IR 05000352/2020002
| ML20216A556 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 08/03/2020 |
| From: | Jon Greives Reactor Projects Region 1 Branch 4 |
| To: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| Greives J | |
| References | |
| IR 2020002 | |
| Download: ML20216A556 (21) | |
Text
August 3, 2020
SUBJECT:
LIMERICK GENERATING STATION, UNITS 1 AND 2 - INTEGRATED INSPECTION REPORT 05000352/2020002 AND 05000353/2020002
Dear Mr. Hanson:
On June 30, 2020, the U.S. Nuclear Regulatory Commission (NRC) completed an inspection at Limerick Generating Station, Units 1 and 2. On July 17, 2020, 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 involved a violation of NRC requirements. We are treating this violation as a non-cited violation (NCV) consistent with Section 2.3.2 of the Enforcement Policy.
If you contest the violation or the significance or severity of the violation documented in this inspection report, you should provide a response within 30 days of the date of this inspection report, with the basis for your denial, to the U.S. 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, Units 1 and 2.
If you disagree with a cross-cutting aspect assignment 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, X /RA/
Signed by: Jonathan E. Greives Jonathan E. Greives, Chief Reactor Projects Branch 4 Division of Reactor Projects 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: 05000352/2020002 and 05000353/2020002 Enterprise Identifier: I-2020-002-0038 Licensee: Exelon Nuclear Facility: Limerick Generating Station, Units 1 and 2 Location: Sanatoga, PA 19464 Inspection Dates: April 1, 2020 to June 30, 2020 Inspectors: H. Anagnostopoulos, Senior Health Physicist C. Bickett, Senior Reactor Inspector S. Haney, Resident Inspector J. Patel, Senior Resident Inspector A. Turilin, Reactor Inspector D. Werkheiser, Senior Reactor Analyst 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 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 Surveillance Test Procedure Resulted in Suppression Pool Atmosphere Oxygen Concentration Exceeding Technical Specification Limit Cornerstone Significance Cross-Cutting Report Aspect Section Barrier Integrity Green [H.13] - 71111.15 NCV 05000352/2020002-01 Consistent Open/Closed Process A self-revealing Green non-cited violation (NCV) of Technical Specification (TS) 6.8.1.d,
Procedures and Programs, was identified when Exelon did not establish nitrogen makeup to the suppression pool as directed in the reactor core isolation cooling (RCIC) surveillance test procedure. Specifically, operators did not recognize that extended operation of the RCIC barometric condenser vacuum pump, during a Unit 1 RCIC pump, valve, and flow test, could cause suppression pool atmosphere oxygen concentration to exceed 4 percent by volume.
The procedure required establishing nitrogen makeup to the suppression pool atmosphere once oxygen concentration reaches 3 percent by volume. Oxygen levels are maintained at less than 4 percent to ensure that any event that produces hydrogen does not result in a combustible mixture in the primary containment atmosphere.
Additional Tracking Items
None.
PLANT STATUS
Unit 1 began the inspection period in a shutdown condition for a planned refueling outage (1R18). The unit was restarted on April 12, 2020, and returned to near rated thermal power on April 16, 2020. The unit 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 June 5, 2020, the unit was down powered to 61 percent for main turbine valve testing, control rod testing, main condenser waterbox cleaning and leak testing, and a control rod sequence exchange. The unit was returned to rated thermal power on June 7, 2020, 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 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 and 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 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 summer readiness of offsite and onsite alternate current power systems on June 23, 2020
Impending Severe Weather Sample (IP Section 03.02) (1 Sample)
- (1) The inspectors evaluated readiness for impending adverse weather conditions for a high wind and heavy rain forecast on April 30, 2020
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 1 B residual heat removal loop on April 21, 2020
- (2) Unit 1 A residual heat removal loop on May 21, 2020
- (3) Unit 2 D22, 'D23, and D24 emergency diesel generators on May 28, 2020
