05000416/LER-2010-001, Regarding Automatic Reactor Scram on Decreasing Reactor Water Level Due to Inadvertent Reactor Feed Pump Trip
| ML101250552 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 05/05/2010 |
| From: | Perino C Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GNRO-2010/00036 LER 10-001-00 | |
| Download: ML101250552 (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)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 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)(iv)(A), System Actuation 10 CFR 50.73(b)(5) |
| 4162010001R00 - NRC Website | |
text
~Entergy GNRO-2010100036 May 5,2010 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Entergy Operations, Inc.
7003 Bald Hill Road P.O. Box 756 Port Gibson, MS 39150 Tel 601 437 6299 Christina L. Perino Manager Licensing
Subject:
lER 2010-001-00 Automatic Reactor Scram On Decreasing Coolant level Due To Inadvertent Reactor Feed Pump Trip Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 license No. NPF-29
Dear Sir or Madam:
Attached is licensee Event Report (lER) 2010-001-00 which is a final report. This report is submitted in accordance with 10 CFR 73(a)(2)(iv)(A).
This letter does not contain any commitments. If you have any questions regarding the attached report, please call Peggy R. Rescheske at 601-437-1781.
Sincerely, ClPIPRR
Attachment:
lER 2010-001-00 cc:
(See Next Page)
GNRO-2010/00036 Page 2 cc:
NRC Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 U. S. Nuclear Regulatory Commission ATTN: Mr. Elmo E. Collins (w/2)
Regional Administrator, Region IV 612 East Lamar Blvd, Suite 400 Arlington, TX 76011-4125 U.S. Nuclear Regulatory Commission ATTN: Mr. Carl F. Lyon, NRRlADRO/DORL (w/2)
Mail Stop OWFN/8 B1 11555 Rockville Pike Rockville, MD 20852-2378
u.s. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 NRC FORM 386 (9-2007)
LICENSEE EVENT REPORT (LER)
EXPIRES: 0813112010 Estimated burden per response to comply with this mandatory collection request: 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments reaarding burden estimate to the Records and fOIAIPrivacy Service Branch (T-5 F52), U.S.
Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infooolleclsClnrc.gov, and to the Desk Officer, 0IIice of Information and Regulatory Affairs, NEOB-10202, (3150-0104>, 0IIice of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a cumdy valid 0M3 control m.mber, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME Grand Gulf Nuclear Station, Unit 1
- 2. DOCKET NUMBER 05000416
- 13. PAGE 1 of 4 f4. TITLE Automatic Reactor Scram On Decreasing Reactor Water Level Due To Inadvertent Reactor Feed Pump Trip I. EVENT DATE
- 8. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACIUnES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.
FACILITY NAME DOCKET NUMBER NM NM 03 08 2010 2010 - 001 -
00 05 FACILITY NAME 05 2010 N/A DOCKET NUMBER N/A 1
100
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) o 20.2201 (b) 0 20.2203(a)(3)(i) 0 50.73(a)(2)(i)(C) 0 50.73(a)(2)(vii) o 20.2201 (d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) o 20.2203(a)(1) 0 20.2203(a)(4) 0 5O.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B) o 2O.2203(a)(2)(i) 0 50.36(c)(1 )(i)(A) 0 5O.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)
"1-0.-POWE--R-LEVE--L---ID 2O.2203(a)(2)(ii) 0 50.36(c)(1 )(ii)(A)
~ 5O.73(a)(2)(iv)(A) 0 50.73(a)(2)(x) o 20.2203(a)(2)(iii) 0 5O.36(c)(2) 0 5O.73(a)(2)(v)(A) 0 73.71 (a)(4) o 20.2203(a)(2)(iv) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B) 0 73.71 (a)(5) o 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C) 0 OTHER o 20.2203(a)(2)(vi) 0 5O.73(a)(2)(i)(B) 0 5O.73(a)(2)(v)(D)
Specify in Abstract bekMt or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME ITELEPHONE NUMBER Onclude Area Code)
Christina L. Perino, Licensing Manager 1601-437-6299
- 13. COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT
CAUSE
MANU*
REPORTABLE SYSTEM COMPONENT FACTURER TO EPIX
CAUSE
MANU-REPORTABLE SYSTEM COMPONENT FACTURER TO EPIX D
SJ FIT RSMT Y
o SJ SCV BYJK Y
- 14. SUPPLEMENTAL REPORT EXPECTED o YES (Ifyes, complete 15. EXPECTED SUBMISSION DATE)
~ NO ABSTRACT (Umit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
- 11. EXPECTED SUBMISSION DATE MONTH DAY YEAR On March 8, 2010, at approximately 1635 hours0.0189 days <br />0.454 hours <br />0.0027 weeks <br />6.221175e-4 months <br /> Central Standard Time (CST), Grand Gulf Nuclear Station (GGNS) was in Mode 1 operating at approximately 100 percent power, when an actuation of the Reactor Protection System (RPS) occurred due to decreasing reactor water level. The cause of the event was the combination of the Reactor Feed Pump 8 (RFP B) minimum flow valve failing open due to an erroneous signal from flow instrumentation, and the Reactor Feed Pump Turbine A (RFPT A) tripping due to speed demand mismatch caused by control valve linkage binding. One feed pump could not support the reactor feedwater demand, resulting in a reactor scram per design on Reactor Water Level 3 (+11.4 inches narrow range).
