ML12338A553
| ML12338A553 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 10/27/2011 |
| From: | Entergy Nuclear Operations |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| References | |
| RAS 22115, 50-247-LR, 50-286-LR, ASLBP 07-858-03-LR-BD01 0-ELC-418-GEN, Rev 3 | |
| Download: ML12338A553 (30) | |
Text
United States Nuclear Regulatory Commission Official Hearing Exhibit Entergy Nuclear Operations, Inc.
In the Matter of:
(Indian Point Nuclear Generating Units 2 and 3)
ASLBP #: 07-858-03-LR-BD01 Docket #: 05000247 l 05000286 ENT000247 Exhibit #: ENT000247-00-BD01 Identified: 10/15/2012 Submitted: March 29, 2012 Admitted: 10/15/2012 Withdrawn:
Rejected: Stricken:
Other:
Procedure Use Is: Control Copy: _ _ __
LI Continuous Effective Date: I') --:)
7 -//
Page 1 of 30
- Reference Cl Information O-ELC-418-GEN, R V. 3 MA HalE INSPECTtIONS Work Order No.- - - - - . . : . . . . . . . - - - Compon t No._ _ _ _ _ _ __
Reviewer c:;;>
Approved y:
/L7 Pro edure Spans r, OM/Designee V MAINTENANCE PROCEDURE EDITORIAL REVISION
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 2 of 30 REVISION
SUMMARY
(Page 1 of 1) 1.0 REASON FOR REVISION 1.1 EDITORIAL REVISION due to field comments.
2.0
SUMMARY
OF CHANGES 2.1 Added 55 Gallon Drums to step 4.1.3 2.2 Added Step 2.2,4.2.5, 4.2.6.2, 4.2.6.3 4.2.8 2.3 Revised Step 4.2.3, 4.2.6, 4.2.6.1, 4.2.8, 4.2.13 2.4 Added note prior to step 4.2.6.
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 3 of 30 TABLE OF CONTENTS Section Title Page 1.0 PURPOSE .............................................................................................................4 2.0 PRECAUTIONS AND LIMITATIONS.....................................................................5 3.0 PREREQUISITES..................................................................................................6 4.0 PROCEDURE........................................................................................................8 4.1 Recommended Equipment .........................................................................8 4.2 Manhole Inspections...................................................................................9 4.3 Procedure Complete.................................................................................15
5.0 REFERENCES
....................................................................................................16 6.0 RECORDS AND DOCUMENTATION..................................................................17 ATTACHMENT 1 Industry Operating Experiences.....................................................18 ATTACHMENT 2 IPEC Maintenance Document Feedback Form..............................30
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 4 of 30 1.0 PURPOSE 1.1 This procedure establishes the requirements for performing the periodic preventive maintenance on manholes including inspection and dewatering.
1.2 This procedure is applicable for both Unit 2 and Unit 3.
1.3 The sections of this procedure required to be performed have been identified by Planning and have been indicated in the Work Order. The Supervisor SHALL initial those sections below.
- 4.1 Recommended Equipment
- 4.2 Manhole Inspections
- 4.3 Procedure Complete
- Steps within sections indicated by an asterisk
- may be performed concurrently or in any sequence at the discretion of the Maintenance Supervisor.
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 5 of 30 2.0 PRECAUTIONS AND LIMITATIONS 2.1 If required to pump the water as Waste due to contaminants, then control waste in accordance with EN-EV-106, Waste Management Program.
2.2 This procedure is intended to be used for non-intrusive inspections (not for A
confined space entry), unless directed by the work order.
2.3 Additional Information 2.3.1 Follow EN-IS-101, Industrial Safety and Health Program and EN-IS-111, General Industrial Requirements and any other applicable Industrial Safety Procedures.
2.3.2 Follow EN-MA-118, Foreign Material Exclusion while performing maintenance activities. Cover all openings with appropriate covers when work is not in progress.
2.3.3 This procedure requires the use of Maintenance Standard 0-MS-205 (Documenting Work Performed). Maintenance personnel involved in these activities must be familiar with the Standard.
2.3.4 Electrical Safety Program and Electrical Safety Practices shall be observed when working on energized equipment as per EN-IS-123 and IP-SMM-IS-104.
2.3.5 IF any unacceptable as found or as-left inspection results are found in this procedure, THEN contact Maintenance Supervisor/Responsible Engineer for resolution and initiate a Condition Report for adverse conditions as required by EN-LI-102.
