05000254/LER-2011-003, Regarding Control Room Emergency Ventilation Air Conditioning System Inoperable
| ML11252B079 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 09/01/2011 |
| From: | Hanley T Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVP-11-066 LER 11-003-00 | |
| Download: ML11252B079 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2542011003R00 - NRC Website | |
text
Exeln Exelon Generation Company, LLC www.exeloncorp.com Ouad Cities Nuclear Power Station Nuclear 22710 2o6th Avenue North Cordova, I L 61242-9740 September 1, 2011 10 CFR 50.73 SVP-1 1-066 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Quad Cities Nuclear Power Station, Unit 1 Renewed Facility Operating License No. DPR-29 NRC Docket No. 50-254
Subject:
Licensee Event Report 254/2011-003-00, Control Room Emergency Ventilation Air Conditioning System Inoperable Enclosed is Licensee Event Report (LER) 254/2011-003-00, Control Room Emergency Ventilation Air Conditioning System Inoperable, for Quad Cities Nuclear Power Station, Unit 1.
This report is submitted in accordance with 10 CFR 50.73(a)(2)(v)(D), which requires the reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
There are no regulatory commitments contained in this letter.
Should you have any questions concerning this report, please contact Mr. W. J. Beck at (309) 227-2800.
Respectfully, Tim Hanley
' (t Site Vice President Quad Cities Nuclear Power Station cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Quad Cities Nuclear Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 11o-2010)
, the NRC may feach not conduct or sponsor, and a person is not required to respond to, the digits/characters for e block) information collection.
- 3. PAGE Quad Cities Nuclear Power Station Unit 1 05000254 1 OF 5
- 4. TITLE Control Room Emergency Ventilation Air Conditioning System Inoperable
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NTA NO.
MONTH DAY YEAR Quad Cities Nuclear Power Station Unit 2 05000265 FACILITY NAME DOCKET NUMBER 07 06 2011 2011
- - 003 -
00 09 06 2011 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
[I 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 1 El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
[E 20.2203(a)(1)
[I 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
[I 50.73(a)(2)(viii)(B)
E0 20.2203(a)(2)(i).
[I 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
[I 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL [I 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
[I 50.73(a)(2)(iv)(A)
[I 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
[I 50.73(a)(2)(v)(A)
[1 73.71 (a)(4) 100%
[E 20.2203(a)(2)(iv) 0l 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71 (a)(5)
[E 20.2203(a)(2)(v)
[E 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER [E
20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
U 50.73(a)(2)(v)(D)
Specify in Abstract below or in Since the April 2009 compressor replacement, modifications had been made to the system to improve system performance.
Subsequent to the 7/6/11 compressor failure, additional analysis, reviews of available vendor compressor options, and reviews of fleet experience from another Exelon Station determined that installation of an automatic pump-down system would provide additional margin to avoid flooded compressor starts. The automatic pump-down option helps to minimizes buildup of refrigerant during the times when the compressor is sitting idle.
Given the impact on the CREV AC system, this report is submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(v)(D), which requires the reporting of any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
C.
CAUSE OF EVENT
The increased compressor vibration amplitude was the result of a failed bearing and broken connecting rod caused by flooded starts of the compressor. The root cause of the flooded start was an unanticipated failure mode for the design application of the system.
A contributing cause to this event was that station personnel did not select a corrective action that resulted from a similar event at another Exelon Station. In May 2009, a separate Exelon Station experienced a similar failure mode to a Carrier Model 5H compressor. As a result of that failure, that Exelon Station installed an automatic pump-down modification on their Carrier Model 5H compressor in late 2009; the modification has shown success in reducing failure modes. The opportunity to upgrade the Quad Cities CREV RCU design based on this similar Exelon Station event had, however, occurred one month after the completion of the previous (2009) Quad Cities failure investigation.
At that time it was concluded that the Quad Cities plans for compressor improvements were appropriate and that the automatic pump down modification was not essential. Quad Cities Station may have benefitted from implementation of this pertinent Exelon experience and the related modification.
The extent of condition of this event is isolated to the B CREV RCU compressor which is a single train safety-related system that contains one Carrier Model 5H120 reciprocating compressor. There are no other Heating Ventilation and Air Conditioning (HVAC) [AHU] systems or other systems at Quad Cities Station that utilize the same type of compressor or operating conditions. The Train A Control Room HVAC system currently has three Trane reciprocating compressors. These compressors are currently not operating, due to unrelated issues and are being replaced as part of a full system upgrade with screw type compressors in late 2011. Temporary chillers are currently in operation on the Train A Control Room HVAC as part of the upgrade process.
D.
