05000458/LER-2021-004, Core Monitoring System Software Modeling Error Resulted in Conditions Prohibited by Technical Specifications
| ML21228A240 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 08/16/2021 |
| From: | Karenina Scott Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-48111 LER 2021-004-00 | |
| Download: ML21228A240 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 21.21(a)(2), Interim Report for Comply or Defect in Component |
| 4582021004R00 - NRC Website | |
text
Subject:
Entergy Operations, Inc.
River Bend Station 5485 U.S. Highway 61N St. Francisville, LA 70775 Tel 225-381-4374 Kent Scott Site Vice President Licensee Event Report 50-458 I 2021-04-00, Core Monitoring System Software Modeling Error Resulted in Conditions Prohibited by Technical Specifications River Bend Station Unit 1 NRC Docket No. 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. If you have any questions, please contact Mr. Tim Schenk at 225-381-4177.
?nsee Event Report 50-458 I 2021-04-00, Core Monitoring System Software Modeling Error Resulted in Conditions Prohibited by Technical Specifications cc:
NRC Regional Administrator
- - Region IV NRC Project Manager
- - River Bend Station NRC Senior Resident Inspector
- - River Bend Station Louisiana Department of Environmental Quality Public Utility Commission of Texas Entergy0 RBG-481 11 August 16, 2021 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-000 1 10 CFR 50.73 Respectfully, KCSIdmw
Enclosure:
Enclosure RBG-48111 Licensee Event Report 50-458 I 2021 00, Core Monitoring System Software Modeling Error Resulted in Conditions Prohibited by Technical Specifications
APPROVED BY 0MB: NO. 31 50-01 04 EXPIRES: 08/31/2023
- 3. Page River Bend Station, Unit 1 05000
- - 458 1 of 3
- 4. Title Core Monitoring System Software Modeling Error Resulted in Conditions Prohibited by Technical Specifications 5 Event Date 6 LER Number 7 Report Date 8 Other Facilities Involved Sequential R
Facility Name Docket Numbe Month Day Year Year Number No.
Month Day Year N/A 05000 NIA Facility Name Docket Numbe 06 17 202 2021
- - 004 00 06 6
21)21 N/A 05000 NIA
- 9. Operating Mode
- 10. Power Level 1
100
)
16, Abstract (Limit to 1560 spaces. i.e.. approoimately 15 single-spaced typewritten lines)
On June 17, 2021, with River Bend Station (RBS) operating at 100 percent power, Entergy received a letter from GE Hitachi issuing SC 21-04, Revision 1, Fuel Support Side Entry Orifice Meta-Stable Flow for 2 Beam Locations in the BWR/6 Reactors, identifying that the Global Nuclear Fuels (GNF) model for fuel affected by the Side Entry Orifices did not accurately account for the loss coefficients at those core locations causing a local overprediction in Minimum Critical Power Ratio (MCPR) margin. This resulted in the determination by Entergy that a condition prohibited by Technical Specifications (TSs) had existed at RBS and this report being made in accordance with 10 CFR 50.73(a)(2)O)(B).
The cause of the event was GNF had not accurately accounted for the loss coefficients at applicable core locations causing a local overprediction in MCPR margin resulting in exceeding the MCPR TS limit.
Corrective actions include implementing a penalty to Operating Limit MCPR (OLMCPR) in the core monitoring system via an update to the databank to include all penalties associated with GEH letter SC 21-04, Revision 1, and an update to the current Core Operating Limits Report (COLR).
There were no consequences to the general safety of the public, nuclear safety, industrial safety, nor radiological NRC FORM 366 108-2020)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
(See Page 3 for required number of digitslcharacters for each block)
(See NUREG-1022 R.3 for instruction and gsidance for competing this form hltps.n.-.w nrc ov/readrng-riVdrx-co(lectons/nure0s.slafflsr 1022/r31) safety.
Plant Conditions
River Bend Station (RBS) Unit 1 was operating at 100 percent power in MODE 1. There were no Structures, Systems, or Components that were inoperable that contributed to this event.
Event Description
On June 17, 2021, with RBS operating at 100 percent power, Entergy received a letter from GE Hitachi (GEH) concerning a Part 21 Report. This Part 21 Report was transmitted to Entergy and the NRC documenting an update on the issue related to an underprediction of the Side Entry Orifice (SEO) loss coefficients in core analyses, resulting in a local overprediction in MCPR margin.
Specifically, Global Nuclear Fuels (GNF) identified the SEQ loss coefficients for fuel bundle locations adjacent to 2-beam (corner) locations may potentially be higher than the current design basis value that is applied. The MCPR impact on potentially affected bundles that are near limits can potentially reduce this margin by greater than 0.01 in Critical Power Ratio. GEH has completed the evaluation of the condition to determine reportability under 10 CFR Part 21 and is a reportable condition under 10 CFR Part 21.21(a)(2) and a transfer of information under 10 CFR 21.21(b). The basis for reportability is that the change in MCPR associated with this issue could contribute to the exceeding of a Safety Limit, as defined in the RBS TSs.
