Information Notice 2011-14, Component Cooling Water System Gas Accumulation and Other Performance Issues: Difference between revisions
StriderTol (talk | contribs) (Created page by program invented by StriderTol) |
StriderTol (talk | contribs) (Created page by program invented by StriderTol) |
||
| Line 13: | Line 13: | ||
| document type = NRC Information Notice | | document type = NRC Information Notice | ||
| page count = 6 | | page count = 6 | ||
}} | }} | ||
{{#Wiki_filter:ML111150135 July 18, 2011 NRC INFORMATION NOTICE 2011-14: COMPONENT COOLING WATER SYSTEM GAS ACCUMULATION AND OTHER PERFORMANCE ISSUES | {{#Wiki_filter:ML111150135 July 18, 2011 NRC INFORMATION NOTICE 2011-14: COMPONENT COOLING WATER SYSTEM GAS ACCUMULATION AND OTHER PERFORMANCE ISSUES | ||
==ADDRESSEES== | ==ADDRESSEES== | ||
All holders of an operating license or construction permit for a nuclear power reactor issued under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Production and Utilization Facilitie All holders of, or applicants for, an early site permit, standard design certification, standard design approval, manufacturing license, or combined license issued under 10 CFR Part 52, nses, Certifications, and Approvals for Nuclear Power Plants | All holders of an operating license or construction permit for a nuclear power reactor issued under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Production and Utilization Facilitie All holders of, or applicants for, an early site permit, standard design certification, standard design approval, manufacturing license, or combined license issued under 10 CFR Part 52, nses, Certifications, and Approvals for Nuclear Power Plants | ||
==PURPOSE== | ==PURPOSE== | ||
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform addressees of recent operating experience regarding air intrusion into component cooling water (CCW) systems, as well as other CCW system performance issue It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problem However, suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is require | The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform addressees of recent operating experience regarding air intrusion into component cooling water (CCW) systems, as well as other CCW system performance issue It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problem However, suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is require | ||
==DESCRIPTION OF CIRCUMSTANCES== | ==DESCRIPTION OF CIRCUMSTANCES== | ||
St. Lucie Plant On October 16, 2008, at St. Lucie Plant Unit 1, air intrusion into the CCW system from a containment instrument air (IA) compressor resulted in an unanalyzed conditio A similar event subsequently occurred in 200 Had a design-basis accident occurred, the continued air ingress into the CCW system could have led to a loss of safety functio The CCW system is a safety-related system that provides cooling and seal makeup to the non-safety-related containment IA compressor Air intrusion into the CCW system began after a routine shift to the other standby containment IA compresso Air leaked at a slow rate into the CCW system, and took several hours to initiate alarm Operators initially believed that the CCW surge tank high level alarm / condition resulted from reactor coolant system leaking into the CCW system rather than air intrusio Subsequent alarms and indications of fluctuating pump motor current and CCW header flow led operators to conclude that an air intrusion was occurrin The licensee determined that the air intrusion into the CCW system was caused by leakage through two of the inactive IA compressor discharge check valves combined with the failure of the IA compressor unloading solenoid valv Additionally, leakage through the IA seal water makeup solenoid valve, which interfaces with the non-essential CCW header, created a pathway for air to enter the CCW syste root cause evaluation determined that these repetitive events resulted from a latent design issue that did not consider the potential for gas intrusion into the CCW system and from the failure to recognize or understand the potential impact on the CCW and the other safety-related systems that CCW supports during the initial condition report screening proces The original CCW design was vulnerable to gas intrusion that could result in a common mode system failur Gas intrusion was not typically considered in the CCW system design when the St. Lucie plants were designed as is evident from licensing bases document Consequently, St. Lucie operating procedures did not address detection and mitigation of gas intrusion occurrence The CCW system vulnerability to gas intrusion from the containment IA compressors was not recognized because the leakage path required a failure of the IA compressor unloading valve and air leakage through multiple components (i.e., two check valves and a solenoid valve). Licensee corrective actions included a design change to isolate the air intrusion path into the CCW system from the containment IA air compressors, procedure revisions to identify and mitigate air intrusion into the CCW system and revisions to licensed operator and non-licensed operator lesson plans and engineering procedures to reflect lessons learne For additional information, see