05000315/LER-2005-001, Regarding Reactor Trip Following Intermediate Range High Flux Signal
| ML051880077 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 06/24/2005 |
| From: | Jensen J Indiana Michigan Power Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| AEP:NRC:2573-26 LER 05-001-00 | |
| Download: ML051880077 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(iii) |
| 3152005001R00 - NRC Website | |
text
INDIANA MICHIGAN POWERS A unit ofrAmerican Electric Power Indiana Michigan Power Cook Nuclear Plant One Cook Place Bridgman, Ml 49106 AEP.com June 24, 2005 AEP:NRC:2573-26 10 CFR 50.73 Docket No.
50-315 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop O-P1-17 Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Unit 1 LICENSEE EVENT REPORT (LER) 315/2005-001-00, REACTOR TRIP FOLLOWING INTERMEDIATE RANGE HIGH FLUX SIGNAL In accordance with 10 CFR 50.73, "Licensee Event Report System," the following report is submitted:
LER 315/2005-001: "Reactor Trip Following Intermediate Range High Flux Signal" identifies the commitments contained in this submittal.
Should you have any questions regarding this correspondence, Mr. Michael K. Scarpello, Regulatory Affairs Supervisor, at (269) 466-2649.
please contact Sincerely, Joseph N. Jensen Site Vice President RAJ/jen Attachments "I 1-
- ->
,--a 46
U. S. Nuclear Regulatory Commission AEP:NRC:2573-26 Page 2 C:
J. L. Caldwell - NRC Region III K. D. Curry - AEP Ft. Wayne J. T. King - MPSC C. F. Lyon - NRC Washington DC MDEQ - WHMD/HWRPS NRC Resident Inspector Records Center - INPO
ATTACHMENT 1 TO AEP:NRC:2573-26 REGULATORY COMMITMENTS The following table identifies those actions committed to by Indiana Michigan Power Company (I&M) in this document. Any other actions discussed in this submittal represent intended or planned actions by I&M. They are described to the Nuclear Regulatory Commission (NRC) for the NRC's information and are not regulatory commitments.
Commitment
Date Develop preventative maintenance tasks for September 23, 2005 periodic replacement of nuclear instrument bistable relay drivers (CRA 05116001-05).
NRC Form 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB:
NO. 3150-0104 EXPIRES 613012007
,6-2004)
, the NRC may not conduct or sponsor, and a person I not required to respond to, the Information collection.
- 3. PAGE Donald C. Cook Nuclear Plant Unit 1 05000-315 1 of 4
- 4. TITLE Reactor Trip Following Intermediate Range High Flux Signal
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED
_ SEQUENTIAL I REVISION FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR I NUMBER lNUMBER MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 04 26 05 2005 001 00 06 24 05
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
Mode 1 0 20.2201(b) 0 20.2203(aX3Xi) 0 50.73(a)(2)(i)(C) 0 50.73(aX2Xvii) o 20.2201(d) 0 20.2203(aX3Xii) 0 50.73(a)(2)(iIXA) 0 50.73(aX2XviiiXA) o 20.2203(aXl) 0 20.2203(aX4) 0 50.73(a)(2)(IiXB) 0 50.73(aX2XviiiXB) o 20.2203(aX2XI) 0 50.36(cXlXiXA) 0 50.73(a)(2)(iii) 0 50.73(aX2XIxXA)
- 10. POWER LEVEL 0 20.2203(aX2Xli) 0 50.36(cX1XiiXA) 0 50.73(aX2)(ivXA) 0 50.73(aX2Xx) 008 0 20.2203(aX2Xiii) 0 50.36(cX2) 0 50.73(aX2XvXA) 0 73.71(aX4) o 20.2203(aX2Xiv) 0 50.46(aX3Xii) 0 50.73(aX2XvXB) 73.71(aX5) 0 20.2203(aX2Xv) 0 50.73(aX2Xi)(A) 0 50.73(aX2XvXC)
OTHER Specify In Abstract below 0 20.2203(aX2Xvi) 0 50.73(aX2X)l(B) 0 50.73(a)2XvXD) or In (ff more space is required, use additional copies of NRC Form (3664)
Conditions Prior to Event
Donald C. Cook Nuclear Plant (CNP) Unit 1 was at 8% reactor power and stable.
Description of Event
At 0002 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> on April 26, 2005, CNP Unit 1 reactor automatically tripped while at 8% reactor power.
