05000261/LER-2014-001, Regarding Reactor Trip Due to a Two-out-of-Three Logic Signal from Steam Generator Water Level Protection Train B Logic Matrix
| ML14073A062 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 03/10/2014 |
| From: | William Gideon Duke Energy Progress |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RNP-RA/14-0030 LER 14-001-00 | |
| Download: ML14073A062 (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)(viii)(A) 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 |
| 2612014001R00 - NRC Website | |
text
i W. R. Gideon DUKE H. B. Robinson Steam Electric Plant Unit 2
- ENERGY, Site Vice President Duke Energy Progress 3581 West Entrance Road Hartsvile, SC 29550 0: 843 8571701 F: 843 857 1319 Randy. Gideona duke-energy con.
Serial: RNP-RA/14-0030 MAR 1 0 2014 10 CFR 50.73 Attn: Document Control Desk United States Nuclear Regulatory Commission Washington, DC 20555-0001 H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261/RENEWED LICENSE NO. DPR-23 LICENSEE EVENT REPORT NO. 2014-001-00 REACTOR TRIP DUE TO A TWO-OUT-OF-THREE LOGIC SIGNAL FROM STEAM GENERATOR WATER LEVEL PROTECTION TRAIN B LOGIC MATRIX Ladies and Gentlemen:
Pursuant to 10 CFR 50.73, Duke Energy Progress, Inc. is submitting the attached Licensee Event Report. There are no outstanding corrective actions required to restore compliance with NRC requirements; restoration of compliance has been met. Should you have any questions regarding this matter, please contact Mr. R. Hightower, Manager - Nuclear Regulatory Affairs at (843) 857-1329.
This document contains no new Regulatory Commitments.
Sin W. R. Gideon Site Vice President H. B. Robinson Steam Electric Plant, Unit No. 2 WRG/jmw Attachment c:
V. McCree, NRC, Region II Siva Lingam, NRC, NRR NRC Resident Inspector
US NRC Document Control Desk Attachment to Serial: RNP-RAI14-0030 4 pages (including this cover page)
H. B. ROBINSON STEAM ELECTRIC PLANT UNIT 2 LICENSEE EVENT REPORT NO. 2014-001-00 REACTOR TRIP DUE TO A TWO OUT OF THREE LOGIC SIGNAL FROM STEAM GENERATOR WATER LEVEL PROTECTION TRAIN B LOGIC MATRIX
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/3112017 (02-2014) c.'
Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections I
Branch (T-5 F53), U.S, Nuclear Regulatory Commission, Washington, DC 20555-0001, or by LICENSEE EVENT REPORT (LER) internet e-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC each 20503 If a means used to impose an information collection does not display a currently valid OMB digits/characters for e block) control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE H. B. Robinson Steam Electric Plant, Unit 2 05000261 1 OF 3
- 4. TITLE Reactor Trip Due to a Two-out-of-Three Logic Signal from Steam Generator Water Level Protection Train B Logic Matrix
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR UME NOSEQUENTIAL REV MOT A
ER FACILITY NAME DOCKET NUMBER I
YER FACILITY NAME DOCKET NUMBER 01 09 2014 2014 -
001 00 03 10 2014 FACILITY NAME DOCKET NUMBER
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 20.2201(b)
[j 20.2203(a)(3)(i)
LI 50.73(a)(2)(i)(C)
LI 50.73(a)(2)(vii)
MODE 1 20.2201(d)
E] 20.2203(a)(3)(ii)
LI 50,73(a)(2)(ii)(A)
LI 50.73(a)(2)(viii)(A)
LI 20.2203(a)(1)
LI 20.2203(a)(4)
LI 50,73(a)(2)(ii)(B)
LI 50.73(a)(2)(viii)(B)
_ 20.2203(a)(2)(i)
[
50.36(c)(1)(i)(A)
LI 50.73(a)(2)(iii)
LI 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL LI 20.2203(a)(2)(ii)
[L 50.36(c)(1)(ii)(A)
Z 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x) 20.2203(a)(2)(iii)
[
50.36(c)(2)
LI 50.73(a)(2)(v)(A)
LI 73.71(a)(4) 0] 20.2203(a)(2)(iv)
LI 50.46(a)(3)(ii) 50.73(a)(2)(v)(B)
LI 73.71(a)(5) 100 El 20.2203(a)(2)(v)
LI 50.73(a)(2)(i)(A)
LI 50.73(a)(2)(v)(C)
LI 50.73(a)(2)(i)(B)
LI 50.73(a)(2)(v)(D)
Specify in Abstract below or in
PLANT IDENTIFICATION Westinghouse - Pressurized Water Reactor EQUIPMENT IDENTIFICATION Reactor Protection System (RPS) [AA], Auxiliary Feedwater System [BA]
IDENTIFICATION OF EVENT At 2234 hours0.0259 days <br />0.621 hours <br />0.00369 weeks <br />8.50037e-4 months <br /> EST on 1/9/2014, with the Unit in Mode I at 100% power, Robinson Nuclear Plant (RNP) experienced an automatic reactor trip during the performance of Steam Generator (SG) Water Level Protection Channel testing.
