IR 05000255/1987019
| ML18052B349 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 10/07/1987 |
| From: | Norelius C NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML18052B348 | List: |
| References | |
| 50-255-87-19, NUDOCS 8710140359 | |
| Download: ML18052B349 (17) | |
Text
U. S. NUCLEAR REGULATORY COMMISSION
REGION III
AUGMENTED INSPECTION TEAM Report No. 50-255/87019(DRP)
pocket No. 50-255 Licensee:
Consumers Power Company 212 West Michigan Avenue Jackson, MI 49201 Facility Name:
Palisades License No. DPR-20 Investigation At:
Palisades Site, Covert, Michigan Investigation Conducted:
July 14-17, 1987 Team Members: B. L. Burgess, Team Leader, DRP-RII I Z. R. Falevits, Engineering Branch, DRP-RIII
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C. E. Norelius, Director Division of Reactor Projects, RIII E. R. Swanson, Senior Resident Inspector-Palisades J. L. *Knox, Electrical Engineering Branch, DEST, NRR Date
TABLE OF CONTENTS Page General Discussions 7 Background 7 July 14, 1987 Trip 7 Rx Trip Review 8 Sequence of Events 8 Plant Parameter Review 10 Operator.Actions 11 Startup Transformer 1-2 Failure 12' Background 12 Detailed Event Description 13 Corrective Actions 14 Operator Interviews
5.
Persons Contacted
- NRC/Licensee Meeting
7.
Conclusions/Recommendations
- General Discussion Background On April 2, 1987, the Palisades plant returned to power operation following an 11 month outage that had focused on upgrading the overall material condition of the plan As a result of this effort, reoccurring and repetitive equipment and system deficiencies which had plagued plant performance and challenged plant operations were repaire Additionally, a new attitude regarding plant reliability was instilled in plant staff as well as the establishment of higher expectations with regard to quality of corrective and preventative maintenanc As a result, the operating history subsequent to April 2 had been relatively trouble free, with only two manual plant trip The first occurred on May 22 and was the result of an operator inadvertently closing the steam exhaust valve on the operating Mairi Feed Pump Turbine, causing a rupture disk to ruptur As a result of the amount of steam escaping from the blown rupture disk, auxiliary operators in the area concluded that a steam pipe had failed, and immediately informed the control roo Control Room Operators manually tripped the reactor from 40%
power subsequent to the Shift Supervisor responding to the scen The rupture disk was replaced and the plant returned to operation on May 24, 198 The second trip occu~red on July 10, 1987, and was a manual trip caused by the failure of the backstop oil pump discharge pipe which supplied Primary Coolant Pump P-50 The pipe had cracked, causing a loss of oil in the pump upper radial bearing, resulting in a bearing high temperatur In response to the high temperature the operators reduced power from 91% to 14%, and then manually tripped the unit after determining that the power reduction had no effect on bearing temperatur The pipe was replaced and the plant returned to service on July 12, 198 July 14, 1987 Event On July 14, 1987 the Palisades Plant was operating at approximatel % of full powe At 10:24 a.m. the deluge system for the main transformer was isolated to allow troubleshooting of Alarm C47 by I&C technician Isolation of this alarm requires the establishment of compensatory fire tour In addition, security had been notified and was performing the requisite tour At approximately 1:20 p.m., the C-47 alarm was received in the control room and investigation by the operators revealed that the deluge system for Transformer 1-2 had initiate Two minutes later (1:22 p.m.) the rear bus or 11 R 11 bus isolated, the cause unknown at that tim The Shift Supervisor (SS) alerted to the event by the alarms received as a result of the loss of the 11 R 11 bus, responded to the control roo Subsequent to reviewing the status of offsite power and verifying the loss of cooling tower pumps and fans, the
