Information Notice 1997-27, Effect of Incorrect Strainer Pressure Drop on Available Net Positive Suction Head

Effect of Incorrect Strainer Pressure Drop on Available Net Positive Suction Head

ML031060005
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:	05/16/1997
From:	Slosson M Office of Nuclear Reactor Regulation
To:
References
IN-97-027, NUDOCS 9705150337
Download: ML031060005 (8)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 May 16, 1997 NRC INFORMATION NOTICE 97-27: EFFECT OF INCORRECT STRAINER PRESSURE

DROP ON AVAILABLE NET POSITIVE SUCTION

HEAD

Addressees

All holders of operating licenses or construction permits for light-water power reactors, except

those licensees who have permanently ceased operations and have certified that fuel has

been permanently removed from the reactor vessel.

Purpose

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

addressees that two licensees of boiling-water reactors (BWR) have recently identified

inaccurate assumptions in licensing-basis calculations for net positive suction head (NPSH).

One of the licensees has decided to immediately shut down the reactor to replace suction

strainers in the emergency core cooling system (ECCS) before the next refueling outage. It

is expected that recipients will review the information for applicability to their facilities and

consider actions, as appropriate, to detect or avoid similar problems. However, suggestions

contained in this information notice are not NRC requirements; therefore, no specific action or

written response is required.

Description of Circumstances

Monticello

On April 15, 1997, Northem States Power, the licensee for the Monticello Nuclear Power

Plant, notified the NRC staff that the NPSH available to the core spray pumps may not meet

the required NPSH under all accident conditions. During a review of the ECCS pump NPSH

requirements, the licensee calculated a new higher head loss, approximately 3.6 meters

(11.7 feet) per 630 Us (10,000 gpm) rather than 0.3 meter (1 foot) per 630 Us (10,000 gpm),

for clean ECCS suction strainers. The specific scenario of concern involved a failure of the

low-pressure coolant-injection loop select logic to select the intact reactor recirculation loop.

As a result, the licensee determined that the core spray pumps may not have adequate

NPSH available during the first 10 minutes following a design-basis loss-of-coolant accident

(LOCA).

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IN 97-27 May 16, 1997 Dresden Units 2 and 3 On December 20, 1996, Commonwealth Edison, the licensee for the Dresden Nuclear Power

Station Units 2 and 3, notified the NRC staff that the ECCS may be susceptible to NPSH

problems since the suction strainer design was based on an incorrect head loss value. While

conducting a plant-specific analysis in support of its response to NRC Bulletin 96-03, the

licensee discovered that the new value for the head loss across clean suction strainers was

1.8 meters (5.8 feet) per 630 Us (10,000 gpm) versus 0.3 meter (1 foot) per 630 Us

(10,000 gpm) as described in the Updated Final Safety Analysis Report. With the calculated

head loss, no credit taken for containment overpressure, and the accident conditions

described above, the licensee determined that the ECCS may fail to operate as intended.

Discussion

During its review of the Monticello operability evaluation, the NRC staff questioned whether

the licensee would be able to reflood the reactor core following a LOCA and prevent

exceeding the 1204 OC (2200 'F) peak cladding temperature limit as required by 10 CFR

50.46. Monticello has large quantities of fibrous insulation in its drywell. The Monticello

ECCS suction strainers have a very small surface area and very high approach velocities.

Even a small quantity of insulation reaching the suction strainers, which are located in the

torus, can cause sufficient head losses across the strainer to cause a loss of NPSH. This

scenario is outside the original licensing basis of the plant, but it could occur, given the

current knowledge available.

On May 9, 1997, the licensee for Monticello decided to shut down the reactor and replace the

ECCS suction strainers. The existing strainer on each of the four suction lines is a truncated

cone design about 43 cm (17 inches) in diameter and 25 cm (10 inches) long. Each strainer

will be replaced with two larger strainers, each of which is about 102 cm (40 inches) in

diameter and 213 cm (84 inches) long. The plant will remain shut down until the strainers

can be procured and installed, currently estimated to be 3 to 4 months.

The Dresden units have large quantities of reflective metallic insulation (RMI) in their drywell.

The Dresden Units 2 and 3 strainers are also very small with very high approach velocities.