- (4) Unit 1 high pressure coolant injection system on May 29, 2020
Complete Walkdown Sample (IP Section 03.02) (1 Sample)
- (1) The inspector evaluated system configurations during a complete walkdown of the Unit common residual heat removal service water system on June 22, 2020
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 area 45, Unit 1 control rod drive equipment and neutron monitoring areas on April 6, 2020
- (2) Fire area 32, Unit 1 'A' and 'C' residual heat removal heat exchanger and pump rooms on May 8, 2020
- (3) Fire area 33, Unit 1 reactor core isolation cooling pump room on May 8, 2020
- (4) Fire area 31, Unit 1 'B' and 'D' residual heat removal heat exchanger and pump rooms on May 12, 2020
- (5) Fire area 83, Unit 2 D21 emergency diesel generator and fuel oil / lube oil tank room on May 29, 2020
71111.06 - Flood Protection Measures
Inspection Activities - Internal Flooding (IP Section 03.01) (1 Sample)
The inspectors evaluated internal flooding mitigation protections in the:
- (1) Unit 1 high pressure coolant injection pump and reactor core isolation cooling pump rooms from May 29, 2020 through June 4, 2020
71111.07A - Heat Sink Performance
Annual Review (IP Section 03.01) (1 Sample)
The inspectors evaluated readiness and performance of:
- (1) Unit 2 D24 emergency diesel generator lube oil cooler (2D-E506), jacket water heat exchanger (2D-E507), and intercooler water heat exchanger (2D-E586) on June 19, 2020
71111.08G - Inservice Inspection Activities (BWR)
BWR Inservice Inspection Activities Sample - Nondestructive Examination and Welding
Activities (IP Section 03.01)
- (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 during the Limerick Unit 1 1R18 refueling outage from April 2, 2020, to April 10, 2020:
03.01.a - Nondestructive Examination and Welding Activities.
1. Ultrasonic Examination of DCA-319-1 (N5A), B Core Spray Injection Nozzle to Safe End Weld (LIM-1-601990)2. Ultrasonic Examination of CSB 003, Core Spray 12-inch Pipe to Elbow Weld (UT-20-002)3. Magnetic Particle Examination of RHR-HXAR-1-A(IA), RHR Heat Exchanger Support, Top Mtg. A, Outside Support Bracket Weld, (MT-20-002)4. Dye Penetrant Examination of RHR-HXAR-1-A(IA), RHR Heat Exchanger Support, Top Mtg. A, Inside Support Bracket Weld (PT-20-001)5. Visual Examination (VT3) of JP19 SJC, Jet Pump 19 Slip Joint Clamp (Li1-JP 19 Slip Joint Clamp)6. Visual Examination (VT1) of JP19 WD-1, Jet Pump 19 Wedge Bearing Surface (Li1-JP 19 WD-1)7. Visual Examination (EVT1) of P1B, Core Spray 'B' Loop N5A Thermal Sleeve to T-Box Weld (BWRVIP-18) (Li1-CSP P1B)8. Visual Examination (EVT1) of 45-03b N17B, LPCI Coupling Shroud Ring to Shroud Weld 135 Az. (BWRVIP-42) (Li1-135 45-3b)9. Visual Examination (GV) of ASME IWE (Class MC) Containment and IWL (Class CC) Metallic Liners (4.2.1.1 to 4.5.7.1)10. Pipe replacement of DBB-105-1-E09, RWCU 4-inch return to FW header due to FAC (4773734)
71111.11Q - Licensed Operator Requalification Program and Licensed Operator Performance
Licensed Operator Performance in the Actual Plant/Main Control Room (IP Section 03.01)
(1 Sample)
- (1) The inspectors observed and evaluated licensed operator performance in the main control room during the startup of Unit 1 from refueling outage 1R18 on April 12, 2020
Licensed Operator Requalification Training/Examinations (IP Section 03.02) (1 Sample)
- (1) The inspectors observed and evaluated licensed operator requalification training on June 1, 2020
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 2 10 CFR Part 21 report applicable to the 2D safeguard battery on April 28, 2020
71111.13 - Maintenance Risk Assessments and Emergent Work Control
Risk Assessment and Management Sample (IP Section 03.01) (4 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 yellow risk due to lowered inventory during cavity drain down on April 10, 2020
- (2) Unit 1 TS 3.0.4.b risk assessment for one inoperable standby gas treatment train during Unit 1 startup from refueling outage 1R18 on April 14, 2020
- (3) Unit 1 A residual heat removal full flow test valve failure to close on April 20, 2020
- (4) Unit 1 risk informed completion time window for A residual heat removal full flow test valve seat replacement on May 11, 2020
71111.15 - Operability Determinations and Functionality Assessments
Operability Determination or Functionality Assessment (IP Section 03.01) (6 Samples)
The inspectors evaluated the licensee's justifications and actions associated with the following operability determinations and functionality assessments:
