Information Notice 1997-83, Recent Events Involving Reactor Coolant System Inventory Control During Shutdown

Recent Events Involving Reactor Coolant System Inventory Control During Shutdown

ML031050040
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:	12/05/1997
From:	Roe J Office of Nuclear Reactor Regulation
To:
References
IN-97-083, NUDOCS 9712030278
Download: ML031050040 (13)

I

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 December 5, 1997 NRC INFORMATION NOTICE 97- 83: RECENT EVENTS INVOLVING REACTOR COOLANT

SYSTEM INVENTORY CONTROL DURING

SHUTDOWN

Addressees

All holders of operating licenses for pressurized-water reactors (PWRs), 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 to two events involving inadequate control of reactor coolant system (RCS)

inventory. 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

SEQUOYAH UNIT 1

At approximately 11 p.m. on March 23, 1997, with Sequoyah, Unit 1 in Mode 5 (cold shutdown),

operators initiated a draindown of the unit from solid conditions intending to achieve a

pressurizer level of approximately 25 percent. Operators were using cold-calibrated level

instrumentation to monitor pressurizer level during the evolution, as specified in plant

procedures.

The draindown was interrupted at approximately 1:50 a.m. on March 24, 1997, to perform a

diesel generator test and was resumed at approximately 7 a.m. Throughout most of the

draindown, the cold-calibrated level Instrument provided level indications later found to be

inaccurate, but continued to trend down along with actual pressurizer level. Plant operators did

not recognize that the cold-calibrated instrument was providing erroneous indications and

continued the draindown until the problem was discovered at approximately 7:45 a.m. when a

member of the incoming operations crew recognized that the cold-calibrated Instrument had

stopped trending down and was holding steady at 38 percent level. The draindown was

971 030278 A \ _ _ _ _ _ _ _

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IN 97-83 December 5, 1997 stopped and charging flow was Increased until the pressurizer was refilled to approximately

25 percent at 9:16 a.m. Approximately 3300 gallons of water were required to refill the

pressurizer. During this event, shutdown cooling was not affected and the core remained

covered.

The excessive draindown occurred as a result of erroneous level indications due to gas

accumulating in the reference leg of the cold-calibrated instrument. The gas buildup occurred

as a result of depressurization from approximately 325 psig to approximately 30 psig just before

initiating the draindown. The rapid depressurization caused gas within the RCS water to come

• out of solution and displace approximately 182 inches of water from the instrument reference

leg.

Hot-calibrated level instrumentation was also available to monitor pressurizer level during this

evolution. Normally, from solid conditions to approximately 21 percent pressurizer level, the

cold-calibrated level instrument reads lower than the hot-calibrated level instrument and, therefore, is the more conservative measure of pressurizer level. Both plant procedures and

operator training instruct the operator to monitor the cold-calibrated instrument during

draindown from solid conditions to 25 percent pressurizer level. During this event, however, the

cold-calibrated instrument was reading higher than the hot-calibrated instrument due to the

voided reference leg. Plant operators did not recognize that the relationship between the hot- and cold-level instruments was not correct and continued to rely on the cold-calibrated

instrument as the primary level indicator.

Another reactor coolant system draindown event occurred on Unit I in 1993 when

approximately 10,000 gallons of water were drained from the RCS as a result of inaccurate

level indication caused by drainage of the reference leg of the cold-calibrated level instrument.

In this case, level was lost in the reference leg as a result of leakage past an instrument vent

valve. The corrective actions that were developed as a result of this event included

modifications to plant procedures instructing the operators to utilize various pressurizer level

indications during plant evolutions. However, these modifications were only implemented in the

licensee's procedures for reduced inventory and not in the plant shutdown procedures, which

were in use during the event.

ZION UNIT 2 On March 7, 1997, with Unit 2 in cold shutdown, the licensee identified a gas bubble in the

reactor vessel head. It was discovered when an operator questioned the discrepancy between

the computer trend plots for the volume control tank (VCT) and pressurizer levels. The head

was vented and approximately 6900 gallons of water were required to refill the head. It was

later determined that vessel level had decreased to approximately 2.6 feet below the vessel

flange.

