Information Notice 1996-37, Inaccurate Reactor Water Level Indication and Inadvertent Draindown During Shutdown

Inaccurate Reactor Water Level Indication and Inadvertent Draindown During Shutdown

ML031060030
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:	06/18/1996
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-96-037, NUDOCS 9606120154
Download: ML031060030 (12)

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 June 18, 1996 NRC INFORMATION NOTICE 96-37: INACCURATE REACTOR WATER LEVEL INDICATION

AND INADVERTENT DRAINDOWN DURING SHUTDOWN

Addressees

All pressurized water reactor facilities holding an operating license or a

construction permit.

Purpose

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

notice to alert addressees to potential operational errors that may result in

the inadvertent loss of reactor coolant system (RCS) inventory during

refueling operations. It is expected that recipients will review this

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 September 13, 1995, Surry Unit 1 was in a shutdown condition, cooled down, and depressurized, preparatory to a refueling outage. A pressurizer power- operated relief valve (PORV) and its block valve had been opened, connecting

the pressurizer to the pressurizer relief tank (PRT) which was pressurized

with nitrogen to 11 psig. The reactor head vent was open to the top of the

reactor water level indicating standpipe through the vent connection to the

PORY relief line (see Figure 1). The reactor coolant loop stop valves had

been closed, isolating the steam generators and reactor coolant pumps from

the reactor vessel and pressurizer. The water level in the reactor and

pressurizer had been lowered to slightly below the level of the reactor

vessel flange (elevation 18 feet) so that the vessel head studs could be

de-tensioned. The pressurizer was empty, and the reactor coolant piping was

full to part way up the surge line. The isolated portion of the "A" reactor

coolant loop was being drained.

To install the cavity seal ring so that the cavity could be flooded up to

permit lifting the reactor head, the reactor head vent was closed and the

ventline spoolpiece was disconnected. After the seal ring was in place, the

spoolpiece was re-connected but the reactor head vent valve was not reopened

(no step in the procedure being used called for opening the valve). This

resulted in loss of function of the only reactor water level indication

available while the reactor vessel head was still installed. [The reactor

vessel level indication system (RVLIS) had been used during the earlier

draindown process, but had been disconnected, as usual, in anticipation of the

removal of the reactor vessel heads.]

PER15ZE /0Tla6?-037 96COcY1

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.I ,

IN 96-37 June 18, 1996 The PRT nitrogen pressure was gradually being reduced. An operator saw the

standpipe indicated level increase as the gas bubble trapped in the reactor

vessel head expanded, forcing water out of the reactor and up the surge line

and standpipe. Unaware of the closed head vent and believing the standpipe

level indication, the operator increased letdown from the reactor coolant

system cold leg piping to maintain the indicated 18-foot level. As the

increased letdown raised the water level in the volume control tank (VCT), the

automatic VCT level control bypassed some of the letdown from the VCT to a

holdup tank. This effectively reduced the inventory in the reactor coolant

system by approximately 4500 gallons over a period of approximately 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

When the PRT pressure was subsequently reduced to atmospheric pressure and the

reactor vessel head studs were de-tensioned, the vessel internals spring

loading lifted the head enough to relieve the reactor internal pressure, which

caused a sudden drop in indicated level in the standpipe. The indicated level

dropped from elevation 18 feet to elevation 13.3 feet. The operator

immediately took action to restore the level to elevation 18 feet.

The capability to maintain decay heat removal was not reduced during this

event because adequate suction head remained on the residual heat removal

(RHR) pumps; the 13.3-foot water level is 1.5 feet above mid-loop and more

than 6 feet above the core. There was never an indication of reduction in RHR

flow during the event. If the gas bubble had continued to expand, the reactor

vessel water level would not have dropped lower than just below the top of the

reactor coolant system hot leg pipe; at that point the gas bubble would vent

through the hot leg pipe into the pressurizer and into the PRT, equalizing

pressure between the PRT and vessel atmosphere. The standpipe indicated level

would then have been correct.

