The following information was provided by the licensee via email:
On October 13, 2022, during Refueling Outage 25, 2 bolts and 2 washers were discovered in the strainer basket upstream of the main steam stop valve in the steam line from the 'A' steam generator. It was determined that these bolts and washers were from the main steam isolation valve (MSIV) upstream of the stop valve. One bolt and one washer were also determined to be missing from the MSIV on the line from the 'B' steam generator. The MSIVs are a similar design as the Main Feedwater Isolation Valves (MFIVs). It appears that the torque values for these backseat bolts provided by the vendor weren't sufficient to prevent the bolts from coming loose. Wolf Creek Nuclear Operating Corporation personnel evaluated the condition and determined that the inadequate torque values provided by the vendor could have constituted a substantial safety hazard if left uncorrected. In particular, if bolts had come loose from the MFIVs, they could have traveled downstream to the steam generators and then challenged the integrity of steam generator tubes.
The NRC Senior Resident Inspector has been notified.
This is a non-emergency notification required by 10 CFR 21.21(d)(3)(i).
A written notification will be provided within 30 days.
