuclear safety concern, “but it was considered an unusual condition.”