IR 05000352/2018004
| ML19044A637 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 02/13/2019 |
| From: | Jon Greives Reactor Projects Region 1 Branch 4 |
| To: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| Greives J | |
| References | |
| IR 2018004 | |
| Download: ML19044A637 (18) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION ary 13, 2019
SUBJECT:
LIMERICK GENERATING STATION - INTEGRATED INSPECTION REPORT 05000352/2018004 AND 05000353/2018004
Dear Mr. Hanson:
On December 31, 2018, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Limerick Generating Station, Units 1 and 2. On January 11, 2019, the NRC inspectors discussed the results of this inspection with Mr. Rick Libra, Site Vice President, and other members of your staff. The results of this inspection are documented in the enclosed report.
NRC inspectors documented one finding of very low safety significance (Green) in this report.
This finding involved a violation of NRC requirements. The NRC is treating this violation as a non-cited violation (NCV) consistent with Section 2.3.2.a of the Enforcement Policy.
If you contest the violation or significance of the NCV, you should provide a response within 30 days of the date of this inspection report, with the basis for your denial, to the Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, DC 20555-0001; with copies to the Regional Administrator, Region I; the Director, Office of Enforcement; and the NRC Resident Inspector at Limerick Generating Station. In addition, if you disagree with the cross-cutting aspect assignment 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. 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 the NRC Public Document Room in accordance with 10 CFR 2.390, Public Inspections, Exemptions, Requests for Withholding.
Sincerely,
/RA/
Jonathan E. Greives, Chief Reactor Projects Branch 4 Division of Reactor Projects Docket Nos. 50-352 and 50-353 License Nos. NPF-39 and NPF-85
Enclosure:
Inspection Report 05000352/2018004 and 05000353/2018004
Inspection Report
Docket Numbers: 50-352 and 50-353 License Numbers: NPF-39 and NPF-85 Report Numbers: 05000352/2018004 and 05000353/2018004 Enterprise Identifier: I-2018-004-0073 Licensee: Exelon Generation Company, LLC Facility: Limerick Generating Station, Units 1 & 2 Location: Sanatoga, PA 19464 Inspection Dates: October 1, 2018 to December 31, 2018 Inspectors: S. Rutenkroger, PhD, Senior Resident Inspector M. Fannon, Resident Inspector H. Anagnostopoulos, Senior Health Physicist J. DeBoer, Emergency Preparedness Inspector P. Ott, Operations Engineer C. Hobbs, Reactor Inspector M. Rossi, Project Engineer Approved By: Jonathan E. Greives, Chief Reactor Projects Branch 4 Division of Reactor Projects Enclosure
SUMMARY
The U.S. Nuclear Regulatory Commission (NRC) continued monitoring Exelons performance at
Limerick Generating Station (LGS), Units 1 and 2 by conducting the baseline inspections described in this report 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. NRC-identified and self-revealed findings, violations, and additional items are summarized in the table below.
List of Findings and Violations Failure to Maintain the Design Control of the D23 Emergency Diesel Generator Cornerstone Significance Cross-cutting Report Aspect Section Mitigating Green H.11 - Human 71152 Systems NCV 05000353/2018004-01 Performance -
Opened/Closed Challenge the Unknown A self-revealing Green non-cited violation (NCV) of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B, Criterion III was identified when Exelon replaced the D23 emergency diesel generator lube oil heater temperature switch with a new style switch on December 6, 2018. The new style switch subsequently failed on December 7, 2018, due to overheating and charring of the switch wiring when coming in contact with the cover.
Additional Tracking Items Type Issue number Title Report Status Section LER 05000353/2018-001-00 HPCI Inoperability due to 71153 Closed Discharge Check Valve Failure to Close
TABLE OF CONTENTS
PLANT STATUS
INSPECTION SCOPES
................................................................................................................
REACTOR SAFETY
..................................................................................................................
RADIATION SAFETY
................................................................................................................
OTHER ACTIVITIES - BASELINE
............................................................................................
INSPECTION RESULTS
..............................................................................................................
