05000423/LER-2024-001, Loss of Safety Function and Condition Prohibited by Technical Specifications for Loss of Secondary Containment Boundary

Loss of Safety Function and Condition Prohibited by Technical Specifications for Loss of Secondary Containment Boundary

ML24288A015
Person / Time
Site:	Millstone
Issue date:	10/14/2024
From:	O'Connor M Dominion Energy Nuclear Connecticut
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
24-275 LER 2024-001-00
Download: ML24288A015 (1)

LER-2024-001, Loss of Safety Function and Condition Prohibited by Technical Specifications for Loss of Secondary Containment Boundary

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function
4232024001R00 - NRC Website

text

Dominion Energy Nuclear Connecticut, Inc.

Millstone Power Station 314 Rope Ferry Road, Waterford, CT 06385 DominionEnergy.com U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 OCT 1 4 2024 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3 LICENSEE EVENT REPORT 2024-001 -o'o A Dominion

. ii? Energy Serial No.:

24-275 MPS Lie/JP RO Docket No.:

50-423 License No.: NPF-49 LOSS OF SAFETY FUNCTION AND CONDITION PROHIBITED BY TECHNICAL SPECIFICATIONS FOR LOSS OF SECONDARY CONTAINMENT BOUNDARY This letter forwards Licensee Event Report (LER) 2024-001-00, documenting a condition that was discovered at Millstone Power Station Unit 3 (MPS3) on August 21, 2024. This LER is being submitted pursuant to the requirements of 10 CFR 50. 73(a)(2)(v)(C) and 10 CFR 50. 73(a)(2)(v)(D) as a condition that could have prevented the fulfillment of the safety function for systems or structures that are needed to control the release of radioactive material, and to mitigate the consequences of an accident. This LER is also being submitted pursuant to 10 CFR 50. 73 (a)(2)(i)(B) as a condition prohibited by Technical Specifications.

There are no regulatory commitments contained in this letter or its enclosure.

Should you have any questions, please contact Ms. Lori Kelley at (860) 447-1791 x 6520.

Sincerely,

~~

Michael J. O'Connor Site Vice President - Millstone Enclosure: LER 423/2024-001-00

cc:

U.S. Nuclear Regulatory Commission Region I 475 Allendale Road, Suite 102, King of Prussia, PA 19406-1415.

R. V. Guzman NRC Project Manager Millstone Units 2 and 3 U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Serial No.24-275 Docket No. 50-423 Licensee Event Report 2024-001-00 Page 2 of 2

ATTACHMENT Serial No.24-275 Docket No. 50-423 Licensee Event Report 2024-001-00 LICENSEE EVENT REPORT 2024-001-00 LOSS OF SAFETY FUNCTION AND CONDITION PROHIBITED BY TECHNICAL SPECIFICATIONS FOR LOSS OF SECONDARY CONTAINMENT BOUNDARY MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

NRG FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2027 (04-02-2024)

Estimated burden pe, response to comply vAth this mandatOf)' collection r8<juest 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessens

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LICENSEE EVENT REPORT (LER) learned are lnco<porated Into the icensing process and fed back to Industry. Send comments rega-ding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A10M), U. S. Nuclear RegulatOf)'

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(See Page 2 for required number of digits/characters for each block)

Commission, Washington, DC 20555-0001, or by email to lnfoccllects.Resource@nrc.gov, and the 0MB reviewer at 0MB Office of Information and RegulatOf)' Affairs, (3150-0104), Attn: Desk Office, for the Nuclear RegulatOf)'

(See NUREG-1O22, R.3 for instruction and guidance for completing this form Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not conduct or sponsor, and a person Is bttg://www.orc.gov/[eading-[m/doc-collections/ou[egs/staff/sr1022/[3D not required to respond to, a collection of Information unless the document requesting or requiing the collection displays a cLrrently vaid 0MB control number.

1. Facility Name

~ 050

2. Docket Number

3. Page Millstone Power Station - Unit 3 052 00423 1 OF 4

4. Title Loss of Safety Function And Condition Prohibited By Technical Specifications For Loss Of Secondary Containment Boundary

5. Event Date

6. LER Number

7. Report Date

8. Other Facilities Involved Month Day Year Year Sequential Revision Month Day Year Faclllty Name Docket Number Number No.

