ML23318A178
| ML23318A178 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 11/13/2023 |
| From: | Theodore Fanelli NRC/NRR/DRO, NRC/NRR/DRO/IOEB |
| To: | |
| References | |
| Download: ML23318A178 (5) | |
Text
NEI 99-02 [Revision 7]
08/31/2013 Plant: Turkey Point Unit 3 Date of Event: 9/22/23 Submial Date: 11/16/23 Licensee
Contact:
Ken Mack Tel/email: Kenneth.Mack2@FPL.com NRC
Contact:
Theo Fanelli Tel/email: Theodore.Fanelli@NRC.gov Performance Indicator: IE01, Unplanned Scrams per 7000 Crical Hours Site-Speci"c FAQ (see Appendix D)? (X)Yes or ( ) No FAQ requested to become eecve (X) when approved or (other date) ____________
Queson Secon NEI 99-02 Guidance needing interpretaon (include page and line citaon):
NEI 99-02, Revision 7, Page 9, Lines 6-7 Licensees can reduce the likelihood of a reactor accident by maintaining a low frequency of these iniang events.
NEI 99-02, Revision 7, Pg 9 lines 21-22 This indicator monitors the number of unplanned scrams. It measures the rate of scrams per year of operaon at power and provides an indicaon of iniang event frequency.
NEI 99-02, Revision 7, Page 9, Lines 25-26 The number of unplanned scrams during the previous four quarters, both manual and automac, while crical per 7,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />.
NEI 99-02, Revision 7, Appendix D, Page D-1, Lines 14-16 Then, if the licensee believes that there are unique circumstances sucient to warrant an excepon to the guidance as wrien, the licensee should submit a Frequently Asked Queson to NEI for consideraon at a public meeng with the NRC.
NEI 99-02, Revision 7, Appendix E, Page E-1, Line 12, 18-19 There are several reasons for subming an FAQ: 3. To request an exempon from the guidance for plant-speci"c circumstances, such as design features, procedures, or unique condions.
NEI 99-02 [Revision 7]
08/31/2013 Event or circumstances requiring guidance interpretaon:
On September 22, 2023 with Unit 3 at 100% power, a grid disturbance caused by a lightning strike in the switchyard, resulted in a generator lock out. The reactor protecon system automacally actuated, and the unit tripped as designed. Subsequent analysis iden"ed that due to the magnitude of the lightning strike, an induced voltage was created through the switchyard ground grid that arced across the relay contact that drives the string bus dierenal relay, resulng in a generator lockout.
To beer understand the magnitude of the September 22, 2023, lightning strike, Florida Power and Light (FPL) used measurements provided by Vaisala weather services. Vaisala is a large weather services company with over 80 years of experience, currently operang in over 150 countries. The September 22, 2023, strike was of signi"cantly greater magnitude than others historically observed in the area. The lightning strike that caused the scram was measured as 162,000 amperes (kA). The mean lightning strike magnitude was 37 kA. The magnitude of the September 22, 2023, lightning strike is illustrated below.
Figure-1 is based on a data set of lightning strikes occurring within a half mile radius of the Turkey Point switchyard over the last ten years. As is shown, this lightning strike was greater than four standard deviaons (99.85 percenle) above the mean making this lightning strike an extreme stascal outlier.
On September 22, 2023, the lightning arrestor system was fully operaonal. Grounding grid integrity tesng is performed every six years in accordance with Staon Area Operaons Instrucons. The latest tesng results from 2022 showed no signs of degradaon of the equipment that could have contributed to the event. Addionally, the switchyard and lightning arrestor system was in full compliance with design standards; namely, IEEE 998, IEEE Guide for Direct Lightning Stroke Shielding of Substaons and IEEE 80, IEEE Guide for Safety in AC Substaon Grounding. As expected, the substaon lightning protecon system absorbed and diverted the lightning strike to the substaon grounding system, prevenng it from reaching the primary conductors. This was evident by no faults on the primary conductors. As the lightning strike was being dissipated into the earth ground, the ground grid voltage in the staon rose with respect to remote earth. The switchyard ground grid funconed as designed allowing all the equipment in the switchyard to rise at the same relave rate and voltage.
NEI 99-02 [Revision 7]
08/31/2013 The direct cause of the scram was the unprecedented magnitude of the lightning strike which created an induced voltage through the switchyard ground grid that arced across the string bus dierenal relay contact, resulng in a generator lockout. As the lightning strike itself was an extreme stascal outlier, this scram was caused by unique circumstances beyond FPLs ability to foresee or control and there is sucient basis to warrant excepon to the guidance as wrien in accordance with NEI 99-02, Revision 7, Appendix D, Page D-1.
According to SECY 99-007, Recommendaons for Reactor Oversight Process Improvements, an independent regulatory oversight process is one in which the agencys decisions are based on unbiased assessments of licensee performance. The ROP indicators are designed to provide the NRC with a framework to idenfy declining performance. NRC Inspecon Manual Chapter 0305, Page 1, states that the Operang Reactor Assessment Program collects informaon from inspecons and performance indicators (PIs) to enable NRC to develop objecve conclusions about a licensees safety performance.