St. Lucie Unit 1 Licensee Event Report (LER) 2010-001-00 dated February 4, 2010, in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML10103110 In that LER, the licensee concluded that it had missed many opportunities to learn from internal and external operating experience to prevent the 2008 CCW air intrusion even Additional details appear in St. Lucie Nuclear PlantNRC Component Design Bases InspectionInspection Report 05000335/2009006 and 05000389/2009006; Preliminary Greater than Green Findings, dated January 19, 2010 (ADAMS Accession No. ML100210081). In addition, the NRC letter, Final Significance Determination of a Yellow Finding and Notice of Violation (NRC Component Design Bases Inspection Report 05000335/2010007 and 05000389/2010007), St. Lucie Nuclear Plant dated April 19, 2010 (ADAMS Accession No. ML101090509), documents a violation for the licensee failure to identify and correct the source of the air in-leakage into the CCW system that occurred in October 2008 and that the corrective actions failed to preclude a similar air intrusion event into the CCW system in 200 The NRC characterized this violation as ellow, meaning a finding of substantial significance with regard to safet Wolf Creek Generating Station On May 24, 2010, at Wolf Creek Generating Station Unit 1, when operators started CCW pump A, the CCW surge tank A level decreased by 68 gallons and CCW system discharge header pressure dropped, causing CCW pump C to automatically star The following week, the CCW surge tank A level decreased by 65 gallons when CCW pump C was starte Subsequent testing revealed gas pockets in both trains of CC The licensee determined that the CCW system gas voids came from (1) inadequate fill and vent of the CCW system during restoration from the 2009 refueling outage, resulting in air being left in the system, and (2) the use of nitrogen saturated fill water after maintenance conducted on the system during the 2009 refueling outag Between that outage and the time the gas was vented, the CCW system was in a degraded conditio Licensee corrective actions included increased monitoring of the CCW system for voids using ultrasonic testing and venting, revising the CCW fill and vent procedures to incorporate dynamic venting and improve the valve operating sequences, and modifying the CCW surge tank connection piping and installing additional high point vent Additional details appear in Wolf Creek Generating StationNRC Special Inspection Report 05000482/2010008, dated January 7, 2011 (ADAMS Accession No. ML110070347). San Onofre Nuclear Generating Station On March 8, 2006, at San Onofre Nuclear Generating Station Unit 2, the licensee observed unexpected fluctuations in the CCW surge tank A level indication, which troubleshooting revealed were being caused by entrained ga The licensee initiated periodic venting of the CCW system at Unit 2, as well as Unit 3, even though the licensee had not observed similar precursor events ther Nine months later, the licensee vented 120 gallons of entrained gas from the Unit 3 CCW train B return line from the letdown heat exchange The licensee determined that Unit 3 CCW train B may have been inoperable for 21 days because of entrained ga The licensee determined that the CCW system gas voids were caused by (1) improper filling and venting of the CCW system after being drained during outages, and (2) the throttling effect created by letdown heat exchanger throttle valve Licensee corrective actions included installing a bypass line around the letdown heat exchanger throttle valves to ensure that the piping remains full of water, revising the CCW system fill-and-vent procedure, and continuing to vent the CCW systems at an appropriate frequenc Additional details appear in San Onofre Nuclear Generating Station LER 05000362/ 2006-006-00, dated April 9, 2007 (ADAMS Accession No. ML071070320), and in San Onofre Nuclear Generating StationNRC Integrated Inspection Report 05000361/2007003; 05000362/2007003, dated August 9, 2007 (ADAMS Accession No. ML072220153). Prairie Island Nuclear Generating Plant On July 29, 2008, the licensee for Prairie Island Nuclear Generating Plant initiated the first of several corrective action program documents describing that the Unit 2 CCW system was inadequately designed to ensure that the system would be protected from licensing basis events (such as high energy line breaks (HELBs), seismic and tornado events) that could occur in the turbine buildin These events in the turbine building could cause a loss of CCW inventory from both trains of equipment and a loss of safety functio Licensee corrective actions included modifying the CCW lines vulnerable to HELB and revising procedures to isolate non-safety-related portions of the Unit 1 CCW system during adverse weather that were vulnerable to impacts from tornado-borne missile Additional details appear in Prairie Island Nuclear Generating Plant, Units 1 and 2NRC Inspection Report 05000282/2009010; 05000306/2009010 Preliminary White Finding, dated August 5, 2009 (ADAMS Accession No. ML092170122); Final Significance Determination for a White Finding and Notice of Violation; NRC Inspection Report No. 05000306/2009013; Prairie Island Nuclear Generating Plant, Unit 2, dated September 3, 2009 (ADAMS