IR 05000352/2021002

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Integrated Inspection Report 05000352/2021002 and 05000353/2021002
ML21222A003
Person / Time
Site: Limerick  Constellation icon.png
Issue date: 08/10/2021
From: Jon Greives
Division of Operating Reactors
To: Rhoades D
Exelon Generation Co LLC, Exelon Nuclear
Greives J
References
IR 2021002
Download: ML21222A003 (20)
v • d • e


Text

August 10, 2021

SUBJECT:

LIMERICK GENERATING STATION, UNITS 1 AND 2 - INTEGRATED INSPECTION REPORT 05000352/2021002 AND 05000353/2021002

Dear Mr. Rhoades:

On June 30, 2021, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Limerick Generating Station, Units 1 and 2. On July 30, 2021, the NRC inspectors discussed the results of this inspection with Mr. Frank Sturniolo, Site Vice President, and other members of your staff. The results of this inspection are documented in the enclosed report.

One finding of very low safety significance (Green) is documented in this report. This finding did not involve a violation of NRC requirements.

If you disagree with a cross-cutting aspect assignment or a finding not associated with a regulatory requirement in this report, you should provide a response within 30 days of the date of this inspection report, with the basis for your disagreement, to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, DC 20555-0001; with copies to the Regional Administrator, Region I; and the NRC Resident Inspector at Limerick Generating Station, Units 1 and 2. This letter, its enclosure, and your response (if any) will be made available for public inspection and copying at http://www.nrc.gov/reading-rm/adams.html and at the NRC Public Document Room in accordance with Title 10 of the Code of Federal Regulations 2.390, Public Inspections, Exemptions, Requests for Withholding.

Sincerely, Jonathan E. Greives, Chief Projects Branch 4 Division of Operating Reactor Safety

Docket Nos. 05000352 and 05000353 License Nos. NPF-39 and NPF-85

Enclosure:

As stated

Inspection Report

Docket Numbers:

05000352 and 05000353

License Numbers:

NPF-39 and NPF-85

Report Numbers:

05000352/2021002 and 05000353/2021002

Enterprise Identifier: I-2021-002-0028

Licensee:

Exelon Generation Company, LLC

Facility:

Limerick Generating Station, Units 1 and 2

Location:

Sanatoga, PA 19464

Inspection Dates:

April 1, 2021 through June 30, 2021

Inspectors:

A. Ziedonis, Senior Resident Inspector

S. Haney, Resident Inspector

L. Casey, Senior Project Engineer

H. Anagnostopoulos, Senior Health Physicist

N. Floyd, Senior Reactor Inspector

Approved By:

Jonathan E. Greives, Chief

Projects Branch 4

Division of Operating Reactor Safety

SUMMARY

The U.S. Nuclear Regulatory Commission (NRC) continued monitoring the licensees performance by conducting an integrated inspection at Limerick Generating Station, Units 1 and 2, in accordance with the Reactor Oversight Process. The Reactor Oversight Process is the NRCs program for overseeing the safe operation of commercial nuclear power reactors.

Refer to https://www.nrc.gov/reactors/operating/oversight.html for more information.

List of Findings and Violations

Failure to Follow the Temporary Leak Repair Process Results in Internal Flooding Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events Green FIN 05000352,05000353/2021002-01 Open/Closed

[P.3] -

Resolution 71152 The inspectors determined there was a self-revealing Green finding against procedure CC-AA-404, Maintenance Specification: Application Selection, Evaluation and Control of Temporary Leak Repairs, Revision 8, because Exelon did not plan for a permanent method to address a temporary leak repair, performed in 2016, associated with a circulating water pipe leak of approximately 200 to 300 gallons per minute (gpm). Consequently, the temporary repair failed in 2021, resulting in an approximate 400 gpm leak and subsequent internal flooding of the north condenser bay and adjacent condensate pump room.

Additional Tracking Items

Type Issue Number Title Report Section Status LER 05000352/2020-002-00 LER 05000352/2020-002-00,

HPCI and RCIC Were Not Un-Isolated During Startup Resulting in Technical Specification Violations 71153 Closed

PLANT STATUS

Unit 1 began the inspection period at rated thermal power. On June 19, 2021, the unit was down powered to approximately 72 percent for control rod testing and a control rod sequence exchange. The unit was returned to rated thermal power on June 20, 2021, and remained at or near rated thermal power for the remainder of the inspection period.

