05000323/LER-2002-003, Regarding TS 3.7.7 Not Met Due to Cable Fault
| ML023020320 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 10/18/2002 |
| From: | Oatley D Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-02-123 LER 02-003-00 | |
| Download: ML023020320 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3232002003R00 - NRC Website | |
text
Pacific Gas and Electirc Company David H. Oatley Vice President Diablo Canyon Operations Diablo Canyon Power Plant PO Box 56 Avila Beach, CA 93424 805 545 4350 Fax 805 545 4234 October 18, 2002 PG&E Letter DCL-02-123 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 Licensee Event Report 2-2002-003-00 Technical Specification 3.7.7 Not Met Due to Cable Fault
Dear Commissioners and Staff:
In accordance with 10 CFR 50.73(a)(2)(i)(B), PG&E is submitting the enclosed licensee event report regarding Technical Specification 3.7.7 not being met due to a cable fault which caused PG&E to exceed the completion time of restoring vital component cooling water pump 2-3 to operable status.
This event did not adversely affect the health and safety of the public.
Sincerely, 97Iv 42h David H. Oatley smg/22461N00021 50 Enclosure cc/enc: Ellis W. Merschoff David L. Proulx Girija S. Shukla Diablo Distribution INPO (v
1 A member of the STARS (Strategic Teaming and Resource Sharing) Alliance l
Callaway a Comanche Peak
- Diablo Canyon.
Palo Verde
- South Texas Project
- Wolf Creek t I V
LICENSEE EVENT REPORT (LER)
FACILITY NAME (1)
DOCKET NUMBER (2)
PAGE (3)
Diablo Canyon Unit 2 1015101010131213 1 11 OF 7
TITLE (4)
Technical Specification 3.7.7 Not Met Due to Cable Fault EVENT LER NUMBER (6)
REPORT OTHER FACILITIES INVOLVED (8)
DATE (5)
DATE (7)
MO DAY YEAR YERSEQUENTIAL NUMBER IREVISION MO DAY jYEAR FACILITY NAME DOCKET NUMBER 08 22 2002 2002 - 0 0 3 l- 0 10 18 2002 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR (11)
MODE (9) 1 X
POWER TE LEVEL
_OTH E
1 J1 (SPECIFY IN ABSTRACT BELOWAND IN TEXT, NRC FORM 366A)
LICENSEE CONTACT FOR THIS LER (12)
TELEPHONE NUMBER AREA CODE Roger Russell - Senior Regulatory Services Engineer 805 1545-4327 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE
CAUSE
SYSTEM COMPONENT MANUFACTURER REPORTABLE TO EPIX TO EPIX X
ClC CIBIL15 0101410 Yes I
I I
I I
I l SUPPLEMENTAL REPORT EXPECTED (14)
EXPECTED MON DAY YR [X] YES (If yes, complete EXPECTED SUBMISSION DATE)
[1 NO SUBMISSION DATE(15) 01 16 03 ABSTRACT (Limit to 1400 spaces te, approximately 15 single-spaced typewntten lines) (16)
On August 22, 2002, at 03:32 PDT with Unit 2 in Mode 1 (Power Operation) at 100 percent power, Required Action A.1 for Technical Specification 3.7.7, Vital Component Cooling Water (CCW) System, was not met when the completion time was exceeded due to a cable fault.
On August 19, 2002, after receiving brief CCW pump 2-3 ground alarms, operators started CCW pump 2-1, shut down pump 2-3, and declared CCW pump 2-3 inoperable until the cause could be determined.
The immediate cause of the event was a ground fault in the "C" phase power cable to CCW pump 2-3, resulting in pump inoperability.
Immediate corrective actions included replacing all three phases of the CCW pump 2-3 cable.
On August 21, 2002, in response to a request for enforcement discretion, the NRC granted verbal enforcement discretion for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> until the motor feeder cable replacement and post-maintenance testing could be completed. On August 23, 2002, at 13:42 PDT, repairs and testing were completed, and CCW pump 2-3 was declared operable.
The root cause of the problem is still being determined.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION TEXT I.
Plant Conditions
Unit 2 was in Mode 1 (Power Operation) at 100 percent power.
Description of Problem A.
Background
The Component Cooling Water (CCW) System [CC] provides a heat sink for the removal of heat from safety related components during a Design Basis Accident (DBA) or transient. During normal operation, the CCW System provides this function for safety related components, various nonessential components, and the spent fuel storage pool [DA].
The CCW system consists of three CCW pumps [P] powered by separate vital 4.16 kV [EB] buses [BU], two CCW heat exchangers [HX], and a two-chamber CCW surge tank. The piping system consists of three parallel headers. The headers extend from the outlet of the heat exchangers through the header heat loads to the suction of the CCW pumps. Headers A and B supply cooling to safety-related components while header C supplies cooling to non-safety related components.