Accession No. ML092450624); Prairie Island Nuclear Generating Plant, Unit 2NRC Supplemental (95001) Inspection Report 05000306/2010009, dated September 22, 2010 (ADAMS Accession No. ML102660207); and Prairie Island Nuclear Generating Plant, Unit 2NRC Supplemental (95001) Followup Inspection Report 05000306/2010012, dated November 24, 2010 (ADAMS Accession No. ML103280151). Other Component Cooling Water or Closed Cooling Water Systems -Related Licensee Event Reports and NRC Inspection Findings Other LERs and NRC inspection reports have discussed CCW system performance issue The NRC staff developed a list of CCW-related LERs from 2000 to 2010 and a list of NRC inspection findings from 2004 to 2010 that are available in ADAMS under Accession Nos. ML110400155 and ML110060549, respectivel The CCW performance issues described in this IN occurred at pressurized-water reactor unit However, the generic implications could also apply to equivalent systems in boiling-water reactor units such as various closed cooling water system A listing of LERs and NRC Accession Nos. ML111750215 and ML111750219, respectivel | St. Lucie Plant On October 16, 2008, at St. Lucie Plant Unit 1, air intrusion into the CCW system from a containment instrument air (IA) compressor resulted in an unanalyzed conditio A similar event subsequently occurred in 200 Had a design-basis accident occurred, the continued air ingress into the CCW system could have led to a loss of safety functio The CCW system is a safety-related system that provides cooling and seal makeup to the non-safety-related containment IA compressor Air intrusion into the CCW system began after a routine shift to the other standby containment IA compresso Air leaked at a slow rate into the CCW system, and took several hours to initiate alarm Operators initially believed that the CCW surge tank high level alarm / condition resulted from reactor coolant system leaking into the CCW system rather than air intrusio Subsequent alarms and indications of fluctuating pump motor current and CCW header flow led operators to conclude that an air intrusion was occurrin The licensee determined that the air intrusion into the CCW system was caused by leakage through two of the inactive IA compressor discharge check valves combined with the failure of the IA compressor unloading solenoid valv Additionally, leakage through the IA seal water makeup solenoid valve, which interfaces with the non-essential CCW header, created a pathway for air to enter the CCW syste root cause evaluation determined that these repetitive events resulted from a latent design issue that did not consider the potential for gas intrusion into the CCW system and from the failure to recognize or understand the potential impact on the CCW and the other safety-related systems that CCW supports during the initial condition report screening proces The original CCW design was vulnerable to gas intrusion that could result in a common mode system failur Gas intrusion was not typically considered in the CCW system design when the St. Lucie plants were designed as is evident from licensing bases document Consequently, St. Lucie operating procedures did not address detection and mitigation of gas intrusion occurrence The CCW system vulnerability to gas intrusion from the containment IA compressors was not recognized because the leakage path required a failure of the IA compressor unloading valve and air leakage through multiple components (i.e., two check valves and a solenoid valve). Licensee corrective actions included a design change to isolate the air intrusion path into the CCW system from the containment IA air compressors, procedure revisions to identify and mitigate air intrusion into the CCW system and revisions to licensed operator and non-licensed operator lesson plans and engineering procedures to reflect lessons learne For additional information, see St. Lucie Unit 1 Licensee Event Report (LER) 2010-001-00 dated February 4, 2010, in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML10103110 In that LER, the licensee concluded that it had missed many opportunities to learn from internal and external operating experience to prevent the 2008 CCW air intrusion even Additional details appear in St. Lucie Nuclear PlantNRC Component Design Bases InspectionInspection Report 05000335/2009006 and 05000389/2009006; Preliminary Greater than Green Findings, dated January 19, 2010 (ADAMS Accession No. ML100210081). In addition, the NRC letter, Final Significance Determination of a Yellow Finding and Notice of Violation (NRC Component Design Bases Inspection Report 05000335/2010007 and 05000389/2010007), St. Lucie Nuclear Plant dated April 19, 2010 (ADAMS Accession No. ML101090509), documents a violation for the licensee failure to identify and correct the source of the air in-leakage into the CCW system that occurred in October 2008 and that the corrective actions failed to preclude a similar air intrusion event into the CCW system in 200 The NRC characterized this violation as ellow, meaning a finding of substantial significance with regard to safet Wolf Creek Generating Station On May 24, 2010, at Wolf Creek Generating Station Unit 1, when operators started CCW pump A, the CCW surge tank A level decreased by 68 gallons