Exclusive: McGuire inspection reveals safety violations

Valve maintenance and radiation-area access failures follow earlier problems reported by WCAB News. NRC rated the latest violations as having very low safety significance.

An inadequate maintenance procedure left a containment isolation valve unable to fully close at Duke Energy’s McGuire Nuclear Station, while a separate inspection found a radiation-area door lock fell apart when employees tested it, according to a federal report reviewed by WCAB News.

The Nuclear Regulatory Commission documented both violations in an Oct. 14 inspection report covering July through September at the two-reactor plant in Huntersville.

Both were rated “Green,” meaning they had very low safety significance. A second containment isolation valve remained functional, overall containment leakage limits were not exceeded, and the door-lock failure did not involve a radiation overexposure.

The findings add to WCAB’s reporting on maintenance, operating procedures, and federal oversight at McGuire. They involve safeguards intended to limit radioactive releases during an accident and control access to radiation areas.

Valve passed initial test, then failed

The valve problem surfaced March 30 during a periodic leak test on Unit 2.

The affected valve helps isolate the reactor’s containment during a potential accident. During testing, leakage was so substantial that the affected section could not reach test pressure.

Duke’s investigation found that a mechanical stop prevented the valve from fully seating. The problem originated with a September 2024 rebuild, according to the NRC.

The maintenance procedure required a minimum clearance but did not provide adequate allowance for measurement uncertainty and the gradual thinning of an internal diaphragm.

The valve passed testing immediately after the rebuild. As the diaphragm thinned during service, the clearance became insufficient, preventing a tight seal.

A second valve serving the same containment opening passed its leak test. Inspectors cited backup protection and compliance with overall containment leakage limits in determining the finding’s very low safety significance.

Duke rebuilt the affected valve with increased clearance and successfully tested it. The company also revised its maintenance procedure on Aug. 6 and initiated checks for similar conditions.

Radiation-area lock failed during check

The second violation surfaced Aug. 22 when plant employees tested a Unit 1 door during a weekly check.

The door opened, and its locking mechanism fell apart.

Inspectors found that the lock was improperly installed and that Duke’s procedures lacked instructions to ensure radiation-area door locks were properly installed, used, and maintained.

Duke identified the violation and entered it into its corrective action program. Inspectors determined it did not involve a radiation overexposure.

The NRC is treating both issues as non-cited violations under its enforcement policy. Both remain documented violations, per agency requirements.

Earlier WCAB coverage documented maintenance problems

In February, WCAB News reported on a separate McGuire inspection that documented procedural shortcomings and deferred maintenance.

That report described a degraded relief valve condition first documented in 2019.

Maintenance was deferred across multiple outages before the condition worsened into a leak of about four gallons per minute outside containment in October 2025, prompting a manual shutdown of Unit 2.

The valve was replaced, and regulators determined the incident had very low safety significance. The earlier inspection also identified inadequate operating instructions that allowed temperature-change limits to be exceeded in safety-related equipment.

Despite those findings, WCAB reported in March that McGuire remained in the NRC’s highest performance category following its 2025 annual assessment.

Both reactors were in the “Licensee Response Column,” a category allowing routine federal oversight when findings have no more than very low safety significance and performance indicators remain within expected ranges. That assessment covered 2025, before the latest inspection period.

WCAB has also reported on NRC decisions allowing Duke to withhold proprietary portions of reactor safety analyses. Those decisions concern public access to technical information; the NRC retains access to the complete material for its review.

The latest inspection report states that inspectors retained or documented no proprietary information.

Unit 1 shut down Sept. 5 for a planned refueling outage and remained offline through September. Unit 2 operated at or near full rated power throughout the inspection period.

Duke has 30 days from the report’s date to contest the violations or their significance.

You may read the report here.

Regional significance

Nearly 285,000 people live within 10 miles of Duke Energy’s McGuire Nuclear Plant in Mecklenburg County, officials say — and while Rutherford County falls just outside the 50-mile zone that emergency management planners monitor, local fire department sources say it is still close enough to raise concern. FEMA could not provide an exact number of people who might be impacted in the region outside of the 10-mile zone when asked by WCAB News at an August 2025 briefing.