ML24299A263
| ML24299A263 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 10/25/2024 |
| From: | Komm D Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, NRC/RGN-III, Document Control Desk |
| References | |
| IR 2024090 EA-24-075 | |
| Download: ML24299A263 (1) | |
Text
10 CFR 50.4 Post Office Box 2000, Decatur, Alabama 35609-2000 October 25, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 2 Renewed Facility Operating License No. DPR-52 NRC Docket No. 50-260
Subject:
Response to Apparent Violation in NRC Inspection Report 05000260/2024090, EA-24-075
References:
- 1. NRC letter to TVA, Browns Ferry Nuclear Plant - NRC Inspection Report 05000260/2024090; and Preliminary White Finding and Apparent Violation, dated September 17, 2024 (ML24255A027) 2.
TVA letter to NRC, Notice of Intentions Regarding Preliminary Finding from NRC Inspection Report 05000260/2024090, EA-24-075, dated September 27, 2024 (ML24270A216)
The Enclosure to this letter provides Tennessee Valley Authority's (TVA) response to the subject apparent violation. TVA acknowledges that this condition existed as documented in the inspection report and does not contest the apparent violation. TVAs assessment of this event concurs with a 92-day time of exposure which the NRC has determined to be of White significance.
There are no new commitments contained in this letter. If you have any questions, please contact David J. Renn at (256) 729-2636.
I declare under penalty of perjury that the foregoing is true and correct. Executed on this 25th day of October, 2024.
Respectfully, Daniel A. Komm Site Vice-President Browns Ferry Nuclear Plant
U.S. Nuclear Regulatory Commission Page 2 October 25, 2024
Enclosure:
Response to Apparent Violation in NRC Inspection Report 05000260/2024090, EA-24-075 cc: (w/ Enclosure)
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant
Enclosure Tennessee Valley Authority Browns Ferry Nuclear Plant Unit 2 Response to Apparent Violation in NRC Inspection Report 05000260/2024090, EA-24-075 (See Attached)
Enclosure Response to Preliminary White Finding and Apparent Violation in NRC Inspection Report 05000260/2024090, EA-24-075 Restatement of Preliminary White Apparent Violation 05000260/2024090-01, Failure to promptly identify and correct a degraded condition with the U2 HPCI pump turbine exhaust inner rupture disc:
An NRC-identified apparent violation of 10 CFR Part 50, Appendix B, Criterion XVI, was identified for the licensees failure to identify and correct a degraded condition with the U2 High Pressure Coolant Injection (HPCI) pump turbine exhaust inner rupture disc. This resulted in the inoperability of the Browns Ferry Nuclear Plant (BFN), Unit 2 HPCI system on March 19, 2024. Specifically, the licensee failed to promptly identify adverse conditions following a pressure transient event which occurred on the HPCI steam exhaust line on December 15, 2021. Sufficient manufacturer information was available for the licensee to have anticipated material degradation due to system pressure exceeding the lower threshold of disc burst pressure, which could lead to shortened lifespan of the disc. CR 1917980 was initiated for this condition.
TVAs Response to the Apparent Violation:
TVA understands and accepts the Apparent Violation. TVAs assessment of this event concurs that having the HPCI system potentially unavailable for 92 days is of White significance.
Reason for the Apparent Violation:
Following a turbine trip while performing HPCI surveillance testing, troubleshooting identified that the direct cause of the Unit 2 HPCI Turbine Trip was due to leakage through the inner rupture disc.
The rupture disc that failed was installed prior to an event in which the HPCI exhaust line reached a maximum pressure of 161.4 psig. This pressure transient deformed the disc enough to develop an excessive gap between the disc and the vacuum support, leading to the accelerated fatigue and eventual premature failure during subsequent surveillances. BFN personnel were not aware that the recommended operational ratio of the rupture disc had been exceeded and that by doing so, the lifespan of the rupture disc was shortened.
The root cause was determined to be that the operating ratio of the rupture disc was not used to develop effective operating limits to protect the integrity of the disc.
Two contributing causes were identified:
1.
