05000483/LER-2020-004, Violation of Technical Specification 3.8.1, AC Sources-Operating
| ML20310A328 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 11/05/2020 |
| From: | Ameren Missouri, Union Electric Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20310A325 | List: |
| References | |
| ULNRC-06615 LER 2020-004-00 | |
| Download: ML20310A328 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4832020004R00 - NRC Website | |
text
Abstract
On September 9, 2020, a review of trend data identified a significant increase in makeup to the 'A' emergency diesel generator (DG) jacket water expansion tank, as applicable to a period of time that began on August 5, 2020. Specifically, the makeup water supply control valve cycled 25 times between August 5, 2020 and September 9, 2020. Prior to August 5, 2020, this valve had not cycled since April 15, 2020.
The 'A' DG was declared inoperable on September 9, 2020 due to excessive jacket water leakage through KJV00771A, 'A' DG Jacket Water Heater Relief Valve. The 'A' DG was returned to operable status after KJV0771A was isolated on September 9, 2020. The valve was then removed and tested, and a replacement valve was installed in its place on September 10, 2020.
The cause of this event was excessive jacket water leakage through KJV00771A, which had failed to seat due to debris becoming trapped in the valve seat after the valve was opened to manually vent the jacket water system after maintenance on August 5, 2020.
Immediate corrective action for this event was to replace KJV00771A. Additionally, a corrective action to prevent recurrence was implemented, in which a night order was issued prohibiting the use of either KJV00771A or KJV007718,
('B' DG jacket water heater relief valve) for venting the jacket water systems of the DGs, until the final resolution of this issue is complete.
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023
- 1.
DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
YEAR 2020 SEQUENTIAL NUMBER
- - 004 REV NO.
- - 00 The unit Class 1 E AC electrical power distribution system for Callaway Plant includes the offsite power sources (preferred power sources) and the onsite standby power sources (Train A and Train B diesel generators (DGs)). As required by 10 CFR 50, Appendix A, GDC 17, the design of the AC electrical power system provides independence and redundancy to ensure an available source of power to the Engineered Safety Feature (ESF) systems. The onsite Class 1 E AC Distribution System is divided into redundant load groups (trains) so that the loss of any one group does not prevent the minimum safety functions from being performed.
Each DG, i.e., diesel engine and associated generator [EIIS Code: EK], provides emergency standby power to engineered safety features (ESF) electrical loads in sufficient time to provide for safe reactor shutdown and to mitigate the consequences of a Design Basis Accident (DBA). Specifically, the function of each DG is to provide emergency 4.16-kV AC power to its respective bus within 12 seconds of a demand, for up to seven days, in the event of a loss of off-site power to the bus.
The emergency diesel engine cooling water system (EDECWS) [EIIS Code: LBJ provides cooling water to the emergency diesel engines. (One subsystem/train cools each DG. There are no interconnections between the two cooling subsystems/trains.) The EDECWS is a closed cycle system and serves as an intermediate system between the diesel engines and the Essential Service Water system. Each EDECWS subsystem/train provides jacket water and intercooler cooling for the associated diesel engine.
An expansion tank (EIIS Code: TK] is provided for each subsystems/train to accommodate any volumetric changes due to thermal transients or leakage and to absorb pump pulsations. The expansion tank maintains adequate suction at the engine-driven pumps and provides a release point for undissolved gases in the system.
Makeup is provided to the expansion tank in each train; however, the makeup source is the non-safety related Demineralized Water system [EIIS Code: KC], which cannot be credited to provide makeup during a DBA. Therefore, the only margin available to account for leakage in either train is the excess water stored in the expansion tank. Leakage from either the jacket water or intercooler system in excess of the available margin for either train will thus lead to loss of the EDECWS function for that train and consequently, a loss of the function provided by the associated DG. The jacket water expansion tank includes a heater for which a high point vent [EIIS Code: VfV] is provided.
- 2.
INITIAL PLANT CONDITIONS
Callaway was in MODE 1 at 100% rated thermal power at the time of this event.
- 3.
EVENT DESCRIPTION
On September 9, 2020, trend data was reviewed for jacket water makeup valve operation, after chemistry samples showed decreasing levels of corrosion inhibitors in the 'A' DG jacket water expansion tank. A drop in chemical additive levels is indicative of the tank being automatically filled with fresh water, as prompted by leakage or draining and flushing of the system.
Trend data showed that valve KJLCV0067, DG 'A' Jacket Wat.er Expansion Tank Makeup Wat.er Supply Level Control Valve, cycled 25 times between August 5, 2020 (when maintenance was performed on the DG) and September 9, 2020. Prior to the August 5, 2020 maintenance activity, the makeup valve had not cycled since April 15, 2020. The leakage indicated by the cycling makeup valve slowed significantly following an 'A' DG surveillance run on September 2, 2020, as the makeup valve had only cycled once in the 7-day period before declaring the 'A' DG inoperable on September 9, 2020.
Troubleshooting identified the source of the leakage to be from KJV0771A, 'A' DG Jacket Water Heater Relief Valve. This leak path was confirmed when the leakage stoooed after the valve was isolated. Other potential leakage paths were ruled out, including Page i of 1 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023
- 3. LERNUMBER YEAR Callaway Plant Unit 1 05000-483 2020 SEQUENTIAL NUMBER
- - 004 REV NO.
