05000458/LER-2016-001, Regarding Potential Loss of Secondary Containment Safety Function Due to Failure of Auxiliary Building Ventilation System
| ML16084A144 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 03/07/2016 |
| From: | Vazquez S Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-47660 LER 16-001-00 | |
| Download: ML16084A144 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4582016001R00 - NRC Website | |
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- ~Entergy RBG-47660 March 7, 2016 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Licensee Event Report 50-45812016-001-00 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47 RBF1-16-0027
Dear Sir or Madam:
Entergy Operations, Inc.
River Bend Station 5485 U.S. Highway 61 N St. Francisville, LA 70775 In accordance with 10 CFR 50.73, enclosed is the subject Licensee Event Report.
This document contains no commitments. If you have any questions, please contact Mr. Joseph Clark at 225-381-4177.
Sincerely,
- ~~
Sergio Vazquez Director - Engineering Enclosure cc:
U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Blvd.
Arlington, TX 76011-4511
Licensee Event Report 50-458 I 2016-001-00 March 7, 2016 RBG-47660 Page 2 of 2 NRC Sr. Resident Inspector P. 0. Box 1050 St. Francisville, LA 70775 INPO (via ICES reporting)
Central Records Clerk Public Utility Commission of Texas 1701 N. Congress Ave.
Austin, TX 78711-3326 Department of Environmental Quality Office of Environmental Compliance Radiological Emergency Planning and Response Section Ji Young Wiley P.O. Box 4312
_Baton Rouge, LA 70821-4312
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 0113112017 (02-2014)
, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
YEAR
- 6. LER NUMBER I
SEQUENTIAL I REV NUMBER NO.
2016 001 00
- 3. PAGE 2
OF 3
On January 5, 2016, at 10:58 p.m. CST, with the plant operating at 100 percent power, the main control room alarm indicating high pressw:e in the auxiliary building [NF] actuated. Operators confirmed that the building pressure was out of specification. Secondary containment was declared inoperable, and the Division 2 standby gas treatment system [BH] was started. This action restored building pressure to the acceptable range, and secondary containment was declared operable at 12:27 a.m. on January 6. This condition is being reported in accordance wi,th 10 CFR 50.73(a)(2)(iv)(A) as an event that caused the secondary containment to be potentially incapable of performing its safety function.
I BACKGROUND The normal auxiliary building ventilation system [VF] is non-safety related, and comprises two 100 percent capacity supply fans, two 100 percent capacity exhaust fans, and the associated ductwork, dampers, and controls. A supply fan operates continuously, drawing air from outside and distributing it throughout the building. The supply fan discharge*dampers modulate automatically to maintain air flow at a nominal 10,000 standard cubic feet per minute. An exhaust fan continuously draws air from the building and expels it outside. The arrangement of the flow path through the building general equipment areas and pump rooms is balanced such that the system acts to maintain the building at a negative pressure.
During design-basis accident conditions, the auxiliary building is maintained at negative pressure by the standby gas treatment system.
That is a safety-related system that actuates automatically in response to certain plant parameters.
INVESTIGATION and DvIMEDIATE ACTIONS
. The normal ventilation system was inspected, and it was determined that a combination of degraded components caused the condition:
- Seals on the exhaust fan (**FAN**) discharge damper (**BDI\\1P**) vanes were degraded. This allowed air to flow backwards through the idle exhaust fan, causing the total exhaust outflow to decrease and building pressure to increase:
- The flow controller for the supply fan modulating dampers (**CDI\\1P**) had failed, allowing excessive air flow that caused building pressure to increase.
In order to restore the normal ventilation system to service, the troubleshooting plan for this condition temporarily altered the operating configuration of the system to close the suction damper on the i4le exhaust fan. This prevents backflow through the idle fan, allowing the system to control building pressure within the required operating range.
CORRECTIVE ACTION TO PREVENT RECURRENCE Corrective maintenance is being planned to (1) replace the seals in the exhaust fan discharge dampers to eliminate the backflow path, and (2) calibrate the supply fan modulating damper control circuit.
PREVIOUS OCCURRENCE EVALUATION No similar events have been reported by River Bend Station in the last three years.
