05000483/LER-2020-001-01, Emergency Exhaust Inoperable Due to Fan Belt Degradation and Failure

Emergency Exhaust Inoperable Due to Fan Belt Degradation and Failure

ML21040A515
Person / Time
Site:	Callaway
Issue date:	02/09/2021
From:	Bianco F Ameren Missouri
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-06634 LER 2020-001-01
Download: ML21040A515 (8)

LER-2020-001, Emergency Exhaust Inoperable Due to Fan Belt Degradation and Failure

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
4832020001R01 - NRC Website

text

Am818n MISSOURI Callaway Plant February 9, 2021 ULNRC-06634 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 10 CFR 50.73 Ladies and Gentlemen:

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

RENEWED FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 2020-001-01 EMERGENCY EXHAUST INOPERABLE DUE TO FAN BELT DEGRADATION AND FAILURE The enclosed Licensee Event Report is submitted in accordance with 10 CFR 50.73(a)(2)(i)(B), 50.73(a)(2)(v)(C),

and 50.73(a)(2)(v)(D) to report the inoperability ofthe B train Emergency Exhaust System due to fan belt degradation and failure, resulting in an operation or condition prohibited by Technical Specifications and a condition that could have prevented fulfillment of a safety function. This LER Supplement is being submitted to provide the results ofthe cause determination and corrective actions.

If you have any questions concerning this LER, please contact Tom Elwood, Supervising Engineer, Regulatory Affairs and Licensing at (314) 225-1905.

This letter does not contain any new commitments.

Sincer ly, Frederick anco Senior Director, Nuclear Operations

Enclosure:

LER 2020-001-01 8315 County Road 459 Steedman MO 65077 AmerenMissoun corn

ULNRC-06634 February 8, 2021 Page 2 of 3 cc:

Mr. Scott 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

$201 NRC Road Steedman, MO 65077 Mahesh Chawla, Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office ofNuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop O8B1A Washington, DC 20555-0001

ULNRC-06634 February 8, 2021 Page3 of3 Index and send hardcopy to QA file A160.0761 Hardcopy:

Certrec Corporation 6500 West freeway, Suite 400 Fort Worth, TX 76116 (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 LER ULNRC Distribution:

F. M. Diya B. L Cox F. J. Bianco S. P. Banker R. C. Wink S. I. Meyer T. B. Elwood K. A. Mills J. C. Sellers Corporate Oversight NSRB Secretary Performance Improvement Coordinator STARS Regulatory Affairs Mr. Jay Silberg (Pillsbury Winthrop Shaw Pittman LEP)

Missouri Public Service Commission

16 Abstract (Limto 1560 spaces, i.e., approximately 15 single-spaced typewritten lines) on February 18, 2020, one of the two fan belts on the fan unit for the B train of the Emergency Exhaust System (EES) was discovered to be broken. Following replacement of the fan belts on February 22, 2020, it was identified on February 24, 2020 that the fan belts had not been properly tensioned. Based on assessment of these identified conditions, it was determined that the EES B train was inoperable from June 25, 2019 to February 26, 2020 due to degraded/nonconforming fan belts. During this time, the B train of the Emergency Exhaust System would not have been capable of performing its safety function for its required 30-day mission time in the event of an accident. The plant was operating in Mode I, and fuel handling operations involving irradiated fuel assemblies were performed during the period that the B train of emergency exhaust was inoperable.

The causes for the fan belt failure include improper installation technique, improper tension verification, improper alignment technique, and age related embriftiement. The corrective actions include development of procedural guidance for belt installation, tension verification and alignment, and the establishment of an allowable shelf life based on vendor recommendations.

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08131/2023 (08-2020)

3. Page Callaway Plant Unit I 05000483 1 OF 5

4. Title Emergency Exhaust Train Inoperable Due to Fan Belt Degradation and Failure

5. Event Date

6. LER Number

7. Report Date

8. Other Facilities Involved Se uenUal Facility Name Docket Number Month Day Year Year Number Revision Month Day Year 05000 Facility Name Docket Number 02 18 2020 2020

- 001 01 02 08 2021 oo

. OperafingMode

10. PowerLevel I____________________________________________ 100%

)

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

The event reported in this LER involves the Emergency Exhaust System (EES). The EES (EIIS: VF) serves both the auxiliary building and the fuel building. FolloMng a safety injection signal (515), safety related dampers isolate the auxiliary building, and the EES filters and exhausts potentially contaminated air due to leakage from ECCS systems. The EES is also designed to filter airbome radioactive particulates from the area ofthe spentfuel pool followng a fuel handling accident.

The EES consists of two independent and redundanttrains. Each train consists of a heater, a prefilter, a high efficiency particulate air (HEPA) filter bank, an activated charcoal adsorber section for removal of gaseous activity (principally radioiodines), and a fan.

Ductwork, dampers, and instrumentation also form part of the system. A second bank of HEPA filters follows the adsorber section to collect carbon fines.

