05000325/LER-2010-003, Regarding Automatic Reactor Scream Due to Ib Reactor Feed Pump Trip
| ML102010291 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 07/02/2010 |
| From: | Wills E Progress Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BSEP 10-0078 LER 10-003-00 | |
| Download: ML102010291 (6) | |
| 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 |
| 3252010003R00 - NRC Website | |
text
Progress Energy JUL 0 212010 SERIAL: BSEP 10-0078 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 Renewed Facility Operating License No. DPR-71 Docket No. 50-325 Licensee Event Report 1-2010-003 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.
Plant General Manager Brunswick Steam Electric Plant LJG/ljg
Enclosure:
Licensee Event Report Progress Energy Carolinas, Inc.
Brunswick Nuclear Plant PO Box 10429 Southport, NC 28461
Document Control Desk BSEP 10-0078 / Page 2 cc (with enclosure):
U. S. Nuclear Regulatory Commission, Region II ATTN: Mr. Luis A. Reyes, 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: 08/31/2010 (9-2007)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
3PAGE Brunswick Steam Electric Plant (BSEP), Unit 1 05000325 1 of4
- 4. TITLE Automatic Reactor Scram due to I B Reactor Feed Pump Trip.
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
I FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.
05000 FACILITY NAME DOCKET NUMBER 05 05 2010 2010 - 003 - 00 07 02 2010 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check alf that apply)
El 20.2201(b)
(] 20.2203(a)(3)(i)
EL 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 1 Li 20.2201(d)
Li 20.2203(a)(3)(ii)
[] 50.73(a)(2)(ii)(A)
[I 50.73(a)(2)(viii)(A)
Li 20.2203(a)(1)
Li 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
[I 50.73(a)(2)(viii)(B)
__ 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)
[D 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
Li 20.2203(a)(2)(iii)
El 50.36(c)(2)
EL 50.73(a)(2)(v)(A)
[] 73.71(a)(4) 100
[] 20.2203(a)(2)(Nv)
[] 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)
[J 50.73(a)(2)(v)(C)
Li OTHER LI 20.2203(a)(2)(vi)
Li 50.73(a)(2)(i)(B)
Li 50.73(a)(2)(v)(D)
Specify in Abstract below or in The control logic to initiate a RCR pump runback consists of a RFP low suction flow signal from either RFP flow switch 1-FW-FS-175 or 1-FW-FS-176, combined with a low reactor vessel water level (i.e., less than or equal to 182 inches) signal. A runback of the RCR pumps reduces reactor power to a level where flow from one RFP is sufficient to avoid a scram on low reactor vessel level. The event investigation determined that the 1 B RFP indicated suction flow, as measured at the flow switch, remained above the RCR pump runback setpoint for an extended period of time following the RFP trip. This delay prevented a runback signal from being generated in time to prevent the automatic reactor scram on RPV low level.
Failure of the RCR pump to runback upon loss of the 1 B RFP was caused by implementation of an inappropriate design change in 1977. A plant modification installed pulsation dampeners (i.e., snubbers) in each Unit 1 RFP suction flow element sensing line in order to reduce excessive gauge fluctuations and prolong the life of the instruments connected to the sensing lines. The RCR pumps did not runback as expected because the signal for RFP low suction flow did not occur until after reactor vessel level dropped to the scram setpoint. The plant modification was intended to correct a gauge fluctuation problem, but was implemented in such a way that resulted in delayed actuation of the RFP low suction flow signal to the runback logic.
The installed snubbers are adjustable pin stainless steel pulsation dampeners. As a result of the extent of condition investigation, the as-found configuration of the adjustable pin snubbers in both the Unit 1 and Unit 2 RFP sensing lines found that each snubber contained either one or two pins installed.
Troubleshooting determined that the required RCR pump runback signal could only be achieved with all pins removed from the snubbers. With all pins removed from the snubbers, the RCR pump runback function within the required timeframe was restored.
Event Cause
The cause of the event was pulsation dampeners (i.e., with pins installed) in the reactor feed pump suction flow element sensing lines, installed in a 1977 plant modification, delayed the actuation of the low suction flow signal to the pump runback logic. This delay allowed the RPV water level to drop below the Low Level 1 setpoint, causing an automatic reactor scram on Unit 1 and activation of the RPS and the PCIS. The investigation concluded that the adverse condition was a historical problem, which has existed for such a long time that a plausible root cause could not be reasonably determined.
Safety Assessment
The safety significance of this event is considered minimal. In addition to RCIC, the Emergency Core Cooling systems and the Automatic Depressurization system were operable and available to provide adequate core cooling if needed. Operators maintained RPV level within the normal band following the automatic reactor scram. All systems functioned as designed, and there was no nuclear or industrial safety consequence from this event.
Corrective Actions
The following corrective actions will be taken.
" Remove all snubber pins in the Unit 1 and Unit 2 reactor feed pump suction flow element sensing lines. This action is complete.
" Revise Unit 1 and Unit 2 instrument rack piping detail drawings D-70042 and D-07042, respectively, to identify adjustment no. 1 configuration (i.e., no pins) for the instrument snubbers in the RFP suction flow sensing lines. This action is scheduled to be completed by September 9, 2010.
" Revise design basis document DBD-02, "Reactor Coolant Recirculation System," to identify that the RFP low suction flow signal is required to actuate in sufficient time to allow the runback to prevent a scram. This action is scheduled to be completed by September 9, 2010.
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.