05000388/LER-2021-002-01, Loss of Secondary Containment Due to Failed Differential Pressure Transmitter

Loss of Secondary Containment Due to Failed Differential Pressure Transmitter

ML22039A022
Person / Time
Site:	Susquehanna
Issue date:	02/08/2022
From:	Cimorelli K Susquehanna, Talen Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
PLA-7981 LER 2021-002-01
Download: ML22039A022 (4)

LER-2021-002, Loss of Secondary Containment Due to Failed Differential Pressure Transmitter

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function
3882021002R01 - NRC Website

text

Kevin Cimorelli Susquehanna Nuclear, LLC Site Vice President 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.3795 Fax 570.542.1504 Kevin.Cimorelli@TalenEnergy.com

February 8, 2022

Attn: Document Control Desk 10 CFR 50.73 U. S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-388/2021-002-01 UNIT 2 LICENSE NO. NPF-22 PLA-7981 Docket No. 50-388

Attached is Licensee Event Report (LER) 50-388/2021-002-01. The LER supplement reports an event in which the secondary containment was inoperable due to differential pressure exceeding the Technical Specification limit. The condition is being reported in accordance with 10 CFR 50.73(a)(2)(v)(C) as an event or condition which could have prevented the fulfillment of a safety function.

There were no actual consequences to the health and safety of the public as a result of this event.

This letter contains no new or revised regulatory commitments.

K. Cimorelli

Attachment: LER 50-388/2021-002-01

Copy: NRC Region I Mr. C. Highley, NRC Senior Resident Inspector Ms. A. Klett, NRC Project Manager Mr. M. Shields, PA DEP/BRP

Abstract

On August 30, 2021, at 09:55, operators at the Susquehanna Steam Electric Station (SSES), Unit 2, identified that Reactor Building Zone II Pressure Differential Indicator (PDI), PDI-27581, was stuck at a reading of 0.32 water column vacuum. Operators also reported difficulties opening doors in the SSES Unit 2 Reactor Building, indicating a positive secondary containment differential pressure (D/P). At this time, operators determined that a loss of the secondary containment had occurred and entered the off-normal procedure for the condition. Review of alternate indication documented from earlier that day, identified the condition likely existed longer than allowed by the Technical Specification Surveillance Requirement 3.6.4.1.1 associated Note. This condition is being reported under 10 CFR 50.73(a)(2)(v)(C) as a loss of safety function.

Secondary containment was restored to an operable status at 10:30 on August 30.

The cause of the event was determined to be an age-related failure of Pressure Differential Transmitter (PDT) PDT-27581. Corrective actions included replacing PDT-27581. There were no actual safety consequences associated with the described condition.

CONDITIONS PRIOR TO EVENT

Unit 1 - Mode 1, approximately 100 percent Rated Thermal Power (RTP)

Unit 2 - Mode 1, approximately 100 percent RTP

At 04:00 on August 30, 2021, operators at the Susquehanna Steam Electric Station (SSES), Unit 2, identified that both the A and B Standby Gas Treatment (SGT) System Zone 2 Outside Delta Pressure Indicators, pressure differential indicators (PDIs) PDI-07554A2 and PDI-07554B2 [EIIS System/Component Codes BH/PDI], respectively, were indicating below downscale on the associated meters while the digital display was reading -0.25 water column (wc) vacuum. This is indicative of a positive differential pressure (D/P) in the secondary containment. At the time of discovery, this was believed to be an indication-only issue.

EVENT DESCRIPTION

At 09:55 on August 30, 2021, while investigating the downscale indication on the A and B SGT System Zone 2 Outside Delta Pressure Indicators, PDI-07554A2 and PDI-07554B2, operators at SSES, Unit 2, identified that the SGT System Zone 2 Exhaust System Circulating Space/Outside D/P Indicator, PDI-27581 [VA/PDI],

was stuck at a reading of 0.32 wc vacuum. Operators also reported difficulties opening doors in the SSES Unit 2 Reactor Building, indicating a positive secondary containment D/P. At this time, operators determined that a loss of the secondary containment had occurred and entered the off-normal procedure for the condition. Entry into Technical Specification Limiting Condition for Operation (LCO) 3.6.4.1, Condition A was evaluated and determined to be unnecessary at the time of discovery based on no known breach in secondary containment and the SGT subsystem was determined to be capable of drawing down secondary containment to 0.25 wc vacuum. This allowance is defined within the associated Note for Surveillance Requirement (SR) 3.6.4.1.1.

Subsequently, when reviewing the stuck indication on PDI-27581 in aggregate with the downscale readings on PDI-07554A2 and PDI-07554B2, it was determined firm evidence exists that secondary containment D/P was likely lost at 04:00 when PDI-07554A2 and PDI-07554B2 were identified as reading downscale. As a result, the four-hour allowance of the Note modifying SR 3.6.4.1.1 would result in the SR not met at approximately 08:00 and LCO 3.6.4.1, Condition A being entered. Because there is no redundant system to secondary containment, this event requires reporting under 10 CFR 50.73(a)(2)(v)(C) as a condition that could have prevented the fulfillment of a safety function needed to control the release of radioactive material.

CAUSE OF EVENT

The cause of the event was determined to be an age-related failure of Pressure Differential Transmitter (PDT) PDT-27581 [VA/PDT]. The output of PDT-27581 was failed and providing incorrect inputs to the indicators and controllers, which resulted in the loss of Zone 2 D/P.

ANALYSIS/SAFETY SIGNIFICANCE

Based on engineering analysis of the event, secondary containment could have performed its safety function of isolating as assumed in the accident analysis and of re-establishing 0.25 wc vacuum (drawdown) within the assumed accident analysis time (10 minutes).

This event will not be counted as a safety system functional failure for the NRC performance indicator based on the engineering analysis supporting the systems ability to fulfill the safety function.

CORRECTIVE ACTIONS

PDT-27581 was replaced and the SGT System was returned to service.

COMPONENT FAILURE INFORMATION

1. Component Identifier - PDT-27581

Component Name - Reactor Building Zone 2 Exhaust System HVAC

Component Manufacturer - Brandt

Model Number - 21PDT2220-0.5

PREVIOUS OCCURRENCES

LER 50-388(387)/2016-006-00, Loss of Secondary Containment Due to Damper Controller Sticking, dated November 17, 2016.

LER 50-388(387)/2015-010-01, Supplemental Report to LER-2015-010-00, Loss of Differential Pressure in Zone II of Secondary Containment, dated July 6, 2016.