05000413/LER-2010-003
| Catawba Nuclear Station | |
| Event date: | 2-0-2010 |
|---|---|
| Report date: | 07-19-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4132010003R00 - NRC Website | |
BACKGROUND
This event is being reported under the following criterion:
10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications (TS).
Catawba Nuclear Station Unit 1 is a Westinghouse four-loop Pressurized Water Reactor (PWR) [EllS:
RCT].
The Unit 1 Engineered Safety Feature Actuation System (ESFAS) [EllS: JE] Instrumentation initiates necessary safety systems, based on the values of unit parameters, to protect against violating the core design limits, the Reactor Coolant System (RCS) [EllS: AB] pressure boundary, and to mitigate accidents.
The. ESFAS instrumentation is segmented into three distinct but interconnected modules: 1) Field Transmitters or Sensors, 2) Signal Processing Equipment, and 3) Solid State Protection System.
The Solid State Protection System (SSPS) performs the decision logic for most Engineered Safety Feature equipment actuation, generates the electrical output signals that initiate the required actuation, and provides the status, permissive, and annunciator output signals to the main control room of the unit.
ESFAS components are actuated through master and slave relays. The SSPS energizes each master relay appropriate for the condition of the unit. Each master relay then energizes one or more slave relays, which then cause actuation of the end devices. Relay K625 is a slave relay which provides actuation for Phase B Containment Isolation.
The Phase B Containment Isolation specifically has three functional requirements:
1. Manual Initiation 2. Automatic Actuation Logic and Actuation Relays 3. Containment Pressure — High High The Phase B signal isolates the Component Cooling Water [El IS: CC], and the Nuclear Service Water [El IS: BI] Systems at a relatively high containment pressure that is indicative of a large break Loss of Coolant Accident (LOCA) or a Steam Line Break (SLB). Therefore, demonstration of the operability of this Function ensures there is not a potential path for radioactive release from containment in the event of a design basis accident.
Phase B Containment Isolation is accomplished by manual initiation, automatic actuation logic and actuation relays, and containment pressure channels. TS LCO 3.3.2 governs the ESFAS. LCO 3.3.2, Condition B.1, Table 3.3.2-1 Function 3.b.1 requires the manual initiation feature for Phase B Containment Isolation to be operable in Modes 1, 2, 3, and 4.
The following table illustrates the affected components/systems and their governing TS Condition that the SSPS K625 relay latching mechanism failure affected.
Component/System TS Condition Required Action Completion Time ESFAS Phase B TS 3.3.2, Condition B; B.1 Restore channel or 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> Containment Isolation - One channel or train train to operable status Manual Initiation inoperable. OR B.2.1 Be in Mode 3 54 hours6.25e-4 days <br />0.015 hours <br />8.928571e-5 weeks <br />2.0547e-5 months <br />
AND
B.2.2 Be in Mode 5 84 hours9.722222e-4 days <br />0.0233 hours <br />1.388889e-4 weeks <br />3.1962e-5 months <br /> *Containment Valve TS 3.6.17, Condition A; A.1 Restore CVIS train 7 days Injection Water System One CVIWS train to operable status (CVIWS) (NW) inoperable.
- 1NW13A and 1NW46A TS 3.6.17, Condition B; B.1 Be in Mode 3 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> Containment Valve Required Action and AND Injection Water System associated Completion B.2 Be in Mode 5 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> (CVIWS) (NW) Time not met.
- Hydrogen Skimmer TS 3.6.8, Condition A; A.1 Restore HSS train 30 days System (HSS), Train 1A One HSS train to operable status (VX) [EllS: BB] inoperable.
- Air Return System TS 3.6.11, Condition A; A.1 Restore ARS train 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (ARS), Train 1A (VX) One ARS train to operable status [EllS: BB] inoperable.
- Note: Component/System did not exceed TS Required Action Completion Time.
When the SSPS K625 relay latching mechanism failed on April 30, 2010, an Immediate Determination of Operability (IDO) was performed to evaluate the operability of SSPS. It was concluded that the CVIWS, HSS, and ARS were affected, but determined to be operable and capable of meeting their required safety function(s). On May 20, 2010, it was discovered during subsequent investigation that the manual feature for Phase B Containment Isolation (TS 3.3.2, Condition B, Table 3.3.2-1 Function 3.b.1) was inoperable.
This feature was not identified during the IDO on April 30, 2010; therefore, the Required Actions associated with this.TS were not completed, resulting in the unit being in a condition prohibited by TS.
Catawba has determined that the period of past inoperability was from April 30, 2010 through May 21, 2010. The SSPS relay and latching mechanism was successfully replaced and tested on May 21, 2010, and SSPS Train 1A was returned to operable status.
On April 30, 2010, when this event initially occurred, Unit 1 was in Mode 1 at 100% power operation.
EVENT DESCRIPTION
(Certain event times are approximate.) Date/Time� Event Description *04/30/2010/1030 �Latch on K625 relay did not function properly during quarterly testing.
