05000483/LER-2019-005, Inoperability of CREVS B Train

Inoperability of CREVS B Train

ML19255H875
Person / Time
Site:	Callaway
Issue date:	09/12/2019
From:	Bianco F Ameren Missouri
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-06532 LER 2019-005-00
Download: ML19255H875 (8)

LER-2019-005, Inoperability of CREVS B Train

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)
4832019005R00 - NRC Website

text

WAmeren MISSOURI September 12, 2019 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-000 1 ULNRC-06532 Callaway Plant Ladies and Gentlemen:

10 CFR 50.73(a)(2)(i)(B)

DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.

RENEWED FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 2019-005-00 VIOLATION OF TECHNICAL SPECIFICAITON 3.7.10 DUE TO CONTROL ROOM EMERGENCY VENTILATION SYSTEM TRAIN B INOPERABILITY The enclosed licensee event report is submitted in accordance with 10CFR5O.73(a)(2)(i)(B) to report a violation of Technical Specification 3.7. 10, Control Room Emergency Ventilation System (CREVS), due to inoperability ofthe CREVS B train.

This letter does not contain new commitments.

Enclosure: LER 20 19-005-00 8315 County Road 459 Steedman, MO 65077 AmerenMissouri.com Fred Director, Nuclear Operations

ULNRC-06532 September 12, 2019 Page 2 of 3 cc:

Mr. Scott A. Morris Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. L. John Kios Project Manager, Callaway Plant Office ofNuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop O9E3 Washington, DC 20555-0001

ULNRC-06532 September 12, 2019 Page 3 of 3 Index and send hardcopy to QA File A160.0761 Hardcopy:

Certrec Corporation 6100 Western Place, Suite 1050 Fort Worth, TX 76107 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)

Electronic distribution for the following can be made via Tech Spec ULNRC Distribution:

F. M. Diya T. E. Herrmann B. L. Cox F. J. Bianco S. P. Banker R. C. Wink T. B. Elwood Corporate Oversight NSRB Secretary Peformance Improvement Coordinator Resident Inspectors (NRC)

STARS Regulatory Affairs Mr. Jay Silberg (Pillsbury Winthrop Shaw Pittman LLP)

Missouri Public Service Commission

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-201 8)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. Facility Name

. Docket Number

3. Page CallawayPlantUniti 05000483 0F5

4. Title Inoperability of CREVS B Train

5. Event Date

6. LER Number

7. Report Date

8. Other Facilities Involved Sequential Rev Facility Name Docket Number Month Day Year YEAR Number No.

Month Day Year 5000 07 1 7 1 9 201 9

- 005

- 00 09 1 2 201 9 Facility Name Docket Number

9. OpemtingMode

11. This Report isSubmitted Pursuanttothe Requirementsof 10 CFR §: (Check all that app)

D 20.2201(b)

D 20.2203(a)(3)(i)

Q 50.73(a)(2)(ii)(A)

Q 50.73(a)(2)(viii)(A) 1 20.2201(d)

D 202203(a)(3)(ii)

Q 50.73(a)(2)(ii)(B)

Q 50.73(a)(2)(viii)(B)

D 20.2203(a)(1)

D 20.2203(a)(4)

Q 50.73(a)(2)(iii)

Q 50.73(a)(2)(ix)(A) i: 20.2203(a)(2)(i)

Q 50.36(c)(1 )(i)(A)

Q 50.73(a)(2)(iv)(A)

Q 5073(a)(2)(x)

JO. PowerLevel Q 202203(a)(2)(ii)

Q 50.36(c)(1)(ii)(A)

Q 50.73(a)(2)(v)(A)

C 73.71(a)(4)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

Q 50.73(a)(2)(v)(B)

Q 73.71(a)(5)

D 20.2203(a)(2)(iv)

D 5046(a)(3)(ii)

Q 5073(a)(2)(v)(C)

Q 73.77(a)(1) 1 00 i: 202203(a)(2)(v)

D 50.73(a)(2)(i)(A)

C 50.73(a)(2)(v)(D)

Q 7377(a)(2)(i)

D 202203(a)(2)(vi) 0 50.73(a)(2)(i)(B)

Q 50.73(a)(2)(vii)