- (1) Unit 1 '1N' safety relief valve elevated tailpipe temperature following startup from refueling outage 1R18 on April 13, 2020
- (2) Unit 1 suppression pool in leakage on April 24, 2020
- (3) Unit common non-active pin hole leak on B emergency service water pipe on May 3, 2020
- (4) Unit 1 division 1 direct current ground on RCIC system on May 29, 2020
- (5) Unit common B control enclosure chiller tripped during the start of B emergency service water pump on June 11, 2020
- (6) Unit 2 D24 emergency diesel generator 2D1 starting air compressor air leak on June 24, 2020
71111.18 - Plant Modifications
Temporary Modifications and/or Permanent Modifications (IP Section 03.01 and/or 03.02)
(2 Samples)
The inspectors evaluated the following temporary or permanent modifications:
- (1) Unit 1 emergency service water piping flange replacement of dissimilar metal weld on April 28, 2020
71111.19 - Post-Maintenance Testing
Post-Maintenance Test Sample (IP Section 03.01) (8 Samples)
The inspectors evaluated the following post maintenance test activities to verify system operability and functionality:
- (1) Unit 1 C and D main steam isolation valves maintenance on April 5, 2020
- (2) Unit 1 A residual heat removal pump full flow test return valve repair on April 23, 2020
- (3) Unit 2 A residual heat removal pump motor oil cooler cooling water flush and heat exchanger residual heat removal service water inlet valve actuator diagnostic on April 28, 2020
- (4) Unit 1 D13 emergency diesel generator jacket water pump contactor replacement on May 13, 2020
- (5) Unit 1 A residual heat removal heat exchanger outlet bypass valve repairs on May 18, 2020
- (6) Unit common D emergency service water pump discharge vent installation on May 21, 2020
- (7) Unit 1 A standby gas treatment system planned maintenance on June 11, 2020
- (8) Unit 1 RCIC system full flow test valve direct current ground repairs on June 25, 2020
71111.20 - Refueling and Other Outage Activities
Refueling/Other Outage Sample (IP Section 03.01) (1 Sample)
- (1) The inspectors evaluated refueling outage 1R18 activities from March 28 to April 12, 2020
71111.22 - Surveillance Testing
The inspectors evaluated the following surveillance tests:
Surveillance Tests (other) (IP Section 03.01)
- (1) ST-4-095-953-1, Unit 1 Division II 1B1D101 safeguard battery modified performance test on April 2, 2020
- (2) ST-6-092-116-1, Unit 1 'D12 diesel generator 4 kV safeguard bus loss of offsite power and loss of coolant accident testing on April 5, 2020
- (3) RT-6-055-331-1, Unit 1 high pressure coolant injection turbine overspeed trip test on
April 8, 2020 Inservice Testing (IP Section 03.01) (1 Sample)
- (1) ST-6-055-230-2, Unit 2 high pressure coolant injection pump, valve, and flow test on
April 24, 2020 Containment Isolation Valve Testing (IP Section 03.01) (1 Sample)
- (1) Unit 1 1F028A/B/C/D main steam isolation valves local leak rate testing (as found) on
April 1, 2020 FLEX Testing (IP Section 03.02) (1 Sample)
71114.06 - Drill Evaluation
Drill/Training Evolution Observation (IP Section 03.02) (1 Sample)
The inspectors evaluated:
- (1) The inspector evaluated a simulator training evolution on June 8,
RADIATION SAFETY
71124.01 - Radiological Hazard Assessment and Exposure Controls
Radiological Hazard Assessment (IP Section 03.01) (1 Partial)
(1) (Partial)
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 Partial)
(1) (Partial)
The inspectors evaluated radiological protection-related instructions to plant workers.
Contamination and Radioactive Material Control (IP Section 03.03) (1 Partial)
The inspectors evaluated licensee processes for monitoring and controlling contamination and radioactive material.
(1) (Partial)
The inspectors reviewed the criteria for the survey and release of personal items, and evaluated the physical and programmatic controls for materials stored in storage pools.
Radiological Hazards Control and Work Coverage (IP Section 03.04) (1 Partial)
The inspectors evaluated in-plant radiological conditions during facility walkdowns and observation of radiological work activities.
(1) (Partial)
The inspectors monitored pre-job briefings for control rod drive mechanism removal and the removal and cutting of local power range monitors. The inspectors reviewed radiological surveys and documentation associated with repairs to the outboard main steam isolation valves.