SAFETY SIGNIFICANCE
The River Bend Updated Safety Analysis Report describes the sequence of events postulated to occur following a loss of coolant accident (LOCA). Part of that analysis is a projection of the maximum radiation dose received by a person at the site boundary. The LOCA dose calculation assumes that the standby gas treatment system is initiated 20 minutes into the event, and that secondary containment is at the required negative pressure within 30 minutes, such that filtration may be credited. As such, the safety function of secondary containment is maintained as long as the auxiliary building pressure is capable of being established within 30 minutes of the onset of the event. Since the ability of the standby gas treatment system to control building pressure within specifications under accident conditions was* demonstrated in the recovery from this condition, no loss of the safety function of secondary containment actually occurred. This event was, thus, of minimal significance to the health and safety of the public.
(NOTE: Energy Industry Identification System component function identifier and system name of each component or system referred to in the LER are annotated as (**XX**) and [XX], respectively.)
REPORTED CONDITION
, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
YEAR
- 6. LER NUMBER I
SEQUENTIAL I REV NUMBER NO.
2016 001 00
- 3. PAGE 2
OF 3
On January 5, 2016, at 10:58 p.m. CST, with the plant operating at 100 percent power, the main control room alarm indicating high pressw:e in the auxiliary building [NF] actuated. Operators confirmed that the building pressure was out of specification. Secondary containment was declared inoperable, and the Division 2 standby gas treatment system [BH] was started. This action restored building pressure to the acceptable range, and secondary containment was declared operable at 12:27 a.m. on January 6. This condition is being reported in accordance wi,th 10 CFR 50.73(a)(2)(iv)(A) as an event that caused the secondary containment to be potentially incapable of performing its safety function.
I BACKGROUND The normal auxiliary building ventilation system [VF] is non-safety related, and comprises two 100 percent capacity supply fans, two 100 percent capacity exhaust fans, and the associated ductwork, dampers, and controls. A supply fan operates continuously, drawing air from outside and distributing it throughout the building. The supply fan discharge*dampers modulate automatically to maintain air flow at a nominal 10,000 standard cubic feet per minute. An exhaust fan continuously draws air from the building and expels it outside. The arrangement of the flow path through the building general equipment areas and pump rooms is balanced such that the system acts to maintain the building at a negative pressure.
During design-basis accident conditions, the auxiliary building is maintained at negative pressure by the standby gas treatment system.
That is a safety-related system that actuates automatically in response to certain plant parameters.
INVESTIGATION and DvIMEDIATE ACTIONS
. The normal ventilation system was inspected, and it was determined that a combination of degraded components caused the condition:
- Seals on the exhaust fan (**FAN**) discharge damper (**BDI\\1P**) vanes were degraded. This allowed air to flow backwards through the idle exhaust fan, causing the total exhaust outflow to decrease and building pressure to increase:
- The flow controller for the supply fan modulating dampers (**CDI\\1P**) had failed, allowing excessive air flow that caused building pressure to increase.
In order to restore the normal ventilation system to service, the troubleshooting plan for this condition temporarily altered the operating configuration of the system to close the suction damper on the i4le exhaust fan. This prevents backflow through the idle fan, allowing the system to control building pressure within the required operating range.
CORRECTIVE ACTION TO PREVENT RECURRENCE Corrective maintenance is being planned to (1) replace the seals in the exhaust fan discharge dampers to eliminate the backflow path, and (2) calibrate the supply fan modulating damper control circuit.
PREVIOUS OCCURRENCE EVALUATION No similar events have been reported by River Bend Station in the last three years.
SAFETY SIGNIFICANCE
The River Bend Updated Safety Analysis Report describes the sequence of events postulated to occur following a loss of coolant accident (LOCA). Part of that analysis is a projection of the maximum radiation dose received by a person at the site boundary. The LOCA dose calculation assumes that the standby gas treatment system is initiated 20 minutes into the event, and that secondary containment is at the required negative pressure within 30 minutes, such that filtration may be credited. As such, the safety function of secondary containment is maintained as long as the auxiliary building pressure is capable of being established within 30 minutes of the onset of the event. Since the ability of the standby gas treatment system to control building pressure within specifications under accident conditions was* demonstrated in the recovery from this condition, no loss of the safety function of secondary containment actually occurred. This event was, thus, of minimal significance to the health and safety of the public.
(NOTE: Energy Industry Identification System component function identifier and system name of each component or system referred to in the LER are annotated as (**XX**) and [XX], respectively.)