05000483/LER-2024-002, Concurrent Inoperability of Control Room Air Conditioning System Train and Opposite Train Emergency Diesel Generator Results in Condition Prohibited by Technical Specifications Limiting
| ML24275A213 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 10/01/2024 |
| From: | Union Electric Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24275A211 | List:
|
| References | |
| ULNRC-06901 LER 2024-002-00 | |
| Download: ML24275A213 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4832024002R00 - NRC Website | |
text
Abstract
On August 2, 2024, the oil pump drive segment within the compressor for the Control Room Air Conditioning System (CRACS) train A unit was replaced to address a material issue. Based upon review of the removed part and unit operation prior to its replacement, CRACS train A would have failed to support its 30-day mission time starting on June 29, 2024. Between July 8 at 2330 and July 18 at 1622, the B Emergency Diesel Generator (EDG) was out of service. Callaway Technical Specification (TS) 3.8.1
, AC Sources
- - Operating, Condition B, Required Action B.2, directs that required features supported by the inoperable EDG are declared inoperable when the required redundant features are inoperable, within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. With CRACS train A and EDG train B concurrently inoperable, CRACS train B would also be inoperable. As such, both CRACS trains were inoperable during the period of EDG B inoperability. With both CRACS trains inoperable in Modes I
, 2, 3, or 4, TS 3.7.11, Control Room Air Conditioning System (CRACS), Condition E, Required Action E.1 directs that Limiting Condition for Operation 3.0.3 be entered Immediately, which then directs thatthe unit be in Mode 3 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, Mode 4 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and Mode 5 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.
Separately, TS 3.8.1 Condition G requires that when Completion Times or Required Actions of TS 3.8.1 are not met, the plant be in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. These shutdown actions were not met on July 9 at 1030, and 0930, respectively. As such, this condition is being reported as an Operation or Condition Prohibited by Technical Specifications.
1. DESCRIPTION OF STRUCTURE(S), SYSTEM(S), AND COMPONENT(S)
The Control Room Air Conditioning System (CRACS) [EIIS:VIJ provides temperature control for the control room.
The CRACS consists of two independent and redundant trains that provide cooling of recirculated control room air. Each train consists of a prefilter, self-contained refrigeration system (using essential service water [EllS:Bl] as a heat sink),
centrifugal fans, instrumentation, and controls to provide for control room temperature control. Requirements for the CRACS are contained in Technical Specification (TS) Limiting Condition for Operation (LCO) 3.7.1 1, Control Room Air Conditioning System (CRACS). The CRACS operates in conjunction with the Control Room Emergency Ventilation System (CREVS) [EIIS:VlJ, which is separately addressed in TS LCO 3.7.10, Control Room Emergency Ventilation System (CREVS).
The CRACS is an emergency system that also operates during normal unit operations. A single train will provide the required temperature control to maintain the control room less than 84 degrees Fahrenheit. The design basis objective of the CRACS is to maintain the control room temperature for 30 days of continuous occupancy under accident conditions.
Each CRACS train contains a compressor to recirculate refrigerant through the coil of the air conditioning unit. A subcomponent of the CRACS compressor is an oil pump drive segment that assures proper alignment between the oil pump rotor and oil output manifold.
TS LCO 3.8.1, AC Sources - Operating requires, in part, that two diesel generators (DG) capable of supplying the onsite Class 1 E power distribution subsystem(s) be Operable in Modes 1
, 2, 3, and 4. Condition B applies when one DG becomes inoperable. Required Action B.2 requires declaring the required feature(s) supported by the inoperable DG inoperable when its required redundant feature(s) is inoperable, with a Completion Time of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> from discovery of Condition B concurrent with inoperability of redundant required feature(s).
2. INITIAL PLANT CONDITIONS
Callaway Plant was in MODE 1 at 1 00% rated thermal power throughout the entire period of this event.
3. EVENT DESCRIPTION
On July 17, 2024, Callaway received information from the Original Equipment Manufacturer, Carrier, for the compressors installed in the CRACS units regarding a parts material issue impacting the oil pump drive segments used in the compressors. This information ultimately led Callaway to replace the oil pump drive segment in CRACS train A on August 2, 2024. At the time of removal of the oil pump drive segment, there were no external or secondary indications that CRACS train A had any degraded condition. However, Plant Engineering evaluated the removed oil pump drive segment and determined that based upon the operating history of the component and the estimated point of failure due to component wear, the compressor was no longer capable of supporting the 30-day mission time of CRACS after June 29, 2024. The compressor installed in CRACS train A had been installed in the plant and cycled in and out of operation (as required) since September 17, 2022.
