05000324/LER-2011-002, For Brunswick, Unit 2, Regarding Unanalyzed Condition Due to Reactor Pressure Vessel (RPV) Head Detensioned During Startup
| ML12031A167 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 01/16/2012 |
| From: | Wills E Progress Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BSEP 12-0008 LER 11-002-00 | |
| Download: ML12031A167 (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 |
| 3242011002R00 - NRC Website | |
text
hjjr Progress Energy January 16, 2012 SERIAL: BSEP 12-0008 10 CFR 50.73 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Brunswick Steam Electric Plant, Unit No. 2 Renewed Facility Operating License No. DPR-62 Docket No. 50-324 Licensee Event Report 2-2011-002 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 Ms. Annette Pope, Supervisor -
Licensing/Regulatory Programs, at (910) 457-2184.
Sincerely, Edward L. Wills, Jr.
Director - Site Operations Brunswick Steam Electric Plant MAT/mat
Enclosure:
Licensee Event Report Progress Energy Carolinas, Inc.
Brunswick Nuclear Plant P.O. Box 10429 Southport, NC 28461
Document Control Desk BSEP 12-0008 / Page 2 cc (with enclosure):
U. S. Nuclear Regulatory Commission, Region II ATTN: Mr. Victor M. McCree, Regional Administrator 245 Peachtree Center Ave. N.E., Suite 1200 Atlanta, GA 30303-1257 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: 10/31/2013 (10-2010)
, 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 2 05000324 1 of 5
- 4. TITLE Unanalyzed Condition Due to Reactor Pressure Vessel (RPV) Head Detensioned During Startup
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED IIFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.
FACILITY NAME DOCKET NUMBER 11 16 2011 2011 -002-00 01 16 2012
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[1 20.2201(b)
[E 20.2203(a)(3)(i)
[_ 50.73(a)(2)(i)(C)
EL 50.73(a)(2)(vii) 2 El 20.2201(d)
EL 20.2203(a)(3)(ii)
[I 50.73(a)(2)(ii)(A)
EL 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
EL 20.2203(a)(4)
E 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
[_E 20.2203(a)(2)(i)
EL 50.36(c)(1)(i)(A)
LI 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL EL 20.2203(a)(2)(ii)
EL 50.36(c)(1)(ii)(A)
E 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
LI 20.2203(a)(2)(iii)
El 50.36(c)(2)
E] 50.73(a)(2)(v)(A)
El 73.71(a)(4) 007 El 20.2203(a)(2)(iv)
E] 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)
LI 50.73(a)(2)(v)(C)
EL OTHER EL 20.2203(a)(2)(vi)
LI 50.73(a)(2)(i)(B)
EL 50.73(a)(2)(v)(D)
Specify in Abstract below or in to establish contact with its washer on the top of the reactor head flange. Hydraulic pressure is applied to the tensioner and stretches the stud. The mechanic at the tensioner then rotates the stud nut to make firm contact with the washer on the head flange. When the hydraulic pressure is released, the nut maintains the stretch in the stud, applying closing pressure to the flanges of the reactor vessel and head. Once the four studs are tensioned, the tensioners are relocated to the next set of four studs.
Following the event, the tensioning process was assessed through equipment troubleshooting, review of procedure OSMP-RPV502, "Reactor Vessel Reassembly," and interviews with refuel floor personnel. The equipment was found to be filly functional and capable of providing the proper tension to the RPV head stud/nuts. However, it was determined that individuals operating the tensioning equipment misinterpreted the digital display of the hydraulic pressure being applied to elongate the vessel studs and incorrectly believed that the actual pressure being applied was a factor of 10 greater than the indicated pressure. As a result, the studs were not properly elongated during the vessel assembly process.
