05000250/LER-2020-005-01, Technical Specification Action Not Taken for Unrecognized Inoperable Source Range Channel (Rev 1)
| ML21064A218 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 03/05/2021 |
| From: | Pearce M Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2021-037 LER 2020-005-01 | |
| Download: ML21064A218 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2502020005R01 - NRC Website | |
text
U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555-0001 RE: Turkey Point Unit 3 Docket No. 50-250 Reportable Event: 2020-005-01 Date of Event: August 19, 2020 10 CFR 50.73 L-2021-037 March 5, 2021 Title: Technical Specification Action Not Taken for Unrecognized Inoperable Source Range Channel (Rev 1)
The attached Licensee Event Report 05000250/2020-005-01 is submitted pursuant to 10 CFR 50.73 (a)(2)(i)(B) for a condition that was prohibited by plant Technical Specifications. Revision 1 includes additional information that became available during subsequent evaluation of the event.
Ifthere are any questions, please call Mr. Robert Hess at 305-246-4112 or e-mail Robert.Hess@fpl.com.
Sincerely, Michael Pearce Site Vice President - Turkey Point Nuclear Plant Florida Power & Light Company Attachments: USNRC Forms 366 and 366A, current revision cc: USNRC Senior Resident Inspector, Turkey Point Plant USNRC Regional Administrator, Region II Florida Power & Light Company 9760 SW 344th St., Homestead, FL 33035
Abstract
Turkey Point Unit 3 250 3
Technical Specification Action Not Taken for Unrecognized Inoperable Source Range Channel 08 19 2020 2020 005 01 03 05 2021 2
000
David Stoia - Licensing Engineer (305) 246-6538 B
IG DET Yes
On 8/19/2020 during a reactor startup, a disparity was observed between the indicated values of both primary Source Range channels. A prompt investigation determined that one of the two Source Range channels was not indicating properly and that it was inoperable. A subsequent Past Operability Review concluded that the malfunctioning Source Range channel was inoperable from 4/1/2020 until it was repaired and declared operable on 8/24/2020. During this period Unit 3 had performed a total of three (3) reactor power manipulations when Technical Specifications required two Source Range channels to be operable. Since the status of the inoperable Source Range channel was unrecognized, actions prescribed by the applicable Technical Specification were not taken.
This condition is reportable pursuant to 10 CFR 50.73 (a)(2)(i)(B) for a condition that was prohibited by plant Technical Specifications.
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- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
Following the source range high flux reactor trip on 8/19/20, an Engineering evaluation was performed to address the N-3-32 indication anomaly. The evaluation concluded that both N-3-31 and N-3-32 were operable, which prompted the decision to restart the reactor on 8/20/20. The oncoming Operations shift challenged the conclusions of the evaluation, which led to the detailed prompt operability and past operability evaluations that identified the deficiency associated with N-3-32.
The past operability evaluation concluded that N-3-32 was inoperable from 4/1/20 until 8/24/20. TS 3.3.1 equipment requirements were not met during multiple discrete periods within that time frame. For TS 3.9.2, records do not indicate which source range channel was selected for audible counts, although it is likely that N-3-32 was selected during a portion of time during refueling operations. Since the inoperable status of N-3-32 was unrecognized, the TS Action Statements were not applied. This condition is therefore reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) for an operation or condition which was prohibited by Technical Specifications.
CAUSE
The cause of the deficiency associated with N-3-32 was determined to be degradation of the source range detector's sensitivity response. Evaluation by Westinghouse concluded that the symptoms are consistent with a detector that is at or near the end of its service life. A contributing cause was a lack of preventive maintenance activities that would assess the condition of nuclear instrument detectors prior to failure.
SAFETY SIGNIFICANCE
The safety significance of the condition described in this report is low. Source Range functions are not modeled in the plant Probability Risk Assessment. Multiple, redundant trip features are described in the UFSAR Ch 14 Accident Analysis for the postulated control rod withdrawal event. During normal power operation the Source Range channels are not required for service and are deenergized. While N-3-32 was inoperable during reactor startups, N-3-31 was available to generate a reactor trip signal. During refueling operations while N-3-32 was inoperable, N-3-31 and the backup Source Range channels were operable. The cumulative time that a TSAS was applicable and not administered because the status of N-3-32 was unrecognized is small compared to the total time that N-3-32 was inoperable.
CORRECTIVE ACTIONS
N-3-32 was declared operable on 8/24/20 at 06:05 hours following corrective maintenance activities that included high voltage adjustments at discrete count levels and adjustment to the pulse height discriminator (PHD) bias voltage as directed by Westinghouse. Replacement of the detector is scheduled for the fall 2021 refueling outage. To prevent recurrence, maintenance activities based on Westinghouse guidance are currently under development that will allow for more effective and timely evaluation of nuclear instrument performance.
ADDITIONAL INFORMATION
EIIS Codes are shown in the format [IEEE system identifier, component function identifier, second component function identifier (if appropriate)].
SIMILAR EVENTS
A review of Turkey Point reportable events over the previous 15 years was performed to identify potentially similar events or patterns. No events were identified that involved extended or unrecognized inoperability of a Source Range detector.
No pattern characterized by the equipment issue described in this report was identified.
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