Information Notice 1992-36, Intersystem LOCA Outside Containment

Intersystem LOCA Outside Containment

ML031200356
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:	05/07/1992
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-92-036, NUDOCS 9205010045
Download: ML031200356 (10)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 May 7, 1992 NRC INFORMATION NOTICE 92-36: INTERSYSTEM LOCA OUTSIDE CONTAINMENT

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 of potential plant vulnerabilities to intersystem loss-of- coolant accidents (ISLOCAs). It is expected that recipients will review

the information for applicability to their facilities and consider actions, as

appropriate. However, suggestions contained in this information notice are not

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

This information notice provides information gathered during a concerted NRC

staff effort to study plant vulnerabilities to ISLOCAs. The staff gathered

this information by performing (a) detailed evaluations of operating events, (b) inspections of a limited sample of pressurized water reactors (PWRs), and

(c) extensive analyses of the sample PWRs. The information may be of use in

recipients' individual plant examination (IPE) programs.

Background

The ISLOCA is a class of accidents in which a break occurs in a system con- nected to the reactor coolant system (RCS), causing a loss of the primary

system inventory. This type of accident can occur when a low pressure system, such as the residual heat removal (RHR) system, is inadvertently exposed to

high RCS pressures beyond its capacity. ISLOCAs of most concern are those

that can discharge the break flow outside the reactor containment building, primarily because they can result in high offsite radiological consequences but

also because the RCS inventory lost cannot be retrieved for long-term core

cooling during the recirculation phase.

In the "Reactor Safety Study," (WASH-1400), published in 1975, and in

NUREG-1150, "Severe Accident Risks: An Assessment for Five U.S. Nuclear Power

Plants," the NRC described the ISLOCA outside containment as an event of low

core damage frequency, but as one of the main contributors to plant risk. In

those studies the NRC referred to the ISLOCA as "Event-V." Most probabilistic

risk assessments (PRAs) have also shown that the ISLOCA is very unlikely.

However, these PRAs typically have modelled only those Event-V sequences that

include only the catastrophic failure of check valves that isolate the RCS from

AMA

92050_ 45

IN 92-36 May 7, 1992 low pressure systems. These PRAs included little consideration of human errors

leading to an ISLOCA. Also, most existing PRAs have given little or no credit

for operator actions to terminate an ISLOCA or to mitigate its radiological

consequences if core melt were to occur.

On January 22, 1992, the Virginia Electric Power

North Anna Power Station, reported that the RHR Company, licensee for the

relief valves would not pass

the design-basis flow to relieve an overpressurization

the latter is aligned to the RCS. The function of the RHR system when

important when the RCS is water solid and thereforeof these relief valves is

ization events, such as from a charging-letdown susceptible to overpressur- flow mismatch or a temperature

change.

The licensee made this report after conducting

respond to a notification by the nuclear steam an engineering evaluation to

supply vendor, the Westinghouse

Electric Corporation. In February 1990, Westinghouse

valve design basis for the Westinghouse Owners reviewed the RHR relief

customers review the following three items: Group and recommended that its

The adequacy of the RHR relief valves for protecting

overpressure events against cold

Discharge capability of relief valves for probable

back pressures

Design basis commitments for valve specifications, final safety analysis report, and technical specificationscommitments in the

The NRC has issued several information notices

to discuss certain operational

events regarding ISLOCAs. In IN 90-05, "Inter-system

Coolant," the staff. discussed an event during Discharge of Reactor

which

reactor water was discharged outside the containment. about 68,000 gallons of

analyzed operational experience and documented The staff has also

inspection team (AIT) reports. On October 23, its findings in augmented

Report 50-456/90-020 on an event at Braidwood 1990, the staff issued AIT

that resulted in primary water

leakage outside the containment and in the contamination

one of whom received a second degree burn. Table of three personnel, information notices and AIT reports that the 3 is a selected list of

related events. staff has issued on ISLOCAs and

Discussion

Although no ISLOCA has caused core damage, accumulated

both in the United States and abroad, indicates operational experience, occurred at a rate higher than expected. In that ISLOCA-like events have

conducting

defined an ISLOCA-like event, or an ISLOCA precursor, this study, the staff

from the failure, degradation, or inadvertent as an event that results

valves (PIYs) between the RCS and lower pressure opening of the pressure isolation

may become an ISLOCA if it occurs during differentsystems. An ISLOCA precursor

of the failures occur together. plant conditions, or if some

The NRC staff conducted root cause analyses of

plant inspections, and detailed analyses of a ISLOCA precursors, extensive

sample of PWRs. These analyses

IN 92-36 May 7, 1992 to determine the likely

included thermal-hydraulic analyses, fragility analysesanalyses. The staff used

sizes and locations of a break, and human reliability about the significant

the results of these analyses in PRAs to gain insights

contributors to ISLOCA risk.

