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

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 92050_ 45 AMA

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 Company, licensee for the North Anna Power Station, reported that the RHR relief valves would not pass the design-basis

flow to relieve an overpressurization

of the RHR system when the latter is aligned to the RCS. The function of these relief valves is important

when the RCS is water solid and therefore

susceptible

to overpressur- ization events, such as from a charging-letdown

flow mismatch or a temperature

change.The licensee made this report after conducting

an engineering

evaluation

to respond to a notification

by the nuclear steam supply vendor, the Westinghouse

Electric Corporation.

In February 1990, Westinghouse

reviewed the RHR relief valve design basis for the Westinghouse

Owners Group and recommended

that its customers

review the following

three items: The adequacy of the RHR relief valves for protecting

against cold overpressure

events Discharge

capability

of relief valves for probable back pressures Design basis commitments

for valve specifications, commitments

in the final safety analysis report, and technical

specifications

The NRC has issued several information

notices to discuss certain operational

events regarding

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

Discharge

of Reactor Coolant," the staff. discussed

an event during which about 68,000 gallons of reactor water was discharged

outside the containment.

The staff has also analyzed operational

experience

and documented

its findings in augmented inspection

team (AIT) reports. On October 23, 1990, the staff issued AIT Report 50-456/90-020

on an event at Braidwood

that resulted in primary water leakage outside the containment

and in the contamination

of three personnel, one of whom received a second degree burn. Table 3 is a selected list of information

notices and AIT reports that the staff has issued on ISLOCAs and related events.Discussion

Although no ISLOCA has caused core damage, accumulated

operational

experience, both in the United States and abroad, indicates

that ISLOCA-like

events have occurred at a rate higher than expected.

In conducting

this study, the staff defined an ISLOCA-like

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

opening of the pressure isolation valves (PIYs) between the RCS and lower pressure systems. An ISLOCA precursor may become an ISLOCA if it occurs during different

plant conditions, or if some of the failures occur together.The NRC staff conducted

root cause analyses of ISLOCA precursors, extensive plant inspections, and detailed analyses of a sample of PWRs. These analyses

IN 92-36 May 7, 1992 included thermal-hydraulic

analyses, fragility

analyses to determine

the likely sizes and locations

of a break, and human reliability

analyses.

The staff used the results of these analyses in PRAs to gain insights about the significant

contributors

to ISLOCA risk.The staff directed the studies described

in this information

notice towards finding vulnerabilities

of PWR plants to ISLOCAs, since the primary pressures present in PWRs are greater than those found in boiling water reactors (BWRs), while the design pressures

of low pressure systems are about the same in both PWRs and BWRs. However, BWR licensees

also may find this information

to be relevant to their plants.Upon conducting

these studies, the staff made the following

observations

on the ISLOCA risk at nuclear power plants: 1. The estimated

core damage frequency

caused by ISLOCAs could be greater than was estimated

in PRAs for some plants.The ISLOCA risk depends on both the accident initiators

and the capabili-ties for recovery.

These factors vary from plant to plant. The main contributors

to ISLOCA initiation

and/or recovery include (a) human errors and (b) the effects of the accident-caused

harsh environment

on plant equipment

and recovery activities.

Both factors have significant

uncer-tainties.

Existing PRAs have provided little or no treatment

of these factors. Plants that are particularly

vulnerable

to either of these two factors could have a higher ISLOCA risk than indicated

by existing PRAs.2. Most plants lack contingency

plans to provide backup water supplies that can be transferred

readily to provide long-term

core cooling after an ISLOCA.By examining

a plant's emergency

procedures, a licensee can find insights for improving

the plant's features to address the concerns for both ISLOCAs and other accidents.

3. The root cause analyses of operational

events indicate that ISLOCA precur-sors most likely would be initiated

by human errors, notably during testing and maintenance

or because of procedural

deficiencies.

This may be attributed

to the general lack of awareness

of the possibility

or consequences

of an ISLOCA.Licensees

may significantly

reduce the probability

of ISLOCA precursors

by improving

the ability of operators

and maintenance

personnel

to recog-nize ISLOCAs, mechanisms

that can cause them, actions to prevent them, and methods to manage them if they occur.4. Most observed ISLOCA precursors

have low public risk consequences.

However, an ISLOCA precursor

can require a shutdown or extension

of a shutdown, require radioactivity

cleanup operations, and cause personnel

injury.

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.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 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

Attachment

1 IN 92-36 May 7, 1992 Table 1. Observed Plant Vulnerabilities

to ISLOCA Precursors (Obtained

from root cause analyses of ISLOCA precursors

and plant inspections)

1. Lack of awareness

of the nature or consequences

of ISLOCAs 2. Inadequate

emergency

procedures

for ISLOCA outside containment, especially

for non-power

operational

modes 3. Poor or incorrect

valve labels 4. Different

nomenclature

used for the same equipment

in the same plant 5. Poor coordination

between concurrently

run tests 6. Miscommunications

between the control room operators

and auxiliary

opera-tors ("get the valve" is meant as "crack open then close," but understood

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

11. Tendency to commit personnel

to extensive

overtime work, especially

during shutdown and startup operations, thus increasing

the fatigue level and the likelihood

of errors

Attachment

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

from ISLOCA PRAs)1. The staff's studies suggest that the core damage frequency

caused by an ISLOCA could be substantially

greater than previous PRA estimates

for some plants. This is primarily

caused by the effects of operator errors and harsh environments

caused by the accident.

Valve alignment

errors during transition

between operating

modes can be particularly

important.