- *
SS ordered a manual reactor tri Control Room Operators responded immediately and manually tripped the reacto After a brief coastdown of the main generator, all five station power transformers were isolated from the main transformer as designe This isolation resulted in the plant being without an offsite power sourc In response to the loss of all offsite power, both diese1 generators started, paralleled with the safeguards buses, and sequenced on their respective blackout load As the loss of offsite power removed power from the primary coolant pumps, the plant was stabilized in hot standby by establishment of natural circulation flo At this point, a review of the emergency plan was conducted, and at 1:30 p.m., an 11 Unusual Event 11 was declared as required for the loss of offsite powe Requisite notifications were made and a continuous open* ENS communications establishe Preparations were made to allow backfeeding of the main transformer by removal of the Turbine Generator disconnect Subsequent to troubleshooting to assure that the offsite and plant electrical buses were normal, backfeeding began at 8:48 p.m. on July 20, 198 The Unusual Event was terminated one minute late The NRC, in response to the event, activated the incident response centers at the Regional office and Headquarter Immediate oversite of the event was accomplished by dispatching the D. C. Cook Resident Inspectors to the Palisades sit An Augmented Inspection Team (AIT)
arrived onsite (5:00 p.m.) to oversee the licensee's actions and review the even The inspection team consisted of a Projects Section Chief and an electrical engineer from Region III, the Senior Resident Inspector, and an electrical engineer from NR The team observed control room activities, monitored primary and secondary plant conditions, followed the licensee's analysis and evaluations regarding root cause and corrective actions to restore offsite power, and interviewed cognizant operators and plant staff regarding event sequenc The AIT concluded their inspection activities on the morning of July, 17, 198 Reactor Trip Review Sequence of Events The following edited sequence of events was derived by review of the plant Tennecomp Data Logger Printout and review of operator log The editing consisted of extracting selected significant data points and where data points did not exist, estimating approximate data points by the times documented in operational log July 14, 1987 10:24 13:19:34 Deluge system isolated to Main Transformer to allow troubleshooting of Alarm C-4 Main Plant Electric Fire Pump P-9A started (Indicating deluge system actuation).
13:20:55 13:21:20 13:21:20 13:21:21 13:21:22 13:21:24 13:21:25 13:21:25 13:21:31 13:21:33 13:21:34 13:21:52 13:22:36 13: 23: 10 13:23:29 13:23:39 13:26:22 13:26:44 13:28:19 13:28:54-58 13:30:11
13:30:49 13:30:54 13:31:30 Safeguards Buses lF and lG power supply breakers opened (Due to loss of switchyard 11 R 11 bus).
Reactor Trippe Charging Pump P-55A Stoppe Turbine Trip Relays K-305L and K-305R Tripped (Turbine Trip).
Steam Generator E-50A Channel-A Water Level Lo Feedwater Pump P-lB Turbine Trippe Charging Pump P-55A and P-55C Starte Auxiliary Feedwater Pump P-8A Starte Steam Generator Low Level Alarm Primary Coolant Loops A&B Low Flo Primary Coolant Loops C&D Low Flo Steam Dump Valves CV-0781 and CV-0782 Ope Pressurizer Level Lo Steam Dump Valves CV-0781, CV-0782, and CV-0779 Close Primary Coolant Pumps P-50 A, B, C and D Stoppe Condensate Makeup Valve Cycling (this valve will continue to cycle for approximately one minute as condensate hotwell level oscillates due to contraction of condensate water as condensate temp decreases).