Record WO/CR# for any significant as found conditions in the procedure complete section.
Mechanic Date Mechanic/Date Maintenance Supervisor/Date
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 6 of 30 3.0 PREREQUISITES 3.1 Equipment Tagout No._____________________________________ ;
ENSURE tags are hung and verified.
3.2 Notify Radiation Protection (Rad Pro) prior to the start of work in the Radiologically Controlled Area (RCA).
3.2.1 Comply with requirements and instruction of Radiation Work Permit (RWP) #___________________.
3.3 Coordinate with Waste Management (WM) for disposal of any waste generated during this maintenance activity.
3.4 Personnel protection and safety precautions are understood especially when working near and/or on energized equipment 3.5 Maintenance procedure verified to be the latest approved revision, any inclusive DRNs verified to be attached as per IP-SMM-AD-102.
3.6 Read through Attachment 1, Industry Experiences, prior to the start of work.
3.7 Unless otherwise noted, steps marked with a double initial block, SHALL be verified by Maintenance per step criteria.
3.8 ENSURE ONLY approved parts, drawn against this Work Order, are used for this task. Return ALL unused material to be credited back into stock.
3.9 ENSURE personnel performing signoffs during the performance of this procedure, are listed in the Procedure Complete section of this procedure.
3.10 Establish a clean work area per EN-MA-132 and EN-MA-118 prior to the start of work.
3.11 If working on one of the following manholes, then NOTIFY the NRC at 734-5347 that the Manhole PM is going to be performed.
Unit 2 Manholes 21 & 24 Unit 3 Manholes 31, 31A, 31B, and 34 Manhole #:__________ Notified NRC, Name:_________________
Maintenance Supervisor/Date 3.12 RTV sealant will be used at Unit 2 and Unit 3.
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 7 of 30 3.13 INFORM Component Engineering before start of work.
Component Engineer (Print Name) 3.14 All prerequisites have been completed.
Mechanic Date Mechanic/Date Maintenance Supervisor/Date
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 8 of 30 4.0 PROCEDURE 4.1 Recommended Equipment 4.1.1 Test Equipment x None 4.1.2 Special Tools x None 4.1.3 Materials x Hose x Sump Pump x Extension Cords x Caulking Gun x Manhole Cover Hook or Pry bars x RTV sealant x 55 Gallon Drums A
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 9 of 30 4.2 Manhole Inspections 4.2.1 RECORD the following data:
mech Manhole # ______________________
WO# ______________________ Date_____________
4.2.2 ENSURE the open manhole barrier has been set up around the mech manhole.
4.2.3 CALL Security to stand Guard to support manhole work as mech required. R Required: YES /__/ NO /__/
4.2.4 REMOVE manhole cover and all old RTV as necessary.
mech NOTE If water is present then water measurement must be taken.
4.2.5 IF no water is found THEN proceed to step 4.2.9. A mech 4.2.6 MEASURE any water accumulation in the manhole using Dip mech Stick AND RECORD below. Initiate a CR if cables are submerged.
R WATER PRESENT: YES /__/ NO /__/
WATER LEVEL: ____________ INCHES Cables submerged below water level: YES /__/ NO /__/
CR # ________________
Comments:___________________________________________
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 10 of 30 NOTE Chemistry inspections subject to radiological contamination from plant fluids (for gamma or tritium) are only performed for manholes A inside the main protected area fence line. The area between main protected fence line and outer boundary fence is considered outside protected area.
4.2.7 INSPECT manhole for presence of water and oil. A mech IF water is present, inside protected area THEN CONTACT mech chemistry to sample the water for environmental concerns prior to pumping out the manhole. IF water is present perform 4.2.7. IF oil is present perform 4.2.6.3. R Comments:___________________________________________
4.2.7.1 IF water is present outside protected area (if no oil is mech present) proceed with pumping out manhole. IF oil is present perform 4.2.6.3 A
4.2.7.2 IF oil is present, then perform 4.2.8. IF oil is suspected mech but not obvious contact supervisor. Chemistry may need to be called and sample may be required.
WATER SAMPLE: ACC /__/
UNACC /__/ PERFORM Step 4.2.9 Comments: ___________________________________________
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 11 of 30 4.2.8 IF the water sample is acceptable, THEN PUMP OUT manhole mech mech into the drain AND RECORD the as-left water level after pumping.
