05000302/LER-2002-001
| Crystal River Unit 3 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| 3022002001R00 - NRC Website | |
On June 17, 2002, Florida Power Corporation's (FPC's) Crystal River Unit 3 (CR-3) was in MODE 1 (POWER OPERATION) at 100 percent RATED THERMAL POWER (RTP). An electrical storm was in progress in the area. At 10:48, CR-3 experienced a loss of "A" Train offsite power due to loss of Offsite Power Transformer (OPT) MTTR-9 [EB, XFMR]. Emergency Diesel Generator EGDG-1A [EK, DG] automatically started and re-energized 4160 volt (4160V) Engineered Safeguards (ES) Bus "A" [EB, BU]. At 21:05, on June 17, 2002, 4160V ES Bus "A" was aligned to the Backup ES Transformer (BEST) [EB, XFMR] power feed and EGDG-1A was restored to ES standby.
There were no structures, systems or components that were inoperable at the start of the event that contributed to the event. No failure of equipment that should have automatically actuated was noted. CR-3 remained stable and on-line at 100 percent RTP throughout the event.
Improved Technical Specification (ITS) 3.8.1, Condition A, was entered due to loss of the OPT.
ITS 3.8.1, Required Action A.3, states that the required offsite circuit must be restored to an operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. At 23:45, on June 19, 2002, the OPT power feed to 4160V ES Bus "A" was restored to an operable status and ITS 3.8.1, Condition A, was no longer applicable.
On July 20, 2002, FPC's CR-3 was in MODE 1 (POWER OPERATION) at 100 percent RTP. No electrical storm was in progress in the area. At 16:45, CR-3 experienced a loss of "A" Train offsite power due to loss of OPT MTTR-9. EGDG-1A automatically started and re-energized 4160V ES Bus "A." At 21:32, on July 20, 2002, 4160V ES Bus "A" was aligned to the BEST power feed and EGDG-1A was restored to ES standby.
There were no structures, systems or components that were inoperable at the start of the event that contributed to the event. No failure of equipment that should have automatically actuated was noted. CR-3 remained stable and on-line at 100 percent RTP throughout the event.
ITS 3.8.1, Condition A, was entered due to loss of the OPT. ITS 3.8.1, Required Action A.3, states that the required offsite circuit must be restored to an operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. At 11:28, on July 23, 2002, the OPT power feed to 4160V ES Bus "A" was restored to an operable status and ITS 3.8.1, Condition A, was no longer applicable.
Valid starting of an EGDG is reportable to the NRC. At 14:16, on June 17, 2002, a non-emergency eight-hour notification was made to the NRC Operations Center (Event Number 38996) in accordance with 10CFR50.72(b)(3)(iv)(A). At 22:15, on July 20, 2002, a non-emergency eight-hour notification was made to the NRC Operations Center (Event Number 39079) in accordance with 10CFR50.72(b)(3)(iv)(A). This report is being submitted pursuant to 10CFR50.73(a)(2)(iv)(A).
operating or transient conditions have been identified that were coincident with this failure.
vicinity of the splices from the June repairs, where the conductors and the cable grounds are bundled together and covered with a zippered jacket. This configuration actually compressed the uninsulated grounds into the outer surface of the insulation of the conductors, potentially further compromising the insulation. In the unspliced cable sections, a filler material maintains a separation of approximately %-inch between the insulated conductors and the grounds. Additionally, during the July repair, water was found within the zippered jackets that had been removed and replaced in June. The water had leached out of the cable filler material after the repairs were made in June.
CR-3 Engineering has evaluated the normal and post-accident operating conditions for the OPT cables. Insulation failure is primarily related to voltage potential across the insulation.
These cables are relatively lightly loaded even under the most demanding conditions relative to their current carrying capability (1135 amps carrying both ES buses versus 1872 amps capability). The post-accident operating conditions would not place additional stress on the insulation that is not observed during normal operation. Therefore, the cables and the OPT remained operable during June and July until the insulation failure on July 20, 2002.
A risk analysis was performed conservatively assuming a degraded cable condition during the period between the June 17, 2002, event restoration and the restoration following the July 17, 2002, event. This period of time includes two configurations: (1) the 30 day window with a degraded cable and (2) a 3 day window with the OPT out of service. Using the CR-3 Probabilistic Risk Assessment, the total Incremental Core Damage Probability is estimated to be well below 1.0E-06, indicating low risk significance.
CAUSE
June 17, 2002 The cause for loss of the OPT was a lightning induced voltage surge resulting in a short to ground of one 'B' phase conductor. The short occurred at a location where the three- conductor cable jacket had been stripped to splice the conductors on Cable #1, Phase B, when the splice was originally made. The damage was located near the transition of the zippered jacket to the cable outer jacket. During the lightning storm, the ground potential was raised to a point where this pre-existing damage allowed a short to the ground conductor. This caused a current imbalance in the current transformer [EB, XCT] circuit that actuated the Transformer #9 Neutral Differential Relay [EB, 87] and opened breakers 4900, 4902 and 3211 [EB, BKR]. This short during the lightning storm that resulted in the relay actuation is identified as the event cause.
`NRC FORM 366A (1 2001) The cause for loss of the OPT was latent damage from the lightning strike that caused loss of the OPT on June 17, 2002. Upon investigation, Phase B of Cable #4 conductor was found shorted to ground in the CR-1/CR-2 parking lot cable vault. When the Cable #4 splice zippered jacket was opened, approximately 0.5 gallons of water was drained.