- - 00 leakage into the 'A' DG engine (as Operator rounds did not show a significant change in oil level), as well as leakage through the jacket water expansion tank overflow line (as the low-level switch property operated to initiate makeup flow).
On September 9, 2020, valve KJV0771A was isolated, and on September 10, 2020, it was removed and bench tested, and a replacement valve was installed in its place. Maintenance personnel found debris caught in the valve seat, preventing the valve from reseating and allowing jacket water to leak by. It was recognized that by use of its installed manual lift lever, valve KJV0771A had been used as a vent path to manually vent the jacket water system after maintenance on August 5, 2020. This practice had the potential to trap debris between the valve disk and nozzle or guide rings, potentially causing the valve to develop seat leakage.
During the time of the August 5, 2020 'A' DG maintenance, no leakage through valve KJV0771A was observed. After a computer point alarm for 'A' DG jacket water expansion tank auto fill was received on the plant computer, however, the jacket water system was walked down for the purpose of looking for leakage, and KJV0771A was found to be leaking 27 drops per minute (DPM) on the August 6, 2020 night shift. Since this leakage rate was less than a calculated maximum leakage level, of 143 DPM, the 'A' DG was determined to be Operable at that time. Later on, however, based on the subsequent review of trend data as previously described, it became apparent that the observed leak rate was not constant and did not accurately reflect the average system leakage.
It has been determined that the 'A' DG was inoperable from August 5, 2020 to September 9, 2020. This includes the time from the start of increased cycling of valve KJLCV0067 to the time when valve KJV0771 A was isolated (thus eliminating the leakage from the jacket water expansion tank).
- 4.
ASSESSMENT OF SAFETY CONSEQUENCES
The unrecognized inoperability of the 'A' DG during the period of August 5 to September 9, 2020, is not safety significant. A review of the past performance/condition of the redundant ('B' train) DG found that it was capable of performing its specified safety function during the period of 'A' DG inoperability. Consequently, the leakage condition identified for the 'A' DG did not cause a loss of safety function for onsite AC power.
- 5.
REPORTING REQUIREMENTS
This LER is submitted pursuant to 10 CFR 50. 73( a)(2)(i)(B) to report a condition or operation in violation of Technical Specifications.
Technical Specification (TS) LCO 3.8.1, "AC Sources-Operating," states in part that two diesel generators (DGs) capable of supplying the onsite Class 1 E power distribution subsystem(s) shall be OPERABLE in MODES 1-4. Condition Band Required Action B.4 of this TS require that if one DG is inoperable, the inoperable DG must be restored to OPERABLE status within a Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Furthermore, if this required Action and Completion Time are not met, Condition G and Required Actions G.1 and G.2 require the plant to be in MODE 3 within a Completion Time of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and MODE 5 within a Completion Time of 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, respectively. Since the period of 'A' DG inoperabiity was not recognized for a period of approximately one month and four days, it is clear that continued plant operation with the 'A' DG inoperable for more than the TS-allowed period of time constituted an operation prohibited by TS LCO 3.8.1.
A review of 'B' DG operability during the period of concern was performed to determine if there was a complete loss of safety function. A review of trend data indicated that the 'B' train jacket water expansion tank makeup valve, KJLCV0167, had not cycled since April 15, 2020, thus confirming that the 'B' DG was not impacted by the same failure. In addition, review of control room logs showed that although there were three entries into TS LCO 3.8.1 for 'B' train components between August 5 and September 9, a functionality evaluation determined that the 'B' DG remained capable of performing its specified safety function during the noted period of 'A' DG inoperability. Therefore, there was no loss of safety function during this time.
- 6.
CAUSE OF THE EVENT
The cause of this event was excessive jacket water leakage through KJV00771A, 'A' DG Jacket Water Heater Relief Valve.
KJV00771A had failed to seat due to debris becominq traooed in the seat after the valve was opened to manually vent the jacket Page~ of~ (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
- 3. LERNUMBER YEAR Callaway Plant Unit 1 05000-483 2020 SEQUENTIAL NUMBER
- - 004 REV NO.
- - 00 water system. This leak path was confirmed when the leakage stopped after the valve was eventually isolated. After removal of the valve, maintenance personnel found debris caught in the valve seat, which had prevented the valve from reseating, thus allowing jacket water to leak by.
- 7.
CORRECTIVE ACTIONS
The immediate corrective action taken for this event was to replace KJV00771A Additionally, a corrective action to prevent recurrence (CATPR) was implemented, in which a night order was issued prohibiting the use of either KJV00771A or KJV00771 B for venting the jacket water systems of the DGs until the final resolution of this issue is complete.
- 8.
PREVIOUS SIMILAR EVENTS
A review of internal operating experience was performed, and one similar event was identified as documented in the plant's corrective action program. This event, which occurred in 2014, was not reported to the NRC since the period of DG inoperability only lasted for 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> and 4 minutes, which is less than the TS 3.8.1 Action B.4 Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. In this event, leakage from the 'A' DG jacket water expansion tank was caused by the slight mispositioning of KJV0771A during a job to replace the cover on a temperature element, in the vicinity of the KJV0771A manual lift lever. During an Operations walkdown to identify the source of leakage, the manual lift lever on KJV0771 A was noted to be pointing with its handle in the 4 o'clock position instead of its typical 6 o'clock position. The leakage stopped once the relief valve handle was placed back in its proper orientation.