Pressurizer Backup Heater O Pressurizer Level Norma Pressurizer Pressure Norma Steam Dump Valves CV-0781, CV-0779, CV-0780 Not Close Steam Dump Valve CV-0780 Close Steam Dump Valve CV-0779 Close Steam Dump Valve CV-0781 Close Boric Acid Pump P-56B Starte **
- :36 13:37:24 13:38:30 13:39:17 13:40:21 13:40:23 13:40:25 13:40:58 13:42:04 13: 44: 10 13:59:41 13:04:25 13:011:06 13:28:18 13: 38: 13 13:39:05 13:04:42 13:09:23 13: 13: 31 13:30:09 13:30:09 Steam Generator Water Level Normal, Channels A, B,_ C and Pressurizer Spray Valve CV-1059 Not Close Pressurizer Spray Valve CV-1057 Not Close Pressurizer Spray Valve CV-1057 Close Service Water Pump P-7A Stoppe Component Cooling Water Pump P-52A Stoppe Component Cooling Water Pump P-52A Starte Pressurizer Spray Valve CV-1590 Close Pressurizer Backup Heater O Feedwater Valves CV-0703 and DV-0701 Close Chemical and Volume Control Letdown Valve CV-2004 Close Pressurizer Backup Heater Off (Backup Heater will continue to cycle to maintain.PCS temperature).
Charging Pumps P-55 B&C Cycled On and Off to Maintain Pressurizer Level at Progra Steam Generator E-50B Level Norma Steam Generator E-50A Level Norma Radwaste Isolation Norma Main Plant Diesel Fire Pump P-9B Stoppe Auxiliary Feedwater Pump P-8C Starte Auxiliary Feedwater Pump P-SC Stoppe Turbine Coastdown Trip Relay Rese Bus lC Fast Transfer Rese No discrepancies or peculiarities were noted during review of the data logger printout.
Plant Parameter Review The following information was gained by review of selected strip charts and the printout of the_date-logge **
Reactor coolant temperatures, pressure and pressurizer level decreased during the plant response to the manual tripping of the reacto Pressurizer pressure decreased from 2013 psia to 1773 psi Pressurizer level responded to the plant cooldown by decreasing from 56% to a low point of 32%.
Hot leg temperatures decreased from 583°F to 533.3° Cold leg temperature initially increased from 539.9°F to 545.8°F and then started a slow decline to 518° Steam generator water levels decreased from a normal level of 67% to a minimum of 11% *on 11A 11 steam generator and 15% on 118 11 steam generato Steam generator pressures initially increased from 759 psia to approximately 952.8 psia on 11A 11 steam generator and 947.1 psia on 118 11 steam generato At this time the steam dump valves opened to reduce pressure to about 860 psia at which time the dump valves close Steam generator pressure continued to decline to 800 psia and remained at this pressure until plant cooldown was commence As steam generator pressure was stabilized, steam generator level returned to approximately 23-26%, normal levels for post trip condition Pressurizer pressure was returned to normal at 2000 psia and pressurized level responded to the stabilizing primary temperatures to return to 41%.
Primary and secondary plant response to the manual trip was considered to be norma No abnormal equipment operations were identified with the exception of the quick open feature on the atmospheric steam dump Further review and testing of the relays associated with this feature could not determine the delay (approximately 17 secs) before the atmospheric steam dumps opened to control steam generator pressur The licensee plans to continue to monitor these valves as a short term corrective actio Long term corrective actions will replace the valves with a valve more adapted to perform the desired operational functions required during all plant condition Operator Actions
'
At the time of the transformer failure, the Control Room was staffed by a Shift Supervisor (SRO), a Shift Engineer (SRO), a Service Control Room Operator (COl), and a Control Room Operator (C02).