The appropriate off-normal event procedures were entered to mitigate the transient with all systems responding as designed. All control rods inserted to shut down the reactor. No loss of offsite or Engineered Safety Feature (ESF) power occurred. No emergency core cooling system (ECCS) initiation setpoint was reached and no safety relief valves (SRVs) lifted. The normal heat sink (main condenser) remained available during this event. Reactor water level was restored and maintained by the condensate and feedwater system.
NRC FORM 366 (9-2007)
NRC FORM 386A U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 2. DOCKET
- 1. FACILITY NAME
- 8. LER NUMBER
- 3. PAGE I SEQUENTIAL I REV YEAR NUMBER NO.
Grand Gulf Nuclear Station. Unit 1 05000416 2010 001 00 2
of 4
A. REPORTABLE OCCURRENCE On March 8,2010, at approximately 1635 hours0.0189 days <br />0.454 hours <br />0.0027 weeks <br />6.221175e-4 months <br /> Central Standard Time (CSn, Grand Gulf Nuclear Station (GGNS) experienced an automatic reactor scram due to decreasing reactor water level. Upon decreasing to Reactor Water Level 3 (+11.4 inches narrow range), a Reactor Protection System (RPS) [JC] scram signal was automatically initiated. Actuation of the RPS resulting in an automatic reactor scram is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A). Telephone notification was made on March 8,2010, to the NRC Emergency Notification System (ENS) within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of the event pursuant to 10 CFR 72(b)(2)(iv)(B).
B.
INITIAL CONDITIONS At the time of the event, the reactor was in OPERATIONAL MODE 1 with reactor power at approximately 100 percent. There were no additional inoperable structures, systems, or components at the start of the event that contributed to this event.
C.
DESCRIPTION OF OCCURRENCE On March 8, 2010, at 1635 hours0.0189 days <br />0.454 hours <br />0.0027 weeks <br />6.221175e-4 months <br /> CST, an automatic reactor scram occurred on Low Reactor Pressure Vessel (RPV) level (Level 3, +11.4 inches narrow range). Prior to the scram, increasing speed and flow on the Reactor Feed Pump Turbine A (RFPT A) [SJ] was noted, followed by RFPT A Govemor Valve Trouble alarm and subsequent trip of the RFPT A. As the expected Reactor Recirculation System [AD] Flow Control Valve (FCV) runback was being observed, the Recirculation Hydraulic Power Unit A (HPU A) tripped, stopping the FCV runback.
The RFP B minimum flow valve 1N21 F503B failed open due to transmitter 1N21 N088B, Reactor Feed Pump B (RFP B) suction flow, generating an erroneous control signal, driving the RFP B minimum flow valve open.
The erroneous signal was due to an electrical short in the control circuit caused by condensation from a steam leak. As both feed pumps attempted to increase speed, the RFPT A control valve linkage experienced binding and the RFPT A tripped due to speed demand mismatch. When the RFPT A tripped with the higher demand caused by the opening of the 1N21 F503B, the total demand exceeded the caPacity of the RFP B and the reactor automatically scrammed on low reactor water level. Investigation revealed that the plant response would have been the same (i.e., reactor scam) had the Recirculation FCV A tripped or it had successfully runback. The investigation also determined that if the RFP B minimum flow valve had failed open without a RFPT A trip, the reactor would not have scrammed.
