The prime contractor for the National Nuclear Security Administration’s Y-12 National Security Complex continued to grapple with a fix for a hydrogen fluoride system until earlier this month — well after an April leak that prompted an evacuation of the agency’s main uranium processing building.

The system in Building 9212 “returned to operation on Monday, June 10, 2019,” site operator Consolidated Nuclear Security (CNS) told Weapons Complex Morning Briefing on Tuesday.

The restart followed some separate problems with a leaky “section of piping and valves” located in the system between “two failed rupture discs in the vaporizer enclosure,” according to a Friday report from the federal Defense Nuclear Facilities Safety Board (DNFSB). Rupture discs allow gas to escape from upstream plumbing.

Y-12, which assembles and disassembles the uranium-fueled secondary states of thermonuclear weapons, uses hydrogen fluoride in materials production, site operator CNS has said.

The plumbing nearby the rupture discs failed repeatedly in post-maintenance tests after the April incident, the DNFSB reported Friday.

The problematic piping the board described is not the the leaky calibration valve blamed for the April 4 alarm that prompted CNS to evacuate Building 9212 for a couple hours. Nobody was exposed to hydrogen fluoride during that incident, and CNS has since fixed the valve leak.

Consolidated Nuclear Security is on the hook to refurbish secondary stages for active nuclear weapons as part of planned and ongoing life-extension programs. At the same time, the contractor is building the Uranium Processing Facility to replace Building 9212. The NNSA says the new facility will cost $6.5 billion and take until 2025 to complete.

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