Normally, two CCW pumps are operating with the third CCW pump in standby.
Technical Specification (TS) 3.7.7, Vital Component Cooling Water System, requires that two vital CCW loops shall be operable. TS 3.7.7, Bases, Limiting Condition for Operation (LCO) states that in the event of a design basis accident, one vital CCW loop is required to provide the minimum heat removal capability assumed in the safety analysis for the systems to which it supplies cooling water assuming occurrence of a single failure. To ensure this requirement is met, two vital loops of CCW must be operable. To meet the LCO on CCW loops, vital headers A and B, both CCW heat exchangers, the surge tank, and all three CCW pumps must be operable.
B.
Event Description
On August 18, 2002, at 22:00 PDT, with Diablo Canyon Power Plant (DCPP) Unit 2 at 100 percent power and CCW pumps 2-2 and 2-3 running, a brief CCW pump 2-3 feeder ground alarm [VA] was received. A walkdown of CCW pump 2-3 and the associated breaker did not identify any problems. The CCW pump 2-3 stator current and temperature were also normal.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (I)
DOCKET NUMBER (2)
LER NEUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION INUMBER Diablo Canyon Unit 2 0 50 13 2 3 2002 Ij 0 0 3
0 0 3OF T7 TEXT On August 18, 2002, at 22:51 PDT and on August 19, 2002, at 00:04 PDT, additional CCW pump 2-3 feeder ground alarms were received. The duration of each alarm was less than 0.3 seconds. Following the alarm that occurred on August 19 at 00:04 PDT, CCW pump 2-1 was started and CCW pump 2-3 was shut down. The CCW pump 2-3 breaker cubicle was opened and inspected for abnormal indications. No abnormal odors or problems were noted in the breaker cubicle. A review of the plant drawings determined that relay 50NH12, which was the source of the alarm, senses a ground between the CCW pump 2-3 motor [MO] and breaker, indicating an actual ground fault had occurred.
On August 19, 2002, at 03:32, Operations declared CCW pump 2-3 inoperable until investigations of the pump relay, motor, and cable [CBL5]
could be completed.
On August 19, 2002, the feeder cable and motor were meggered at 2500V dc, and no problems were identified. The feeder cable and motor were subsequently tested using a high potential tester. They failed this test when ramping up from 2500V to 4000V. The motor and cables were then determinated and each was tested independently. The motor and feeder cable phases "A" and "B" tested satisfactorily at 2500V, but the phase "C" cable failed this test.
Following the identification of the ground in the CCW pump 2-3 motor feeder cable, additional work was performed to develop the repair plan, repair schedule, work orders, and clearances required to support the removal of the cable for all three phases and the installation of replacement cables.
On August 21, 2002, PG&E submitted letter DCL-02-100 to formally request enforcement discretion. On August 21, 2002 at 13:20 PDT, PG&E telephoned the NRC to request enforcement discretion regarding compliance with TS 3.7.7, and at 14:10 PDT, the NRC verbally granted enforcement discretion until August 25, 2002 at 03:32 PDT (72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> past the required completion time).
On August 22, 2002, at 03:32 PDT, Required Action A.1 of TS 3.7.7 was not met when the required completion time was exceeded.
On August 23, 2002, at 13:42 PDT, CCW pump 2-3 was declared operable following completion of cable replacement and post-maintenance testing, and on August 25, 2002, at 03:32 PDT, the enforcement discretion expired. CCW pump 2-3 was inoperable for 106.2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (I)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
SEQUENTIAL NUMBER REVISION NUMBER Diablo Canyon Unit20 1510,l 0 l 0 0 3 l 2 l 3 2002
--l- 0 03 3
- - 0 04 4 OF l 7 TEXT C.
Status of Inoperable Structures, Systems, or Components that Contributed to the Event There were no other inoperable structures, systems, or components that contributed to the event.
D.
Other Systems or Secondary Functions Affected
To ensure personnel safety during the cable replacement, Safety Injection (SI) [BQ] pump 2-2 and Residual Heat Removal (RHR) [BP] pump 2-2 were cleared due to the proximity of their power cables to the CCW pump 2-3 motor feeder cable.
E.
Method of Discovery
I On-shift PG&E licensed operators received CCW pump 2-3 feeder ground alarms in the control room during normal operation. After pump and breaker walkdowns, operators inspected the breaker cubicle and identified relay 50NH12 as the source of the alarms. High potential testing of the cables identified the ground fault.
F.
Operator Actions
After receiving a third brief ground alarm, operators started CCW pump 2-1 and shut down CCW pump 2-3 and declared it inoperable.
G.
Safety System Responses None Ill.
Cause of the Problem A.