EXIT MEETINGS AND DEBRIEFS
............................................................................................ 13 THIRD PARTY REVIEWS .......................................................................................................... 13
DOCUMENTS REVIEWED
......................................................................................................... 14
PLANT STATUS
Unit 1 began the inspection period at rated thermal power. On December 16, 2018, operators
reduced power to 57 percent for power suppression testing. The unit was returned to rated
thermal power on December 20, 2018, and remained at or near rated thermal power for the
remainder of the inspection period.
Unit 2 began the inspection period at rated thermal power. On December 29, 2018, operators
reduced power to 70 percent for repairs on the main turbine control valve #4. The unit was
returned to rated thermal power on December 30, 2018, 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 also performed plant status activities described
in IMC 2515, Appendix D, Plant Status, and conducted routine reviews using IP 71152,
Problem Identification and Resolution. 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.
REACTOR SAFETY
71111.01 - Adverse Weather Protection
Seasonal Extreme Weather (1 Sample)
The inspectors evaluated readiness for seasonal extreme weather conditions prior to
seasonal cold temperatures.
71111.04 - Equipment Alignment
Partial Walkdown (3 Samples)
The inspectors evaluated system configurations during partial walkdowns of the following
systems/trains:
(1) Unit common A control room fresh air system on October 11, 2018
(2) Unit common emergency service water system on October 19, 2018
(3) Unit common residual heat removal service water system on October 22, 2018
Complete Walkdown (1 Sample)
The inspectors evaluated system configurations during a complete walkdown of the Unit 2
high pressure coolant injection system.
71111.05AQ - Fire Protection Annual/Quarterly
Quarterly Inspection (5 Samples)
The inspectors evaluated fire protection program implementation in the following selected
areas:
(1) Fire areas 122 and 123, Unit common spray pond pump structure, on October 19, 2018
(2) Fire area 56, Unit 2 reactor core isolation cooling pump room, on November 15, 2018
(3) Fire area 80, Unit 1 D13 emergency diesel generator and fuel oil-lube oil tank room, on
November 16, 2018
(4) Fire areas 31 and 32, Unit 1 residual heat removal heat exchanger and pump rooms 203
and 204, elevation 201, on November 19, 2018
(5) Fire areas 54 and 55, Unit 2 residual heat removal heat exchanger and pump rooms 280
and 281, elevation 201, on November 19, 2018
71111.06 - Flood Protection Measures
Internal Flooding (1 Sample)
The inspectors evaluated internal flooding mitigation protections in the Unit 2 A and C
residual heat removal pump room on December 27, 2018.
71111.11 - Licensed Operator Requalification Program and Licensed Operator Performance
Operator Requalification (1 Sample)
The inspectors observed and evaluated licensed operator requalification training on
October 23, 2018.
Operator Performance (1 Sample)
The inspectors observed Unit common A loop residual heat removal service water pump
testing, Unit common emergency service water throttle valve flushing, and Unit 1 redundant
reactivity control system restoration on December 1, 2018. The inspectors also observed
Unit 1 power suppression testing on December 17, 2018.
71111.11A - Licensed Operator Requalification Program and Licensed Operator Performance
(Annual)
Operator Requalification Exam Results (Annual) (1 Sample)
The inspectors reviewed and evaluated requalification examination results on December 10,
2018.
