05000325/LER-2016-006
| Brunswick Steam Electric Plant (Bsep) Unit 1 | |
| Event date: | 12-13-2016 |
|---|---|
| Report date: | 02-13-2017 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3252016006R00 - NRC Website | |
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to 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.
Brunswick Steam Electric Plant (BSEP) 006 05000-325 2016 - 000 Energy Industry Identification System (EllS) codes are identified in the text as [XC].
Background
Initial Conditions On December 13, 2016, at 16:27 Eastern Standard Time (EST), Unit 1 was in Mode 1 at approximately 98 percent of rated thermal power. Unit 2 was in Mode 1 at approximately 97 percent of rated thermal power. Other than the components specifically named in this report, no out-of-service equipment contributed to, or affected the course of, this event.
Reportability Criteria This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) because Units 1 and 2 were operated in a condition which is prohibited by the Technical Specifications (TS). Specifically, air conditioning units 1D and 2D for the Main Control Room [NA] were inoperable on account of seismically- qualified structural supports being degraded due to corrosion. The duration of the inoperability could not be conclusively determined. Therefore, the air conditioners are conservatively concluded to have been inoperable for longer than the 30 days allowed by TS 3.7.4, Condition A (i.e., one Control Room Air Conditioning subsystem inoperable) and the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed by TS 3.7.4, Condition B (i.e., two Control Room Air Conditioning subsystems inoperable). Since these times were exceeded, the plant was in a condition prohibited by the TS. The condition applies to both units because the air conditioning system serves the shared Control Room.
The event is also reportable per 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. With two air conditioning units inoperable, the safety function of maintaining Control Room habitability could not be assured. The condition applies to both units because the air conditioning system serves the shared Control Room.
Event Description
On December 13, 2016, a periodic inspection was being performed on the Control Building [NA] air conditioner compressors and condensing coils of air conditioner 2D. During the inspection, seismically qualified support members were found to be degraded due to corrosion. This condition was reported to shift personnel in the Main Control Room, and further assessment was initiated. On December 14, 2016, it was determined that the air conditioning unit supported by the corroded members could not be reasonably assured of meeting its seismic qualifications. Therefore, air conditioner 2D was declared inoperable and TS 3.7.4, Condition A was entered. The affected support members for air conditioning unit 2D were replaced under Work Order 20132955 on December 22, 2016, and the TS condition was exited.
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to 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.
Brunswick Steam Electric Plant (BSEP) 006 05000-325 2016 - 000 Additionally, on January 30, 2017, an inspection, as part of the extent of condition, determined that significant corrosion existed on support members for the 1D air conditioner. Therefore, the 1D air conditioner was declared inoperable, and TS 3.7.4, Condition A was entered.
On both air conditioners, the duration of the corroded condition could not be established with certainty. The periodic maintenance activity which resulted in identifying the corrosion is performed approximately every six months. The last inspection for the 2D air conditioner took place on June 15, 2016, and was completed satisfactorily at that time. The last inspection for the 1D air conditioner took place on May 31, 2016, and was completed satisfactorily at that time. Since corrosion is typically a slow-acting phenomenon, it is concluded that the affected structural members had degraded to the point of becoming inoperable more than 30 days before discovery (i.e., for longer than the TS allowable out-of-service time).
Review of plant history revealed that the only remaining Control Room air conditioning unit, the 2E, had been removed from service during the period when the 2D and 1D are believed to have been inoperable due to compromised seismic qualifications. This occurred on October 18, 2016, from 04:42 EST until 11:54 EST for a total of 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, 12 minutes. During this time, only the two seismically unqualified air conditioning unit units remained in operation.
Event Causes The corrosion of steel supports for the two air conditioning units resulted from exposure to a marine environment coupled with trapped moisture. This degraded the protective phenolic coating and then the underlying metal.
Safety Assessment Three 50 percent capacity Control Room air conditioning units provide temperature and humidity control for the Control Room during normal and accident conditions. Two units are normally required to maintain the designed environmental conditions.
Since the air conditioning system is required to be seismically qualified, it was declared inoperable until the corroded support members were replaced or repaired. However, during this event, the affected air conditioning system remained capable of performing its function under all but seismic conditions. Per normal operating practices, at least two air conditioning units were always operating, including those times when safety function could not be credited due to compromised seismic qualifications.
Based on this analysis, this event had no adverse impact on the health and safety of the public.
Corrective Actions
Any changes to the corrective actions and schedules noted below will be made in accordance with the site's corrective action program.
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to 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.
Brunswick Steam Electric Plant (BSEP) 006 05000-325 2016 - 000 The affected support members for air conditioning unit 2D were replaced under Work Order 20132955 on December 22, 2016. This action is complete.
The affected support members for air conditioning unit 1 D were replaced under Work Order 20139332 on February 2, 2017. This action is complete.
The support members for the 2E air conditioner were inspected by engineers on January 31, 2017, and were found to be acceptable.
The model work order for the air conditioning unit inspection task will be revised to specify initiation of a Work Request (WR) if corrosion is identified which might weaken the structural integrity of supports. Site procedure AD-WC-ALL-210, "Work Request Initiation, Screening, Prioritization and Classification," already requires a WR to be written for plant material deficiencies. The revision to the model work order will strengthen that existing guidance. This action is scheduled to be completed by May 1, 2017.
Previous Similar Events
No events have occurred in the past three years in which a plant structure, system, or component was found to be inoperable due to general environmental corrosion or similar degradation mechanisms.
Commitments This report contains no new regulatory commitments.