05000315/LER-2012-001
| Donald C. Cook Nuclear Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 3152012001R00 - NRC Website | |
Conditions Prior to Event 100 percent reactor power.
Description of Event
Synopsis On February 17, 2012, at 1005 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.824025e-4 months <br />, Donald C. Cook Nuclear Plant control room operators declared entry into LCO 3.0.3 when they discovered that two Power Range Nuclear Instrumentation (NI) channels [IG] were inoperable at the same time. This is contrary to Technical Specification (TS) Limiting Condition for Operation (LCO) 3.3.1 which provides for inoperability of only one NI channel at a time. LCO 3.0.3 was exited on February 17, 2012, at 1046 when one of the two inoperable NI channels was restored to operable.
The final NI was restored to operable on February 17, 2012, at 1208.
Further investigation identified that the conditions for entry into LCO 3.0.3 were met earlier, but were not discovered at the time because the incorrect calibration of any of the NI channels was not discovered until after technicians questioned the accuracy of the calibration instrumentation (recorder) [SR] during calibration of the Channel 4 NI's Neutron Flux High Positive Rate circuit. Troubleshooting later provided confirmation that the recorder was providing inaccurate information. A replacement recorder was used and the Channel 4 NI calibration was completed satisfactorily.
Timeline A review of the following timeline reveals that the conditions for LCO 3.0.3 entry, though not discovered at the time, were met on February 16, 2012, at 2050 when the Channel 3 NI was declared inoperable for calibration. Though not known, the Channel 2 NI was already inoperable due to the Neutron Flux High Positive Rate time constant being adjusted out of tolerance as a result of using a recorder that was later discovered to be providing inaccurate data.
February 16, 2012 0736� Channel 1 NI declared inoperable for calibration 1154� Channel 1 NI declared operable following calibration (Later validation showed that this channel was operable following calibration.) 1343� Channel 2 NI declared inoperable for calibration 1950 � Channel 2 NI declared operable following calibration (later validation showed this channel was inoperable following calibration due to an incorrectly calibrated Neutron Flux High Positive Rate time constant).
2050� Channel 3 NI declared inoperable for calibration.
February 17, 2012 0121� Channel 3 NI declared operable following calibration (Later validation showed this channel was inoperable following calibration due to an incorrectly calibrated Neutron Flux High Positive Rate time constant.) 0222� Channel 4 NI declared inoperable for calibration.
During calibration, technicians questioned the accuracy of the recorder being used.
Troubleshooting confirmed that the recorder was not providing accurate information. Calibration was resumed and subsequently completed successfully using a replabement recorder. No adjustments were made to the Neutron Flux High Positive Rate time constant.
0814CChannel 4 NI declared operable following calibration.
Upon completing the calibration of the Channel 4 NI, technicians commenced rechecking the other three NI channels' Neutron Flux High Positive Rate time constant settings to validate the as-left calibration condition in order to determine operability status. This validation was performed via partial use of an NI calibration procedure. No adjustments had been performed on the Channel 1 NI Neutron Flux High Positive Rate time constant during its calibration, so validation commenced on the Channel 2 NI Neutron Flux High Positive Rate time constant which was adjusted during calibration, as was the Channel 3 NI Neutron Flux High .
Positive Rate time constant.
February 17, 2012 0906CChannel 2 NI declared inoperable for calibration validation.
1005 Channel 2 NI Neutron Flux High Positive Rate time constant was validated to be out of tolerance. At this time, Operations conservatively declared the Channel 3 NI inoperable due to having been adjusted using the same recorder used to adjust the Channel 2 NI out of tolerance.
With two NI channels inoperable, Operations entered LCO 3.0.3, and calibration of the Channel 2 NI commenced.
1046CChannel 2 NI declared operable following calibration. Operations exited LCO 3.0.3 at this time with three NI channels operable.
1055CChannel 3 NI noted to remain inoperable when calibration validation commenced.
1208 Channel 3 NI Neutron Flux High Positive Rate time constant was validated to be out of tolerance and was calibrated, Channel 3 NI declared operable following calibration.
1216CChannel 1 NI declared inoperable for rate circuit time constant calibration validation.
1339 Channel 1 NI declared operable following validation that the Neutron Flux High Positive Rate time constant was within calibration tolerance. No out of calibration condition existed.