71111.12 - Maintenance Effectiveness
Routine Maintenance Effectiveness (1 Sample)
The inspectors evaluated the effectiveness of routine maintenance activities associated with
the following equipment and/or safety significant functions:
(1) Unit 2 high pressure coolant injection system
71111.13 - Maintenance Risk Assessments and Emergent Work Control (4 Samples)
The inspectors evaluated the risk assessments for the following planned and emergent work
activities:
(1) Unit 2 D23 emergency diesel generator fuel oil storage tank cleaning and inspection on
October 15, 2018
(2) Unit 2 A division 1 nuclear steam supply shutoff system logic test on November 2, 2018
(3) Unit 1 high pressure coolant injection testing on November 6, 2018
(4) Unit 2 reactor core isolation cooling flow controller replacement on November 13, 2018
71111.15 - Operability Determinations and Functionality Assessments (6 Samples)
The inspectors evaluated the following operability determinations and functionality
assessments:
(1) Issue Report (IR) 4178994, Unit 1 D11 emergency diesel generator speed meter
fluctuations on October 1, 2018
(2) IR 4185363, Unit 2 standby liquid control tank foreign material on October 24, 2018
(3) IR 4183163, Unit 2 D22 emergency diesel generator discharge coupling lube oil leak on
October 25, 2018
(4) IR 4166174, Unit 2 emergency diesel generator keepwarm system issues on
October 26, 2018
(5) IR 4192575, Unit 1 division 2 battery room low temperature on November 7, 2018
(6) IR 4195383, Unit 1 reactor core isolation cooling pump suction valve from the
condensate storage tank had a torque switch trip that was outside the allowable value
during diagnostic testing on November 15, 2018
71111.19 - Post Maintenance Testing (4 Samples)
The inspectors evaluated post maintenance testing for the following maintenance/repair
activities:
(1) Unit 2 reactor core isolation cooling flow transmitter venting, filling, and alignment on
October 29, 2018
(2) Unit 2 reactor core isolation cooling maintenance outage on November 14, 2018
(3) Unit common D residual heat removal service water pump replacement on
November 16, 2018
(4) Unit 1 D11 emergency diesel generator speed switch replacement on November 29,
2018
71111.22 - Surveillance Testing
The inspectors evaluated the following surveillance tests:
Routine (1 Sample)
(1) ST-6-092-311-1, Unit 1 D11 emergency diesel generator instrumented run on
October 30, 2018
In-service (1 Sample)
(1) ST-6-049-230-2, Unit 2 reactor core isolation cooling pump, valve, and flow test on
November 15, 2018
71114.02 - Alert and Notification System Evaluation (1 Sample)
The inspectors evaluated the maintenance and testing of the alert and notification system
from December 2016 to November 2018.
71114.03 - Emergency Response Organization Staffing and Augmentation System (1 Sample)
The inspectors conducted a review of Exelons Emergency Response Organization (ERO)
augmentation staffing requirements and the process for notifying and augmenting the ERO.
71114.04 - Emergency Action Level and Emergency Plan Changes (1 Sample)
The inspectors verified that the changes made to the emergency plan were done in
accordance with 10 CFR 50.54(q)(3), and any change made to the Emergency Action
Levels, Emergency Plan, and its lower-tier implementing procedures, had not resulted in any
reduction in effectiveness of the Plan. This evaluation does not constitute NRC approval.
71114.05 - Maintaining Emergency Preparedness (1 Sample)
The inspectors reviewed a number of activities to evaluate the efficacy of Exelons efforts to
maintain LGSs emergency preparedness programs.
RADIATION SAFETY
71124.04 - Occupational Dose Assessment
Source Term Characterization (1 Sample)
The inspectors evaluated Exelons source term characterization.
External Dosimetry (1 Sample)
The inspectors evaluated Exelons external dosimetry program.
Internal Dosimetry (1 Sample)
The inspectors evaluated Exelons internal dosimetry program.
Special Dosimetric Situations (1 Sample)
The inspectors evaluated Exelons performance for special dosimetric situations.
OTHER ACTIVITIES - BASELINE
71151 - Performance Indicator Verification
The inspectors verified Exelons performance indicator submittals listed below for the period
October 1, 2017 through September 30, 2018. (9 samples)
(1) Unit 1 and Unit 2 cooling water
(2) Unit 1 and Unit 2 reactor coolant system leak rate
(3) Unit 1 and Unit 2 reactor coolant system specific activity
(4) Alert and Notification Reliability
(5) Drill and Exercise Performance
(6) ERO Drill Participation
The inspectors verified Exelons performance indicators submittals listed below for the
period from December 6, 2017 through November 16, 2018. (2 Samples)
(1) Occupational Exposure Control Effectiveness
(2) Radiological Effluent Technical Specifications/Offsite Dose Calculation Manual
Radiological Effluent Occurrences (RETS/ODCM) Radiological Effluent Occurrences
71152 - Problem Identification and Resolution
Semiannual Trend Review (1 Sample)
The inspectors reviewed Exelons corrective action program for trends that might be
indicative of a more significant safety issue.