Discussion

Factors contributing to this event involved apparent weaknesses in operational

procedures:

1. The procedure for reconnecting the standpipe did not require re-opening

of the vessel head vent valve.

2. Operability of the water level indication system was not determined

after it had been disabled when the cavity seal ring was to be

installed.

3. The relationship between the reactor vessel head vent and the capability

of the standpipe to indicate water level accurately was apparently not

clear to the control room operators.

4. With the loop stop valves closed, there was no apparent reason why

standpipe level should rise. This relationship apparently was not clear

to the operators.

IN 96-37 June 18, 1996 5. Although tank levels were noted three times a day, inventory balances

were not determined from the data.

Surry and a few other pressurized water reactor (PWR) plants have reactor

coolant loop stop valves. Most PWRs do not. Should a similar event occur at

a plant without these valves, the course of the event would not be

significantly different from that which occurred at Surry. The water in the

steam generator tubes would drain through the reactor coolant piping into the

reactor vessel as the gas pressure in the PRT was reduced, extending the time

required for reactor vessel water level to reach the top of the inside of

the hot leg pipe. An event similar to this Surry event occurred at the

Sequoyah Nuclear Plant, which does not have loop stop valves. The Sequoyah

event was the subject of NRC Tnformation Notice 94-36, "Undetected

Accumulation of Gas in Reactor Coolant System," issued May 24, 1994.

Further information concerning the Surry event may be found in NRC Inspection

Report 50-280/95-20 and 50-281/95-20.

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

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

any of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

-. ian K. Grimes, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Muhammad M. Razzaque, NRR

(301) 415-2882 Internet:mmrl~nrc.gov

Morris Branch, RII

(804) 357-2101 Internet:mxb2@nrc.gov

Robert A. Benedict, NRR

(301) 415-1157 Internet:rablnrc.gov

Attachments:

1. Figure 1. Reactor Vessel Head Vent and Standpipe Diagram

2. List of Recently Issued NRC Information Notices

AWr1 F1\bG OAfc-arT

- l

Attachment 1 IN 96-37 June 18, 1996 Reactor Coolant

Loop Cold Leg

Figure 1. Reactor Vessel Head Vent and Standpipe Diagram

kJ-)

Attachment 2 IN 96-37 June 18, 1996 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

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 of 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

96-33 Erroneous Data From 05/24/96 All material and fuel cycle

Defective Thermocouple licensees that monitor tem- Results in a Fire perature with thermocouples

96-32 Implementation of 10 CFR 06/05/96 All holders of OLs or CPs

50.55a(g)(6)(ii)(A), for nuclear power reactors

"Augmented Examination

of Reactor Vessel"

96-31 Cross-Tied Safety Injec- 05/22/96 All holders of OLs or CPs

tion Accumulators for pressurized water

reactors

96-30 Inaccuracy of Diagnostic 05/21/96 All holders of OLs or CPs

Equipment for Motor- for nuclear power reactors

Operated Butterfly Valves

96-29 Requirements in 10 CFR 05/20/96 All holders of OLs or CPs

Part 21 for Reporting and for nuclear power reactors

Evaluating Software Errors

96-28 Suggested Guidance Relating 05/01/96 All material and fuel cycle

to Development and Imple- licensees

mentation of Corrective

Action

OL - Operating License

CP - Construction Permit

IN 96-37 June 18, 1996 5. Although tank levels were noted three times a day, inventory balances

were not determined from the data.

Surry and a few other pressurized water reactor (PWR) plants have reactor

coolant loop stop valves. Most PWRs do not. Should a similar event occur at

a plant without these valves, the course of the event would not be

significantly different from that which occurred at Surry. The water in the

steam generator tubes would drain through the reactor coolant piping into the

reactor vessel as the gas pressure in the PRT was reduced, extending the time

required for reactor vessel water level to reach the top of the inside of

the hot leg pipe. An event similar to this Surry event occurred at the

Sequoyah Nuclear Plant, which does not have loop stop valves. The Sequoyah

event was the subject of NRC Information Notice 94-36, "Undetected

Accumulation of Gas in Reactor Coolant System," issued May 24, 1994.

