Information Notice 1991-38, Thermal Stratification in Feedwater System Piping

Thermal Stratification in Feedwater System Piping

ML031190533
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:	06/13/1991
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-91-038, NUDOCS 9106060294
Download: ML031190533 (9)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 June 13, 1991 NRC INFORMATION NOTICE NO 91-38: THERMAL STRATIFICATION IN FEEDWATER SYSTEM

PIPING

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is intended to alert addressees to feedwater system

(FWS) piping that could be subjected to thermal stratification and cause- unacceptable pipe movement. 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

information notice do not constitute NRC requirements; therefore, no specific

action or written response is required.

Description of Circumstances

On December 12, 1990, the Duquesne Light Company (the licensee) discovered

global thermal stratification over a long stretch of horizontal FWS piping

inside containment at the Beaver Valley Power Station, Unit 1 (BV-1) during

followup activities related to NRC Bulletin No. 79-13, "Cracking in Feedwater

System Piping."' Global thermal stratification results in low-cycle fatigue, pipe movement, and stresses that might not have been considered in the design

of the piping system (as opposed to cyclic thermal stratification-and thermal

striping which result in high-cycle fatigue and pipe cracks.) The licensee

detected global thermal stratification at BV-1 using instrumentation installed

to monitor the behavior of the feedwater line following unexpected movement of

the feedwater piping in November 1989 (see Figure 1). This instrumentation

detected feedwater temperatures at the top and bottom of the feedwater line

that varied as much as 2001F. The licensee attributed this thermal stratifi- cation to inadequate mixing of feedwater along a 90-foot section of horizontal

piping inside the containment. Although a vertical section of piping might be

expected to provide sufficient mixing to prevent stratification, the horizontal

section at BV-1 is preceded by a 20-foot vertical section that apparently did

not provide adequate mixing to prevent stratification. This global thermal

stratification phenomenon was not previously considered in the design of the

main feedwater piping system for BV-1.

9106060294 Uf t a Loi

PDR fT~ E /

IN 91-38 June 13, 1991 Discussion:

BV-1 is a 3-loop pressurized water reactor (PWR) designed by the Westinghouse

Electric Corporation. The three-loop design may be particularlysusceptible

global thermal stratification in the FWS piping because it typically includes to

long section of horizontal piping just inside containment. However, other a

plant designs, including boiling water reactors (BWRs), may be susceptible to

this phenomenon. For instance, a similar FWS event occurred on August 22, 1984, at the Washington Nuclear Plant, Unit 2, (WNP-2) and is discussed in NRC

Information Notice (IN)84-87, "Piping Thermal Deflection Induced by Stratified

Flow." In this event, the BWR wags operating at about 1 percent power when the

introduction of cold feedwater into hot feedwater piping, heated by the reactor

water cleanup system, caused the pipe to deflect and damage the hangers and

snubbers.

Thermal stratification of the feedwater line may occur while a plant is starting

up or cooling down, or when auxiliary feedwater (AFW) is being injected into

the steam generator through the feedwater line. While a BWR plant is starting

up, stratified flow can be introduced when cold feedwater is added to hot FWS

piping (as was the case at WNP-2). While a BWR or PWR plant is cooling down, especially from full-power operation (Mode 1) to hot standby (Mode 3), the

significant decrease in the FWS flow rate and temperature make the FWS piping

susceptible to stratification. For a PWR, AFW injection probably introduces

the greatest potential for thermal stratification; When cold AFW is injected

just after the full flow of hot feedwater, the temperature differential across

the pipe can become as large as 200 0F.

In long, horizontal lengths of piping, 2 (or more) streams of fluid of different

temperatures can flow in separate layers without appreciable mixing, making

long sections of pipe susceptible to thermal stratification. This piping may

be subjected to stresses that were not-previously accounted for in the piping

design. The BV-1 event also demonstrates that a vertical section of pipe

just upstream of a long section of horizontal pipe offers little (if any)

protection from stratification.

Another concern resulting from the BY-1 event is the adequacy of the design of

supports for piping that may undergo thermal stratification. Supports located

along such piping may restrict pipe movement and contribute to pipe deformation

or support damage. A similar concernexisted at Trojan during an event in 1988 (see NRC Bulletin 88-11, "Pressurizer Surge Line Thermal Stratification").

These concerns are similar to those described in NRC Bulletin 79-13 (Revision

October 16, 1979) and NRC IN 84-87. However, this NRC information notice 2, addresses primarily the effects of thermal stratification on feedwater system

piping, whereas NRC Bulletin 79-13 addressed primarily the effects of thermal

stratification on the steam generator nozzles. IN 84-87 addresses thermal

stratification in the feedwater system at BWRs.

