Air ducts associated with a Holden Gas Furnace at Y-12 last month reportedly had a build-up of uranium particles that exceeded nuclear safety limits, prompting a temporary pause in operations associated with the recycling of highly enriched uranium.

The issue was reported in a recently released May 23 staff memo by staff of the Defense Nuclear Facilities Safety Board assigned to the Oak Ridge plant.

The ventilation duct systems are associated with the furnace and other operations in the plant’s 9212 uranium-processing facility.

The DNFSB staff memo said Consolidated Nuclear Security — the government’s managing contractor at Y-12 — discovered the back-up in the duct while preparing the furnace for “production-scale processing” of briquettes containing enriched uranium.

The CNS team at 9212 asked workers to  perform additional surveys to confirm the amount of “hold-up fissile material” in the furnace’s ventilation exhaust ducts. Those surveys showed the uranium particulates exceeded the administrative limits for nuclear criticality safety, the report said.

Y-12 spokeswoman Ellen Boatner said CNS was aware there was a build-up of uranium in those ducts and had been monitoring them over time.

The DNFSB memo said uranium-holdup in the ventilation duct was attributed to “roughly 50 years of (furnace) operations.” The backup was reportedly  not deemed to require cleaning until the recent measurements were taken.

It is not clear how much uranium was housed in the ducts.

According to the report, the shift manager at 9212 placed operations at the Holden Gas Furnace on hold while a Y-12 team worked “to determine a path forward.” The report said Y-12 maintenance personnel “cleaned a flame arrester-type filter” to reduce the amount of fissionable material.   “But that effort was only partially successful in restoring the system to below (nuclear criticality) limits,” the report stated, but other measures were taken later.

Boatner last week said the operations at the furnace had resumed.

Asked about the briquettes that wer being heated in the oven, Boatner said, “A briquette is material that has been compacted into a small brick-like shape. It is placed in the furnace as part of the recovery process that captures enriched uranium for reuse.”

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