The automatic reactor scram occurred as designed on low RPV level (Level 3, +11.4 inches narrow range) due to loss of feedwater flow. Level 3 is also a setpoint for Group 2 (Residual Heat Removal (RHR) to Radwaste) and Group 3 (Shutdown Cooling Isolation). No valves isolated in these systems due to their being in their normally closed position. The appropriate off-normal event procedures were implemented to mitigate the transient with all systems responding as designed after the scram. The lowest reactor water level observed was approximately -31 inches Wide Range. All withdrawn control rods inserted to the full in position; sixteen (16) control rods did not indicate a position of 00, but did have their green "full-in" indication.
Subsequent investigation determined these sixteen rods fully inserted Past position "00" but did not settle back to position "00." No loss of offsite or Engineered Safety Feature (ESF) power occurred. No emergency core cooling system (ECCS) initiation setpoint was reached and no safety relief valves (SRVs) lifted.
NRC FORM 388A U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 2. DOCKET
- 1. FACILITY NAME
- 8. LER NUMBER
- 3. PAGE I SE~~Al I REV YEAR NO.
Grand Gulf Nuclear Station. Unit 1 05000416 2010 001 00 3
of 4
All safety related equipment operated as expected. The normal heat sink (main condenser) remained available during this event. Reactor water level was restored and maintained by the condensate and feedwater system.
D.
APPARENT CAUSE The cause of the event was the combination of the RFP B minimum flow valve failing open due to an erroneous signal from flow instrumentation, and the RFPT A tripping due to speed demand mismatch caused by control valve linkage binding. One feed pump could not support the reactor feedwater demand and the reactor scrammed on low level.
The erroneous signal from the flow instrumentation was a result of an electrical short in the control circuit.
An inadequate splice assembly allowed water to penetrate the cable jacket at the spliced connedion causing a short, which affected the signal for the flow transmitter driving the minimum flow valve open. The junction box where the splice was located was discovered to be full of water due to condensation from a steam leak on valve Packing in the feedwater heater room. RFP A tripped when the demand signal exceeded the actual flow. The speed demand mismatch was created due to binding in the control valve linkage for the RFPT A, which prevented the valve from opening to match the demand. The binding was due to a lack of lubrication and a build up of wear material between the gears.
The root cause of the event was determined to be a lack of adequate work instrudions for: (1) installing outer jacket sealing on cable splices, and (2) inspection and lubrication of rack and pinion gears. Contributing causes included the magnitude of the steam leak, the water accumulation in junction boxes in the turbine building (e.g., no weep holes in bottom of box), and not effectively implementing measures to mitigate the potential effects of a steam leak.
E.
CORRECTIVE ACTIONS
Immediate Corredive Actions - Reactor water level was restored and the plant was placed in a stable condition. Condition Report CR-GGN-201Q-01503 was written to document and investigate the event and a Root Cause Evaluation was initiated.
Long Term Corrective Actions - The Root Cause Evaluation will address additional corrective actions.
F.
SAFETY ASSESSMENT
Immediate actions performed by the Operations staff were adequate and appropriate in placing and maintaining the reador in a safe shutdown condition. The lowest reador level indicated was -31 inches Wide Range. This is above the initiation setpoint for ECCS systems. Reador vessel water level was restored and maintained by the condensate and feedwater system. The Group 2 Residual Heat Removal (RHR) to Radwaste and Group 3 RHR Shutdown Cooling automatic isolations were received; however, no valves isolated because they were in their normally closed position prior to the event. No Safety Relief Valves lifted as a result of this event and all other systems performed as required. This event did not prevent the fulfillment of a safety function, and therefore there were no safety system functional failures. Based on the discussion provided above, the health and safety of the public was not compromised by this event.
NRC FORM 388A U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 2. DOCKET
- 1. FACILITY NAME
- 6. LER NUMBER
- 3. PAGE I SEQUENTIAL I REV YEAR NUMBER NO.
Grand Gulf Nuclear Station, Unit 1 05000416 2010 001 00 4
of 4
G.
ADDITIONAL INFORMATION
Previous Similar Events - Pursuant to 10CFR50.73(b)(5) this issue is considered an infrequent event. There has not been any occurrence of the same underlying concem in the past two years at Grand Gulf Nuclear Station. Although GGNS has experienced RFPT transients and/or scrams in the past, this event was caused by a unique combination of circumstances involving both trains (i.e., steam leaks inducing eledrical faults on train B along with control valve linkage binding on train A).