notice towards

The staff directed the studies described in this information

since the primary pressures

finding vulnerabilities of PWR plants to ISLOCAs, water reactors (BWRs),

present in PWRs are greater than those found in boiling

systems are about the same in both

while the design pressures of low pressure this information to be

PWRs and BWRs. However, BWR licensees also may find

relevant to their plants.

following observations on the

Upon conducting these studies, the staff made the

ISLOCA risk at nuclear power plants:

could be greater

1. The estimated core damage frequency caused by ISLOCAs

than was estimated in PRAs for some plants.

and the capabili- The ISLOCA risk depends on both the accident initiatorsto plant. The main

ties for recovery. These factors vary from plant

and/or recovery include (a) human errors

contributors to ISLOCA initiation on plant

and (b) the effects of the accident-caused harsh environment significant uncer- equipment and recovery activities. Both factors have treatment of these

tainties. Existing PRAs have provided little or noto either of these two

factors. Plants that are particularly vulnerable by existing PRAs.

factors could have a higher ISLOCA risk than indicated

water supplies that

2. Most plants lack contingency plans to provide backup cooling after an

can be transferred readily to provide long-term core

ISLOCA.

can find

By examining a plant's emergency procedures, a licensee the concerns for

insights for improving the plant's features to address

both ISLOCAs and other accidents.

indicate that ISLOCA precur-

3. The root cause analyses of operational events errors, notably during

sors most likely would be initiated by human This may

testing and maintenance or because of procedural deficiencies.

of the possibility or

be attributed to the general lack of awareness

consequences of an ISLOCA.

ISLOCA precursors

Licensees may significantly reduce the probability of personnel to recog- by improving the ability of operators and maintenance

to prevent them, and

nize ISLOCAs, mechanisms that can cause them, actions

methods to manage them if they occur.

risk consequences. However,

4. Most observed ISLOCA precursors have low publicextension of a shutdown, an ISLOCA precursor can require a shutdown or

injury.

require radioactivity cleanup operations, and cause personnel

IN 92-36 May 7, 1992 Table 1 presents the staff's observations from root

inspections. Table 2 presents insights gained from cause analyses and plant

the ISLOCA PRAs.

The staff is completing its ISLOCA research program

"Intersystem Loss of Coolant Accidents in Light Waterunder Generic Issue 105, ing this research, the staff may issue further generic Reactors." Upon complet- licensees. correspondence to

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.

es ERossi, Drectr

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: Kazimieras Campe, NRR

(301) 504-1092 Sammy Diab, RES

(301) 492-3914 Gary Burdick, RES

(301) 492-3812 Attachments:

1. Table 1. "Observed Plant Vulnerabilities to

2. Table 2. "ISLOCA Risk Insights" ISLOCA Precursors"

3. Table 3. "A Selected List of ISLOCA Reports

and References"

4. List of Recently Issued NRC Information Notices

Attachment 1 IN 92-36 May 7, 1992 Table 1. Observed Plant Vulnerabilities to ISLOCA Precursors

plant inspections)

(Obtained from root cause analyses of ISLOCA precursors and

1. Lack of awareness of the nature or consequences of ISLOCAs

especially

2. Inadequate emergency procedures for ISLOCA outside containment, for non-power operational modes

3. Poor or incorrect valve labels

plant

4. Different nomenclature used for the same equipment in the same

5. Poor coordination between concurrently run tests

opera-

6. Miscommunications between the control room operators and auxiliary

but understood

tors ("get the valve" is meant as "crack open then close,"

to mean "open")