High Radiation Area and Very High Radiation Area Controls (IP Section 03.05) (1 Partial)
The inspectors evaluated licensee controls of the following High Radiation Areas and Very High Radiation Areas:
(1) (Partial)
The inspectors reviewed procedures and procedure changes for adequacy of access controls.
Radiation Worker Performance and Radiation Protection Technician Proficiency (IP Section 03.06) (1 Partial)
(1) (Partial)
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 Exelons performance indicator submittals listed below for the period April 1, 2019, through March 31, 2020.
MS05: Safety System Functional Failures (SSFFs) Sample (IP Section 02.04) ===
- (1) Unit 1 safety system functional failures
- (2) Unit 2 safety system functional failures
MS06: Emergency AC Power Systems (IP Section 02.05) (2 Samples)
- (1) Unit 1 emergency alternating current power systems
- (2) Unit 2 emergency alternating current power systems
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) (3 Samples)
The inspectors reviewed the licensees implementation of its corrective action program related to the following issues:
- (1) Unit 2 adjustable speed drive (ASD) failure and associated reactor recirculation (RRP) pump trip from full power that occurred on May 26, 2019 as documented in issue report (IR) 4251852
- (2) Inadvertent Nuclear Steam Supply Shutoff System (NSSSS) Isolation Adverse Trend (IRs 4222608 and 4240807)
- (3) Standby Gas Treatment System Flow Issues (IRs 4231418, 4229920, 4229238, and 4230005)
INSPECTION RESULTS
Failure to Follow Surveillance Test Procedure Resulted in Suppression Pool Atmosphere Oxygen Concentration Exceeding Technical Specification Limit Cornerstone Significance Cross-Cutting Report Aspect Section Barrier Integrity Green [H.13] - 71111.15 NCV 05000352/2020002-01 Consistent Open/Closed Process A self-revealing Green non-cited violation (NCV) of Technical Specification (TS) 6.8.1.d, Procedures and Programs, was identified when Exelon did not establish nitrogen makeup to the suppression pool as directed in the reactor core isolation cooling (RCIC) surveillance test procedure. Specifically, operators did not recognize that extended operation of the RCIC barometric condenser vacuum pump, during a Unit 1 RCIC pump, valve, and flow test, could cause suppression pool atmosphere oxygen concentration to exceed 4 percent by volume.
The procedure required establishing nitrogen makeup to the suppression pool atmosphere once oxygen concentration reaches 3 percent by volume. Oxygen levels are maintained at less than 4 percent to ensure that any event that produces hydrogen does not result in a combustible mixture in the primary containment atmosphere.
Description:
The RCIC system assures adequate core cooling in the event of a reactor isolation from the primary heat sink and the loss of feedwater flow to the reactor pressure vessel (RPV) without requiring actuation of the emergency core cooling systems. The RCIC system automatically initiates when RPV level falls below -38 inches (Level 2). The RCIC turbine steam supply valve automatically opens upon receipt of the initiation signal. During RCIC system operation, its barometric condenser condenses small amounts of RCIC steam and condensate from the turbine gland seals, stop valve drains, governor valve leak off, and exhaust line drain pot. The barometric condenser vacuum pump starts simultaneously with the opening of RCIC turbine steam supply valve. The barometric condenser vacuum pump maintains negative pressure in the barometric condenser and discharges non-condensable gases directly into the suppression pool. Consequently, continuously running the vacuum pump can cause an oxygen level increase in the suppression pool through RCIC gland seal air in-leakage to the barometric condenser and subsequent discharge to the suppression pool. The Limerick Unit 1 updated final safety analysis report, Section 6.2.5, Combustible Gas Control in Containment, states the containment atmosphere is inerted with nitrogen gas during power operation of the reactor to preclude the possibility of a combustible mixture of hydrogen and oxygen accumulating in primary containment during a postulated loss of coolant accident (LOCA). With the concentration of oxygen controlled to below the lower flammability limit, the level of hydrogen buildup in the primary containment following a postulated LOCA is of no concern for combustible gas control.
On May 29, 2020, at approximately 09:54 a.m., the Unit 1 RCIC pump was placed in service in accordance with surveillance test procedure ST-6-049-230-1, RCIC Pump, Valve, and Flow Test, for the performance of its quarterly test per TS surveillance requirement 4.7.3.b.
