ML20055H015
| ML20055H015 | |
| Person / Time | |
|---|---|
| Issue date: | 07/23/1990 |
| From: | Su N NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD) |
| To: | |
| Shared Package | |
| ML20055H014 | List: |
| References | |
| TASK-AE, TASK-E90-07, TASK-E90-7 AEOD-E90-07, AEOD-E90-7, NUDOCS 9007250055 | |
| Download: ML20055H015 (13) | |
Text
_
f
/n c.
c 1
4
~ AEOD ENGINEERING EVALUATION REPORT i
UNIT:.
' Multiple EE REPORT No.: AEOD/E90-07.
DOCKET NO.:
Multiple DATE: July 23,1990 LICENSEE:
Multiple.
EVALUATOR / CONTACT: Nelson T. Su NSSS/AE:
Multiple
SUBJECT:
EFFECT OF INTERNAL FLOODING OF NUCLEAR POWER PLANTS ON SAFETY-EQUIPMENT EVENT DATES:
MULTIPLE l
SUMMARY
This report documents the tc.?;lts of a review of operational events in the past 10 years (1980 to 1989) that resulted in internal flooding in the secondary containment, auxiliary
- building, and turbine building of nuclear power plants. Some of these events caused a sig-nificant loss of safety-related equipment needed for decay heat removal, plant shutdown and
. cooldown and have resulted in precursors to potential severe core damage accidents.
The review indicates that internal flooding often resulted in common mode failure of essential equipment for multiple safety-related systems. In some instances, the extent of damage could have challenged the plant's capability to achieve safe shutdown and cooldown.
Some operational events resulted in unisolable flooding which caused the plants to be flooded to the same water level as that of the source such as a lake or river. Several events involving failure of a single component of a liquid carrying system that was disassembled for testing or maintenance during cold shutdown or a refueling outage caused significant L
internal flooding that disabled other safety-related systems. The review also addresses the potential for internal flooding due to design deficiencies of flood protection.
Results of evaluation of the operational events identify errors by maintenance personnel, y
procedural deficiencies, and inadequate design as the key elements causing internal flooding.
Based upon the findings, AEOD suggests the following:
a.
Re-evaluation of Existing Flood Protection
' Re-evaluate existing flood protection to address the concerns about the potential for unisolable flooding and common mode flooding. The areas of evaluation include:
L adequacy of flood barriers to prevent unisolable flooding and common mode L.
flooding; adequacy of the floor drain system to prevent flooding of one area of the l_
plant from propagating to other areas; and adequacy of flood warning instrumentation to provide the operators an early signal of flooding in th:: plant.
1 9007250055 900723 I
y =
3.:
r t
b.-
Review of Maintenance Procedures and Personnel Trainine Ruview maintenance procedures and personnel training to minimize risk of.
unanalyzed internal flooding events caused by single component failure or personnel error. As indicated earlier, several significant flooding events occurred during cold shutdown or refueling outage. This indicates a need to strengthen maintenance -
planning and administrative controls to minimize the risk of flooding, j
The lessons learned from the operating experiences discussed in this report provide guidance to conduct this evaluation.
1.
INTRODUCTION l
There have been occurrences of internal flooding at nuclear power plants. Such flooding has caused many safety-related systems to be inoperable. Some of these systems are required to maintain core cooling. Because of this potential safety significance, one plant probabilistic risk assessment (Ref.1) has identified internal flooding to be a significant contributor to the risk of core damage (8.8 E 5 per reactor year).
1 Flooding related issues have been evaluated in the past. In 1972, because of an operational i
event at Quad Cities that caused some degradation of safety equipment from flooding, a generic review entitled " Flood of Equipment Important to Safety" was initiated. This review effort, however, was phased out in 1974 and the evaluation was never completed. Other activities include a review of an event at Calvert Cliffs Units 1 and 2 on November 11,1981, regarding the potential flooding of safety equipment compartments as a result of backflow through a floor drain. AEOD issued a report (Ref. 2) that presents the results of the evaluation of the generic implications of the floor drain problem.
