05000323/LER-2021-002, Manual Reactor Trip Due to Increased Water Level in a Feedwater Heater
| ML21348A112 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 12/14/2021 |
| From: | Harbor C Pacific Gas & Electric Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| DCL-21-093 LER 2021-002-00 | |
| Download: ML21348A112 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3232021002R00 - NRC Website | |
text
Cary D. Harbor Station Director Diablo Canyon Power Plant Mail code 104/5/502 P.O. Box 56 Avila Beach, CA 93424 805.545.4102 Internal: 691.4102 A member of the STARS Alliance Callaway x Diablo Canyon x Palo Verde x Wolf Creek PG&E Letter DCL-21-093 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 2021-02-00, Unit 2 Manual Reactor Trip Due to Increased Water Level in a Feedwater Heater
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 due to increasing water level in Feedwater Heater (FWH) 2-5B.
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.
If you have any questions or require additional information, please contact Mr. James Morris, Regulatory Services Manager, at (805) 545-4609.
Sincerely, Date Cary 'Harbor dqmg/51133409 Enclosure cc/enc:
Samson S. Lee, NRR Senior Project Manager Scott A. Morris, NRC Region IV Administrator Winston C. Smith, Acting NRC Senior Resident Inspector INPO Diablo Distribution 12/14/2021 Pacific Gas and Elecmc Campany"
Abstract
On October 15, 2021, at 17:49 Pacific Daylight Time, with Diablo Canyon Power Plant Unit 2 operating at 90 percent power, the reactor was manually tripped in accordance with plant procedures due to increasing water level in Feedwater Heater (FWH) 2-5B.
This event included actuation of the auxiliary feedwater system as expected following manual reactor trip.
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 feedwater level was due to failure of multiple tubes in the FWH.
There was no impact to the health and safety of the public or plant personnel.
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I. Reporting Requirements
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 55526 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 90 percent power.
III. Problem Description A. Background The condensate system and main feedwater system (MFWS) are non-safety-related systems whose function is to supply preheated feedwater to the steam generators (SGs). These systems improve overall plant efficiency by regeneratively heating feedwater as it is pumped through low and high-pressure feedwater heaters (FWHs) prior to the entering the SGs. The condensate and MFWS are not required to ensure safe shutdown of the nuclear steam supply system.
The condensate and MFWS receive condensate from the main condenser hotwell and deliver it as feedwater to the SGs at the required pressure and temperature. Condensate is normally pumped to the main feedwater pump suction header through FWHs 2 through 6. Feedwater is then pumped through the tube sides of FWH 1.
Extraction steam from the low and high-pressure turbines is piped to the shell sides of these feedwater heaters.
All FWHs are horizontal type with three parallel heat exchangers comprising each level of FWH heating.
The AFW system is an engineered safety system that serves as a backup supply of feedwater to the secondary side of the SGs when the condensate and MFWS are not available, thereby maintaining the heat sink capabilities of the steam generators.
B. Event Description
On October 15, 2021, at 17:49 Pacific Daylight Time, with DCPP Unit 2 operating at 90 percent power, while diagnosing a potential tube leak in FWH 2-5B, the reactor was manually tripped in accordance with plant procedures due to increasing water level in the feedwater heater.
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....... NRC FORM 366A (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 05000323 YEAR SEQUENTIAL NUMBER REV NO.
2021 002 00 C. Status of Inoperable Structures, Systems, or Components that Contributed to the Event This event included actuation of the AFW system as expected following manual reactor trip. There were no inoperable Technical Specification structures, systems, or components that contributed to the event.
D. Method of Discovery
Increased water level in FWH 2-5B was validated by Operations personnel following the receipt of the associated 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 water level increase was a result of multiple tube failures in FWH 2-5B.
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
FWH 2-5B was repaired and returned to service. The other two No. 5 FWHs (2-5A and 2-5C) were verified to exhibit no indication of leakage. 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.
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