Information Notice 1998-02, Nuclear Power Plant Cold Weather Problems and Protective Measures

Nuclear Power Plant Cold Weather Problems and Protective Measures

ML031050304
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	01/21/1998
From:	Roe J Office of Nuclear Reactor Regulation
To:
References
IN-98-002, NUDOCS 9801200034
Download: ML031050304 (7)

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, DC 20555-0001 January 21, 1998 NRC INFORMATION NOTICE 98-02: NUCLEAR POWER PLANT COLD WEATHER

PROBLEMS AND PROTECTIVE MEASURES

Addressees

All holders of operating licenses for nuclear power reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert

addressees to potential common-cause failure mechanisms of safety-related systems and will

systems important to safety caused by extremely cold weather. It is expected that recipients to

review the information for applicability to their facilities and consider actions, as appropriate,NRC

avoid similar problems. However, suggestions contained in this information notice are not

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

Description of Circumstances

Wolf Creek

on

IN 96-36, "Degradation of Cooling Water Systems Due to Icing," described the effects of icing

intake trash racks and traveling screens which resulted in a manual reactor/turbine trip on

January 30, 1996, at Wolf Creek. In addition to the degradation of the circulating water and

essential service water systems, the turbine-driven auxiliary feedwater pump was degraded

during this event. The NRC identified the event as a precursor within the framework of the

NRC's accident sequence precursor program, and calculated a conditional core-damage

probability of 2.1 x 104.

Circulating water system degradation was initially attributed to water from the spray-wash system

freezing on the traveling screens, making them inoperable. To improve the reliability of the

circulating water system, the licensee revised plant procedures (1) to eliminate the requirement

to operate traveling screens continuously in slow manual mode during cold weather or underin

unusual icing conditions and (2) to allow the screens to be operated in the automatic mode

which the screens remained stationary without sprays until the system was started either by a

timer or a high differential level. The traveling screens were also enclosed in a heated

environment.

After IN 96-36 was issued, more information became available about the degradation of the

circulating water system. Specifically, on August 5, 1997, the licensee reported that during the

event, two of three air release valves on the circulating water warming line had been plugged.

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IN 98-02 January21, 1998 Failure of these valves caused air binding in the piping and caused the warming

flow to be

nearly zero.

The effect of the resultant air binding was demonstrated during a 5-day test

in January 1997 with 2.8 'C (37 °F) lake water, when warming line flow was reduced from

1388 liters per second

(22,000 gpm) to approximately 347 liters per second (5,500 gpm). This warming

flow

degradation would have been more pronounced during the event because

the temperature of

the lake water was approximately 0 OC (32 OF) during the event and, therefore, contained more

air in solution. Although air removal by the water box venting system should

have significantly

reduced the potential for air binding, approximately one-half of the water box

air release valves

had been isolated during the January. 1996 event.

In response to these findings, the three air release valves on the warming

line were replaced

and incorporated into the preventive maintenance program. The licensee

also revised

procedures to ensure (1) manual venting of the circulating water warming

line when the inlet

temperature fell below 1.1 'C (34 0F), and (2) verification of the presence

of circulating water

warming flow and the passing of air from the air release valves when the warming

line valve

was opened in the fall. A procedural step was also added to verify that the

water box air

release valves were not isolated.

Millstone Unit 2 On January 8, 1996, with the plant at 100-percent power, an ice plug formed

in a horizontal, common, service water (SW) strainer backwash drain line that ran through

the intake wall in a

trough toward a fish basket. This would have prevented automatic backwash

of the SW

strainers. This pipe had been welded onto the end of the original vertical discharge

leg in a

modification that had not undergone a formal engineering review. Minor leakage

through the

strainer backwash isolation valves and an unusually long period of subfreezing

temperatures

created the conditions needed to form the ice plug. Removal of the ice plug

restored the SW

strainer backwash capability and operators backwashed the strainers every

4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> to ensure

that another ice plug would not form until the horizontal pipe was eliminated.

Nonetheless, the

open end of the line was still susceptible to ice buildup. The licensee later

reported that the

operators had failed to recognize that the ice plug that made the backwash

functions of the SW

strainers inoperable also made both SW system trains inoperable. The

licensee should have

declared the SW system inoperable during the event and entered Technical

Specification

Limiting Condition for Operation 3.0.3, which required a plant shutdown.

On February 29, 1996, the licensee reported that the SW strainer backwash

system was also

susceptible to a common-mode failure if the intake structure's nonvital

heating system failed to

operate. The licensee changed an operating procedure to require (1)

monitoring of the intake

structure temperature when temperature fell below 4.4 OC (40 OF) and (2)

using portable space

heaters or manual operation of the strainers to prevent freezing. The licensee

also proposed

replacing the common line with three independent backwash lines, locating

the discharge points

to minimize the effect of outdoor weather conditions, and protecting differential

pressure

instrumentation from freezing.

