Inspectors found a flaw in a South Carolina reactor’s coolant boundary that fails the code’s acceptance test

Duke Energy Progress told the Nuclear Regulatory Commission on October 15, 2026, that the reactor coolant system pressure boundary at H.B. Robinson Unit 2 in South Carolina did not meet the acceptance criteria of the ASME Boiler and Pressure Vessel Code, Section XI. The condition, logged as Event Notification 58498, was found at 1:05 p.m. Eastern time while the unit was shut down with its fuel removed.

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No power was being produced and the reactor was not critical, so the report describes a flaw caught during an outage rather than a failure in operation. The licensee said the condition would be resolved before the plant starts up again, and it reported no effect on the health and safety of the public or plant personnel.

The flaw at the pressurizer pipe elbow

According to the NRC event notification report, the finding came from ultrasonic testing, a method that sends sound waves into metal to detect internal discontinuities. The licensee’s text gives the location in one sentence: “The flaw is located between the pressurizer and the “A” pressurizer safety valve at a pipe elbow.” The pressurizer is the vessel that holds the pressure of the reactor coolant system, and the safety valve on that line is one of the devices that protect the system from overpressure.

That location is why the event carries a regulatory label that sounds more alarming than the circumstances. The pressure boundary is the set of pipes, vessels and welds that keep reactor coolant contained, and the NRC treats degradation of any part of it as reportable even when the plant is cold and unfueled. The report classifies the event as non-emergency.

ASME Section XI and the acceptance test

The licensee cited ASME Section XI, paragraph IWB-3514, which sets the acceptance standards used when examinations of pressure-retaining components find indications. Section XI is the part of the code that governs in-service inspection of nuclear plant components, and a flaw that exceeds its limits must be evaluated and repaired or otherwise justified before the component returns to service. The NRC report text lists the examination category language but does not give the size or type of the indication, nor does it say how it will be fixed.

Federal regulations lay out the code requirements that plants follow for in-service inspection in Title 10, section 50.55a, which is the rule that makes the ASME code binding on licensees. A finding that fails the acceptance criteria does not by itself mean a leak or a breach. It means the component cannot be accepted as is under the standard, and the owner must act.

Why an eight-hour report for a defueled unit

Duke Energy Progress made the notification under 10 CFR 50.72(b)(3)(ii)(A), an eight-hour category for non-emergency events. The text of that provision covers a nuclear plant whose condition, including its principal safety barriers, is seriously degraded, and the outer deadline is within eight hours of the occurrence. The licensee notified the NRC at 4:56 p.m. Eastern time, a little under four hours after the 1:05 p.m. discovery, and the NRC Resident Inspector was also informed.

Because the reactor was in the defueled mode at zero percent power both before and after the event, the report records no scram and no change in plant status. The practical consequence falls on the outage schedule rather than on safety margins: the unit cannot restart until the flaw is dispositioned, and the licensee has committed to doing that first.

The plant and the rest of the daily report

H.B. Robinson Unit 2 is a Westinghouse three-loop pressurized water reactor near Hartsville, South Carolina, operated by Duke Energy Progress, according to the NRC’s unit page, which lists a licensed thermal power of 2,339 megawatts and a license that expires on July 31, 2030. The plant’s reference history places the site beside Lake Robinson in Darlington County.

The same daily report includes four other entries that have nothing to do with Robinson. They cover a Part 21 report on an ABB valve assembly motor in Flowery Branch, Georgia, a lost tritium exit sign in Boulder, Colorado, a moisture density gauge backed over by a vehicle in Ville Platte, Louisiana, and an automatic reactor trip at Waterford Unit 3 in Louisiana. Each carries its own event number and licensee, and none of them bears on the pressure-boundary flaw in South Carolina.

The open questions for Event 58498 are those the notification leaves unanswered: how large the flaw is, whether the licensee will repair or replace the elbow or analyze it for continued service, and when the unit is due to return to power. Updates would appear in later NRC event reports and in the licensee’s follow-up documents. Until those details are published, the public record amounts to a location, a code citation, a discovery method and a commitment to fix the problem before the reactor makes power again.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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