The history of variable Maximum Fraction of Limiting Core Power Ratio (MFLCPR) for the last 3 years was reviewed.
The objective was to identify any period where the MFLCPR (corrected for SC 21-04) exceeded 1.0 for more than 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. During Cycle 20 (May 2018 through March 2019) and Cycle 21 (May 2019 through February 2021) there were multiple periods where MFLCPR was greater than 1.0 for longer than 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. During these instances, the requirements of TS 3.2.2 were not met; however, during this time period there were no limiting transients that would be a challenge to the Safety Limit and there were no Safety Limit violations.
RBS previously performed an Operability Evaluation for SC 21-04 Revision 0 in CR-RBS-2021-3221 CA-Cl, which resulted in the implementation of a compensatory measure for tracking CR-RBS-202l-03221. To ensure compliance until the new COLR is approved, the site issued a standing order to implement the reduced administrative MFLCPR.
The sites review of SC 21-04 Revision 1 was performed and based on that review; the standing order was updated to add additional conservatism.
The BWR/6 plant design has supporting cross beams that form a grid structure underneath the core plate. The orientation of SEOs relative to the beams produces different losses due to the difference in upstream flow areas.
These variations influence the SEQ flow patterns and the potential for a meta-stable pressure loss. Because the frequency at which meta-stable losses may occur has not been determined, RBS was evaluated using a bounding loss coefficient (1.9 times the current loss value) at the 2-beam locations. Results show the potential MCPR impact at limiting locations can be greater than 0.01 and will vary by plant and power/flow condition. The MCPR impact is greater than the 0.01 criterion that GEH has historically applied for reporting that a TS Safety Limit (as found in TS 2.1) could have been exceeded as defined under 10 CFR Part 21.
If the MCPR impact is greater than 0.01 due to possible meta-stable losses at the 2-beam locations, and if not addressed, the condition could occur at a limiting bundle location and reduce transient margin. This could have resulted in exceeding the Safety Limit Minimum Critical Power Ratio (SLMCPR) if a limiting transient were to have occurred.(08-2020)
Page2of3U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 31 50-0104 EXPIRES: 08/31/2023 (08-2020)
- 3. LERNUMBER YEAR SEQUENTIAL REV River Bend Station, Unit 1 05000
- - 458 NUMBER NO.
2021
- - 004
- - 00
Safety Assessment
There were no actual consequences for this event. The RBS Operating Limit MCPR (OLMCPR) is set such that if the plant is operating within this limit, the most limiting operational transient for the cycle will not result in violation of the SLMCPR. The site reviewed the unit operating history for limiting transients and other analyzed transients that are close to being limiting in the Supplemental Reload Licensing Reports. This review concluded that, for the period reviewed, the limiting transients were turbine trip without bypass, feedwater controller failure, generator load reject without bypass, rod withdrawal error, and loss of feedwater heating.
Because these limiting transients were not identified in the period reviewed, the margin between the SLMCPR and OLMCPR was adequate for continued SLMCPR protection. The SLMCPR was not exceeded in previous analyzed cycles and the margin between SLMCPR and OLMCPR was sufficient to accommodate the penalty evaluated in SC 21-04, Revision 1. As a result, there was no impact to the health and safety of the public or plant personnel from this condition.
In addition, this event does not meet the criteria for a Safety System Functional Failure.
Event Cause(s):
Based on the Entergy internal review, it was determined that the cause of this event was: GNF did not accurately account for loss coefficients at those core locations causing a local overprediction in MCPR margin resulting in exceeding the MCPR TS limit.
These occurrences of exceeding the MCPR TS limit were beyond the control of Entergy to predict or prevent because it is a legacy design calculation error. Entergy does not have the capability to check these calculations, nor does Entergy have the resources to perform an independent review of all GNF calculations. The methodology used in the reload process has been accepted by Entergy and we do not check underlying calculations that have existed unchanged for multiple cycles. Entergy will credit actions taken by GNF as part of the Part 21 notification, including actions they are taking for extent of condition in their calculations. This would include the results of any technical audit they are performing. Entergy Supplier Quality Assurance was notified of this Part 21 for follow-up on the GNF
corrective action
Corrective Actions
To ensure compliance with the MCPR TS, RBS issued the standing order as described above. Complete.
RBS will implement a penalty to OLMCPR in the core monitoring system through an update to the databank to include all penalties associated with GEH letter SC 2 1-04, Revision 1. Completion tracked by Corrective Action Program.
RBS will update the current COLR and associated documents to account for all penalties associated with GEH letter SC 21-04, Revision 1. Completion tracked by Corrective Action Program.
Entergys Supplier QA has added CR-HQN-2021-0 1048 and SC 21-04 Ri to the Qualified Supplier List comments sections for GEH/GNF Fuels for follow-up in the next audit. Complete.
Previous Similar Events
None.(08-2020)
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