Q 7377(a)(2)(ii)

D 50.73(a)(2)(i)(C)

Q OTHER Specify in Abstract below or in NRC Form 366A

12. Licensee Contact for this LER Licensee Contact Telephone Number (Include Area Code)

TB. Elwood, Supervising Engineer, Regulatory Affairs and Licensing 14-225-1 905

13. COMPLETE ONE UNE FOR EACH COMPONENT FAiLURE DESCRIBED INTHIS REPORT

Cause

System Component Manufacturer Reportable to ICES

Cause

System Component Manufacturer Reportable to ICES A

VI RLY Eaton Y

14. Supplemental Report Expected Month Day Year Yes (if yes, complete 1 5. EXPECTED SUBMISSION DATE)

L1 No Expected Submission Date 2

2019 BSTRACT (Limitto 1400 spaces, i.e., apprmdmately 14 single-spaced typewritten lines)

Dn July 1 7, 201 9, the thermal overload relay for control room filtration fan B tripped when the fan was secured from surveillance testing. This resulted in the B train of the Control Room Emergency Ventilation System (CREVS) being leclared inoperable at 2134 CDT, at which time Condition A of TS 3.7.10 was entered. The trip occurred approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 48 minutes after the fan was started. The CREVS B train was restored to operable status on July 1 9, 201 9 at 1 71 0 CDT after the thermal overload relay was adjusted to prevent inadvertent tripping during normal operation.

ti modification to replace the motor control center bucket for control room filtration fan B was installed June 1 8, 201 9. The hermal overload settings and the thermal overload device used in this modification were in accordance with electrical design calculation NG-23 which used design documents specifying a 3.15 brake horsepower (BHP). The calculation, 9owever, was based on design documents specifying a brake horsepower value that had not been updated to reflect the results of testing performed on the fan by its manufacturer prior to installation at the Callaway Plant (i.e., during plant

onstruction). This resulted in the establishment of a thermal overload relay setting too close to actual fan performance.

Past operability was evaluated and could not be supported from the time the modification was installed to the time when the

ontrol room filtration fan tripped.

This condition is required to be reported pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition or operation prohibited by the echnical Specifications.

Zause(s) and corrective actions will be reoorted in a suoolement to this LER.

NRC FORM 366 (04-2018)

1.

DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):

rhe Control Room Emergency Ventilation System (CREVS) [EllS System: VlJ provides a protected environment from vhich operators can control the unit following an uncontrolled release of radioactivity. The CREVS consists of two independent, redundant trains that pressurize, recirculate, and filter the control room air.

Each CREVS train consists of a filtration system train and a pressurization system train. Each filtration system train consists of a fan, a prefilter, a high efficiency particulate air (HEPA) filter, an activated charcoal adsorber section for removal of gaseous activity (principally iodines), and a second HEPA filter that follows the adsorber section to collect carbon fines. Each pressurization system train consists of a fan, a moisture separator, an electric heater, a HEPA filter, and an activated charcoal adsorber followed by a second HEPA filter.

Ductwork, valves or dampers, and instrumentation also form part of the CREVS system. The CREVS is an emergency system which may also operate during normal unit operations. Actuation of the CREVS by a Control Room Ventilation Isolation Signal (CRVIS) places the system in the emergency mode of operation. Actuation of the system to the emergency mode of operation closes the unfiltered outside air intake and unfiltered exhaust dampers, and aligns the system for recirculation of the air within the control room envelope (ORE) through the redundant trains of HEPA and harcoal filters. The emergency (CRVIS) mode also initiates pressurization and filtered ventilation of the air supply to the the control room pressurization system draws in outside air, processing it through a particulate filter and charcoal adsorber train for cleanup. This outside air is diluted with air drawn from the cable spreading rooms and the electrical quipment floor levels within the control building and distributed back into those spaces for further dilution. The control oom filtration units take a portion of air from the exhaust side of the system for dilution with portions of the exhaust air rom the control room air-conditioning system, and then process it through the control room filtration system adsorption rain for additional cleanup. This air is then further diluted with the remaining control room air-conditioning system return air, cooled, and supplied to the CRE.

2.

