05000336/LER-2021-001, Incorrectly Placed Spent Fuel Assemblies in Unit 2 Spent Fuel Pool
| ML21267A024 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 09/23/2021 |
| From: | Daugherty J Dominion Energy Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 21-274 LER 2021-001-00 | |
| Download: ML21267A024 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2) |
| 3362021001R00 - NRC Website | |
text
Dominion Energy Nuclear Connecticut, Inc.
Millstone Power Station 314 Rope Ferry Road, Waterford, CT 06385 Dominion Energy.com U.S. Nuclear Regulatory Commission Attention: Document Contrd Desk Washington, DC 20555 SEP 2 3 2021 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 2 LICENSEE EVENT REPORT 2021-001-00 Dominion
-=
Energy Serial No.: 21-274 MPS Lie/LO RO Docket No.: 50-336 License No.: DPR-65 INCORRECTLY PLACED SPENT FUEL ASSEMBLIES IN UNIT 2 SPENT FUEL POOL This letter forwards Licensee Event Report (LER) 2021-001-00, documenting a condition that was discovered at Millstone Power Station Unit 2, on July 27, 2021. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.
There are no regulatory commitments contained in this letter or its enclosure.
Should you have any questions, please contact Mr. Jeffry A. Langan at (860) 444~5544.
Sincerely,
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~YC/7~.*
John R. Daugherty Site Vice President - Millstone Enclosure: LER 336/2021-001-00
cc:
U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd.
Suite 100 King of Prussia, PA 19406-2713 R.V. Guzman NRC Senior Project Manager Millstone Units 2 and 3 U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 C-2 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Serial No.21-274 Docket No. 50-336 Licensee Event Report 2021-001-00
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ATTACHMENT Serial No.21-274 Docket No. 50-336 Licensee Event Report 2021-001-00 LICENSEE EVENT REPORT 2021-001-00 INCORRECTLY PLACED SPENT FUEL ASSEMBLIES IN UNIT 2 SPENT FUEL POOL MILLSTONE POWER STATION UNIT 2 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
Abstract
On July 27, 2021, with Millstone Power Station Unit 2 (MPS2) in operational Mode 1, 100 percent reactor power, it was discovered that four spent fuel assemblies were placed in a region of the MPS2 Spent Fuel Pool (SFP) on July 15, 2021, for which they were not qualified by measured burnup. The configuration violated Technical Specifications, resulting in Technical Specification 3.9.18 Action Statement being entered on July 27, 2021, at 15: 18. The direct cause of this condition was the incorrectly calculated projected burnup values for all fuel assemblies resident in the MPS2 Cycle 26 core which impacted fuel assemblies BB-65, BB-66, BB-67, and BB-68. The root cause was lack of specific guidance in the engineering standard used to calculate projected burn up values.
The non-complying spent fuel assemblies were immediately moved to an acceptable location in Region 1 of the MPS2 SFP, and the TS 3.9.18 Action Statement was exited on July 27, 2021, at 17:29. The engineering standard used to perform the calculations to qualify spent fuel for storage in the SFP is being revised to include specific guidance to use measured assembly burnup values for MPS2 SFP qualification and to prohibit projection of assembly burnup. Additional corrective actions are being taken in accordance with the Corrective Action Program.
The spent fuel assemblies placed in the incorrect location in MPS2 SFP is being reported in accordance with 10 CFR 50.73(a)(2)
(i)(B) as a condition prohibited by technical specifications.
1. EVENT DESCRIPTION
On July 27, 2021, with Millstone Power Station Unit 2 (MPS2) in operational Mode 1, 100 percent reactor power, it was discovered that four spent fuel assemblies were placed in a region of the MPS2 Spent Fuel Pool (SFP), on July 15, 2021,
for which they were not qualified by measured burnup. The four MPS2 fuel assemblies BB-65, BB-66, BB-67, and BB-68, were determined to have a lower measured burn up than the minimum burnup requirement for the MPS2 SFP Region 3 storage with borated stainless-steel poison rodlets. The configuration violated Technical Specifications, resulting in Technical Specification 3.9.18 Action Statement being entered on July 27, 2021, at 15:18.