The source of the gas was the nitrogen blanket on the VCT. As nitrogen is water soluble, the

nitrogen gas present in the free space of the VCT tends to dissolve in the VCT water volume

until an equilibrium is established. Because the VCT-temperature was lowver than that of the

RCS, the solubility of nitrogen in the RCS was less than that of the VCT. When water was

IN 97-83 December 5, 1997 transferred from the VCT to the RCS, the water was heated, causing nitrogen gas to come out

of solution and accumulate in the reactor vessel head.

Given the geometry and configuration of the facility, the plant conditions and the operating

practices at that time, the potential existed for a void to have been created in the reactor vessel

that could have impacted decay heat removal. Additionally, the accumulation of gas in the

steam generators could have prevented the preferred alternative method of RCS cooling due to

obstruction of primary natural circulation flow in the steam generators.

The Reactor Vessel Level Indicating System (RVLIS) was available but not in service during

this event. The licensee's procedures did not require RVLIS to be in service and did not direct

the operators to monitor RVLIS during this mode of operation (cold shutdown) nor during a loss- of-shutdown-cooling condition.

A precursor to this event occurred on Unit 1 in September of 1996 when Unit 1 experienced an

unexpected gas accumulation in the reactor vessel head. The licensee initiated a root cause

investigation. However, approval of the investigation and implementation of the corrective

actions were postponed by plant management pending completion of the ongoing Unit 2 refueling outage. Ifthe identified corrective actions had been implemented in a timely manner

on both units, the March 7 event probably would not have occurred. Further, had the licensee

more aggressively reviewed operating experience and applied industry lessons leamed, both

events might have been avoided.

Discussion

These events illustrate the importance of timely review of operating experience and prompt

implementation of corrective actions. In each case, the timely review of previous events and

implementation of corrective actions for those events, including modifications to operating

procedures and operator training (in particular, procedures and training stressing the

importance of monitoring and understanding the relationship between multiple level indicators)

could have prevented these similar loss-of-RCS-inventory events. In addition to monitoring

level indications, routine inventory balances provide another independent method to determine

RCS inventory.

Related Generic Communications

Information Notice (IN) 96-65, "Undetected Accumulation of Gas In Reactor Coolant System

and Inaccurate Reactor Water Level Indication During Shutdown," dated December 11, 1996.

IN 96-37, "Inaccurate Reactor Water Level Indication and Inadvertent Draindown During

Shutdown," dated June 18, 1996.

IN 96-15, "Unexpected Plant Performance During Performance of New Surveillance Tests,"

dated March 8, 1996.

• <2 <-,

IN 97-83 December 5, 1997 IN 95-03, 8Loss of Reactor Coolant Inventory and Potential Loss of Emergency Mitigation

Functions While in a Shutdown Condition," dated January 18, 1995.

Bulletin 93-03, "Resolution of Issues Related to Reactor Vessel Water Level Instrumentation in

BWRs," dated May 28, 1993.

IN 94-36, "Undetected Accumulation of Gas in Reactor Coolant System," dated May 27, 1994.

IN 93-27, "Level Instrumentation Inaccuracies Observed During Normal Plant

Depressurization," dated April 3, 1993.

IN 92-54, "Level Instrumentation Inaccuracies Caused by Rapid Depressurization," dated

July24, 1992.

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.

JA* W. Roe, Acting Director

tision of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb~nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Al

Attachment

IN 97-83 December 5, 1997 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

97-82 Inadvertent Control Room 11/28/97 All holders of OLs for nuclear

Halon Actuation Due to a power reactors

Camera Flash

97-81 Deficiencies in Failure 11/24/97 All holders of OLs for nuclear

Modes and Effects Analyses power reactors except those

for Instrumentation and Control who have ceased operations

Systems and have certified that fuel

has been permanently removed

from the vessel

97-80 Licensee Technical 11/21/97 All holders of OLs for

Specifications nuclear power reactors

Interpretations

97-79 Potential Inconsistency 11/20/97 All holders of OLs for

in the Assessment of pressurized-water reactors

the Radiological Conse- implementing a steam

quences of a Main Steam generator tube voltage- Line Break Associated based repair criteria in

with the Implementation accordance with the

of Steam Generator Tube guidance presented in

Voltage-Based Repair Generic Letter 95-05, Criteria Voltage-Based Repair

Criteria for Westinghouse

Steam Generator Tubes

Affected by Outside

Diameter Stress Corrosion

Cracking," issued August 3,

1995 OL = Operating License

CP = Construction Permit

• * 'I

IN 97-83 December 5, 1997 IN 95-03, tLoss of Reactor Coolant Inventory and Potential Loss of Emergency Mitigation

Functions While in a Shutdown Condition," dated January 18, 1995.

