RA-22-0308, Proposed Alternative in Accordance with 10 CFR 50.55a(z)(1) for Inservice Inspection of the Torus Metallic Liner
| ML22349A655 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 12/16/2022 |
| From: | Krakuszeski J Duke Energy Progress |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RA-22-0308 | |
| Download: ML22349A655 (1) | |
Text
a,DUKE John A. Krakuszeski Vice President ENERGY Brunswick Nuclear Plant 8470 River Rd SE Southport, NC 28461 o: 910.832.3698 December 15, 2022 10 CFR 50.55a Serial: RA-22-0308 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Brunswick Steam Electric Plant, Unit Nos. 1 and 2 Renewed Facility Operating License Nos. DPR-71 and DPR-62 Docket Nos. 50-325 and 50-324
SUBJECT:
Proposed Alternative in Accordance with 10 CFR 50.55a(z)(1) for lnservice Inspection of the Torus Metallic Liner Ladies and Gentlemen:
Pursuant to 10 CFR 50.55a(z)(1), Duke Energy Progress, LLC (Duke Energy) is requesting NRC approval of a proposed alternative to certain requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI for Brunswick Steam Electric Plant (BNP) Units 1 and 2. Specifically, Duke Energy is proposing an alternative to examination requirements found in the ASME Code, subsection IWE for visual examination of the metallic liner surrounding the Suppression Chamber (torus) containment for Units 1 and 2.
The proposed alternative is provided as Enclosure 1 to this letter.
No new regulatory commitments are contained in this submittal. Duke Energy requests NRC approval of this proposed alternative within one year from the date of acceptance for review.
Please refer any questions concerning this letter and its enclosures to Ryan Treadway, Director - Nuclear Fleet Licensing, at (980) 373-5873.
Sincerely, John A. Krakuszeski Vice President, Brunswick Nuclear Plant
Enclosure:
- 1. Proposed Alternative in Accordance with 10 CFR 50.55a(z)(1) for lnservice Inspection of the Torus Metallic Liner
U.S. Nuclear Regulatory Commission RA-22-0308 Page 2 cc:
L. Dudes, USNRC, Region II Regional Administrator L. Haeg, USNRC NRR Project Manager for BNP G. Smith, USNRC Senior Resident Inspector for BNP
RA-22-0308 Enclosure 1 Proposed Alternative in Accordance with 10 CFR 50.55a(z)(1) for Inservice Inspection of the Torus Metallic Liner Page 1 of 14
Relief Request Serial # RA-22-0308 Enclosure 1
- 1. ASME Code Component(s) Affected:
Suppression Chamber (torus) submerged surfaces of the containment metal liner for Brunswick Steam Electric Plant (Brunswick), Units 1 and 2.
List of Applicable Components:
1(2)-SC-ML-B1-BWL Torus Bay 01 (Az. 0 Deg.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B2-BWL Torus Bay 02 (Az. 22 Deg., 30 Min.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B3-BWL Torus Bay 03 (Az 45 Deg.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B4-BWL Torus Bay 04 (Az. 67 Deg., 30 Min.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B5-BWL Torus Bay 05 (Az. 90 Deg.) submerged surfaces of containment metal liner and steam vent header downcomers 1(2)-SC-ML-B6-BWL Torus Bay 06 (Az. 112 Deg., 30 Min.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B7-BWL Torus Bay 07 (Az. 135 Deg.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B8-BWL Torus Bay 08 (Az. 157 Deg., 30 Min.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B9-BWL Torus Bay 09 (Az. 180 Deg.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B10-BWL Torus Bay 10 (Az. 202 Deg., 30 Min.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B11-BWL Torus Bay 11 (Az. 225 Deg.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B12-BWL Torus Bay 12 (Az. 247 Deg., 30 Min.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B13-BWL Torus Bay 13 (Az. 270 Deg.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B14-BWL Torus Bay 14 (Az. 292 Deg., 30 Min.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B15-BWL Torus Bay 15 (Az. 315 Deg.) submerged surfaces of containment metal liner and steam vent header downcomer 1(2)-SC-ML-B16-BWL Torus Bay 16 (Az. 337 Deg., 30 Min.) submerged surfaces of containment metal liner and steam vent header downcomer
2. Applicable Code Edition and Addenda
The applicable Edition and Addenda of the ASME B&PV Code,Section XI is identified below in Table 1 and referenced in the Brunswick Unit 1 and 2 Fifth Interval Inservice (ISI) plan document, BNP-PM5-002.
