05000289/LER-2006-003, Re Automatic Reactor Trip Due to a Design Application Deficiency within the Reactor Coolant Pump Power Monitors Initiated by an Off-Site Grid Disturbance
| ML070530310 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 02/12/2007 |
| From: | Dougherty T AmerGen Energy Co |
| To: | Document Control Desk, NRC/NRR/ADRO |
| References | |
| 5928-07-20026 LER 06-003-00 | |
| Download: ML070530310 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(b)(2) |
| 2892006003R00 - NRC Website | |
text
AmerGenSM AmerGen Energy Company, LLC Three Mile Island Unit i Route 441 South, P.O. Box 480 Middletown, PA 17057 Telephone: 717-948-8000 An Exelon Company February 12, 2007 5928-07-20026 10 CFR 50.73 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 THREE MILE ISLAND NUCLEAR STATION, UNIT 1 (TMI-1)
OPERATING LICENSE NO. DPR-50 DOCKET NO. 50-289
SUBJECT:
LICENSEE EVENT REPORT (LER) NO. 2006-003-00 "Automatic Reactor Trip Due to a Design Application Deficiency Within the Reactor Coolant Pump Power Monitors Initiated by an Off-Site Grid Disturbance" This report is being submitted in accordance with 10 CFR 50.73 (a)(2)(iv)(A). For additional information regarding this LER contact Adam Miller of TMI Unit 1 Regulatory Assurance at (717) 948-8128.
Thomas J.Dou Plant Manager TJD/awm ATTACHMENT: List of Regulatory Commitments cc:
TMI Senior Resident Inspector Administrator, Region I TM I-1 Senior Project Manager File No. 07011
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SUMMARY OF AMERGEN ENERGY CO.,L.L.C. COMMITMENTS The following table identifies commitments made in this document by AmerGen Energy Co. L.L.C.
(AmerGen). Any other actions discussed in the submittal represent intended or planned actions by AmerGen. They are described to the NRC for the NRC's information and are not regulatory
commitments
FORM 366 U.S. NUCLEAR REGULATORY COMMISSION FORM 366 U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
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05000289 1
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TITI P fid Automatic Reactor Trip Due to a Design Application Deficiency Within the Reactor Coolant Pump Power Monitors Initiated bv an Off-Site Grid Disturbance EVENT DATE (5)
LER NUMBER (6)
REPORT DATE (7)
OTHER FACILITIES INVOLVED (8)
ISEQUENTIALIREVISNFACILITY NAME DOCKET NUMBER SEQUENTIAL REVISION MONTH DAY YEAR YEAR NUMBER NUMBER MONTH DAY YEAR N/A N/A FACILITY NAME DOCKET NUMBER 12 13 2006 2006 003 00 02 12 2007 N/A N/A OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check one or more) (11)
MODE (9)
N 20.2201 (b) 20.2203(a)(2)(v) 50.73(a)(2)(i) 50.73(a)(2)(viii)
POWER 20.2203(a)(1) 20.2203(a)(3)(i) 50.73(a)(2)(ii) 50.73(a)(2)(x)
LEVEL (10) 100 20.2203(a)(2)(i) 20.2203(a)(3)(ii) 150.73(a)(2)(iii) 173.71 20.2203(a)(2)(ii) 20.2203(a)(4)
X 50.73(a)(2)(iv)
OTHER I
20.2203(a)(2)(iii) 50.36(c)(1) 50.73(a)(2)(v)
- - Specify in Abstract below or
_ _ _ _ _ _ _ _ I
,20.2203(a)(2)(iv) 50.36(c)(2) 50.73(a)(2)(vii) in NRC Form 366A LICENSEE CONTACT FOR THIS LER {12)
NAME TELEPHONE NUMBER (include Area Code)
Adam W.Miller of TMI-1 Regulatory Assurance 1
(717) 948-8128 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)
REPORTABLE REPORTABLE
CAUSE
SYSTEM COMPONENT MANUFACTURER TO EPIX l
CAUSE
SYSTEM COMPONENT MANUFACTURER TO EPIX N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A SUPPLEMENTAL REPORT EXPECTED (14)
EXPECTED MONTH DAY YEAR A ES (cen IS)16 F(fyes. comp~lete EXPECTED SUBMISSION DATE).
NODAE()
ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)
At 1748 hours0.0202 days <br />0.486 hours <br />0.00289 weeks <br />6.65114e-4 months <br /> on December 13, 2006, the Three Mile Island, Unit 1 (TMI-1) reactor tripped from 100% power following a short duration power disturbance on a 230 kV transmission line located approximately 4 miles from TMI-1. This short duration power disturbance was caused by the failure of a 230 kV transmission line cable -
splice, which resulted in a single-phase ground fault. This short duration ground fault affected power supplied to the reactor coolant pump motors, which in turn caused actuation of the Reactor Coolant Pump Power Monitors (RCPPM). The RCPPM's actuation sends a signal to the Reactor Protection System (RPS) to trip the unit if a
- decrease in reactor coolant pump motor power consumption is detected., This reactor trip is designed to protect the fuel rods from overheating upon a sudden loss of Reactor Coolant flow. The RCPPM design includes. a time delay to prevent inadvertent reactor trips due to short duration electrical-disturbances; which would not affect the reactor coolant pump's ability to maintain adequate Reactor Coolant System flow. The RCPPM time delay has a maximum setting of less than 525 milliseconds. The root cause of the event, is a design application deficiency.
