05000244/LER-2023-002, Overtemperature Delta Temperature Reactor Protection System and Auxiliary Feedwater System Actuations on Due to 100% Load Rejection Caused by Turbine Overspeed Circuit Card Failure
| ML23312A176 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 11/08/2023 |
| From: | Blankenship J Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LER 2023-002-00 | |
| Download: ML23312A176 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2442023002R00 - NRC Website | |
text
James 0. Blankenship Sile Vice President R E G1nna Nuc lear Power Plant 1503 Lake Rd Ontario. NY 14519 315* 791-5200 Office 1ames blankensh1p,a constellat,on com Constellation www constellat,on.com
November 8, 2023
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 2023-002, Overtemperature Delta Temperature reactor protection system and auxiliary feedwater system actuations on due to 100% load rejection caused by turbine overspeed circuit card failure (parts quality initiative inspection bypassed).
The attached Licensee Event Report (LER) 2023-002 is submitted in accordance with 10 CFR 50.73 under the provisions of NUREG-1022, Revision 3, Event Reporting Guidelines 10 CFR 50.72 and 50.73. There are no new commitments contained in this submittal. This submittal is for Revision O of the LER.
Should you have any questions regarding this submittal, please contact Justin Knowles at (315) 791-3393.
Sincerely,
Attachment: LER 2023-002, Revision 0
cc: NRC Regional Administrator, Region 1 NRC Project Manager, Ginna NRC Resident Inspector, Ginna (e-mail)
Attachment
LER 2023- 002, Revision 0
Abstract
On 9/9/2023 at 1143, Ginna Unit 1 tripped from a 100% power steadystate condition. No plant evolutions were in progress at the time. Operators initially noticed vibration coming from the turbine building, indication of open steam dump valves, and control rods inserting. All turbine control and intercept valves had closed causing a 100% load rejection transient. The reactor tripped approximately 7 seconds into the transient on Overtemperature Delta Temperature (protection from departure from nucleate boiling). Closure of both the control and intercept valves indicates that the auxiliary governor solenoids on the governor pedestal actuated upon a signal from the Overspeed Protection Circuit (OPC). Troubleshooting revealed that OPC circuitry was actuating while at / below rated input speed (1,800 RPM). Two Root Causes were identified: RC1: failure of Analog Comparator 8, EHCC1/1A08R, and subcomponent R2C (Resistor), and RC2: failure by personnel to implement the Parts Quality Initiative process which allowed material not from inventory to be installed in the plant. The failed card was replaced with a stock spare, and system tests were then satisfactory. Corrective actions for RC2 have been identified and are ongoing.
I. PRE-EVENT PLANT CONDITIONS
At the time of the component failure, the plant was in MODE 1 at 100% rated thermal power.
II. DESCRIPTION OF EVENT
A. EVENT
On 9/9/2023 at 1143, Ginna Unit 1 tripped from a 100% power steady state condition. No plant evolutions were in progress at the time. Operators initially noticed vibration / noise coming from the turbine building, indication of steam dump valves being open, and control rods inserting. All the turbine control and intercept valves had closed resulting in a 100% load rejection transient. The reactor tripped approximately 7 seconds into the transient. The first out annunciator was for an Overtemperature Delta Temperature (OTDT) Trip (protection from departure from nucleate boiling).
As expected for a complete load rejection, the Power Operated Relief Valves (PORVs) opened to mitigate the pressure transient prior to the setpoint for reactor trip being reached. The Auxiliary Feedwater (AFW) pumps started on an Anticipated Transient Without Scram (ATWS) Mitigation System Actuation Circuitry (AMSAC) signal. Following the trip and entry into MODE 3, Reactor Coolant System (RCS) temperature lowered (later identified to be due to seat leakage on some of the steam dump valves). The Operators stabilized the plant in by closing the Main Steam Isolation Valves and then controlled Tavg using Atmospheric Relief Valves (ARVs).
Closure of both the control and intercept valves indicates that the auxiliary governor solenoids (201AG and 202AG) on the governor pedestal actuated upon a signal from the Overspeed Protection Circuit (OPC). Troubleshooting revealed that OPC circuitry was actuating while at / below rated input speed (1,800 RPM). Two Root Causes (RC) were identified:
RC1 - an operational equipment failure of component Analog Comparator 8, EHCC1/1A08R, and subcomponent R2C (Resistor), and RC2 - failure by personnel to implement the Parts Quality Initiative (PQI) process which allowed material not from inventory to be installed in the plant. The failed card was replaced with a stock spare, and system tests were then satisfactory. Corrective actions for RC2 have been identified and are ongoing.
B. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT:
No other Systems, Structures, or Components (SSCs) were inoperable at the start of the event and contributed to the event.