Page 2 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 Table 1 Containment Applicable ASME Interval Interval Plant/Unit(s) ISI Interval Section XI Code Start Date End Date1 Brunswick Steam Third 2007 Edition 05/11/2018 05/10/2028 Electric Plant, through 2008 Units 1 & 2 Addenda Note 1: The Interval End Date is subject to change in accordance with IWA-2430(c).
3. Applicable Code Requirements
3.1 IWE-2500, Table IWE-2500-1, Examination Category E-A, Item Number E1.12 requires that 100% of wetted surfaces of submerged areas receive a VT-3 examination once each inspection interval in accordance with the acceptance standards in IWE-3510. Deferral of inspection to the end of the interval is permissible.
3.2 IWE-3513 Visual Examination VT-3 states that relevant conditions shall require correction or evaluation to meet the requirements of IWE-3122 prior to continued service. In accordance with IWE-3513(a), relevant conditions include pressure-retaining component corrosion that exceeds 10% of the nominal wall thickness.
3.3 IWE-3122.3(a) states that components whose examinations detected flaws or areas of degradation that do not meet the acceptance standards of IWE-3500 are accepted for continued service without a repair/replacement activity if engineering evaluation indicates that the flaw or area of degradation is nonstructural in nature or has no unacceptable effect on the structural integrity of the component.
3.4 IWE-3122.3(b) states that when flaws or areas of degradation are accepted by engineering evaluation, the area containing the flaw or degradation shall be reexamined in accordance with IWE-2420(b), (c), and (d).
3.5 IWE-2420(b) requires that examinations resulting in areas of flaws or degradation that require an engineering evaluation and the component is acceptable for continued service, the areas containing such flaws, areas of degradation, or conditions shall be reexamined during the next inspection period in accordance with Table IWE-2500-1, Examination Category E-C, Containment Surfaces Requiring Augmented Examination
4. Reason for Request
4.1 The Brunswick Unit 1 and 2 Suppression Chamber (torus) containment metallic liner plate is 3/8-inch (375 mils) nominal thickness and backed by reinforced concrete. In accordance with IWE-3513(a), relevant conditions include substrate pit corrosion and general area degradation of the torus metallic liner that exceeds a depth of 37 mils (i.e.
10% of the nominal wall thickness). 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 187 mils (tmin=3/16 or 50% nominal wall thickness) and with general area corrosion that does not result in a remaining wall thickness of less than 250 mils (tmin = 1/4" or 66% nominal wall thickness).
Page 3 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 4.2 Discussion of Examinations Performed During the Second Containment Inspection Interval which began May 11, 2008 and ended May 10, 2018 During the third period of the second interval, visual (VT-3) examinations were performed on 100% of the submerged surfaces of the torus containment metallic liners on Brunswick Units 1 & 2 in accordance with Table IWE-2500-1, Examination Category E-A, Item Number E1.12, of the ASME B&PV Code,Section XI, 2001 Edition through 2003 Addenda.
In accordance with ASME Section XI, 2001 Edition through 2003 Addenda, Table IWE-2500-1, Examination Category E-A, Item Number E1.12, Wetted Surfaces of Submerged Areas shall receive a general visual (VT-G) examination on 100% of the submerged surfaces during the inspection interval. In this earlier code edition and addenda, IWE-3510.1 states that the Owner shall define acceptance criteria for visual examination of containment surfaces (i.e. the 10% of nominal wall thickness defined in IWE-3513(a) of the current applicable code of record was not applicable).
IWE-3510.2 of the 2001 Edition through 2003 Addenda states that the condition of the inspected area is acceptable if there is no evidence of damage or degradation which exceeds the visual examination acceptance criteria specified by the Owner.
Areas that are suspect shall be accepted by engineering evaluation or corrected by repair/replacement activities or by corrective measures in accordance with IWE-3122.