This staffing met facility minimum shift staffing requirement The Shift Supervisor, responding to alarms alerting the operators to a loss of Startup Transformer 1-2, immediately left his office to observe plant condition After identifying a loss of condenser cooling by observing a loss of both cooling tower pumps and fans, and the loss of Startup Transformer 1-2, ordered Control Room Operators to trip the plan By ordering a manual plant trip at this point, the shift supervisor limited the extent of the primary and secondary plant transients in response to the loss of all offsite powe Additionally, this action enhanced the establishment of primary cooling via natural circulation flo These actions are considered by the AIT to be conservative and appropriat ** *
No adverse, unexpected or unplanned operator actions were identifie Startup Transformer 1-2 Failure Background The Palisades offsite power system (Figure 1) consists of a switchyard, six transmission lines connecting the grid network to the switchyard, and an immediate and delayed access circuit connecting the switchyard to the onsite Class lE distribution syste The immediate access circuit consists of a 345KV transmission line, 345KV t6 24KV Startup Transformer 1-2 which failed July 14, 1987, and a 2400 volt bus duc The delayed access circuit consists of 345KV transmission line, 345KV to 24KV main transformer, 24KV bus duct, 24KV to 2. 4KV station power tr.ans former (No. 1-2), and 2.4KV bus duc The 24KV bus duct associated with each actess circuit (immediate and delayed) are routed in physically separate ducts through the Turbine Building to the Class lE onsite power syste This aspect of the design was reviewed and found acceptable as part of the staff 1s evaluation of SEP Topic VII-3 dated December 31, 198 The 345KV transmission lines between the switchyard and startup and main transformers associated with each access circuit (immediate and delayed) are routed on the same towers for one-half mil The staff 1 s* evaluation of this aspect of the design was included as part of a report to ACRS dated October 23, 196 The staff concluded that in consideration of the slight increase in reliability which would result from adding another line between the switchyard and transformers and the low probability of a tower failure (which would cause loss of both of the lines), backfittirig should not be require This aspect of the design was not addressed in the staff evaluation of SEP Topic VII-dated December 31, 198 The startup transformer associated with the immediate access circuit and the main and station power transformers associated with the delayed access circuit are separated by about 25 feet and a cinder block wal The adequacy of this separation was not included as part of the SEP review of Topic VII-3 dated December 31, 198 The delayed access circuit is established by removing disconnect links at the main generato In accordance with GDC-17, this delayed acces.s circuit must be designed to be avail ab 1 e in sufficient time, following a loss of all onsite AC power supplies and the other immediate access circuit, to assure that specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceede In the Palisades design, the time required to remove the disconnect links is four to six hour This design capability was accepted though not confirmed as part of the staff 1 s evaluation of SEP Topic VII- /
The Palisades DC battery system is designed to supply the required shutdown loads, with total loss of AC power,*for more than six hour The SEP review of this aspect of the design (as indicated in the staff's evaluation of SEP Topic VII-3 dated December 31, 1981), concluded that the DC design has sufficient capacity to permit establishment of the delayed access circuit in four hours without load stripping and that it also has sufficient capacity to permit establishment of the delayed access circuit in six hours if loads are stripped. *Accordingly, the staff recommended (as part of the SEP review) that the licensee provide an operating procedure for stripping de loads-after a two hour loss of AC power in order to assure that GDC 17 can be me The licensee's subsequently updated their procedures to include this recommendatio In the Palisades design, station safety loads are normally supplied, during power operation, from the main_generator through the station power transforme On loss of the main generator there is an automatic transfer from this normal source to the immediate access circui The SEP review of this aspect of the design (as indicated in the staff's evaluation of SEP Topic VII~3 dated December 31, 1981) was limited to the design capability to test this automatic transfer during plant operatio The reliability and actual periodic testing of this transfer were not addresse In addition, the susceptibility of the Palisades design to plant trip due to testing of the transfer during power operation was not addresse Detailed Event Description To correct a problem with the main transformer deluge system alarm not alarming upon actuation, I&C technicians were in the process of calibrating the main transformer pressure switch and placing it in servic System air pressure for the cross connected main and startup transformers deluge systems was identified to be too-lo After adjusting the regulator, air pressure was too high, and to compensate, the technician adjusted the regulator and bled off the excess pressur This rapid drop in pressure caused