05000325/LER-2008-007, Automatic Reactor Scram Due to Electro-Hydraulic Control System Failure
| ML090420273 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 01/26/2009 |
| From: | Wills E Progress Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BSEP-09-0007 LER-08-007-00 | |
| Download: ML090420273 (7) | |
| 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 |
| 3252008007R00 - NRC Website | |
text
Progress Energy January 26, 2009 SERIAL: BSEP 09-0007 10 CFR 50.73 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Brunswick Steam Electric Plant, Unit No. 1 Docket No. 50-325/License No. DPR-71 Licensee Event Report 1-2008-007 Ladies and Gentlemen:
In accordance with the Code of Federal Regulations, Title 10, Part 50.73, Carolina Power
& Light Company, now doing business as Progress Energy Carolinas, Inc., submits the enclosed Licensee Event Report (LER). This report fulfills the requirement for a written report within sixty (60) days of a reportable occurrence.
Please refer any questions regarding this submittal to Mr. Gene Atkinson, Supervisor -
Licensing/Regulatory Programs, at (910) 457-2056.
Sincerely, Edward L. Wills, Jr.
Plant General Manager Brunswick Steam Electric Plant MAT/mat
Enclosure:
Licensee Event Report Progress Energy Carolinas, Inc.
Brunswick Nuclear Plant PO Box 10429 Southport, NC 28461
Document Control Desk BSEP 09-0007 / Page 2 cc (with enclosure):
U. S. Nuclear Regulatory Commission, Region II ATTN: Mr. Luis A. Reyes, Regional Administrator Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, GA 30303-8931 U. S. Nuclear Regulatory Commission ATTN: Mr. Philip B. O'Bryan, NRC Senior Resident Inspector 8470 River Road Southport, NC 28461-8869 U. S. Nuclear Regulatory Commission (Electronic Copy Only)
ATTN: Mrs. Farideh E. Saba (Mail Stop OWFN 8G9A) 11555 Rockville Pike Rockville, MD 20852-2738 Chair - North Carolina Utilities Commission P.O. Box 29510 Raleigh, NC 27626-0510
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Brunswick Steam Electric Plant (BSEP), Unit 1 05000325 1 of 5
- 4. TITLE Automatic Reactor Scram due to Electro-Hydraulic Control System Failure
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED 1I TAL E
FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR EQUENTIAL REV MONTH DAY YEAR 05000 NUMBER NO.
05000 FACILITY NAME DOCKET NUMBER 11 26 2008 2008 - 007 - 00 01 26-2009 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
LI 20.2201(b)
El 20.2203(a)(3)(i)
[L 50.73(a)(2)(i)(C)
L] 50.73(a)(2)(vii) 1 El 20.2201(d)
LI 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
LI 50.73(a)(2)(viii)(A)
LI 20.2203(a)(1)
EL 20.2203(a)(4)
[L 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
[LI 50.36(c)(1)(i)(A)
[_
50.73(a)(2)(iii)
EI 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL EI 20.2203(a)(2)(ii)
LI 50.36(c)(1)(ii)(A)
M 50.73(a)(2)(iv)(A)
LI 50.73(a)(2)(x)
[I 20.2203(a)(2)(iii)
LI 50.36(c)(2)
Ej 50.73(a)(2)(v)(A)
LI 73.71(a)(4) 022 [E 20.2203(a)(2)(iv)
LI 50.46(a)(3)(ii)
[: 50.73(a)(2)(v)(B)
LI 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
Ej 50.73(a)(2)(v)(C)
El 50.73(a)(2)(i)(B)
F1 50.73(a)(2)(v)(D)
Specify in Abstract below or in
Event Cause
An initial investigation was performed to support startup of Unit 1. This investigation determined that the Pressure-Load Gate Amplifier (PLGA) circuit board (A58), in the Electro-Hydraulic Control (EHC) system [TG], was.found to have an intermittent connection. Technicians found that the circuit board voltages varied when flexing the circuit board (i.e., pushing it in) indicating that there were loose connection(s) within the A58 blade / blade receptacle connection. Trends of the event confirmed that the PLGA did not limit the Control Valve Amplifier's (CVA) output to the control valve servos. As a result, the turbine control valves opened too far, causing Main Steam Line pressure to drop and a Group 1 isolation. The Group 1 isolation, caused by the erroneous operation of circuit board A58, was the direct cause of the November 26, 2008, Unit 1 scram.
The root cause of the erroneous operation of circuit board A58 is that the key slot in circuit board A58 was not squared at the bottom mating surface. This circuit board is original plant equipment. Resin at the bottom mating surface, present since original manufacturing of the circuit board, prevented full seating with the terminal receptacle. Since this circuit board has operated since original plant startup without causing a scram, this condition alone would not result in erroneous operation of circuit board A58. However, 100 percent engagement of the blades would have prevented the November 26, 2008, scram from occurring.
