Information Notice 1996-27, Potential Clogging of High Pressure Safety Injection Throttle Valves During Recirculation

Potential Clogging of High Pressure Safety Injection Throttle Valves During Recirculation

ML031060080
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:	05/01/1996
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-96-027, NUDOCS 9604260077
Download: ML031060080 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 May 1, 1996 NRC INFORMATION NOTICE 96-27: POTENTIAL CLOGGING OF HIGH PRESSURE SAFETY

INJECTION THROTTLE VALVES DURING RECIRCULATION

Addressees

All holders of operating licenses or construction permits for pressurized

water reactors (PWRs).

Purpose

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

notice to alert addressees to potential clogging of high pressure safety

injection (HPSI) throttle valves during the recirculation phase of a design- basis loss-of-coolant accident because of restrictive flowpaths in the valves.

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 are not

NRC requirements; therefore, no specific action or written response is

required.

Description of Circumstances

On February 20, 1996, Northeast Utilities (the licensee) shut down Millstone

Unit 2 because of the discovery of a potential common-mode failure mechanism

affecting the HPSI system.

During a review of an Institute of Nuclear Power Operations (INPO) Operational

Experience report concerning potential clogging of emergency core cooling

system (ECCS) throttle valves at the Diablo Canyon Nuclear Power Plant, the

licensee determined that eight throttle valves in the HPSI injection lines in

Unit 2 were susceptible to the failure mechanism identified in the INPO

report. The failure mechanism described in the INPO report was the potential

for clogging of ECCS throttle valves because of entrained debris that could

pass through the containment sump strainers but not be able to pass through

the throttle valves. The licensee based its susceptibility determination on.

the fact that the openings in the containment sump strainers were 0.47 cm

[0.187 inch] and the minimum dimension within the valve flow-path was 0.32 cm

[0.125 inch]. The throttle valves cannot be remotely actuated and are

inaccessible during a design-basis accident.

Discussion

Because the containment sump strainer openings are 0.47 cm [0.187 inch] and

the most restrictive dimension through which flow must pass within the n

throttle valve is 0.32 cm [0.125 inch], the potential exists for particles 11C/

960426007J7Xjo O

DQ I% b/

IN 96-27 May 1, 1996 of sizes between these dimensions to pass through the containment sump

strainers, clog the throttle valves, and cause a partial or complete loss of

post-accident HPSI flow during the recirculation phase of an accident.

At Millstone Unit 2, the normal lineup for the recirculation phase is such

that all recirculation flow passes through the HPSI system. The licensee has

adopted this arrangement because of potential structural and vibrational

loading of the LPSI system during recirculation operation.

The licensee is evaluating this condition for a more thorough determination of

operability.

Similar Events

The safety assessment performed by Pacific Gas and Electric for the Diablo

Canyon plant indicated that the LPSI system, which does not have as

restrictive a flowpath, can provide both cold-leg and hot-leg flow during the

recirculation phase of a design-basis accident. Therefore, core cooling would

not be compromised even if no flow were able to pass through the HPSI system.

Also, Pacific Gas and Electric has indicated that, because of the small

difference in size between the containment sump strainers and the minimum

throttle valve dimension, debris that could pass through the sump strainers

that could be larger than the throttle valve minimum dimension would likely be

fragmented as it passed through the LPSI and HPSI pumps, and that high

differential pressure at the valve would likely force the debris through the

opening.

The safety assessment performed by Northeast Utilities for another unit, Millstone Unit 3, indicated that the ECCS pumps in the recirculation flow path

will pulverize any material that passes through the sump screens, preventing

clogging of the throttle valves. Also, the licensee stated that the flow

velocity at the sump strainer will be approximately 0.05 m/sec [0.15 ft/sec]

during a large-break loss-of-coolant accident. The licensee has stated it

expects that at this flow velocity debris would settle out and not be

transported through the sump strainers. In addition, the licensee stated that

even if two of the eight throttle valves become clogged, the system would

still perform its safety function of providing long-term cooling to the

reactor core.

On the basis of its review of the information provided by the licensee of

Millstone Unit 3 and as discussed above, the NRC staff concluded that fragile

debris entering the sump screens is likely to be fragmented by the charging

pumps and the HPSI pumps so that there is reasonable assurance that this

debris is unlikely to clog the throttle valves at Millstone Unit 3. As this

conclusion is based on specific design features at Millstone Unit 3, it may

not be applicable to other plants.

~.I

IN 96-27 May 1, 1996 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.

