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{{#Wiki_filter:UNITED STATES | {{#Wiki_filter:UNITED STATES | ||
COMMISSION | NUCLEAR REGULATORY COMMISSION | ||
OFFICE OF NUCLEAR REACTOR REGULATION | |||
NOTICE 92-36: INTERSYSTEM | WASHINGTON, D.C. 20555 May 7, 1992 NRC INFORMATION NOTICE 92-36: INTERSYSTEM LOCA OUTSIDE CONTAINMENT | ||
==Addressees== | ==Addressees== | ||
All holders of operating | All holders of operating licenses or construction permits for nuclear power | ||
licenses or construction | |||
reactors. | |||
==Purpose== | ==Purpose== | ||
The U.S. Nuclear Regulatory | The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice | ||
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 | |||
to their facilities | 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 | |||
to | 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 | |||
of | 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 | |||
for | 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 | |||
of | 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 | 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 | |||
In | |||
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 | |||
of | testing and maintenance or because of procedural deficiencies. | ||
of the possibility or | |||
the | be attributed to the general lack of awareness | ||
consequences of an ISLOCA. | |||
ISLOCA precursors | |||
to recog- | 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 | |||
of a shutdown, require | |||
injury. | 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 | |||
notice requires no specific action or written response. | 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 | Office of Nuclear Reactor Regulation | ||
Technical | Technical contacts: Kazimieras Campe, NRR | ||
(301) 504-1092 Sammy Diab, RES | |||
(301) 492-3914 Gary Burdick, RES | |||
Plant Vulnerabilities | (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 | |||
Notices | and References" | ||
4. List of Recently Issued NRC Information Notices | |||
Attachment | 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 | |||
to | 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 | |||
the | 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 | |||
of the | |||
Inspection | Inspection | ||
Report | Report plants | ||
plants | |||
50-413,414/90-200 | |||
Inspection ISLOCA Program Inspection of the Davis 12/21/89 Report Besse plant | |||
to Memorandum | 50-346/89-201 Audit Haddam Neck ISLOCA Audit Report: July 24 - 09/20/89 Report August 4, 1989, Enclosure to Memorandum | ||
from Frank J. Congel, NRC, to | Docket No. 50-213 from Frank J. Congel, NRC, to | ||
for ISLOCA Risks -Draft Methodology | Steven A. Varga, NRC* | ||
NUREG/CR-5745 Assessment for ISLOCA Risks - June 91 Draft Methodology and Application: | |||
Combustion Engineering Plant | |||
and Application: | 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 | |||
with | 92-32 Problems Identified with 04/29/92 All holders of OLs or CPs | ||
Ventilation | Emergency Ventilation for nuclear power reactors. | ||
Systems for Near-Site | Systems for Near-Site | ||
Facili-ties and Technical | (Within 10 Miles) Emer- gency Operations Facili- ties and Technical Support | ||
Centers | |||
Connection | 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 | |||
of Plant | 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. | |||
All holders of OLs or CPs | 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 | |||
from root cause analyses and plant | IN 92-36 May 7, 1992 Table 1 presents the staff's observations from root cause analyses and plant | ||
Table 2 presents insights gained from the ISLOCA PRAs. | inspections. Table 2 presents insights gained from the ISLOCA PRAs. | ||
its ISLOCA research program under Generic Issue 105,"Intersystem | 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 | Office of Nuclear Reactor Regulation | ||
Technical | Technical contacts: Kazimieras Campe, NRR | ||
(301) 504-1092 Sammy Diab, RES | |||
(301) 492-3914 Gary Burdick, RES | |||
Plant Vulnerabilities | (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 | |||
C/OGCB:DOEA:NRR | |||
D/DOEA:NRR | |||
*CHBerlinger | *CHBerlinger | ||
04/24/92 RPB:ADM | 04/24/92 RPB:ADM D/DSIR:RES C/RPSIB:DSIR:RES RPSIB:DSIR:RES C/EIB:DSIR:RES | ||
*WMinners | *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 | |||
contacts | |||
(301) 504-1092 Sammy Diab, RES | |||
(301) 492-3914 Gary Burdick, RES | |||
(301) 492-3812 Attachments: | |||
1. Table 1. "Observed | 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> | |||
04/ | CVHodge US9 KCaiimp WBeckner Xyt FCongel SDiab | ||
04/od/92 04/ I9/9 04/A /92 04/9 /92 04/,3/92/}} | |||
04/ | |||
{{Information notice-Nav}} | {{Information notice-Nav}} |
Latest revision as of 03:22, 24 November 2019
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
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 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
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
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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/