Following the AEOD review, Generic Issue 77, " Flooding of Safety Equipment Com-partments by Back-Flow Through Floor Drains," was initiated. The NRC staff concluded that this issue would have a high priority. IE Information Notice 83-44 (Ref. 3) was issued to alert licensees to the potential problems associated with this issue.
Since then, there have no flooding-related issues being actively evaluated by the gaff. And since the safety implications of internal flooding are significant, AEOD initiated the effort to re-evaluate this issue from a broader view point.
This report documents the review of operational events from 1980 to 1989 that involved significant internal flooding. These events caused unisolable flooding and common mode flooding inside the secondary containment and turbine building. Events which would potentially cause flooding due to design deficiencies are also included.~ Operational events which involve flooding in the primary containment are not included in this review.
2
1 4
q?
a.
D
- 2.
OPERATING EXPERIENCE 2.1_
Flooding of Diesel Generator. Ouad Cities Unit 2 On October 23,1980, an equipment operator conducting his rounds discovered that the cooling water pump for the Units 1 and 2 (shared) diesel generator was submerged in water '
y resulting from flooding in the circulating / service water pump house (Ref. 4). This condition rendered the diesel generator inoperable.
This incident was reported in the preliminary notification; however, the information was limited. Searches of various data bases revealed no further related information. The root causes of the flooding and corrective actions, therefore, are unknown at the present.
(
' 2.2 Flooding of Residual Heat Removal Service Water / Emergency Equipment Coolwater (RHRSW/EECW) Pumps. Browns Ferry l
On August 22,-1981,. the "A" residual heat removal (RHR) service water pump room at-
[,
Browns Ferry was flooded. The flooding rendered the A1, A2, and A3 RHRSW/EECW L
pumps inoperable. This also-made the "A" RHR heat exchanger at Units 2 and 3 L
inoperable. The RHRSW/EECW system is common to all units (Ref. 5).
The flooding was caused by an RHRSW pump air vacuum valve that failed to seal. 'Ihe licensee's corrective actions included replacement of damaged equipment and inspection of all flooded components.
The licensee event report provided only the above limited information. However, this information indicates that the failure of a single component (air vent valve failure to seal) caused the inoperability of multiple safety related equipment. It also indicates a common y
mode failure of a safety system shared by all units.
2.3 Flooding in Saltwater Pump Bav. San Onofre Unit 1 4
L On May 13,1982, flooding occurred in the saltwater pump bay at San Onofre Unit 1 (Ref. 6). The saltwater cooling system is the ultimate heat sink for the facility. The reactor was in a cold shutdown condition.
i Removal of the saltwater pump internals during maintenance activities caused the flooding.
Because the floor of the pump bay was below sea level, the seawater inlet gate was open, and the main circulating water pumps were secured, flooding began from the sea into the pump bay. Flooding eventually reached the same level as the sea level at low tide, which resulted in about 4 feet of water in the bay. The licensee replaced the pump internals to stop the flooding.
3 I
)
k s.
j De flooding disabled the entire saltwater cooling system. The root causes and corrective actions were not identified in the licensee's report. However, judging from the_ description 1
in the report, the event was caused by procedural deficiencies. De report also indicated m
that the licensee was unable to isolate the flooding until the pump internals were replaced.
2.4 Flooding of Service Water Bav. Salem Unit 2 On June 23, 1983, during routine shutdown operation, an operator performing routine surveillance discovered a large leak in the No. 2 service water bay. An attempt to isolate the leak failed, and.the water level continued to rise until more than 6 feet of water had accumulated in the bay. All service water pumps were stopped, resulting in the loss of flow to the boron injection, residual heat removal, and dief cenerator systems (Ref. 7). The investigation conducted by the licensee revealed that th.peakage was due to a failed gasket in the joint downstream of a check valve. Corrective actions taken by the licensee included replacement of the connection and design changes to correct related problems with the bay
' sump pumps and alarms.