The EES is on standby for an automatic start folloMng receipt of a fuel building ventilation isolation signal (FEVIS) or a safety injection signal (515). Initiation ofthe 515 mode of operation takes precedence over any other mode of operation. In the SIS mode, the system is aligned to exhaustthe auxiliary building.

Technical Specification (TS) 3.7.13, Emergency Exhaust System (EES), provides the Limiting Condition for Operation (LCO),

Required Actions and Surveillance Requirements forthe EES.

2.

INITIAL PLANT CONDITIONS

Atthe time ofthe event, Callaway was operating in Mode I at 100% power.

3.

EVENT DESCRIPTION

On February 18, 2020, the Primary Operations Technician, a nonlicensed operator, reported that one ofthe two belts on the CGGO2B Emergency Exhaust fan (EIIS FAN) was broken. The second belt was visually verified to still be intact and installed on the sheaves. The Shift Manager was notified, and CGGO2B was declared inoperable, Condition A of Technical Specification 3.7.13 was entered for the inoperable EES B train.

Dunng the performance ofthe as-found inspection, the inner beltwas discovered lying on the bottom ofthe belt guard and appeared to have undergone a tensile break. No evidence of long term wear of the belt was observed, and no foreign material was identified in the belt guard or around the v-belt drive. A work history search confirmed the belts had been replaced on June 25, 2019, and that the belts had approximately 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> of run-time priorto the failure. Since the mission time forthe EES is 30 days, failure ofthe belt after I 0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of run time is contraryto the capability ofthe EES B to meet its 30-day mission time requirement This vulnerability existed throughout the time period from when the belts were replaced on June 25, 2019 to when they were again replaced on February 22, 2020. Followng replacement of the belts on Saturday February 22, 2020 the unit was returned to service at 13:05 that same day.

After discovery ofthe beltfailure and subsequent replacement of the belts, as described above, an additional condition was identified on February 24, 2020 from discussion with the maintenance supervisor who oversaw the belt replacement. The new/additional condition was based on the supervisors observation thatfolIong replacement of the outer belt, the belt tenelon appeared to have relaxed as the fan continued to operate, a newtask was added to the belt replacementjob to check belt tension.

The as-found tension values of both belts were measured and found to be outside ofthe acceptance cntena established in the job.

A corrective action document was written to documentthe inadequate belttensions, and the EES B train was again declared inoperable on February 24, 2020 at 19:23. Adjustments to the v-belttension and dilve alignment were made under the new tasks I

added to the belt replacementjob. The motor sheave was replaced Mth a spare sheave, and the belts were replaced. Following an 8-hour run, belttensions were measured and verified to be thin acceptance ctitena. After a minor adjustmentto fan speed and(08-2020)

Page ofU.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 0813112023 (08-2020)

1. FACILITY NAME Z DOCKET NUMBER

3. LERNIfiVIBER YEAR SEQUENTIAL REV Callaway Plant Unit I 05000-483 NUMBER NO.

2020

- 001

- 01 another belttension verification, EES B train was declared operable at 14:42 on February 26,2020.

It has been determined thatthe B train of the Emergency Exhaust System was inoperable from June 25, 2019 to February 26, 2020. This overall time period includes the time from when the belts for CGGO2B were replaced on June 25, 2019 to when they were again replaced on February 22, 2020. It also includes the time from when the second belt replacementto when the belts were properly tensioned and minor adjustments were completed on February 26, 2020, after recognizing (and correcting)the need for proper belttensioning. Dunng this entire time, the plant was in Mode 1.

4.

ASSESSMENT OF SAFETY CONSEQUENCES

The degraded/nonconforming condition ofthe EES B train fan belt reported in this LER did not significantly degrade plant safety.

The Emergency Exhaust system is credited with mitigating radiological consequences of two licensing basis post-accident release pathways.

Post LOCA leakage of containment sump recirculalion fluids (FSAR Section 15.6.5.4.1.2)

Fuel Building Fuel Handling Accident (FSAR Section 15.7.4.5)

With regards to the postulated post-LOCA leakage of containment sump fluids, subsequentto the injection phase ofthe accident sequence, the water in the containment recirculation sumps is recirculated by the residual heat removal, ECCS centnfugal charging and safety injeclion pumps, and the containment spray pumps. Due to the operation of the ECCS and the containment spray system, most ofthe radioiodine released from the core may be assumed to be contained in the containment sump fluids. The licensing basis analysis assumes that a portion of the recirculated fluids leaks intothe auxiliary building during the recirculation phase of operation. Ten percent of the leaked fluids is assumed to flash to steam and become airborne. The radioiodines contained in this flashed fraction of ECCS leakage provide the radioacthie inventory that drives radiological consequences associated Mth this pathway.