However, the head loss associated with debris beds composed mostly of RMI is typically less

severe than head loss associated with debris beds composed of fibrous materials. The

existing strainers are being replaced with larger strainers at Dresden Unit 3 during the current

refueling outage and the licensee plans to replace them at Unit 2 during the next outage. As

an interim corrective action the licensee submitted on January 13, 1997, an emergency

technical specification amendment requesting that the staff evaluate an Unreviewed Safety

Question (USQ) associated with the operation of Dresden Units 2 and 3 with the existing

strainers. The licensee's submittal sought staff approval of operation of both units with the

increased head loss across the clean ECCS strainers; revised Technical Specifications (TS)

values for a lower allowable water temperature in the suppression chamber and the ultimate

heat sink; and a revised TS bases that states credit was taken for 13.8 kilopascals (2 psig) of

containment pressure (this compensates for a slight increase in the amount of NPSH

deficiency during the first 10 minutes following a LOCA). The NRC staff issued the

amendments on January 28, 1997.

11_ ti,/

IN 97-27 May 16, 1997 The staff notes that continued operation by BWR licensees during the development of the

resolution of the BWR ECCS strainer clogging issue is based on the premise that licensees

will be able to reflood the reactor core immediately following a design-basis LOCA. In

response to NRC Bulletin 93-02, Supplement 1, BWR licensees implemented interim

measures to ensure that they could mitigate a design-basis LOCA should the ECCS strainers

clog. The acceptability of the licensees' interim measures depended upon (1) adequate time

for operators to respond to clogged strainers to align alternate water sources (both safety- related and nonsafety-related sources), (2) emergency operating procedures (EOPs) which

provide adequate guidance on mitigating a strainer clogging event, (3) operator training to

mitigate a strainer clogging event, (4) recent cleaning of suppression pools, and (5) the

removal of loose and temporary fibrous materials stored in the containment.

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 Office of Nuclear Reactor Regulation (NRR) project manager.

/`

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Elliott, NRR

301-415-1397 E-mail: rbe@nrc.gov

Kerri Kavanagh, NRR

301-415-3743 E-mail: kak~nrc.gov

Attachment: List of Recently Issued NRC Information Notices

V3 7i1

i T I>

Attachment

IN 97-27 May 16,'1997 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

97-26 Degradation in Small- 05/19/97 All holders of OLs or CPs

Radius U-Bend Regions for pressurized-water

of Steam Generator Tubes reactors

87-10, Potential for Water 05/15/97 All holders of OLs or CPs

Sup. 1 Hammer During Restart of for boiling-water reactors

Residual Heat Removal

Pumps

97-25 Dynamic Range Uncertain- 05/09/97 All holders of OLs or CPs

ties in the Reactor Vessel for Westinghouse pressurized- Level Instrumentation water reactors

97-24 Failure of Packing Nuts 05/08/97 All U.S. Nuclear Regulatory

on One-Inch Uranium Commission licensees and

Hexafluoride Cylinder certificatees authorized

Valves to handle uranium hexa- fluoride in 30- and 48-inch

diameter cylinders

97-23 Evaluation and Reporting 05/07/97 All fuel cycle conversion, of Fires and Unplanned enrichment, and fabrication

Chemical Reactor Events facilities

at Fuel Cycle Facilities

97-22 Failure of Welded-Steel 04/25/97 All holders of OLs or

Moment-Resisting Frames CPs for nuclear power

During the Northridge reactors

Earthquake

97-21 Availability of Alternate 04/18/97 All holders of OLs

AC Power Source Designed for nuclear power

for Station Blackout Event reactors

OL = Operating License

CP = Construction Permit

IN 97-27 May 16, 1997 The staff notes that continued operation by BWR licensees during the development of the

resolution of the BWR ECCS strainer clogging issue is based on the premise that licensees

will be able to reflood the reactor core immediately following a design-basis LOCA. In

response to NRC Bulletin 93-02, Supplement 1, BWR licensees implemented interim

measures to ensure that they could mitigate a design-basis LOCA should the ECCS strainers

clog. The acceptability of the licensees' interim measures depended upon (1) adequate time

for operators to respond to clogged strainers to align alternate water sources (both safety- related and nonsafety-related sources), (2) emergency operating procedures (EOPs) which

provide adequate guidance on mitigating a strainer dogging event, (3) operator training to

mitigate a strainer clogging event, (4) recent cdeaning of suppression pools, and (5) the

removal of loose and temporary fibrous materials stored in the containment.

