05000414/LER-2003-001
| Catawba Nuclear Station, Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4142003001R00 - NRC Website | |
BACKGROUND
This event is being reported under 10CFR50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications, and 10CFR50.36(c)(2)(i), Limiting Condition for Operation (LCO) not met.
Catawba Nuclear Station Unit 2 is a Westinghouse four-loop pressurized water reactor [EIIS: RCT].
The function of the RWST [EIIS: DA, TK] is to store borated water for the Emergency Core Cooling Systems (ECCS) and the Containment Spray System [EIIS: BE] for use during accident conditions and to provide a source of water to the spent fuel pool during refueling and makeup operations and to the Chemical and Volume Control System [EIIS: CB] during abnormal operating conditions. Each Catawba unit has its own RWST.
Four water level indicator channels [EIIS: LI, CHM, with gauges in the control room [EIIS: NA], are provided for the RWST. Each level indicator channel provides input to a one-out-of-four (1/4) annunciator [EIIS: ANN] logic for the following annunciators:
Annunciator Designation High level Makeup level Low level Low-low level Annunciator Function Protection against RWST overflow Makeup to RWST required Automatic Residual Heat Removal (RHR) pump [EIIS: P] swapover Containment spray pumps must be secured and pump suction swapped to containment sump The RWST level channels also provide a low level signal to the 2/4 logic of the Solid State Protection System (SSPS) [EIIS: JC]. This signal, in conjunction with a Safety Injection signal, initiates the automatic RHR pump swapover. In addition, the SSPS low level setpoint also deenergizes the RWST heaters.
Each of the level indicator channels is fed from a level transmitter [EIIS: LT] located at the RWST. In addition to the above function, RWST level indication serves as a post-accident monitoring variable.
TS LCO 3.3.2 governs the Engineered Safety Feature Actuation System (ESFAS) [EIIS: JE] Instrumentation. Table 3.3.2-1 delineates requirements for the ESFAS Instrumentation. Function 7b governs the RWST level - low function. This function is applicable in Modes 1, 2, 3, and 4 and requires four channels of this instrumentation. Condition N states that with one channel inoperable, the channel must be placed in bypass within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> or the unit must be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Mode 5 within 42 hours4.861111e-4 days <br />0.0117 hours <br />6.944444e-5 weeks <br />1.5981e-5 months <br />. There is no condition listed for more than one channel inoperable; therefore, TS LCO 3.0.3 applies with more than one channel inoperable. TS LCO 3.0.3 requires that action be initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to place the unit, as applicable, in Mode 3 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, in Mode 4 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and in Mode 5 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.
When this event occurred, Unit 2 was operating in Mode 1 at 100% power.
No structures, systems, or components were out of service that had any effect on the event.
EVENT DESCRIPTION
(Certain event times are approximate) Date/Time � Event Description August 16, 2003/0730 � Severe thunderstorms were occurring in the vicinity of Catawba Nuclear Station.
0753 � Channels 1 and 3 of RWST level instrumentation failed high as a result of an apparent lightning strike in the area.
The affected channels were declared entered LCO 3.0.3.
0800 Plant personnel from various groups began assembling to determine the best course of action. Site management made the decision to pursue a NOED while troubleshooting and repair of the failed channels was in progress. The NOED would request an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to complete the repairs prior to Unit 2 having to be in Mode 3.
0850 � Unit 2 began a load reduction to be in Mode 3 by 1453, as required by LCO 3.0.3.
Operations personnel subsequently made a telephone notification to the NRC Operations Center pursuant to 10 CFR 50.72(b)(2)(i) regarding the initiation of a TS required shutdown.
1030 � A conference call was held between Duke Energy Corporation and the NRC concerning the NOED.
1115 � NRC verbally granted approval of the NOED.
1357 1715 Channel 1 operable.
Channel 3 operable.
Condition was repaired and declared Unit 2 exited LCO 3.0.3.
was repaired and declared Unit 2 exited LCO 3.3.2, N.
CAUSAL FACTORS
The root cause of this event was determined to be the fact that Channels 1 and 3 of RWST level instrumentation appear to be more sensitive than other channels of this instrumentation to the effects of lightning. The increased sensitivity of Channels 1 and 3 is most likely due to differences in the grounding geometry and the quality of the ground connections. Significant differences were observed between Unit 1 and Unit 2 regarding the RWST level transmitter grounding configuration. These differences primarily involve the location and orientation of grounding cables relative to the RWST structure.
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CORRECTIVE ACTIONS
Immediate:
1. Operations declared Channels 1 and 3 of RWST level instrumentation inoperable and placed both channels in bypass.
Subsequent:
1.A NOED was requested and approved by the NRC, which allowed 48 additional hours prior to Unit 2 having to be placed in Mode 3.
2. Channels 1 and 3 of RWST level instrumentation were subsequently repaired and Unit 2 exited LCO 3.0.3 and LCO 3.3.2, Condition N.
Planned:
1. Catawba will improve RWST level transmitter grounding circuits and quality of ground connections to minimize the impact of lightning strikes on the operation of the circuits.
The planned corrective action is being addressed via the Catawba Corrective Action Program. There are no NRC commitments contained in this LER.
SAFETY ANALYSIS
Following the failure of Channels 1 and 3 of RWST level instrumentation, Operations placed the channels in bypass. The functional capability of the RWST level - low function then changed from a 2/4 logic to a 2/2 logic. Although functional reliability was decreased, the capability to transfer suction of the RHR pumps from the RWST to the containment sump was still maintained, assuming no single failure occurred on the remaining two channels.
Duke Energy Corporation evaluated the risk implications of remaining at power with the existing 2/2 logic configuration and submitted a NOED to the NRC to request an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> for troubleshooting and repair of the two failed channels. It was determined that it was acceptable to remain at power for this limited period of time given the establishment of proper compensatory actions (i.e., there was no net increase in overall plant risk). These compensatory actions consisted of stationing a MC FORM 3116A (14001) dedicated operator in the control room to monitor level indication on the two operable. channels upon receipt of a Safety Injection signal. The operator was to monitor the RWST level channels for proper tracking by monitoring RWST level decrease and corresponding containment sump level increase during the injection phase of a loss of coolant accident. If automatic swapover did not occur, the dedicated operator was to inform the control room Senior Reactor Operator (SRO) that manual swapover to the containment sump was required. This dedicated operator was also to inform the control room SRO to perform a manual swapover if containment sump level reached 4.5 feet, regardless of RWST level (this action would only have been necessary if both of the operable RWST level channels were to fail). Additionally, no other Unit 2 ECCS related components, trains, or systems were to have been removed from service for maintenance or testing during the time period that the NOED was in effect. The NRC subsequently approved the NOED. The first of the two failed RWST level channels was subsequently repaired and declared operable prior to the expiration of the original LCO time limit for Unit 2 to be in Mode 3. Therefore, the NOED was never actually utilized. The second of the two failed RWST level channels was subsequently repaired and declared operable shortly thereafter.
This event was of no significance with respect to the health and safety of the public.
ADDITIONAL INFORMATION
Within the last three years, no other LERs occurred at Catawba involving instrumentation channel failures resulting from lightning strikes. Therefore, this event was determined to be non-recurring in nature.
Energy Industry Identification System (EIIS) codes are identified in the text as (EIIS: XX]. This event is considered reportable to the Equipment Performance and Information Exchange (EPIX) program.
This event did not involve a Safety System Functional Failure.
There were no releases of radioactive materials, radiation exposures, or personnel injuries associated with this event.