05000416/LER-2018-010, Reactor Manual Scram Due to Main Turbine Bypass Valve Drifting Open
| ML19039A342 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  (NPF-029) |
| Issue date: | 02/08/2019 |
| From: | Emily Larson Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GNRO-2019/00008 LER 2018-010-00 | |
| Download: ML19039A342 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4162018010R00 - NRC Website | |
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- -=-- n ergy GNR0-2019/00008 February 8, 2019 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Entergy Operations, Inc.
P. o. Box756 Port Gibson, MS 39150 Eric A. Larson Site Vice President Grand Gulf Nuclear Station Tel. (601) 437-7500 10CFR50.73
SUBJECT:
Licensee Event Report 2018-010-00, Reactor Manual Scram due to Main Turbine Bypass Valve Drifting Open Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 License No. NPF-29
Dear Sir or Madam:
Attached is Licensee Event Report 2018-010-00, Reactor Manual Scram due to Main Turbine Bypass Valve Drifting Open. This report is being submitted in accordance with 1 QCFRSO. 73(a)(2)(jv)(A) for any event or condition that resulted in a manual or automatic actuation of systems listed in 10CFR50.73(a)(2)(iv)(B).
This letter contains no new commitments. If you,have any questions or require additional information, please contact Douglas Neve at 601-437-2103.
Sincerely, Eric A. Larson EAL/jep
Attachment:
Licensee Event Report 2018-010-00 cc: see next page
GNR0-2019/00008 Page 2 of 2 cc:
NRC Region IV-Regional Administrator NRC Senior Resident Inspector, Grand Gulf Nuclear Station NRR Project Manager
GNR0-2019/00008 Attachment Licensee Event Report 2018-010-00
NRCFORM U,S. NUCLEAR REGULATORY COMMISSION APP~OVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 366.
(04-2018)
, the NRG may not conduct or sponsor, and a
- ~*
oerson is not reauired to respond to the information collection.
3.Page Grand Gulf Nuclear Station, Unit 1 05000416 1 OF4
- 4. Title Reactor Manu~I Scram due to Main Turbine Bypass Valve Drifting Open
- 5. Event Dc1te
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Sequential Rev Facility Name Docket Number Month Day Year Year Month Day Year N/A Number No.
05000N/A 12 12 2018 2018
- - 010
- - 00 02 08 2019 Facility Name Docket Number N/A 05000N/A
- 9. Operating Mode, -
07 01 2019
~bstract (Limit to 1400 spaces, i,e., approximately 14 single-spaced typewritten lines)
At approximately 1351 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.140555e-4 months <br /> on Wednesday, December 12, 2018, while operating in MODE 1 at approximately 100 percent power, the Grand Gulf Nuclear Station was manually shutdown in response to Main Steam Bypass and Control Valve "A" drifting open. The Main Steam Line Isolation Valves were manually closed as a mitigating action to control reactor pressure vessel rate of depressurization and cooldown. During the scram recovery, the Reactor Core' Isolation Cooling (RCIC) System injection was delayed. During preparation to initiate High Pressure Core Spray (HPCS) System the operator noted that RCIC had started to inject but due to the water level and the rate of change the operator started HPCS. HPCS was secured once water level was trending higher. RCIC was utilized for reactor water level control until RCIC was placed in standby at 1645 hours0.019 days <br />0.457 hours <br />0.00272 weeks <br />6.259225e-4 months <br />.
There were no consequences to the general safety of the public, nuclear safety, industrial safety and radiological safety for this event.
This report is made pursuant to 10CFR50.73(a)(2)(iv)(A) for any event or condition that resulted in manual or automatic actuation of systems as listed in 1 OCFR50. 73(a)(2)(iv)(B), specifically the Reactor Protection System, HPCS, and RCIC systems were actuated.
NRC FORM 366 (02-2018)
A. PLANT CONDITIONS PRIOR TO THE EVENT YEAR 2018
- 3. LER NUVIBER SEQUENTIAL NUMBER
- - 010 Grand Gulf Nuclear Station (GGNS) Unit 1 was operating at approximately 100 percent power in Mode 1. There were no Structures, Systems, or Components that were inoperable that contributed to this event.
B. DESCRIPTION
At appoximately 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> CDT on Wednesday, December 12, 2018 while operating in MODE 1 at appoximately 100 percent power the GGNS*Main Steam Bypass Stop and Control Valve 'A' [JI] began~drifting open. The valve began to modulate between O -10% open over the course of 90 minutes. After 90 minutes, the valve began to open at an increased rate, reaching approximately 50% open. The reactor was manually scrammed at 1351 hours0.0156 days <br />0.375 hours <br />0.00223 weeks <br />5.140555e-4 months <br />. The Main Steam Line Isolation Valves [SB] were manually closed as a mitigating action to control reactor pressure vessel rate of depressurization and cooldown. Reactor pressure was controlled through the use of the Safety/Relief Valves [SB] and ultimately the Reactor Core Isolation Cooling (RCIC)
System [BN].