within the RCPPM. The RCPPM circuit design focuses on fuel protection and specifies a maximum time delay, but does not consider the effects of a grid transient of short duration. The RCPPM calibration procedure, will be revised to establish a minimum allowed time delay for the Reactor Coolant Pump Power Monitor circuit. A maintenance activity has been scheduled for the next available opportunity,: but no later than the October 2007 refueling outage, to calibrate the RCPPM using the revised setpoint tolerance. The actuation of the Reactor Protection System was reported to the NRC in accordance with 10CFR 50.72 (b)(2)(iv)(B), reference EN 43050. Submittal of this LER constitutes reporting to the NRC in accordance with 10 CFR 50.73 (a)(2)(iv)(A).
DOCKET 121 LER NUMBER (6)
PAGE (3)
SEQUENTIAL REVISION YEAR NUMBER NUMBER 05000289 2006 003 00 2
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EVENT DESCRIPTION
Plant Conditions before the event:
Babcock & Wilcox - Pressurized Water Reactor - 2568 MWth Core Power Date/Time: December 13, 2006/1748 hours Power Level: 100% steady state power prior to the event Mode: Power Operations There were no structures, systems, or components out of service that contributed to this event.
At 1748 hours0.0202 days <br />0.486 hours <br />0.00289 weeks <br />6.65114e-4 months <br /> on December 13, 2006, the Three Mile Island, Unit 1 (TMI-1) reactor tripped from 100% power following a short duration power disturbance on a 230 kV transmission line located approximately 4 miles from TMI-I. This short duration power disturbance was caused by the failure of a 230 kV transmission line cable splice, which resulted in a single-phase ground fault. This short duration ground fault affected power supplied to the reactor coolant pump motors, which in turn caused actuation of the Reactor Coolant Pump Power Monitors (RCPPM) *[JC]. The RCPPM's actuation sends a signal to the Reactor Protection System (RPS) to trip the unit if a decrease in reactor coolant pump motor power consumption is detected. This reactor trip is designed to protect the fuel rods from overheating upon a sudden loss of Reactor Coolant flow. The RCPPM design includes a time delay to prevent inadvertent reactor trips due to short duration electrical disturbances, which would not affect the reactor coolant pump's ability to maintain adequate Reactor Coolant System flow.
The RCPPM time delay has a maximum setting of less than 525 milliseconds.
Plant systems responded properly to the reactor trip transient and the plant was stabilized at hot shutdown conditions.
The actuation of the Reactor Protection System was reported to the NRC in accordance with 1 OCFR 50.72 (b)(2)(iv)(B), reference EN 43050; and submittal of this LER constitutes reporting to the NRC in accordance with 10 CFR 50.73 (a)(2)(iv)(A).
CAUSE OF EVENT
The root cause of the event is a design application deficiency within the RCPPM. The RCPPM circuit design focuses on fuel protection and specifies a maximum time delay, but does not consider the effects of a grid transient of short duration. Although the grid transient only lasted for approximately 60 milliseconds, the RCPPM circuitry response to this grid transient resulted in the actuation of the RCPPM. The calibration procedure for the time delay instrumentation of the RCPPM does not specifya minimum-setting.
ANALYSIS / SAFETY SIGNIFICANCE The reactor protection system functioned as designed to initiate the automatic reactor trip-in response to the trip signals from the RCPPM. The reactor coolant pumps did. not actually trip. There were no engineered safeguard system actuations. The post-trip equipment response was within the expected range, operator response was appropriate, and stable hot shutdown conditions were established. The existing plant risk assessment (PRA) assumptions for reactor trip probability bound this event. The PRA assumes a probability of 4.28E-01/ yr for reactor trip frequency. This is based on generic industry and plant specific historical trip data. Therefore, this event had minimal safety significance.
This event does not involve a safety system functional failure, which would be reported in accordance with
DOCKET (21 LER NUMBER (6)
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OF 3
NEI 99-02. All safety-related equipment performed in accordance with design in response to the event.
CORRECTIVE ACTIONS
Prior to plant restart, the RCPPM was functionally tested to verify that its safety function was operable.
The faulted 230 kV transmission line was repaired and returned to service.
The RCPPM calibration procedure will be revised to establish a minimum allowed time delay for the Reactor Coolant Pump Power Monitor circuit. A maintenance activity has been scheduled for the next available opportunity, but no later than the October 2007 refueling outage, to calibrate the RCPPM using the revised setpoint tolerance.
PREVIOUS OCCURENCES
There are no previous TMI Unit 1 reactor trips related to problems associated with the design application deficiency within the RCPPM in its response to a transmission line transient.
- Energy Industry Identification System (EIIS), System Identification (SI) and Component Function Identification (CFI) Codes are included in brackets, [SI/CFI] where applicable, as required by 10 CFR 50.73 (b) (2) (i i)(F).