Information Notice 1996-42, Unexpected Opening of Multiple Safety Relief Valves

Unexpected Opening of Multiple Safety Relief Valves

ML031060129
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:	08/05/1996
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-96-042, NUDOCS 9607300191
Download: ML031060129 (7)

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 August 5, 1996 NRC INFORMATION NOTICE 96-42: UNEXPECTED OPENING OF MULTIPLE SAFETY RELIEF

VALVES

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

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

notice to alert addressees to a recent event in which indication was received

that multiple safety relief valves (SRVs) had opened during steady-state

reactor operation without any apparent initiating cause. 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 June 6, 1996, Grand Gulf Nuclear Station was being operated at about 100-

percent power when alarms sounded and the control room operators noticed that

the reactor vessel water level was decreasing, the suppression pool

temperature was increasing, and six SRVs were open. No maintenance or test

activities related to SRV operation were being performed. Because the

suppression pool temperature was increasing rapidly, operators scrammed the

plant to prevent exceeding the maximum temperature limit of 43 °C [110 OF].

Neither the emergency core cooling system nor the reactor core isolation

cooling system was challenged by this event. However, both the 'A' and 'BW

residual heat removal systems were placed in the suppression pool cooling mode

of operation to reduce the suppression pool temperature. The main steam

isolation valves remained open, and steam continued to go to the main

condenser. There was no appreciable cooldown of the reactor vessel during

this transient until after the reactor was scrammed.

The six open SRVs automatically closed after the scram when reactor pressure

decreased. The six SRVs were open for approximately 2.5 minutes. Reactor

pressure was subsequently controlled with the main turbine bypass valves. The

reactor water level was restored to the normal range through use of the

feedwater control system. The rest of the reactor shutdown was routine, and

there were no further complications.

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IN 96-42 August 5, 1996 Discussion

Grand Gulf uses a BWR-6 reactor having four steam lines, each with either four

or six SRVs. All SRVs have the same design and each has a relief capacity of

approximately 6 percent of the full steam flow. The SRVs have both spring

safety operation and a power-operated (relief) mode. SRV power actuation may

be accomplished either automatically at a predetermined relief set pressure or

manually at any desired pressure. Actuation is achieved by positioning

solenoid-operated valves that either admit compressed air into an operating

cylinder or vent compressed air from the cylinder. Two of the SRVs on each

steam line are also actuated by the automatic depressurization system logic.

Six of the SRVs are provided with a low-low set relief logic that minimizes

the number of valves that reopen following a reactor isolation event. The

low-low set relief logic provides all six SRVs with lower closing setpoints

and two of these valves with lower opening setpoints that are below the normal

operating reactor pressure of 7.1 Megapascals [1025 psig]. These setpoints

override the normal set points following initial opening of the SRVs and act

to hold these valves open longer and prevent simultaneous reopening of

multiple SRVs. This low-low set relief logic seals in when the SRVs receive

an opening signal. The function of this logic is to prevent hydrodynamic

loads during subsequent SRV actuations from exceeding the containment design

basis.

The control logic for the relief mode of operation consists of two divisional

trains (safety groups), with two logic channels per division. Both logic

channels must be satisfied in order to operate the respective divisional

solenoid valves on the SRV air actuators. Logic cards for both channels of

each respective division are located in the same card file. The SRV logic

card files are one of four card files supplied from the 24-Vdc power supply.

The licensee identified a transient in the 24-Vdc power supply circuit of the

Division II SRV logic as the root cause for the lifting of the SRVs. All

20 SRVs can be actuated by either Division I or Division II logic, and the

20 SRVs received an unanticipated 200-millisecond open signal. This open

signal was sufficient to actuate the "seal-in" for the six SRVs that have the

low-low set relief feature. However, the signal duration was too short to

sustain opening of the other 14 SRVs. The SRV logic card file is one of four

card files supplied from the Division II 24-Vdc power supply. Each card file

contains several trip unit cards that have logic circuits for safety-related

components. Licensee personnel found a blown fuse to one of the other circuit

card files and determined that a trip unit card in the card file associated

with the failed fuse had a failed capacitor.

IN 96-42 August 5, 1996 The licensee determined that this event was bounded by the safety analysis, which includes opening of all 20 SRVs. The component loading effects were

determined to be within the piping design capabilities for the SRV transients, as well as for the containment. In addition, the design of the SRV and the

low-low set logic was verified as meeting the single-failure criterion for

initiation of a safety system and that inadvertent system actuations were

analyzed for acceptable safety consequences. However, to prevent future

occurrence of a similar event, the licensee is pursuing the following

corrective actions:

1. Evaluation of design modifications to minimize the vulnerability to a

single failure actuating several SRVs.

2. Evaluation of the consequences of failures in similar logic cards in

other safety systems that are also subject to a similar initiating event

(high-voltage spike) to verify that the design-basis accident analyses

are bounding.

In addition, the licensee plans to revise of the final safety analysis report

description to clarify the application of the single-failure criterion.