050 08 21 2024 2024 -

001 -

00 10 14 2024 Faclllty Name Docket Number 052

9. Operating Mode 110. Power Level 1

100

)

Abstract

On August 21, 2024 at 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br />, while Millstone Power Station Unit 3 was in Mode 1 at 100 percent reactor power, it was discovered that the 'A' waste disposal building exhaust fan, 3HVR-FN8A, which is part of the secondary containment boundary, was removed during maintenance activities. Operations determined that this configuration rendered secondary containment inoperable and entered Technical Specification Action Statement (TSAS) 3.6.6.2 for a loss of secondary containment boundary. It was determined that the fan had been removed for longer than allowed by TSAS. Maintenance reinstalled the exhaust fan which restored the secondary containment boundary to operable status. An eight-hour non-emergency notification was made to the NRC pursuant to the requirements of 10 CFR 50.72(b)(3)(v)(C) and 10 CFR 50.72(b)

(3)(v)(D). This condition is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by plant technical specifications, 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D) as a condition that could have prevented the fulfillment of the safety function of structures or systems needed to control the release of radioactive material and mitigate the consequences of an accident.

I

2. DOCKET NUMBER

3. LER NUMBER I YEAR SEQUENTIAL REV NUMBER NO.

00423

- I I -0 I2024 I 001 On August 21, 2024 at 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> while Millstone Power Station Unit 3 (MPS3) was in Mode 1 at 100 percent reactor power with RCS pressure 2250 psia and RCS Tavg temperature of 586 deg F, a plant equipment operator identified air flowing past the mesh foreign material exclusion (FME) covers of the ductwork with 'A' waste disposal building exhaust fan, 3HVR-FN8A, physically removed from the system. Operations determined that this configuration rendered secondary containment inoperable and entered Technical Specification Action Statement (TSAS) 3.6.6.2 for a loss of secondary containment boundary. An eight-hour non-emergency notification was made to the NRC pursuant to the requirements of 10 CFR 50.72(b)(3)(v)(C) and 10 CFR 50.72(b)(3)(v)(D) as an event or condition that could have prevented the fulfillment of a safety function of structures or systems needed to control the release of radioactive material and mitigate the consequences of an accident.

On August 21, 2024, at 1612 hours0.0187 days <br />0.448 hours <br />0.00267 weeks <br />6.13366e-4 months <br /> Operations performed SP 36141.1, "Supplemental Leak Collection and Release System Operability Test" to determine if the secondary containment boundary was lost, and the test failed to meet the acceptance criteria. Maintenance reinstalled the exhaust fan 3HVR-FN8A which restored the secondary containment boundary. Operations performed a successful surveillance test and exited TSAS 3.6.6.2 on August 21, 2024, at 2136 hours0.0247 days <br />0.593 hours <br />0.00353 weeks <br />8.12748e-4 months <br />.

3HVR-FN8A, is located within the Supplementary Leak Collection and Release System (SLCRS) boundary in the auxiliary building. Though not a component in SLCRS, it can impact SLCRS boundary. The secondary containment is comprised of the containment enclosure building, main steam valve building, engineering safety features building, hydrogen recombiner building and auxiliary building. The safety function of SLCRS is to maintain a negative pressure in the secondary containment to ensure there is no unfiltered leakage to the outside environment from these areas in the event of any loss of coolant accident. The secondary containment ensures that the release of radioactive materials from the primary containment atmosphere will be restricted to leakage paths and rates assumed in the safety analysis.

The secondary containment, in conjunction with SLCRS and auxiliary building filtration system, will limit site boundary radiation doses to within the dose guideline values of 10 CFR 50.67 during an accident.

Per plant Technical Specifications (TS) 3.6.6.2, the secondary containment is required to be OPERABLE in Modes 1, 2, 3, and 4. If the OPERABILITY of secondary containment cannot be met within 24-hours then the plant must be in Mode 3 within 6-hours and Mode 5 within the following 30-hours.

