05000323/LER-2020-002, Manual Reactor Trip Due to Increased Main Generator Hydrogen Usage
| ML20259A183 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 09/15/2020 |
| From: | Gerfen P Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-20-077 LER 2020-002-00 | |
| Download: ML20259A183 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3232020002R00 - NRC Website | |
text
Paula Gerfen Site Vice President Diablo Canyon Power Plant Mail code 104/6/605 P.O. Box 56 Avila Beach, CA 93424 805.545.4596 Internal: 691.4596 Fax: 805.545.4234 A member of the STARS Alliance Callaway
- Diablo Canyon
- Palo Verde
- Wolf Creek September 15, 2020 PG&E Letter DCL-20-077 U.S. Nuclear Regulatory Commission 10 CFR 50.73 ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Power Plant, Unit 2 Unit 2 Licensee Event Report 2020-002-00, Unit 2 Manual Reactor Trip Due to Increased Main Generator Hydrogen Usage
Dear Commissioners and Staff,
In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Pacific Gas and Electric Company (PG&E) hereby submits the enclosed Diablo Canyon Power Plant (DCPP) Unit 2 Licensee Event Report regarding a manual reactor trip and the automatic actuation of the auxiliary feedwater system as expected, due to increased main generator hydrogen usage.
PG&E makes no new or revised regulatory commitments (as defined by NEI 99-04) in this report. All corrective actions identified in this letter will be implemented in accordance with the DCPP Corrective Action Program.
This event did not adversely affect the health and safety of the public.
Sincerely, Paula Gerfen dqmg/51082265 Enclosure Cc/enc:
Samson S. Lee, NRR Senior Project Manager Scott A. Morris, NRC Region IV Administrator Christopher W. Newport, NRC Senior Resident Inspector INPO Diablo Distribution
NRC FORM 366 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
(See Page 3 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 1. Facility Name Diablo Canyon Power Plant, Unit 2
- 2. Docket Number 05000323
- 3. Page 1 OF 3
- 4. Title Unit 2 Manual Reactor Trip Due to Increased Main Generator Hydrogen Usage
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Mon th Day Year Year Sequential Number Rev No.
Month Day Year Facility Name Docket Number 05000 07 17 2020 2020 - 002 -
00 09 15 2020 Facility Name Docket Number 05000
- 9. Operating Mode 1
- 10. Power Level 100
)
Abstract
On July 17, 2020, at 13:46 Pacific Daylight Time, with Diablo Canyon Power Plant Unit 2 operating at 100 percent power, the reactor was manually tripped in accordance with plant procedures due to increasing hydrogen usage in the Unit 2 Main Generator.
The reactor trip was uncomplicated, and the auxiliary feedwater system started as expected.
This event is being reported per 10 CFR 50.73(a)(2)(iv)(A) due to a manual reactor trip and the associated automatic actuation of a specified safety system.
The cause of the increased hydrogen usage was due to a leak in a weld segment located on the Unit 2 Main Generator exciter end stator coil cooling water manifold.
There was no impact to the health and safety of the public or plant personnel.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) and the associated guidance of NUREG-1022, Revision 3, due to a manual reactor trip and the subsequent automatic actuation of the auxiliary feedwater (AFW) system as expected This event was initially reported in Event Notification 54789 in accordance with the requirements of 10 CFR 50.72(b)(2)(iv)(B) as a manual actuation of the reactor protection system and 10 CFR 50.72(b)(3)(iv)(A) as an automatic actuation of a specified safety system.
II. Plant Conditions
At the time of the event, Diablo Canyon Power Plant (DCPP) Unit 2 was in Mode 1 at 100 percent power.
III. Problem Description A. Background The basic function of the turbine generator is to convert thermal energy initially to mechanical energy and finally to electrical energy. The generator is cooled by hydrogen, which is circulated by a blower inside the generator. The hydrogen gas system, which is part of the turbine generator system, dissipates the heat, provides a safe means of adding or removing hydrogen, maintains the gas pressure, dries the gas to remove undesired vapors, and monitors the hydrogen for pressure, temperature and purity.
The AFW system serves as a backup supply of feedwater to the secondary side of the steam generators when the main feedwater system is not available, thereby maintaining the heat sink capabilities of the steam generators. As an engineered safety feature system, the AFW system is directly relied upon to prevent core damage and reactor cooling system over pressurization in the event of transients such as a loss of feedwater or a secondary system pipe rupture, and to provide a means for plant cooldown following any plant transient.
B. Event Description
On July 17, 2020, at 13:46 Pacific Daylight Time, with DCPP Unit 2 operating at 100 percent power, the reactor was manually tripped in accordance with plant procedures due to increasing hydrogen usage in the Unit 2 Main Generator.
C. Status of Inoperable Structures, Systems, or Components that Contributed to the EventPage 3 of 3 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: 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 https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Diablo Canyon Power Plant, Unit 2 05000-323 YEAR SEQUENTIAL NUMBER REV NO.
2020
- - 002
- - 00 The reactor trip was uncomplicated, and the AFW system started as expected. There were no inoperable Technical Specification structures, systems, or components that contributed to the event.
D. Method of Discovery
Self-revealing. Increased hydrogen usage was validated following the receipt of the low hydrogen pressure control room annunciator.
E. Operator Actions
The Operations crews responded to this event in accordance with plant operating procedures.
F. Safety System Responses The AFW system responded as expected following the manual reactor trip.
IV. Cause of the Problem The cause of the increased hydrogen usage was due to a leak in a weld segment located on the Unit 2 Main Generator Exciter End stator coil cooling water manifold.
V. Assessment of Safety Consequences
There were no safety consequences as a result of this event.
There was no impact on health and safety of the public or plant personnel.
VI. Corrective Actions
The Unit 2 Main Generator Exciter End manifold was repaired. Follow-up corrective actions to prevent recurrence will be managed in accordance with the DCPP Corrective Action Program.
VII. Additional Information
There have been no similar events at DCPP in the previous three years.