Annual Follow-up of Selected Issues (2 Samples)
The inspectors reviewed Exelons implementation of its corrective action program related to
the following issues:
(1) Emergent shutdown of the Unit 1 D12 emergency diesel generator due to high
scavenging air temperatures (IR 4081882)
(2) Unit 1 recirculation pump adjustable speed drive (ASD) failures (IR 4168043, 4145616,
4044408)
71153 - Follow-up of Events and Notices of Enforcement Discretion
Licensee Event Reports (1 Sample)
The inspectors evaluated the following licensee event reports (LERs):
(1) LER 05000353/2018-001-00, HPCI Inoperability due to Discharge Check Valve Failure
to Close (ADAMS Accession No. ML18037A914). The inspectors determined that it was
not reasonable for Exelon to foresee or correct the cause discussed in the LER, and
therefore no performance deficiency was identified. The inspectors also concluded that
no violation of NRC requirements occurred.
INSPECTION RESULTS
Failure to Maintain the Design Control of the D23 Emergency Diesel Generator
Cornerstone Significance Cross-Cutting Report
Aspect Section
Mitigating Green H.11 - Human 71152
Systems NCV 05000353/2018004-01 Performance -
Opened/Closed Challenge the
Unknown
A self-revealing Green NCV of 10 CFR Part 50, Appendix B, Criterion III was identified when
Exelon replaced the D23 emergency diesel generator lube oil heater temperature switch with
a new style switch on December 6, 2018. The new style switch subsequently failed on
December 7, 2018, due to overheating and charring of the switch wiring when coming in
contact with the cover.
Description: The emergency diesel generator systems are safety-related standby emergency
power systems for LGS Units 1 and 2 consisting of four diesel generator sets per unit. Each
diesel generator has a lube oil heater that is used to maintain lube oil temperatures above
105 degrees Fahrenheit to ensure system operability. On December 6, 2018, Exelon
replaced the lube oil heater temperature switch with a new style temperature switch under
Engineering Change 619379 for the D23 emergency diesel generator due to a failure of the
previous style switch and repeated reliability issues. After replacing the temperature switch,
the lube oil heater system operated normally until an alarm was received on December 7,
2018, after approximately 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of operation (IR 4201280). The alarm was caused by low
lube oil temperature, subsequently measured at 103 degrees Fahrenheit, which rendered the
D23 emergency diesel generator inoperable.
At the time of the low lube oil temperature alarm for the D23 emergency diesel generator,
the D22 emergency diesel generator was inoperable and unavailable for a similar issue with
its lube oil heater temperature switch (IR 4200941). With two emergency diesel generators
inoperable, Technical Specification 3.8.1.1.b 72-hour limiting condition for operation action
statement was entered. The temperature switch was replaced with the new style switch, the
D22 emergency diesel generator was declared operable, and the 72-hour action statement
was exited. The unit remained in the 30 day action statement (Technical Specification 3.8.1.1.a) for one emergency diesel generator inoperable.
Exelon performed troubleshooting and identified an uninsulated wire lug with a raised arch at
the terminal block. This uninsulated wire came into contact with the cover gasket due to the
lower profile design of the new switch housing. The other two wires on adjacent terminals
were installed with insulated lugs that prevented electrical contact with the cover. While the
heaters were energized, current passing through the uninsulated wire resulted in heating and
decomposition of the gasket. The decomposition continued and allowed current to flow
through the cover to ground, which resulted in a blown fuse for the circuit. Exelon inspected
the D22 emergency diesel generator and identified similar decomposition of the gasket.
After completing troubleshooting, the D22 and D23 emergency diesel generator lube oil
heater temperature switches were sequentially replaced with the previous style switches.
The modification to replace these switches with the new style had not been performed on any
other emergency diesel generators.
The inspectors interviewed engineering personnel, reviewed the engineering change request,
and reviewed the prompt investigation. The inspectors determined that the modification
process (development through installation) reasonably should have identified the potential
impact from the wiring and cover clearance due to the lower profile design of the new style.
Walkdowns were performed in accordance with Exelon procedure CC-AA-106-1001,
Configuration Change Walkdowns, as a part of the configuration change process by
engineering and maintenance personnel that identified the preference to use a lower profile
terminal housing to limit interferences during installation, removal, and testing. The change to
the lower profile switch configuration was not fully evaluated, and the potential issues caused
by reduced clearance between the wiring and cover were not identified.
