Surprising and Unpredictable Events Continue to Occur At Nuclear Plants.

This is going to intensify as these obsolete plants age. The fix must be very expeensive and just eat up refueling opertunities. 

New Degradation mechanism IN Westinghouse CRDMs 

Part 21

Event Number: 54440

Rep Org: WESTINGHOUSE

Licensee: WESTINGHOUSE

Region: 1

City: CRANBERRY TOWNSHIP State: PA

County:

License #:

Agreement: Y

Docket:

NRC Notified By: CAMILLE T. ZOZULA

HQ OPS Officer: OSSY FONT

Notification Date: 12/12/2019

Notification Time: 19:24 [ET]

Event Date: 12/12/2019

Event Time: 00:00 [EST]

Last Update Date: 12/12/2019

Event Text

PART 21 REPORT - FRACTURED AND DISLOCATED CONTROL ROD DRIVE MECHANISM THERMAL SLEEVE

"During a 2019 planned outage at a Westinghouse plant, site personnel identified a fractured and dislocated control rod drive mechanism (CRDM) thermal sleeve. The fracture occurred just beneath the worn area of the flange in the full cross-section of the thermal sleeve tube. A stress concentration exists at this transition. Previous operating experience (OE) with thermal sleeve failures did not include a cross-sectional thermal sleeve fracture such as this.

"Additional data supplied from the affected plant showed evidence of additional thermal sleeve locations with crack-like indications in the flange collar region (i.e., evidence of degradation but not failure). Although there was no evidence that control rod motion was hindered, Westinghouse is conservatively reporting this condition as having the potential to create a SSH (substantial safety hazard), were it to remain uncorrected.

"Based on new OE provided to Westinghouse, a defect has been identified that is associated with a previously unseen form of thermal sleeve degradation (i.e., mechanical fatigue and fracture that leads to flange separation). Control rod functionality could become adversely impacted not only due to the flange wear reported in LTR-NRC-18-34, but due to the additional coincident fracture and separation of the thermal sleeve tube from its flange. This condition could exist prior to reaching the flange wear criteria established in PWROG-16003-P, Revision 2. The information supplied in PWROG-16003-P, Revision 2 and NSAL-18-1 also does not address this new OE. If no action is taken to monitor and/or correct this condition, an SSH could occur if the insertion of more than one control rod is prevented.

"The probability for this to result in a SSH is low given that this is the very first observance of this phenomenon. Westinghouse does not expect that an affected plant would experience two or more stuck control rods during its current operating cycle. Even if multiple stuck control rods were to occur, such an event would be bounded by the licensee's ATWS analysis. Based on known wear conditions and wear rates, plants can safely operate for at least one cycle or until the next opportunity to perform a visual inspection.

"The potentially affected plants listed below are Westinghouse design plants that:

1. Operate with higher upper head bypass flow conditions, known as 'T-cold' head plants, and

2. Operate with thermal sleeves containing a collar (or upper centering pad ring) just below the flange.

Asco 2, Braidwood 1, Braidwood 2, Byron 1, Byron 2, Callaway 1, Catawba 1, Catawba 2, Comanche Peak 1, Comanche Peak 2, Doel 4, Hanbit 1, Hanbit 2, Kori 3, Kori 4, Maanshan 1, Maanshan 2, Seabrook, Sizewell B, Tihange 3, Vogtle 1, Vogtle 2, and Wolf Creek.

"A Westinghouse communication will be supplied to affected licensees in early 2020 to inform them that this defect has been reported. The communication will provide updated recommendations concerning future inspection guidance."

The person informing the Nuclear Regulatory Commission:

Camille T. Zozula

Westinghouse Electric Company

1000 Westinghouse Drive

Cranberry Township, Pennsylvania 16066

Direct tel: (412) 374-2577

Direct fax: (724) 940-8542

e-mail: zozulact@westinghouse.com