7. Poor shift turn-over communications

8. Poor post-maintenance testing or operability checks

9. Inadequate application of independent verification

10. Tendency not to check diverse instrument indications

during

11. Tendency to commit personnel to extensive overtime work, especially

level and the

shutdown and startup operations, thus increasing the fatigue

likelihood of errors

Attachment 2 IN 92-36 May 7, 1992 Table 2. ISLOCA Risk Insights

(Obtained from ISLOCA PRAs)

by an

1. The staff's studies suggest that the core damage frequency caused for some

ISLOCA could be substantially greater than previous PRA estimates

and

plants. This is primarily caused by the effects of operator errors during

harsh environments caused by the accident. Valve alignment errors

transition between operating modes can be particularly important.

the

2. Equipment qualified for a harsh environment is likely to survive submersion

adverse ISLOCA temperature and humidity, but not the possible

caused by flooding.

or

3. Multiple system failures may result from the ISLOCA harsh environment to

flooding, depending on the size and location of the break in relation

of

affected equipment, the separation of redundant trains, and the effect

fire sprays on flooding.

essen-

4. ISLOCA recovery is limited by harsh environments, which may damageof loss

tial equipment thus complicating long-term cooling, and the rate

of reactor water outside the containment. If the water is not quickly has

replenished, an ISLOCA may lead to core damage, even after the leak

been isolated.

an ISLOCA

5. Symptom-based procedures may lead the operator to realize that to plant

has occurred. However, unless the emergency procedures refer

water, the operator may have

provisions for conserving and replenishing

difficulty managing the accident.

6. Most observed ISLOCA precursors have low risk consequences, primarily small

because of the presence of one or more of the following conditions:low

leak size, redundant means of detecting and isolating a leak, and

power or shutdown conditions.

Attachment 3 IN 92-36 May 7, 1992 Table 3. A Selected List of ISLOCA Reports and References

Identification Title or Subject Date

Potential for Common-Mode Failure of 10/04/90

IN 90-64 HPSI Pumps or Release of Reactor Coolant

Outside Containment During a LOCA

Inter-system Discharge of Reactor Coolant 01/29/90

IN 90-05 IN 89-73 Potential Overpressurization of Low 11/01/89 Pressure Systems

AIT Report An assessment of the 10/4/90 Braidwood 10/23/90

50-456/90-20 loss of reactor coolant inventory and

personnel contamination and injury

AIT Report An assessment of the 4/12/89 Pilgrim 05/08/89

50-293/89-80 overpressurization event, which occurred

during the conduct of the RCIC logic test

ISLOCA Program Inspection of the Waterford 09/14/90

Inspection

Report plant

50-382/90-200

ISLOCA Program Inspection of the Catawba 06/11/90

Inspection

Report plants

50-413,414/90-200

Inspection ISLOCA Program Inspection of the Davis 12/21/89 Report Besse plant

50-346/89-201 Audit Haddam Neck ISLOCA Audit Report: July 24 - 09/20/89 Report August 4, 1989, Enclosure to Memorandum

Docket No. 50-213 from Frank J. Congel, NRC, to

Steven A. Varga, NRC*

NUREG/CR-5745 Assessment for ISLOCA Risks - June 91 Draft Methodology and Application:

Combustion Engineering Plant

NUREG/CR-5744 Assessment for ISLOCA Risks - Feb 91 Draft Methodology and Application:

Westinghouse Four-Loop Ice Condenser Plant

NUREG/CR-5604 Assessment for ISLOCA Risks - Feb 91 Draft Methodology and Application: Babcock

and Wilcox Nuclear Power Station

NUREG/CR-5124 Interfacing Systems LOCA, Boiling Feb 89 Water Reactors

NUREG/CR-5102 Interfacing Systems LOCA, Pressurized Feb 89 Water Reactors

-A COpy OT this report is available in the NRC Public Document Room,

2120 L Street, N.W., Washington, DC.

Attachment 4 IN 92-36 May 7, 1992 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

92-35 Higher Than Predicted Ero- 05/06/92 All holders of OLs or CPs

sion/Corrosion in Unisol- for nuclear power reactors.

able Reactor Coolant Pres- sure Boundary Piping Inside

Containment at A Boiling

Water Reactor

92-34 New Exposure Limits for 05/06/92 All licensees whose opera- Airborne Uranium and tions can cause airborne

Thorium concentrations of uranium

and thorium.