This event is safety significant because: (1) a single-component failure resulted in the loss of an entire safety system and jeopardized other safety related systems, and (2) the operators were unable to isolate the flooding.
L l
2.5 Flooding of Comoonent Cooling Water Pump Motors. Indian Point Unit 2
(
'On August 13, 1984, Indian Point Unit 2 was at cold shutdown for a refueling and maintenance outage. One of two service water trains was out of service for maintenance and was isolated from the operating train. A service water valve from the inoperable train was removed for a planned inservice inspection test. No leakage was noticed at the time the valve was partially removed (Ref. 8).
Plant personnel later found that service water was rapidly filling the room through the open l
pipe. Floor drainage and a sump pump were unable to accommodate the incoming water.
Ultimately, the pump motors were submerged. The two operating component cooling water pumps tripped on an overcurrent protection signal. The standby pump attempted to start on a low pressure signal but it also tripped on the overcurrent protection signal. The flooding stopped when all service water pumps were shut down.
The flooding was caused by wate-flowing from the operating service water train to the non, operating train through a partiali, open valve and two defective check valves. The flooding resulted in a complete loss of the safety related component cooling water system. It also could have damaged other safety-related components in the auxiliary building.
This event is significant because one common cause disabled an entire safety-related system including a standby pump. It is also significant in that multiple failures (one isolation valve and two check valves) occurred simultaneously.
4
2.6 InternM Flooding of Pump House. IMalle Units 1 and 2 On May 31,1985, LaSalle Unit I was operating at about 85 percent power and Unit 2 was j
in cold shutdown. The IB circulating water (CW) pump tripped. An operator went to the pump house to determine the cause of the pump trip. He discovered that water was flowing j
rapidly from a rubber exp nsionjoint between the IB CW pump discharge'and its discharge j
valve and was beginning to flood the. basement of the pump house. Since the rubber expansion joint was located upstream of the discharge valve, the flooding could not be
. isolated. Flooding finally stopped when the water level in the pump house basement reached the same water lev;1 as that of the lake; that is, the pump house was filled with about 15 feet of water (Ref. 9),
i The flooding of the pump house basement disabled the entire service water system and circulating water pumps for both units. The loss of the service water system raised concerns about the potential loss of the instrument air system, the drywell pneumatic system,' the drywell cooling system, and the turbine lube oil cooling system. The plant operators managed to keep these systems in operation by connecting other sources of cooling water to these systems.
The licensee determined that the primary cause of the event was fatigue failure of the IB circulating pump discharge valve gear operator mounting bolts. As a result, the valve disc rotated rapidly in the reverse-to-normal direction, thus creating a rapid transient hydraulic r
pressure spike, which was sufficient to blow the expansion joint out of its retaining bars.
This occurred while the pump.was running, thus causing rapid flooding of the pump house.
The licensee also determined that the failure was caused by a design deficiency in the gear operator and its associated attachment bolting. To prevent a recurrence, the licensee conducted a test of the valve to determine if any changes to its design were necessary. The licensee also initiated a program to prevent the loss of all circulating water and service water systems resulting from flooding.
This event was identified as a precursor to potential severe core damage accidem with an -
estimated conditional core damage probability of 7.2E-5 (Ref.10).
2.7 Flooding of an Emergency Core Cooling System Pumo Room. Hatch Unit 1 L
On December 21,1985, Hatch Unit 1 was in a refueling mode and all fuel was removed from the reactor vessel. An emergency core cooling system (ECCS) pump room was flooded to a level of about 14 feet. The flooding was caused by water flowing out from an open air-operated maintenance isolation valve on a residual heat removal (RHR) pump suction line (Ref.11).
The isolation valve failed open because of a loss of power to its solenoid valve during a planned loss-of-offsite-power test. Water flowed from the torus through the failed-open 5
- g
. valve and through a disassembled RHR pump suction valve into an ECCS pump room. All equipment including two RHR pumps and one low pressure core spray pump and-
-instrumentation were submerged.