Unit 2 began the inspection period at approximately 84 percent power in its end-of-cycle coastdown. On April 25, 2020, the unit was down powered and then shut down on April 26, 2021, for a planned refueling outage (2R16). The unit was restarted on May 14, 2021, and returned to rated thermal power on May 18, 2021. On May 19, 2021, the unit was down powered to approximately 81 percent for a control rod pattern adjustment, and was returned to rated thermal power on May 20, 2021. On May 28, 2021, the unit was down powered to approximately 83 percent for a control rod pattern adjustment. The unit was returned to rated thermal power on May 29, 2021, and remained at or near rated thermal power for the remainder of the inspection period.

INSPECTION SCOPES

Inspections were conducted using the appropriate portions of the inspection procedures (IPs) in effect at the beginning of the inspection unless otherwise noted. Currently approved IPs with their attached revision histories are located on the public website at http://www.nrc.gov/reading-rm/doc-collections/insp-manual/inspection-procedure/index.html. Samples were declared complete when the IP requirements most appropriate to the inspection activity were met consistent with Inspection Manual Chapter (IMC) 2515, Light-Water Reactor Inspection Program - Operations Phase. The inspectors reviewed selected procedures and records, observed activities, and interviewed personnel to assess licensee performance and compliance with Commission rules and regulations, license conditions, site procedures, and standards.

Starting on March 20, 2020, in response to the National Emergency declared by the President of the United States on the public health risks of the coronavirus (COVID-19), resident and regional inspectors were directed to begin telework and to remotely access licensee information using available technology. During this time, the resident inspectors performed periodic site visits each week, increasing the amount of time on site as local COVID-19 conditions permitted.

As part of their onsite activities, resident inspectors conducted plant status activities as described in IMC 2515, Appendix D; observed risk significant activities; and completed on site portions of IPs. In addition, resident and regional baseline inspections were evaluated to determine if all or a portion of the objectives and requirements stated in the IP could be performed remotely. If the inspections could be performed remotely, they were conducted per the applicable IP. In some cases, portions of an IP were completed remotely and on site. The inspections documented below met the objectives and requirements for completion of the IP.

REACTOR SAFETY

71111.01 - Adverse Weather Protection

Seasonal Extreme Weather Sample (IP Section 03.01) (1 Sample)

(1) The inspectors evaluated readiness for seasonal extreme weather conditions prior to the onset of seasonal hot temperatures for the offsite and onsite alternate current power systems on June 3, 2021

71111.04 - Equipment Alignment

Partial Walkdown Sample (IP Section 03.01) (4 Samples)

The inspectors evaluated system configurations during partial walkdowns of the following systems/trains:

(1) Unit common 'A' emergency service water following pipe section 15A replacement on April 20, 2021
(2) Unit 2 alternate decay heat removal with the reactor cavity flooded up and the spent fuel gate removed on May 4, 2021
(3) Unit 2 water inventory control associated with control rod drive mechanism changeout on May 4, 2021
(4) Unit 2 hydraulic control unit 42-11 control rod drive system alignment with directional control valve (SV-047-2-23LC) leakage on June 2, 2021

Complete Walkdown Sample (IP Section 03.02) (1 Sample)

(1) The inspectors evaluated system configurations during a complete walkdown of the Unit 1 and Unit 2 safety-related 4 kilovolt electrical distribution on June 24, 2021

71111.05 - Fire Protection

Fire Area Walkdown and Inspection Sample (IP Section 03.01) (5 Samples)

The inspectors evaluated the implementation of the fire protection program by conducting a walkdown and performing a review to verify program compliance, equipment functionality, material condition, and operational readiness of the following fire areas:

(1) Fire Areas 83-86, Unit 2 emergency diesel generator rooms on April 5, 2021
(2) Fire Area 70, Unit 2 standby liquid control and general equipment areas on April 20, 2021
(3) Fire Area 24, Unit common main control room and associated safe shutdown strategies on May 15, 2021
(4) Fire Area 34, Unit 1 high pressure coolant injection pump and turbine room on June 25, 2021
(5) Fire Area 32, Unit 1 'A' residual heat removal pump and heat exchanger room on June 28, 2021