C. DATES AND APPROXIMATE TIMES OF MAJOR OCCURENCES:
09/09/2023 @ 1143:18 (MODE 1) All turbine control and intercept valves close.
09/09/2023 @ 1143:24 (MODE 1) PORVs open to mitigate pressure rise.
09/09/2023 @ 1143:25 (MODE 1) Reactor trip on OTDT 09/09/2023 @ 1143:59 (MODE 3) Auxiliary Feedwater Pumps start on AMSAC 09/09/2023 @ 1154 (MODE 3) Closed Main Steam Isolation Valves; stabilized Tavg with ARVs 09/11/2023 @ 0549 The plant has entered MODE 2.
09/11/2023 @ 1540 The plant has entered MODE 1.
D. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED
None
E. METHOD OF DISCOVERY
Self-revealing: while at a 100% power steadystate condition with no plant evolutions in progress, Operators initially noticed vibration / noise coming from the turbine building, indication of steam dump valves being open, and control rods inserting. Within approximately 7 seconds, the reactor tripped on OTDT.
F. SAFETY SYSTEM RESPONSES:
During the transient, prior to the reactor trip, Reactor Coolant System (RCS) pressure reached the Power Operated Relief Valve (PORV) actuation setpoint. The PORVs opened to mitigate the pressure increase. The reactor trip on OTDT was not complex, and all systems responded normally post-trip. The Auxiliary Feedwater (AFW) System actuated as expected based on a signal from the Anticipated Transient Without Scram (ATWS) Mitigation System Actuation Circuitry (AMSAC)).
III. CAUSE OF EVENT
Root Cause 1 is the operational equipment failure of the Analog Comparator 8 card in the 1A08R location (EHCC1/1A08R) due to failure of a subcomponent, resistor R2C.
Root Cause 2 is the failure by personnel to implement the Parts Quality Initiative (PQI) process which allowed material not from inventory to be installed in the plant.
IV. ASSESSMENT OF THE SAFETY CONSEQUENCES OF THE EVENT:
Per UFSAR 15.0.8.2, this reactor trip falls under Condition II - Faults of Moderate Frequency. The plant was capable of being returned to operation after corrective action. As there was no loss of any barrier to the escape of radioactive products, there was no release of radioactive materials in effluents to unrestricted areas (in conformance with 10 CFR 20, Standards for Protection Against Radiation). The event did not propagate to a more serious incident of the Condition III or Condition IV type.
Due to the Reactor Protection System (RPS) actuation while critical, this event was reportable as a four-hour, non-emergency notification per 10 CFR 50.72(b)(2)(iv)(B) and an eight-hour non-emergency notification per 10 CFR 50.72(b)
(3)(iv)(A) for a valid specified system actuation (AFW). The event is 60-day reportable under 10 CFR 50.73(a)(2)(iv)(A) for actuation of both the RPS and the AFW system. There was no violation of Technical Specifications.
As such, this event is not considered to have had any significant effect on the health and safety of the public.
V. CORRECTIVE ACTIONS
For the equipment root cause, the Analog Comparator 8 card at 1A08R was replaced with a stock spare and the system was tested satisfactory.
An extent of condition was performed, limited to the failed resistor (R2C 10k ) on the EHCC1/1A08R card. The resistor that failed was a precision wire wound resistor (model SX158D manufactured by Precision Resistor Company (PRC)) and is utilized on multiple SPV card locations within the EH control cabinet. These other card locations are susceptible to the same condition and failure mode. Additionally, precision wire wound resistors may be utilized in other electronic systems within the plant which contain SPV circuit cards. Actions were created to address locations within the EHC cabinet and other systems which may be susceptible to the same condition.
For the human performance root cause, proper procedural guidance exists but was not implemented before this event.
Corrective actions focus on compliance / extent of condition and include:
- Completing PQI for all stock and uncontrolled (not from inventory) EH cards.
- In G1R45 (next RFO), performing PQI on all installed cards and replacing all degraded resistors.
- Adding PQI to all card refurbishment strategies, both site-and vendor-performed.
- Ensuring that per SM-AA-4003 critical spares are properly identified, as this identification drives inspections per the PQI.
VI. ADDITIONAL INFORMATION
This failure was documented in Corrective Action Program Issue Report (IR) 04701420.
A. FAILED COMPONENTS:
Analog Comparator 8 card in the 1A08R location (EHCC1/1A08R) in the turbine Overspeed Protection Circuit.
B. PREVIOUS LERs ON SIMILAR EVENTS:
A search of all Ginna LERs submitted to the NRC determined that no similar event has occurred.
C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO IN THIS LER:
COMPONENT - Device, Overspeed IEEE 803 FUNCTION NUMBER - 12 IEEE 805 SYSTEM IDENTIFICATION - JJ