Preparations were being made to synchronize the main generator with the offsite electrical power grid. The post-trip investigation determined that the trip was caused by an intermediate range high flux reactor trip signal. The intermediate range high flux reactor trip occurred below the reactor protection system actuation normally set at 22% reactor power. This reactor trip has a one-of-two channel trip logic. The trip is interlocked to be active below 10% reactor power. It was determined the cause was a spurious lowering of the trip setpoint due to age related degradation of the level adjust potentiometer in the circuitry of 1-NRI DWR, Nuclear Instrumentation Channel 1 Intermediate Range Neutron Flux Detector Drawer [JD].
The automatic plant trip at low power functioned as expected. The auxiliary feedwater [BA] system actuated and operated as expected. Operators took procedurally directed actions and responded to the transient in an appropriate and timely manner, resulting in a safe and stable plant configuration. Automatic post-trip features functioned dependably with the exception of 1-FMO-242, West Motor Operated Auxiliary Feedwater Pump Supply to Steam Generator OME4-4 Control Valve, not throttling closed following the trip. An engineering evaluation concluded this was an expected response under the circumstance, and no equipment failure was indicated.
This event was reported under event notification system number 41639 per 10 CFR 50.72(b)(2Xiv)(B) and 10 CFR 50.72(b)(3Xiv)(A), as a valid reactor trip and actuation of the auxiliary feedwater system, respectively.
This LER is being reported per requirements of 10 CFR 50.73(aX2)(ivXA).
Cause of Event
The cause of the spurious reactor trip signal was determined to be drying out of the lubricant internal to the level adjust potentiometer (R4E) associated with 1-NRI-35-NC35F, Nuclear Instrumentation Intermediate Range Channel 1 High Neutron Flux Bistable, due to the age of the component and environmental conditions.
A recently completed single point vulnerability (SPV) study was not chartered to include conditions at less than 100% power operation. This was considered to be a contributing cause to this event.
The level adjust potentiometers, at the root of this event, are not a critical component above 10% power. The coincidence logic of the source and intermediate range instrumentation is a one-out-of-two trip logic, vice a two-out-of-four trip logic with the power range instrumentation. CNP will evaluate the need to expand the SPV study to operations less than 100% power.
(If more space Is required, use additional copies of NRC Form (3664)
Analysis of Event
An assessment of this event was performed and it was determined that this event was bounded by the existing accident analysis associated with unplanned reactor trips with the main condenser available. This assessment is based on the following considerations:
- 1. The automatic plant trip at low power, caused by Intermediate Range nuclear instrument 1-NRI-35, functioned as expected.
- 2. The reactor trip was inadvertent. The intermediate range nuclear instrument, 1-NRI-35, normally has a trip setpoint of 22%. In this event, a reactor trip was initiated at 7-8% power. This does not contribute to the increased likelihood of any initiators, other than transients that result in or from a reactor trip.
- 3. Neither the failure of the intermediate range nuclear instrument, nor the subsequent unit trip, degraded any system used to mitigate core damage, assure containment integrity, or maintain defense-in-depth and safety margins.
- 4. The low initial power level removes any risk contribution due to Anticipated Transient Without Scram (ATWS) initiators at 40% power or above. This initiator contributes about 90% of the ATWS core damage contribution, and corresponds to about 1% of the overall CDF.
Conclusion:
The significance associated with this event is non-risk significant. Additionally, there were no radiological or industrial safety risks created or affected by the event.
Corrective Actions
Immediate Corrective Actions:
Replaced the affected bistable and relay driver assembly, 1-NRI-35-NC35F, for the intermediate range channel 1-NRI-35 (JO 05116001, Activity 01).
High Level Trip bistables for the other Unit 1 nuclear instrumentation detector channels, 1-NRI-31, 1-NRI-32 and 1-NRI-36, were inspected. The potentiometers were manipulated to confirm they operated correctly (JO 05116001, Activity -02, -03, and -04).
Action to Address Extent of Condition:
CNP will evaluate expanding the single point vulnerability study to include operations less than 100% power.
(CR 05159006, due7/9105).
Corrective Action to Prevent Recurrence:
Develop preventive maintenance tasks for periodic replacement of nuclear instrument bistable relay drivers (CRA 05116001-05, due 9/23/05).
(if more space Is required, use additional copies of NRC Form (366A)
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