71111.07A - Heat Sink Performance

Annual Review (IP Section 03.01) (1 Sample)

The inspectors evaluated readiness and performance of:

(1) Unit 2 'A' residual heat removal heat exchanger on April 30, 2021

71111.08G - Inservice Inspection Activities (BWR)

BWR Inservice Inspection Activities Sample - Nondestructive Examination and Welding

Activities (IP Section 03.01)

Main article: IP 71111.08G
(1) The inspectors verified that the reactor coolant system boundary, reactor vessel internals, risk significant piping system boundaries, and containment boundary are appropriately monitored for degradation and that repairs and replacements were appropriately fabricated, examined and accepted by reviewing the following activities from April 26 through May 7, 2021:

03.01.a - Nondestructive Examination and Welding Activities.

===718100)

  • Manual ultrasonic testing of the control rod drive return nozzle to vessel weld, N9 (NDE Report LIM-2-711500)
  • Visual examinations of the in-vessel visual inspection of reactor components, including the jet pumps, anti-vibration system modification, and core spray piping (WO 05085728)

71111.11Q - Licensed Operator Requalification Program and Licensed Operator Performance

Licensed Operator Performance in the Actual Plant/Main Control Room (IP Section 03.01)

=

Main article: IP 71810
(1) The inspectors observed and evaluated licensed operator performance in the Control Room during Unit 2 reactor shutdown on April 26, 2021 and Unit 2 reactor startup on May 14, 2021

Licensed Operator Requalification Training/Examinations (IP Section 03.02) (1 Sample)

(1) The inspectors observed and evaluated licensed operator requalification training on June 14, 2021

71111.12 - Maintenance Effectiveness

Maintenance Effectiveness (IP Section 03.01) (1 Sample)

The inspectors evaluated the effectiveness of maintenance to ensure the following structures, systems, and components (SSCs) remain capable of performing their intended function:

(1) Unit 1 high pressure coolant injection system and reactor core isolation cooling system steam supplies isolated during startup on November 16, 2020

Quality Control (IP Section 03.02) (1 Sample)

The inspectors evaluated the effectiveness of maintenance and quality control activities to ensure the following SSC remains capable of performing its intended function:

(1) Unit 2 'A' reactor recirculation pump seal replacement on May 1, 2021

71111.13 - Maintenance Risk Assessments and Emergent Work Control

Risk Assessment and Management Sample (IP Section 03.01) (6 Samples)

The inspectors evaluated the accuracy and completeness of risk assessments for the following planned and emergent work activities to ensure configuration changes and appropriate work controls were addressed:

(1) Unit 1 circulating water system pipe leak repair on April 1, 2021
(2) Unit 2 yellow risk condition for reactor lowered inventory during cavity draindown on May 9, 2021
(3) Unit 2 reactor coolant system heatup and cooldown during reactor pressure vessel hydrostatic testing on May 27, 2021
(4) Unit 1 protected equipment walkdown during 'D12' emergency diesel generator planned maintenance on June 7 and 8, 2021
(5) Unit 1 action green risk condition during a high pressure coolant injection system planned maintenance window the week of June 20, 2021
(6) Unit 1 'A' train shutdown cooling valve actuator maintenance during hot weather alert on June 28, 2021

71111.15 - Operability Determinations and Functionality Assessments

Operability Determination or Functionality Assessment (IP Section 03.01) (5 Samples)

The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:

(1) Unit 2 circulating water nondestructive evaluation and pipe functionality on May 2, 2021
(2) Unit 2 reactor core isolation cooling pump lube oil cooler tube plugging on May 4, 2021
(3) Unit common emergency service water discharge check valve to residual heat removal service water (11-65A) on May 12, 2021
(4) Unit 1 high pressure coolant injection pump seal gland pitting and inboard mechanical seal leak on June 28, 2021
(5) Unit 1 'D13' bus undervoltage relay (127Z-11709) found out of calibration (IR

===4429953) on June 30, 2021

71111.18 - Plant Modifications

Temporary Modifications and/or Permanent Modifications (IP Section 03.01 and/or 03.02)

=

Main article: IP 44299

The inspectors evaluated the following temporary or permanent modifications:

(1) Unit 2 primary containment instrument gas tubing supply to the main steam isolation valves on April 29, 2021
(2) Unit 2 'A' residual heat removal heat exchanger partition plate repair on April 30, 2021

71111.19 - Post-Maintenance Testing

Post-Maintenance Test Sample (IP Section 03.01) (9 Samples)

The inspectors evaluated the following post-maintenance test activities to verify system operability and functionality:

(1) Unit 1 circulating water pipe clamp installation and leak injection on April 14, 2021
(2) Unit 2 main steam relief valves 'B', 'D', 'G', 'H', and 'J' replacement on May 7, 2021
(3) Unit 2 suppression pool coating inspection and application on May 10, 2021
(4) Unit 2 circulating water pipe penetration wrap curing on May 10, 2021
(5) Unit 2 'B' shutdown cooling valve (HV-051-2F050B) air operator repair on May 13, 2021
(6) Unit 2 drywell purge exhaust instrument line primary containment isolation solenoid valve repair on June 1, 2021
(7) Unit 1 average power range monitor #1 following high voltage power supply replacement on June 4, 2021
(8) Unit 1 'D12' emergency diesel generator 'A' and 'B' emergency start relays replacement on June 11, 2021
(9) Unit 1 'D12' emergency diesel generator following planned maintenance on June 15, 2021

71111.20 - Refueling and Other Outage Activities

Refueling/Other Outage Sample (IP Section 03.01) (1 Sample)

(1) The inspectors evaluated Unit 2 refueling outage (2R16) activities from April 26, 2021 through May 14, 2021

71111.22 - Surveillance Testing

The inspectors evaluated the following surveillance tests:

Surveillance Tests (other) (IP Section 03.01)

Main article: IP 71111.22
(1) ST-6-088-323-2, Unit 2 remote shutdown system 'D23' safeguard breaker operability test on May 4, 2021
(2) ST-6-092-117-2, Unit 2 'D23' emergency diesel generator loss of coolant accident/

loss of offsite power test on May 4, 2021

(3) ST-4-041-210-2, Unit 2 main steam relief valve test on May 6, 2021
(4) ST-6-055-231-1, Unit 1 high pressure coolant injection pump comprehensive test on June 29, 2021

Inservice Testing (IP Section 03.01) (1 Sample)

(1) ST-6-041-202-2, Unit 2 main steam isolation valve cold shutdown valve test on April 27, 2021

Containment Isolation Valve Testing (IP Section 03.01) (1 Sample)

(1) ST-4-LLR-03/4/5/61-2, Unit 2 main steam line 'A'/'B'/'C'/'D' local leak rate tests on May 6,

RADIATION SAFETY

71124.01 - Radiological Hazard Assessment and Exposure Controls

Radiological Hazard Assessment (IP Section 03.01) (1 Sample)

(1) The inspectors evaluated how the licensee identifies the magnitude and extent of radiation levels and the concentrations and quantities of radioactive materials and how the licensee assesses radiological hazards.

Instructions to Workers (IP Section 03.02) (1 Sample)

The inspectors evaluated instructions to workers including radiation work permits used to access high radiation areas.

(1) The inspectors reviewed the following:

Radiation Work Packages

  • LG-0-21-00701
  • LG-0-21-00711
  • LG-0-21-00508

Electronic Alarming Dosimeter Alarms

  • Alarm on March 28, 2021 at 1547 Labeling of Containers
  • B-25 box of diver's equipment at the suppression pool control point
  • Drum of local leak rate test equipment at the control rod drive mechanism hydraulic control units
  • Bags of dry active waste on the refuel floor

Contamination and Radioactive Material Control (IP Section 03.03) (2 Samples)

The inspectors evaluated licensee processes for monitoring and controlling contamination and radioactive material.

(1) Observed in-process radiological controls while removing equipment from the water during local power range monitor removal
(2) Observed personnel and material being released from the suppression pool contamination area control point

Radiological Hazards Control and Work Coverage (IP Section 03.04) (3 Samples)

The inspectors evaluated in-plant radiological conditions during facility walkdowns and observation of radiological work activities.

