05000458/LER-2017-002, Regarding Loss of Safety Function of Onsite Electrical Distribution Due to Malfunction of Control Building HVAC System
| ML17116A297 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 04/18/2017 |
| From: | Maguire W Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-47749 LER 17-002-00 | |
| Download: ML17116A297 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 4582017002R00 - NRC Website | |
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RBG-47749 April 18, 2017 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
RBF1-17-0041 Licensee Event Report 50-458 I 2017-002-00 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47
Dear Sir or Madam:
Entergy Operations, Inc.
River Bend Station 5485 U.S. Highway 61 N St. Francisville, LA 70775 Tel 225-381-4157 William F. Maguire Site Vice President 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. Tim Schenk at 225-381-4177.
Sincerely, WFM/dhw Enclosure cc:
U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Blvd.
Arlington, TX 76011-4511 NRC Sr. Resident Inspector P. 0. Box 1050 St. Francisville, LA 70775 INPO (via ICES reporting)
Licensee Event Report 50-458 I 2017-002-00 April 18, 2017 RBG-47749 Page 2 of 2
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Central Records Clerk Public Utility 9ommission 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
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NRCFORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017) httg://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/!3[)
the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
~.PAGE River Bend,Station - Unit 1 05000-458 1 OF4
- 4. TITLE I n~~ of <"'-~~+~. F11nr.tion of nn~iti:1 Fl-*..... 1 ni~trin11tinn n11i:1 tn IJl~lf1 mr.tinn nf I.runrrn R11ilrlinn HVAr. C'.--t;:;1
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR MONTH DAY YEAR NUMBER NO.
05000 FACILITY NAME DOCKET NUMBER 02 1*a 2017 2017 002 00 04 18 2017 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: Check all that aoplv) 5 D 20.2201 (b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2201 (d)
D 20.2203(a)(3)(ii) 181 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)(1)
D 20.2203(a)(4)
D so.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A) 181 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D so.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71 (a)(S) 0 D 20.2203(a)(2)(iv)
- o so.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1)
D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
D 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in NRG Form 366A -
- 12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT liLEPHONE NUMBER (Include Area Code) ff"im Schenk, Manaaer - Reaulatorv Assurance
~25-381-4177 _/
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE I
FACTURER TOEPIX FACTURER TOEPIX (see text)
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
~NO SUBMISSION DATE
!ABSTRACT (Umit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On February 18, 2017, at 3:37 p.m. CST, while a refueling outage was in progress, the operators were shifting subsystems of the main control building ventilation system. The Division 2 "B" chiller had been in service, and it was intended to start
~he Division 1 "C" chiller to facilitate the outage work schedule. After the swap, operators noted that the air flow was abnormally low, and within approximately four minutes, the "C" chiller tripped. The operators were unsuccessful in attempts to restore the Division 2 subsystem to service,'and the abnormal operating procedures for the loss of control building ventilation were then implemented. The electrical distribution subsystems in the control building were declared inoperable due to the loss of the ventilation system. This condition is being reported in accordance with 10 CFR S0.73(a)(2)(v)(A). As described in the causal analysis, a circuit breaker manufacturing defect that violated the single
~ailure requirements of 10 CFR 50 Appendix A, General Design Criteria, was discovered. This is being reported in accordance with 10 CFR SO. 73(a)(2)(ii)(B) as an unanalyzed condition. During the restoration of the ventilation system, main control room temperature increased from approximately 73F to 81F as recorded in the operator's logs. No high emperature alarms from the electrical equipment rooms actuated. Thus, this event was of minimal significance to the health and safety of the public.
NRC FORM 366 (04-2017)
- J REPORTED CONDITION SEQUENTIAL I
NUMBER 002 REV NO.
00 On February 18, 2017, at 3:37 p.m. CST, while a refueling outage was in progress, the operators were shifting subsystems of the main control building ventilation system (VI]. The Division 2 "B" chiller (**CHU**) had been in service, and it was intended to start the Division 1 "C" chiller to facilitate the outage work schedule. After the swap, operators noted that the air flow was abnormally low, and within approximately four minutes, the "C" chiller tripped. The operators attempted to restore the Division 2 subsystem to service, but tliey were unsuccessful, and the abnormal operating procedures for the loss of control building ventilation were then implemented. The electrical distribution subsystems [ED] in the control building were declared inoperable due tot.he loss of the ventilation system. This condition is being reported in' accordance with 10 CFR 50.73(a)(2)(v).
As described in the causal analysis below, a circuit breaker (**BKR**) manufacturing defect that violated the single failure requirements of 10 CFR 50 Appendix A, General Design Criteria, was discovered. This is being reported in accordance with 10 CFR 50.73(a)(2)(ii)(B) as an unanalyzed condition.
