05000440/LER-2017-007
| Perry Nuclear Power Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 53137 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 4402017007R00 - NRC Website | |
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to NEOB-10202, (3150-0104). Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 007 - 00 Perry Nuclear Power Plant Unit 1 05000-440 YEAR 2017 Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
INTRODUCTION
On December 22, 2017 at 2348 hours0.0272 days <br />0.652 hours <br />0.00388 weeks <br />8.93414e-4 months <br />, the High Pressure Core Spray (HPCS) [BG] system was declared inoperable due to a piping [PSP] leak. Limiting Condition of Operation (LCO) 3.5.1 Condition B was entered for HPCS inoperability. This resulted in a loss of safety function for a single train system.
EVENT DESCRIPTION
On December 22, 2017 at 2348 hours0.0272 days <br />0.652 hours <br />0.00388 weeks <br />8.93414e-4 months <br />, the HPCS system was declared inoperable due to discovery of a through-wall leak on the minimum flow line piping. The leak was on the outside bend of the first elbow downstream of the minimum flow restricting orifice [OR] and was leaking at approximately 60 drops per minute. TS LCO 3.5.1 Condition B was entered for HPCS inoperability.
On December 23, 2017 at 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br />, event notification EN# 53137 was made to the NRC Operations Center in accordance with 50.72(b)(3)(v)(D).
The flaw was characterized as thinning across an approximately one square inch area. Pipe wall thickness outside the thinned area was at or above nominal wall thickness of 0.438 inches for a 4-inch diameter schedule 120 pipe. High water flow concentrated to the center-line of the upstream piping (caused by the restricting orifice) would impact directly to the thinned area of the elbow.
A weld overlay (approximately 3-inch circle and 0.50 inches thick) was added over the thinned elbow area in accordance with ASME Code Case N-561-2, "Alternative Requirements for Wall Thickness Restoration of Class 2 and High Energy Class 3 Carbon Steel Piping Section XI, Division 1." The TS LCO was exited and the HPCS system was declared operable on 12/25/2017 at 2213 hours0.0256 days <br />0.615 hours <br />0.00366 weeks <br />8.420465e-4 months <br />.
CAUSE
The cause was pipe wall loss due to a combination of cavitation and mechanical erosion wear.
EVENT ANALYSIS
A Probabilistic Risk Assessment (PRA) evaluation was performed. While the associated maintenance activity resulted in unplanned unavailability hours and was assessed via 10 CFR 50.65 (a)(4) requirements, a bounding analysis to account for "the event or condition that could have prevented the fulfillment of a safety function" condition conservatively indicates that the given event resulted in a very small change to overall plant risk with a change (delta) in core damage frequency (CDF) of 6.11E-07/yr, and a change (delta) in the large early release frequency (LERF) of 3.52E-09/yr. The delta CDF and delta LERF values are well below the acceptable thresholds of 1.0E-06/yr and 1.0E-07/yr, respectively, as discussed in Regulatory Guide 1.174.
The risk of this event is therefore considered very small in accordance with the Regulatory Guidance.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.Resource@nrc.gov. and to the Desk Officer, Office of Information and Regulatory Affairs.
NEOB-10202: (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 007 2017 - 00
CORRECTIVE ACTIONS
The permanent repair will be implemented by the end of the next refueling outage. Ultrasonic testing (UT) thickness readings will be performed on the HPCS minimum flow line first elbow downstream of restricting orifice at an initial periodicity of four years. For extent of condition, UT readings will be performed on similar elbow configurations for the minimum flow lines in the Reactor Core Isolation Cooling (RCIC) [BN], Low Pressure Core Spray (LPCS) [BM] systems, and an additional elbow in the HPCS minimum flow line.
PREVIOUS SIMILAR EVENTS
A review of LERs and the Corrective Action database for the past three years identified no similar events.
COMMITMENTS
There are no regulatory commitments contained in this report. Actions described in this document represent intended or planned actions, are described for the NRC's information, and are not regulatory commitments.