(1) Initial entry into the condenser hotwell
(2) Diving operations in the suppression pool
(3) Work on nuclear detectors under-vessel

High Radiation Area and Very High Radiation Area Controls (IP Section 03.05) (2 Samples)

The inspectors evaluated licensee controls of the following High Radiation Areas and Very High Radiation Areas:

(1) The drywell personnel access airlock
(2) The reactor pressure vessel head insulation package on the refuel floor

Radiation Worker Performance and Radiation Protection Technician Proficiency (IP Section 03.06) (1 Sample)

(1) The inspectors evaluated radiation worker and radiation protection technician performance as it pertains to radiation protection requirements

OTHER ACTIVITIES - BASELINE

===71151 - Performance Indicator Verification

The inspectors verified licensee performance indicators submittals listed below:

MS05: Safety System Functional Failures (SSFFs) Sample (IP Section 02.04)===

Main article: IP 71151
(1) Unit 1 SSFFs April 1, 2020 through March 31, 2021
(2) Unit 2 SSFFs April 1, 2020 through March 31, 2021

MS06: Emergency AC Power Systems (IP Section 02.05) (2 Samples)

(1) Unit 1 Emergency AC Power Systems April 1, 2020 through March 31, 2021
(2) Unit 2 Emergency AC Power Systems April 1, 2020 through March 31, 2021

MS07: High Pressure Injection Systems (IP Section 02.06) (2 Samples)

(1) Unit 1 High Pressure Injection System January 1, 2020 through December 31, 2020
(2) Unit 2 High Pressure Injection System January 1, 2020 through December 31, 2020

MS08: Heat Removal Systems (IP Section 02.07) (2 Samples)

(1) Unit 1 Heat Removal System January 1, 2020 through December 31, 2020
(2) Unit 2 Heat Removal System January 1, 2020 through December 31, 2020

71152 - Problem Identification and Resolution

Semiannual Trend Review (IP Section 02.02) (1 Sample)

(1) The inspectors reviewed the licensees corrective action program for potential adverse trends that might be indicative of a more significant safety issue.

Annual Follow-up of Selected Issues (IP Section 02.03) (1 Sample)

The inspectors reviewed the licensees implementation of its corrective action program related to the following issues:

(1) Unit 1 circulating water pipe leak and associated corrective action program evaluation (CAPE) 4410585-22

71153 - Follow-up of Events and Notices of Enforcement Discretion Event Report (IP Section 03.02)

Main article: IP 71153

The inspectors evaluated the following licensee event reports (LERs):

(1) LER 05000352/2020-002-00, HPCI and RCIC Were Not Un-Isolated During Startup Resulting in Technical Specification Violations (ADAMS Accession No. ML21015A017). The inspection conclusions associated with this LER are documented in Inspection Report 05000352/2021001 under the Inspection Results Section. This LER is closed.

INSPECTION RESULTS

Failure to Follow the Temporary Leak Repair Process Results in Internal Flooding Cornerstone Significance Cross-Cutting Aspect Report Section Initiating Events

Green FIN 05000352,05000353/2021002-01 Open/Closed

[P.3] -

Resolution 71152 The inspectors determined there was a self-revealing Green finding against procedure CC-AA-404, Maintenance Specification: Application Selection, Evaluation and Control of Temporary Leak Repairs, Revision 8, because Exelon did not plan for a permanent method to address a temporary leak repair, performed in 2016, associated with a circulating water pipe leak of approximately 200 to 300 gallons per minute (gpm). Consequently, the temporary repair failed in 2021, resulting in an approximate 400 gpm leak and subsequent internal flooding of the north condenser bay and adjacent condensate pump room.

Description:

On March 21, 2021, Unit 1 placed the B loop of circulating water in service during power ascension following a planned load reduction to perform maintenance and testing activities. Operators identified an estimated 400 gpm un-isolable leak from the B circulating water piping inside the north condenser bay area during leak investigation in response to a significant increase in radwaste system water inventory with continuous operation of the radwaste floor and equipment drain sump pumps. Operators placed the power ascension on hold at 8:15 PM and entered the applicable special event procedure to respond to the internal flooding. The leakage resulted in several inches of standing water on the floor of the north condenser bay area, and overfilled an adjacent sump pit at a lower elevation in the condensate pump room. Operators were dispatched to install multiple submersible sump pumps in the condensate pump room, which contains all three condensate system pumps and motors for Unit 1. In parallel, operators in the main control room conducted a contingency briefing for a rapid plant shutdown if water level in the condensate pump room reached a level that would potentially cause a loss of main feedwater event.

