05000416/LER-2020-006-02, Primary Water Tank Low Level Causing Turbine Trip and Subsequent Reactor Scram
| ML21231A139 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 08/19/2021 |
| From: | Hardy J Entergy Operations |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML21231A134 | List:
|
| References | |
| GNRO-2021/00023 LER 2020-006-02 | |
| Download: ML21231A139 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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) 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ix)(A) |
| 4162020006R02 - NRC Website | |
text
-~~Entergy G N RO-2021 /00023 August 19, 2021 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Entergy Operations, Inc.
P.O. Box 756 Port Gibson, Mississippi 39150 Jeff A. Hardy Regulatory Assurance Manager Grand Gulf Nuclear Station Tel: 601-437-7500 10 CFR 50.73
SUBJECT:
Grand Gulf Nuclear Station, Unit 1 Revised Licensee Event Report 2020-006-02 Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 Renewed License No. NPF-29 Attached is revised Licensee Event Report 2020-006-02, Primary Water Tank Low Level Causing Turbine Trip and Subsequent Reactor Scram. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(iv)(A), for any event or condition that resulted in manual or automatic actuation of the Reactor Protection System (RPS).
This letter contains no new Regulatory Commitments. Should you have any questions concerning the content of this letter, please contact Jeff Hardy, Regulatory Assurance Manager at 269-764-2011.
Q4~t;,
Jeff A. Hardy y JAH/fas Attachments: Revised Licensee Event Report 2020-006-02
GN RO-2021 /00023 Page 2 of 3 cc:
NRG Senior Resident Inspector Grand Gulf Nuclear Station Port Gibson, MS 39150 U.S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
G N RO-2021 /00023 Page 3 of 3 Attachment Revised Licensee Event Report 2020-006-02
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 (08-2020)
- 1. Facility Name
~ - Docket Number
- 13. Page Grand Gulf Nuclear Station, Unit 1 05000416 1 OF3
- 4. Title Primarv Water Tank Low Level Causina Turbine Trio and Subseauent Reactor Scram
- 5. Event Date
- 6. LEA 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.
~5000 N/A 12 11 2020 2020
- - 006 -
02 08 19 2021 Facility Name Docket Number N/A 5000 N/A
- 9. Operating Mode 1 10. Power Level 1
100
- 11. This RMOrt is Submitted Pursuant to the Reauirements of 1 O CFR §: (Check all that ann/v) 10 CFR Part 20 D 20.2203(a)(2)(vi)
D 50.36(c)(2) 181 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x) 20.2201 (b)
D 20.2203(a)(3)(i)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(A) 10CFRPart73 0 20.2201 (d)
D 20.2203(a)(3\\/ii\\
0 50.69(0)
D 50.73(a\\/2Hv\\/B)
D 73.7HaH4\\
D 20.2203(a\\/1 \\
n 20.2203(a\\/4) 0 50.73(aH2HiHA\\
n 50.73(a)(2)(v\\/C\\
0 73.71 (a)(5)
D 20.2203(a)(2)(i) 10CFRPart21 50.73(a)(2)(i)(B)
D 50.73(a)(2)(v)(D)
D 73.77(a)(1 Hi)
D 20.2203(a)(2)(ii)
D 21.2(c) 0 50.73(a)(2)(i)(C)
D 50.73(a)(2)(vii)
D 73.77(a)(2Hi)
D 20.2203(a\\/2Hiii\\
10CFR PartSO 0 50.73(a)(2\\/ii\\/A)
D 50.73(aH2Hviii\\/A)
D 73.77(aH2Hii\\
D 20.2203(a\\/2Hivl n 50.36(cl(1 Hi\\/Al 0 50.73(aH2HiiHBl n 50.73(a)(2)(viiil(Bl D 20.2203(a)(2)(v) 0 50.36(cH1 HiiHA)
D 50.73(aH2l(iii)
D 50.73(a)(2)(ix)(A)
D Other (Specify here, in abstract, or NRC 366A)
- 12. Licensee Contact for this LEA Licensee Contact r elephone Number (Include Area Code)
I Jeff Hardy, Manager Regulatory Assurance I (269)-764-2011 Cause System Component Manufacturer Reportable To IRIS
Cause
System Component Manufacturer Reportable To IRIS N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
- 14. Supplemental Report Expected Month Day Year D Yes (If yes, complete 15. Expected Submission Date) [8J No
- 15. Expected Submission Date N/A N/A N/A
~bstract (Limit to 1560 spaces, i.e., approximately 15 single-spaced typewritten lines)
On December 11, 2020, at 1204 CT, while operating in MODE 1 at 100 percent power, Grand Gulf Nuclear Station experienced an Automatic Reactor Scram after a main turbine and generator trip. All Control Rods fully inserted and there were no complications associated with the Scram. All systems responded as designed and the plant was stabilized in MODE 3.
