05000263/LER-2023-003, Condition Prohibited by Technical Specifications Due to Inoperable Main Steam Line Low Pressure Isolation Switch

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)

LER-2023-003, Condition Prohibited by Technical Specifications Due to Inoperable Main Steam Line Low Pressure Isolation Switch

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2632023003R00 - NRC Website

text

fl Xcel Energy* 2807 West County Road 75 Monticello, MN 55362

December 4, 2023 L-MT-23-053 10 CFR 50.73

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 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.

Greg, D,efe'o,/~ -Bro.)H11 / ~-

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 Pr essure 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.

EVENT DESCRIPTION

On October 10, 2023 at 0826, with Monticello Nuclear Generating Plant in Mode 1 at 100 percent power, testing commenced for PS-2-134B [EIIS CODE: JM], the B1 Channel Main Steam Line Low Pressure Isolation switch, per the quarterly Technical Specification (TS) Surv eillance Requirem ent (SR) 3.3.6.1.4 channel calibration procedure for function 1.b. Function 1.b is the Low Main Steam Line (MSL) Pressure Isolation function for TS 3.3.6.1, Primary Containment Isolation Instrumentation. The B1 Channel switch was found out of tolerance at 641.6 psig compared to the TS allowable value of greater than or equal to 815 psig. The B1 Channel switch was brought into tolerance prior to completion of the B1 Channel switch SR 3.3.6.1.4 channel calibration procedure on October 10, 2023 at 0901.

On October 24, 2023, a review of past Operability was completed for the B1 Channel switch. The B1 Channel switch as-found and as-left values were acceptable during the previous SR 3.3.6.1.4 channel calibration procedure on July 3, 2023.

Based on review of the plant process computer MSL pressure data, the B1 Channel switch acceptably tripped at greater than the TS allowable value during the September 27, 2023 Scram. However, when the plant was starting up, in Mode 2, at 4 percent power on October 7, 2023 at 0047, the data showed the B1 Channel switch reset prior to 686.7 psig. Since this switch is designed to reset at a higher pressure than the trip pressure, this was the first indication that the B1 Channel switch was below the allowable value. Since the plant mode switch was in Startup, the MSL low pressure Containment Isolation signal was bypassed.

On October 7, 2023 at 0228 while at 10 percent power, the plant entered Mode 1, which is the Mode of Applicability for Technical Specification 3.3.6.1 function 1.b. 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.

The Primary Containment Isolation system receives inputs from four channels for the MSL Low Pressure trip function. The trip function, active only during Mode 1, uses a one-out-of-two taken twice logic to initiate isolation of all Main Steam Isolation valves (MSIVs), MSL drain valves, and recirculation sample isolation valves. One of the two A channels and one of the two B channels must trip to initiate the Primary Containment Isolation. In Mode 1, with one channel inoperable, TS 3.3.6.1 Condition A requires placing that channel in trip within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. When Condition A is not met, Condition E, as directed by Condition C and Table 3.3.6.1-1 requires entry to Mode 2 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

This event is reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by TS 3.3.6.1.

DATES AND APPROXIMATE TIMES OF MAJOR OCCURANCES

• July 3, 2023 at 0850: The B1 Channel switch as-found and as-left values were acceptable per the SR 3.3.6.1.4 channel calibration procedure.

• September 27, 2023 at 1041: During Reactor Scram and Group 1 isolation on C channel MSL high flow, the B1 Channel switch tripped at 925.5 psig, which is acceptably greater than the TS minimum allowable value.

• October 7, 2023 at 0047: During plant startup, the B1 Channel switch reset prior to 686.7 psig, which is less than the TS minimum allowable value.

• October 7, 2023 at 0228: Event Date. Plant mode switch was placed in r un and the plant entered Mode 1.

• October 8, 2023 at 0228: The required completion time to place the B1 Channel in trip based on TS 3.3.6.1 Condition A for One or more required channels inoperable.

• October 8, 2023 at 0828: The required completion time to be in Mode 2 due to TS 3.3.6.1 Condition E, as directed by Condition C and Table 3.3.6.1-1.

• 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 identifie d 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 commence d 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.