Event Notification Report for July 27, 2026

PART 21 - THERMAL OVERLOAD FOR EMERGENCY DIESEL GENERATOR

The following summary of information was provided by the licensee via phone and email:

On July 15, 2026, Cook Nuclear Plant completed a Part 21 evaluation concerning an issue with the thermal overload (TOL) used in the electric starter for the Unit 1 emergency diesel generator (EDG) room exhaust fan.
Failure investigation determined that a TOL line-side conductor had a loose electrical connection causing a high-resistance condition and elevated temperature on one phase.
The defect caused the Unit 1 'AB' EDG room exhaust fan to trip and resulted in the associated EDG being declared inoperable and unable to perform its safety-related function.

The starter was replaced and the preventative maintenance and testing procedure was revised to check the TOL for proper assembly prior to installation.

Cook Nuclear Plant is the only facility known to be affected at the time of this report.

The NRC Resident has been notified.

INVALID ACTUATION

The following information was provided by the licensee via phone and email:

"This 60-day optional telephone notification is being made in lieu of a licensee event report (LER) as allowed by 10 CFR 50.73(a)(1). This notification is made pursuant to the reporting requirements specified in 10 CFR 50.73(a)(2)(iv)(A) for an invalid actuation of one of the systems listed in 10 CFR 50.73(a)(2)(iv)(B).

"At approximately 0634 MST on 5/30/2026, Palo Verde Nuclear Generating Station Unit 2 had an invalid actuation of the train 'B' balance of plant engineered safety feature actuation system (BOP ESFAS). This resulted in an auto start of the train 'B' essential chiller, spray pond pump, essential cooling water pump, high pressure safety injection, low pressure safety injection, containment spray, and auxiliary feedwater pump. No valves actuated and the plant remained stable. This event was the result of an invalid BOP ESFAS actuation due to a load sequencer failure.

"Since the actuation was not initiated in response to actual plant conditions, it was not an intentional manual initiation, and there were no parameters satisfying the requirements for initiation of the systems, this event has been determined to be an invalid actuation.

"There was no impact on the health and safety of the public or plant personnel.

"The NRC Resident has been notified."

DAMAGED MOISTURE DENSITY GAUGE

The following information was provided by the licensee via phone:

On July 18, 2026, at 0432 CDT, a Humboldt model 5001 moisture density gauge, with the source in the unshielded position, was struck and crushed by a 12-ton roller at a road construction site in Manchester, Missouri. The gauge contains 10 mCi of Cs-137 and 40 mCi of Am-241:Be. A Cochran Engineering field technician secured the area and contacted the radiation safety officer (RSO), who responded to the scene. The RSO's survey meter was unavailable due to calibration. The St. Louis County Fire Department responded with a hazardous materials team. The RSO reported that both sealed sources remained intact. The damaged gauge was placed into a lead-lined drum and transported to the licensee's facility in St. Charles, Missouri. The licensee intends to ship the device to the manufacturer for disposition and will provide a written follow-up report.

No overexposures or contamination were reported.

AGREEMENT STATE REPORT - LOST SOURCES

The following information was provided by the Illinois Emergency Management Agency (the Agency) via email:

"The Agency was contacted on July 20, 2026, by the Agency's own radiation safety officer informing them of a missing shipment of Eckert and Ziegler calibration/check sources. While the carrier indicated delivery on July 17, 2026, the package was not received and was signed for by someone who is not an agency employee. An investigation has been opened with the carrier and Eckert and Ziegler have been notified.

"The package contained five sources. Each source contains a mixture of Cd-109, Co-57, Ce-139, Hg-203, Sn-113, Cs-137, Y-88, Co-60, Sr-85, and Am-241, ranging in activity from 6 to 36 microcuries. Isotope-specific activities are not available. Three are considered sealed sources with a foam matrix within a stainless-steel chamber. Two are face-loaded filter papers that are taped within a charcoal cartridge. These sources would be characterized as International Atomic Energy Agency (IAEA) Category 5 sources, meaning they are the least likely to be dangerous to a person, and no one could be permanently injured, even if dispersed. Due to the low reporting thresholds for Am-241, this has an immediate reporting requirement to the Nuclear Regulatory Commission."

Illinois event number: IL260023

THIS MATERIAL EVENT CONTAINS A 'Less than Cat 3' LEVEL OF RADIOACTIVE MATERIAL

Sources that are "Less than IAEA Category 3 sources," are either sources that are very unlikely to cause permanent injury to individuals or contain a very small amount of radioactive material that would not cause any permanent injury. Some of these sources, such as moisture density gauges or thickness gauges that are Category 4, the amount of unshielded radioactive material, if not safely managed or securely protected, could possibly - although it is unlikely - temporarily injure someone who handled it or were otherwise in contact with it, or who were close to it for a period of many weeks. For additional information go to http://www-pub.iaea.org/MTCD/publications/PDF/Pub1227_web.pdf

* * * UPDATE FROM GARY FORSEE TO BRIAN P. SMITH ON 07/22/2026 AT 1657 EDT * * *

The following information was provided by the Illinois Emergency Management Agency via email:

"The package was located by the carrier and successfully delivered. The matter is considered closed."

Notified R3DO (Sanchez Santiago)