During the second containment inspection interval, the Owner (Duke Energy) elected to perform visual examinations using VT-1/VT-3 methods on the submerged surfaces of the torus containment metallic liner. For these visual (VT-1/VT-3) examinations, the Owner (Duke Energy) established the acceptance criteria that substrate corrosive degradation less than 90 mils in the submerged surfaces of the torus containment metallic liners was acceptable for continued service without engineering evaluation or correction by repair/replacement or other applicable code corrective measures.
4.2.1 During Brunswick Unit 1 second interval inspections (March 2016), five (5) submerged surface areas distributed over the sixteen (16) total torus metallic liner bays were discovered with substrate pit corrosion that exceeded a depth of 90 mils. An engineering evaluation determined that these five (5) areas and all other areas of corrosive degradation of less depth were acceptable for continued service without a repair/replacement activity. Prior to continued service, protective coating restoration was applied to the five (5) torus submerged surface areas of corrosive pit degradation exceeding a depth of 90 mils. Protective coating restoration was not applied to other torus submerged surface areas where corrosive degradation was discovered but did not exceed the Owner specified acceptance criteria of 90 mils.
Augmented visual (VT-1) examinations were performed on the five areas that exceeded the Owners specified acceptance criteria in accordance with IWE-2420(b) during the next inspection period, which was the first period of the third containment inspection interval. The results of these subsequent augmented examinations are provided below in Section 4.3.1.
Page 4 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 4.2.2 During Brunswick Unit 2 second interval inspections (March 2015), there were no (0) discovered submerged surfaces in the sixteen (16) submerged torus bays with substrate pit corrosion exceeding the Owner specified acceptance criteria of 90 mils. All discovered conditions were acceptable for continued service in accordance IWE-3510.2 of the 2001 Edition through 2003 Addenda without evaluation or repair/replacement activity. Prior to continued service, protective coating restoration was applied to the submerged surfaces in all sixteen (16) torus bays to arrest further corrosive degradation. With all visual examination results within the acceptance criteria established by the Owner, successive examinations in accordance with IWE-2420(b) were not required during the subsequent inspection period.
4.3 Discussion of Examinations Performed During the Third Containment Inspection Interval which began May 11, 2018 and is projected to end May 10, 2028 In accordance with ASME Section XI, 2007 Edition through 2008 Addenda, Table IWE-2500-1, Examination Category E-A, Item Number E1.12, Wetted Surfaces of Submerged Areas shall receive a visual (VT-3) examination on 100% of the submerged surfaces during the inspection interval. In this current applicable code edition and addenda, IWE-3513(a) states that relevant conditions shall include pressure-retaining component corrosion that exceeds 10% of the nominal wall thickness of the component examined. For Brunswick Units 1 and 2, relevant conditions include torus metallic liner degradation that exceed a depth of 37 mils (i.e. 10% of the torus liner nominal wall thickness).
IWE-3511 of the 2007 Edition through 2008 Addenda states that the condition of the examined area is acceptable if the Responsible Individual (IWE-2320) determines that there is no evidence of damage or degradation sufficient to warrant further evaluation or performance of a repair/replacement activity. Suspect conditions shall be evaluation to the extent necessary to ensure that the component function is not impaired.
During the first period of the third interval, visual examinations on a selected number of the torus submerged surface bays were performed on Brunswick Unit 1 and 2 in accordance with Table IWE-2500-1, Examination Category E-A, Item Number E1.12 (VT-3), and Examination Category E-C, Item Number E4.11 (VT-1) of the ASME B&PV Code,Section XI, 2007 Edition through 2008 Addenda. The results of these examinations are described below in Sections 4.3.1 and 4.3.2.
Page 5 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 4.3.1 On Brunswick Unit 1, visual examinations (VT-3) were performed on four (4) submerged surface bays of the torus containment metallic liners. Substrate pit corrosion was discovered in all torus submerged surface bays, including several areas of substrate pit corrosion with measured depths between 37 mils (10% liner plate thickness) and 126.3 mils (34% liner plate thickness maximum recorded pit depth) distributed across these four (4) torus submerged surface bays. Also, augmented visual (VT-1) examination was performed on the five (5) previously discovered submerged surfaces with substrate pit corrosion exceeding a depth of 90 mils and previously receiving protective coating restoration. During these augmented examinations, there was no observed degradation discovered in the five (5) submerged surface areas of previously restored protective coating. An engineering evaluation identified that all discovered relevant conditions not meeting the acceptance standards of IWE-3500 were accepted for continued service without a repair/replacement activity. Prior to continued service, the submerged surface of these four (4) examined torus bays had the protective coatings restored to arrest further degradation of the torus containment metallic liner.