Brian K. Grimes, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Eric J. Benner, NRR

(301) 415-1171 Internet:ejblnrc.gov

Chu-Yu Liang, NRR

(301) 415-2878 Internet:cyl@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Attachment

IN 96-27 May 1, 1996 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

96-26 Recent Problems with Over- 04/30/96 All holders of OLs or CPs

head Cranes for nuclear power reactors

96-25 Transversing In-Core Probe 04/30/96 All holders of OLs or CPs

Overwithdrawn at LaSalle for nuclear power reactors

County Station, Unit 1

96-24 Preconditioning of Molded- 04/25/96 All holders of OLs or CPs

Case Circuit Breakers for nuclear power reactors

Before Surveillance Testing

96-23 Fires in Emergency Diesel 04/22/96 All holders of OLs or CPs

Generator Exciters During for nuclear power reactors

Operation Following Unde- tected Fuse Blowing

96-22 Improper Equipment Set- 04/11/96 All holders of OLs or CPs

tings Due to the Use of for nuclear power reactors

Nontemperature-Compensated

Test Equipment

96-21 Safety Concerns Related 04/10/96 All U.S. NRC Medical to the

to the Design of the Door Licensees authorized to use

Interlock Circuit on brachytherapy sources in

Nucletron High-Dose Rate high- and pulsed-dose-rate

and Pulsed Dose Rate remote afterloaders

Remote Afterloading

Brachytherapy Devices

96-20 Demonstration of Associ- 04/04/96 All industrial radiography

ated Equipment Compliance licensees and radiography

with 10 CFR 34.20 equipment manufacturers

96-19 Failure of Tone Alert 04/02/96 All holders of OLs or CPs

Radios to Activate When for nuclear power reactors

Receiving a Shortened

Activation Signal

OL = Operating License

CP = Construction Permit

• AIN 96-27 May 1, 1996 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.

nbacgied by Brtan K.GNmes

Brian K. Grimes, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Eric J. Benner, NRR

(301) 415-1171 Internet:ejbl@nrc.gov

Chu-Yu Liang, NRR

(301) 415-2878 Internet:cyl@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: 96-27.IN

Tech editor reviewed and concurred on 4/17/96 No comments by Region per e-mail with NBlumberg on 4/11/96

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• SEE PREVIOUS CONCURRENCE

• • Concurrence per phonecon with EBenner

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OFFICE ITECH CONTS I PECB:PDRM I - R IlII

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DATE 03/12/96 04/18/96* 04 /96

04/03/96

______ COPY

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OFFICIAL RECORD COPY

K> IN 96-XX

April xx, 1996 This information notice requires no specific action or written response.

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

one of the technical contacts listed below or the appropriate OfficHof

Nuclear Reactor Regulation (NRR) project manager.

Dennis M. Crutchfie d, Director

Division of React Program Management

Office of Nucle Reactor Regulation

Technical contacts: Eric J. Benner, NRR

(301) 415-1171 Internet: ejblnrc.gov

Chu-Yu Liang, NRR

(301) 415-2878 Internet:cyl nrc. v

Attachment:

1. List of Recently Issued NRC In rmation Notices

DOCUMENT NAME: G:\EJB1\MILLSTO .IN

Tech editor reviewed and con rred on 4/17/96 No comments by Region per e all with NBlumberg on 4/11/96

• SEE PREVIOUS CONCURREN

• • Concurrence per phon on with EBenner

To receive a copy of this docunent, fndicat in the box C=Copy W/o attachment/enclosure EnCopy with attachment/erictosure N = No copy

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OFFICE PECB* SRXB I -iAC:SCSB* I BC:EMEB* iBC:SRXB* I e

NAME EBenner:jkd / CBerlinger DWessman RJones

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DATE 3/12/96 4/3 - 3/18/96 4/02/96 4/03/96 OFFICE BC: PECB / I D:DRPM I

NAME AChaj.X / DCrutchfield

DATE /17/961 3/ /96 OICIAL KELUKR LUPY

IN 96-XX

March xx, 1996 This information notice requires no specific action or written response.

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

one of the technical contacts listed below or the appropriate Office

Nuclear Reactor Regulation (NRR) project manager.

Dennis M. Crutchfiel , Director

Division of Reacto Program Management

Office of Nuclea Reactor Regulation

Technical contact: Eric J. Benner, NRR

(301) 415-1171 Internet: ejbl@nrc.gov

Attachment:

1. List of Recently Issued NRC Informati Notices

DOCUMENT NAME: G:\EJB1\MILLSTON.IN

To receive a copy of this document, Indicate In the box C°Wo attachment/enclosure EsCopy with attachment/enclosure M

• No copy

PM1E d

OFFICE PECB I BC:SCSBjjjmjI BC:EMEB -\ I jjBCSC l

NAME EBenner:jkd CBerlJ ,ger DWess R_ _ones_/

DATE 3//1;96 3 /96 &tj 4122/96 _/_f2/9__ _

OFFICE DBC: PECB I L:DRPM I

NAME AChaffee DCrutchfield

DATE 3/ /96 / 3/ /96 OFFICIAL RECORD COPY

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