During the scram recovery, at 1358 hours0.0157 days <br />0.377 hours <br />0.00225 weeks <br />5.16719e-4 months <br /> the operator proceeded into the steps for a controlled start of RCIC.
The expected RCIC injection response was delayed due to discharge pressure indication and governor valve light indications were not as expected. Therefore, the operator prepared to initiate the High Pressure Core Spray (HPCS) System [BG] based on current reactor water level and its trend.
During preparation to initiate HPCS, the operator noted that RCIC had started to inject but reactor level was in the low end of the d~sired control band at-24.8 11 Wide Range (WR) with a downward trend and'current RCIC injection was not arresting the decreasing trend in a timely manner. After evaluating the reactor water level and rate of change, the operator completed manually starting H PCS injection at 1408 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.35744e-4 months <br />. At 1409 hours0.0163 days <br />0.391 hours <br />0.00233 weeks <br />5.361245e-4 months <br />, the HPCS injection was secured with reactor water level at 7.4" WR and trending higher and RCIC still ihjecting.
RCIC and Safety/Relief Valves were utilized for reactor water level control until RCIC was placed in standby at 1645 hours0.019 days <br />0.457 hours <br />0.00272 weeks <br />6.259225e-4 months <br />.
C. REPORTABILITY
This event was reported under 1 OCFR50. 72(b )(2)(iv)(A) and 1 OCFR50. 72(b )(2)(iv)(B) for any event that results in the Emergency Core Cooling System discharge to the Reactor Coolant System, actuation of the Reactor Protection System while the reactor is critical, and under 10CFR50.72(b)(3)(iv)(A) for any specified system actuation (HPCS and RCIC) in Emergency Notification System (ENS) Notification 53788.
This report is made pursuant to 10CFR50.73(a)(2)(iv)(A) for any event or condition that resulted in manual or automatic actuation of systems as listed in 1 OCFR50. 73(a)(2)(iv)(B), specifically the reactor protection system, HPCS, and RCIC systems were actuated.
REV NO.
- - 00 NRC FORM 3668 (02-2018)
Page 2 of 4. (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-.1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rrn/doc-collections/nuregs/staff/sr10221r3D
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
1 Grand Gulf Nuclear Station, Unit 1 05000-416 D.CAUSE YEAR 2018
- 3. LERNUIIIBER SEQUENTIAL NUMBER
- - 010 The reactor was manually shutdown by Operators in response to the Main Steam Bypass Stop and Control Valve "A" drifting open.
The direct cause of the event was a failed Linear Variable Differential Transformer (L VDT) in the actuator for the Main Steam Bypass Stop and Control Valve 'A' that directy resulted in the inability of the valve primary controller to properly position the valve. Failure of the L VDT resulted in a constant error signal being present at the controller, which allowed the valve to integrate open over time.
The cause evaluation is in progress. A supplemental LER will be submitted if the results of the cause evaluation or corrective actions warrant.
E. CORRECTIVE ACTIONS
The following corrective actions are completed.
Completed:
The Linear Variable Differential Transformer on the Main Steam Bypass Stop and Control Valve 'A' was replaced, retested the valve control, and returned valve to service.
Operating instruction (ONEP-05-1-02-V-1) was updated with guidance to manually swap bypass control valve control to the auxiliary controller which will drive the valve to its proper position should a similar issue occur and the automatic transfer to the auxiliary controller not occur.
The mitigating actions listed above have been completed and further corrective actions may be generated as part of the on-going causal evaluation.
F. SAFETY SIGNIFICANCE
The manual Reactor SCRAM and manual closure of the MSIVs did not result in actual consequences to safety of the general public, nuclear safety, industrial safety or radiological safety.
If manual operation of the Safety/Relief Valves (SRVs) was not performed following this event, the potential consequence to safety of the general public, nuclear safety, industrial safety and radiological safety would have been mitigated by automatic operation of the SRVs to control Reactor pressure.
Based on the above, the safety significance of this event is determined to be low. The response to the manual scram was performed in accordance with plant procedures. Plant parameters (reactor level, pressure) were maintained within procedure and safety limits. There were no actual nuclear safety consequences or radiological consequences during the event.
REV NO.
- - 00 NRC FORM 3668 (02-2018)
Page 3 of 4 (04-2017)
U:S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020
/
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LER NUVIBER Grand Gulf Nuclear Station, Unit 1 05000-416 G. PREVIOUSLY SIMILAR EVENTS YEAR 2018 SEQUENTIAL NUMBER
- - 010 Entergy conducted a three-year review of the relevant licensee event reports and determined that there were no
similar events
REV NO.
- - 00 NRC FORM 3668 (02-2018)