05000458/LER-2023-002, Division I and II Diesel Generators Inoperable Due to Exceeding Load Sequence Times
| ML23180A213 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 06/29/2023 |
| From: | Crawford R Entergy Nuclear |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RBG-48239 LER 2023-002-00 | |
| Download: ML23180A213 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor |
| 4582023002R00 - NRC Website | |
text
entergy RBG-48239 Randy Crawford Manager Regulatory Assurance 225-381-4177 10 CFR 50.73 June 29, 2023 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Licensee Event Report 50-458 / 2023-002-00, Division I and II Diesel Generators Inoperable due to Exceeding Load Sequence Times River Bend Station - Unit 1 NRC Docket Nos. 50-458 Renewed Facility Operating License No. NPF-47 In accordance with 10 CFR 50.73, enclosed is the subject Licensee Event Report.
This document contains no commitments.
Should you have any questions, please contact Mr. Randy Crawford, Regulatory Assurance Manager, at 225-381-4177.
Respectfully, RTC/dmw Enclosure: Licensee Event Report 50-458 / 2023-002-00, Division I and II Diesel Generators Inoperable due to Exceeding Load Sequence Times cc:
NRC Region IV Regional Administrator - Region IV NRC Senior Resident Inspector - River Bend Station
Enclosure RBG-48239 Licensee Event Report 50-458 / 2023-002-00, Division I and II Diesel Generators Inoperable due to Exceeding Load Sequence Times
Abstract
On February 12, 2023, with River Bend Station (RBS) in Mode 4 during Refueling Outage 22, testing of the Division II Emergency Core Cooling System (ECCS) revealed that both Division II Control Building Chillers (HVK-CHL 18 and HVK-CHL 1 D) failed to sequence onto the emergency bus within the Technical Specification (TS) required time. Investigation of the issue revealed that the same condition was present for the Division I Control Building Chillers (HVK-CHL 1A and HVK-CHL 1 C). The condition described above was caused by a modification that replaced the Control Building Chiller controllers.
The preliminary root cause identified that when the controllers were replaced, a delay was introduced in the start logic.
Corrective actions to restore TS compliance were completed prior to the next mode of applicability.
This condition resulted in the inability to comply with a Surveillance Requirement of TS 3.8.1. At the time of discovery, RBS was in a mode of operation that is not applicable to TS 3.8.1. An evaluation determined that the TS 3.8.1 Surveillance Requirement was previously not met and appropriate actions were not taken in accordance with TS 3.8.1 - AC Sources -
Operating.
EVENT DESCRIPTION
Estimated luden ps response to comply with this mandatory collectioo request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessoos le,rned,re incorporated into the licensing process and fed back to induslry Send comments reg,rding b1rden estimate to the FOIA, Lit.ary, and lnfoonatioo CoUectioo Branch (T <I A IOM), US, Nude,r Regulatory Commission, Washington, DC 20555-0001, or by e-,naH to lnfocolleds.Reso1rce@rvc.gov, and the 0MB re,iewe, at: 0MB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nucle,r Regulatory Commission, 725 17th Sbeet NW, Washington, DC 20503: e-,nail:
ona submission@omb.eop.gov The NRC may not c:onduc1 or sponSCN', c11d a person is not requiled to respond to, a collection of information unless the downent requesting or requiring the collection displays a tllTently valid 0MB contol number.
- 2. DOCKET NUMBER 458 3.LERNl.M:IER YEAR SEQUENTIAL NUMBER 2023
- - 002 -
REV NO. On February 12. 2023. RBS performed STP-309-0602. DIVISION II ECCS TEST. During the performance of Section 7.4.
ECCS/LOP/LOCA Test Initiation. HVK-CHL 1 B [KM] did not load sequence within the required time. Load sequence time was 237.1 seconds with acceptance criteria of 180.9 to 221.1 seconds. During performance of Section 7.25. ECCS/LOP Test Initiation. HVK-CHL 1 D [KM] did not load sequence within the required time. Load sequence time was 241 seconds with acceptance criteria of 180.9 to 221.1 seconds. Condition Reports were generated for both issues.
On May 2. 2023. the station determined that the Division I and Division II Diesel Generators [EK] had been inoperable as a result of the chiller controller modification. HVK-CHL 1 C [KM] and HVK-CHL 1 D modifications were completed in 2014.