IF needed, THEN PUMP water down to less than 2 inches AND ENSURE water is not making contact with cables.
WATER LEVEL: ACC /__/ UNACC /__/
As Found Water Level: ____________inches As Left Water Level: _____________ inches CR # ________________
Comments:___________________________________________
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 12 of 30 4.2.9 IF the water sample is unacceptable, THEN CONTACT Rad mech mech Waste for assistance (drum labels needed) and drums will be needed ( may need to requisition from warehouse).
Pump waste into drums as required, AND DISPOSE of the drums properly. RECORD the as-left water level after pumping. IF R needed, THEN PUMP water down to less than 2 inches AND ENSURE water is not making contact with cables.
Water Pumped into Drums: YES /__/ NO /__/ N/A /__/
Water Level: ACC /__/ UNACC /__/
As Found Water Level: ____________inches As Left Water Level: _____________ inches CR # ________________
Comments:___________________________________________
4.2.10 PERFORM a visual inspection of the condition of cables. This mech inspection is to be performed from top, outside manhole.
DOCUMENT the as-found condition below AND NOTIFY the Maintenance Supervisor and/or Responsible Engineer of any unacceptable conditions or degraded cables. (0-MS-412)
Burning, Charring, or Bubbling: YES /__/ NO /__/
Discoloration: YES /__/ NO /__/
Swelling or blistering: YES /__/ NO /__/
Cracking: YES /__/ NO /__/
Gouges, Nicks, or scratches: YES /__/ NO /__/
Lack of Cleanliness: YES /__/ NO /__/
Frayed cables: YES /__/ NO /__/
Kinks, sharp bends, pinches: YES /__/ NO /__/
Overall As Found cable condition: ACC /__/ UNACC /__/
CR # ________________
Comments:___________________________________________
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 13 of 30 4.2.11 PERFORM a visual inspection of the condition of cable supports.
mech This inspection is to be performed from top, outside manhole.
DOCUMENT the as-found condition below AND NOTIFY the Maintenance Supervisor and/or Responsible Engineer of any unacceptable conditions, or degraded cables.
Condition of Concrete and Masonry: ACC /__/ UNACC /__/
(Check for chipping, spalling or other degradation)
Condition of the Cable Supports: ACC /__/ UNACC /__/
(Check for excessive deflection under load, rusting, loose parts, missing bolts or nuts):
Condition of the Anchorage of the Supports:
ACC /__/ UNACC /__/
(Anchor pullout, anchor looseness, missing anchors):
Water made contact with or submersed the cables:
YES /__/ NO /__/
Supports were found corroded / damaged:
YES /__/ NO /__/
CR # ________________
Comments:___________________________________________
4.2.12 Mechanically CLEAN AND PERFORM a close out inspection of mech mech the accessible areas for FME as per EN-MA-118.
ACC /__/ UNACC /__/
CR # ____________________________
Comments:___________________________________________
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 14 of 30 4.2.13 REPLACE the manhole cover.
mech 4.2.14 RESEAL the round steel covers and any cover that had previous mech R RTV sealant installed with RTV sealant as necessary.
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 15 of 30 4.3 Procedure Complete 4.3.1 The Maintenance Supervisor SHALL record any known CRs generated during and against this maintenance activity.
List of written CRs: ____________________________________
Maintenance Supervisor/Date 4.3.2 NOTIFY Responsible Engineer of the level of water found in the manhole for trending (Lou Lubrano ext. 6681).
Maintenance Supervisor/Date 4.3.3 The personnel listed below have performed signoffs in this The personnel listed below have performed signoffs in this procedure:
Print Name Signature Initials (First, Last) 4.3.4 Procedure complete; Acceptance Criteria, if applicable, has been met.