Between July 8 at2330 and July 18 at 1622, the EDG train B was outofservice for planned maintenance. TS LCD 3.8.1, AC Sources Operating, Condition B, Required Action B.2, directs that required features supported by the inoperable EDG must be declared inoperable when the required redundant features are inoperable, within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. With CRACS train A inoperable, as determined by the Engineering review of operation, and with EDG train B concurrently inoperable for
maintenance, CRACS train B would also have been required to be declared inoperable. As such, both CRACS trains were inoperable during the period of EDG B inoperability. Specifically, accounting for the 4-hour Completion time of Required Action B.2 of LCO 3.8.1, the period when both CRACS trains were concurrently inoperable was between July 9 at 0330 and July 18 at 1622.
TS LCO 3.7.11 requires two CRACS trains to be Operable in Modes 1 through 6 and during movement of irradiated fuel assemblies. Required Action E.1, Enter LCO 30.3, with a Completion Time of Immediately, for Condition E, Two CRACS trains inoperable in Mode 1, 2, 3, or 4, was not met from July 9 at 0330 to July 18 at 1622, when the B Emergency Diesel Generator (EDG) was inoperable for planned maintenance. With LCO 3.0.3 not having been entered during this period, the requirement to be in Mode 3 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, Mode 4 within 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />, and Mode 5 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br /> was also not met. Atthe same time, with Action B.2 of TS LCO 3.8.1 in effect, Condition G of LCO 3.8.1 applied, Required Action and associated Completion Time of Condition A, B, C, D, E, or F [are] not met. Condition G of TS LCO 3.8.1 required that the plant be in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and be in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, which was also not met during the same period. Ultimately, the shutdown requirements ofTS LCO 3.8.1 Required Action G.1 and LCO 3.0.3 were not met at 0930 and 1030 on July 9, 2024, respectively.
Other than having CRACS train A and EDG train B (and corresponding CRACS train B due to Required Action B.2 of TS LCO 3.8.1) inoperable, there were no other pertinent system or component inoperabilities that contributed to or complicated this event.
4. ASSESSMENT OF SAFETY CONSEQUENCES
There were no actual nuclear, radiological, or personnel safety impacts associated with this issue. The potential impact was on personnel and radiological safety with respect to ensuring that the control room temperature could be maintained suitable for 30 days of continuous occupancy, post-accident.
The TS 3.7.11 Bases describe the design basis and safety analyses applicable to the CRACS system. The CRACS components are arranged in redundant, safety related trains. During normal or emergency operations, the CRACS maintains the temperature of the control room at less than or equal to 84 degrees Fahrenheit. A single active failure of a component of the CRACS, with a loss of offsite power, does not impair the ability of the system to perform its design function. Redundant detectors and controls are provided for control room temperature control. The CRACS is designed in accordance with Seismic Category I requirements. The CRACS is capable of removing sensible and latent heat loads from the control room, which include consideration of equipment heat loads and personnel occupancy requirements, to ensure equipment OPERABILITY. The CRACS satisfies Criterion 3 of 10 CFR 50.36(c)(2)(ii).
Given that offsite power remained available during the maintenance evolution on EDG train B, CRACS train B remained able to support the required functions of the CRACS system as described above and was inoperable only due to the TS LCO 3.8.1 support system relationship and Required Action B.2 ofthe same LCO.
If a loss of offsite power had been experienced during the period when EDG train B was inoperable, CRACS train B would have had no available power source, and the plant would have had to rely upon CRACS train A to provide a source of cooling to the control room.
It is not exactly known when CRACS train A would have failed under these conditions, but engineering review of the degraded part determined that the CRACS train would not have been able to meet its 30-day mission time. Under these conditions, equipment repairs or an alternate means of cooling the control room would have had to be pursued to maintain a habitable environment for control room operators.
5. REPORTING REQUIREMENTS
This LER is submitted pursuant to 1 0 CFR 50.73(a)(2)(i)(B) to report a condition prohibited by TS LCO 3.7. 1 1 Required Action El, Enter LCO 3.0.3, Immediately, as required for Condition E, Two CRACS trains inoperable in Mode 1, 2, 3, or 4, since the Required Action was not met from July 9 at 0330 to July 18 at 1622. This period exceeds the TS LCO 3.0.3 time requirements to be in Mode 3 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, Mode 4 within I 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, and Mode 5 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />. At the same time, with Action B.2 ofTS LCO 3.8.1 in effect, Condition G of LCO 3.8.1 applied, Required Action and associated Completion Time of Condition A, B, C, D, E, or F [are] not met. Condition G of TS LCO 3.8.1 required thatthe plant be in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and be in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, which was also not met during the same period. Ultimately, the shutdown requirements ofTS LCO 3.8.1 Required Action G.1 and LCO 3.0.3 were not met at 0930 and 1030 on July 9, 2024, respectively.