and CCW system discharge header pressure dropped, causing CCW pump C to automatically star The following week, the CCW surge tank A level decreased by 65 gallons when CCW pump C was starte Subsequent testing revealed gas pockets in both trains of CC The licensee determined that the CCW system gas voids came from (1) inadequate fill and vent of the CCW system during restoration from the 2009 refueling outage, resulting in air being left in the system, and (2) the use of nitrogen saturated fill water after maintenance conducted on the system during the 2009 refueling outag Between that outage and the time the gas was vented, the CCW system was in a degraded conditio Licensee corrective actions included increased monitoring of the CCW system for voids using ultrasonic testing and venting, revising the CCW fill and vent procedures to incorporate dynamic venting and improve the valve operating sequences, and modifying the CCW surge tank connection piping and installing additional high point vent Additional details appear in Wolf Creek Generating StationNRC Special Inspection Report 05000482/2010008, dated January 7, 2011 (ADAMS Accession No. ML110070347). San Onofre Nuclear Generating Station On March 8, 2006, at San Onofre Nuclear Generating Station Unit 2, the licensee observed unexpected fluctuations in the CCW surge tank A level indication, which troubleshooting revealed were being caused by entrained ga The licensee initiated periodic venting of the CCW system at Unit 2, as well as Unit 3, even though the licensee had not observed similar precursor events ther Nine months later, the licensee vented 120 gallons of entrained gas from the Unit 3 CCW train B return line from the letdown heat exchange The licensee determined that Unit 3 CCW train B may have been inoperable for 21 days because of entrained ga The licensee determined that the CCW system gas voids were caused by (1) improper filling and venting of the CCW system after being drained during outages, and (2) the throttling effect created by letdown heat exchanger throttle valve Licensee corrective actions included installing a bypass line around the letdown heat exchanger throttle valves to ensure that the piping remains full of water, revising the CCW system fill-and-vent procedure, and continuing to vent the CCW systems at an appropriate frequenc Additional details appear in San Onofre Nuclear Generating Station LER 05000362/ 2006-006-00, dated April 9, 2007 (ADAMS Accession No. ML071070320), and in San Onofre Nuclear Generating StationNRC Integrated Inspection Report 05000361/2007003; 05000362/2007003, dated August 9, 2007 (ADAMS Accession No. ML072220153). Prairie Island Nuclear Generating Plant On July 29, 2008, the licensee for Prairie Island Nuclear Generating Plant initiated the first of several corrective action program documents describing that the Unit 2 CCW system was inadequately designed to ensure that the system would be protected from licensing basis events (such as high energy line breaks (HELBs), seismic and tornado events) that could occur in the turbine buildin These events in the turbine building could cause a loss of CCW inventory from both trains of equipment and a loss of safety functio Licensee corrective actions included modifying the CCW lines vulnerable to HELB and revising procedures to isolate non-safety-related portions of the Unit 1 CCW system during adverse weather that were vulnerable to impacts from tornado-borne missile Additional details appear in Prairie Island Nuclear Generating Plant, Units 1 and 2NRC Inspection Report 05000282/2009010; 05000306/2009010 Preliminary White Finding, dated August 5, 2009 (ADAMS Accession No. ML092170122); Final Significance Determination for a White Finding and Notice of Violation; NRC Inspection Report No. 05000306/2009013; Prairie Island Nuclear Generating Plant, Unit 2, dated September 3, 2009 (ADAMS Accession No. ML092450624); Prairie Island Nuclear Generating Plant, Unit 2NRC Supplemental (95001) Inspection Report 05000306/2010009, dated September 22, 2010 (ADAMS Accession No. ML102660207); and Prairie Island Nuclear Generating Plant, Unit 2NRC Supplemental (95001) Followup Inspection Report 05000306/2010012, dated November 24, 2010 (ADAMS Accession No. ML103280151). Other Component Cooling Water or Closed Cooling Water Systems -Related Licensee Event Reports and NRC Inspection Findings Other LERs and NRC inspection reports have discussed CCW system performance issue The NRC staff developed a list of CCW-related LERs from 2000 to 2010 and a list of NRC inspection findings from 2004 to 2010 that are available in ADAMS under Accession Nos. ML110400155 and ML110060549, respectivel The CCW performance issues described in this IN occurred at pressurized-water reactor unit However, the generic implications could also apply to equivalent systems in boiling-water reactor units such as various closed cooling water system A listing of LERs and NRC Accession Nos. ML111750215 and ML111750219, respectivel | ||
==BACKGROUND== | ==BACKGROUND== | ||
