05000387/LER-2019-001-01, Loss of Both Control Structure Chillers Due to Misaligned Breaker Stab
| ML19345F675 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 12/11/2019 |
| From: | Cimorelli K Susquehanna, Talen Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| PLA-7827 LER 2019-001-01 | |
| Download: ML19345F675 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3872019001R01 - NRC Website | |
text
Kevin Cimorelli Site Vice President Attn: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 Susquehanna Nuclear, LLC 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.3795 Fax 570.542.1504 Kevin.Cimorelli@TalenEnergy.com SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-387(388)/2019-001-01 UNIT 1 LICENSE NO. NPF-14 UNIT 2 LICENSE NO. NPF-22 PLA-7827 TALEN~
ENERGY 10 CFR 50.73 Docket No. 50-387 and 50-388 Attached is a supplement to Licensee Event Report (LER) 50-387(388)/2019-001-00. The LER reported a condition in which there was a loss of both the A and B Control Structure Chillers.
This condition was determined to be reportable in accordance with 10 CFR 50.73(a)(2)(v)(A),
(B), (C), and (D) as a condition that could have prevented the fulfillment of a safety function.
There were no actual consequences to the health and safety of the public as a result of this event.
This letter contains no new or revised regulatory commitments.
K. Cimorelli Attachment: LER 50-387(388)/2019-001-01 Copy:
NRC Region I Ms. L. H. Micewski, NRC Sr. Resident Inspector Ms. S. Goetz, NRC Project Manager Mr. M. Shields, PA DEPIBRP 12/11/2019
NRC FORM 366 (04-2018)
NRC FORM 366 (04-2018)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
(See Page 2 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 1. Facility Name Susquehanna Steam Electric Station Unit 1
- 2. Docket Number 05000387
- 3. Page 1 OF 3
- 4. Title Loss of Both Control Structure Chillers due to Misaligned Breaker Stab
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Month Day Year Year Sequential Number Rev No.
Month Day Year Facility Name Susquehanna Steam Electric Station Unit 2 Docket Number 05000388 05 22 2019 2019 001 01 12 11 2019 Facility Name Docket Number 05000
- 9. Operating Mode 1
)
No Abstract (Limit to 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)
On May 22, 2019, at 0240, the A Control Structure (CS) Chiller tripped due to a loss of power to Motor Control Center (MCC) 0B136. At the time of the trip, the B CS Chiller was out of service for planned maintenance on the Emergency Service Water (ESW) System. The CS Chillers are required to be operable by Technical Specifications (TS) Limiting Conditions for Operation (LCOs) 3.7.3, Control Room Emergency Outside Air Supply (CREOAS) System and 3.7.4, Control Room Floor Cooling System. The CREOAS and Control Room Floor Cooling systems provide cooling and ventilation to various safety-related loads including the control room, computer room, relay rooms, and emergency switchgear rooms. The loss of both chillers required entry in LCOs 3.7.3, 3.7.4, and 3.0.3, thereby requiring the commencement of a dual unit shutdown. As a result, this event was reported in accordance with 10 CFR 50.72(b)(3)(v) as a condition which could have prevented the fulfillment of a safety function and 10 CFR 50.72(b)(2)(i) for the initiation of a plant shutdown required by TS. The power reduction was halted upon restoration of the A CS Chiller. The condition was also determined to be reportable in accordance with 10 CFR 50.73(a)(2)(v) as a condition that could have prevented the fulfillment of a safety function.
The direct cause was determined to be inadequate engagement of cubicle stabs. The root cause was determined to be vendor design differences in cubicle stab assemblies introduced during replacement of original plant equipment. Corrective actions include removing the misaligned breaker stab from service and de-energizing, cleaning, and inspecting MCC 0B136.
There were no actual safety consequences associated with the condition.
CONDITIONS PRIOR TO EVENT
Unit 1 - Mode 1, approximately 100 percent Rated Thermal Power Unit 2 - Mode 1, approximately 100 percent Rated Thermal Power At the time of the event, Division II of the ESW System was out of service for planned maintenance. This rendered the B CS Chiller inoperable.