IN 98-02 January 21, 1998 LaSalle Unit 2 On February 4, 1996, operators shut the plant down manually when the oil temperature in the

main transformer could not be maintained within design limits because of the loss of the

transformer cooling fan and cooling pump. Ice severed the transformer cooling logic cable in its

conduit where it entered the underground cable trough. Licensee corrective actions included

inspecting other transformer conduits, clearing water and ice from conduits, and sealing the

conduits.

McGuire Unit 2

On February 8, 1996, with the plant at 100 percent power, two of three refueling water storage

tank (RWST) level transmitters were found to be inoperable because of frozen impulse lines.

The lines froze because thermostat setpoints for the strip heaters were set too low for cold

weather conditions. The frozen impulse lines affected control room RWST level indication and

the ability to automatically switch to the emergency core cooling system sump. To correct this

problem, the licensee increased the thermostat setpoint and added inspection of the level

transmitter panels to its cold weather preventive maintenance procedure.

Discussion

The January 1996 event at Wolf Creek, described above, led the NRC Office for the Analysis

and Evaluation of Operational Data (AEOD) to review the extent of cold weather-related

problems at U.S. nuclear power plants over the past 6 years. The results of this study are

given in Engineering Evaluation Report AEOD/E97-03, "Nuclear Power Plant Cold Weather

Problems and Protective Measures." It contains a compendium of recent cold weather-related

events and corrective actions, as well as design, operations, and training lessons learned by

the nuclear industry and the U.S. Army Corps of Engineers Cold Regions Research and

Engineering Laboratory. The report noted 37 cold weather related events at 23 different sites

between 1991 and 1997. The study also reported an increasing trend in the number of these

events.

Licensees continue to find that icing and freezing from extreme cold weather conditions is a

common-cause failure mechanism that can quickly affect a variety of systems unless mitigating

actions are taken in a timely manner. The recent operating experience described in this study

suggests that, despite NRC and industry communications on this subject, some licensees have

not effectively protected components whose failure could degrade safety-related systems and

systems important to safety. Extreme cold weather conditions continued to affect intake

structures; process lines; instrument lines; emergency diesel generator oil and grease

viscosities; essential chillers; electrical systems; and heating, ventilation, and air conditioning

systems. Lack of design oversight, incomplete review of operating experience, and insufficient

attention to cold weather preparations were responsible for most of the events.

IN 98-02 January 21, 1998 This information notice requires no specific action or written response. However, recipients are

reminded that they are required by 10 CFR 50.65 to take industry-wide operating experience

(including information presented in NRC information notices) into consideration, where practical, when setting goals and performing periodic evaluations. If you have any questions about the

information in this notice, please contact one of the technical contacts listed below or the

appropriate Office of Nuclear Reactor Regulation project manager.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical Contacts: John R. Tappert, NRR

301- 415-1167 E-mail: jrt@nrc.gov

L. Mark Padovan

301- 415-1423 E-mail: Imp@nrc.gov

Robert A. Spence

301- 415-6346 E-mail: ras2@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

"-S 98-02 January 21, 1998 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

98-01 Thefts of Portable Gauges 1/15/98 All portable gauge licensees

97-91 Recent Failures of Control 12/31/97 All industrial radiography

Cables Used on Amersham licensees

Model 660 Posilock Radiography

Systems

97-90 Use of Nonconservative 12/30/97 All holders of OLs for nuclear

Acceptance Criteria in power reactors except those

Safety-Related Pump who have ceased operations

Surveillance Tests and have certified that fuel has

been permanently removed from

the vessel

97-89 Distribution of Sources and 12/29/97 All sealed source and device

Devices Without Authorization manufacturers and distributors

97-88 Experiences During Recent 12/16/97 All holders of OLs for pressurized- Steam Generator Inspections water reactors except those who

have permanently ceased

operations and have certified that

fuel has been permanently

removed from the reactor

97-87 Second Retrofit to 12/12/97 All industrial radiography

Industrial Nuclear Company licensees

IR 100 Radiography Camera, to Correct Inconsistency in

10 CFR Part 34 Compatibility

97-86 Additional Controls for 12/12/97 Registered users of the Model

Transport of the Amersham No. 660 series packages, and

Model No. 660 Series Nuclear Regulatory Commission

Radiographic Exposure Devices industrial radiography licensees

OL = Operating License

CP = Construction Permit