Related Generic Communication NRC Generic Letter 2008-01Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems,dated January 11, 2008, did not specifically cover the CCW system, however, insights provided in the generic letter related to gas accumulation may appl | Related Generic Communication NRC Generic Letter 2008-01Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems,dated January 11, 2008, did not specifically cover the CCW system, however, insights provided in the generic letter related to gas accumulation may appl | ||
==DISCUSSION== | ==DISCUSSION== | ||
Licensees are required to maintain the CCW system in an operable condition as specified in the technical specification Gas accumulation in nuclear power plant systems can cause water hammer, gas binding of pumps, and inadvertent relief valve actuation that may damage pumps, valves, piping, and supports and may render the CCW system inoperabl The CCW system is a safety-related system that provides cooling to components in other safety-related systems and in non-safety-related system This IN describes examples where malfunctions of non-safety-related components could render the safety-related CCW system inoperabl Appendix B to 10 CFR Part 50, requires licensees to establish measures to assure that conditions adverse to quality be promptly identified and correcte The events in this IN illustrate the importance of effectively using internal and external operating experience and appropriate corrective action investigations to avoid similar problem Timely corrective actions are particularly important for issues involving gas accumulation, HELB, and tornado vulnerabilities because they have the potential to render both trains of CCW inoperable and impact nuclear safet | Licensees are required to maintain the CCW system in an operable condition as specified in the technical specification Gas accumulation in nuclear power plant systems can cause water hammer, gas binding of pumps, and inadvertent relief valve actuation that may damage pumps, valves, piping, and supports and may render the CCW system inoperabl The CCW system is a safety-related system that provides cooling to components in other safety-related systems and in non-safety-related system This IN describes examples where malfunctions of non-safety-related components could render the safety-related CCW system inoperabl Appendix B to 10 CFR Part 50, requires licensees to establish measures to assure that conditions adverse to quality be promptly identified and correcte The events in this IN illustrate the importance of effectively using internal and external operating experience and appropriate corrective action investigations to avoid similar problem Timely corrective actions are particularly important for issues involving gas accumulation, HELB, and tornado vulnerabilities because they have the potential to render both trains of CCW inoperable and impact nuclear safet | ||
==CONTACT== | ==CONTACT== | ||
This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manage /RA/ /RA/ Timothy J. McGinty, Director Laura A. Dudes, Director Division of Policy and Rulemaking Division of Construction Inspection and Office of Nuclear Reactor Regulation Operational Programs Office of New Reactors | This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manage /RA/ /RA/ Timothy J. McGinty, Director Laura A. Dudes, Director Division of Policy and Rulemaking Division of Construction Inspection and Office of Nuclear Reactor Regulation Operational Programs Office of New Reactors | ||
===Technical Contact:=== | ===Technical Contact:=== | ||
Mark King, NRR/DIRS 301-415-1150 E-mail: msk1@nrc.gov Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Librar | Mark King, NRR/DIRS 301-415-1150 E-mail: msk1@nrc.gov Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Librar | ||
==DISCUSSION== | ==DISCUSSION== | ||
Licensees are required to maintain the CCW system in an operable condition as specified in the technical specification Gas accumulation in nuclear power plant systems can cause water hammer, gas binding of pumps, and inadvertent relief valve actuation that may damage pumps, valves, piping, and supports and may render the CCW system inoperabl The CCW system is a safety-related system that provides cooling to components in other safety-related systems and in non-safety-related system This IN describes examples where malfunctions of non-safety-related components could render the safety-related CCW system inoperabl Appendix B to 10 CFR Part 50, el requires licensees to establish measures to assure that conditions adverse to quality be promptly identified and correcte The events in this IN illustrate the importance of effectively using internal and external operating experience and appropriate corrective action investigations to avoid similar problem Timely corrective actions are particularly important for issues involving gas accumulation, HELB, and tornado vulnerabilities because they have the potential to render both trains of CCW inoperable and impact nuclear safet | Licensees are required to maintain the CCW system in an operable condition as specified in the technical specification Gas accumulation in nuclear power plant systems can cause water hammer, gas binding of pumps, and inadvertent relief valve actuation that may damage pumps, valves, piping, and supports and may render the CCW system inoperabl The CCW system is a safety-related system that provides cooling to components in other safety-related systems and in non-safety-related system This IN describes examples where malfunctions of non-safety-related components could render the safety-related CCW system inoperabl Appendix B to 10 CFR Part 50, el requires licensees to establish measures to assure that conditions adverse to quality be promptly identified and correcte The events in this IN illustrate the importance of effectively using internal and external operating experience and appropriate corrective action investigations to avoid similar problem Timely corrective actions are particularly important for issues involving gas accumulation, HELB, and tornado vulnerabilities because they have the potential to render both trains of CCW inoperable and impact nuclear safet | ||