4.3.2 On Brunswick Unit 2, visual examination (VT-3) was performed on the submerged surfaces of five (5) submerged surface bays of the torus containment metallic liner. In these five (5) submerged surface bays, most discovered areas of substrate pit corrosion did not exceed the acceptance standard of IWE-3500 (i.e. did not exceed 10% of nominal wall thickness). In a single torus bay, a single substate pit corrosion area with metal loss exceeding 10% nominal wall thickness was discovered (i.e. measured depth 42 mils or 11% nominal wall thickness). Augmented (VT-1) examinations were neither required nor performed during these Brunswick Unit 2 inspections. An engineering evaluation identified that the discovered relevant condition not meeting the acceptance standards of IWE-3500 was accepted for continued service without a repair/replacement activity. Prior to continued service, the submerged surface of the five (5) examined torus bays had the protective coatings restored to arrest further degradation of the torus containment metallic liner.
4.3.3 On Brunswick Units 1 and 2, successive inspections in accordance with IWE-2420(b) and Table IWE-2500-1, Examination Category E-C, are currently scheduled for all discovered areas with substrate pit corrosion with metal loss exceeding 10% nominal wall thickness and evaluated acceptable for continued service in accordance with IWE-3122.3. The Owner (Duke Energy) proposes that restoration of torus metallic line protective coatings mitigates further corrosive degradation and thereby seeking relief from the requirement to perform these successive inspections.
4.4 Using engineering evaluation, Duke Energy has established the visual (VT-3) examination acceptance criteria for use to demonstrate reasonable assurance that the torus containment metallic liner remains fully capable of performing its intended design function(s). The acceptance criteria is identified below in Section 5.1.
Page 6 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 4.4.1 For Brunswick Units 1 and 2, the restored protective coatings of submerged surfaces, the proposed alternative acceptance criteria for visual (VT-3) examinations (Section 5.1), and engineering evaluation of discovered relevant conditions provide reasonable assurance that the thickness of the submerged surfaces of the torus metallic liner will remain above the design minimum allowable wall thickness for the remainder of the current third containment inspection interval and until their next scheduled visual (VT-3) examinations.
4.4.2 For Brunswick Unit 1 torus submerged surfaces with substrate pit corrosion areas left uncoated during the second inspection interval (Brunswick Unit 1, March 2016), the engineering evaluation, proposed alternative visual (VT-3) examination acceptance criteria (Section 5.1), and the scheduled visual examinations during the next two refueling outages of the current third containment inspection interval provides reasonable assurance that the thickness of the submerged surfaces will remain above the design minimum allowable wall thickness until after these next scheduled visual (VT-3) examinations.
During Brunswick Unit 1 third containment inspection interval, there are three (3) remaining refueling outages. With the conservatism applied by the engineering evaluation to establish visual (VT-3) examination acceptance criteria and design minimum allowable thickness for the torus metallic liner, additional remaining service life may be attained and applied through additional design analysis. This additional analysis may allow extending the current scheduled visual examinations and protective coating restorations to the third remaining refueling outage of the current Brunswick Unit 1 current third containment inspection interval.
4.5 Duke Energy proposes that engineering evaluation and established visual (VT-3) acceptance criteria for the Brunswick Unit 1 and 2 Suppression Chamber (torus)
Containment Metallic Liner proves an acceptable alternative to the acceptance criteria specified in IWE-3513 (i.e. exceed 10% of the nominal wall thickness) in the ASME B&PV Code,Section XI, 2007 Edition and including 2008 Addenda.
4.6 Duke Energy proposes that restoration of protective coatings upon completion of examination provides reasonable assurance that further degradation of the torus containment metallic liner is being arrested. Subsequently, successive examination during the current third containment inspection interval required by IWE-2420(b) provides minimal value since further corrosion and degradation of the metallic liner is arrested by the protective coating restoration.