FPL recognizes that Performance Indicator IE01, Unplanned Scrams per 7000 Crical Hours does not generally dierenate scrams which should or should not be counted based on the cause of the scram.
However, FPL seeks clari"caon of whether counng the September 22, 2023, scram would align with the purpose of the indicator. In general, IMC 308 and SECY-99-007 provide a framework for establishing NRC indicators that are risk informed and performance based. IMC 308 states, The concept for seng performance thresholds includes consideraon of risk and regulatory response to dierent levels of licensee performance. SECY-99-007, Appendix H, provides the basis for the establishment of risk-informed performance indicator thresholds. In these basis documents, consideraon was given to liming false posives which would unnecessarily trigger increased regulatory oversight. As described in SECY-99-007, Secon H.2, When establishing the thresholds, it was taken as guiding principles that they should not result in a large number of false posives (resource concern), and that thresholds should be set to capture meaningful changes. Counng the September 22, 2023, lightning strike scram would bring Turkey Point one step closer to increased regulatory oversight and the associated resource burden without a corresponding nexus to safety.
According to NEI 99-02, Revision 7, Page 9, the frequency of iniang events is an indicaon of the licensees ability to minimize plant vulnerability. Page 9 also states the purpose of the Unplanned Scrams per 7000 Hours indicator is to provide an indicaon of iniang events frequency. The only similar event to this one is from a potenal lightning induced scram in 1985. The Licensee Event Report (LER) for the 1985 scram (ML20134G691) does not state a lightning strike was the de"nive cause of the scram, only that heavy electrical and rain storms were in progress and that lightning was the most probable cause.
Prior to September 22, 2023, a lightning strike in the switchyard inducing a spurious scram such as this has not occurred at Turkey Point. Therefore, this scram is not an indicaon of Turkey Point Nuclear Plants ability to minimize plant vulnerability. Addionally, as the lightning strike itself was an extreme stascal outlier, nor does it provide an indicaon of Turkey Points performance. As such, the September 22, 2023, scram is a unique condion caused by plant-speci"c circumstances as described by NEI 99-02, Revision 7, Appendix E, Page E-1 and FPL believes counng this scram against the Unplanned Scrams per 7000 Crical Hours indicator would not align with the indicators purpose.
NEI 99-02 [Revision 7]
08/31/2013 This interpretaon is consistent with NRC guidance regarding Performance Indicator IE03, Unplanned Power Changes per 7,000 Crical Hours. Indicator IE03 provides an excepon for unique environmental condions, stang:
Unique environmental condions which have not been previously experienced and could not have been ancipated and migated by procedure or plant modi"caon, may not count, even if they are reacve.
This excepon was incorporated into NEI 99-02 Revision 7 even though there is similar language in SECY-99-007 regarding the counng of unplanned power changes and scrams. In the case of both unplanned scrams and power changes SECY-99-007 Appendix A states the measure is a count of the number of events. SECY-99-007 regards both indicators as a rate and is not concerned with the cause of either scrams or power changes.
The September 22, 2023, scram is not indicave of Turkey Points performance and counng it would not align with the purpose of the Unplanned Scrams Per 7000 Crical Hours indicator. FPL requests NRC guidance on whether this scram should be counted.
NEI 99-02 [Revision 7]
08/31/2013 If licensee and NRC resident/region do not agree on the facts and circumstances, explain:
Potenally relevant FAQs:
FAQ 20-06: The licensee proposed counng two scrams as a single scram because the scrams had a related cause. In this case the NRC found the scrams in queson had suciently dierent causes such that they should count as separate scrams. The NRC cited IMC 308 and SECY-99-007 indicang the IE01 performance indicator is a count of the number of unplanned scrams, manual or automac, that have occurred regardless of cause. FPL understands and agrees performance indicator IE01 does not generally dierenate scrams which should or should not be counted based on the cause of the scram. However, FPL believes there are cases when the cause of a scram should be considered when determining whether or not to count a scram. For example, scrams that are not performance based, beyond the licensees ability to foresee and control, and represent outlier events, should not be counted. FPL believes this excepon is in alignment with the guidance contained in NEI 99-02, the purpose of the IE01 performance indicator, and the bases for the indicator described in IMC 308 and SECY-99-007.
Response Secon Proposed Resoluon of FAQ:
FPL proposes to not count the September 22, 2023, lightning strike scram against the IE01 performance indicator.
If appropriate, provide proposed rewording of guidance for inclusion in next revision:
Add the following excepon to the IE01 Performance Indicator:
Unique environmental condions which have not been previously experienced and could not have been ancipated and migated by procedure or plant modi"caon, may not count even if reacve, if all operator acons and equipment responds to the event as expected.