The first contributing cause is that the existing vendor manual for the HPCI rupture disc did not have all the available pertinent information on the operating limits for the rupture disc. Technical Bulletin CS7000-1, which discusses the rupture disc operating ratio, was not included in the manual.
2.
The second contributing cause is that ODM 4.7, Operations Work Control Interface, does not address evaluating the possibility of over pressurizing low pressure system components during online maintenance.
Enclosure Response to Preliminary White Finding and Apparent Violation in NRC Inspection Report 05000260/2024090, EA-24-075 Corrective Steps That Have Been Taken and the Results Achieved:
As an immediate corrective action, BFN replaced the Unit 2 HPCI inner and outer rupture discs, as well as all BFN Unit 1 and 3 HPCI rupture discs. The removed discs were inspected for similar damage.
Additionally, an Operations standing order was put in place that, when an operability determination is being made, an interim action will be in place to contact the vendor for the components within the scope of the evaluation to determine if any applicable operating limitations exist.
Finally, BFN conducted a training needs analysis (Analysis and Design Worksheet) in accordance with NPG-SPP-17.1.0, Systematic Approach to Training Process, which determined that the following two training actions are required:
1.
A case study will be developed and delivered by line management regarding the engineering evaluation of Unit 2 HPCI system pressurization event. The case study will discuss performing evaluations of system pressurization events with specific focus on rupture disc "operating ratio" and any other operational limits.
2.
Lesson Plan ESP070.010 will be revised to ensure that future incumbents have a solid understanding of system pressure events with specific focus on rupture disc.
This action addressed the Cross-Cutting Aspect of H.9 - Training, which was identified by the NRC.
Corrective Steps that Will Be Taken:
BFN plans to implement the following Corrective Actions to Prevent Recurrence (CAPR):
1.
Create or revise a design output document to determine the operating pressure limit for the HPCI and RCIC System turbine exhaust line rupture discs.
2.
Revise the following drawings to update the NOTES section to specify the operating pressure limit for the turbine exhaust line rupture discs:
a.
1-, 2-, 3-47E812-1, Flow Diagram High Pressure Coolant Injection System b.
1-, 2-, 3-47E610-73-1 Mechanical Control Diagram HPCI System c.
1-, 2-, 3-47E813-1, Flow Diagram Reactor Core Isolation Cooling System d.
1-, 2-, 3-47E610-71-1 Mechanical Control Diagram RCIC System
Enclosure Response to Preliminary White Finding and Apparent Violation in NRC Inspection Report 05000260/2024090, EA-24-075 3.
Revise the following procedures to specify the operating pressure limit for the turbine exhaust line rupture discs:
a.
1-, 2-, 3-OI-71, Reactor Core Isolation Cooling System [Note:
Changes needed for Section 3.0 Precautions and Limitations, and Section 8.4. RCIC Turbine Trip]
b.
1-, 2-, 3-OI-73, High Pressure Coolant Injection System [Note:
Changes needed for Section 3.0 Precautions and Limitations, and Section 8.3 HPCI Turbine Trip]
c.
1-, 2-, 3-ARP-9-3B, Alarm Response Procedure [Note: Changes needed for Window 28 alarm response. (RCIC)]
d.
1-, 2-, 3-ARP-9-3F, Alarm Response Procedure [Note: Changes needed for Window 25 alarm response. (HPCI)]
Additionally, BFN plans to implement the following Corrective Actions to address contributing causes:
1.
Revise Vendor Manual BFN-VTD-F103-0050, Installation and Maintenance Instructions for Fike Rupture Disc Assemblies, to include all pertinent operating limits for operating rupture discs on HPCI systems.
2.
Revise Vendor Manual BFN-VTD-F103-0050, Installation and Maintenance Instructions for Fike Rupture Disc Assemblies, to include all pertinent operating limits for operating rupture discs on RCIC systems.
3.
Revise ODM 4.7, Operations Work Control Interface, Attachment 2, to warn against the possibility of over pressurizing low pressure system components during online maintenance, such as when closing the HPCI/RCIC steam exhaust isolation valve with potential valve leak by.
Date When Full Compliance Will Be Achieved:
All CAPRs are expected to be complete by January 15, 2025, or earlier.