This event was not reported in a licensee event report. Instead, the licensee submitted a special report and indicated that it provided information only. However, this event should be considered as a significant event because it resulted in the disabling of extensive safety-related equipment and instrumentation. This event also reveals that safety related systems are vulnerable not only to single failure but to common mode failure.
2.8 Flooding of the Nuclear Auxiliary Building. Foreign Plant
}
T On February 22,1986, while a foreign pressurized water reactor plant was operating at normal power, the plant operator discovered that the charging pump room was flooded.
The neighboring rooms, turbine hall, and part of the corridor in the auxiliary building were also flooded. It was estimated that 17,000 gallons of radioactive water had accumulated in these areas, s
The flooding was caused by water leaking as a result of a spurious opening of a control valve of the chemical and volume control system (CVCS). The control valve opened because ofloss of power to its solenoid. The operator tried to close the valve, but the valve reopened shortly afterwards. The control valve was finally isolated approximately 30 minutes after the leak first started.
The flooding disabled the CVCS..Since the charging pumps of the CVCS also act as the high-pressure safety injection pumps, the flooding virtually disabled one of the important safety related systems.
To prevent a recurrence, the licensee of the plant took actions to improve the system for L
locking out the charging pump isolation valves. The licensee also conducted an investigation to determine if modifications to the drainage system for the affected rooms were necessary.
L This event is significant because it was caused by a single component failure. It also could have caused a common mode failure of all high-pressure safety injection pumps. If the water level had risen a few inches more, the terminal boxes (not guaranteed to be watertight) of the three charging pumps would have been submerged. The event is also significant because it resulted in the contamination of personnel by radioactive water.
2.9 Flooding of Service Water Bav. Salem Unit 1 i
On December 22,1987, Salem Unit I was shut down in Mode 5 for a refueling outage. The
.No.11 service water header was isolated and tagged for repair work on valves in that i
L header. Two isolation valves and two blind flanges were supposed to isolate the header.
l However, the first 30-inch isolation valve failed because the rubber seat had partially 6
_, 9
- o..
disengaged from the valve body. The indication for the second isolation valve showed that -
it was shut, when in fact it was partially open. In addition, the two blind flanges were-J loosely installed.' As a result, a leak path was created, which allowed water to flood the ser-vice water bay.. The flooding caused a loss of the operating service water pump and endangered other equipment in the turbine building, the Cardox room, and the motor contml center (Ref.12).
The flooding was unisolable because of the failure of all isolation valves. The water level did not recede until a 2,000-gpm sump pump was installed in the service water bay.
The licensee's corrective actions included changes in maintenance procedures and evaluation of the vaive failure.
2.10 Floodine of the Auxiliary Buildine. River Bend Unit 1 On April 19,1989, while River Bend Unit I was operating in Mode 5 (refueling), a freeze plug on a standby service water line in the auxiliary building failed. This caused a release of approximately 15,000 gallons of water that flooded the auxiliary building. The flooding-damaged electrical equipment causing a loss of RHR shutdown cooling (Ref.13).
The licensee contributed the failure of the freeze plug to a deficient maintenance procedure and personnel errors. Corrective actions included review of the maintenance procedure and additional training of operations personnel.
In addition, the licensee conducted an investigation of the floor drain system in the auxiliary building to determine if it was adequate to prevent future flooding.
3.
REVIEW OF POTENTIAL EVENTS Since.1984, plants have reported deficiencies in the design for internal flood protection.
These design deficiencies could lead to. the flooding of safety-related equipment compartments. A brief discussion of these deficiencies follows:
- 3.1 On June 18,1984, the licensee for Davis-Besse Unit 1 discovered that an tmanalyzed situation existed in two auxiliary feedwater pump rooms with regard to the potential l
effects of a break of the non seismic piping located in these rooms. This non-seismic 1
piping is associated with the startup feedwater pump. A break of the non-seismic piping would flood these rooms and disable the auxiliary feedwater systent.
Corrective actions included changes to operational procedures, relocation of the non-I seismic piping, and modification of hardware design (Ref.14).
