05000278/LER-2009-001, Regarding Control Rods Inoperable During Mode 2 Operations as a Result of Interferences
| ML090710258 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 03/06/2009 |
| From: | Stathes G Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 09-001-00 | |
| Download: ML090710258 (6) | |
| 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 |
| 2782009001R00 - NRC Website | |
text
Exeln Exelon Nuclear www.exeloncorp.com Nuclear Peach Bottom Atomic Power Station 1848 Lay Road Delta, PA 17314-9032 10CFR 50.73 March 6, 2009 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Peach Bottom Atomic Power Station (PBAPS) Unit 3 Facility Operating License No. DPR-56 NRC Docket No. 50-278
Subject:
Licensee Event Report (LER) 3-09-01 This LER reports a condition discovered during a recent outage involving the inoperability of control rod drives.
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.
Sincerely, Parjyý StatohesýD Plant Manager Peach Bottom Atomic Power Station GLS/djf/IR 874398/871573 Attachment cc:
- - S. J. Collins, US NRC, Administrator, Region I F.. L. Bower, 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: 09-26
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the infnrmatinn n oll~nntionn.
- 3. PAGE Peach Bottom Atomic Power Station Unit 3 05000278 1 OF 5
- 4. TITLE Control Rods Inoperable During Mode 2 Operations as a Result of Interferences
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
FACILITY NAME DOCKET NUMBER Y
SEQUENTIAL REV MONTH DAY YEAR 05000
_I II_
IF II--ACILITY NAME DOCKET NUMBER 01 21 2009 09
" 01 00 03 06 2009 05000
- 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)
[l 50.73(a)(2)(i)(C)
[D 50.73(a)(2)(vii) 2 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
Cl 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL
[: 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
[: 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
[] 50.73(a)(2)(v)(A)
El 73.71(a)(4) 1%
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
E] OTHER El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in Description of the Event, continued This report is being submitted pursuant to:
10CFR 50.73(a)(2)(vii) - Common Cause Inoperability of Independent Trains - This occurrence is reportable under this criterion since three control rods were inoperable for approximately 4.75 hours8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br /> on 1/21/09 during Mode 2 unit operations for a common cause (i.e., control rod interferences).
Control Rods 14-55, 18-55 and 42-55 were restored to an OPERABLE status on 1/28/09 at approximately 0630 hours0.00729 days <br />0.175 hours <br />0.00104 weeks <br />2.39715e-4 months <br /> subsequent to control rod interference monitoring testing. The three control rods are only considered OPERABLE for time periods when reactor pressure is at or above 850 psig.
Analysis of the Event
There were no actual safety consequences associated with this event.
The control rod blade and drive mechanism provides control of reactor power, including the ability to provide a sufficiently rapid insertion of control rods (scram) so that no fuel damage results from any abnormal operating transient and limits fuel damage under accident conditions. The 185 control rods are located uniformly throughout the core on a 12-inch pitch. Four fuel assemblies surround each control rod. Control Rods 14-55 and 18-55 are adjacent control rods. Peach" Bottom Units 2 and 3 are 'D-lattice' reactor fuel design units. Global Nuclear Fuels (GNF) is the fuel vendor. The fuel is GE14 type fuel. The control rod blades are original equipment supplied by General Electric.
Control Rod Drive (CRD) System Hydraulic Control Unit (EIIS: HCU) scram accumulators are designed with a limited nitrogen pressure and volume, which are sufficient to initiate control rod scram motion.
Any force necessary to complete the insertion stroke is supplied by reactor coolant delivered at reactor pressure. As reactor pressure decreases, the amount of pressure available to complete the control rod stroke also decreases, and for pressure down to approximately 550 psig, this means less control rod friction can be overcome.
Two low-pressure scram events are identified as bounding:
The Main Steam Isolation Valve (MSIV) isolation pressure scram (Mode 1 operations)
" Scram at lower pressures near 550 psig. The scram at pressures near 550 psig would occur only during startup and soft shutdown conditions (Mode 2 operation).
Concerning the MSIV isolation pressure scram, Control Rods 14-55, 18-55 and 42-55 were considered OPERABLE throughout the event. The unit Primary Containment Isolation System (PCIS) setpoint for low reactor pressure is > 850 psig while the unit is in Mode 1. Decreasing reactor pressure to this isolation setpoint would result in a Group I PCIS isolation, resulting in a unit scram when in Mode 1.
Analysis of the Event, continued If a low reactor pressure scram was required during the 1/21/09 Mode 2 soft shutdown, it is possible that Control Rods 14-55, 18-55, and 42-55 may not have properly inserted due to the lower reactor pressures at the time the control rods were withdrawn.
However, following incomplete insertion during a low-pressure scram due to control rod friction, the control rod could have been manually inserted by re-setting and re-applying the scram. This would have re-established adequate CRD scram accumulator pressure allowing the capability of overcoming channel-control blade friction at lower reactor pressures. In addition, the control rods could also have been manually inserted using normal control rod insertion via the reactor manual control system.
In addition, an event specific analysis was performed that determined that appropriate shutdown margin was maintained, assuming that the affected control rods and the rod of highest reactivity worth in the core did not insert.
Cause of the Event
The cause of the inoperability of Control Rods 14-55, 18-55 and 42-55 is apparently due to fuel channel distortion as discussed in the fuel vendor's safety information communication on this topic (GEH SC08-05, Rev. 1, Updated Surveillance Program for Channel-Control Blade Interference Monitoring). Since control rod slow settle times is the earliest indication of elevated cell friction, the observations made during the events described in this report are consistent with channel distortion.
A root cause investigation is in-progress for this event. Appropriate causes will be determined and corrective actions will be implemented in accordance with the Corrective Action Program.
Corrective Actions
A control rod interference monitoring / testing program has been established. This program is based on the recommendations of the vendor-issued safety information communication concerning channel - control blade interference monitoring.
Control rod interference monitoring / testing was performed on Control Rods 14-55, 18-55, 42-55 and 46-55.
Based on the testing results, Control Rods 14-55, 18-55 and 42-55 were determined to be INOPERABLE for reactor pressures below 850 psig.
Other control rods on Unit 3 were tested (stroked and settle time tested) during the planned outage. Other appropriate control rods are being tested in accordance with the methodologies and frequencies of the control rod interference monitoring testing with no additional inoperabilities discovered to-date.
Corrective Actions, continued Control rod interference monitoring testing was performed for Unit 2 control rods. There were no inoperable control rods detected on Unit 2.
Additional actions, including resolution of the control rod interferences on Unit 3, will be performed in accordance with the Corrective Action Program.
Previous Similar Occurrences There were no previous LERs related to control rod interferences.PRINTED ON RECYCLED PAPER NRIC FORM 366A (9-2007)
PRINTED ON RECYCLED PAPER