BACKGROUND Two 100-percent capacity chillers provide cooling to each ventilation system sub-loop, each of which provides cooling, heating, ventilation, pressurization, and smoke removal for several areas within the building. The ventilation system comprises two independent, redundant trains of components and subsystems either of which supports the safety "unction of providing a controlled environment in the main control room (MCR) and the environmental requirements of
,he safety-related electrical equipment in the building. Each control building ventilation subsystem is supported by the respective safety-related emergency diesel generator.
The control building chilled water system (HVK) provides chilled water to the cooling coils in three separate air handlers within each division. The air handling system (HVC) removes the heat generated within the MCR and electrical equipment rooms. Air handlers serve the MCR, standby switchgear rooms, battery charger rooms, inverter rooms, and chiller rooms. Each air handler serves both trains of their assigned areas (i.e., both ~he Division 1 and 2 standby switchgear rooms cooling may be fully served by the air handler in either train). In the event of a total ventilation system "ailure, the current Technical Specification action to restore the ventilation system is bounded by the 2-hour completion imes for DC sources IMMEDIATE ACTIONS In troubleshooting the abnormally low air flow with the Division 1 subsystem in service, it was discovered that air flow control dampers in the system had not operated correctly, which diverted air flow from the operating air. handler.
Operators implemented abnormal operating procedures to provide alternate means of cooling to the affected areas and monitored the areas for temperature rise. Page 2 of 4
J (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 r""""'**
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LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NU REG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rrn/doc-collections/nuregs/staff/sr1022/r3/)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LER NUMBER YEAR River Bend Station - Unit 1 05000-458 2017 SEQUENTIAL NUMBER 002 REV NO.
00 Under temporary configuration controls, operators closed the air dampers by removing their control power fuses, and restored the normal air flow path. The Division 1 "C" HVI< chiller was successfully started at 5:37 p.m. CST. At the onset of the event, MCR temperatures were approximately 73F. The highest temperature recorded before the restoration of the cooling system was approximately 81F.
CAUSAL ANAL VSIS The failure of the air handler dampers to close correctly was traced to an internal failure in the 480-volt circuit breaker for the Division 2 switchgear. room air handling unit. It was found that a mechanism operated cell (MOC) switch positioner linkage screw had fallen out, causing the logic circuit for the damper controls to fail to actuate. The screw in the MOC linkage failed because it was shorter than required by the circuit breaker design (i.e., one-quarter inch in length versus three-eighths inch).
"Single failure" is defined by 10 CFR 50 Appendix A, General Design Criteria for Nuclear Power Plants. A single failure means an occurrence which results in the loss of capability of a component to perform its intended safety functions.
Multiple failures resulting from a single occurrence are considered to be a single failure. The control building ventilation system is required to be designed against an assumed single failure. Failure of the screw caused the failure of both the Division 1 and Division 2 ventilation subsystems.
It is possible that the MOC screw may have been loose since the last time the breaker was successfully closed on January
- 31. However, its actual failure can be pinpointed only to the opening of the breaker the on date of the event.
CORRECTIVE ACTIONS TO PREVENT RECURRENCE
~II safety-related, electrically operated Masterpact NT breakers were categorized with regard to the design of their MOC logic circuit switches. Those breakers with the potential to cause the mis-operation of other components by the same failure mechanism of the February 18 event were inspected to verify that correct screws and lock washers were installed.
The remaining population of Masterpact NT breakers will be inspected.
Design changes were implemented to alter the damper logic circuits for the main control room and electrical equipment area air handlers to eliminate the cause of this event as a potential failure mode for damper actuation.
Technical and quality requirements for receipt inspections of Masterpact circuit breakers will be revised to specifically examine the MOC hardware. Similar breakers already in the warehouse will be inspected. These actions are being tracked in the corrective action program.
EVALUATION OF PRIOR OCCURRENCES No events reported in the last three years by RBS have occurred as a result of the breaker failure mode discovered in this evaluation. Page 3 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020
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LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/readinq-rm/doc-collections/nuregs/staff/sr1022/r31)
, the NRC may not conduct or sponsor, and a person is not required to. respond to, the information collection.
- 3. LEA NUMBER River Bend Station - Unit 1 OS000-458 YEAR 2017
SAFETY SIGNIFICANCE
SEQUENTIAL NUMBER 002 REV NO.
00
!The normal operating upper temperature limit for the main control room and electrical equipment rooms served by the HVC system is 104F. During the restoration of the ventilation system, main control room temperature increased from approximately 73F to 81F as recorded in the operator's logs. The electrical distribution equipment rooms are served by remote temperature monitors, and none of those associated alarms actuated in the MCR during the time that the rventilation system was out of service. Thus, this event was 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.) Page 4 of 4