At 11:10 a.m., the main control room received an alarm for detecting a division 1 direct current system ground associated with the RCIC system. When this alarm did not clear, operators decided to secure the RCIC pump and commenced troubleshooting to investigate the cause of and to correct the ground issue. The decision was subsequently made to abandon the in-progress surveillance test while troubleshooting the ground alarm. Because of this delayed progression through the surveillance test, the vacuum pump continued to run and exhausted air to the Unit 1 suppression pool for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, which resulted in elevated oxygen levels in the suppression pool atmosphere. On May 30, 2020, at 10:04 a.m.,
suppression pool atmosphere oxygen level was obtained for the post RCIC run as well as the weekly TS surveillance and were measured to be 4.63 volume percent, greater than the 4.0 volume percent required TS limit, requiring an unplanned entry into TS 3.6.6.3, Drywell and Suppression Chamber Oxygen Concentration. Due to the elevated oxygen level, at 11:25 a.m., the vacuum pump was secured by de-energizing the pump.
The inspectors reviewed the RCIC pump, valve, and flow surveillance test procedure and found that it provided cautionary steps regarding elevated suppression pool oxygen levels when the RCIC system is in service. Specifically, step 3.18 in the procedure discussed that extended RCIC runs can cause increases in suppression pool oxygen levels. It stated the source of oxygen level increase is gland seal air in-leakage to the barometric condenser and subsequent discharge to the suppression pool via the vacuum pump. Step 3.19 required operators to establish monitoring of suppression pool oxygen level when the RCIC system has been operating for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Additionally, Step 3.20 required establishing nitrogen makeup to the suppression pool when suppression pool oxygen level reaches 3.0 percent by volume.
Based on the operators decision to leave the surveillance test in-progress and troubleshoot the ground issue, the inspectors determined that Exelon did not properly secure the RCIC system in a timely manner. Specifically, Exelon left the vacuum pump in service for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, during which it introduced air into the suppression pool atmosphere. The inspectors found that the RCIC surveillance test procedure contained adequate guidance about potential challenges to the suppression pool oxygen level; however, operators did not implement those procedure steps correctly.
Corrective Actions: Exelons immediate corrective action included stopping the vacuum pump and establishing nitrogen feed and bleed to restore oxygen concentration in the suppression pool atmosphere to within TS limits. Exelon also entered this issue into their corrective action program and initiated a corrective action program evaluation.
Corrective Action References: IRs 4346892, 4346995, and 4346520
Performance Assessment:
Performance Deficiency: The inspectors determined that Exelon not implementing surveillance test procedure requirements for monitoring suppression pool oxygen levels and establishing nitrogen makeup when required was a performance deficiency within their ability to foresee and correct and which should have been prevented.
Screening: The inspectors determined the performance deficiency was more than minor because it was associated with the Configuration Control attribute of the Barrier Integrity cornerstone and adversely affected the cornerstone objective to provide reasonable assurance that physical design barriers protect the public from radionuclide releases caused by accidents or events. Specifically, Exelon did not implement surveillance test procedure requirements which resulted in exceeding the acceptable oxygen level concentration in the Unit 1 suppression pool atmosphere.
Significance: The inspectors assessed the significance of the finding using Appendix A, The Significance Determination Process (SDP) for Findings At-Power. The inspectors assessed the significance of the finding using Exhibit 3, Barrier Integrity Screening Questions, of IMC 0609, Appendix A, and determined this finding was of very low safety significance (Green)because Yes was not answered to any of the Reactor Containment screening questions.
Cross-Cutting Aspect: H.13 - Consistent Process: Individuals use a consistent, systematic approach to make decisions. Risk insights are incorporated as appropriate. Specifically, operators did not invoke a more rigorous decision-making process when securing the Unit 1 RCIC pump from operation while keeping the barometric condenser vacuum pump running for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
Enforcement:
Violation: Limerick Generating Station, Unit 1, TS 6.8.1.d, Procedures and Programs, requires, in part, that written procedures shall be established, implemented, and maintained for surveillance and test activities of safety-related equipment.
Exelon procedure ST-6-049-230-1, RCIC Pump, Valve, and Flow Test, Revision 93, is executed to satisfy surveillance requirements for the RCIC system per TS 3/4.7.3 and is, therefore, required by TS 6.8.1.d. Step 3.19 of that procedure states, If RCIC run is expected to last more than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, then suppression pool oxygen level must be monitored once RCIC has been operating for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Additionally, step 3.20 of that procedure states, if suppression pool has been inerted, and suppression pool oxygen level reaches 3.0%, then nitrogen makeup per S57.3.B, Primary Containment Pressure Control and Nitrogen Make-up, is required to ensure oxygen level remains less than 4%.
