05000416/LER-2020-005-02, Primarv Water Svstem Flow Lowered Causinc Turbine Trio and Subseauent Reactor Scram
| ML21231A138 | |
| 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-2021/00022 LER 2020-005-02 | |
| Download: ML21231A138 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(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 |
| 4162020005R02 - NRC Website | |
text
--=-* Entergy GNRO-2021/00022 August 19, 2021 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Entergy Operations, Inc.
P.O. Box756 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 2020-005-02 Grand Gulf Nuclear Station, Unit 1 Docket No. 50-416 Renewed License No. NPF-29 Attached is revised Licensee Event Report 2020-005-02, Primary Water System Flow Lowered 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.
Sincerely,
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Jeff A. Hardy JAH/fas Attachments: Licensee Event Report 2020-005-02
GNRO-2021/00022 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
GNRO-2021/00022 Page 3 of 3 Attachment Revised Licensee Event Report 2020-005-02
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
- 3. Page Grand Gulf Nuclear Station, Unit 1 05000416 1 OF3
- 4. Title Primarv Water Svstem Flow Lowered Causinc 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 NIA Number No.
05000 NIA 11 06 2020 2020
- - 005 -
02 08 19 2021 Facility Name Docket Number NIA 05000 NIA
- 9. Operating Mode
- 10. Power Level 1
84
- 11. This Reoort is Submitted Pursuant to the Reauirements of 1 O CFR §: (Check all that annlv) 10 CFR Part 20 0 20.2203(aH2Hvil 0 50.36(cH2l 18] 50.73(aH2)(iv\\(A\\
n 50.73(aH2Hx) 0 20.2201 (b)
O 20.2203(a)(3)(i) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(A) 10CFR Part73 0 20.2201 (dl O 20.2203(a)(3)(ii) 0 50.69(0)
D 50.73(a)(2)(v)(B)
O 73.71(a)(4)
D 20.2203(a)(1 l D 20.2203(a)(4) 0 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(C)
O 73.71!aH5l D 20.2203(aH2Hil 10 CFR Part 21 50.73(aH2HiHBl n 50.73(aH2HvHDl O 73.77(aH1l/il 0 20.2203(a)(2Hiil 021.2(c) 0 50.73(aH2l(i)(C) 0 50.73(a)(2)(vii)
O 73.77(a)(2)(i)
O 20.2203(a)(2)(iii) 10CFRPart50 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A)
D 73.77(a)(2)(iil 0 20.2203(a)(2)(iv) 0 50.36(c)(1 HiHAl 0 50.73(a)(2)(ii)(B)
D 50.73(aH2HviiiHB) 0 20.2203(aH2Hvl 50.36(cH1 Hii\\!Al 50.73(aH2Hiii\\
0 50.73(aH2HixHAl 0 Other (Specify here, in abstract, or NRC 366A)
- 12. Licensee Contact for this LEA L,censee Contact l elephone Number (Include Area Code)
I Jeff Hardv, Manaqer Requlatorv Assurance I (269)-764-2011 Cause System Component Manufacturer Reportable To IRIS
Cause
System Component Manufacturer Reportable To IRIS NIA NIA NIA NIA NIA NIA NIA NIA NIA NIA
- 14. Supplemental Report Expected Month Day Year D Yes (If yes, complete 15. Expected Submission Date) 1:8] No
!Abstract (Limit to 1560 spaces, i.e., approximately 15 single-spaced typewritten lines)
On November 6, 2020 at 0239 CT, while operating in MODE 1 at approximately 84 percent power, Grand Gutt Nuclear Station received a signal for low Primary Water system flow to generator bushing C, which resulted in an automatic turbine trip and reactor Scram. 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.
Primary water is non-radioactive ultra-purified water circulated to and from the generator to cool the generator stator, bushings, and rotor. The root cause of the event is that Entergy Engineering Leadership (Corporate Projects and Site Engineering) made changes to the design of the primary water bushing flow instrumentation loop without fully evaluating the impacts of the changes to the instrumentation feedback quality and existing operating margins to a generator trip.