Maintenance Supervisor/Date
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 16 of 30
5.0 REFERENCES
5.1 Commitment Documents 5.1.1 NONE 5.2 Development Documents 5.2.1 EPG-16, INPO Engineering Program Guide - Electric Cable Reliability 5.2.2 TR-1016689, Medium Voltage Cable Aging Management Guide 5.2.3 EPRI Report No. 1003663, Integrated Cable System Aging Management Guidance 5.2.4 EN-DC-346, Cable Reliability Program 5.2.5 EN-DC-348, Non-EQ Insulated Cables and Connections Inspection Program 5.3 Interface Documents 5.3.1 EN-IS-101, Industrial Safety and Health Program 5.3.2 EN-IS-111, General Industrial Requirements 5.3.3 EN-IS-123, Electrical Safety 5.3.4 EN-MA-118, Foreign Material Exclusion 5.3.5 EN-MA-132, Housekeeping/Facility and Grounds Maintenance 5.3.6 EN-EV-106, Waste Management Program 5.3.7 ENN-EE-S-008-IP, Electrical Cable Installation Standard 5.3.8 IP-SMM-IS-104, Electrical Safety Program 5.3.9 0-MS-412, Inspection and Cleaning of Bus Bars, Contacts, Ground Connections, Wiring and Insulators
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 17 of 30 6.0 RECORDS AND DOCUMENTATION 6.1 Records The following required records are generated by this procedure and SHALL be maintained in accordance with Records Retention Schedule:
6.1.1 Complete Procedure and associated forms are a part of the Maintenance Work Package.
6.2 Documentation The following documentation resulting from this procedure are NOT required to be controlled and maintained in accordance with the Records Retention Schedule:
None
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 18 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 1 of 12)
NOTE This Attachment shall be used to add Industry Experiences as they occur or are found.
March 26, 2008 SEN 272 Underground Cable Ground Fault Causes Forced Shutdown Executive Summary On January 15, 2008, Point Beach Nuclear Plant Unit 1 experienced a lockout of a low-voltage station auxiliary transformer when degraded underground cables caused a phase-to-ground fault and loss of off-site power to the safety-related buses. A 480-volt safeguards (safety-related) bus 1B-04 was also de-energized as a result of the electrical transient. Degradation of the cables, caused by chronic wetting from periodic flooding of the underground conduits, resulted in the cable failure. Although the potential for cable degradation in a wetted environment was recognized, periodic cable testing indicated a very low probability of failure. The extent of exposure of the affected cables to a wetted environment as a result of previous damming of the conduit was not realized.
Following the lockout of the station auxiliary transformer, the emergency diesel generators automatically started and loaded to supply safety-related 4-kV buses and the 1B-03 480-volt safeguards bus. The loss of off-site power to the safety-related buses resulted in the declaration of an unusual event emergency classification. Additionally, the safety monitor statuses of both units were in a red risk condition.
Off-site power was restored to de-energized 480-volt safeguards bus 1B-04 approximately six hours following the initial loss of power after troubleshooting confirmed the failure was located on the transformer side of the bus supply breaker. The Unit 2 safety monitor status returned to green, and the Unit 1 status lowered to orange. Off-site power to the Unit 1 4-kV safeguards buses was restored on the following day by the cross-connecting of electrical supplies from Unit 2. On January 19, off-site power to the Unit 1 safeguards buses was aligned through the Unit 1 generator step-up transformers by the use of a back-feed configuration.
As a result of the loss of off-site power, Unit 1 was shut down for 20 days to replace the power cables. One of the cables in the underground conduits from the 1X-04 station auxiliary transformer to the 4-kV buses was determined to have caused the ground fault. Five other cables were also damaged and required replacement.
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 19 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 2 of 12)
Significant aspects of the event are as follows:
x An off-site electrical supply to safety-related buses failed, resulting in a required plant shutdown, an unusual event emergency classification, and an abnormal electrical alignment for several days.
x A 20-day forced outage was necessary to replace 6 damaged and 24 additional power cables.
x Periodic testing, in lieu of cable replacements recommended by Engineering in 2003, was not effective in predicting cable degradation or preventing cable failure.
Description On January 15, 2008, Point Beach Nuclear Plant Unit 1 experienced a loss of the 1B-04 480-volt safeguards (safety-related) bus, followed shortly by a lockout and loss of low-voltage station auxiliary transformer 1X-04.
Approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> earlier, Unit 1 control room operators received a report of loud, multiple abnormal noises emanating from manhole number 3. The noises lasted approximately five minutes. No visual arcing was observed from the cables inside the manhole, and the cables were not submerged in water at that time. Additionally, no abnormal indications were noted on the control room electrical panels. The plant manager, operations manager, and the duty engineering supervisor were informed. The outage control center was staffed for the pending investigation, and the manhole was inspected hourly. The hourly inspections were subsequently changed to twice per shift, based on guidance from Engineering. Additionally, walk-downs of the plant 4-kV and 13.8-kV buses were completed, with no abnormalities noted.