Contrary to the above, on May 29, 2020, Exelon did not appropriately implement the RCIC pump, valve, and flow test. Specifically, Exelon did not monitor suppression pool atmosphere oxygen or establish nitrogen make-up to the suppression pool as required by procedure ST-6-049-230-1, RCIC Pump, Valve, and Flow Test. Consequently, on May 30, 2020, Unit 1 suppression pool atmosphere oxygen levels were measured to be in excess of the TS limit of 4.0 percent, which required unplanned entry into TS 3.6.6.3, Drywell and Suppression Chamber Oxygen Concentration.
Enforcement Action: This violation is being treated as a non-cited violation, consistent with Section 2.3.2 of the Enforcement Policy.
Observation: Semiannual Trend Review 71152 The inspectors performed a semiannual 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.
In particular, the inspectors performed an in-depth review of Exelons evaluation and corrective actions related to a potential adverse trend in foreign material exclusion (FME)practices. From January 1, 2020 to June 30, 2020, Exelon initiated several IRs related to the FME program, including foreign material found inside the Unit 1 'A' residual heat removal system full flow test valve; foreign material was identified as a potential cause of two defects on two fuel assemblies that were removed during the Unit 1 refueling outage in March 2020; and additionally during the refueling outage eight foreign material intrusion events were documented in IRs. Exelons immediate corrective actions were to remove foreign material from systems, perform a work group evaluation, and perform a focused area assessment of their FME program. Exelon developed a plan to track gaps and performance monitoring of the FME program and included it in their performance improvement action plan. The inspectors assessed Exelons problem identification threshold, evaluations, and corrective actions related to these IRs. The inspectors determined that for each IR that documented foreign material in the plant, Exelon either retrieved the foreign material before restoring the system to service or adequately evaluated the impact of leaving it in the plant for later retrieval.
Based on the overall results of the semiannual trend review, the inspectors did not identify an adverse trend that might indicate the existence of a more significant safety concern during this semiannual period. The inspectors determined Exelons actions were appropriate and were commensurate with the issue's safety significance.
Observation: Unit 2 ASD failure and associated RRP trip from full power that 71152 occurred on May 26, 2019 as documented in IR 4251852 The inspectors reviewed the cause analysis, the corrective actions taken, and extent of condition. The most probable cause was determined, based on forensic analysis by Exelon and vendor, to be conductive foreign material between the power cell plates that punctured the insulator and caused the ASD to fail. This resulted in a 2B RRP trip and rapid reactor down power. The inspectors determined the response by the ASD and RRP systems were as designed and that the casual analysis was comprehensive. Immediate corrective actions included replacement and retest of the failed power cell (B1), including other affected cells from secondary damage or elevated voltages during the B1 power cell failure. Based on the review of forensic information, the inspector agreed with Exelon's conclusion that the foreign material could not have been identified by Exelon during receipt inspection. However, Exelon implemented a review of their FME practices regarding ASD power cells. This resulted in the purchase of fiberglass clamshell cases to protect the cells during shipping and inspection between Exelon and vendor. Exelon also visited the refurbishing vendor to assess FME work practices and identified areas for vendor improvement, mainly the segregation of any grinding activities from the refurbishment production line. The actions taken and the monitoring of vendor activities by Exelon regarding ASD power cells provides reasonable confidence that the FME issues been addressed. In general, the inspectors concluded that the cause analysis was thorough, the extent of condition was reasonable, and the corrective actions were effective.
Observation: Inadvertent NSSSS Isolation Adverse Trend (IRs 4222608 and 71152 4240807)
The inspectors reviewed the evaluations and corrective actions associated with a Unit 1 inadvertent NSSSS isolation of Group 6C, which occurred on February 22, 2019, and a Unit 2 inadvertent NSSSS isolation of Groups 2, 3, 7, and 8, which occurred on April 18, 2019.
The cause of the Unit 1 isolation was a blown fuse resulting from a degraded power cable on a radiation monitor drawer that caused a short when the drawer was pulled during maintenance. Exelons corrective actions included replacing the fuse and repairing the power supply cable, which was likely original plant equipment. Exelon also revised the associated routine test procedure to add a visual inspection of the power supply cable and replace as necessary. This procedure revision will ensure that the cable is inspected every two years.