the heat actuated device to actuate and in turn initiated the deluge syste A short time after deluge system actuation, a flash over arc jumped from the 11Y 11 phase insulator bushing cap to the transformer case on the 1-2 Startup Transforme The arc traveled through the conductive environment provided by corrosion and debris in the deluge spra Through a combination of thermal and mechanical shock the initial fault caused a center section of porcelain insulator to separate at a segment joint or break establishing a path for fault current to the center tube of the bushin At this time the porcelain catastrophically failed (exploded) before the fault could clea The ground fault was sensed by the differential relay scheme which initiated trips on the 345KV switchyard 11 R 11 bus and the startup power breaker Since the sole source of power to the cooling towers is supplied by these transformers a manual reactor trip was initiate *
The normal fast transfer to the startup power transformers was blocked due to the ground fault and the emergency diesel generators were loaded on their respective buses by the normal shutdown sequencer The control room operators completed immediate actions and emergency procedures for plan~ shutdown and initiated the process for establishing the delayed access offsite circuit to safety load This process involved a tagging out procedure to assure 345KV transmission lines are deenergized and a procedure for removing the mechanical disconnect links located below the main generato The time required to complete this process was approximately 7.26 hours3.009259e-4 days <br />0.00722 hours <br />4.298942e-5 weeks <br />9.893e-6 months <br /> from initiation of the event to the time when power was reestab 1 i shed through the de 1 ayed access ci rc-ui t to safety 1 oad Because the plant was in a stable operating condition with shutdown loads being supplied from the onsite power system diesel generators, the licensee used additional time'to allow the balance of switchyard breakers to be checked, verify status of the main transformer, and to assure all relaying had properly functione Also, additional time was used to investigate an omission in the procedure for loss of AC power which prevented reconnection of offsite powe Startup transformer auxiliary relays were not identified to be reset in the procedur This omission was subsequently correcte The root cause of the fault was determined to be contaminants in the transformer deluge system water caused by combined buildup of corrosion products with wind currents which carried the water spray up to the transformer bushing ca These contaminants provided a path to ground for the electrical ar Upon irispection there was no indication that the insulator was degraded prior to the fault and prior power factor testing of the bushing had proved satisfactor A survey by Doble Engineering indicates that nationwide one or two bushing failures are caused each year by deluge operatio Corrective Actions The startup transformer which failed (and the damage caused by its failure) was repaire The repair included drainage of oil,
inspection of internals, removal of some small pieces of the porcelaih insulator found inside the transformer, replacement of failed insulator, repair of adjacent insulators damaged during event, and testing of the transforme Additionally, quarterly deluge system flushes to reduce contamination and a test of the deluge spray pattern to verify that the spray was not directed towards the bushings were implemente Because it is believed that the root cause of the event was due to inadvertent actuation of the deluge system, the licensee is investigating (1) improvements for maintenance procedures and practices to minimize future inadvertent actuations of the deluge and (2) increased frequency of maintenance on the deluge system to
reduce contaminants in the deluge water which may have contributed to the likelihood of arcing and transformer failur Th~ licensee is also continuing their analysis of the failed porcelain insulato.
Operator Interviews Licensed plant operators were interviewed to ascertain operator actions and response to the plant event equipment problems; management support and overall event respons The operators expressed opinions regarding plant response to the trip that were favorable, and stated the equipment performance (with minor exceptions) was very goo Additionally, operators felt that management support and attention to the plant event was excellen The only concern operators expressed regarding the plant event involved the ability of a shift to establish backfeeding during a backshif Because of the reduced complement of operations and maintenance personnel onshift, the time required to implement the actions necessary to establish backfeeding may be delayed until additional personnel arrive onsit Recommendations derived from operator interview included the following:
A motor operated valve on the air ejector line to allow isolation of the condenser to help maintain condenser vacuum and reduce offsite released during a steam generator tube ruptur *
A blast proof wall between the startup and main transformer *
Fast transfer features between the main and startup transformers (i.e., motor operator disconnects, breakers_,
etc.).
Separate power supplies for the two cooling tower pump *
A ready made tagout for initiating backfeeding available to reduce administrative actions during ldss of offsite powe.