92-33 Increased Instrument 04/30/92 All holders of OLs or CPs

Response Time When for nuclear power reactors.

Pressure Dampening

Devices are Installed

92-32 Problems Identified with 04/29/92 All holders of OLs or CPs

Emergency Ventilation for nuclear power reactors.

Systems for Near-Site

(Within 10 Miles) Emer- gency Operations Facili- ties and Technical Support

Centers

92-31 Electrical Connection 04/27/92 All holders of OLs or CPs

Problem in Johnson for nuclear power reactors.

Yokogawa Corporation

YS-80 Programmable Indi- cating Controllers

92-30 Falsification of Plant 04/23/92 All holders of OLs or CPs

Records for nuclear power reactors

and all licensed operators

and senior operators.

92-21, Spent Fuel Pool Re- 04/22/92 All holders of OLs or CPs

Supp. 1 activity Calculations for nuclear power reactors.

OL = Operating License

CP = Construction Permit

IN 92-36 May 7, 1992 Table 1 presents the staff's observations from root cause analyses and plant

inspections. Table 2 presents insights gained from the ISLOCA PRAs.

The staff is completing its ISLOCA research program under Generic Issue 105,

"Intersystem Loss of Coolant Accidents in Light Water Reactors." Upon complet- ing this research, the staff may issue further generic correspondence to

licensees.

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

Charles E Rei

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: Kazimieras Campe, NRR

(301) 504-1092 Sammy Diab, RES

(301) 492-3914 Gary Burdick, RES

(301) 492-3812 Attachments:

1. Table 1. "Observed Plant Vulnerabilities to ISLOCA Precursors'

2. Table 2. "ISLOCA Risk Insights"

3. Table 3. "A Selected List of ISLOCA Reports and References"

4. List of Recently Issued NRC Information Notices

Document Name: IN 92-36

• See previous concurrence.

C/OGCB:DOEA:NRR D/DOEA:NRR

• CHBerlinger

04/24/92 RPB:ADM D/DSIR:RES C/RPSIB:DSIR:RES RPSIB:DSIR:RES C/EIB:DSIR:RES

• TechEd *WMinners *KKniel *GBurdick *RLBaer

04/09/92 04/15/92 04/14/92 04/13/92 04/13/92 OGCB:DOEA:NRR SC/RAB:DREP:NRR C/RAB:DREP:NRR D/DREP:NRR EIB:DSIR:RES

• CVHodge *KCampe *WBeckner *FCongel *SDiab

04/08/92 04/09/92 04/09/92 04/09/92 04/13/92

IN 92-XX

April xx, 1992 Table 1 presents the staff's observations from root cause analyses and plant

inspections. Table 2 presents insights gained from the ISLOCA PRAs.

The staff is completing its ISLOCA research program under Generic Issue 105,

"Intersystem Loss of Coolant Accidents in Light Water Reactors." Upon complet- ing this research, the staff may issue further generic correspondence to

licensees.

This information notice requires no speci fic action or written response. If

you have any questions about the informat ion in this notice, please contact one

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

Reactor Regulation (NRR) project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: Kazimieras Campe, NRR

(301) 504-1092 Sammy Diab, RES

(301) 492-3914 Gary Burdick, RES

(301) 492-3812 Attachments:

1. Table 1. "Observed Plant Vulnerabilities to ISLOCA Precursors"

2. Table 2. "ISLOCA Risk Insights"

3. Table 3. "A Partial List of ISLOCA Reports and References"

4. List of Recently Issued NRC Information Notices

Document Name: ISLOCA REV 2 C/OGCB:DOEA:NRR D/D1DOEA: NRR

CHBerling~* fj, CER tossi l

04/21/92gq"' 04/

RPB:ADM D/D g kS CL SI R:RES RQ DSIR:RES C/EIB:D IRRES

TechEd J7Hh9q W" GB k RLBaerXiF'

04/ q/92 04/ 15~/ 92 04/A//92 04//3/92 04//3/92 OGCB:DOEA: RR SC/IRAB: REP:NRR C/RAB:DREP:IER D/DREP:N EIB:DSIR L>

CVHodge US9 KCaiimp WBeckner Xyt FCongel SDiab

04/od/92 04/ I9/9 04/A /92 04/9 /92 04/,3/92/