Immediate Cause TS 3.7.7 LCO and Required Action A.1 were not met because the phase "C" power cable to CCW pump 2-3 shorted to ground and could not be replaced within the TS required completion time.
- t LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (I)
DOCKET NUMBER (2)
LER NUMBER (6)
PAGE (3)
YEAR SEQUENTIAL NUMBER REVISION Diablo Canyon Unit2_
0 0
0 3
32002 O 0 3 0 0 5 1OF 7
TEXT B.
Root Cause All three phases of the feeder cable were sent to an offsite vendor for failure analysis. Preliminary failure analyses have shown no obvious initiator of the fault. The failure and cause analyses are ongoing.
Evaluations being performed by the offsite vendor include a detailed visual examination to locate the fault site and any other anomalies, characterization of the fault site (microscopic examination of thin cross sections, identification of possible water trees, and infrared spectroscopy to identify gross changes in the base compound), and testing of the tensile and elongation properties of the cable insulation and jacket.
The electrical evaluation of the cable includes partial discharge inception (per ICEA T-24-380-1994) and AC breakdown of cable sections (per ASTM D 149, voltage values per IEEE Standard 4).
To date, investigation of the cable environment has identified no chemical contaminants. Gas chromatography and elemental analysis are ongoing to identify possible trace organic contaminants and inorganic contaminants, respectively. PG&E has determined that the cable was not submerged in water and no water, excessive heat, or foreign agents were present in the cable conduit. Also, PG&E has preliminarily ruled out possible installation damage, manufacturing defects, increased electrical operating stresses, thermal aging, or damage due to maintenance practices.
Although the above evaluations are ongoing, preliminary results point to no specific cause and no generic implications.
IV.
Assessment of Safety Consequences
There were no actual safety consequences involved in this event since one vital CCW loop, which included two CCW pumps and one heat exchanger, remained operable after CCW pump 2-3 was declared inoperable. In the event of a design basis accident, the CCW system serves as a mitigating system and one vital loop provides the minimum heat removal capability assumed in the safety analysis for the systems to which it supplies cooling water. The design basis of the CCW System is for one vital CCW loop to remove the post-DBA heat load without exceeding a CCW supply temperature of 120 degrees Fahrenheit with an allowable transient not to exceed 140 degrees Fahrenheit for more than 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (I)
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LER NUMBER (6)
PA(
YEAR SEQUENTIAL NUMBER REVISION Diablo Canyon Unit 20 0 0 5
1 3 l 2 l 3 2002 0
0 l
3 3 0 0 TEXT With one vital CCW loop inoperable, PG&E used the "at power" probabilistic risk assessment model to calculate the change in core damage frequency associated with increasing the completion time to 144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br /> (72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> beyond the 72-hour TS completion time). Three configurations were considered in the risk assessment:
- 1. CCW pump 2-3 out of service.
- 3. CCW pump 2-3 out of service, with SI pump 2-2 and RHR pump 2-2 de-energized to ensure personnel safety of the maintenance workers.
The corresponding change in core damage frequency (ACDF) was calculated as 2.60E-7 and, therefore, not significantly sensitive to small changes in duration of each one of the configurations. Based on the above information and analyses, PG&E used the NRC's significance determination process and believes the event caused very low risk.
The event did not adversely affect the health and safety of the public.
V.
Corrective Actions
A.
Immediate Corrective Actions
PG&E replaced all three phases of the CCW pump 2-3 motor feeder cable with similar Okonite 5 kV cable (red EPR insulation, copper foil shield, LLDPE jacket). The pump was declared operable on August 23, 2002 at 13:42 PDT and the failed cable was shipped to a laboratory for failure analysis.
B.
Corrective Actions to Prevent Recurrence Pending the results of the final cause analysis, PG&E will submit a supplemental licensee event report with appropriate corrective actions.
VI.
Additional Information
A.
Failed Components Okonite 5 kV CCW pump 2-3 motor feeder cable (copper conductor, black EPR insulation, copper foil shield, neoprene jacket).
1
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME (I)
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LER NUMBER (6)
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YEAR SEQUENTIAL NUMBER EVISION NUMBER DiabloCanyonUnit2 0l5 0l0l31213 2002 D l 0 Q 3 l -
Q 7 IOF] 7 TEXT B.
Previous Similar Events
DCPP has experienced eight medium voltage cable failures since 1989.
Five of these cases involved water accumulation in the cable vaults and pull boxes. All of these failures were associated with cables exposed to an outside environment, but in all cases a root cause could not be determined. For the three cases in which water was not a factor, the CCW pump 2-3 cable failure is similar in that the preliminary evaluation shows no evidence of installation damage, manufacturing defects, electrical operating stresses, inadequate maintenance practices, thermal aging, or degradation.