Operators reviewed the Emergency Action Levels (EALs) for internal flooding, and determined that no EAL conditions were applicable, since the flooding did not impact any safety systems required by technical specifications. At 4:25 AM on March 22, 2021, level in the condensate pump room was reported to have peaked at approximately 50 inches and began to lower (pump motors were measured at 104 inches), based on the capacity of multiple installed submersible sump pumps. The inspectors responded to the internal flooding event, walked down the areas impacted by the flooding, interviewed operators, and determined the actions taken during the event were timely and appropriate.

During subsequent days, Exelon planned temporary leak repair solutions, and staged additional back-up sump pumps in the vicinity of the condensate sump pump room and north condenser bay area. Following inquiries by the inspectors, Exelon took additional actions, including protecting the high pressure coolant injection and reactor core isolation cooling systems, staging sandbags in adjacent areas of the plant, and establishing an adverse condition monitoring plan. On April 14, 2021, Exelon successfully completed a temporary leak repair that consisted of a 2000-pound carbon steel ring clamp, bolted to the floor, with multiple leak injection ports. The inspectors walked down the temporary leak repair and independently verified no active leakage from the ring clamp, interviewed maintenance staff, reviewed the applicable documentation regarding the temporary leak repair, and determined Exelons actions were appropriate.

Exelon conducted a CAPE under IR 4410585, and determined the cause of the leak was removal of the temporary repair from the tracking list without a permanent repair or an engineering evaluation. Exelon determined this was a failure to comply with CC-AA-404, Maintenance Specification: Application Selection, Evaluation and Control of Temporary Leak Repairs, Revision 8. Specifically, an estimated 200-300 gpm leak was identified at the same location in April 2016, while restoring circulating water to service during cold shutdown conditions in a refueling outage. To address the leakage, Exelon removed the circulating water system from service, and installed a concrete grout curb around the 78-inch diameter pipe at the floor penetration, where the leak was located. Engineering performed a technical evaluation which approved the housekeeping curb as a corrosion prevention measure, but did not evaluate the curb as a long term repair option. Additionally, the temporary leak repair was never formally approved or tracked, and was removed from the Plan of Day tracking list in July of 2017, with no subsequent engineering evaluation or permanent repair plan. In April 2018, leakage from the same location was identified during startup from a refueling outage, and rubber gasket material was used with a load binding strap to mitigate the leakage, but with no temporary repair documentation. In June of 2020, IR 4351278 was written to capture minor leakage from the same circulating water pipe location on Unit 1, which discussed the 2016 repair attempt, but did not evaluate the temporary nature of the repairs nor perform a justification of the allowable duration.

The inspectors reviewed the CAPE, as well as CC-AA-404, Revision 8. The inspectors noted step 8.1.1.2 required generating a work order to plan the removal of the temporary leak repair (system outage, load drop, refuel outage, etc.), and step 8.1.1.4.5 required engineering evaluation if the temporary repair was to remain installed greater than one refueling cycle.

Contrary to this, no work order was generated to plan the removal of the temporary repair, and no engineering approval was completed to authorize installation for greater than one refueling cycle following the 2016 installation.

Corrective Actions: Exelon corrected the leakage by installing a temporary injection ring clamp external to the piping. Exelon performed a CAPE, which identified the cause of the leak was the failure to adequately address a previous temporary leak repair at the same location from 2016. Exelon assigned corrective actions to perform a permanent repair, and to address the extent of condition on similar circulating water piping on Unit 1 and Unit 2.

Corrective Action References: IR 4410585

Performance Assessment:

Performance Deficiency: The inspectors determined that Exelons actions to address a previous circulating water leak from the same location did not comply with the temporary leak repair process, as outlined in the station procedure, was reasonably within Exelons ability to foresee and prevent, and therefore was a performance deficiency. Specifically, procedure CC-AA-404, Maintenance Specification: Application Selection, Evaluation and Control of Temporary Leak Repairs, Revision 8, steps 8.1.1.2 and 8.1.1.4.5 were not complied with regarding the generation of a work order to plan removal of the temporary leak repair from 2016 and perform and engineering evaluation to authorize installation for greater than one refueling cycle. The inspectors also noted more recent performance opportunities to reassess the 2016 temporary repair, in 2018 and 2020, when subsequent leakage was identified from the same location.

Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Protection Against External Factors attribute of the Initiating Events cornerstone and adversely affected the cornerstone objective to limit the likelihood of events that upset plant stability and challenge critical safety functions during shutdown as well as power operations. Specifically, the inspectors determined that the 400 gpm circulating water system leak increased the likelihood of a loss of feedwater event, which is a complicated scram that would challenge reactor vessel level control during power operation.

Significance: The inspectors assessed the significance of the finding using Appendix A, The Significance Determination Process (SDP) for Findings At-Power. The inspectors determined that the finding resulted in internal flooding in the turbine building and increased the likelihood of a loss of condensate and feedwater, which would result in a plant trip. As directed by IMC 0609, Appendix A, Exhibit 1, Section E a detailed risk evaluation was required.

The evaluation was conducted with the aid of SAPHIRE 8.2.3 using Limerick (Unit 1) SPAR Model version 8.59, with LERF assessment screening factors enabled. The finding resulted in turbine building flooding and is originally modeled in SPAR as internal flooding in the turbine building enclosure (IE-FLI-TE). For this finding, consequential turbine building flooding would result when flooding level reaches over 104 inches resulting in the loss of condensate pumps which causes a loss of main feedwater and reactor trip. This also closely represents the dominant accident sequence: turbine building enclosure flood, loss of main feedwater and the condenser, failure of high pressure injection, and the failure to depressurize the reactor to permit low pressure injection.

An appropriate surrogate for consequential flooding for this finding is represented by the initiating event (IE-FLI-TE) multiplied by a non-recovery probability estimated by evaluating plant and licensee response to the flooding during the exposure period. SPAR-H, a human reliability analysis tool, was used to estimate a non-recovery probability. Based on the initial response and subsequent staging of pumps and monitoring, a consequential impact time of greater than 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> was assumed. The human reliability analysis considered an obvious diagnosis of flooding with extra time available. It also considered the situation to be high-stress and that there were no direct procedures to mitigate flooding. Other input factors were left at nominal values. The resulting estimate for non-recovery probability ranged from 0.1 to 0.2. A value 0.15 was used for the nominal analysis. The analyst also considered potential failure of the sump pumps, but their failure probability was bounded by the human error probability. Also, based on operating history and low decay heat, early control rod drive injection credit was applied by adjusting, as surrogates, high pressure coolant injection and reactor core isolation cooling failure-to-run probabilities.

Based on these inputs, an estimated increase in core delta frequency (CDF) is 4E-7/year, bounded by the increase in frequency of the initiating event (consequential turbine building flooding) minus the baseline risk. The risk, based on delta-CDF, was determined to be of very low safety significance, Green.

The finding being evaluated directly relates to flooding; it dominates the risk from any other external event. Other external events and fire risk to the turbine building are primarily determined by external event initiating frequencies. These frequencies are very low compared to the case evaluated, and hence, are not considered in this evaluation.

Since the delta-CDF is >1E-7/year, a large early release frequency (LERF) phase 2 assessment was conducted as required by IMC 0609, Appendix H. This is conducted by reviewing dominant accident sequences that contribute more than 1E-8/year and assessing their LERF contribution based on IMC 0609, Appendix H, Table 6.2, LERF factors. These Appendix H LERF factors are considered conservative bounding values. The resulting SAPHIRE LERF screening estimate for this analysis was less than <1E-7/year, which results in a very low risk safety significance, Green. This bounds any LERF contribution from internal events and is consistent with risk estimate from delta-CDF. The overall conclusion is that risk was determined to be of very low significance, Green.

Cross-Cutting Aspect: P.3 - Resolution: The organization takes effective corrective actions to address issues in a timely manner commensurate with their safety significance. Specifically, Exelon did not take effective corrective actions to address a temporary leak repair on the B circulating water pipe to ensure that a permanent repair method was planned in a timely manner to appropriately address the cause of the leakage.

Enforcement:

Inspectors did not identify a violation of regulatory requirements associated with this finding.

EXIT MEETINGS AND DEBRIEFS

The inspectors verified no proprietary information was retained or documented in this report.