Corrective Actions: Following the failure on December 7, 2018, Exelon declared the D23
emergency diesel generator inoperable, performed a prompt investigation, and replaced the
new switch assembly with an old style switch. Since the D22 emergency diesel generator
also had the same switch installed for the lube oil heater system, an inspection was
performed and identified similar issues with the wiring and cover clearance resulting in
decomposition of the gasket. Exelon replaced the new D22 emergency diesel generator
switch with an old style switch.
Corrective Action Reference: IR 4201280
Performance Assessment:
Performance Deficiency: The inspectors determined that the failure to ensure the design
control of the emergency diesel generator lube oil heater system was maintained during the
modification process was reasonably within Exelons ability to foresee and correct and should
have been prevented.
Screening: The inspectors determined the performance deficiency was more than minor
because it adversely affected the Design Control attribute of the Mitigating Systems
cornerstone to ensure the availability, reliability, and capability of systems that respond to
initiating events to prevent undesirable consequences (i.e., core damage). Specifically, the
modification of the D23 emergency diesel generator lube oil heater temperature switch failed
and resulted in the inability to maintain lube oil temperatures above the 105 degrees
Fahrenheit operability limit for the emergency diesel generator to perform its technical
specification required function.
Significance: The inspectors assessed the significance of the finding using IMC 0609,
4, Initial Characterization of Findings, and IMC 0609, Appendix A, The
Significance Determination Process (SDP) for Findings at Power. The inspectors determined
that the finding was of very low safety significance (Green) because the D23 emergency
diesel generator maintained the ability to perform its probabilistic risk assessment function.
Cross-Cutting Aspect: The inspectors determined this finding has a cross-cutting aspect in
the area of Human Performance, Challenge the Unknown, because Exelon personnel did not
maintain a questioning attitude during the modification process up to, and including, the
installation in order to identify and resolve unexpected conditions. [H.11]
Enforcement:
Violation: 10 CFR Part 50, Appendix B, Criterion III states, in part, that design changes,
including field changes, shall be subject to design control measures commensurate with
those applied to the original design. Contrary to this, on December 6, 2018, Exelon did not
maintain the design control of the D23 emergency diesel generator such that a modification
to the lube oil heater temperature switch failed and resulted in the inoperability of the
emergency diesel generator. In addition, on December 7, 2018, Exelon performed the same
modification on the D22 emergency diesel generator. The D23 and D22 emergency diesel
generators were restored to operable status following replacement of the lube oil heater
temperature switches with the previous design on December 8, 2018.
Disposition: This violation is being treated as an NCV, consistent with Section 2.3.2 of the
Observations 71152 Semiannual Trend Review
The inspectors performed a semi-annual review of site issues to identify trends that might
indicate the existence of more significant safety concerns. As part of this review, the
inspectors included repetitive or closely-related issues documented by Exelon in the
corrective action program database, trend reports, site performance indicators, major
equipment problem lists, system health reports, maintenance rule assessments, and
maintenance or corrective action program backlogs. The inspectors also reviewed how
Exelons corrective action program evaluated and responded to individual issues identified by
the NRC inspectors during routine plant walkdowns and daily condition report reviews. The
inspectors specifically reviewed and assessed one adverse trend in equipment reliability, last
discussed in the 2018 second quarter integrated inspection report (ADAMS Accession No.
Regarding equipment reliability, the inspectors noted two findings documented in inspection
reports during the period related to equipment reliability that were identified during reviews of
LERs (ADAMS Accession No. ML18317A116 and ML18347A403). The inspectors also noted
additional examples evaluated during the period that impacted operations. However, the
inspectors determined the issues substantially consisted of trends in systems with appropriate
actions planned by Exelon, such as the Unit 1 ASD system, emergency diesel generator
keepwarm systems, and the control enclosure chiller system. The inspectors reviewed these
trends and determined Exelon implemented mitigating actions and initiated planned
permanent modifications to restore the systems to reliable operation. The inspectors noted
Exelons actions to improve interdepartmental communication, heighten personnels sensitivity
to recognizing degraded conditions, and increase the sites response to more proactively
resolve degraded conditions. Notwithstandign this, the inspectors identified a finding
associated with the modification to the emergency diesel generator keepwarm systems that is
documented in this report. However, though associated with actions being taken to address
reliability challenges, it was not determined to be indicative of ineffective corrective actions to
address the adverse trend.