The corrective actions to preclude repetition was to revise EN-HU-104, Technical Task Risk & Rigor, to require creation of a detailed table listing generation risk parameters (setpoints, settings, dimensions) for engineering changes with high generation risk.
Corrective action to preclude repetition included modifying the sensing lines for all primary water flow transmitters to obtain the proper slope and to allow back filling the flow instruments. Addrrionally, the margin between the low flow alarm and low flow trip setpoint was increased.
There were no consequences to the general safety of the public, nuclear safety, industrial safety, or radiological safety. No radiological release occurred due to this event. This report is made in accordance with 10 CFR 50.73(a)(2)(iv)(A), any event or condrrion that resulted in manual or automatic actuation of the Reactor Protection System.
Plant Conditions
SEQUENTIAL NUMBER
- - 005 REV NO.
- - 02 Grand Gulf Nuclear Station (GGNS) Unit 1 was operating at 84 percent power in MODE 1. There were no Structures, Systems, or Components that were inoperable that contributed to this event.
Event Description
Primary water is non-radioactive ultra-purified water circulated to and from the generator to cool the generator stator, bushings, and rotor.
On November 6, 2020 at 0132 CT, during normal steady state operation, the control room received and alarm for low Primary Water (PW) system flow to main generator bushing Phase C. One of the three channels for bushing C flow caused the alarm and then cleared. Indication for all nine flow transmitters in Phases A, B, and C had drifted down in a slow trend over the course of 2-3 hours, with C phase having a steeper rate of degradation. Overall flow indications degraded slightly and the instrument noise level increased significantly the combination of which eventually led to the low flow trip. An actual low flow condition (overall bushing flow below trip setpoint) did not exist in any of the Primary Water flow paths. Alarms continued to come in with increasing frequency.
On November 6, 2020 at 0239 CT, while operating in MODE 1 at 84 percent power, GGNS received a signal for primary water system flow to generator bushing C, which lowered below its trip setpoint resulting in an automatic generator and turbine (TA) trip and subsequent automatic reactor Scram.
All control rods fully inserted and there were no complications associated with the Scram. All system 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 54986)
This report is made in accordance with 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 reactor Scram due to the turbine trip 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 gas voids in the primary water system, which degraded generator bushing primary water flow and increased instrument noise in the bushing primary water flow transmitters. This resulted in the bushing flow indication dropping and then reaching its trip setpoint.
The root cause of the event is that Entergy Engineering Leadership (Corporate Projects and Site Engineering) made changes to the design of the primary water bushing flow instrumentation loop without fully evaluating the impacts of the changes to the instrumentation feedback quality and existing operating margins to a generator trip. Page 2 of 3 (08-2020)
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U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LEA)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/stafflsr1022/@0 APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Information Services Branch (T-6 A10M), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to lnfocollects.Resource@nrc.gov, and the 0MB reviewer at: 0MB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503; e-mail: oira submission@omb eop gov. The NRC may not conduct or sponsor, and a person is not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid 0MB control number.
- 3. LEA NUMBER YEAR Grand Gulf Nuclear Station, Unit 1 05000-416 2020
Corrective Actions
SEQUENTIAL NUMBER
- - 005 REV NO_
- - 02 To preclude repetition, the Primary Water system flow to generator bushing Phase A, B, and C flow instrument tubing slope was corrected and backfill valves were added. This action is complete.
To preclude repetition, Entergy increased primary water flow transmitter damping and trip delay. This action is complete.
To preclude repetition, lowered the low bushing flow trip setpoint from 27.9 gpm to 25.5 gpm in order to increase margin between normal operating flow and the trip point. This action is complete.
To preclude repetition, Entergy raised primary water bushing flow alarm setpoint from 29.8 gpm to 31.5 gpm in order to increase margin between receipt of the alarm and when the trip signal is received. This action is complete.
To preclude repetition, increased primary water head tank level alarm setpoint to increase margin between receipt of the alarm and when the trip signal is received. 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 is complete.
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