INITIAL PLANT CONDITIONS

Dn July 1 7, 201 9 the plant was operating in Mode 1 at 1 00 percent power. Apart from the CREVS B train being declared noperable, no other significant equipment was concurrently inoperable.

3.

EVENT DESCRIPTION

Dn July 1 7, 201 9 while securing control room filtration fan B after a period of operation, the fan tripped on a thermal overload relay actuation [EllS Component: RLY]. The fan was being tested per Job 1 8500461 in accordance with the Control Building Emergency Ventilation Train B Flow Rates procedure, MSE-GK-QGOO3, and ran for approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 48 minutes before ittripped. (The fan was started at 1646 and tripped at 2134.)

Subsequent bench testing of the thermal overload relay indicated that there was no degradation or setpoint drift; the results were comparable to the results obtained during initial installation.

rhe inability of control room filtration fan B to run continuously without tripping on thermal overload under all expected onditions and for its mission time (30 days) challenged its ability to function as designed, thus calling into question its past operability.(04-2018)

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1. FACILITY NAME Z DOCKErNUMBER

3. LERNU4BER YEAR SEQUENTIAL REV Callaway Plant 05000-483 NUMBER NO.

2019

- 005

- 00 The thermal overload relay that was in place for the B filtration fan when the trip occurred on July 1 7, 201 9 was one of several replacement thermal overload relays installed per a recent plant modification. Specifically, modification package MP) 1 8-0003 approved new thermal overload relays for numerous motor control center (MCC) cubicles which included he cubicle for control room filtration fan B. All components affected by this modification (which was only partially mplemented) were evaluated, and it was confirmed that there were no other components adversely affected by the eplacement thermal overload relays.

The thermal overload settings and the thermal overload device used in this modification were configured using nformation from electrical design calculation NG-23 which established the setpoints and time-current coordination curves or replacement cubicles installed in safety-related MCC cubicles. The calculation used design documents specifying a 3.15 brake horsepower (BHP), butthose documents had not been updated to reflect the results of testing performed on he fan by its manufacturer prior to installation at the Callaway Plant (i.e., during plant construction). The thermal

)verload relay setting was consequently set to a value established too close to the actual fan performance, as part of the

\\AP 1 8-0003. After the trip that occurred on July 1 7, 201 9, it was determined that the thermal overload relay required adjustment to prevent inadvertent tripping during normal operation.

4.

ASSESSMENT OF SAFETY CONSEQUENCES

The CREVS filtration fans are important for maintaining post-accident control room habitability. Specifically, the CREVS provides airborne radiological protection for ORE occupants, as demonstrated by the ORE occupant dose analysis for the most limiting design basis accidentfission product release presented in the FSAR. As described in Section 15A.3.1 of the Oallaway FSAR, for the determination of doses to ORE occupants, the worst single failure postulated is the failure of the iltration fan in one of the two filtration system trains. However, and by design, the worst-case single active failure of a CREVS component, assuming a loss of offsite power, does not impair the ability of the system to perform its design unction. Operator action is required to isolate the train with the failed filtration fan since a potential pathway exists, prior tc isolation, that would allow air from the control building to enter the control room, bypassing the control room filtration fan.

Following isolation of the partially failed OREVS train, no bypass pathway exists for the remainder of the accident.

The licensing basis analysis of radiological consequences to ORE occupants performed by Oalculation ZZ-428 credits manual operator action to identify and isolate the partially failed CREVS train within 30 minutes of initiation of the accident sequence. The credited 30-minute operator action is identified in FSAR Table 1 5A-1

. Procedural guidance to diagnose and mitigate a partial OREVS train failure is provided in the Emergency Operating Procedures.

As explained further in the Event Description and Reporting Requirements section of this LER, only one CREVS filtration rain was affected by the condition being reported by this LER. Based on the following considerations, it can be concluded hat the degraded condition of the CREVS filtration fan was not significant with regard to safety consequences:

Failure of a CREVS filtration fan is addressed by FSAR Section 1 5A and Oalculation ZZ-428.

The applicable Emergency Operating Procedure provides specific guidance to diagnose and mitigate failure of a OREVS filtration fan.