3.2 -
On January 15, 1985, the licensee for Sequoyah Unit 1 performed a design review and identified a design deficiency in the support of some Class C piping for the diesel generator coolers. The design deficiency would result in failure of essential raw I
L 7
V
j'y.
i.
{
cooling water piping downstream 'of the diesel generator coolers during a seismic event. The failure would cause flooding of the diesel generator. The licensee has modified the pipe support to ensure that it is seismically qualified (Ref.15).
1 3.3 On October 8,1985, the licensee for the Limerick plant conducted a design review in support of a proposed modification. The licensee discovered that both redundant control structure chilled water systems could be lost if the chillers or circulating pumps were flooded. This potential was not considered in the plant's ops. rating or emergency procedures. The flooding could occur from a cooling tower basin break or a circulating water line break.
Corrective actions included installation of necessary engineered barriers to block the entry of water into the structure housmg the chilled water system (Ref.16).
3.4 On March 9,1987, during a review of the Trojan turbine building flooding der.ign L
basis, the licensee found that the flood relieflouver.;in the west wall of the turbine l.
building were not adequately designed to release a sufficient quantity of water to L
prevent flooding of safety-related equipment in the event of a circulating water line L
failure. The affected equipment in the turbine building includes the auxiliary l
feedwater (AFW) pumps and emergency diesel generators (EDGs). Corrective actions consisted of redesigning the louver and raising the flood protection dike to prevent flood water from entering the AFW pump rooms, EDG rooms, and remote shutdown panel room (Ref.17).
3.5 On June 7,1988, the licensee for Virgil C. Summer discovered that a design defect existed that could lead to the creation of a steam / water propagation path that could affect safe shutdown equipment. The path would be the result of a steamline break that released steam / water that would travel through fire doors and floor penetrations leading to the safe shutdown equipment.
Corrective actions' consisted of the L
reinforcement of the doors and the addition of sealing materials to the doors to l
prevent steam / water from entering the safe shutdown equipment (Ref.18).
1 3.6 During an inspection of the residual heat removal service water (RHRSW) pump rooms on June 17, 1988, the licensee for Browns Ferry Unit 7 discovered that L
groundwater was entering the pump room through a subterranean pipe penetration, y
A review of the penetiation drawings revealed that a water seal at the pipe.
penetration had not been provided and the seal at the flocr penetration was
. inadequate. The licensee determined that the lack of an adequr.te water seal was a condition that violated the requirement that the RHRSW pump "ooms be watertight.
y The licensee indicated that a watertight seal was being designed and will be installed on the floor piping penetrations of all RHRSW pump rooms (Ref.19).
3.7 In November 1988, the licensee for Peach Bottom Unit 2 found that several conditions existed that resulted in the plant being outsid: the design basis as de;cribed in the updated Final Safety Analysis Report for ir,ternal flood protection 8
4
. p,... -
of the' emergency l core cooling system compartments.
Equipment penetrations =
through the walls were not sealed, and various spillways connecting the compartments to the torus room were blocked. LConduits were not sealed. In regard to the room
. rain piping inspection ports on the funnel covers were not scaled adequately and d
floor' cleanouts were open.
These conditions would allow flooding between compartments. In addition, the drain piping in these rooms was welded to closed
. funnels. Corrective actions consisted of scaling the penetrations, modifying the drain lines, and resealing the inspection ports and floor cleanouts (Ref. 20).
3.8 On December 9,1988, an operator discovered that a drain line in the Calvert Cliffs Unit 1 service water pump room did not have backflow protection (Ref. 21). This.
protection ensures the watertight integrity of the service water pump room in order to protect safety related equipment if the turbine building should be flooded. A similar deficiency was also discovered in-the Unit 2 service' water pump room Corrective actions included: installation of float valves in the drain lines, reevaluation' of the existing method for providing backflow protection, and other administrative measures.
4.