Validation BSEP uses the Stud Elongation Measurement System (SEMS I11) to validate proper tensioning. Based on interviews conducted with the Maintenance mechanics, Quality Control (QC) inspector, and refuel floor supervisor, who were involved in obtaining and verifying the final elongation readings, it was determined that the individual recording the data on the refuel floor identified that the elongation values were low and did not match acceptance criteria (i.e., 0.045 inches + 0.004 inches) specified in OSMP-RPV502. At this point, the individuals involved in the task convened to discuss the readings. The crew erroneously concluded that the target elongation value of 0.045 inches was automatically deducted from the post-tensioned measured value indicated by the SEMS III equipment. The values obtained from the SEMS III equipment were compared to the specified tolerance in OSMP-RPV502. Since the values obtained from the SEMS III equipment were between + 0.004 inches, the crew determined that acceptable stud elongation had been achieved. The QC inspector concurred with the consensus opinion of the crew.
As a result of these errors, the RPV head studs were tensioned only approximately 10 percent of the required amount. During the ensuing power ascension, Unit 2 exited Mode 5 and ultimately reached Mode 2 with the vessel head not properly tensioned, resulting in an unanalyzed condition. The increase in unidentified drywell leakage, and subsequent reactor scram, was a direct result of this condition.
Event Cause
The root cause of this event is the failure to provide the proper training and procedure guidance to correctly interpret critical data used to validate that the RPV head nuts were properly tightened.
During reactor reassembly, operators applied less than adequate hydraulic pressure to the tensioner during the tensioning of the RPV head stud/nut assemblies. This occurred because the pressure readings were not correctly determined due to an inadequate understanding of the digital readings displayed on the hydraulic pressure indicator. In addition, the subsequent stud elongation measurement readings taken were incorrectly concluded to meet the specified acceptance criteria for proper tensioning. This occurred because the individuals involved had an inadequate understanding of how the SEMS III equipment functioned. In both cases the crews involved relied on erroneous assumptions that led to incorrect conclusions.
Safety Assessment
The safety significance of this event is minimal. The maximum calculated leakage resulting from the event was 10.11 gpm. Operations personnel took appropriate action to shutdown the unit in a timely manner.
All Emergency Safety Feature equipment was operable during this time.
To determine the increase in risk due to reactor head leakage, the risk was quantified over a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> exposure period. This covers the time during initial pressurization to the final de-pressurized state. For the evaluation, small, medium and large break initiators were chosen to represent the leak. This Probabilistic Risk Assessment (PRA) evaluation demonstrated that the impact to the risk model is below 1 E-06 for each break size and; therefore, this event had a minimal impact on risk.
Corrective Actions
The following actions have been completed.
Unit 2 was manually scrammed on November 16, 2011.
Procedure OSMP-RPV502 was revised with respect to conducting stud elongation measurements.
The refuel floor crews were trained on the proper operation of the SEMS III equipment and display of hydraulic pressure indicator for the tensioner.
A structural integrity evaluation of the reactor pressure vessel components was performed prior to restart.
Vessel hydrostatic testing was completed, prior to Unit 2 restart, verifying proper tensioning had been achieved.
The following corrective actions to prevent recurrence are planned.
Revise procedure TRN-NGGC-0003, "Refueling Personnel Qualification Program," to include BSEP personnel. This action is expected to be completed by February 3, 2012.
Revise lesson plan ME501B, "Mechanical Refuel Support," to include specific discussion on operation of SEMS III and proper hydraulic pressure readings during tensioning. This action is expected to be completed by February 2, 2012.
Revise procedures OSMP-RPV501, "Reactor Vessel Disassembly," and OSMP-RPV502, "Reactor Vessel Resassembly," to include the need for initial refuel floor training (i.e., provided in ME501B) prior to work on refuel floor. This action is expected to be completed by February 28, 2012.
Revise procedure OSMP-RPV502 to include detailed guidance on use of the SEMS III equipment.
This action is expected to be completed by February 28, 2012.
Revise OSMP-RPV501 and OSMP-RPV502 procedure instructions for the layout and interpretation of the hydraulic tensioner pressure indicator. This action is expected to be completed by February 28, 2012.
The BSEP Refueling Team training program and content, associated with RPV disassembly and reassembly, will be reconstituted using the systematic approach to training. This action is expected to be completed by March 1, 2012.
Previous Similar Events
A review of LERs and corrective action program condition reports for the past three years did not identify any similar previous occurrences.
Commitments
No regulatory commitments are contained in this report.