Bulletin 93-03, "Resolution of Issues Related to Reactor Vessel Water Level Instrumentation in

BWRs," dated May 28, 1993.

IN 94-36, "Undetected Accumulation of Gas in Reactor Coolant System," dated May 27, 1994.

IN 93-27, "Level Instrumentation Inaccuracies Observed During Normal Plant

Depressurization," dated April 3, 1993.

IN 92-54, "Level Instrumentation Inaccuracies Caused by Rapid Depressurization," dated

July 24, 1992.

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.

original signed by J.W. Roe

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb~nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Tech Editor has reviewed and concurred on 8/11/97 DOCUMENT NAME: G:\WFB\INVENTOR

• See previous concurrence

To receive a copy of this document, Indicate In the box C=Copy wlo attachmenVenclosure E=Copy with attachment/enclosure N = No copy

OFFICE 7PECB I RlIl Il7 l SRXB Il PECB T(A)C:PECB l

NAME WBurton GCobey* DSeymour* TCollins* RLDennig* SRichards*

DATE 11/ 197

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09/18/97 09/9/97 08/26/97 10/14/97 j 10/14/97 1 (A)D:DRPM I ll

JRoe*

117

10/14/97 OFFICIAL RECORD COPY

\J IN 97- November, 1997 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.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Tech Editor has reviewed and concurred on 8/111/97 DOCUMENT NAME: G:\WFB\INVENTOR

• See previous concurrence

To recehve a conv Of this document. inricte hI the boy C=Canv wdo tta hmantlandnsura E=COnv with attachmantandosure N a NO conv

OFFICE PECB l i I RZ I J C:SRXB I PEC (A)C:PECB l

NAME WBurton V GCobey* DSeymourl TCoIlins* RLDennig* SRichards*

DATE 11$/97 09/18/97 09/9/97 j 08/26/97 j 10/14/97 10/14/97 I

(A)D:DRPM (I 41L4K$ 7_

JRoe* ^59 '

10/114/97 OFFICIAL RECORD COPY

IN 97- Octo xx, 1997 Pa 4 of 4 IN 95-03, "Loss of Reactor Coolant Inventory and Potential Loss of mergency Mitigation

Functions While in a Shutdown Condition,' dated January 18, 19 Bulletin 93-03, "Resolution of Issues Related to Reactor Ve el Water Level Instrumentation

in BWRs," dated May 28, 1993.

IN 94-36, "Undetected Accumulation of Gas in React Coolant System," dated May 27,

1994.

IN 93-27, "Level Instrumentation Inaccuracies served During Normal Plant

Depressurization," dated April 3, 1993.

IN 92-54, "Level Instrumentation Inaccu ies Caused by Rapid Depressurization," dated

July 24, 1992.

This information notice requires no ecfc action or written response. If you have any

questions about the information in is notice, please contact the technical contact listed

below or the appropriate Office Nuclear Reactor Regulation (NRR) project manager.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMET NAME: G:\WFB\INVENTOR

• See p ious concurrence

To receive a copy of is document, Indicate In the box C=Copy wlo attachmentlenclosure E=Copy Wth attachmentendosure N = No copy

OFFICE PEC3l Rilll Rl C:SRXI3 l jC PEB

NAME WBurton* GCobey* DSeymour* TCollins* nig SRichards

DATE 09/8/97 09118/97 09/9/97 08126/97 104197 1Jg/97 (A)D:D,3P.M

JRoerOFFCIA R DC PY

101$L97 OFFICIAL RECORD COPY

\K> \KJ

IN 97-76 October 22, 1997 IN 95-03, 61oss of Reactor Coolant Inventory and Potential Loss of Emergency Mitigation

Functions While in a Shutdown Condition,' dated January 18, 1995.

Bulletin 93-03, "Resolution of Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs," dated May 28, 1993.

IN 94-36, "Undetected Accumulation of Gas in Reactor Coolant System," dated May 27,

1994.