  • On May 7, 2021, the inspectors presented the Unit 2 ISI inspection results to Mr. Frank Sturniolo, Site Vice President, and other members of the licensee staff.
  • On July 30, 2021, the inspectors presented the integrated inspection results to Mr. Frank Sturniolo, Site Vice President, and other members of the licensee staff.

DOCUMENTS REVIEWED

Inspection

Procedure

Type

Designation

Description or Title

Revision or

Date

71111.01

Procedures

GP-7.1

Summer Weather Preparation and Operation

Revision 44

WC-AA-107

Seasonal Readiness

Revision 22

71111.04

Corrective Action

Documents

2593375,

246283,

23895

Drawings

E-0015, Sheet 1

Unit 1 Single Line Meter and Relay Diagram 4kV Safeguard

Power System

Revision 31

E-0016, Sheet 1

Unit 2 Single Line Meter and Relay Diagram 4kV Safeguard

Power System

Revision 27

Miscellaneous

L-S-05

4kV System

Revision 10

L-S-15

Control Rod Drive System

Revision 11

71111.05

Fire Plans

F-D-315A

Unit 2, D21 Diesel Generator and Fuel Oil-Lube Oil Tank

Room, RMS 315A and 316A (EL 217), Fire Area 83

Revision 10

F-D-315B

Unit 2, D22 Diesel Generator and Fuel Oil-Lube Oil Tank

Room, RMS 315B and 316B (EL 217), Fire Area 85

Revision 11

F-D-315C

Unit 2, D23 Diesel Generator and Fuel Oil-Lube Oil Tank

Room, RMS 315C and 316C (EL 217), Fire Area 84

Revision 11

F-D-315D

Unit 2, D24 Diesel Generator and Fuel Oil-Lube Oil Tank

Room, RMS 315D and 316D (EL 217), Fire Area 86

Revision 10

F-R-574

Unit 2, Standby Liquid Control and General Equipment

Areas, RWCU Compartments, FPCW Area, and Main Steam

Tunnel, RMS 574 thru 585, 593, and 594 (EL 283 and 295),

Fire Area 70

Revision 17

71111.07A

Work Orders

260566

71111.08G Miscellaneous

ER-LG-330-1001

ISI Program Plan Fourth Ten-Year Inservice Inspection

Interval

Revision 19

71111.11Q Miscellaneous

LG2C16-90.1

Unit 2 Reactor Shutdown Reactivity Maneuver Approval

04/22/2021

Procedures

GP-3

Normal Plant Shutdown

Revision 17

71111.12

Corrective Action

Documents

4384739

Corrective Action

Documents

4432028

NRC ID: IR 4384739 Incorrectly Screened for MR Functional

Failure

06/28/2021

Inspection

Procedure

Type

Designation

Description or Title

Revision or

Date

Resulting from

Inspection

Procedures

ER-AA-320-1004

Maintenance Rule 18-10 - Performance Monitoring and

Dispositioning Between (a)(1) and (a)(2)

Revision 1

71111.13

Corrective Action

Documents

4392945,

4402480,

4404073,

4432134,

4432413,

4432792

RHR SDC valve maintenance (1F006A) IRs

2/30/2020,

2/15/2021,

2/23/2021,

06/29-

30/2021,

07/01/2021

71111.15

Corrective Action

Documents

01048641,

04395937,

04431048,

04431706

01197319,

01422546,

04420968

Procedures

M-C-750-003

RCIC Turbine Lube Oil Cooler Maintenance

Revision 2

MA-AA-716-010-

1104

Mechanical Seal Leakage Evaluation and Reporting

Revision 0

Work Orders

250488,

4754310

28979

71111.18

Engineering

Changes

ECR 01-00969

RHR Heat Exchanger Partition Plate Repair

Revision 2

71111.19

Corrective Action

Documents

28139,

28187,

28748,

28499

D12 inspection IRs

06/08-

11/2021

Work Orders

4941164,

4941113

71111.20

Corrective Action

Documents

Resulting from

23238

NRC ID: 2A RHR HX Outlet Temp Higher than Inlet Temp

05/12/2021

Inspection

Procedure

Type

Designation

Description or Title

Revision or

Date

Inspection

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