FINDINGS AND CONCLUSIONS Section 3.4.1, " Flood Protection," of the Standard Review Plan (Ref. 22) requires that failures of liquid-carrying systems should n at prevent safety related systems from performing their required functions. However, the in'ent of this requirement has not been met in many operational events. As discussed in the preceding section, internal flooding, that resulted R
in a loss of safety systems or safety system support components,~had occurred in many
' nuclear power plants during the review period from 1980 to 1989. The root causes of these events were contributed to the following:
4.1 -
Deficiencies in Flood Protection Design Deficiencies in flood protection design had caused unisolable flooding and common-mode flooding. Unisolable flooding had occurred at LaSalle, Salem, and other plants. The licensees of these plants were not able to stop the flooding until the flooding level reached the source's (e.g., lake's) water level. As a result, the flooding disabled much of the plant's safety equipment.
~
Common-mode flooding results in equipment to be ficwded directly or indirectly by water flowing from one compartment building to another. Some plants may be especially vulnerable to common-mode flooding because safety-related equipment are located in the lower levels of the turbine, auxiliary, or reactor building. Review of the operating expe-rience indicates that deficiencies in the design of the flood barriers and floor drains were the root causes for common mode flooding.
9
r 3,$ 4 The concern on flooding of safety equipment compartments as a result of backflow through a floor drain is discussed in an AEOD report issued in 1983 and IE Information Notice 83-44 because of the deficiencies in the design of the floor drain at Calvert Cliffs. Even though the problems at Calvert Cliffs were first discovered in 1981:(Ref. 23,24), they remain
- unresolved as reported in the licensee's 'most recent event report issued on January 16,1989.-
The event at Indian Point further demonstrates that some utilities have not taken corrective actions to prevent the plant from flooding as a result of floor drain backflow despite the NRC warning in 1983.
4.2 Deficiencies in Maintennnee Procedures and Personnel Training Operating experience indicates that deficiencies in maintenance procedures and personnel e
errors have been the causes of significant internal flooding. For instance, the internal flooding events at Hatch and a foreign plant were caused by a single-component failure ~-
during testing of a disassembled system that resulted in a loss of function of many other safety related systems. These incidents were the result of the misuse of an air-operated control valve as an isolation valve.
The event at Salem provides another example of deficiencies in maintenance procedures and personnel training. During this event, the service water system was disassembled for L
. maintenance. A blind flange was installed but was loosened as a leakoff point. When the l
isolation valves failed, the loosened flange became an open end and allowed water to flood -
[
the plant.
l l
5.
SUGGESTIONS L
On the basis of the findings and conclusions presented in the preceding section, the staff l
suggests the following:
i L
5.1 Re-evaluation of Existing Flood Protection Re evaluate existing flood protection to address the concerns on the potential for unisolable L
flooding and common-mode flooding. The areas of evaluation include the following:
a.
Adequacy of flood barriers - Is plant equipped with means to prevent unisolable flooding? For instance, the licensee for LaSalle has installed stop-logs on the intake structure for the circulating water pump to provide a means to stop flooding. Are barriers installed where the potential for common mode flooding exists? Is the height of the barrier designed on the basis of the worst possible flood? The highest rate of flooding has been that caused by water flowing from the rubber expansion joint of the recirculating water pipe, which normally is the largest pipe in a plant.
1 10
-~
.,n.
~. - >.
sf2 y
J f..
j
. b.
Adequacy of the floor' drain system - Is the floor drain system adequate to.
prevent the flooding of one area of the plant from propagating to other areas?
Has the plant installed block valve to prevent backflow of water in the drain j
line to address the safety concerns discussed in IE Information Notice 83-447 Is the capacity of the floor drain system sufficient to handle the worst possibl*
flood as above mentioned?
H c.'
. Adequacy of flood warning instrumentation -Is flood warning instrumentation installed in-areas where the potential for flooding exists to provide the operators an early signal of flooding in the plant? Events such as those that ~
occurced at 12Salle and Indian Point indicate that the plants had not been-equipped with water-level alarms to provide an indication of flooding. ' As a
. result, plant personnel were not able to take actions promptly to mitigate the consequences of flooding.-
5.2 Review of Maintenance Procedures and Personnel Trainine Review maintenance procedures and personnel training to minimize risk of unanalyzed i
internal flooding events caused by single component failure or personnel error..
