05000366/LER-2023-002, Manual Scram Due to Trip of Both Reactor Recirculation Pumps
| ML23146A191 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 05/26/2023 |
| From: | Weissinger J Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-23-0409 LER 2023-002-00 | |
| Download: ML23146A191 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3662023002R00 - NRC Website | |
text
~ Southern Nuclear May 26, 2023 Regulatory Affairs 3535 Colonnade Parkway Birmingham. AL 35243 205 992 5000 Docket Nos.: 50-366 NL-23-0409 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant - Unit 2 Licensee Event Report 2023-002-00 Unit 2 Manual SCRAM due to Trip of both Reactor Recirculation Pumps Ladies and Gentlemen:
In accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A), Southern Nuclear Operating Company hereby submits the enclosed Licensee Event Report.
This letter contains no NRC commitments. If you have any questions, please contact the Plant Hatch Licensing Manager, Jimmy Collins, at 912.453-2342.
Respectfully submitted,
-~v-------
John Weissinger Vice President - Plant Hatch HJW/CJC Enclosure: LER 2023-002-00 Cc:
NRC Regional Administrator, Region II NRR Project Manager - Plant Hatch NRC Senior Resident Inspector-Plant Hatch RTYPE: CHA02.004
Edwin I. Hatch Nuclear Plant - Unit 2 Licensee Event Report 2023-002-00 Unit 2 Manual SCRAM due to Trip of both Reactor Recirculation Pumps Enclosure LER 2023-002-00
Abstract
On March 31, 2023 at 1430, with Unit 2 in mode 1 at 97 percent power, the reactor was manually tripped due to a loss of both recirculaion pumps. The recirculation pumps tripped due to a loss of the 2A and 2B Adjustable Speed Drives (ASOs). All safety equipment responded as expected.
The cause of the ASD trip was due to the high speed stops for the ASDs being set at a value greater than the over frequency relay trip setpoints. This resulted in the relay over frequency trip setpoint being reached prior to the ASD High Speed Stops when increasing ASD speed.
To correct the issue, the ASD High Speed Stop setpoints values were returned to values less than the relay setpoint, to ensure the drive will not be able to be raised to a speed that would result in a trip due to over frequency.
This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in manual actuation of the reactor protection system.
EVENT DESCRIPTION
Estimated burden per re.sponse to comply with this mandatory coHection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reportea lessons learned are incorporated into !he licensing process and fed back to industry. Send oomments regarding burden estimate to the FOIA, Libra,y, and Information Collections Branch (T-6 A10M), U. S.
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- 2. DOCKET NUMBER
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00366 NUMBER NO.
I YEAR SEQUENTIAi..
REV
~M, 002 ING On March 31, 2023 at 1430, with Unit 2 in MODE 1 at 97 percent power, the reactor was manually tripped due to a loss of both recirculation pumps [EIIS Code: AD]. The recirculation pumps tripped due to a loss of the 2A and 2B Adjustable Speed Drives (ASDs) [EIIS Code: AD, SC]. Over frequency relays [EIIS Code: AD,81] associated with the ASD's actuated at their trip setpoints based on recirculation pump motor speed.
This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in manual actuation of the reactor protection system.
EVENT CAUSE ANALYSIS
Causal analysis revealed that the 2A and 2B ASDs tripped due to actuation of over frequency relays when recirculation pump motor speed reached the actuation setpoints. System parameters for the 2A and 28 ASD were reviewed and found that during implementation of a design modification the high speed stop setpoints for the ASD's were set higher than the over frequency relay trip setpoints. The conflicting setpoints is the reason the over frequency trip setpoint was reached prior to the ASD high speed stops and resulted in the ASD trips.
SAFETY ASSESSMENT
There were no actual safety consequences as a result of this event. The Recirculation Pumps tripped as designed to prevent damage due to overspeed. A manual scram was inserted as required by procedures and the reactor protection system worked as expected. Pressure was controlled by EHC and Bypass valves.
CORRECTIVE ACTIONS
To correct the issue the ASD High Speed Stop setpoint values were adjusted lower than the over frequency relay trip setpoint. This change ensures the drive is not able to be raised to a speed that will result in a premature over frequency trip.
PREVIOUS SIMILAR EVENTS
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