IN 93-27, "Level Instrumentation Inaccuracies Observed During Normal Plant

Depressurization," dated April 3, 1993.

IN 92-54, "Level Instrumentation Inaccuracies Caused by Rapid Depressurization," dated

July 24, 1992.

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.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Tech Editor has reviewed and concurred on 8/11/97 DOCUMENT NAME: G:\WFBUlNVENTOR

• See previous concurrence

To receive a copy of this document Indicate Inthe box cC-opy wlo attachmentlenclosure E=Copy with attachmentlenclosure N = No copy

OFFICE PECB I Rill I RH I C:SRXB Il PEC' lI (A)C:PECBl

NAME WBurton* GCobey* DSeymour* TCollins* RLDennig* SRichards*

DATE J. 09/8/97 d

1 09118197 109/9/97 08126/97 1 0/14197 10/1 497 m-

(A)D:DRPM Il

JRoe

101 /97 l l

OFFICIAL RECORD COPY

v 4 S j

v- IN 97-XX

September xx, 1997 IN 94-36, "Undetected Accumulation of Gas in Reactor Coolant System," dated May 27,

1994.

IN 93-27, "Level Instrumentation Inaccuracies Observed During Normal Plant

Depressurization," dated April 3, 1993.

IN 92-54, "Level Instrumentation Inaccuracies Caused by Rapid Depressurization," dated

July 24, 1992.

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.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb@nrc.gov

Attachments:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\WFB\INVENTOR

To receive a copy of this document, Indicate In the box C=Copy wlo attadimentlendosure E=Copy with attachment/endosure N = No copy

OFFICE PECB l l Il R l C:SRXB I PEC l (A)C:PECB I j

NAME j WBurtond GCobey DSeymour TCollins* TKoshy EGoodwin

-

DATE l 091397 T09197 I 09lq/97 l 08126/97 109/ /97 l 09/ /97 l

(A)D:DRPMI

JRoe

09/ /97 OFFICIAL RECORD COPY

IN 97-XX

October xx, 1997 Bulletin 93-03, "Resolution of Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs," dated May 28, 1993.

IN 94-36, "Undetected Accumulation of Gas in Reactor Coolant System," dated May 27,

1994.

IN 93-27, "Level Instrumentation Inaccuracies Observed During Normal Plant

Depressurization," dated April 3, 1993.

IN 92-54, "Level Instrumentation Inaccuracies Caused by Rapid Depressurization," dated

July 24, 1992.

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.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb@nrc.gov

Attachments:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\WFBUlNVENTOR

To receive a copy of this document, Indicate In the box C=Copy wlo attachment/enclosure E=Copy with attachmentlenclosure N = No copy

OFFICE PECB l l Rill I Rh C:SRXB I PECB l (A)C:PECB I

NAME WBurton* GCobey* DSeymour* l TCollins* EGoodwin l SRichards

DATE l 09/8/97 109118/97 [0919/97 1 08126197 110/ /97 l 101 /97 (A)D:DRPMI

JRoe

101 /97 OFFICIAL RECORD COPY

IN 97-XX

August xx, 1997 IN 92-54, "Level Instrumentation Inaccuracies Caused by Rapid Depressurization," dated

July 24, 1992.

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.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb@nrc.gov

Attachments:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\WFBMWNVENTOR

To receive a copy of this document, indicate in the box C=Copy wlo attachment/endosure E=Copy with attachmentlenclosure N = No copy

I OFFICE PECB I SRXB I (A)C:PECB I (A)D:DRPM IL

NAME WBurton rCC10 64 Rqe*fti- awyg JRoe

lDATE 8197 I J/97 _ fg/ /97

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IN 97-XX

August xx, 1997 IN 92-54, "Level Instrumentation Inaccuracies Caused by Rapid Depressunzation," dated

July 24, 1992.

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.

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contact: William F. Burton, NRR

301-415-2853 E-mail: wfb@nrc.gov

Attachments:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:AWFBlNVENTOR

To receive a copy of this document, Indicate In the box C=Copy wlo ttadimentlendosure E=Copy with attachment/endosure N = No copy

E OFFICE

NAME

PECB

WBurton

I SRXB

JCA_

C*k

I C:PECB

AChaffee

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l DATE j 8M97 O F8CI/97 1 81 /97 81197 1 OFFICIAL RECOJRD COPY