Oallaways significant operator response timing program demonstrates the validity of the 30-minute credited operator action to diagnose and mitigate failure of a CREVS filtration fan.

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a LER NUMBER YEAR SEQUENTIAL REV Callaway Plant 05000-483 NUMBER NO.

2019

- 005

- 00 5.

REPORTING htUUIhtMti I This LER is submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) to report a condition prohibited by the Technical Specifications.

The CREVS is subject to the requirements of Callaway Technical Specification (TS) 3.7.1 0, Control Room Emergency Ventilation System (CREVS) The Limiting Condition for Operation (LCO) for this Technical Specification states that two CREVS trains shall be Operable during Modes 1 2, 3, and 4 and during movement of irradiated fuel assemblies. When one CREVS train is inoperable for reasons other than an inoperable control room envelope (CRE) or control building envelope (CBE) boundary, Condition A applies and associated Required Action A.1 must be entered, which requires restoring the inoperable CREVS train to Operable status within the specified Completion Time of 7 days. When TS 3.7.10 Required Action A.1 and its associated Completion Time is not met in Modes 1, 2, 3, or 4, Condition C applies such that Required Actions C.1 and C.2 must be entered, which direct the plant to be in Mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, respectively.

The B CREVS train was declared inoperable on July 17, 2019 due to control room filtration fan B tripping on thermal overload relay actuation. Past operability was reviewed, and it was determined that past operability could not be supported due to the potential for inadvertent tripping of the fan. The modification to replace the MCC bucket replaced the entire contents of the bucket with a new design. The thermal overload settings and the thermal overload device used in his modification were configured per electrical design calculation NG-23 which used design documents that specified a 3.15 BHP. The calculation used design documents specifying a brake horsepower value that had not been updated to reflect the results of testing performed on the fan by its manufacturer prior to installation at the Callaway Plant (i.e., during plant construction). The thermal overload relay setting was consequently set to a value established too close to actual fan performance.

For the period from when the new MCC bucket was installed for the fan motor associated with control room filtration fan B (on June 1 8, 201 9) to the time when the thermal overload relay actuation occurred (on July 1 7, 201 9), operability of the B control room filtration train was not supported due to the potential for inadvertent tripping as a result of the marginal overload settings. This period of inoperability exceeded the time allowed by TS 3.7.1 0 for an inoperable CREVS train (i.e.,

he Completion Time for restoration as allowed per Required Action A.1 plus the shutdown time allowed per Required Action Cl).

Based on the above, this condition is required to be reported pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition or

)peration prohibited by the Technical Specifications.

It may be noted that review of control room logs and maintenance records for the CREVS A train, during the period of CREVS B train inoperability from June 1 8, 201 9 at 0332 CDT to July 1 7, 201 9 at 21 34 CDT, did not identify any Concurreni periods of the CREVS A inoperability. Consequently, the identified condition did not involve a condition that could have prevented fulfillment of a safety function.

6.

CAUSEOFTHE EVENT:

Investigation into the event is ongoing, cause(s) and corrective actions wilt be provided in a supplement to this LER once he root cause process is complete. The cause(s) of the event wilt be identified as part of the root cause analysis process.Page 4 of 5U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2018)

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sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME a DOCKErNUMBER a LERNIMI4BER YEAR SEQUENTIAL REV Callaway Plant 05000-483 NUMBER NO.

2019

- 005

- 00 7.

i.UMt1ti.I IVt ACTIONS:

Investigation into the event is ongoing, cause(s) and corrective actions will be provided in a supplement to this LER once he root cause process is complete. Corrective action to prevent recurrence will be identified as part of the root cause analysis process.

8.

PREVIOUS SIMILAR EVENTS

A review of internal operating experience was performed and one similar event was identified that was previously reported 0 the Nuclear Regulatory Commission.

On March 23, 201 3, Control Room Filtration Fan B tripped on thermal overload relay actuation during restoration from surveillance testing. The Control Room Emergency Ventilation System (CREVS) B train was declared inoperable as a result. The most probable cause was determined to be a high resistance connection on the CREVS B train control room iltration fan starter which tripped on thermal overload. This event was reported under LER 201 3-003-00 per Ameren Missouri letter ULNRC-05993.Page 5 of 5