A historical review determined that on August 2, 2024, 3HVR-FN8A was removed for scheduled maintenance. With the waste disposal building exhaust fan removed, a path was created from the MPS3 auxiliary building to the outside environment. This pathway constituted a breach of the secondary containment boundary. This condition existed for greater than the 24-hour allowed outage time, which is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B), "any operation or condition which was prohibited by the plant's Technical Specifications."

This condition is also reportable pursuant to the requirements of 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D) as a "condition that could have prevented the fulfillment of the safety function of structures or system that are needed to control the release of radioactive material and to mitigate the consequences of an accident."

CAUSE

2. DOCKET NUMBER

3. LER NUMBER I

00423 D

NUMBER NO.

I YEAR SEQUENTIAL REV

~-I 001 1-0 The removal of 3HVR-FN8A, created a breach in the secondary containment boundary. The root cause was the lack of identifying information in the work management database for 3HVR-FN8A to identify a potential to impact SLCRS.

ASSESSMENT OF SAFETY CONSEQUENCES

SLCRS is designed to mitigate the radiological consequences of postulated accidents by filtering the exhaust air from the secondary containment. SLCRS is comprised of two redundant trains of exhaust fans and filter units. The safety function of SLCRS is to maintain a negative pressure in the secondary containment to ensure there is no unfiltered leakage to the outside environment from these areas in the event of a loss of coolant accident, other than those releases from SLCRS bypass and damper leakage accounted for in the dose analyses.

SLCRS is not normally in operation but is required to be OPERABLE in Modes 1-4. The SLCRS system and the auxiliary building filtration portion of the auxiliary building ventilation system (ABVS) start on receipt of a Safety Injection Signal (SIS). SLCRS is required to draw down the secondary containment to a negative pressure within 120 seconds after the accident. The negative pressure provided by SLCRS ensures the containment releases occur through the release pathways modeled in the design basis dose analysis.

With secondary containment breached, the ability for SLCRS to achieve negative pressure was impacted. The acceptability of the condition with respect to the station dose analyses is established on the basis of the conservatisms in the existing dose analysis of record for the LOCA event and the fact that the auxiliary ventilation system was operable at the time of this event. One of the largest conservatisms in the analysis is the assumption of containment leak rate during a LOCA event. This assumption is set at the Technical Specification leak rate limit La [0.3 % by weight of the containment air (wt.%)/day]. Replacing the assumed value with the current Integrated Leak Rate Test (ILRT) test result of 0.0506 wt.%/day and assuming 100% SLCRS bypass [i.e., no filtration and ground level release], the calculated potential doses to the public from a postulated LOCA event remain below those documented in FSAR Table 15.0-8 and the 10CFR50.67 criteria.

Therefore, this event is determined to be of low safety significance.

CORRECTIVE ACTION

2. DOCKET NUMBER

3. LER NUMBER I

00423 D

NUMBER NO.

I YEAR SEQUENTIAL REV

~-I 001 1-0 3HVR-FN8A was reinstalled in the system and the secondary containment boundary was restored to operable status on August 21, 2024, at 2136 hours0.0247 days <br />0.593 hours <br />0.00353 weeks <br />8.12748e-4 months <br />. The description of 3HVR-FN8A was updated with information to identify it as a potential impact to SLCRS in the work management system. An indicator will be added to the work management system for any components that may impact the secondary containment boundary. Additional corrective actions will be taken in accordance with the station's corrective action program.

PREVIOUS OCCURRENCES

There have been similar occurrences at MPS3 in the past that resulted in rendering secondary containment inoperable, however the cause was different and therefore this is not a repeat condition.

LER 2020-005 On October 1, 2020, at MPS3, there was a SLCRS Door in the secondary containment blocked open rendering secondary containment inoperable. The identified apparent cause was a weakness within the process of notifying the control room prior to block open doors as it is not fully bounded by the procedures and lacks clear ownership. The contributing factor was inadequate communication.

LER 2017-001 On January 20, 2017, at MPS3, there was a mechanical failure of SLCRS door latch mechanism which prevented the door from automatically closing, rendering secondary containment boundary inoperable.

ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES SLCRS - VF, VG, VH Fan - Fan Auxiliary Building - NF Page 4

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