The cause of the Unit 2 isolation was a blown fuse during a planned preventive maintenance task to replace main steam line isolation logic relays during a refueling outage. Exelon determined that the fuse likely blew during replacement of the B21H-K14D relay. Exelons corrective actions included replacing the old fuse with a more reliable type of fuse and replacement of the relay base plate. Exelon also planned to reevaluate the risk of all NSSSS and reactor protection system relay replacements to eliminate the consequence of an upstream fuse failure. This action would result in adding extra precautions to associated work orders and procedures as well as additional contingency planning for any fuses that can be affected by relay replacement.
The inspectors determined that Exelons corrective actions were adequate in both cases. For the Unit 1 issue, the inspectors reviewed maintenance rule scoping information, environmental qualification requirements, preventive maintenance templates, and vendor manual information to determine whether replacement of this power cable was required on a certain frequency. Because no such information was available, the inspectors determined that the issue was not reasonably within Exelons ability to foresee and correct, and therefore there was no performance deficiency associated with the failed cable.
For Unit 2, the inspectors reviewed associated work orders, procedures, and scheduling and determined that the issue was not reasonably within Exelons ability to foresee and correct, and therefore there was no performance deficiency associated with the relay replacement.
This maintenance is scheduled during outage periods to limit plant impact in the event of an inadvertent NSSSS isolation. However, the inspectors did note an observation with regards to the timeliness of the action associated with reevaluating the risk of this preventive maintenance. Specifically, Exelon assigned the action to maintenance with an original due date of July 26, 2019. The due date of this action has since been pushed back to June 30, 2020. Given the date of the original event and the fact that this work occurs during an outage, a due date prior to the 2020 refueling outage would have been more appropriate.
The inspectors determined this issue was minor, as there had not been any related issues during the last outage.
Observation: Standby Gas Treatment System Flow Issues (IRs 4231418, 71152 4229920, 4229238, and 4230005)
In the process of troubleshooting high system flow rates identified during performance of ST-6-076-310-0 on March 14, 2019, Exelon identified a pinched wire which resulted in degraded wire insulation and intermittent contact with the damper actuator housing. Exelon determined that the pinched wire occurred during a system outage window two weeks prior. Corrective actions for this issue included conducting a human performance review board, coaching the individuals involved in the work, evaluating the adequacy of the system outage window post-maintenance test, and enhancing procedures with additional cautions and operating experience. Exelon concluded that the post-maintenance test following the system outage window was adequate and because the failure was intermittent, was not able to be detected by the test. The inspectors determined that this assessment was reasonable and that the corrective actions associated with the issue were appropriate. Following repair of the wire, the station reperformed ST-6-076-310-0. Though the system maintained acceptable differential pressure, flow oscillations occurred during the test which exceeded 764 scfm.
Engineering performed a technical evaluation to assess the issue and concluded that the oscillations were normal considering the outside wind conditions (17 - 28 mph) during the test, and that the average system flow was less than 764 scfm. The system works to maintain differential pressure on the refueling floor by varying system flow. A differential pressure control loop compares refueling area pressure to outside air pressure and controls system flow to maintain vacuum at least -0.25 water column. The station confirmed this by reviewing data for system testing since 2012 and noting similar performance during periods of high winds. The inspectors determined that this evaluation was reasonable.
The station performed ST-6-076-310-0 again on March 21, 2019, and noted that average flow was 859 scfm. Troubleshooting revealed that the setpoint for the fan controller was -0.345 water column, which was a higher vacuum than expected. Per the calibration sheet, the setpoint should be -0.27 water column. The setpoint is permitted to be at a higher vacuum, and the last known setpoint was -0.295 water column, as verified on March 16, 2019. Based on discussions with the vendor, Exelons investigation revealed that these controllers have a feature that when the input parameter reads upscale, the controller will assume the process variable input has been lost and will swap to manual control for a short period of time. In this configuration, the setpoint can be inadvertently changed. This condition could occur during the initial drawdown of secondary containment when the standby gas treatment system is started. Considering the troubleshooting that occurred over this time period and the multiple performances of ST-6-076-310-0, Exelon determined that it was possible that the setpoint was inadvertently changed as a result of this feature, and the inspectors concluded that this was reasonable. Exelon created an action to revise applicable I&C procedures with a note about this feature. However, the action was never assigned, and the original due date of March 13, 2020 has since passed with no action taken. The inspectors determined that this issue was minor, as there has not been any related standby gas treatment system issues since March
EXIT MEETINGS AND DEBRIEFS
The inspectors verified no proprietary information was retained or documented in this report.