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

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

the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager. 1 Brian K. Grimes, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Jerry Carter, NRR

(301)415-1153 Internet:tjc~nrc.gov

Jeff Tedrow, RIV

(601)437-4620

Internet:jet@nrc.gov

S.V. Athavale, NRR

(301)415-2974 Internet:svalnrc.gov

Attachment: List of Recently Issued NRC Information Notices

U

Attachment

IN 96-42 August 5, 1996 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

96-41 Effects of a Decrease in 07/26/96 All holders of OLs or Cps

Feedwater Temperature on for pressurized water

Nuclear Instrumentation reactors

96-40 Deficiencies in Material 07/25/96 All holders of OLs or CPs

Dedication and Procurement for nuclear power reactors

Practices and in Audits of

Vendors

96-09, Damage in Foreign Steam 07/10/96 All holders of OLs or CPs

Supp. 1 Generator Internals for pressurized-water

reactors

96-39 Estimates of Decay Heat 07/05/96 All holders of OLs or CPs

Using ANS 5.1 Decay Heat for nuclear power reactors

Standard May Vary Signi- ficantly

96-38 Results of Steam Generator 06/21/96 All holders of OLs or CPs

Tube Examinations for pressurized water

reactors

96-37 Inaccurate Reactor Water 06/18/96 All pressurized water

Level Indication and Inad- reactor facilities holding

vertent Draindown During an operating license or a

Shutdown construction permit

96-36 Degradation of Cooling 06/12/96 All holders of OLs or CPs

Water Systems Due to Icing for nuclear power reactors

96-35 Failure of Safety Systems 06/11/96 All U.S. Nuclear Regulatory

on Self-Shielded Irradia- Commission irradiator

tors Because nf Inadequate licensees and vendors

Maintenance and Training

96-34 Hydrogen Gas Ignition 05/31/96 All holders of OLs or CPs

during Closure Welding for nuclear power reactors

of a VSC-24 Multi-Assembly

Sealed Basket

OL - Operating License

CP - Construction Permit

IN 96-42 August 5, 1996 The licensee determined that this event was bounded by the safety analysis, which includes opening of all 20 SRVs. The component loading effects were

determined to be within the piping design capabilities for the SRV transients, as well as for the containment. In addition, the design of the SRV and the

low-low set logic was verified as meeting the single-failure criterion for

initiation of a safety system and that inadvertent system actuations were

analyzed for acceptable safety consequences. However, to prevent future

occurrence of a similar event, the licensee is pursuing the following

corrective actions:

1. Evaluation of design modifications to minimize the vulnerability to a

single failure actuating several SRVs.

2. Evaluation of the consequences of failures in similar logic cards in

other safety systems that are also subject to a similar initiating event

(high-voltage spike) to verify that the design-basis accident analyses

are bounding.

In addition, the licensee plans to revise of the final safety analysis report

description to clarify the application of the single-failure criterion.

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

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

the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

[Original sed by]

Brian K. Grimes, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Jerry Carter, NRR

(301)415-1153 Email: tjc@nrc.gov

Jeff Tedrow, RIV

(601)437-4620

Email: Jetenrc.gov

S.V. Athavale, NRR

(301)415-2974 Email: sval@nrc.gov Tech Editor reviewed &

concurred on 07/11/96 Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: 96-42.IN *SEE PREVIOUS CONCURRENCES

To receive sac

• this document, hinlcate the box: 'C' - Copy w/o

attmhmntiananaur *'F

-sw@w-- _-

Cnnv urlcff.hmnntl

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OFFICE TECH CONTS l PECB:DRPM I (A)D:WP" I lI

NAME JCarter* AEChaffee* BK e

JTedrow* l

SVAthavale* _ _ _ __

DATE 07/16/96 07/29/96 k_ /96 _ _

OFFICIAL RECORD'COPY

IN 96-xx

July xx, 1996 The licensee determined that this event was bounded by the safety analysis, which includes opening of all 20 SRVs. The component loading effects were

determined to be within the piping design capabilities for the SRV transients, as well as for the containment. In addition, the design of the SRV and the

low-low set logic was verified as meeting the single-failure criteria for

initiation of a safety system and that inadvertent system actuations were

analyzed for acceptable safety consequences. However, to prevent future

occurrence of a similar event, the licensee is pursuing the following

corrective actions:

1. Evaluation of design modifications to minimize the vulnerability to a

single failure actuating several SRVs.

2. Evaluation of the consequences of failures in similar logic cards in

other safety systems that are also subject to a similar initiating event

(high-voltage spike) to verify that the design-basis accident analyses

are bounding.

In addition, the licensee plans to revise of the final safety analysis report

description to clarify the application of the single-failure criterion.

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

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

the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

Brian K. Grimes, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Jerry Carter, NRR

(301)415-1153 Email: tjc@nrc.gov

Jeff Tedrow, RIV

(601)437-4620

Email: jet@nrc.gov

S.V. Athavale, NRR

(301)4X5-2974 Email: sval@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: P:30587_in.je2 *SEE PREVIOUS CONCURRENCES

To receive a copy of this document, Indicate in the box: "C" = Copy without enclosures "E" = Copy with enclosures "N" = No copy -

OFFICE PECB I ADM:PUB C:HICB C:PECB D:DRPM I

NAME TJCarter* Tech Editor* JWermiel* AEChaffee* BKGrimes

DATE 07/16/96 07/11/96 07/17/96 07/29/96 07/ /96

.OFFI CIAL RECORD 4X x

V.;

IN 96-xx

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

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

the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

Brian K. Grimes, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Jerry Carter, NRR

(301)415-1153 Internet:tjc@nrc.gov

Jeff Tedrow, RIV

(601)437-4620

Internet:jet@nrc.gov

S.V. Athavale, NRR

(301)415-2974 Internet:sval@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: P:30587_in.je2 To receive a copy of this document, Indicate In the box: 'C' = Copy without enclosures BED = Copy with enclosures "ND = No copy

OFFICE PECB ,A-[Z DM:PUB I C:HIC Ald" Ea C - D:DRPM

NAME TJCa1'g:ci' ITech Editor* JWermic'f A ff@

fCh BKGrimes

lDATE 107//1/96 107/11/96 07/17/9 07/ /96 OFFICIAL RECORD