==CONTACT== | ==CONTACT== | ||
This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manage /RA/ /RA/ Timothy J. McGinty, Director Laura A. Dudes, Director Division of Policy and Rulemaking Division of Construction Inspection and Office of Nuclear Reactor Regulation Operational Programs Office of New Reactors | This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manage /RA/ /RA/ Timothy J. McGinty, Director Laura A. Dudes, Director Division of Policy and Rulemaking Division of Construction Inspection and Office of Nuclear Reactor Regulation Operational Programs Office of New Reactors | ||
===Technical Contact:=== | ===Technical Contact:=== | ||
Revision as of 04:01, 4 March 2018
| ML111150135 | |
| Person / Time | |
|---|---|
| Issue date: | 07/18/2011 |
| From: | Dudes L A, McGinty T J Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| Beaulieu, D P, NRR/DPR, 415-3243 | |
| References | |
| IN-11-014 | |
| Download: ML111150135 (6) | |
ML111150135 July 18, 2011 NRC INFORMATION NOTICE 2011-14: COMPONENT COOLING WATER SYSTEM GAS ACCUMULATION AND OTHER PERFORMANCE ISSUES
ADDRESSEES
All holders of an operating license or construction permit for a nuclear power reactor issued under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Production and Utilization Facilitie All holders of, or applicants for, an early site permit, standard design certification, standard design approval, manufacturing license, or combined license issued under 10 CFR Part 52, nses, Certifications, and Approvals for Nuclear Power Plants
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform addressees of recent operating experience regarding air intrusion into component cooling water (CCW) systems, as well as other CCW system performance issue It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problem However, suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is require
DESCRIPTION OF CIRCUMSTANCES
St. Lucie Plant On October 16, 2008, at St. Lucie Plant Unit 1, air intrusion into the CCW system from a containment instrument air (IA) compressor resulted in an unanalyzed conditio A similar event subsequently occurred in 200 Had a design-basis accident occurred, the continued air ingress into the CCW system could have led to a loss of safety functio The CCW system is a safety-related system that provides cooling and seal makeup to the non-safety-related containment IA compressor Air intrusion into the CCW system began after a routine shift to the other standby containment IA compresso Air leaked at a slow rate into the CCW system, and took several hours to initiate alarm Operators initially believed that the CCW surge tank high level alarm / condition resulted from reactor coolant system leaking into the CCW system rather than air intrusio Subsequent alarms and indications of fluctuating pump motor current and CCW header flow led operators to conclude that an air intrusion was occurrin The licensee determined that the air intrusion into the CCW system was caused by leakage through two of the inactive IA compressor discharge check valves combined with the failure of the IA compressor unloading solenoid valv Additionally, leakage through the IA seal water makeup solenoid valve, which interfaces with the non-essential CCW header, created a pathway for air to enter the CCW syste root cause evaluation determined that these repetitive events resulted from a latent design issue that did not consider the potential for gas intrusion into the CCW system and from the failure to recognize or understand the potential impact on the CCW and the other safety-related systems that CCW supports during the initial condition report screening proces The original CCW design was vulnerable to gas intrusion that could result in a common mode system failur Gas intrusion was not typically considered in the CCW system design when the St. Lucie plants were designed as is evident from licensing bases document Consequently, St. Lucie operating procedures did not address detection and mitigation of gas intrusion occurrence The CCW system vulnerability to gas intrusion from the containment IA compressors was not recognized because the leakage path required a failure of the IA compressor unloading valve and air leakage through multiple components (i.e., two check valves and a solenoid valve). Licensee corrective actions included a design change to isolate the air intrusion path into the CCW system from the containment IA air compressors, procedure revisions to identify and mitigate air intrusion into the CCW system and revisions to