ML24032A139
| ML24032A139 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 02/12/2024 |
| From: | Luke Haeg Plant Licensing Branch II |
| To: | Krakuszeski J Duke Energy Progress |
| Haeg, L E | |
| References | |
| Download: ML24032A139 (1) | |
Text
February 12, 2024 John A. Krakuszeski Site Vice President Brunswick Steam Electric Plant Duke Energy Progress, LLC 8470 River Rd. SE (M/C BNP001)
Southport, NC 28461
SUBJECT:
BRUNSWICK STEAM ELECTRIC PLANT, UNIT NOS. 1 AND 2 - CORRECTION OF ERRORS WITHIN AUTHORIZED ALTERNATIVE REQUEST RA-22-0308
Dear Mr. Krakuszeski:
On November 27, 2023, the U.S. Nuclear Regulatory Commission (NRC) authorized alternative request (RA-22-0308) for Brunswick Steam Electric Plant, Unit Nos. 1 and 2 (Brunswick)
(Agencywide Documents Access and Management System (ADAMS) Accession No. ML23297A026). The authorization allowed for the performance of alternatives to certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI, Subsection IWE, Requirements for Class MC [metal containment] and Metallic Liners of Class CC [concrete containment] Components of Light-Water Cooled Plants, requirements for the third 10-year containment inservice inspection interval at Brunswick. The request related to alternative examination and associated acceptance criterion of the submerged surfaces of torus bays for Brunswick.
Recently, the NRC was notified of errors within Section 3.2.1.1, Proposed Acceptance Criterion for Relevant Conditions, of the NRC staffs safety evaluation (SE) enclosed within the authorized RA-22-0308 (ML23297A026). The errors concerned an incorrectly stated proposed acceptance criteria and the incorrect statement for a licensee-imposed limitation.
The purpose of this letter is to issue a correction with clarifying changes to Section 3.2.1.1 (pages 5 and 6) of the SE. The NRC concludes that the corrections do not change the staffs previous overall conclusions in the SE for the authorized RA-22-0308. Enclosed, please find the corrected SE pages 5 and 6, with revision bars indicating the areas of change.
If you have any questions regarding this matter, please contact me at (301) 415-0272 or by email at Lucas.Haeg@nrc.gov Sincerely,
/RA/
Luke Haeg, Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-325 and 50-324
Enclosure:
Correction to Authorized RA-22-0308 cc: Listserv
ENCLOSURE BRUNSWICK STEAM ELECTRIC PLANT, UNITS 1 AND 2 DOCKET NOS. 50-324 AND 50-325 CORRECTION TO AUTHORIZED RA-22-0308 SAFETY EVALUATION PAGES 5 AND 6 3.1.5 Duration of Proposed Alternatives The licensee requested that the proposed alternatives be effective for the duration of Brunswick, Unit Nos. 1 and 2, third 10-year CISI interval, which is currently scheduled to end no later than May 10, 2028. In response to RAI-9(2) in its supplement, the licensee stated that the duration of the proposed alternatives would not extend to the Brunswick, Unit Nos. 1 and 2, fourth 10-year CISI interval, which is scheduled to begin on May 11, 2028.
3.2
NRC Staff Evaluation
The NRC staff focused its evaluation on: (1) the three proposed alternatives, (2) the proposed inspection during the remainder of the third 10-year CISI interval, (3) proposed corrective actions, and (4) defense-in-depth measures.
3.2.1 Proposed Alternatives 3.2.1.1 Proposed Acceptance Criterion for Relevant Conditions The ASME Code,Section XI, IWE-3513(a) specifies that pressure-retaining component corrosion or erosion (degradation) that exceeds 10 percent of the nominal wall thickness shall require correction or evaluation to meet the requirements of IWE-3122 prior to continued service. The nominal torus liner wall thickness is 0.375 inch. Therefore, a relevant condition includes pit corrosion that exceeds the depth of 0.0375 inch (10 percent of 0.375 inch) in accordance with the ASME Code,Section XI.
For the design minimum allowable wall thickness discussed in Section 4.1 of RA-22-0308, and established in a current engineering calculation (Enclosure 2 to the supplement), the torus metallic liner remains fully capable of performing its intended design function with local substrate pit corrosion that does not result in a remaining wall thickness of less than 3/16 (0.1875) inch and with general area corrosion that does not result in a remaining wall thickness of less than 1/4 (0.250) inch. The licensee proposed acceptance criterion was that if the remaining wall thickness, at a pitted location, was less than 145 percent of the design minimum allowable wall thickness, the pit corrosion would be considered a relevant condition.