Based on the guidance within NUREG 1 022, Revision 3, Section 3.2.7, Page 39, this event does not represent an event or condition that could have prevented fulfillment of a safety function pursuant to 1 0 CFR 50.73(a)(2)(v). The guidance states, In addition, unless a condition is discovered that would have resulted in the system being declared inoperable, reports are not required when systems are declared inoperable solely as a result of Required Actions for which the bases is the assumption of an additional random single failure (i.e. Westinghouse STS, Revision 4, LCO 3.8.1
, AC Sources
Operating, Required Actions A.2, B.2, or C.1 (ADAMS Accession No.ML12100A222)).
Under this event, CRACS train B would have been declared inoperable solely based upon Required Action B.2 of TS LCO 3.8.1
, which the Bases is based upon presuming the occurrence of an additional random single failure. Specifically, TS LCO 3.8.1, Required Action B.2 Bases state, In this Condition, the remaining OPERABLE DG and offsite circuits are adequate to supply electrical power to the onsite Class 1 E Distribution System. Thus, on a component basis, single failure protection for the required features function may have been lost; however, function has not been lost. The 4-hour Completion Time takes into account the OPERABILITY of the redundant counterpart to the inoperable required feature.
Additionally, the 4-hour Completion Time takes into account the capacity and capability of the remaining AC sources, a reasonable time for repairs, and the low probability of a Design Bases Accident occurring during this period. During the period where EDG train B was inoperable under this event, offsite power remained available to support CRACS train B, if required.
6. CAUSE OF THE EVENT
The cause of this issue is that the oil pump drive segments installed in the CRACS units did not undergo a post-manufacturing hardening process, which allowed for an accelerated wear rate when placed in an operating unit. Prior to July 17, 2024, Callaway had not received information from the original equipment manufacturer regarding this parts issue.
These parts were not originally safety-related parts under a 10 CFR 50, Appendix B, Quality Assurance program, but were commercially dedicated by an external vendor, Paragon, for use in safety-related applications at the Callaway plant. The external vendor performing the dedication similarly did not receive information from the original equipment manufacturer regarding this parts issue. Callaway discovered the parts issue through communications with the original equipment manufacturer, while investigating failures of a similar compressor in a different system under a corrective action program causal evaluation.
Further evaluation of this condition is ongoing, and if pertinent supplementary information is identified, this Licensee Event Report may be revised with additional information.
7. CORRECTIVE ACTIONS
Replacement of the oil pump driVe segment with a properly hardened drive segment in both of the CRACS units was Completed on August 2, 2024, and August 7, 2024, for the A and B trains, respectively.
Additionally, it should be noted that the Class 1 E Electrical Equipment Room Air Conditioning (Class 1 E AC) system
[EllS:Vl] utilizes similar compressors and oil pump drive segments that exhibit the same vulnerability. Replacement of the drive segments for the Class I E AC units was completed on August 2, 2024, and August 1, 2024, for the A and B trains, respectively. The Class I E Electrical Equipment Room Air Conditioning system is covered under TS LCO 3.7.20, Class 1 E Electrical Air Conditioning (NC) System. There were no compliance issues with respect to this Technical Specification since the oil pump drive segments for this equipment had not reached a state that made the equipment inoperable.
Further evaluation of this condition is ongoing and if pertinent supplementary information is identified, this Licensee Event Report may be revised with additional information.
8. PREVIOUS SIMILAR EVENTS
There have been no similar previous events that required reporting under a Licensee Event Report for Callaway plant.
Inoperability of CRACS train B, due to an oil pump drive segment failure, was experienced by Callaway on May 26, 2024.
This failure was not reportable since CRACS train A was Operable during the period of train B inoperability. However, that event led to the initiation of a causal evaluation to investigate the failure, which led to the vendor communication on July 1 7, and ultimately to replacement of the oil pump drive segment in CRACS train A on August 2. A historical review of CRACS and Class 1 E AC unit issues did not identify any other previous similar events at Callaway or any other operating nuclear unit.
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