- On July 17, 2020, the inspectors presented the integrated inspection results to Mr. Frank Sturniolo, Site Vice President, and other members of the licensee staff.
- On April 10, 2020, the inspectors presented the In-Service Inspection results to Frank Sturniolo, Site Vice President, and other members of the licensee staff.
DOCUMENTS REVIEWED
Inspection Type Designation Description or Title Revision or
Procedure Date
71111.06 Corrective Action IR 4347246
Documents
71111.08G Corrective Action IR 4332524 1R18 ISI CNF-002: DCA-319-1 N5A Embedded Indication 04/03/2020
Documents
Engineering 0000631225 EVALUATION OF UNIT 1 DCA-319-1 N5A FLAW Revision 0
Changes IDENTIFIED IN IR 04332524
NDE Reports 4.2.1.1 to 4.5.7.1 Final Report Visual Examination of ASME IWE (Class MC) 04/02/2020
Containment and IWL (Class CC) Metallic Liners to
04/06/2020
Li1-135 45-3b LPCI 135 45-3b, Shroud Attachment Ring to Shroud Weld, 04/07/2020
N17B
Li1-CSP P1B CSP P1B, Thermal Sleeve to Junction Box Weld 04/04/2020
Li1-JP 19 Slip Jet Pump 19 Slip Joint Clamp 04/07/2020
Joint Clamp
Li1-JP 19 WD-1 JP19 WD-1, Wedge Bearing Surface 04/07/2020
LIM-1-601990 Ultrasonic Examination of Core Spray 'B' Injection Nozzle 04/06/2020
Safe End to Nozzle Weld
MT-20-002 RHR-HXAR-1-A(IA), Heat Exchanger Support, Top Mtg. A 04/08/2020
PT-20-001 RHR-HXAR-1-A(IA), Heat Exchanger Support, Top Mtg. A 04/08/2020
UT-20-002 CSB-003 12" Pipe to Elbow 04/06/2020
Work Orders WO 4773734 1R18 FAC Piping Replacement of RWCU Return to FW Line
71111.13 Corrective Action IR 2496286
Documents IR 4334840
Corrective Action IR 4342856
Documents IR 4346184
Resulting from
Inspection
71111.15 Corrective Action IR 4346520
Documents
71111.18 Engineering EC 628776 Flange Replacement of Dissimilar Metal Weld, Revision 0
Changes
Inspection Type Designation Description or Title Revision or
Procedure Date
71111.19 Corrective Action IR 4346359
Documents
Resulting from
Inspection
Work Orders WO 4371274
WO 4911674
71152 Corrective Action ECAPE 2B Reactor Recirculating Pump Tripped During 100% Power 08/09/2019
Documents 04251852-13 Operation
IR 4251852-21 Certify Siemens Foreign Material Exclusion Program 11/24/2019
Changes
Engineering EC 627613 Evaluate SGTS Flow during Performance of ST-6-076-310-0 03/16/2019
Evaluations LD-NKNH-00293 SIEMENS - Failure Analysis of Power Cell at Exelon 07/25/2019
Limerick
LIM-78029 Exelon PowerLabs - Failure Analysis of a Siemens, ASD, 08/02/2019
Battery Plates, AR/CR/WO: 04251852 for Limerick Station
MPR 0092-0053- Summary of MPR Support of Exelon Apparent Cause 06/26/2019
LTR-001(MC) Evaluation for ASD Failure at Limerick Generating Station
Miscellaneous Photograph of ASD Clamshell Shipping and Storage 04/29/2020
Container at Limerick warehouse storage location
Maintenance Rule System Basis Document: System 72
Maintenance Rule System Basis Document: System 26
ST-6-076-310-0 SGTS Refuel Area Secondary Containment Integrity Test 03/21/2019
Inspection Type Designation Description or Title Revision or
Procedure Date
(completed)
ST-6-076-310-0 SGTS Refuel Area Secondary Containment Integrity Test 03/16/2019
(completed)
ST-6-076-310-0 SGTS Refuel Area Secondary Containment Integrity Test 03/13/2019
(completed)
Work Orders WO 4259493
WO 4281279
WO 4898033
18