Persons Contacted F. W; Buckman, Vice President, Nuclear Operations D. P. Hoffman, Plant General Manager
_
W. L. Beckman, Radiological Services Manager R. D. Orosz, Engineering/Maintenance Manager R~ M. Rice, Operation Manager K. W. Barry, Director, Nuclear Licensing J. G. Lewis, Technical Director, Palisades T. J. Pa 1 mi sano, System Engineering Superintendent R. M. Hamm, Project Engineering R. A. Vincent, Administrator, Plant Safety and Engineering R. A. Fenech, Operation Superintendent R. E. McCaleb, Quality Assurance Director P. P. Margol, Quality Assurance Administrator T. A. Buczwinski, Technical Support Supervisor
-. NRC/Licensee Meeting On July 24, 1987 the NRC met with the licensee in Region III to discuss the progress and scope of its corrective actions in response to the July 14, 1987 loss of Startup Transformer 1-2 Even During the meeting the licensee reviewed the event and outlined the status of its analysis and evaluations regarding acceptability of offsite power supplie The licensee stated that several modifications were under consideration that will provide greater reliability to offsite power supplie.
Conclusion/Recommendations At the termination*of the Augmented Inspection Team 1s onsite review, event root cause determination was still in progress and the analysis of the failed insulator had not reached completio However, the following
- conclusions and recommendations were reached:
Conclusions (l} The offsite circuits between the switchyard and Class lE safety buses marginally meet the design requirements of GDC-1 (2)
The single transmission tower line for* both immediate and delayed access circuits between the switchyard and the startup and main transformers is vulnerable to a single event which could cause both circuits to be lost and does not meet current NRC standard review plan recommended practice for two physically separate line (3) Operator response to the event was outstanding as evidenced by the operator initiated manual plant trip prior to the automatic trip which was eminent, thereby reducing the extent of the primary and secondary plant transient (4)
Plant management and staff response to the trip was conservative, well thought out and appropriately planne Although the current offsite configuration meets GDC-17, the licensee has initiated efforts to enhance offsite power supply reliabilit (5) The licensee 1 s engineers and management personnel contacted during the inspection were receptive, solution oriented, and at eas The needed documents and cognizant personnel were readily availabl Recommendations (1) Compliance with GDC-17 with respect to separation between main and startup transformers appears to be dependent on proper operation.of the fire protection deluge system and the capability of the rock reservoir below the transformers to contain oil from the transformers and water from the deluge syste Periodic testing of the deluge system and an analysis of the design and capability of the rock reservoir should be considered as an operability requirement if required to assure adequate separation of offsite circuit (2)
Th'e cinder block wall between the main and startup transformers which may minimize the possibility of loss both offsite circuits due to missiles generated by failure of a transformer should be analysed to assure that it provides adequate separatio (3) Testing of the.procedure for establishing the delayed access circuit should be performed on a periodic basis in order to demonstrate the design commitment for its establishment in four to six hour The procedure should be streamlined to the extent practical and be performed during each planned station shutdown or when station shutdown is greater than 30 day (4)
Improvement of the four to six hour time required to establish the delayed access circuit should be considered as part of planned modifications to the offsite syste Each of the options being considered by the licensee for the planned modification (Figures 2, 3, 4) add additional circuits between the switchyard and the onsite ~lass lE syste Each of the options removes the*
design requirement for the establishment of the delayed access circuit in four to six hours, meets the requirements of GDC-17, and is acceptabl Other options which should be considered include:
(1) the use of a motor operated disconnect or breaker in place of the disconnect links and (2) an independent offsite circuit which is physically and electrically independent of the existing switchyard and circuits between the switchyard and Class lE buse (5) *The Commission 1s proposed station blackout rule would require that the Palisades design have sufficient capacity and capability to cope with a station blackout for a specified duratio The licensee may find it advantageous to consider this for plant modifications which are being planned for the offsite syste I
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