KIj

IN 91-38 June 13, 1991 The staff addressed thermal stratification in other systems important to safety

in NRC Bulletins 88-08; 88-08, Supplement 1; and 88-08, Supplement 3; "Thermal

Stress in Piping Connected to Reactor Coolant Systems," and in NRC INs 88-01,

"Safety Injection Pipe Failure," and 88-80, "Unexpected Piping Movement

Attributed to Thermal Stratification."

Although thermal stratification is not a new problem, the most recent event

demonstrates that mechanisms for thermal stratification continue to be

identified. This most recent finding indicates that stresses produced by

stratification in systems with long sections of horizontal piping may result in

an unanalyzed condition which can affect the integrity of piping and supports.

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact one

of the technical contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Angie P. Young, NRR James E. Beall, RI

(301) 492-1167 (412) 643-2000

Andrew J. Kugler, NRR Shou-Nien Hou, NRR

(301) 492-0834 (301) 492-0793 Attachments:

1. Figure 1. Beaver Valley Unit 1 Main Feedwater

System Piping Configuration Inside Containment

2. List of Recently Issued NRC Information Notices

Figure 1. Beaver Valley Unit 1 Main Feedwater System Piping Configuration Inside Containment

-Ba

Displaced Piping

CONTAINMENT

.,

11 90'

MAIN - SUPPORT I l

FEEDWATER -4

6 lWlfOCUI-ES 6 MWfUJo.ES

SYSTEM

7tF PIPE

SUPPORTS

I STEAM GENERATOR .w cC~- >

3 Ow W~q

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Attachment 2 IN 91-38 June 13, 1991 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

91-37 Compressed Gas Cylinder 06/10/91 All holders of OLs or CPs

Missile Hazards for nuclear power reactors.

91-36 Nuclear Plant Staff 06/10/91 All holders of OLs or CPs

Working Hours for nuclear power reactors.

91-35 Labeling Requirements for 06/07/91 All U.S. Nuclear Requlatory

Transporting Multi-Hazard Commission (NRC) licensees.

Radioactive Materials

91-34 Potential Problems in 06/03/91 All holders of OLs or CPs

Identifying Causes of for nuclear power reactors.

Emergency Diesel Generator

Malfunctions

91-33 Reactor Safety Information 05/31/91 All holders of OLs or CPs

for States During Exercises for nuclear power reactors.

and Emergencies

91-32 Possible Flaws in Certain 05/15/91 All holders of OLs or CPs

Piping Systems Fabricated for nuclear power reactors.

by Associated Piping and

Engineering

91-31 Nonconforming Magnaflux 05/09/91 All holders of OLs or CPs

Magnetic Particle (14AM) for nuclear power reactors.

Prepared Bath

91-30 Inadequate Calibration of 04/23/91 All fuel cycle licensees and

Thermoluminescent Dosi- other licensees routinely

meters Utilized to Monitor handling unshielded uranium

Extremity Dose at Uranium materials.

Processing and Fabrication

Facilities

OL = Operating License

CP = Construction Permit

IN 91-38 June 13, 1991 to safety

The staff addressed thermal stratification in other systems important 3; "Thermal

in NRC Bulletins 88-08; 88-08, Supplement 1; and 88-08, Supplement INs 88-01, in NRC

Stress in Piping Connected to Reactor Coolant Systems," and Movement

"Safety Injection Pipe Failure," and 88-80, "Unexpected Piping

Attributed to Thermal Stratification."

recent event

Although thermal stratification is not a new problem, the most to be

demonstrates that mechanisms for thermal stratification continue

indicates that stresses produced by

identified. This most recent finding may result in

stratification in systems with long sections of horizontal piping

and supports.

an unanalyzed condition which can affect the integrity of piping

response. If

This information notice requires no specific action or writtenplease contact one

you have any questions about the information in this notice, project manager.

of the technical contacts listed below or the appropriate NRR

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Angie P. Young, NRR James E. Beall, RI

(301) 492-1167 (412) 643-2000

Andrew J. Kugler, NRR Shou-Nien Hou, NRR

(301) 492-0834 (301) 492-0793 Attachments:

1. Figure 1. Beaver Valley Unit 1 Main Feedwater

System Piping Configuration Inside Containment

2. List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCE

• DOEA:OGCB  :*NRR:EMEB  :*RI

OFC  :*DOEA:EAB  :*SC:DOEA:EAB:*C:DOEA:EAB :*Tech Ed

AChaffee  : :AKugler :SNHou :JBeall

NAME :AYoung:atb :DFischer

05/20/91  : / /91 :06/ /91 :06/ /91 :04/24/91 DATE :04/25/91 :05/20/91 OFC :C:DOEA:OGCB :D:DOEA

NAME :CBerlinger

DATE :06/04/91 :06/ 7 /91 OFFICIAL RECORD COPY

Document Name: IN 9138

-3- The staff addressed thermal stratification in other systems important to safety

in NRC Bulletins 88-08, 88-08 Supplement 1, and 88-08 Supplement 3, uThermal

Stress in Piping Connected to Reactor Coolant Systems," and in NRC Ills 88-01,

"Safety Injection Pipe Failure," and 88-80, "Unexpected Piping Movement

Attributed to Thermal Stratification."

