Nuclear regulators are investigating why Westinghouse Electric Co. ended up with three times the safe amount of uranium stuck inside a scrubber at its nuclear fuel factory in Columbia, S.C., and why it took the company more than a month to notify regulators when the situation should have been reported within 24 hours.

When the Cranberry-based company did contact the Nuclear Regulatory Commission in mid-July, federal regulators sent out a team to investigate, and Westinghouse shut down that portion of the plant. The NRC is still piecing together what happened and might be finished with its investigation in several weeks, said spokesman Roger Hannah.

In the meantime, the agency has deemed the uranium concentration was high enough that there might have been potential for an uncontrolled nuclear reaction that could have caused a small explosion. Last week, it sent a memo to Westinghouse outlining what the company will need to do before it can apply to restart that portion of the plant.

The NRC and Westinghouse have stressed that there were no health- or safety-related consequences from the accumulation of uranium.

The Columbia fuel plant makes fuel assemblies and components for commercial nuclear power plants.

The uranium was found in a scrubber in the plant’s chemical area, which is staffed by 170 employees. They are temporarily not working as the investigation proceeds.

The scrubber pulls in air from processing equipment in the area and filters out particulates, including uranium.

Westinghouse spokesperson Courtney Boone said the company does an annual, external inspection of the scrubber. The last one, performed in late May, warranted a more extensive probe and a cleaning, she said.

On May 31, employees cleaned the scrubber. The debris removed from it was analyzed to get an accurate read on how much uranium was present. The level was determined to be 87 kilograms, while the safe limit was 29 kilograms.

The company is investigating why it took its employees more than a month to tell the NRC, Ms. Boone said.

A potentially serious incident

Federal regulators have deemed this incident serious enough that it could have resulted in a criticality — a nuclear term for when conditions are right for a nuclear reaction.

“The way a chain reaction occurs is you have to enough material, close enough together, in a particular configuration” along with other conditions such as moisture and pressure that set events in motion, said Mr. Hannah at the Nuclear Regulatory Commission.

In a nuclear power plant, those conditions are desired and meticulously maintained.

“In a fuel facility, you don’t want that to happen,” he said. There, nuclear criticality safety professionals work to ensure such conditions don’t align.

That’s why there are safety limits on the amount of uranium that can accumulate in a particular component before a criticality event is considered possible.

Mr. Hannah said the federal investigation is focused on human performance — how Westinghouse established safety protocols and how it trained its employees to follow them.

“We will look at past actions,” he said. “If they had had something similar, should they have learned [from it]?”

The Columbia facility has been the subject of 11 NRC significant enforcement actions over the past 20 years, some of which involved the accumulation of fissile material.

In 2004, for example, the company found unsafe levels of uranium in several parts of an incinerator in the chemical area. The NRC concluded the company did not properly consider the risk that such build-up could lead to a critical event and therefore didn’t set safety standards for accumulation and failed to monitor the equipment to diagnose if concentrations were getting high.

The agency also learned in the course of its investigation that Westinghouse failed to tell regulators about problematic uranium accumulation found at several other points in the incinerator between 1996 and 2004.

Westinghouse was eventually fined $24,000 for the event and agreed to examine its nuclear safety culture.

Ms. Boone said Westinghouse’s internal investigation will review lessons learned from the 2004 events.

Mr. Hannah said there is no NRC standard for how frequently a regulated company must clean its scrubbers, only that its uranium concentrations must stay below the safety limit.

It’s up to the company to figure out how to adhere to that standard.

Ms. Boone said the scrubber, which was installed in 2002, was cleaned in 2006 and 2009.

On both occasions, the uranium concentrations did not exceed the safety limit, she said. But that limit was lowered in 2009.

In another letter to the NRC sent late last month, Westinghouse reported that it failed to properly check the disposal bags for the scrubber clean-out.

The company also said that nobody from its nuclear criticality safety department was present for the pre-job brief before the cleaning “because the invitation had been sent via e-mail on a holiday weekend.” The cleaning was scheduled for the day after Memorial Day.

Safety culture assessment

Among the steps that Westinghouse has pledged to take in the wake of this incident is to hire an independent third party to carry out a nuclear safety culture assessment. It also disclosed that the Columbia facility is looking for a new manager for its nuclear criticality safety department.

The temporary shutdown is not expected to have an impact on the company’s clients, Ms. Boone said. While Westinghouse has identified one customer that might be affected, she said the company has two other fuel fabrication plants — one in the U.K. and another in Sweden — that can pick up the slack to make sure power plants get their fuel.

“The reality is that we have a global fuel supply system,” Ms. Boone said.

While the chemical area of the Columbia plant is shut down, the much-larger mechanical area — which employs more than 800 workers — is still operating. Both sides are needed to produce fuel assemblies, but the mechanical area can continue to work as long as it has inventory built up from the chemical work done before the shutdown.

Anya Litvak: alitvak@post-gazette.com or 412-263-1455.

First Published: August 17, 2016, 4:00 a.m.