05000278/LER-2012-001, For Peach Bottom Atomic, Unit 3 Regarding Concurrent Inoperability of Two Trains of Core Spray Pressure Switches Results in Condition Prohibited by TS
| ML12167A272 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 06/13/2012 |
| From: | Stathes G Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 12-001-00 | |
| Download: ML12167A272 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2782012001R00 - NRC Website | |
text
AMMEW lc:z=
Ar,"W, Exeton Generation.
I OCFR 50.73 June 13, 2012 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Peach Bottom Atomic Power Station (PBAPS) Unit 3 Renewed Facility Operating License No. DPR-56 NRC Docket No. 50-278 Subject: Licensee Event Report (LER) 3-12-001 Enclosed is a Licensee Event Report concerning a condition prohibited by Technical Specifications and a common cause failure related to Barton pressure switches.
In accordance with NEI 99-04, the regulatory commitment contained in this correspondence is to restore compliance with the regulations. The specific methods that are planned to restore and maintain compliance are discussed in the LER. If you have any questions or require additional information, please do not hesitate to contact us.
lSi
- erely, Plant Manager Peach Bottom Atomic Power Station GLS/dnd/IR 1355773 Attachment cc:
US NRC, Administrator, Region I US NRC, Senior Resident Inspector R. R. Janati, Commonwealth of Pennsylvania S. Grey, State of Maryland P. Steinhauer, PSE&G, Financial Controls and Co-owner Affairs INPO Records Center CCN: 12-46 AV,
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, 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 Peach Bottom Atomic Power Station (PBAPS) Unit 3 05000278 1 OF 4
- 4. TITLE Concurrent Inoperability of Two Trains of Core Spray Pressure Switches Results in Condition Prohibited by TS
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR ISEQUENTIAL REV MONTH DAY YEAR
_NUMBER NO.
_I FACILITY NAME DOCKET NUMBER 04 19 2012 12 001 00 06 13 2012
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[l 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii)
[1 20.2201(d)
[I 20.2203(a)(3)(ii)
[I 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
[1 20.2203(a)(1)
[I 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
[:_ 20.2203(a)(2)(i) 0l 50.36(c)(1)(i)(A)
[I 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[I 50.36(c)(1)(ii)(A)
[I 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
[I 50.36(c)(2)
[I 50.73(a)(2)(v)(A)
El 73.71(a)(4) 100%
El 20.2203(a)(2)(iv) 0l 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
[1 73.71 (a)(5)
El 20.2203(a)(2)(v)
[I 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER [I 20.2203(a)(2)(vi)
ED 50.73(a)(2)(i)(B) rl50.73(a)(2)(v)(D)
Specify in Abstract below or in
Reportability
This report is being submitted pursuant to:
10CFR 50.73(a)(2)(i)(B) - Any operation or condition which was prohibited by the plant's TS, and 1 OCFR 50.73(a)(2)(vii) - Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system.
Based on the amount that DPIS 3-14-081 D was out of calibration (53 psi) on 4/19/12, it is likely that it was inoperable on 4/18/12 when DPIS 3-14-081A was out of calibration and inoperable. In addition, a single cause resulted in more than one instrument channel in one system being inoperable.
Analysis of the Event
The Core Spray System consists of two independent trains (subsystems), each with two 50% capacity pumps (four pumps total). Each pump has a minimum flow bypass valve that provides a safety related function for both its opening and closing operations. In the event that less than minimum flow exists through the pump discharge line, the valve opens to prevent overheating and pump damage. This condition could occur in response to a loss of coolant accident (LOCA), when an initiation signal starts the pumps prior to the injection signal. Once an injection signal is received, the bypass valve is required to close to ensure the full design flow to the core is provided.
To detect flow through the pump, a pressure switch detects the differential pressure between the suction and discharge lines of the pump. The switches are Barton Model 580A differential pressure indicating switches (DPIS), currently manufactured by Cameron Measurement Systems. Each DPIS contains two internal switches which actuate at the high and low setpoints. A series of gears, cams and pivots transmit movement from the bellows to the internal switches. Accurate operation of the DPIS requires correct alignment of the internal mechanical components and wear and corrosion can affect reliability of the switches.
The preferred method for corrective maintenance is replacement of the entire pressure switch instead of replacement of worn components or recalibration of the internal switches. Replacement of the entire switch and obtaining replacement parts became increasingly difficult following a change in ownership in 2007 and production of qualified Barton replacement switches was discontinued until 2010. As a result, PBAPS began to place more emphasis on adjustments to the internal components of the switch instead of replacement.
In January 2012, two Barton pressure switches on the Unit 3 Core Spray system were found out of calibration (one 4.6% high and the other 10.6% low). A cause evaluation was performed and a degrading trend in component performance was identified that started in 2008. Several corrective actions were initiated, including switch replacement and improvements in training. Cameron established an environmental qualification program in 2010 and has begun supplying qualified Barton pressure switches. PBAPS has established an expedited procurement and replacement schedule for the Core Spray system. A training and qualification program was established to develop site subject matter
experts for Barton pressure switches. The training included a Barton training lab, with a technical representative from Cameron to provide guidance on design and adjustments to the switches.
The out of calibration events described above occurred during normal scheduled surveillance testing.
There were no actual safety consequences associated with this event. In the event of a valid signal, it has been determined that the Core Spray system would still have been able to perform its safety function.
Cause of the Event
The declining trend in performance of Barton pressure switches at PBAPS since 2008 was due to insufficient knowledge and skill by maintenance personnel to effectively troubleshoot and maintain the instruments. Prior to 2008, maintenance personnel would typically have replaced the entire switch.
During the period of time when qualified Barton pressure switches were no longer being manufactured, additional emphasis was placed on adjustments to the internal components of the switch.
In addition, during lab training with a Cameron technical representative, it was determined that the high and low trip setpoints for the switches in the Core Spray system are sufficiently close together such that it can cause setpoint interferences and create additional drag on the cam assemblies. This makes the switches sensitive to wear, increases the potential for setpoint drift and increases the level of knowledge and skill needed to maintain them. It was also identified during the lab training that maintenance procedures did not provide adequate guidance for detecting component failures and to differentiate them from instrument drift.
Corrective Actions
Replacement of the eight Barton pressure switches for the Core Spray pump bypass valves in the Units 2 and 3 Core Spray systems has begun and is being tracked within the corrective action program.
A site training and qualification program has been developed to establish a group of subject matter experts for Barton pressure switches. Also, procedure enhancements have been made to provide improved guidance for troubleshooting.
The site corrective action program is tracking these corrective actions and has evaluated the extent of condition.
Previous Similar Occurrences As stated above, there has been a declining trend in Barton pressure switches for the Core Spray system being out of calibration or failing since 2008. From 1998 to 2007 there were approximately 6 occurrences. From 2008 to present, there have been approximately 8 occurrences. Setpoint drift issues for Barton pressure switches have also been identified as an industry issue (reference NRC Information Notice 86-065).