Maintenance procedures and personnel training could be improved by lessons learned from g
events at Hatch and Salem in which a failed solenoid valve caused a significant flooding.
Several significant flooding events occurred during cold shutdown or refueling outage. This -
indicates a need to strengthen maintenance planning and administrative controls on these systems which are either in operation, stand by or, maintenance to minimize the risk of flooding.
l 6.
REFERENCES 1.
NSAC-60,"Oconee PRA; A Probabilistic Risk Assessment of Oconee Unit 3," June 1
1984.
2.
.- AEOD/E304, " Investigation of Backflow Protection in Common Equipment and
.i L
Floor Drain Systems To Prevent Flooding of Vital Equipment in Safety Related l
Compartments," T. C. Cintula, March ~11,1983.
t l
3.
IE Information Notice 83 44, " Potential Damage to Redundant Safety Equipment as a Result of Backflow Through the Equipment and Floor Drain System," U.S. Nuclear Regulatory Commission, July 1,1983.
4.
PNO-III 80-198. Commonwealth Edison Co., Docket No. 50-265, October 27,1980.
11
7 eJ n.
L 5.
Licensee Event Report 81-047, Tennessee Valley Authority, Docket No. 50 259, September 18,1981.
6.
Licensee Event Report 82-015, Southern California Edison Co., Docket No. 50-206,,
May 13,1982.
7.
Licensee Event Report 83-032, Public Service Electric and Gas Company, Docket No. 50 272, July 13,1983.
o 8.
Licensee Event Report 84-011, Consolidated Edison Co., Docket No. 50 247, September 12,1984.
9.
Licensee Event Report 85-045, Commonwealth Edison Co., Docket No. 50373, June 26,-1985.
10.
NUREG/CR-4674, Vol. 2," Precursors to Potential Severe Core Damage Accidents:
1985 A Status Report." December 1986.
11.
.Special report, " Plant Hatch Unit 1 Report on ECCS Room Flooding," Georgia O
Power, January 10,1986.
1
- 12.
Special Report No. 8710, Public Service Electric and Gas Company April 15, 1988.
j i
13.
Licensee Event Report 89 020, Gulf States Utilities Co., Docket No. 50-458, May 19, 1989.
14.
Licensee Event Report 84-009, Toledo Edison Co., Docket No. 50-346, November 9, l
1984.
I l
15.
Licensee Event Report 85 005, Tennessee' Valley Authority, Docket No. 50327, February 13, 1985.
16.
Licensee Event Report 85-080, Philadelphia Electric Co., Docket No. 50-352, October 8,1985.
l L
17.
- Licensee Event Report 87-006, Portland General Electric Co., Docket No. 50-344, 1
L June 8,1987.
18.
Licensee Event Report 88-008, South Carolina Electric & Gas Co., Docket No. 50-
~ 395, July 7,1988.
19.
Licensee Event Report 88-023, Tennessee Valley Authority, Docket No. 50 259, August 18,1988.
l l-12 L
z;
=-
-." cr _ -
20.
Ucenwe Event Report 88-029, Philadelphia Electric Co.' Docket No. 50 277, April 4
19,1989.
- 21. -
Ucensee Event Report 88-013, Baltimore Gas and Electric Co., Docket No. 50-317, January 6,1989, 22.
NUREG-0800, "Standnu Review Plan for the Review of Safety Analysis reports for Nuclear Power Plann," U.S. Nuclear Regulatory Commission, July 1981, 23.
Ucensee Event Report 8179, Baltimore Gas and Electric Co., Docket No. 50 317.-
24.
Ucensee Event Report 8147, Baltimore Gas and Electric Co., Dockce No. 50 318.
i s
I i
i 1
l
.-j 13