Federal officials are scrutinizing a Mississippi nuclear plant after an unplanned shutdown, a development following years of stops and starts at the facility. But the plant's operator and a state regulator said they see no cause for reliability concerns stemming from the most recent incident.

The U.S. Nuclear Regulatory Commission announced Dec. 18 that it began a special inspection at the Grand Gulf facility in Port Gibson, Miss., near the Mississippi-Louisiana border. The plant, owned by Entergy Corp. subsidiary System Energy Resources Inc. and Cooperative Energy, had experienced an unexpected increase in reactor power six days earlier and decided to shut down as a precautionary measure.

This development is not the first of its kind for Grand Gulf, which has dispatched at low levels for a nuclear plant over the past two years. Grand Gulf was taken offline for four months in late 2016, first for equipment maintenance and then for a facilitywide review, Entergy spokesperson Mike Bowling said in an interview.

In November, the NRC notified Entergy in a letter that it was downgrading the safety rating of Grand Gulf from "Green," its safest rating, to "White," its second-safest, citing "five unplanned downpower events that occurred from the fourth quarter of 2017 through the third quarter of 2018."

The NRC said in a statement that two surveyors are spending a week on-site to take record of what occurred. "We don't know" what the equipment issues were, agency spokesperson Victor Dricks said in an interview.

"They've had an unusual number of unplanned shutdowns over the last year or two, but all of different descriptions," Dricks added. "They seem to be related to the material condition of the plant and operator issues."

Entergy is aware of the problem "and is taking corrective action ... They're making a significant investment in the material condition of the plant," Dricks said.

Bowling said Entergy workers identified last week that a turbine bypass valve was "opening and moving in an off-normal way," adding that the problem has "basically been fixed and repaired." While the company cannot provide an exact timeline for when Grand Gulf will come back online due to security and business concerns, "folks should expect us to return fairly soon," Bowling said. "We're prepping for that right now."

"We welcome their involvement," Bowling said of the NRC.

Regulatory perspective

While the Mississippi Public Service Commission has limited jurisdiction over Grand Gulf, it oversees Entergy in the state. "We are following it closely," Commissioner Cecil Brown said in an interview.

According to the Democratic regulator, the PSC has met with Grand Gulf's operators and Entergy representatives twice in the past several days. He added that a commission staffer attended a recent Midcontinent Independent System Operator meeting where Grand Gulf was discussed.

"We've got an engineering firm that's been over there for several months now looking at their operations and will be giving us a report in January," Brown said. "We're not taking any action at this point, just trying to make sure we understand from their perspective what's going on."

There are no reliability concerns with Grand Gulf being offline right now, Brown said, as MISO manages supply and demand across its 15-state territory. The plant cannot be immediately turned back on as the process takes time and needs to be staggered. "I don't see a large outage on the horizon."

Brown likened Grand Gulf to an older house that needs repairs. "Things like that are going to happen." Entergy has "identified where they think their weaknesses are and they say need to be concerned about, and they're working hard."

Past problems

The Dec. 12 incident was yet another for Grand Gulf, a 1,428-MW facility that first came online in 1985. The reactor provides electricity via power purchase agreements to Entergy utilities in Mississippi, Louisiana, New Orleans and Arkansas.

According to S&P Global Market Intelligence data, Grand Gulf logged a capacity factor of 59% in 2017. Nuclear units, with their high output that provides emissions-free baseload power, usually achieve capacity factors close to 100%.

Bowling said Grand Gulf was taken offline in September 2016 for a pump repair, with Entergy management then deciding to take extra time before reconnecting the plant to the grid to evaluate overall operations. That year saw Grand Gulf shut down "several times" for required maintenance, he added.

"Before ending the maintenance outage ... plant employees and leadership took a deliberate, thorough and conservative review of processes, procedures and protocols to ensure we are operating to high standards," Bowling said. "The decision resulted in a longer period offline — through late January 2017 — but it ensured worker knowledge and training are at high levels."

Grand Gulf's capacity factor in 2016 was 47%.

"I feel as good as I can feel knowing the facts," Brown said. "I would prefer it was running 98%, but it's not. We hope it soon will be and that we won't have any more problems like this. I like what I've seen in terms of [Entergy's] plan."

The extended outage saw more than 3,100 hours of training in operations, maintenance and technical fields, Bowling said. A year after that offline time, the plant underwent a scheduled refueling outage during which other improvements to equipment were made. The Dec. 12 outage was not related to either of the previous events, Bowling said.