Information Notice 2011-14, Component Cooling Water System Gas Accumulation and Other Performance Issues

Component Cooling Water System Gas Accumulation and Other Performance Issues
	ML111150135
Person / Time
Issue date:	07/18/2011
From:	Laura Dudes, Mcginty T; 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)
	v • d • e

ML111150135 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

OFFICE OF NEW REACTORS

WASHINGTON, DC 20555-0001

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, Domestic Licensing of

Production and Utilization Facilities.

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, Licenses, 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 issues. It is expected that

recipients will review the information for applicability to their facilities and consider actions, as

appropriate, to avoid similar problems. However, suggestions contained in this IN are not NRC

requirements; therefore, no specific action or written response is required.

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 condition. A similar event

subsequently occurred in 2009. Had a design-basis accident occurred, the continued air

ingress into the CCW system could have led to a loss of safety function.

The CCW system is a safety-related system that provides cooling and seal makeup to the

non-safety-related containment IA compressors. Air intrusion into the CCW system began after

a routine shift to the other standby containment IA compressor. Air leaked at a slow rate into

the CCW system, and took several hours to initiate alarms. 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 intrusion. Subsequent alarms and indications of fluctuating

pump motor current and CCW header flow led operators to conclude that an air intrusion was

occurring. 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 valve. 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 system.

The licensees 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 licensees 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

process. The original CCW design was vulnerable to gas intrusion that could result in a

common mode system failure. Gas intrusion was not typically considered in the CCW system

design when the St. Lucie plants were designed as is evident from licensing bases documents.

Consequently, St. Lucie operating procedures did not address detection and mitigation of gas

intrusion occurrences. 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 learned.

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. ML101031100. 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 event.

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 licensees 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 2009.

The NRC characterized this violation as Yellow, meaning a finding of substantial significance

with regard to safety. 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 start. The following week, the CCW

surge tank A level decreased by 65 gallons when CCW pump C was started. Subsequent

testing revealed gas pockets in both trains of CCW.

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 outage. Between that outage and the time the gas was

vented, the CCW system was in a degraded condition.

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 vents.

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 gas. 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 there. Nine months later, the licensee vented 120 gallons of entrained gas

from the Unit 3 CCW train B return line from the letdown heat exchanger. The licensee

determined that Unit 3 CCW train B may have been inoperable for 21 days because of

entrained gas.

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 valves. 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 frequency.

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 building. These events in the turbine building could cause a loss of CCW inventory from

both trains of equipment and a loss of safety function. 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 missiles.

Additional details appear in Prairie Island Nuclear Generating Plant, Units 1 and 2-NRC

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 2-NRC Supplemental

(95001) Inspection Report 05000306/2010009, dated September 22, 2010 (ADAMS Accession

No. ML102660207); and Prairie Island Nuclear Generating Plant, Unit 2-NRC 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 issues.

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, respectively.

The CCW performance issues described in this IN occurred at pressurized-water reactor units.

However, the generic implications could also apply to equivalent systems in boiling-water

reactor units such as various closed cooling water systems. A listing of LERs and NRC

inspection findings involving closed cooling water systems is available in ADAMS under

Accession Nos. ML111750215 and ML111750219, respectively.

BACKGROUND

Related Generic Communication

NRC Generic Letter 2008-01, Managing 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 apply.

DISCUSSION

Licensees are required to maintain the CCW system in an operable condition as specified in the

technical specifications. 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 inoperable. The CCW system is

a safety-related system that provides cooling to components in other safety-related systems and

in non-safety-related systems. This IN describes examples where malfunctions of

non-safety-related components could render the safety-related CCW system inoperable.

Appendix B to 10 CFR Part 50, Quality Assurance Criteria for Nuclear Power Plants and Fuel

Reprocessing Plants, Criterion XVI, Corrective Action, requires licensees to establish

measures to assure that conditions adverse to quality be promptly identified and corrected. The

events in this IN illustrate the importance of effectively using internal and external operating

experience and appropriate corrective action investigations to avoid similar problems. 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 safety.

CONTACT

This IN requires no specific action or written response. Please direct any questions about this

matter to the technical contact listed below or the appropriate Office of Nuclear Reactor

Regulation (NRR) project manager.

/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 Library.