CVIWS Train 1A and HSS Train 1A were declared inoperable and logged into the Technical Specification Action Item Log (TSAIL).
Work request was written concerning the latching failure.
05/01/2010/2330�It was determined that K625 relay affected ARS Train 1A. ARS Train 1A was retroactively declared inoperable from 04/30/2010/1030.
05/02/2010/2210 � ARS Train 1A was declared operable following completion of surveillance testing and approval of the IDO.
- 05/20/2010/1359�Subsequent investigation revealed the IDO was incorrect. Manual Phase B Containment Isolation was declared inoperable and logged into TSAIL.
Work request was written to repair/replace relay and latching mechanism.
05/21/2010/2200 Relay and latching mechanism were successfully replaced; testing was completed. Manual Phase B Containment Isolation was declared operable.
- Note: Event occurrence was on April 30, 2010, although discovery of Manual Phase B Containment Isolation inoperability was on May 20, 2010.
CAUSAL FACTORS
The root cause of this event was the perceived understanding of the governing administrative procedure for the operability/functionality process which led Engineering and Operations to not refer to the content of the procedure when completing and concurring with the IDO.
When determining the operability based upon the identified SSPS K625 relay failure to latch properly, all functions required by TS were not considered in the origination and concurrence of the IDO. Not referring to the administrative procedure for guidance resulted in an incorrect IDO, in which the Manual Phase B Containment Isolation Function was determined to be operable when it was not. This led to the Manual Phase B Containment Isolation Function to be inoperable throughout this entire time period.
The second root cause identified for this event was the decision to declare the downstream affected components/systems inoperable rather than the SSPS per TS LCO 3.3.2. The interpretations and decision to declare the downstream components/systems inoperable upon identification of the relay failure was based upon precedent from previous operating experience and the desire to remain consistent with this operating experience. However, in retrospect, the proper application of TS would have been to enter TS LCO 3.3.2 and utilize the provisions of TS LCO 3.0.6 for the applicable affected downstream components/systems.
CORRECTIVE ACTIONS
Immediate:
1. The on-duty Operations Shift Manager was notified.
2. A Unit Threat Team was formed due to entry into a 48-hour shutdown TS Action Statement and a contingency shutdown plan was generated. A maintenance plan was developed to replace the failed relay.
Subsequent:
1. Interim corrective action was taken to enhance the IDO process until administrative procedures are revised to prevent future events of this type.
2. SSPS Train to slave relay K625 and its latching mechanism were replaced.
Planned:
1. Administrative procedures governing the IDO process will be revised to include a prompt to the originator, reviewer, concurring supervisor, and Operations Shift Manager to ensure applicable TS Surveillance Requirements are listed and evaluated.
2. Administrative procedures will be revised to require at a minimum, completion of the IDO template as described in each section when performing operability determinations.
3. Revise the administrative procedure governing TSAI L to provide guidance that when faced with an Auxiliary Safeguards testing failure, TS LCO 3.3.2 will be entered and TS LCO 3.0.6 provisions will be utilized in lieu of declaring supported components/systems inoperable.
4. Licensed personnel will perform an extent of condition review of TSAIL models to verify accuracy against plant design and licensing basis documents. Models will be adjusted based on these reviews.
There are no NRC commitments contained in this LER.
SAFETY ANALYSIS
This event was analyzed using the Duke Catawba Revision 3a Probabilistic Risk Assessment (PRA). The components affected due to the failure of the K625 relay to latch were HSS fan Train 1A, valves 1NW13A and 1NW46A, and ARS fan Train 1A. (Note: Only the ARS fan is modeled in the PRA. The remaining components were determined to have no impact to Core Damage Frequency (CDF) or Large Early Release Frequency (LERF) and were therefore excluded from the model.) The PRA model was solved with the ARS fan assumed unavailable.
The Incremental Conditional Core Damage Probability (ICCDP) associated with this event was determined to be less than 1E-06. The Incremental Conditional Large Early Release Probability (ICLERP) associated with this event was determined to be less than 1E-07.
Therefore, there was no safety significance to this event and the health and safety of the public were not adversely affected.
ADDITIONAL INFORMATION
Within the previous three years, there have been no LER events involving the failure to perform associated TS Required Actions based upon an incorrect operability determination. This event is therefore considered to be non-recurring. There has been a recently identified trend of LER events involving inadequate application of TS requirements at Catawba. This trend has been evaluated under the Corrective Action Program and actions are being taken in response.
Energy Industry Identification System (EllS) codes are identified in the text as [EllS: XX]. This event is not considered reportable to the Equipment Performance and Information Exchange (EPIX) program.
This event is not considered to constitute a Safety System Functional Failure. This event only affected the operability of one train of the Manual Phase B Containment Isolation Function (Train 1A).
The automatic actuation function for Phase B Containment Isolation was not affected by the failure of the K625 relay latching mechanism. There was no release of radioactive material, radiation overexposure, or personnel injury associated with the event described in this LER.