- 5. Proposed Alternatives and Bases for Use:
5.1 On Brunswick Units 1 and 2, visual (VT-3) examinations will be performed on 100% of the submerged surfaces of the torus containment metallic liners during the third containment inspection interval in accordance with Table IWE-2500-1, Examination Category E-A, Item Number E1.12, of the ASME B&PV Code,Section XI, 2007 Edition through 2008 Addenda. As an alternative to the 10% loss of nominal wall thickness specified in IWE-3513(a), Duke Energy proposes visual (VT-3) examinations revealing substrate pitting or other corrosive degradation that results in a remaining wall thickness of less than 145% of the design minimum allowable for substrate pit corrosion of the metallic liner nominal wall thickness will be considered relevant conditions. Relevant conditions that exceed this Page 7 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 proposed alternative for acceptance criteria will require evaluation or corrective measures or repair/replacement activity to the extend necessary to meet the acceptance standards of IWE-3122 prior to continued service. Using engineering evaluation, Duke Energy proposes that the acceptance criteria of 145% design minimum allowable for identification of relevant conditions provides adequate design margin and reasonable assurance torus metallic liner submerged surfaces remain fully capable of performing their intended design function(s) until the next scheduled containment inspection (as proposed in next paragraph) in accordance with Table IWE-2500-1, Examination Category E-A, Item Number E1.12.
When examination results detect areas of corrosive degradation where the remaining wall thickness of less than 145% of the design minimum allowable and the component is acceptable for continued service by engineering evaluation in accordance with IWE-3122.3, restoration of the torus metallic liner protective coating provides reasonable assurance that further corrosive degradation of torus submerged surfaces is arrested. When areas of corrosive degradation are accepted by engineering evaluation and protective coating is restored to arrest further corrosive degradation, the area containing the corrosive degradation shall be reexamined during the successive inspection interval in accordance with Table IWE-2500-1, Examination Category E-A, Item Number E1.12, This visual (VT-3) reexamination shall be performed during the successive inspection interval at a frequency not to exceed every third inspection period from the previously visual (VT-3) examination. Duke Energy proposes that successive inspection during the current inspection interval in accordance with IWE-2420(b) is unnecessary (see Section 5.3.1). When protective coating is restored to the torus submerged surfaces prior to return to service, Duke Energy proposes that reexamination during the next inspection period in accordance with Table IWE-2500-1, Examination Category E-C, and using the acceptance standard of IWE-3520 is not required.
5.2 On Brunswick Units 1 and 2, there are sixteen (16) submerged torus metallic liner bays (Attachment 1). To complete torus liner visual examinations, torus bays are approximately equally distributed and scheduled for examination over three (3) or more of the total five (5) refueling outages during the current third containment inspection interval. During examinations performed in the first period of the third interval on Brunswick Unit 1 and 2, torus metallic liner protective coating restoration was applied to discovered areas of substrate pit corrosion to arrest further liner plate corrosive degradation. In lieu of performing successive visual (VT-1) examinations during the next inspection periods in accordance with IWE-2420(b) and the acceptance standard of IWE-3520, Duke Energy proposes using the alternatives specified above in Section 5.1.
Page 8 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 On Brunswick Unit 1, visual (VT-3) examinations and protective coating restoration were performed on four (4) torus bays during the first period of the third containment inspection interval. Also, augmented visual (VT-1) examinations were performed on five (5) previously discovered submerged surfaces with substrate pit corrosion exceeding the Owner specified acceptance criteria (90 mils) during the third period of the second containment inspection interval. During these visual (VT-1/VT-3) examinations, the maximum depth of substrate pit corrosion was recorded as 126.3 mils, which is a torus metallic liner loss to 133% of design minimum allowable thickness.
An engineering evaluation determined that this area of maximum recorded pit depth and all other discovered areas of substrate pit corrosion were accepted for continued service without a repair/replacement activity. Prior to continued service, submerged surface protective coatings were restored to arrest further degradation of the torus containment metallic liner. For these four (4) torus bays on Brunswick Unit 1, Duke Energy proposes that successive visual (VT-1) examination during the next inspection period will not be performed and the next schedule visual (VT-3) examination will be performed during the fourth containment inspection interval.
