A possible defect in safety-related electric motors has been traced to exactly one nuclear plant in the United States: Palo Verde, the three-reactor station near Tonopah, Arizona. The finding sits in an updated federal event report, number 58330, that the Nuclear Regulatory Commission posted with an Oct. 20 update. The motors drive valves, and the manufacturer says the fault was caught during commissioning of new equipment, not during plant operation.
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The report is a Part 21 notification, the channel suppliers use to tell the NRC about deviations that could create a substantial safety hazard. The originator is ABB Motors and Mechanical of Flowery Branch, Georgia, and the motors reached nuclear customers through Flowserve. Part 21 reports are not recalls; they put a possible problem on the public record so that every licensee that bought the part can check its own inventory. In this case the update names a single licensee, and the technical fix described so far is testing and a design change, not a shutdown.
What ABB found in the motors supplied through Flowserve
The NRC event report says potential defects were identified in safety-related AC motors used on motor-operated valves and supplied via Flowserve. During commissioning of a new SBD-3 actuator and valve assembly, the motor failed to operate. A third-party analysis by Bruce Power pointed to a rotor balance weight that had contacted the stator winding, damaging the insulation and causing a turn-to-turn short. The failed motor was never returned to ABB for inspection, so the diagnosis rests on that outside analysis. The unit in question was a 100 foot-pound, three-phase, 575-volt, two-pole motor supplied to Flowserve’s Limitorque line.
Bruce Power operates the Bruce Nuclear Generating Station in Ontario, Canada, according to its encyclopedia entry, a site with eight reactors. Flowserve, headquartered in Irving, Texas, is described in its company profile as a supplier of pumps, valves, seals and automation, with Limitorque among its brands.
How the report moved from unknown plants to one
The record shows a slow narrowing. The event date is April 28, 2026, and ABB notified the NRC on June 26, with Sam Bosworth, the company’s interim quality manager, as the contact. Under 10 CFR 21.21(a)(2), a supplier that cannot finish evaluating a possible substantial safety hazard within 60 days of discovery must send an interim report saying when the evaluation will be completed. This one was filed on that basis, and the first version listed the affected plants as unknown.
A July 31 update said ABB had removed the balance weights from the design and revised its work instructions. It identified seven at-risk motors by serial number and recommended megger insulation-resistance testing, with a 5 megohm minimum where no baseline reading exists. Flowserve was asked to help locate the end users.
On Aug. 14 the final report added that 150 foot-pound, two-pole motors with aluminum rotors could also be affected, and that these had been evaluated. An Oct. 16 update added the suffix “-C” to two serial numbers at the end user’s request. The Oct. 20 update gave the corrected serials as B9160683-010-2-CT and B1199658-010-1-CT, and stated that Palo Verde is the only U.S. unit affected.
Palo Verde, the only U.S. site named
Palo Verde sits about 45 miles west of downtown Phoenix and has three pressurized water reactors that entered commercial operation between 1986 and 1988, with a combined nameplate capacity of 3,937 megawatts, according to its encyclopedia entry. Arizona Public Service operates the station and owns 29.1 percent of it. The NRC report does not say which of the three units holds the affected motors, and it does not say a motor has failed in service at Palo Verde.
That gap is the main thing to watch. A possible defect with a stated remedy, removal of the balance weights plus insulation testing, is a different matter from a confirmed failure in a running plant, and the report reads as the former. The Oct. 20 update was sent by email to the NRC’s Region 4 reactor events desk and to its Part 21 and 50.55 reactors list.
The report also leaves several things open. It does not say how many motors at Palo Verde carry the listed serial numbers, whether testing has been completed there, or when ABB expects to close its evaluation. It names the failed motor’s serial number, GG215020118, and a Flowserve part number, R-403-F03-080000A20, but the originating commissioning site is not identified. Readers who want the current status should look for further updates to event 58330 on the NRC’s event-notification pages, which is where ABB’s supplements have appeared so far.
The sequence of serial-number corrections is also worth reading closely. Two of the seven at-risk motors originally listed by ABB, B9160683-010-002 and B1199658-010-001, were later restated with suffixes. The update says only that the change was made at the end user’s request, and the corrected forms, ending in -CT, are the ones now on the record.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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