05000244/LER-2021-002, Valid Auxiliary Feedwater System Actuation on Lowered Steam Generator Level Due to Failure to Control Main Feed Water Flow and Delay in Closing Main Steam Isolation Valves
| ML21336A082 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 12/02/2021 |
| From: | Swift P Exelon Generation Co LLC |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2021-002-00 | |
| Download: ML21336A082 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 2442021002R00 - NRC Website | |
text
Paul M. Swift Site Vice Pres ident
R.E. Ginna Nuclear Power P lant 1503 Lake Rd.
Exelon Generation Ontario. NY 14519
315-791-5200 Office www.exeloncorp.com
December 2, 2021
U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
RE. Ginna Nuclear Power Plant Renewed Facility Operating License No. DPR-18 NRC Docket No. 50-244
Subject: LER 2021-002, Valid Auxiliary Feedwater System Actuation on Lowered Steam Generator Level due to Failure to Control Main Feed Water Flow and Delay in Closing Main Steam Isolation Valves
The attached Licensee Event Report (LER) 2021-002 is submitted under the provisions of NUREG-1022, Event Reporting Guidelines. There are no new commitments contained in this submittal. This submittal is for revision O of the LER.
Should you have any questions regarding th is submittal, please contact Chris Bradshaw at (315) 791-3246.
Sincerely,
~ ~ ~
Paul Swift
Attachment: LER 2021-002
cc : NRC Regional Administrator, Region 1 NRC Project Manager, Ginna NRC Resident Inspector, Ginna (e-mail)
Attachment
LER 2021-002, Revision 0
Abstract
On 10/4/21 during a shutdown for the 2021 Refueling Outage, following the planned reactor trip, Reactor Coolant Average Temperature (Tavg) lowered due to overfeeding the 'B' Steam Generator (S/G). To maintain Tavg, feed to the S/Gs was minimized. During the cooldown, 'A' S/G lowered and a valid actuation of the Auxiliary Feedwater (AFW) System occurred. The valid actuation of the AFW System is reportable per 10CFR50.72(b)(3)(iv)(A) and 10CFR50.73.(a)(2)(iv)(A).
No equipment position changes were noted as a result of the actuation, which is the expected response for the given plant conditions. The causes of this event were Operators failed to control Main Feedwater Flow following Reactor Trip resulting in a cooldown and did not promptly close the Main Steam Isolation Valves (MSIVs).
Corrective actions include procedures revisions to include specific guidance on FRV Bypass Valve and MSIV closure. Training will be conducted to address gaps in Tavg control following Reactor Trip.
I. PRE-EVENT PLANT CONDITIONS
At the time of the event, the plant was in MODE 3 following a planned manual reactor trip during a plant shutdown.
II. DESCRIPTION OF EVENT
A. EVENT
On 10/4/21 during a shutdown for the 2021 Refueling Outage, following the planned reactor trip, Reactor Coolant Average Temperature (Tavg) lowered due to overfeeding the 'B' Steam Generator (S/G). To maintain Tavg, feed to the S/Gs was minimized. During the cooldown, 'A' S/G lowered and resulted in an unplanned entry into LCO 3.4.5, Reactor Coolant System (RCS) Loops - MODES 1, </=8.5% rated thermal power (RTP), 2, and 3.
As S/G Level lowered, a valid Auxiliary Feedwater (AFW) actuation signal was generated. The 'A' Train AFW System was already in service and aligned when the actuation signal was generated. No equipment position changes were noted as a result of the actuation, which is the expected response for the given plant conditions. Prior to the reactor trip, the 'B' Feedwater Regulating Valve (FRV) Bypass Valve was placed in manual. Following the reactor trip, the 'B' FRV Bypass Valve did not close. When in manual, FRVs and FRV Bypass Valves will not automatically close on a reactor trip. B S/G level rose to a maximum of 63% over 8 minutes prior to the FRV Bypass Valve being manually closed by Operators.
Feedwater was secured to the S/Gs; however, Tavg lowered and stabilized at approximately 535 degrees. During this time the B Main Feedwater Pump was secured so AFW flow could be established and was subsequently minimized to reduce the cooldown effects on Tavg. A S/G level lowered to 6% and the Main Steam Isolation Valves (MSIVs) were closed to limit secondary side steam flows and raise Tavg. After closing the MSIVs, Tavg stabilized at approximately 547 degrees and A S/G level was restored to approximately 52%.
B. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT:
None
C. DATES AND APPROXIMATE TIMES OF MAJOR OCCURENCES:
0010 10/04/2021 Manual Reactor Trip 0031 10/04/2021 AFW System actuation signal due to low 'A' S/G water level 0032 10/04/2021 'A' RCS Loop declared inoperable due to low 'A' S/G water level 0041 10/04/2021 Main Steam Isolation Valves Closed 0046 10/04/2021 'A' RCS Loop declared Operable
D. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED
'A' RCS Loop declared inoperable due to low water level in the 'A' S/G in MODE 3
E. METHOD OF DISCOVERY
Self-revealing: At 0031 on 10/04/2021 in MODE 3, S/G 'A' Narrow Range Water Level went low causing an AFW System actuation signal. AFW was in service at the time of the event providing decay heat removal.
F. SAFETY SYSTEM RESPONSES:
The 'A' Train AFW System was already in service and aligned when the actuation signal was generated. No equipment position changes were noted as a result of the actuation, which is the expected response for the given plant conditions.
III. CAUSE OF EVENT
Operators did not close the 'B' Main Feedwater Regulating Valve Bypass Valve following Reactor Trip resulting in a cooldown and did not promptly close the Main Steam Isolation Valves
IV. ASSESSMENT OF THE SAFETY CONSEQUENCES OF THE EVENT:
In Mode 1 </= 8.5% Power and Mode 2, the Reactor Coolant Pumps (RCP) are used to provide forced circulation of the reactor coolant to ensure mixing of the coolant for proper boration and chemistry control and to remove the limited amount of reactor heat. In MODE 3, the RCPs are used to provide forced circulation for heat removal during heatup and cooldown.
The Mode 1 </= 8.5% Power, Mode 2, and Mode 3 reactor and decay heat removal requirements are low enough that a single RCS loop with one RCP running is sufficient to remove core decay heat. However, two RCS loops are required to be Operable to ensure redundant capability for decay heat removal.
Operator action restored the 'A' RCS Loop to Operable within 14 minutes. RCS decay heat removal was not challenged during the event. As such this event was not significant with respect to the health and safety of the public.
V. CORRECTIVE ACTIONS
Operations guidance for closure of both the Main Feedwater Regulating Valves and Main Steam Isolation Valves will be added to the shutdown procedures. Training solutions will be used to address the gaps in temperature control following Reactor Trip.
VI. ADDITIONAL INFORMATION
None
A. FAILED COMPONENTS:
None
B. PREVIOUS LERs ON SIMILAR EVENTS:
A LER historical search was conducted and no similar LER events were identified.
C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO IN THIS LER:
COMPONENT - Flow Control Valve
IEEE 803 FUNCTION NUMBER - FCV
IEEE 805 SYSTEM IDENTIFICATION - SJ