Based on the overall results of the semi-annual trend review, the inspectors did not identify
additional trends not being resolved by Exelon and determined that Exelon was appropriately
identifying and entering issues into the corrective action program, adequately evaluating the
issues, and properly resolving adverse trends before they became more safety significant
problems.
Observations 71152 Annual Follow-Up of Selected Issues
Emergent shutdown of the Unit 1 D12 emergency diesel generator due to high scavenging
air temperatures (IR 4081882)
The inspectors reviewed Exelons subsequent actions after the Unit 1 D12 emergency diesel
generator was declared inoperable due to high scavenging air temperatures. The inspectors
reviewed Exelons cause evaluation, operability determination, problem analysis, extent-of-
condition reviews, operating experience reviews, and corrective actions to determine whether
Exelon was appropriately identifying, characterizing, and correcting problems associated with
this issue and whether the planned corrective actions were appropriate. The inspectors
evaluated the actions taken to the requirements of Exelons corrective action program and 10 CFR Part 50, Appendix B, Criterion XVI, Corrective Action.
The inspectors determined that Exelon identified and implemented corrective actions for each
identified deficiency commensurate with their safety significance. In addition, Exelon has
implemented revised procedures and communications to site personnel, engaged industry
with operating experience, and has performed an effectiveness review to ensure the
timeliness and adequacy of corrective measures. Exelon is also continuing additional
monitoring of the system for subsequent issues and evaluating potential changes to training
requirements based on events.
Observations 71152 Annual Follow-up of Selected Issues
Unit 1 recirculation pump adjustable speed drive (ASD) failures (IR 4168043, 4145616,
4044408)
The ASD provides variable speed control for a reactor recirculation pump. The ASD is a solid
state, digital based system that replaced a mechanical, analog based motor-generator set
that previously provided the same function. There is one ASD for each reactor recirculation
pump for a total of two ASDs on Unit 1 and two ASDs on Unit 2. Failure of one ASD results in
a loss of a reactor recirculation pump and a power reduction for the unit. Failure of two ASDs
results in loss of both reactor recirculation pumps, and a reactor shutdown. The reactor
recirculation system is a non-safety-related system on both LGS units. ASDs were first
installed at LGS on Unit 1 in the 2012 refueling outage and on Unit 2 in the 2013 refueling
outage. Since that time, there have been no significant failures on the Unit 2 ASDs and 3
significant failures on the Unit 1 ASDs as follows.
In August 2017, the Unit 1 A recirculation pump tripped due to an arc fault in the b4 power
cell. This resulted in single loop operation and reactor power reduction to 36%. The cause of
the arc fault was determined to be tin whiskering in the internal metal bus plane of the power
cell. As a result of this event, LGS replaced all 24 power cells for the Unit 1 ASDs with power
cells containing nickel plated buses in the 2018 refueling outage. Replacement power cells
with nickel plated buses have been procured and staged for installation for the Unit 2 ASDs,
and Exelon has work orders prepared for installation of the power cells at the next available
forced outage or refueling outage.
In June 2018, a leak developed in the supply coolant hose for the a1 power cell on Unit 1 B
single loop operation and a manual reactor power reduction to 31%. The coolant hose was
sent to Exelon power labs for failure analysis. The failure mechanism was determined to be
stress corrosion cracking of a brass fitting on the end of the hose. As a result of this event,
corrective actions are planned for the next Unit 1 and Unit 2 refueling outages as follows. A
sampling of power cell and heat exchanger hoses will be selected for disassembly and
inspection for evidence of cracking, and containment devices will be installed over the power
cell and heat exchanger coolant hoses to direct any leaks away from electrical components.
In August 2018, an uninterruptable power supply (UPS) failure occurred on the Unit 1 A ASD
and caused the recirculation pump to automatically runback to 28% speed. This resulted in a
manual reactor power reduction to 32%. As a result of this event, failure analysis was
performed by the supply vendor of the UPS which determined two circuit cards had failed in a
manner that was not deemed plausible by the vendor. As a result, Exelon continues to
evaluate solutions to this failure.