Two contributing causes were identified. First, spring cyclic fatigue associated with the blade receptacles within the EHC circuit board terminals further reduced blade engagement. Circuit board A58 is removed and inserted from the cabinet frequently during a refueling outage in support of calibration activities. It is estimated that this occurs ten or more times an outage. Frequent cycling of the spring will cause fatigue and relaxation. Spring relaxation will adversely affect the circuit board A58 blade / blade receptacle connection. However, it was determined that spring relaxation alone would not have caused the scram.
With fully failed springs, there is still adequate contact with 100 percent insertion of the blade.
The second contributing cause was trouble shooting activities associated with circuit board A52 which resulted in further loosening of the connections associated with circuit board A58. Trouble shooting activities were performed on circuit board A52 during the maintenance outage. There is previous Brunswick specific operating experience (i.e., LER 2-2003-03, Nuclear Condition Report (NCR) 89705) which documents a Unit 2 scram on April 4, 2003, due to the Steam Line Resonance Compensator (SLRC) circuit board not being fully seated. The root cause evaluation for NCR 89705 determined that flexing of the slot or connector associated with circuit boards can cause loosening of surrounding circuit boards.
Since the A58 circuit board is relatively close to the A52 circuit board (i.e., 5 slots, 3 circuit boards separation), it is probable that the trouble shooting of circuit board A52 negatively affected the A58 blade /
blade receptacle connections.
Safety Assessment
The safety significance of this event is considered to be minimal. All required safety-related systems responded to the transient as designed. The consequences of this low power transient on the fuel and vessel were minimal. The analyses in Chapter 15 of the Updated Final Safety Analysis Report fully bound this event.
Corrective Actions
The A58 circuit board was replaced to support Unit 1 startup.
The following corrective actions to prevent recurrence have been identified.
" The Unit 1 and Unit 2 circuit board connections within the EHC cabinets will be visually inspected to ensure surface to surface engagement between the blade and receptacle housings, and actions will be taken, as necessary, to achieve surface to surface engagement. This action will be completed during the next Unit 1 and 2 outages that result in the unit being taken to Mode 4, but no later than during the spring 2009 Unit 2 refueling outage (i.e., B219R1) and the spring 2010 Unit 1 refueling outage (i.e., B118R1).
- Procedure 0SMP-EHC001, "Electro Hydraulic Controls System Alignment," was revised to require visual confirmation of 100 percent engagement between the blade and receptacle housings for the EHC circuit boards. This action was completed on January 14, 2009, to support the 2009 Unit 2 refueling outage
- A methodology will be established to ensure visual confirmation of 100 percent engagement between the blade and receptacle housings for the EHC circuit boards after work or trouble shooting not controlled by OSMP-EHCOO.
This action will be completed by March 16, 2009.
Additional corrective actions include the following.
" Appropriate Unit 1 and Unit 2 EHC blade receptacles, determined by an evaluation of the potential consequences of failure and susceptibility to fatigue based on typical outage activities, will be replaced during the spring 2010 Unit 1 refueling outage (i.e., Bi 18R1) and the spring 2011 Unit 2 refueling outage (i.e., B220R1).
" A means to ensure positive seating of the EHC circuit boards (e.g., harness) will be implemented during the spring 2010 Unit 1 refueling outage (i.e., B1 18R1) and the spring 2011 Unit 2 refueling outage (i.e., B220R1).
Previous Similar Events
A review of LERs and corrective action program condition reports identified the following similar event.
LER 2-2003-003, dated June 2, 2003, documents a Unit 2 scram on April 4, 2003, due to the Steam Line Resonance Compensator (SLRC) circuit board not being fully seated. The root cause evaluation for NCR 89705 determined that flexing of the slot or connector associated with circuit boards can cause loosening of surrounding circuit boards. The corrective actions for the event described in LER 2-2003-003 implemented a change to Maintenance procedure 0SPP-EHC001, "Electro Hydraulic Control Systems Alignment," to include new details for verifying proper EHC card engagement (i.e., firmly seat all circuit boards in the EHC cabinet by pushing on the boards).
The trouble shooting activities that were performed during the Unit 1 maintenance outage were completed in accordance with work orders and not via plant procedure OSMP-EHCOO1 (i.e., formerly OSPP-EHCOO) which is for an integrated checkout of the EHC system normally performed during a refueling outage and not intended for specific trouble shooting activities. As such, the EHC cards were not verified to be properly engaged after the trouble shooting activities associated with circuit board A52, though it is not likely that such verification would have prevented the November 26, 2008, Unit 1 scram. Trouble shooting activities associated with circuit board A58 demonstrated that: (1) the inadequate connection could be readily repeated with minimal pull on the A58 circuit board, and (2) no actual inward movement was observed when the A58 circuit board was pushed. Given the condition of the key slot (i.e., root cause of the Unit 1 scram) and the suspected spring fatigue, unless circuit board A58 was the last circuit board to be verified it is likely that subsequent seating verification manipulation of adjacent circuit boards would have negated any benefit derived from verifying circuit board A58 was seated.
Commitments
No regulatory commitments are contained in this report.