HVK-CHL 1A [KM] and HVK-CHL 1 B modifications were completed in 2020.
The discovery date was determined to be February 12. 2023. The event is reportable as an Operation or Condition Prohibited by Technical Specifications per 10 CFR 50.73(a)(2)(i)(B) and an Event or Condition that Could Have Prevented Fulfillment of a Safety Function per 10 CFR 50.73(a)(2)(v)(A) and (D).
EVENT CAUSE
This event was caused by the HVK-CHL 1 (A)(B)(C)(D) Controller Modifications that were installed in 2014 and 2020.
SAFETY ASSESSMENT
The Division I and II Diesel Generators were declared inoperable based on load sequence time of the HVK Chillers exceeding TS SR 3.8.1.18 requirements. The following engineering analysis provided evidence that the delay had no effect on the generator loading sequence.
Calculation E-192. STANDBY DIESEL GENERATOR LOADING CALCULATION. evaluates the loading of the standby diesel generators during the worst-case loading conditions (LOP concurrent with LOCA). The calculation verifies that the maximum magnitude for the load blocks is within the tested values of loading established by the vendor. HVK-CHL 18/0 are in the 1.5-10-minute load block for the Division II Diesel Generator. The chiller is the last component in the load block to start with a listed start time of 211 seconds from the LOP. The next component to start is at the 10-minute mark. HVK CHL 1A/C are in the 1.5-10-minute load block for the Division I Diesel Generator. The chiller is the last component to start in the 1.5-10-minute load block with a start time of 241 seconds. Even with the additional 40 second delay. the chiller will remain in the 1.5-10-minute load block and there will be at least 5 minutes between a chiller start and the start of the next component. Therefore. the delay has no effect on the generator loading sequence.
Based on the engineering analysis. the Division I and II Diesel Generators remained capable of performing their required safety function for the duration of the event and the event will not be counted as a Safety System Functional Failure (SSFF) for the NRC Performance Indicators. The analysis also supports that there were no consequences to the health and safety of the public.
ADDITIONAL INFORMATION
- 3. I.ER
YEAR SEQUENTIAL NUMBER 2023
- - 002 -
REV NO. The Control Building [NA) Air Conditioning System (CBAC) consists of two independent, redundant subsystems that provide cooling and heating of the control building air. The associated control building chilled water subsystem (HVK) supplies chilled water to both subsystem AC units, as well as to the Main Control Room AC units.
The design of the AC electrical power system provides independence and redundancy to ensure an available source of power to the Engineered Safety Feature (ESF) systems. Each ESF bus has a dedicated onsite Diesel Generator (DG). A DG starts automatically on loss of coolant accident (LOCA) or an ESF bus degraded voltage, undervoltage/loss of power (LOP) signal. Certain required plant loads in Divisions I and II (including HVK) are returned to service in a predetermined sequence to prevent overloading the DG.
RBS completed controller modifications for HVK-CHL 1 C and HVK-CHL 1 D in 2014. HVK-CHL 1A and HVK-CHL 1 B modifications were completed in 2020. A review of historical chiller data logs shows that since the HVK chiller controls upgrade, the start of HVK chillers may be delayed past the design start time by approximately 40 seconds.
TS Surveillance Requirement (SR) 3.8.1.18 states, "Verify sequence time is within +/- 10% of design for each load sequencer timer."
CORRECTIVE ACTIONS
Completed Corrective Actions
- 1. Engineering Change Modifications were completed for all Control Building Chillers to correct sequence delays as detailed below:
Work Order 594333-01 Modify HVK-CHL 1A Start Logic per EC-95152 - COMPLETE Work Order 594334-01 Modify HVK-CHL 1 B Start Logic per EC-95151 - COMPLETE Work Order 594335-01 Modify HVK-CHL 1C Start Logic per EC-95153 - COMPLETE Work Order 594336-01 Modify HVK-CHL 1 D Start Logic per EC-95150 - COMPLETE
Planned Corrective Actions
- 1. Complete Root Cause Evaluation.
PREVIOUS SIMILAR OCCURRENCES This section will be updated in the supplemental report following completion of Root Cause Analysis.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX). River Bend equipment codes are identified as (XX). Page _3_ of _3_