EVENT DESCRIPTION
On May 19, 2019, at approximately 2230, Division II of the ESW system was removed from service for planned maintenance. This rendered the B CS Chiller inoperable. Subsequently, on May 22, 2019, at 0240, the A CS Chiller [EIIS Code: VI] tripped due to a loss of power to MCC 0B136 [EIIS Code/Component Code:
ED/MCC]. Susquehanna Steam Electric Station TS LCO 3.7.3, Control Room Emergency Outside Air Supply (CREOAS) System, and LCO 3.7.4, Control Room Floor Cooling System, require entry into LCO 3.0.3 upon loss of both CS Chillers. At 0256, operators declared the CREOAS and Control Room Floor Cooling Systems inoperable and entered LCO 3.0.3. Unit shutdown commenced at 0340 and 0350 for Units 2 and 1, respectively.
The MCC 0B136-044 A-phase cubicle stab [Component Code: 52] was not engaged correctly on the vertical bus resulting in arcing conditions that created the conditions for a fault on the MCC bus. The bus was tested with satisfactory results and was reenergized. Power was restored to MCC 0B136 at 0901 on May 22, LCO 3.0.3 was exited, and the power reductions were halted.
The CS Chillers are required to be operable to support operation of the CREOAS and Control Room Floor Cooling systems. The CREOAS and Control Room Floor Cooling systems provide cooling and ventilation to various safety-related loads including the control room, computer room, relay rooms, and emergency switchgear rooms. As a result, the condition was determined to be reportable in accordance with 10 CFR 50.73(a)(2)(v) as a condition that could have prevented the fulfillment of a safety function of systems that are required to; (A) shut down the reactor and maintain it in a safe shutdown condition; (B) remove residual heat; (C) control the release of radioactive material; or (D) mitigate the consequences of an accident.
CAUSE OF EVENT
The direct cause of the event was determined to be that the 0B136-044 A-phase primary disconnect cubicle stab was not engaged on both sides of the bus bar. The root cause of the event was determined to be vendor design differences between the previous Cutler Hammer and replacement Nuclear Logistics Industries (NLI) assemblies affected the self-aligning capability which ensure cubicle stab engagement on the bus bar. On October 4, 2019, in accordance with 10 CFR 21, AZZ Nuclear notified the NRC of a Page 3 of 3 (04-2018)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Susquehanna Steam Electric Station Unit 1 05000-387 YEAR SEQUENTIAL NUMBER REV NO.
2019 001 01 deviation affecting F10 series MCC cubicles supplied by NLI with the current design of stab assembly P/N:
5600-SA3-1.
ANALYSIS/SAFETY SIGNIFICANCE
Due to the concurrent loss of the A and B CS Chillers, neither division of the Control Room Floor Cooling and CREOAS systems were available to perform their safety functions in the event of a design basis accident (DBA) (e.g., Loss of Coolant Accident Coincident with a Loss of Offsite Power). Any operator action to restore either CS Chiller would have required significant time and, therefore, would not have supported the safety function of the systems.
Based on engineering analysis, this event will be counted as a safety system functional failure under the NRC Reactor Oversight Process Performance Indicator.
CORRECTIVE ACTIONS
The load on Breaker 44 from MCC 0B136 was moved to a different breaker location within MCC 0B136.
Additional corrective actions will include de-energizing, cleaning, and inspecting the entirety of MCC 0B136; and revising the procedures for NLI 480 VAC cubicle installation and maintenance to require verification of proper stab alignment.
COMPONENT FAILURE INFORMATION
Component Identification - 0B136044 Component Name - Control Structure Passenger Elevator Disconnect Switch 0DS108 Breaker Manufacturer - Nuclear Logistics Industries Model Number - F10 MCC Cubicle Breaker Rating - 480 VAC
PREVIOUS OCCURRENCES
LER 50-388(387)/2015-015-00, Loss of Safety Function due to Inoperability of Both Trains of the Control Room Emergency Outside Air Supply (CREOAS) System, dated May 5, 2016 LER 50-387(388)/2014-009-00, Loss of Both Trains of Control Structure Chilled Water during Application of Clearance Order, dated August 11, 2014 LER 50-387(388)/2014-008-00, Loss of Both Trains of Control Structure Chilled Water due to Personnel Error, dated August 11, 2014