Prior to the loss of power, several control room alarms and panel indications alerted operators that the 1B-04 480-volt safeguards bus de-energized. Approximately 30 seconds later, a lockout of the 1X-04 low voltage station auxiliary transformer occurred. This transformer provided off-site power to the 1A-03 and 1A-04 4-kV buses and to the 4-kV safeguards buses 1A-05 and 1A-06 that in turn supplied the 1B-03 and 1B-04 480-volt safeguards buses (refer to attachments 1 and 2). The emergency diesel generators automatically started and supplied power to the 4-kV safeguards buses. As a result of the loss of one off-site power source, an unusual event emergency classification was declared and the safety monitors on both units were in a red risk condition.
The operating charging pump was lost as a result of the loss of the 1B-04 bus. The 1B-04 480-volt safeguards bus supplies power to B train emergency core cooling equipment (for example, normal power to P-32C service water pump, 1P-11B component cooling water pump, 1P-14B containment spray pump, 1W-C1 and 1W-D1 containment accident recirculation fans, 1P-2C charging pump, normal power to 1P-10B residual heat removal pump, the 1B-42 primary auxiliary building safeguards motor control center, and other equipment).
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 20 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 3 of 12)
The 1B-04 480-volt safeguards bus was lost prior to the transformer lockout when supply breaker 84 tripped because ground fault protection relay 50G/A52-84 actuated. Approximately seven hours after the loss of the 1B-04 bus and following verification that a fault of the bus supply transformer did not exist, the bus was restored from the 1A-06 4-kV safeguards bus by the closing of the normal power supply circuit breaker. Unit 2 safety monitor status returned to green, and Unit 1 status lowered to orange.
On January 16, a technical specification required plant shutdown was commenced, and the unusual event emergency was terminated.
Emergency power to 4-kV safeguards buses 1A-05 and 1A-06 from the diesel generators was terminated when the Unit 2 cross-connect feeder breakers were closed. As a prerequisite to closing the cross-tie breakers, the Unit 2 fast-bus transfer function for the non-safety-related 4-kV buses was defeated. This configuration lasted for approximately three days. Without the fast-bus transfer function, a reactor scram/turbine trip on Unit 2 would have resulted in the loss of forced circulation, thereby requiring a natural circulation cooldown. However, the decision for this configuration ensured that Unit 1 could complete the planned shutdown and cooldown with forced circulation.
On January 19, off-site power was restored to Unit 1 through the generator step-up transformers by the use of a back-feed configuration.
Causes and Contributing Factors Cable Degradation The cause of the 1X-04 transformer lockout was the direct result of a ground fault on the B5 cable to the 1A-03 4-kV bus (refer to Attachment 3). This fault was most likely caused by long-term degradation of the cables outer jacket, shield, and insulation. The cables connecting the 1X-04 transformer to the 1A-03 and 1A-04 buses were Okonite 10000KCMIL single conductor cables, rated for 5,000 volts with butyl rubber insulation and a neoprene jacket. These cables, including the failed cable, were installed during original plant construction. Butyl rubber insulated medium-voltage cables subjected to a wet environment or submergence are susceptible to a shortened life span.
The conduits in the Unit 1 facade associated with the failed cable had been dammed with a sealant in the 1990s in an attempt to stop water from running out of the conduits and creating an ice hazard during winter (refer to Attachment 4). A drain path for the conduits was reestablished in 2003. As a result of the conduits being sealed, the failed cable likely had been submerged in water for an extended time. Laboratory analysis indicates the cable failed because of water treeing. Water treeing is a term used to describe a series of tiny, hollow channels that develop within an insulation exposed to water. The physical evidence and reviews of operating experience suggest the cable insulation material, aging, and excessive wet environment contributed to its failure.
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 21 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 4 of 12)
In the 1990s, when the foam sealant was applied to the conduit to the Unit 1 facade, there were no work order documentation requirements for the housekeeping/moisture seal applications. Station personnel did not understand the potential for cable degradation from a wetted environment.