The inspectors noted that the ASD system has been scoped into the maintenance rule since
original installation, and that the Unit 1 ASDs were appropriately moved into a(1) status in
September 2018, following the three significant failures described above. The reliability
performance criteria for the system to return to a(2) status is no unplanned reactor power
changes greater than 20% in the 12 month period following completion of planned corrective
actions. The inspectors determined that corrective actions taken and planned are
reasonable, timely, and commensurate with the safety significance of the issue.
EXIT MEETINGS AND DEBRIEFS
The inspectors verified no proprietary information was retained or documented in this report.
On January 11, 2019, the inspectors presented the quarterly integrated inspection results to
Mr. Rick Libra, Site Vice President, and other members of the Exelon staff.
THIRD PARTY REVIEWS
Inspectors reviewed Institute of Nuclear Power Operations reports that were issued during the
inspection period.
DOCUMENTS REVIEWED
Miscellaneous
Evaluation 17-68, EP-AA-1000, Exelon Nuclear Standardized Radiological Emergency Plan,
Revision 29
Procedures
EP-AA-1000, Exelon Nuclear Standardized Radiological Emergency Plan, Revision 29
EP-AA-1008, Exelon Nuclear Radiological Emergency Plan Annex for Limerick Generating
Station, Revision 30
Procedures
OT-104, Unexpected / Unexplained Positive or Negative Reactivity Insertion, Revision 56
OT-112, Unexpected / Unexplained Change in Core Flow, Revision 59
PI-AA-125, Corrective Action Program (CAP) Procedure, Revision 6
PI-AA-125-1003, Corrective Action Program Evaluation Manual, Revision 4
S.43.1.F, Responding to Alarms at ASD HMI, Revision 4
S.43.8.F, Unit 1 Adjustable Speed Drive, Runback UPS Operation, Revision 0
S.43.8.F, Unit 2 Adjustable Speed Drive, Runback UPS Operation, Revision 0
S92.9.N, Routine Inspection of the Diesel Geenrators, Revision 73
ST-6-092-112-1, D12 Diesel Generator 24 Hour Endurance Test, Revision 39
ST-6-092-322-1, D12 Diesel Generator LOCA/Load Reject Testing and Fast Start Operability
Test Run, Revision 30
Temporary Procedure Change 17-0305-1
Temporary Procedure Change 17-0323-1
Condition Reports
20972 4133876 4148177 4160975 4166177 4183163
21268 4134063 4150473 4160976 4166690 4180366
4044408 4135378 4150687 4163928 4166263 4184570
4044613 4138517 4151972 4164099 4167604 4184725
4081882 4140885 4154318 4164464 4168136 4188572
4081907 4141042 4154379 4166740 4166738 4190560
4082335 4141257 4154414 4166743 4170168 4189992
4083987 4141279 4155154 4166744 4173191 4190614
4084040 4141283 4155315 4166745 4173171 4191872
4084043 4143573 4155343 4168043 4177545 4193458
4084045 4143776 4155545 4168892 4178994 4193541
4092404 4144866 4157093 4181540 4179096 4196956
4099289 4145616 4157170 4184778 4178980 4196957
4100187 4145776 4157772 4195250 4178984 4196958
24183 4147127 4158171 4164597 4178987 4198316
24674 4147134 4159137 4165589 4178989 4198633
25208 4147137 4160972 4166119 4178998 4200177
25416 4147140 4160974 4166174 4181413 4199902
200941 4201280 4201364
Maintenance Orders/Work Orders
4665744 4777106 4780170 4794531
Miscellaneous
Adjustable Speed Drive PCM Template, dated 7/16/18
Limerick Generating Station Unit 1 Technical Requirements Manual, Revision 64
Limerick Generating Station Unit 1 Technical Specifications, revised through Amendment 231
Limerick Generating Station Unit 2 Technical Requirements Manual, Revision 63
Limerick Generating Station Unit 2 Technical Specifications, revised through Amendment 194
Limerick Generating Station Updated Final Safety Analysis Report, Revision 19
L-S-19, Design Basis Document for Recirculation System, Limerick Generating System
Units 1 & 2, Revision 11
Root Cause Investigation Report RCR 04081882-15
Condition Reports
2496668 4082181
Work Orders
22137