Although thermal stratification is not a new problem, the most recent event

demonstrates that mechanisms for thermal stratification continue to be

identified. This most recent finding indicates that stresses produced by

stratification in systems with long sections of horizontal piping may result in

an unanalyzed condition which can pose a threat to the integrity of piping

and supports.

This information notice requires no specific action or written response. If

you have any questions about this matter, please contact one of the technical

contacts listed below or the appropriate HRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Angie P. Young, NRR James E. Beall, RI

(301) 492-1167 (412) 643-2000

Andrew J. Kugler, NRR Shou-Nien Hou, NRR

(301) 492-0834 (301) 492-0793 Attachments:

1. Figure 1. Beaver Valley Unit 1 Main Feedwater System Piping Configuration

Inside Containment

2. List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCE

OFC  :*DOEA:EAB  :*SC:DOEA:EAB:*C:DOEA:EAB :*Tech Ed  :*DOEA:OGCB  :*NRR:EMEB  :*RI

_____ ____________ - ----------- ______ _____ ____________ ____________ _ -------

NAME :AYoung:atb :DFischer :AChaffee  : :AKugler :SNHou :JBeall

DATE : / :1

9191 /91  : /91: / /

/91: /91 :/ /91 OFC :C:D 0

OGCB :D:DOEA  :

NAME :CB r'hnge :CERossi QY  :  :

DATE :t /1 /91 : / /91  :  :

OFFICIAL RECORD COPY

Document Name: STRAT

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has been addressed

Thermal stratification in other systems important to safety 3, "Thermal

1, and 88-08 Supplement

in NRC Bulletins 88-08, 88-08 Supplement and in NRC Information

Stress in Piping Connected to Reactor Coolant Systems,"

"Unexpected Piping

Notices 88-01, "Safety Injection Pipe Failure," and 88-80,

Movement Attributed to Thermal Stratification."

most recent event

Although thermal stratification is not a new problem, thecontinue to surface

demonstrates that mechanisms for thermal stratification

and can pose a threat to the integrity of piping and supports.

response. If

This information notice requires no specific action or written one of the technical

you have any questions about this matter, please contact

contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Angie P. Young, NRR James E. Beall, RI

(301) 492-1167 (412) 643-2000

Andrew J. Kugler, NRR Shou-Nien Hou, NRR

(301) 492-0834 (301) 492-0793 Attachments: Piping Configuration

1. Figure 1. Beaver Valley Unit 1 Main Feedwater System

Inside Containment

2. List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCE

DOEA:OGCB :NRR:EMEB  :'RI

OFC  :*DOEA:EAB  :*SC:DOEA:EAB:`C:D0EA:EAB :Tech Ed

AChaffee  : J31n 91 :AKugler > :SNHou :JBeall

NAME :AYoung:atb :DFischer

/ /91  : / /91  : /29 /91  :

£1/2/91 ~F/?O/91  : / /91 DATE : / /91  :

OFC :C:DOEA:OGCB :D:DOEA

NAME :CBerlinger :CERossi  :

DATE: / /91  : I /91 OFFICIAL RECORD COPY

Document Name: STRAT

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important to safety has been addressed

Thermal stratification in other systems 1, and 88-08 Supplement 3, "Thermal

in NRC Bulletins 88-08, 88-08 Supplement

Coolant Systems," and NRC Information

Stress in Piping Connected to Reactor

Failure," and 88-80, "Unexpected Piping

Notices 88-01, "Safety Iniection Pipe

Movement Attributed to Thermal Stratification."

If

specific action or written response.

This information notice requires no the technical

please contact one of

you have any questions about this matter, NRR project manager.

contacts listed below or the appropriate

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Angie P. Young, NRR James E. Beall, RI

Technical Contacts: (412) 643-2000

(301) 492-1167 Andrew J. Kugler, NRR Shou-Nien Hou, NRR

(301) 492-0834 (301) 492-0793 Attachments:

Main Feedwater System Piping Configuration

1. Figure 1. Beaver Valley Unit 1 Inside Containment

Notices

2. List of Recently Issued NRC Information

RDOEA:OGCB

OFC :DOEA:EAB :SC 0 A:EAB :C:DOEA:EAB :Tech Ed --:NRR

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OFC :C:DOEA:OGCB :D:DOEA

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DATE : / /91  : / /91 OFFICIAL RECORD COPY

Document Name: STRAT