05000336/LER-2024-001, Control Room Air Conditioning Unit Inoperable Due to Refrigerant Overcharge Resulting in a Condition Prohibited by Technical Specifications

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Control Room Air Conditioning Unit Inoperable Due to Refrigerant Overcharge Resulting in a Condition Prohibited by Technical Specifications
ML24162A088
Person / Time
Site: Millstone Dominion icon.png
Issue date: 06/10/2024
From: O'Connor M
Dominion Energy Nuclear Connecticut
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
24-191 LER 2024-001-00
Download: ML24162A088 (1)
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LER-2024-001, Control Room Air Conditioning Unit Inoperable Due to Refrigerant Overcharge Resulting in a Condition Prohibited by Technical Specifications
Event date:
Report date:
3362024001R00 - NRC Website
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text

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U. S. Nuclear Regulatory Commission Serial No.: 24-191 Attention: Document Control Desk MPS Lic/JNP RO Washington, DC 20555 Docket No.: 50-336 JUN 1 0 2024 License No.: DPR-65

DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2 LICENSEE EVENT REPORT 2024-001-00

CONTROL ROOM AIR CONDITIONING UNIT INOPERABLE DUE TO REFRIGERENT OVERCHARGE RESULTING IN A CONDITION PROHIBITED BY TECHNICAL SPECIFICATIONS

This letter forwards Licensee Event Report (LER) 2024- 001-00, documenting a condition that was discovered at Millstone Power Station Unit 2 (MPS2) on Ap ril 14, 2024. This LER is 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 Mr. Dean E. Rowe, Manager of Emergency Preparedness and Licensing fo r Millstone Power Station, at (860) 444-5292.

Since rely,

\\

Michael J. O'Connor Site Vice President - Millstone

Enclosure: LER 336/2024-001 - 00 Serial No.24-191 Docket No. 50-336 Licensee Event Report 2024-001-00 Page 2 of 2

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.24-191 Docket No. 50-336 Licensee Event Report 2024-001-00

ATTACHMENT

LICENSEE EVENT REPORT 2024-001-00

CONTROL ROOM AIR CONDITIONING UNIT INOPERABLE DUE TO REFRIGERENT OVERCHARGE RES UL TING IN A CONDITION PROHIBITED BY TECHNICAL SPECIFICATIONS

MILLSTONE POWER STATION UNIT 2 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

Abstract

On April 14, 2024, at 1407 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.353635e-4 months <br /> while Millstone Power Station Unit 2 was in Mode 1 at 100 percent reactor power, it was discovered that the 'A' Control Room Air Conditioning (CRAC) compressor assembly was not running following an increase in temperatures in the control room. Troubleshooting determined that the refrigerant in the 'A' CRAC was overcharged following the replacement of a leaking pressure switch. Following trimming of the refrigerant charge for the 'A' CRAC compressor, the 'A' Control Room Emergency Ventilation system was declared operable on April 20, 2024 at 2025 hours0.0234 days <br />0.563 hours <br />0.00335 weeks <br />7.705125e-4 months <br />. A historical review determined that this condition existed starting on April 10, 2024, and therefore existed for greater than the 7-day allowed outage time of the Technical Specification. This report is being submitted as a condition that was prohibited by plant Technical Specifications pursuant to 10 CFR 50.73(a)(2)(i)(B).

I

On April 14, 2024, at 1407 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.353635e-4 months <br /> while Millstone Unit 2 was in Mode 1 operating at 100 percent reactor power, Operations entered Technical Specification Action Statement (TSAS) 3.7.6.1.a due to rising temperatures in the control room. A walk down of the 'A' Control Room Air Conditioning (CRAC) compressor assembly, M2F22A, found the compressor not running. Troubleshooting by station personnel with vendor support determined that the compressor was in an overcharged condition. Following trimming of the refrigerant charge, the 'A' CRAC compressor was returned to service. Operations declared the 'A' Control Room Emergency Ventilation (CREV) system OPERABLE on April 20, 2024, at 2025 hours0.0234 days <br />0.563 hours <br />0.00335 weeks <br />7.705125e-4 months <br />.

The 'A' CRAC compressor assembly (Trane 2F5C88) is part of the control room emergency ventilation system. The OPERABILITY of the control room emergency ventilation system as described in Technical Specifications (TS) 3.7.6.1 ensures that the ambient temperature does not exceed the allowable temperature for continuous duty rating for the equipment and instrumentation cooled by this system, and the control room will remain habitable for Operations personnel during and following all credible accident conditions. The OPERABILITY of this system in conjunction with control room design provisions is based on limiting the radiation exposure to personnel occupying the control room.