EVENT DATE January 09, 2014 REPORT DATE March 10, 2014
CONDITIONS PRIOR TO EVENT
MODE 1, 100% Power with no structures, systems or components out of service at the time of this event that contributed to this event.
BACKGROUND This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) due to the event resulting in an automatic actuation of the Reactor Protection System (RPS) and Auxiliary Feedwater System (AFW).
The RPS monitors all parameters related to safe operation of the reactor. The system is designed to protect the core against fuel rod cladding damage caused by departure from nucleate boiling (DNB), and to protect the Reactor Coolant System (RCS) against damage caused by overpressure. The Low-Low Steam Generator Water Level Trip circuit protects the Steam Generator (SG) in case of a sustained steam/feedwater flow mismatch of insufficient magnitude to cause a flow mismatch reactor trip. This reactor trip circuit actuates on two-out-of-three low-low water level signals in any SG.
MST-0 13, "Steam Generator Water Level Protection Channel Testing," provides the instruction necessary for performing the Surveillance Test which will determine the operability of the Steam Generator Water Level Protection Channel Sets 1, II, and III.
MST-02 1, "Reactor Protection Logic Train 'B' at Power," provides the instructions necessary to determine the operability of Reactor Protection Logic Train 'B'.
DESCRIPTION OF EVENT
At 2234 on 1/9/2014, with the Unit in Mode 1 at 100% power and during the performance of MST-013, Robinson Unit 2 experienced an automatic reactor trip. SG Water Level Channel III was tested in accordance with MST-013 and returned to service upon verification that all bistables and alarms were cleared. However, unbeknownst to technicians, contact 2-6 on relay LC-496A I -X(B) was in the half-tripped condition and not annunciated in the Control Room (CR). When technicians proceeded with MST-0 13 placing SG Water Level Channel I in the tripped condition, a two-out-of-three logic signal was generated causing the 'B'
Reactor Trip Breaker to open, causing a turbine trip followed by a reactor trip signal which opened the 'A' Reactor Trip Breaker.
Auxiliary Feedwater automatically started as expected. There were no other equipment performance issues.
Circuit troubleshooting revealed that the LC-496A1-X(B) 2-6 contact ('B' train), while appearing to be in the correct position, had 133.2 VDC across it (showing an open contact). This contact failure, coupled with the LC-494A1-X(B) contacts being open from the Channel I test, broke continuity to the relays for the 'B' train, which broke continuity to the 'B' reactor trip breaker undervoltage coil and automatic shunt trip coil, causing the 'B' reactor trip breaker to open. The trip of the 'B' reactor trip breaker initiated a turbine trip, as expected. Per design, a turbine trip results in a reactor trip at greater than 40% reactor power and led to the 'A' reactor trip breaker opening and subsequent reactor trip.
During a visual examination of relay LC-496A I-X(B) after being removed from the RPS relay rack, it was discovered that a small piece of plastic material was wedged between the plates of its 2-6 contact. The material, determined to be a piece of a degraded wire label that had become dislocated from a wire, prevented the contacts from fully closing. Since relay LC-496AI-X(B) passed surveillance test MST-021 performed on 12/02/2013, it has been concluded that the foreign material fell into the relay contacts after this test and prior to MST-013 testing on 1/9/2014. RPS relays were subsequently tested to verify that no foreign material was present that could prevent correct relay operation. Both trains of relay racks were inspected to identify and remove any potential foreign material that could fall into a relay contact.
CAUSAL FACTORS The direct cause of the reactor trip event is foreign material preventing closure of contacts 2-6 of relay LC-496AI-X(B). This created an undetected condition of having one channel of the 'C' steam generator low-low level protection matrix in a tripped condition. When another channel was placed in the tripped condition for testing, the reactor trip breaker circuit was opened causing the reactor trip.
CORRECTIVE ACTIONS
Corrective Actions - Completed:
Both trains of RPS relays were tested to verify that no foreign material was present that could prevent correct relay operation.
Both trains of relay racks were inspected to identify and remove any potential foreign material that could adversely affect proper operation of RPS relay contacts.
Corrective Actions - Planned:
Corrective action to address foreign material exclusion consists of the replacement of wire labels in reactor protection and safeguards relay racks. Revision of the model work order instructions for the relay rack clean-and-inspect preventive maintenance procedures to include inspection of wiring, labels, cable raceways and other passive components for evidence of degradation.
SAFETY ANALYSIS
The reactor was operating at full power during the performance of MST-0 13 when an automatic reactor trip occurred. The mitigating equipment, including AFW functioned as expected and plant shutdown proceeded normally without further challenge.
The cause of the plant trip was determined to be from foreign material being caught between two contacts in the course of MST-013. The trip logic performed as designed and there were no other equipment performance issues. Therefore, the risk consequence of this event was small based on a successful reactor trip with no equipment or operational challenges.
ADDITIONAL INFORMATION
A search of internal and external operating experience for the previous three years did not identify events with a similar failure mechanism that would have prevented the failure of relay contacts resulting from degrading wire labels.