1B-04 480-Volt Safeguards Bus Supply Breaker Trip The 1B-04 480-volt safeguards bus was lost when its supply breaker opened prior to the 1X-04 transformer lockout. The bus ground fault protection relay, 50G/A52-84, actuated and isolated power to the bus. The 50G relay spuriously operated in response to the fault condition; but the cause, although not fully conclusive, is suspected to be high-frequency energy from the ground fault. The high-frequency current flow through the cable capacitance-to-ground reached sufficient magnitudes to actuate the 50G relay. The 50G relay on 1B-04 is a solid-state design and was set at 10 amperes, the lower end of the range (10 to 50 amps) per generic industry guidance. The companion 50G/1A52-58 relay on the other safeguards train, 1B-03, is an older style electromechanical relay and was also set at the low end of the 2.5 to 5 amperes range. The station replaced the 50G/A52-84 train B relay. The settings of both relays were increased to approximately midrange within the acceptable bands.
Operating Experience The station has a history of underground cables in a wet environment. Interim measures were implemented in the 1990s to monitor and pump cable manholes and vaults with sump pumps, particularly during the summer.
In 2003, planning for cable replacement was undertaken. The replacement cable was purchased.
Based on options analysis, a decision was made not to replace the cables because no data had been recorded to indicate cable degradation or imminent failure. In lieu of cable replacement, annual cable testing by an independent vendor was implemented. The test methodology chosen was on-line partial discharge testing.
Based on the results of cable testing in May 2005, the vendor recommended a change in testing frequency from annually to every three years; however, the testing frequency was unchanged so that further trend data could be obtained. Test results from June 2006 indicate that 12 cable sections associated with 1X-04 primary side were assessed at condition level 3a low probability of failure. It was recommended that these components be reassessed within two years to look for changes in the condition. The remainders of the cables were classified condition level 2a very low level of deterioration with no action required. All cables from 1X-04 transformer to the switchgear room tested to a level 2 condition
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 22 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 5 of 12)
Cable failure susceptibility was recognized as an industry problem in the early 1990s and was studied by an industry group. In 1994, a summary report, TR-103834-P1-2, Effects of Moisture on the Life of Power Plant Cables, was published by the Electric Power Research Institute (EPRI).
Cable condition monitoring methods and evaluation techniques in 1994 were described as a go/no go test, which could provide an acceptable result with only a very thin layer of insulation left to prevent an impending failure. EPRI continues research in this area and issued EPRI Document 1015070, Plant Support Engineering: Failure Mechanism Assessment of Medium-Voltage Ethylene Propylene Rubber Cables, in August 2007 to improve cable testing methodologies.
The Nuclear Energy Institute has also issued a report?NEI 06-05, Medium Voltage Underground Cable White Paper?that addresses failure modes, materials, effects of a wet environment, and testing method benefits and limitations. It also provides recommendations that utilities be prepared to replace at-risk cables because of the current limitations of diagnostic testing and the random failures of affected cables.
The Nuclear Regulatory Commission issued Generic Letter (GL) 2007-01, Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients, in February 2007. This GL informs the industry that failure of certain power cables can hinder the functionality of multiple accident mitigation systems or cause plant transients and that sufficient monitoring of cable insulation could prevent equipment failures, transients, and the disabling of accident mitigation systems. Additionally, the industry was requested to provide information on the monitoring of inaccessible or underground electrical cables.
Corrective Actions
- 1. The 1X-04 low-voltage station auxiliary transformer was verified to be in good condition.
- 2. A temporary modification installed 30 replacement cables above ground instead of in the previous underground conduits. A permanent modification is scheduled for a future refueling outage.
- 3. The 50G/A52-84 relay setting was raised from 10 amperes to 30 amperes to reduce the potential for spurious trips. The companion 50G/1A52-58 relay setting on safeguards train 1B-03 was raised to 3 amperes. The solid state design relays are within IEEE generic guidance.
No guidance was located for the older electromechanical design relays
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 23 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 6 of 12)
Lessons Key lessons from this event include the following:
- 1. Replace aging or degrading underground cables with appropriate priority, considering the risk associated with their failure and recognizing limitations in current condition monitoring technologies.
- 2. Medium-voltage cables with butyl rubber insulation subjected to a wet environment are susceptible to a shortened life span.
- 3. Stations should consider establishing planned contingencies for failure of underground cables, especially for those installed in poor environmental conditions.