Reporting Requirements On February 16, 2012, at 2050, the Channel 3 NI was declared inoperable to commence the Nuclear Instrumentation Power Range Channel Operational Test and Calibration. At that time, the Channel 2 NI was already inoperable due to incorrect calibration of the Neutron Flux High Positive Rate time constant; therefore, two Power Range Nuclear Instrumentation channels were inoperable at the same time. In accordance with LCO 3.0.3, action should have been initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> (by February 16, 2012, at 2150) to place the unit, as applicable, in:
a. MODE 3 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />; b. MODE 4 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />; and c. MODE 5 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.
Operators had no knowledge that the Channel 2 NI had not been calibrated correctly when the Channel 3 NI was declared inoperable for calibration. As such, LCO 3.0.3 was not entered and the action time limits were therefore not met. Not meeting the action time limits is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) "Any operation or condition which was prohibited by the plant's technical Specifications...". Further, this condition is reportable in accordance with direction provided in NUREG 1022, section 3.2.2 which states: An LER is required if a condition existed for a time longer than permitted by the technical specifications even if the condition was not discovered until after the allowable time had elapsed and the condition was rectified immediately upon discovery.
This condition is also reportable in accordance with 10 CFR 50.73(a)(2)(vii) "Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system..." Two channels became inoperable in a single system (Power Range Nuclear Instrumentation) as a result of the same faulty recorder being used to adjust multiple channels.
Cause of Event
A single piece of test equipment (a recorder) failed to provide accurate data during calibration of two Power Range Neutron Flux High Positive Rate time constant circuits. This caused both NI channels to be inoperable at the same time.
Analysis of Event
During the restoration portion of the calibration procedure, the Channel 4 NI was not capable of providing a valid output to the Solid State Reactor Protection System during bistable verification. At that time, the Power Range Neutron Flux High Positive Rate time constants set for Channel 2 and Channel 3 were non-conservative due to the faulty recorder. Channel 1 was the only NI channel with an operable Power Range Neutron Flux High Positive Rate trip. All other bistables on Channels 1, 2, and 3, including the High Neutron Flux trip, had been validated and were providing proper input to the Solid State Reactor Protection System prior to declaring Channel 4 inoperable for calibration.
The Power Range Neutron Flux High Positive Rate trip provides a trip signal during rod ejection accidents. The reactor protection modeled in the safety analysis for a rod ejection accident is only the High Neutron Flux trip.
The event does not constitute a degraded or unanalyzed condition because the reactor protection modeled in the safety analysis is the Power Range Neutron Flux High trip which remained available as described above.
As such, Power Range NI Channels 1, 2, and 3 were capable of providing the High Neutron Flux trip.
Corrective Actions
Completed Corrective Actions
Power Range NI channels' rate circuits were calibrated to within the required tolerance using a replacement recorder.
Planned Corrective Actions
Revise the Power Range NI Channel Operational Test and Calibration procedures as follows:
Add guidance to provide a peer check of the rate circuit time constant checks and, before making any adjustments, to verify with other test equipment if an out of tolerance condition is identified with the time constant.
Create a Pre Job Brief database entry to address the lessons learned from this calibration evolution.
Communicate lessons learned and extent of cause to promote critical analysis of small deviations from expected performance and maintaining a strong questioning attitude.
Review other Reactor Protection surveillance procedures that use the same brand of recorder, and initiate actions as needed to incorporate cautionary steps based on the lessons learned from this event.
Previous Similar Events
LERs for both CNP Unit 1 and Unit 2 for the past three years were reviewed for similar events related to 10 CFR 50.73(a)(2)(i)(B) and 10 CFR 50.73(a)(2)(vii) reporting criteria. The following were identified:
315-2010-001-00 1AB EDG Fuel Oil Transfer Pumps Inoperable With one EDG Fuel Oil Transfer Pump out of service for power cable replacement, the power cable for the remaining Fuel Oil Transfer Pump was cut inadvertently resulting in no AB Fuel Oil Transfer Pumps being operable. This is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) 316-2010-002-00 Containment Divider Barrier Seal Mounting Bolts Not Properly Installed Containment divider barrier bolts were identified to be missing or loose during inspection taking place during an outage. This is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) 316-2010-003-00 Changed Modes from Mode 5 to Mode 4 with Divider Barrier Inoperable Operators determined that the containment divider barrier was inoperable approximately 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the unit ascended from Mode 5 to Mode 4. The seal had recently been reassembled, but the assembly was not properly verified prior to mode change. This is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B)