During the June event, this cable had an as-found phase-to-ground insulation resistance of 10.4 megohms. After inspection and replacing the zippered jacket, the return to service phase-to-ground insulation resistance was 1.37 megohms. The change in resistance value could have been due to changing the configuration of the ground wire and individual conductors during the installation of the zippered jacket. It could have also been due to pressing the ground wire into the conductor insulation during the installation of the zippered jacket. Changing the configuration of the cable in the zippered jacket could have moved the ground wire closer to a portion of the insulation material degraded by the June lighting strike.
The collected water inside the zippered jacket then created a path for tracking through the degraded insulation to the ground wire.
On July 21, 2002, the cables in the field were meggered. The following values in megohms were recorded.
1. � After the initial readings were recorded, the cables were cleaned at the termination building and examined for areas where the cable insulation was damaged due to a lightning strike.
Nine of the conductors were found to exhibit damage to the insulation. These conductors were repaired using Raychem 5KV rated NMCK8-2L insulation kits.
A cable fault test was performed to determine the location of any additional faults in the cables. This test determined that Phase B of Cable #1 was damaged north of the cable bridge. Further investigation determined the cable was damaged at an area adjacent to a splice in the cable vault. This cable vault is located in the CR-1/CR-2 parking lot and was found to contain water. The cable vault was drained of water. The cable was dried and repaired using insulation material rated for the required 5KV application. The cable fault test was performed again and no additional defects were discovered.
The other cable vaults were opened and inspected for water intrusion. Cable vaults containing water were pumped and the cables were inspected for water intrusion.
After the cables were repaired, the cables were meggered for phase to ground resistance.
The following values in megohms were recorded (values for the previous readings are in parenthesis).
Cable Phase A to Ground Phase B to Ground Phase C to Ground 1 4.3 (6.8) 36 (0.48) 2.6 (3.0) 2 22 (17.5) 9.7 (8.0) 2.3 (18.4) 3 1.55 (2.0) 7.9 (7.3) 6.5 (7.0) 4 13.8 (20.2) 1.37 (10.4) 13.1 � (13.8) 5 14.3 (11.5) 11.7 (8.5) 9.22 (9.6) 6 8.8 (3.24) 16.6 (5.0) 18.5 (15.01) 2. Nuclear Condition Report (NCR) 63221 was initiated to evaluate the long-term resolution of water in the cable vaults.
3. NCR 62928 will track evaluations of: (1) the adequacy of switchyard lightning protection; (2) the addition of lightning protection for the termination building; (3) the adequacy of the switchyard grounding design; and, (4) the water submergence question for medium voltage cables.
July 20, 2002 1. � The zippered jackets were removed from the cable splices in both the CR-1/CR-2 parking lot cable vault and the cable vault located near the CR-1/CR-2 gate for this cable run. The exposed conductor insulation and splices were dried and wiped clean. The zippered jackets were not re-installed over the splices in order to prevent water accumulation and to provide separation similar to nominal conductor-to-ground spacing.
Scotch 130C Linerless Rubber Splicing Tape was used to repair and enhance the conductor insulation. A minimum of four half lapped layers of Scotch 130C was applied to the maximum extent possible to the exposed conductor insulation where the zippered jacket was removed from the six Kerite 750 MCM cables (see Drawing #2 - Page 10/12). The insulation properties provided by the tape will ensure that at least 5KV of insulation is available in this section of the cabling and that a minimum separation of approximately %-inch between the insulated conductors and the grounds is maintained.
The as-left phase-to-ground megger readings in megohms (1 minute/10 minute values) of the cables after cleaning and repair tasks were performed.
Cable Phase A to Ground Phase B to Ground Phase C to Ground 1 305/347 263/292 680/838 2 �
- 273/321 211/238 132/146 3 41/55.5 135/137 68.4/73.3 4 274/293 27.0/27 62.7/69.8 5 32/33 16.3/15 31.6/32 6 14.4/13.7 10.7/11.1 25.6/38.8 2. � Engineering Change Request 1066 was initiated to evaluate replacing the cables from the OPT to the termination building.
4. Work Order Task Profile 292154-01 was initiated to periodically inspect the cable vaults and remove water as needed.
5. NCR 66692 was initiated to document the repeat failure of the OPT feeder circuit (MTM241).
PREVIOUS SIMILAR EVENTS
No previous similar events involving loss of the OPT have been reported to the NRC.
DRAWINGS
Drawing #1 - OPT Cable Layout Drawing #2 - OPT Cable Spice
ATTACHMENTS
Attachment 1 - Abbreviations, Definitions, and Acronyms Attachment 2 - List of Commitments ) NRC FORM 366A (1-2001 Fr Offsite Power Transformer � Substation Riser X � UNITS 1, 2 & 3
SUBSTATION
Duct Bank — Vault (underground) CR 1&2
PARKING
Vault (above ground) X
MI
X 4 U U Backup E S Trans! Office Bldg.
Neutralizing Tank Condensate Storage Tank Start-uVrranst Train Transf.
Turbine Bldg.
Heater Bay Intermediate Bldg Fire Sere Water taras
BEST
CFR
CR-1/CR-2 CR-3
FPC
ITS
EGDG
ES
ITS
NCR
KV
OPT
RAW
PRA
RTP
SDP
V
NOTES:
The following table identifies those actions committed to by Florida Power Corporation in this document. Any other actions discussed in the submittal represent intended or planned actions by Florida Power Corporation. They are described to the NRC for the NRC's information and are not regulatory commitments. Please notify the Supervisor, Licensing & Regulatory Programs of any questions regarding this document or any associated regulatory commitments.
RESPONSE
SECTION
COMMITMENT DUE DATE
No regulatory commitments are being made in this submittal.