- 4. On-line partial discharge testing of medium-voltage underground cables may not provide sufficient indication of overall cable condition or early warning of cable failures. Redundant off-line testing methods should be considered in higher-risk, high-susceptibility conditions.
- 5. Stations should stay informed of developments in testing methodologies and consider their implementation.
- 6. The potential for spurious relay actuation can be reduced by ensuring actuation setpoints account for appropriate margins.
Attachments : Simplified Unit 1 Electrical Schematic of 4.16-kV System : Simplified Unit 1 Electrical Schematic of 480-Volt System : Faulted B5 Cable : Affected Cable Penetration Dammed with Sealant : Conditions within the Cable Trench (Manhole 3)
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 24 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 7 of 12)
References
- 1. NRC Generic Letter (GL) 2007-01, Inaccessible or Underground Power Cable Failures that Disable Accident Mitigation Systems or Cause Plant Transients, February 7, 2007.
- 2. NRC Information Notice (IN) 2002-12, Submerged Safety-Related Electrical Cables, March 21, 2002.
- 3. EPRI Document TR-103834-P1-2, Effects of Moisture on the Life of Power Plant Cables, 1994.
- 4. NEI 06-05, Medium Voltage Underground Cable White Paper, April 2006.
- 5. EPRI Document 1015070, Plant Support Engineering: Failure Mechanism Assessment of Medium-Voltage Ethylene Propylene Rubber Cables, August 2007.
- 6. Nuclear Network Operating Experience Message OE26183, Unit Shutdown Due to Transformer Lockout on Ground Fault (Preliminary), January 31, 2008.
Utilities are requested to provide information on similar occurrences and solutions at their plants or on their equipment to INPO Events Analysis at e-mail: EventsAnalysis2@inpo.org.
Aging, Bus, Cable, Degraded, Electrical Equipment, Ground Fault, Loss of Off-Site Power, Transformer LIMITED DISTRIBUTION: Copyright © 2008 by the Institute of Nuclear Power Operations. Not for sale nor for commercial use. Unauthorized reproduction is a violation of applicable law. Each INPO member and participant may reproduce this document for its business use. This document should not be otherwise transferred or delivered to any third party, and its contents should not be made public, without the prior agreement of INPO.
All other rights reserved.
NOTICE: This information was prepared in connection with work sponsored by the Institute of Nuclear Power Operations (INPO). Neither INPO, INPO members, INPO participants, nor any person acting on the behalf of them (a) makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this document, or that the use of any information, apparatus, method, or process disclosed in this document may not infringe on privately owned rights, or (b) assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this document.
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 25 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 8 of 12)
Attachment 1: Simplified Unit 1 Electrical Schematic of 4.16-kV System 21 14 22 V 1 3 .8 KV X2 7 1 X0 4 B0 7 4160V PP4 4 B7 1 56 PP4 5 36 PP4 6 PP6 5 PP4 7 PP4 8 1 A0 3 1 A0 4 PP6 0 PP6 2 37 40 55 54 53 52 PP29 1X704 PP21 PP3 5 PP3 0 57 77 SOUTH GATEHOUSE 1 A0 5 1 A0 6 2 A0 6 58 60 66 84 81 80 86 93 NEW G0 4 1 B4 0 G0 3 G0 1 1 X1 3 1 X1 4
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 26 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 9 of 12)
Attachment 2: Simplified Unit 1 Electrical Schematic of 480-Volt System G0 1 2 1 X1 3 1 X1 4 16 17 B B 16 1 B0 3 C 1 B0 4 15 14 14 13 PP1 2 C C B C PP1 3 PP1 4 18 23 21 24 C C C C B
1 B4 2 1 B4 9 1 B3 1 B4 3 1 B3 9 7
PP4 2 PP1 1 B3 2
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 27 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 10 of 12)
Attachment 3: Faulted B5 Cable
---~I====I I_------==~====-
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 28 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 11 of 12)
Attachment 4: Affected Cable Penetration Dammed with Sealant
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 29 of 30 ATTACHMENT 1 INDUSTRY OPERATING EXPERIENCES (Page 12 of 12)
Attachment 5: Conditions within the Cable Trench (Manhole 3)
No. 0-ELC-418-GEN REV.3 MANHOLE INSPECTIONS Page 30 of 30 ATTACHMENT 2 IPEC MAINTENANCE DOCUMENT FEEDBACK FORM (Page 1 of 1)
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