05000263/LER-2023-003, Condition Prohibited by Technical Specifications Due to Inoperable Main Steam Line Low Pressure Isolation Switch
| ML23338A184 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 12/04/2023 |
| From: | Brown G Northern States Power Company, Minnesota, Xcel Energy |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-MT-23-053 LER 2023-003-00 | |
| Download: ML23338A184 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2632023003R00 - NRC Website | |
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December 4, 2023 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Renewed Facility Operating License No. DPR-22 Monticello Nuclear Generating Plant Licensee Event Report 2023-003-00 Northern States Power Company, a Minnesota corporation, doing business as 2807 West County Road 75 Monticello, MN 55362 L-MT-23-053 10 CFR 50.73 Xcel Energy (hereafter "NSPM"), hereby submits Licensee Event Report (LER) 50-263/2023-003-00 per 10 CFR 50. 73(a)(2)(i)(B).
If you have any questions about this submittal, please contact Carrie Seipp, Senior Regulatory Engineer, at 612-330-5576.
Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.
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Greg D Bro.)H11 /
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Plant Manager, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:
Administrator, Region 111, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC State of Minnesota
ENCLOSURE MONTICELLO NUCLEAR GENERATING PLANT LICENSEE EVENT REPORT 50-263/2023-003-00 3 pages follow
Abstract
On October 10, 2023 at 0826, with Monticello Nuclear Generating Plant in Mode 1 at 100 percent power, calibration commenced for PS-2-134B, the B1 Channel Main Steam Line Low Pressure Isolation switch. The calibration is required for the Low Main Steam Line Pressure Isolation function for Technical Specification 3.3.6.1, Primary Containment Isolation Instrumentation. The B1 Channel switch was found out of tolerance low.
On October 7, 2023 at 0228, while at 10 percent power, the plant entered Mode 1, which is the Mode of Applicability for this Technical Specification 3.3.6.1 function. The condition of inoperability of the B1 Channel was not known upon entering Mode 1 and the required technical specification actions to place this Channel in trip were not taken. This event is reportable under 10CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by TS 3.3.6.1.
The cause of the inoperability was instrument drift. The B1 Channel switch was brought within tolerance prior to completion of the B1 channel calibration procedure on October 10, 2023 at 0901.
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- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
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October 10, 2023 at 0801: PS-2-134A, the A1 Channel MSL Low Pressure Isolation switch, SR 3.3.6.1.4 channel calibration procedure commenced and identified an acceptable as-found value.
October 10, 2023 at 0825: The A1 Channel switch SR 3.3.6.1.4 channel calibration procedure concluded with an acceptable as-left value.
October 10, 2023 at 0826: Discovery Date. The B1 Channel switch SR 3.3.6.1.4 channel calibration procedure commenced and identified an unacceptable as-found value of 641.6 psig.
October 10, 2023 at 0901: The B1 Channel switch SR 3.3.6.1.4 channel calibration procedure concluded with an acceptable as-left value of 842.1 psig.
October 24, 2023: Past Operability review concluded the B1 Channel switch was inoperable since entering Mode 1 on October 7, 2023 at 0228 until the condition was identified and corrected on October 10, 2023.
November 20, 2023 at 0825 CST: The B1 Channel switch SR 3.3.6.1.4 procedure commenced at half of the required Surveillance Frequency and identified an acceptable as found value.
November 20, 2023 at 0915 CST: The B1 Channel switch SR 3.3.6.1.4 procedure concluded at half of the required Surveillance Frequency with an acceptable as left value.
ASSESSMENT OF SAFETY CONSEQUENCES
There were no radiological, environmental, or industrial impacts associated with this event. The health and safety of the public and site personnel were not impacted during this event.
The Primary Containment Isolation function was maintained during the period of inoperability of the B1 Channel since at least one A Channel and one B Channel would have initiated a Primary Containment Isolation if low MSL pressure was present. The three other MSL Low Pressure Isolation Channels were operable in the condition of inoperability of the B1 Channel prior to performance of the SR 3.3.6.1.4 channel calibration procedure. When PS-2-134A, the A1 Channel MSL Low Pressure Isolation switch, was removed from service for calibration per the SR 3.3.6.1.4 channel calibration procedure prior to the testing of the B1 Channel switch, both the A2 Channel and B2 Channel were Operable.
There were no structures, systems, or components (SSCs) whose inoperability contributed to this event.
CAUSE OF THE EVENT
The cause of the failure of the B1 Channel switch was instrument drift. Since no specific failure mechanism was identified, a performance at half of the required SR 3.3.6.1.4 channel calibration procedure period was performed on November 20, 2023. The as-found and as-left values were acceptable.
CORRECTIVE ACTIONS
The B1 Channel switch was brought within tolerance prior to completion of the SR 3.3.6.1.4 channel calibration procedure on October 10, 2023.
PREVIOUS SIMILAR EVENTS
No previous similar events have occurred at MNGP in the prior 3 years.
NOTES All times are in Central Daylight Time (CDT) unless otherwise noted.
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Monticello Nuclear Generating Plant 263 2023 003 00
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