The 145 percent of the design minimum allowable wall thickness of 0.1875 inch is 0.2719 inch (145 percent of 0.1875 inch). In response to RAI-8 as shown in its supplement, the licensee stated that the material allowance for future pitting corrosion is 0.084 inch (45 percent of 0.1875 inch) for previously detected corroded areas that are not repaired. In other words, if a pit was discovered at a depth equal to the proposed acceptance criteria of 145 percent of the minimum allowable wall thickness, future corrosion of 0.084 inch would be required to reach the design minimum allowable wall thickness of 0.1875 inch.
The licensee stated that once a pit corrosion exceeds the specified depth, it will take corrective action, such as restoring the protective coating on the pitted location to prevent further degradation.
In response to RAI-8(2) as shown in its supplement, the licensee stated that the proposed alternative does not apply to discovered corroded areas of the torus metallic liner that have not been recoated to prevent further corrosion degradation.
The NRC staff finds the proposed acceptance criterion acceptable because with the postulated metal loss, the torus liner would still maintain the design function minimum wall thickness for the remainder of the third CISI interval.
3.2.1.2 Proposed Alternate Examination As stated above, the licensee proposed to: (1) perform an inspection at a frequency not to exceed every third inspection period from the previous visual (VT-3) examination, and (2) not to perform VT-1 examination. The licensee stated that the corrosion rate is 7.5 mils/year based on operating experience. In response to RAI-8 as shown in its supplement, the licensee stated that considering the 0.084 inch of liner material available for future corrosion and a corrosion rate of 7.5 mils/year, an uncoated pitted area (i.e., protective coating was not applied, or the applied protective coating failed) would not be expected to violate the design minimum wall thickness for approximately 11.2 years (0.084 inch / 0.0075 inch/year). As such, in lieu of performing a successive examination in the subsequent inspection period per the ASME Code,Section XI, IWE-2420(b), the licensee proposed that inspection at a frequency not to exceed every third inspection period from the previous visual (VT-3) examination.
In response to RAI-5 as shown in its supplement, the licensee stated that it will apply the proposed acceptance criterion to discovered exposed substrate areas and corrosive pit indications on the submerged surfaces of the torus liner. The licensee also stated that this new acceptance criteria will be applied to the exposed substrate areas and corrosive pit indications discovered with previously restored protective coatings and to the areas of exposed substrate corrosion left uncoated during the second inspection interval in the 2016 Unit 1 refueling outage.
The licensee stated that any discovered corrosive pit indications that exceed the proposed acceptance criterion will be dispositioned in accordance with the requirements of IWE-3122.2, Acceptance by Corrective Measures or Repair/Replacement Activity, or IWE-3122.3 prior to continued service.
The NRC staff noted that the ASME Code,Section XI, IWE-1241, Examination Surface Areas, requires augmented inspection in accordance with Table IWE-2500-1, Examination Category E-C for surface areas that are subject to accelerated degradation and aging. Examination Category E-C requires the use of the VT-1 examination during the augmented examination. As an alternative, the licensee proposed that when protective coating is restored, reexamination during the next inspection period in accordance with Table IWE-2500-1, Examination Category E-C, is not required, meaning that the use of the acceptance standard of IWE-3520 and VT-1 examination are not required.
However, the licensee imposed a limitation on its proposed alternative examination. In response to RAI-8(4) in its supplement, the licensee stated that for discovered indications that do not receive protective coating restoration and are determined acceptable by engineering evaluation in accordance the ASME Code,Section XI, IWE-3122.3, the inspection frequency will be in accordance with IWE-2420. The NRC staff determined that the licensee-imposed limitation will ensure that the proposed acceptance criterion will be applied judiciously and appropriately.
In addition, the NRC noted that as discussed in RA-22-0308 and the supplement, the inspection results from the second and third CISI intervals do show many corroded locations. Several indications were within the 37 mils depth (e.g., 10 percent of design thickness). Some of the indications exceeded the ASME Code limit of 37 mils depth. The maximum depth for the pitted corrosion was 131 mils as presented in response to RAI-5(1) in the supplement. The NRC staff noted that the degradation mechanism of pitted indications is general corrosion, not stress
ML24032A139 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NVIB/BC NAME LHaeg ABaxter ABuford JTsao for DATE 01/31/2024 02/06/2024 02/01/2024 OFFICE NRR/DORL/LPL2-2/BC NRR/DORL/LPL2-2/PM NAME DWrona LHaeg DATE 02/09/2024 2/12/2024