licensed operator and non-licensed operator lesson plans and engineering procedures to reflect lessons learne For additional information, see St. Lucie Unit 1 Licensee Event Report (LER) 2010-001-00 dated February 4, 2010, in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML10103110 In that LER, the licensee concluded that it had missed many opportunities to learn from internal and external operating experience to prevent the 2008 CCW air intrusion even Additional details appear in St. Lucie Nuclear PlantNRC Component Design Bases InspectionInspection Report 05000335/2009006 and 05000389/2009006; Preliminary Greater than Green Findings, dated January 19, 2010 (ADAMS Accession No. ML100210081). In addition, the NRC letter, Final Significance Determination of a Yellow Finding and Notice of Violation (NRC Component Design Bases Inspection Report 05000335/2010007 and 05000389/2010007), St. Lucie Nuclear Plant dated April 19, 2010 (ADAMS Accession No. ML101090509), documents a violation for the licensee failure to identify and correct the source of the air in-leakage into the CCW system that occurred in October 2008 and that the corrective actions failed to preclude a similar air intrusion event into the CCW system in 200 The NRC characterized this violation as ellow, meaning a finding of substantial significance with regard to safet Wolf Creek Generating Station On May 24, 2010, at Wolf Creek Generating Station Unit 1, when operators started CCW pump A, the CCW surge tank A level decreased by 68 gallons and CCW system discharge header pressure dropped, causing CCW pump C to automatically star The following week, the CCW surge tank A level decreased by 65 gallons when CCW pump C was starte Subsequent testing revealed gas pockets in both trains of CC The licensee determined that the CCW system gas voids came from (1) inadequate fill and vent of the CCW system during restoration from the 2009 refueling outage, resulting in air being left in the system, and (2) the use of nitrogen saturated fill water after maintenance conducted on the system during the 2009 refueling outag Between that outage and the time the gas was vented, the CCW system was in a degraded conditio Licensee corrective actions included increased monitoring of the CCW system for voids using ultrasonic testing and venting, revising the CCW fill and vent procedures to incorporate dynamic venting and improve the valve operating sequences, and modifying the CCW surge tank connection piping and installing additional high point vent Additional details appear in Wolf Creek Generating StationNRC Special Inspection Report 05000482/2010008, dated January 7, 2011 (ADAMS Accession No. ML110070347). San Onofre Nuclear Generating Station On March 8, 2006, at San Onofre Nuclear Generating Station Unit 2, the licensee observed unexpected fluctuations in the CCW surge tank A level indication, which troubleshooting revealed were being caused by entrained ga The licensee initiated periodic venting of the CCW system at Unit 2, as well as Unit 3, even though the licensee had not observed similar precursor events ther Nine months later, the licensee vented 120 gallons of entrained gas from the Unit 3 CCW train B return line from the letdown heat exchange The licensee determined that Unit 3 CCW train B may have been inoperable for 21 days because of entrained ga The licensee determined that the CCW system gas voids were caused by (1) improper filling and venting of the CCW system after being drained during outages, and (2) the throttling effect created by letdown heat exchanger throttle valve Licensee corrective actions included installing a bypass line around the letdown heat exchanger throttle valves to ensure that the piping remains full of water, revising the CCW system fill-and-vent procedure, and continuing to vent the CCW systems at an appropriate frequenc Additional details appear in San Onofre Nuclear Generating Station LER 05000362/ 2006-006-00, dated April 9, 2007 (ADAMS Accession No. ML071070320), and in San Onofre Nuclear Generating StationNRC Integrated Inspection Report 05000361/2007003; 05000362/2007003, dated August 9, 2007 (ADAMS Accession No. ML072220153). Prairie Island Nuclear Generating Plant On July 29, 2008, the licensee for Prairie Island Nuclear Generating Plant initiated the first of several corrective action program documents describing that the Unit 2 CCW system was inadequately designed to ensure that the system would be protected from licensing basis events (such as high energy line breaks (HELBs), seismic and tornado events) that could occur in the turbine buildin These events in the turbine building could cause a loss of CCW inventory from both trains of equipment and a loss of safety functio Licensee corrective actions included modifying the CCW lines vulnerable to HELB and revising procedures to isolate non-safety-related portions of the Unit 1 CCW system during adverse weather that were vulnerable to impacts from tornado-borne missile Additional details appear in Prairie Island Nuclear Generating Plant, Units 1 and 2NRC Inspection Report 05000282/2009010; 05000306/2009010 Preliminary White Finding, dated August 5, 2009 (ADAMS Accession No. ML092170122); Final Significance Determination for a White Finding and Notice of