The direct cause of the generator and turbine trip was while adding makeup water to the primary water system, the Operator misdiagnosed the response of the Leakage Water Return Valve and closed the valve manually. This led to a trip of the main turbine when primary water system tank level lowered to the trip setpoint of 78 percent. Primary water is non-radioactive, ultra-purified water circulated to and from the generator to cool the generator stator, bushings and rotor.
The root causes for this event were: 1) Entergy Engineering Leadership established a design for the Leakage Water Return Valve control logic which was not fully understood and 2) the operating crew lacked adequate knowledge of the Primary Water System to control and stabilize the leakage water standpipe level.
To preclude repetition, continuing training on the Primary Water system will be provided to GGNS License Operator and Non-License Operator. Entergy's procedure EN-HU-104, Technical Task Risk and Rigor, was revised requiring a detailed table listing generation risk parameters being revised for engineering changes with high generation risk.
Corrective actions included revising the primary water system operating procedure with specific instructions for local manual standpipe level control.
There were no consequences to the general safety of the public, nuclear safety, industrial safety, or radiological safety. No radiological releases occurred due to this event.
Plant Conditions
Grand Gulf Nuclear Station (GGNS) Unit 1 was operating at 100 percent power in MODE 1. There were no Structures, Systems, or Components that were inoperable that contributed to this event.
Event Description
On December 11, 2020 at 1204 CT, while operating in MODE 1 at 100 percent power, GGNS received a signal for low primary water tank level resulting in an automatic generator and turbine [TA] trip and subsequent automatic reactor Scram.
Primary water is non-radioactive ultra-purified water circulated to and from the generator to cool the generator stator, bushings, and rotor.
All Control Rods fully inserted and there were no complications associated with the Scram. All systems responded as designed and the plant was stabilized in MODE 3. No radiological releases occurred due to this event.
This event was reported under 10 CFR 50.72(b)(2)(iv)(B), as any event or condition that results in actuation of the Reactor Protection System when the reactor is critical. (EN 55030)
This report is made pursuant to 10 CFR 50.73(a)(2)(iv)(A), any event or condition that resulted in manual or automatic actuation of the Reactor Protection System.
Safety Assessment
The automatic turbine trip and subsequent reactor Scram did not result in actual consequences to safety of the general public, nuclear safety, industrial safety, or radiological safety. The safety significance of this event is determined to be low.
Event Cause(s):
The direct cause of the generator and turbine trip was while adding makeup water to the primary water system, the Turbine Building Operator misdiagnosed the response of the Leakage Water Return Valve and closed the valve manually.
This prevented transfer of makeup water from the standpipe to the Primary Water tank.
This action initiated a sequence of events which led to a Main Turbine/Generator trip and Reactor Scram.
The first root cause of the event was that Entergy Engineering Leadership (Corporate Projects and Site Engineering) established a design for the Leakage Water Return Valve control logic which was not fully understood and had impacts that changed the operation which were not desired in Engineering Change, EC 72780, Turbine Control Protection System - Non-Safety, resulting in an automatic plant trip. This ultimately reduced the operational margin causing a plant trip.
The second root cause of the event was that the operating crew lacked adequate knowledge of the Primary Water System to control and stabilize the leakage water standpipe level. Page 2 of 3 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 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/nureqs/staff/sr1022/r30
- 3. LEA NUMBER YEAR Grand Gulf Nuclear Station, Unit 1 05000-416 2020
Corrective Actions
SEQUENTIAL NUMBER
- - 006 REV NO
- - 02 Following the turbine trip, GGNS remained in hot shutdown from December 11, 2020 until December 13, 2020.
Corrective actions were made to issue a Standing Order detailing oversight for plant manipulations and issue a revision to the Primary Water system operating instruction with specific instructions for local manual standpipe level control. This action is complete.
To preclude repetition, Entergy's procedure EN-HU-104, Technical Task Risk and Rigor, was revised to require creation of a detailed table listing generation risk parameters (setpoints, settings, dimensions) being revised for engineering changes with high generation risk. This table is to list the old parameter, new, and basis for acceptability.
This table would then be presented for challenge such as Independent Third-Party Review, and challenge board. This action has been completed.
To preclude repetition, the long-range training plans for the Primary Water System will be updated and will be included in continuing training plans for GGNS License Operator and Non-License Operator. This action has been completed.
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