Further information concerning the Surry event may be found in NRC Inspection

Report 50-280/95-20 and 50-281/95-20.

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

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

any of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager. mtu r ntb>BrinKCGfmes

Brian K. Grimes, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Muhammad M. Razzaque, NRR

(301) 415-2882 Internet:mmrl@nrc.gov

Morris Branch, RII

(804) 357-2101 Internet:mxb2@nrc.gov

Robert A. Benedict, .NRR

(301) 415-1157 Internet:rablenrc.gov

Attachments:

1. Figure 1. Reactor Vessel Head Vent and Standpipe Diagram

2. List of Recently Issued NRC Information Notices

NOTE: Regional and Project Manager comments have been included.

Tech Editor has reviewed and concurred on 02/20/96

• See previous concurrence

DOCUMENT NAME: 96-37.IN

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OFFICE TECH CONT PECB:DRPM (A M

NAME RABenedict* AEChaffee* B itl- DATE 02 1696 04/26/96 06/ /06 OFFICIAL RECORD COPY

KU

IN 96-xx

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

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

the technical contact 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: Muhammad M. Razzaque, NRR

(301) 415-2882 Internet:mmrlnrc.gov

Morris Branch, RII

(804) 357-2101 Internet:nxb22nrc.gov

Robert A. Benedict

(301) 415-1157 Internet:rabl@nrc.gov

Attachments:

1. Figure 1. Reactor Vessel Head Vent and Standpipe Diagram

2. List of Recently Issued NRC Information Notices

NOTE: Regional and Project Manager comments have been included.

• See previous concurrence

DOCUMENT NAME: G:\RAB1\IN-LEVEL.REV

To receive a copy of thi document. Indicate In the box: 'C - Copy Without enclosures 'E' - Copy with enclosures 'N No copy

OFFICE PECB E TECH ED SRXB E SC:PECB C:PECB

NAME RABenedict/vsb* MMajac* RCJones* EFGoodwin* ALChaffee*

DATE 02/16/96 02/20/96 02/28/96 04/21/96 04/26/96 Acting Dir:DRPM

BKGrimes

06/ /96 06/ /96

_6FFICIAL RECORD COPY

' Y

IN 96-xx

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

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

the technical contact 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: Muhammad M. Razzaque, NRR

(301) 415-2882 Internet:mmrlnrc .gov

Morris Branch, RII

(804) 357-2101 Internet:mxb22nrc.gov

Robert A. Benedict

(301) 415-1157 Internet:rablnrc.gov

Attachments:

1. Figure 1. Reactor Vessel Head Vent and Standpipe Diagram

2. List of Recently Issued NRC Information Notices

NOTE: Regional and Project Manager comments have been included.

• See previous concurrence

DOCUMENT NAME: G:\RAB1\IN-LEVEL.REV

To recelwe copy of WIs document, Idicate hi the box: 'C-

• Copy without enclosures 'E - Copy with enclosures N- - No copy

OFFICE PECB I E TECH ED SRXB E SC:PECB C:PECB

NAME RABenedic 0* MMajac* RCJones* EFGoodwin ALChaffee

DATE 02/16/96 J- r 02/20/96 02/28/96 04 96 04/ 6/96 VS8 Actin Dir:DRPM

BKGrimes

04/ /96 04/ /96 OFFICIAL RECORD COPY

IN 96-xx

March xx, 1996 5. Although tank levels were noted three times a day, inventory balances

were not determined from the data.