Violation; NRC Inspection Report No. 05000306/2009013; Prairie Island Nuclear Generating Plant, Unit 2, dated September 3, 2009 (ADAMS Accession No. ML092450624); Prairie Island Nuclear Generating Plant, Unit 2NRC Supplemental (95001) Inspection Report 05000306/2010009, dated September 22, 2010 (ADAMS Accession No. ML102660207); and Prairie Island Nuclear Generating Plant, Unit 2NRC Supplemental (95001) Followup Inspection Report 05000306/2010012, dated November 24, 2010 (ADAMS Accession No. ML103280151). Other Component Cooling Water or Closed Cooling Water Systems -Related Licensee Event Reports and NRC Inspection Findings Other LERs and NRC inspection reports have discussed CCW system performance issue The NRC staff developed a list of CCW-related LERs from 2000 to 2010 and a list of NRC inspection findings from 2004 to 2010 that are available in ADAMS under Accession Nos. ML110400155 and ML110060549, respectivel The CCW performance issues described in this IN occurred at pressurized-water reactor unit However, the generic implications could also apply to equivalent systems in boiling-water reactor units such as various closed cooling water system A listing of LERs and NRC Accession Nos. ML111750215 and ML111750219, respectivel
BACKGROUND
Related Generic Communication NRC Generic Letter 2008-01Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems,dated January 11, 2008, did not specifically cover the CCW system, however, insights provided in the generic letter related to gas accumulation may appl
DISCUSSION
Licensees are required to maintain the CCW system in an operable condition as specified in the technical specification Gas accumulation in nuclear power plant systems can cause water hammer, gas binding of pumps, and inadvertent relief valve actuation that may damage pumps, valves, piping, and supports and may render the CCW system inoperabl The CCW system is a safety-related system that provides cooling to components in other safety-related systems and in non-safety-related system This IN describes examples where malfunctions of non-safety-related components could render the safety-related CCW system inoperabl Appendix B to 10 CFR Part 50, requires licensees to establish measures to assure that conditions adverse to quality be promptly identified and correcte The events in this IN illustrate the importance of effectively using internal and external operating experience and appropriate corrective action investigations to avoid similar problem Timely corrective actions are particularly important for issues involving gas accumulation, HELB, and tornado vulnerabilities because they have the potential to render both trains of CCW inoperable and impact nuclear safet
CONTACT
This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manage /RA/ /RA/ Timothy J. McGinty, Director Laura A. Dudes, Director Division of Policy and Rulemaking Division of Construction Inspection and Office of Nuclear Reactor Regulation Operational Programs Office of New Reactors
Technical Contact:
Mark King, NRR/DIRS 301-415-1150 E-mail: msk1@nrc.gov Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Librar
DISCUSSION
Licensees are required to maintain the CCW system in an operable condition as specified in the technical specification Gas accumulation in nuclear power plant systems can cause water hammer, gas binding of pumps, and inadvertent relief valve actuation that may damage pumps, valves, piping, and supports and may render the CCW system inoperabl The CCW system is a safety-related system that provides cooling to components in other safety-related systems and in non-safety-related system This IN describes examples where malfunctions of non-safety-related components could render the safety-related CCW system inoperabl Appendix B to 10 CFR Part 50, el requires licensees to establish measures to assure that conditions adverse to quality be promptly identified and correcte The events in this IN illustrate the importance of effectively using internal and external operating experience and appropriate corrective action investigations to avoid similar problem Timely corrective actions are particularly important for issues involving gas accumulation, HELB, and tornado vulnerabilities because they have the potential to render both trains of CCW inoperable and impact nuclear safet
CONTACT
This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manage /RA/ /RA/ Timothy J. McGinty, Director Laura A. Dudes, Director Division of Policy and Rulemaking Division of Construction Inspection and Office of Nuclear Reactor Regulation Operational Programs Office of New Reactors
Technical Contact:
Mark King, NRR/DIRS 301-415-1150 E-mail: msk1@nrc.gov Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under NRC Librar ADAMS Accession Number: ML111150135 TAC ME5436 OFFICE NRR/DIRS/IOEB Tech Editor BC:NRR/DIRS/IOEB D:NRR/DIRS NAME MKing KAKribbs JThorp FBrown TPruett for DATE 5/31 /11 06/04/11 e-mail 06/01/11 06/26/11 OFFICE BC:NRR/DSS/SBPB D:NRR/DSS BC:NRO/DSRA/SBPB NRR/DPR/PGCB NAME GCasto SBahadur JDreisbach for SLee CHawes CMH DATE 07/ 07 /11 07/ 11 /11 06/ 29 /11 e-email 07/12 /11 OFFICE NRR/DPR/PGCB BC:NRR/PGCB D:DCIP/NRO D: NRR/DPR NAME MBanic SRosenberg LDudes TMcGinty OFFICE 07/11/11 07/14/11 07/15/11 07/15/11 OFFICIAL RECORD COPY