SAFETY ANALYSIS
The purpose of the CREV system is to maintain the proper air environment for instrumentation and personnel in the Control Room [NA]. The Train B CREV AC system is a single train safety-related system that is designed to operate in a post-accident condition to maintain design temperature in the Control Room Envelope (CRE). The Train B CREV RCU 0-9400-102 is a Carrier reciprocating compressor; Model 5H120, with a capacity of 90 tons. The backup to the Train B CREV system is the Train A Control Room HVAC system, which is a non-safety-related system. This event is a Maintenance Rule Functional Failure of the Z5795 - Control Room HVAC System.
The increased vibration amplitudes during this event resulted in declaring the "B" CREV and RCU inoperable and subsequently securing the system. Operators performed required actions safely, in accordance with procedures and training, and without complications.
This resulted in entering Technical Specification 3.7.5, Condition A (30 day Action). The loss of the CREV AC could impact the plant's ability to mitigate the consequences of an accident.
The safety significance of this event was minimal. The CREV system filtration capability was not lost, and control room temperature was maintained during this event. In addition, the non-safety related Train A Control Room HVAC system (currently replaced with temporary chillers), was available and operating throughout this event.
The CREV AC system is not explicitly modeled in the Plant Probabilistic Risk Assessment (PRA). Certain Operator Actions (OAs) are modeled in the PRA, however, the effect of this event on OA human error probabilities (HEPs) would have a negligible quantitative impact on the calculated Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) since loss of CREV AC events are slow progressing events (being reduced temperature control of the Control Room). In the loss of CREV system event, Station procedures direct the opening of doors and use of temporary fans, as necessary. Applicable Operator training is performed on these actions and the equipment is pre-staged as a part of the response to station blackout requirements.
Although opening Control Room doors to support room cooling would introduce the increased potential for radiological or chemical events impacting the Main Control Room, the probability of a loss of CR HVAC event coincident with a radiological or chemical event is small and therefore, would also have a negligible quantitative impact on CDF and LERF.
In conclusion, the degradation of the 0-9400-102 CREV system AC chiller was not risk significant.
E.
CORRECTIVE ACTIONS
Immediate:
- 1. Replaced the failed compressor with a new compressor on July 12, 2011.
- 2.
Revised the frequency for vibration analysis on the B CREV RCU from 6 months to monthly.
Follow-up:
- 1.
Install an automatic pump-down modification for the B CREV RCU compressor. This is the most effective method of keeping liquid refrigerant out of the compressor crankcase during idle periods.
- 2.
Review operating history and other indications for the B CREV RCU compressor. Determine if the compressor should be replaced at the same time the pump-down modification is to be installed.
- 3.
Review operating events associated with Carrier Model 5H condensing unit compressors and disposition the
corrective actions
F.
PREVIOUS OCCURRENCES
The station events database, LERs, EPIX, and NPRDS were reviewed for similar events at Quad Cities Nuclear Power Station. This event was a CREV RCU chiller connecting rod failure due to flooded starts of the compressor, which was caused by an unanticipated failure mode for the design application of the system.
Station Events Database -
IR 910666 (04/23/09), Old B CR HVAC RCU Found With Broken Rod (Equipment Apparent Cause Evaluation) - Train B CREV RCU was found with a broken piston connecting rod. This condition was found during a compressor replacement activity (due to vibrations on the compressor had increased and could not be resolved through other maintenance activities).
Since this April 2009 compressor replacement, modifications had been made to the system to improve system performance.
Subsequent to the 7/6/11 compressor failure, additional analysis, reviews of available vendor compressor options, and reviews of fleet experience from another Exelon Station, determined that installation of an automatic pump-down system would provide additional margin to avoid flooded compressor starts.
The automatic pump-down option helps to
minimize buildup of refrigerant during the times when the compressor is sitting idle. This issue and resulting actions are addressed in the Cause of Event and Corrective Actions sections of this LER.
LER 254-2005-006-00 (01/27/06), Failure of the Control Room Emergency Ventilation Air Conditioning Compressor Due to a Manufacturing Defect in an Electrical Relay - This event was an electrical relay failure caused by a manufacturing deficiency (bound armature retaining pin) specific to this relay. Based on the causes of this event and associated corrective actions, this previous LER although similar in topic area (CREV AC compressor), is not considered a significant station experience that would have directly contributed to preventing this event.
G.
COMPONENT FAILURE DATA
The component that failed was the Train B CREV RCU 0-9400-102, which is a Carrier Model 5H120 reciprocating air conditioning compressor with a capacity of 90 tons.
This event has been reported to EPIX as Failure Report No. 1120.