For all postulated design basis accidents, the radiation exposure to personnel occupying the control room shall be 5 rem total effective dose equivalent (TEDE) or less consistent with the requirements of 10 CFR 50.67.

In Modes 1, 2, 3, and 4, Technical Specifications (TS) 3.7.6.1 "Control Room Emergency Ventilation System," requires two independent Control Room Emergency Ventilation Trains to be OPERABLE. If one Control Room Emergency Ventilation Train is inoperable, it must be restored to OPERABLE within 7 days or be in HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

A historical review was performed on the 'A' CRAC compressor. On April 7, 2024, at 1945 hours0.0225 days <br />0.54 hours <br />0.00322 weeks <br />7.400725e-4 months <br />, Operations entered the 7-day Technical Specification Action Statement (TSAS) 3.7.6.1.a due to the compressor not running. Maintenance determined that there was no refrigerant in the compressor assembly due to a leaking pressure switch. The pressure switch was replaced, and on April 10, 2024, at 1720 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.5446e-4 months <br />, the 'A' CRAC compressor assembly was charged with 200 lbs. of refrigerant, chlorodifluoromethane (R-22). Following successful completion of the surveillance test, the 'A' CREV system was placed into service, and Operations exited the TSAS on April 10, 2024, at 2340 hours0.0271 days <br />0.65 hours <br />0.00387 weeks <br />8.9037e-4 months <br />.

The historical review determined that the compressor overcharge condition was present from April 10, 2024, at 1720 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.5446e-4 months <br /> until April 20, 2024, at 2007 hours0.0232 days <br />0.558 hours <br />0.00332 weeks <br />7.636635e-4 months <br />. This condition would have prevented reliable operation of the 'A' CRAC, and it would not have met its required mission time. This condition existed for a period greater than the 7-day 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." From April 7 to April 20, 2024 the 'B' CRAC was functional, and the

'B' Control Room Emergency Ventilation (CREV) was OPERABLE.

CAUSE

The overcharge condition in the ' A' CRAC compressor assembly following the replacement of the leaking pressure switch caused the compressor to run inconsistently. The use of an uncontrolled job aid indicated that the compressor should be charged to 200 lbs., which led to the overcharged condition.

ASSESSMENT OF SAFETY CONSEQUENCES

Operation of the Control Room Emergency Ventilation (CREV) System is credited to limit dose to personnel in the control room to the 10 CFR 50.67 limit of 5 rem Total Effective Dose Equivalent (TEDE), and to maintain a suitable environment for personnel and safety related equipment in the control room. The CREV system is made up of two subsystems : control room air conditioning (CRAC) and control room filtration system (CRFS). During this period, with the unit in Mode 1, 'A' CREV was declared inoperable because the ' A' CRAC was unable to perform its cooling function.

This condition is considered to be of low safety significance based upon the availability of the 'B' CREV for the entire period. Per Millstone Power Station Unit 2 (MPS2) FSAR section 9.9.11.2.1, the CRAC subsystem consists of two full capacity, independent air handling and mechanical refrigeration subsystems with the exception of some common ductwork and dampers. Therefore, 'B' CRAC was capable of fulfilling the cooling requirement inside the control room.

MPS2 FSAR Chapter 14 dose analyses only credit one train of CRFS for mitigation of radiological consequences and calculated control room doses are below the 10 CFR 50.67 limit. Based on the discussion above, the safety functions of the CREV system were met with 'B' CREV operable.

CORRECTIVE ACTIONS

The refrigerant charge was trimmed from the 'A' CRAC compressor. This allowed the ' A' CREV system to be restored to OPERABLE on April 20, 2024, at 2025 hours0.0234 days <br />0.563 hours <br />0.00335 weeks <br />7.705125e-4 months <br />. Refrigerant charge values for the CREV system will be captured in station procedures. Additional corrective actions will be taken in accordance with the station ' s corrective action program.

PREVIOUS OCCURRENCES

There have been no similar events related to refrigerant levels causing a Control Room Emergency Ventilation system to be inoperable for a period longer than the Technical Specification Action Statement allowed outage time of 7 days at Millstone Power Station over the last three years.

In 2012, maintenance questioned the use of 200 lbs. of refrigerant following completion of maintenance on the 'A' CRAC:

Engineering performed an evaluation and determined the refrigerant charge, but that information was never incorporated into the maintenance procedure for charging the compressor. The maintenance work performed in 2012 did not cause the Control Room Emergency Ventilation system to be inoperable for a period longer than Technical Specification Action Statement allowed outage time of 7 days.

ENERGY IN DUSTRY IDENTIFICATION SYSTEM (EIIS) CODES

VI Control Building/Control Complex Environmental Control System

CMP Compressor

NRG FOR M 366A (0 4-02-2024) Page 3 of 3

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