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

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Muhammad M. Razzaque, NRR

(301) 415-2882 Robert A. Benedict

(301) 415-1157 Attachments:

1. Figure 1. Reactor Vesse 1 Head Vent and Standpipe Diagram

2. List of Recently Issued NRC Information Notices

NOTE: Regional and Project Manager comments have been included.

• See previous concurrence orp

Aihu 9 w37nSuroo

DOCUMENT NAME: G:\RAB1\IN-LEVEL.REV

To receiw copy of this document, indicate Int box: 'C',= Copy nrithout enclosures 'E - Copy withi nclosures 'U' - No copy

OFFICE PECB I E TECH ED I SRXB I E SC:PECB C:PECBZ

NAME IRABenedict/vsb* MMaJac* RCJones* EFGoodwin* ALChaffee

DATE 02/16/96 02/20/96 02/28/96 03/12/96 03/Az/96 ID: DRPM I I I

DMCrutchfield I

03//9-6 103/ /96 OFFICIAL RECORD COPY

1-1--1/

IN 96-xx

February xx, 1996 5. although tank levels were noted three times a day, there was no

determination of inventory balances from the data.

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

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: Muhammad M. Razzaque, NRR

(301) 415-2882 Attachment: List of Recently Issued NRC Information Notices

P /e A x

DOCUMENT NAME: G:\RABI\IN-LEVEI.. REV

To ffaetva a COnY of Ods document. Idicate in the box: 'C - Copy without enclosures 'E' - Copy with enclosures UN - No copy

OFFICE PECB pe-um TECH ED I SRXB - A- - SC:PECB C:PECB

NAME RABenedict/vsb ' h JRCJonesJ*- i" / IEFGoodwin ALChaffee

DATE 2//96 02/no/96 -02/1, 56 / 02/ /96 02/ /96

- . - I,

D:DRPM I I I

DMCrutchfield

02/ /96 02/ /96 OFFICIAL RECORD COPY

IN 96-xx

March xx, 1996 5. Although operators noted tank levels three times a day, they did not

determine inventory balances from the data.

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

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Muhammad M. Razzaque, NRR

(301) 415-2882 Robert A. Benedict

(301) 415-1157 Attachments:

1. Figure 1. Reactor Vessel Head Vent and Standpipe Diagram

2. List of Recently Issued NRC Information Notices

• See previous concurrence

DOCUMENT NAME: G:\RAB1\IN-LEVEL.REV

To receive a copy of Whidocument, Indicate In the box: 'C'- Copy without enclosures 'E' - Copy with enclosures 'N' - No copy

-

OFFICE PECB I E TECH ED I SRXB I E SC:PECB I C:PECB

NAME RABenedict/vsb* IMMajac* RCJones* EFGoodwin* ALChaffee

DATE 02/16/96 02/20/96 02/28/96 03/12/96 03 /96 R . .,

D:DRPM

DMCrutchfield

I I 1 0

03/ /96 03/ /96 OFFICIAL RECORD COPY

/Z I

IN 96-xx

February xx, 1996 5. Although operators noted tank levels three times a day, they did not

determine inventory balances from the data.

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

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

the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Muhammad M. Razzaque, NRR

(301) 415-2882 Robert A. Benedict

(301) 415-1157 Attachments:

1. Figure 1. Reactor Vessel Head Vent and Standpipe Diagram

2. List of Recently Issued NRC Information Notices

N.

N_

• See previous concurrence

DOCUMENT NAME: G:\RAB1\IN-LEVEL.REV

To reive a copy of th" document, Indicate In e box: 'C'-Covp without enclosures 'E' - Cov with enclosures 'N' w No cony

OFFICE PECB I E TECH ED l SRXB I E SC:PECB C:PECB I

NAME RABenedict/vsb* MMaac* RCJones* EFGoodwin ALChaffee

DATE 02/16/96 02/20/96 02/28/96 I i/96 OR/ /96 ID: DRPM l I

DMCrutchfield _

02/ /96 02/ 196 OFFICIAL RECORD COPY