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 Office of Nuclear Reactor Regulation (NRR) project manager.

original signed by S.H. Weiss for

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Elliott, NRR

301-415-1397 E-mail: rbeenrc.gov

Kerri Kavanagh, NRR

301-415-3743 E-mail: kak@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Tech Editor reviewed and concurred on 05/14197

• SEE PREVIOUS CONCURRENCE

DOCUMENT NAME: G:\TJC\MONTICEL.IN1

_ with enclosures

To recelve a copy of this document, Indicate In the box: AC" a Copy without enclosures "E" Copy N No copy

OFFICE TECH

CONTACT

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NAME JCarter 5/14/97 AChaffee MSlosspq

RElliott 5/14/97

.__ KKavanagh 5/14/97 _ {V u__

DATE 05/14/97 05/15/97 05/_5 l97 OFFICIAL RECORD COPY

-Y

IN 97-xx

May xx, 1997 measures to ensure that they could mitigate a design-basis LOCA should the ECCS strainers

clog. The acceptability of the licensees' interim measures depended upon (1) adequate time

for-operators to respond to clogged strainers to align alternate water sources (both safety- related and nonsafety-related sources), (2) emergency operating procedures (EOPs) which

provide adequate guidance on mitigating a strainer clogging event, (3) operator training to

mitigate a strainer clogging event, (4) recent cleaning of suppression pools, and (5) the

removal of loose and temporary fibrous materials stored in the containment.

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 Office of Nuclear Reactor Regulation (NRR) project manager.

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Elliott, NRR

301-415-1397 E-mail: rbe@nrc.gov

Kerri Kavanagh, NRR

301-415-3743 E-mail: kak@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCE

DOCUMENT NAME: G:%TJCUWONTICEL.lN1 To receive a copy of hius document indicate In the box: "C"a Copy without enclosures E- Copy with enclosures "N - No copy

OFFICE TECHC:SCSB* C:SRXB* C:PECB D:(A)DRPM

CONTACT

S* l

NAME JCarter 5/14/97 CBerlinger JLyons AChaffee MS1o

RElliott 5/14/97 KKavanagh 5/14/97 ___I

JDATE 05/14/97 05/14/97 05/14/97 05/1(197 1051y197

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IN 97-xx

May xx, 1997 clog. The acceptability of the licensees' interim measures depended upon (1) adequate time

for operators to respond to clogged strainers to align alternate water sources (both safety- related and non-safety-related sources), (2) emergency operating procedures (EOPs) which

provide adequate guidance on mitigating a strainer clogging event, (3) operator training to

mitigate a strainer clogging event, (4) recent cleaning of suppression pools, and (5) the

removal of loose and temporary fibrous materials stored in the containment.

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 Office of Nuclear Reactor Regulation (NRR) project manager.

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Robert Elliott, NRR Kerri Kavanagh, NRR

301-415-1397 301-415-3743 E-mail: rbe@nrc.gov E-mail: kak@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCE

DOCUMENT NAME: G:ITJCWMONTICEL.lN1 Tn rmehro a etmv of this docwnent. Indicate In the box: wC" wCopy without enclosures "EF U Copy with enclosures "N"w No copy

OFFICE ITECH C: I C:ID:(A)

IC:PECB SRXB* DRPM

CONTACT

S* I l I lIl

NAME JCarter 5/14/97 CBerlinger JLyons AChaffee MSlosson

RElliott 5/14/97 KKavanagh 5/14/97 .-

DATE 05/14/97 05/14/97 05/14/97 05/ /97 05/ /97 OFFICIAL RECORD COPY IC%/

IN 97-xx

May xx, 1997 This information notice requires no specific action or written response. If you h any

questions about the information in this notice, please contact one of the tech contacts

Ical

listed below or the appropriate Office of Nuclear Reactor Regulation (NR project manager.

Marylee M. Slosson cting Director

Division of React Program Management

Office of NueI Reactor Regulation

Technical contacts: Robert Elliott, NRR K Kavanagh, NRR

301-415-1397 153743 E-mail: rbe@nrc.gov E-mail: kak@nrc.gov

Attachment: List of Recently Issued NRC Inf mation Notices

DOCUMENT NAME: G:ITJC\MONTl L.IN1 To receive a copy of this document, Indicate the box: "C"u Copy without enclosures "E"- Copy wfth enclosures W'm No copy

OFFICE TECH l  :

-SCSB l C: SUB l .C: PECB l D: (A)DRPMl

CONIDCTS I I I I I

NAME Rl /.a9 er Jy i "aAChaffee MSlosson

DATE 05/iy/97 / 05//4/97 M 05/97 105/ /97 05/ /97 EFCIAL RECORD COPY