One EES train is credited with performing a 90% efficient removal of the iodines associated vth the described pathway. Calculated consequences forthe pathway are direcily proportional to the leak rate of ECCS fluids into the auxiliary building. Technical Specification 5.5.2.b requires that Callaway monitor and minimize the leak rates of sources of recirculated sump fluids. Results of the Technical Specification 5.5.2.b leak rate monitoiing indicate that forthe extended period oftime thatthe EES B train was inoperable, leak rates were significantly lowerthan operational limits and much lowerthan the values assumed in the licensing basis analysis of record. Measured leak rates for all trains combined were less than I drop per minute. The analysis of record is based on a combined leak rate of 2 gallons per minute. The reduced leak rates corresponding to actual plant conditions forthe idenlified time period would have resulted in calculated releases from the post-accident ECCS pathway being significaniiy lowerthan the calculated values reported in the FSAR even thout credit taken forthe Emergency Exhaust charcoal filter adsorber beds.

With regards to the fuel building fuel handling acddent, fuel handling operations of irradiated assemblies were performed during December 2019. One EES train is credited vth performing a 90% efficient removal of radioiodines that would emerge from the surface ofthe spentfuel pool following a postulated fuel handling accident. The licensing basis fuel handling accident described in the Callaway FSAR is based on a limiting fuel assembly that is dropped after 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of subcritical decay time. Callaways FSAR Chapter 1 5 radiological consequence analysis of accidents considers 5 iodine isotopes. The longest-lived ofthese isotopes, 1-131, has a radiological ha[f-life of approximately 8 days. The irradiated fuel handled during December 2019 had at least 8 months of subcritical decaytime. Gap inventories in the handled assemblies were sufficiently low such thatthe calculated release of iodines to the environmentfollong a postulated fuel building fuel handling accident during the period of EES train B inoperability would have been significantly lowerthan those reported in the FSAR even without credit taken for the Emergency Exhaust charcoal filter adsorber beds.U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 0813112023 (08-2020)

1. FACILITY NAME 2 DOCKEi PlUMBER

3. LER NUMBER YEAR SEQUENTIAL REV Callaway Plant Unit I 05000-483 NUMBER NO.

2020

- 001

- 01 The above evaluation of safety consequences is based on complete unavailability ofthe EES function (i.e., both trains inoperable).

Throughout the time thatthe EES B train was determined to be inoperable, the EES Atrain was OPERABLE except only for a brief period oftime on February 12, 2020.

Based on the above considerations, it has been concluded that the degraded/nonconforming condWon ofthe B train Emergency Exhaustfan best did not significantly degrade plant safety.

5.

REPORTING REQUIREMENTS

This LER is submitted pursuantto 50.73(a)(2)(i)(B) as an operation or condition prohibited by Technical Specifications. AddWonally, this LER is submitted pursuant to 50.73(a)(2)(v)(C) and 50.73(a)(2)(v)(D) as a condWon that would have prevented fuWillment of a safety function.

Technical Spedflcation (TS) LCO 3.7.13 requires two trains of the Emergency Exhaust System (EES) to be OPERABLE for the Safety Injection Signal (515) mode of operation during Modes 1, 2, 3, and 4, and during the movement of irradiated fuel assemblies in the fuel building.

The EES B train was inoperable for a duration of approximately 246 days. During this period of inoperability, the plant was operatin in Mode 1. With one EES train inoperable, Required Action A.1 of TS 3.7.13 requires restoring the EES train to OPERABLE status within 7 days. With the Complelion Time of Required Action A.1 not met, Required Actions C.1 and C.2 of TS 3.7.13 require the plant be in Mode 3 Athin 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 Mthin 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. The condition reported in this LER represents an operation or condition not in compliance with the restoralion and shutdown Completion limes of Technical Specification 3.7.13.

Additionally, during December of 2019, a fuel handling campaign was performed in the fuel building. Movement of irradiated fuel assemblies in the fuel building is a specified condition of applicability for TS 3.7.13. With the Required Action and Completion Time of Condition A not met during movement of irradiated fuel assemblies in the fuel building, Required Aclions D.1 and D.2 require either the OPERABLE EES train to be placed in FBVIS mode orthe movement of irradiated fuel assemblies in the fuel building to b immediately suspended. Due to the unknown inoperability ofthe EES B train atthe time ofthe fuel handling campaign, the requirements of Conditions D.1 and D.2 of TS 3.7.13 were not met during the movement of irradiated fuel assemblies in the fuel building.

The EES performs a function that reduces the post-acddent release of radioactive material and mitigates the consequences of an accident. The EES B train was inoperable from June 25, 2019 to February 26, 2020. A review of work history forthe EES A train identified that it was concurrently out of service forthree hours and six minutes for in-place filtertesting on February 12, 2020.

Therefore, on February 12, 2020, both trains of emergency exhaust were unavailable. This represents a condWon thatwould have prevented the fulfillment of a safety function.

Based on the above, this event is being reported as an operation or condition prohibited by Technical Specifications in accordance with 50.73(a)(2)(i)(B) and as a condition that would have prevented fulfillment of a safety function in accordance with 50.73(a)(2)(v)(C) and 50.73(a)(2)(v)(D).

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