In January 2020, approximately 4 months before the end of operating cycle 26, a calculation was performed to qualify cycle 26 fuel assemblies for SFP storage by SFP Region. The calculation was initially conducted using the current Cycle 26 measured cycle burnup at the time of the calculation. Using measured burnup, a larger than expected number of fuel assemblies were not cleared to be placed in Region 3 of the Millstone Unit 2 Spent Fuel Pool. To account for approximately 4 months of cycle operation remaining, a burn up augmentation factor was generated to project the burnup of the fuel assemblies currently in the core to a near end-of-cycle core burn up. This burn up augmentation factor was incorrectly applied to the burn up of the fuel assemblies over their entire operating history as opposed to just applying the augmentation factor to the current cycle burnup. This incorrect burnup augmentation factor increased the projected calculated burn up greater than these four fuel assemblies physically achieved when they were discharged from the core in May 2020. The error was not caught during the preparation, review, or approval of the calculation.
Spent fuel assemblies BB-65, BB-66, BB-67, and BB-68 were discharged from the MPS2 Cycle 26 Core to MPS2 SFP Region 2 in May 2020. These four spent fuel assemblies remained in Region 2 of MPS2 SFP until July 2021. On July 15, 2021, the spent fuel assemblies were placed into Region 3 following the July 2021 Independent Spent Fuel Storage Installation (ISFSI) Campaign. On July 27, 2021, the failure of these four fuel assemblies to meet the burn up requirements for storage in Region 3 was identified when their calculated burnup was updated to actual Cycle 26 burnup.
The spent fuel assemblies placed in the incorrect location in the MPS2 SFP is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by technical specifications.
2. CAUSE
The direct cause of this condition was the incorrectly calculated projected burn up values for all fuel assemblies resident in the MPS2 Cycle 26 core which impacted fuel assemblies BB-65, BB-66, BB-67, and BB-68.
The root cause was the lack of specific guidance in the engineering standard used to calculate projected burn up values for compliance with Technical Specifications. As a result, the calculation preparer developed an incorrect calculation methodology.
With no detailed instructions provided, the preparer developed an alternate method for calculating projected assembly burnup based on a correction factor. The preparer made an error in applying the correction factor, which resulted in projected burn up values for the four fuel assemblies being higher (non-conservative) than their actual values.
3. ASSESSMENT OF SAFETY CONSEQUENCES
There were no safety consequences rela_ted to this condition.
The MPS2 criticality safety analysis considered multiple potential failures, including analyzing 90 fuel assemblies with burn up significantly lower than the four fuel assemblies had. The results of this analysis concluded that with a 2100 ppm soluble boron in the SFP, the regulatory requirements for keff remained met even with the four fuel assemblies loaded in the incorrect location. Therefore, the current MPS2 SFP never entered an unanalyzed condition and did not exceed any safety limits.
No safety functions were challenged, and this condition did not challenge the health and safety of the public or the environment.
4. CORRECTIVE ACTION
The four non-complying spent fuel assemblies were immediately moved to an acceptable location in Region 1 of the MPS2 SFP, and the TS 3.9.18 Action Statement was exited on July 27, 2021, at 17:29. The engineering standard used to perform the calculations to qualify spent fuel for storage in the SFP is being revised to include specific guidance to use measured assembly burnup values for MPS2 SFP qualification and to prohibit projection of assembly burnup. Additional corrective actions are being taken in accordance with the Corrective Action Program.
5. PREVIOUS OCCURRENCES
There have been no spent fuel assemblies loaded in the incorrect location in MPS2 SFP in the past 3 years.
- 6. Energy Industry Identification System (EIIS) codes
- None (no broken equipment) Page 3
of 3,