2. Equipment

qualified

for a harsh environment

is likely to survive the adverse ISLOCA temperature

and humidity, but not the possible submersion

caused by flooding.3. Multiple system failures may result from the ISLOCA harsh environment

or flooding, depending

on the size and location of the break in relation to affected equipment, the separation

of redundant

trains, and the effect of fire sprays on flooding.4. ISLOCA recovery is limited by harsh environments, which may damage essen-tial equipment

thus complicating

long-term

cooling, and the rate of loss of reactor water outside the containment.

If the water is not quickly replenished, an ISLOCA may lead to core damage, even after the leak has been isolated.5. Symptom-based

procedures

may lead the operator to realize that an ISLOCA has occurred.

However, unless the emergency

procedures

refer to plant provisions

for conserving

and replenishing

water, the operator may have difficulty

managing the accident.6. Most observed ISLOCA precursors

have low risk consequences, primarily because of the presence of one or more of the following

conditions:

small leak size, redundant

means of detecting

and isolating

a leak, and low power or shutdown conditions.

Attachment

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

Identification

IN 90-64 IN 90-05 IN 89-73 Title or Subject Potential

for Common-Mode

Failure of HPSI Pumps or Release of Reactor Coolant Outside Containment

During a LOCA Inter-system

Discharge

of Reactor Coolant Potential

Overpressurization

of Low Pressure Systems Date 10/04/90 01/29/90 11/01/89 10/23/90 05/08/89 AIT Report 50-456/90-20

AIT Report 50-293/89-80

An assessment

of the 10/4/90 Braidwood loss of reactor coolant inventory

and personnel

contamination

and injury An assessment

of the 4/12/89 Pilgrim overpressurization

event, which occurred during the conduct of the RCIC logic test Inspection

Report 50-382/90-200

Inspection

Report 50-413,414/90-200

Inspection

Report 50-346/89-201

ISLOCA Program Inspection

plant ISLOCA Program Inspection

plants ISLOCA Program Inspection

Besse plant of the Waterford of the Catawba of the Davis 09/14/90 06/11/90 12/21/89 Audit Report Docket No. 50-213 NUREG/CR-5745 NUREG/CR-5744 NUREG/CR-5604 NUREG/CR-5124 NUREG/CR-5102 Haddam Neck ISLOCA Audit Report: July 24 -August 4, 1989, Enclosure

to Memorandum

from Frank J. Congel, NRC, to Steven A. Varga, NRC*Assessment

for ISLOCA Risks -Draft Methodology

and Application:

Combustion

Engineering

Plant Assessment

for ISLOCA Risks -Draft Methodology

and Application:

Westinghouse

Four-Loop

Ice Condenser

Plant Assessment

for ISLOCA Risks -Draft Methodology

and Application:

Babcock and Wilcox Nuclear Power Station Interfacing

Systems LOCA, Boiling Water Reactors Interfacing

Systems LOCA, Pressurized

Water Reactors 09/20/89 June 91 Feb 91 Feb 91 Feb 89 Feb 89-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 92-34 92-33 92-32 92-31 92-30 Higher Than Predicted

Ero-sion/Corrosion

in Unisol-able Reactor Coolant Pres-sure Boundary Piping Inside Containment

at A Boiling Water Reactor New Exposure Limits for Airborne Uranium and Thorium Increased

Instrument

Response Time When Pressure Dampening Devices are Installed Problems Identified

with Emergency

Ventilation

Systems for Near-Site (Within 10 Miles) Emer-gency Operations

Facili-ties and Technical

Support Centers Electrical

Connection

Problem in Johnson Yokogawa Corporation

YS-80 Programmable

Indi-cating Controllers

Falsification

of Plant Records Spent Fuel Pool Re-activity Calculations

05/06/92 05/06/92 04/30/92 04/29/92 04/27/92 04/23/92 04/22/92 All holders of OLs or CPs for nuclear power reactors.All licensees

whose opera-tions can cause airborne concentrations

of uranium and thorium.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors and all licensed operators and senior operators.

All holders of OLs or CPs for nuclear power reactors.92-21, Supp. 1 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 you have any questions

about the of the technical

contacts listed Reactor Regulation (NRR) project no specific action or written response.

If information

in this notice, please contact one below or the appropriate

Office of Nuclear 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*TechEd 04/09/92 D/DSIR:RES

• WMinners 04/15/92 C/RPSIB:DSIR:RES

• KKniel 04/14/92 RPSIB:DSIR:RES

• GBurdick 04/13/92 C/EIB:DSIR:RES

• RLBaer 04/13/92 OGCB:DOEA:NRR

• CVHodge 04/08/92 SC/RAB:DREP:NRR

• KCampe 04/09/92 C/RAB:DREP:NRR

• WBeckner 04/09/92 D/DREP:NRR

• FCongel 04/09/92 EIB:DSIR:RES

• SDiab 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 you have any questions

about the informat of the technical

contacts listed below or Reactor Regulation (NRR) project manager.fic action or written response.

If ion in this notice, please contact one the appropriate

Office of Nuclear 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: C/OGCB:DOEA:NRR

D/D1 CHBerling~*

fj, CER 04/21/92gq"'

04/RPB:ADM D/D TechEd J7Hh9q W" 04/ q/92 04/OGCB:DOEA:

RR SC/I CVHodge US9 KCai 04/od/92 04/ISLOCA REV 2 DOEA: NRR tossi l g kS 15~/ 92 RAB: REP:NRR imp I9/9 C L SI R:RES 04/A//92 C/RAB:DREP:IER

WBeckner Xyt 04/A /92 R Q DSIR:RES GB k 04//3/92 D/DREP:N FCongel 04/9 /92 C/EIB:D IRRES RLBaerXiF'

04//3/92 EIB:DSIR L>SDiab 04/,3/92/