On Brunswick Unit 1, visual (VT-3) examinations and protective coatings restoration of submerged surfaces in the remaining twelve (12) torus bays will continue during the current third inspection interval in accordance with Table IWE-2500-1, Examination Category E-A, Item Number E1.12. These twelve (12) torus bays did not receive protective coating restoration during the third period of the previous second containment inspection interval. Visual (VT-3) examinations during the current third containment inspection interval and engineering evaluation facilitate the monitoring of degradation of these torus metallic liner submerged surfaces. Duke Energy proposes that the engineering evaluation provides reasonable assurance that these torus submerged surfaces remain fully capable of performing its intended design function(s) during the current third containment inspection interval and until the next visual (VT-3) examination during the next two refueling outages of the current inspection interval.
On Brunswick Unit 2, visual (VT-3) examinations and protective coating restoration were performed on five (5) torus bays during the first period of the third containment inspection interval. Augmented visual (VT-1) examinations were neither required nor performed during these containment liner inspections. During visual (VT-3) examinations performed during the first period of the third interval, the maximum depth of substrate pit corrosion was recorded as 42 mils, which is a torus metallic liner loss to 178% of the design minimum allowable thickness. An engineering evaluation determined that all discovered areas of substrate pit corrosion were accepted for continued service without a repair/replacement activity. Prior to continued service, submerged surface protective coatings were restored to arrest further degradation of the torus containment metallic liner. For these five (5) torus bays on Brunswick Unit 2, Duke Energy proposes that successive visual (VT-
- 1) examination during the next inspection period will not be performed and the next scheduled visual (VT-3) examination will be performed during the fourth containment inspection interval.
Page 9 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 On Brunswick Unit 2, visual (VT-3) examinations and protective coatings restoration of submerged surfaces of the containment metallic liner in the remaining eleven (11) torus bays will continue during the current third containment inspection interval in accordance with Table IWE-2500-01, Examination Category E-A, Item Number E1.12. These visual (VT-3) examinations and engineering evaluation will facilitate the monitoring of any relevant conditions discovered in the torus submerged surfaces. Duke Energy proposes that the engineering evaluation will provide reasonable assurance torus submerged surfaces remain fully capable of performing their intended design function(s) during the current third containment inspection interval and until the next visual (VT-3) examination during the fourth containment inspection interval.
5.3 Basis for use of the Proposed Alternative in 5.1 and 5.2 5.3.1 To perform both (i) successive examination of submerged surfaces previously receiving protective coating repairs and (ii) scheduled examination of the remaining submerged surfaces during a single refueling outage creates an unnecessary challenge to personnel safety and radiation exposure.
Page 10 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 5.3.2 To complete the submerged surface inspections, divers manually clean the torus liner plate surfaces to be examined and a filtration system must be used to attain water clarity before divers can perform torus liner visual examinations under water.
x Cleaning liner plate surfaces and performing visual examinations on torus bays that have previously been recoated results in unnecessary worker radiation exposure due to the additional diver hours needed to complete these activities. With protective coating restored, Duke Energy proposes that there is reasonable assurance that further degradation of the torus containment metallic liner is arrested for the remainder of the current inspection interval and until the subsequent scheduled visual (VT-3) examination during the successive containment inspection interval.
x Using a filtration system to attain water clarity results in unnecessary worker radiation exposure and radioactive material disposal. To attain the needed water clarity, the full volume of water in the torus must be circulated several times through the filtration system. This activity typically generates depleted filters, which requires handling and disposal of highly radioactive material. The cleaning of submerged surfaces that previously received protective coating restoration extends the filtration duration necessary to attain water clarity and, thereby, increases the radiation material disposal.
5.3.3 Restoration of protective coatings on the submerged surfaces of the torus containment protective liner is implemented as necessary when examination results reveal areas of degradation that do not meet the acceptance criteria of IWE-3500. Duke Energy considers that surfaces where protective coatings have been restored no longer warrant successive inspections in accordance with IWE-2420(b), and that restoration of protective coating following the examination provides reasonable assurance that continued degradation of these submerged surfaces is arrested and mitigated.
5.3.4 ASME Section XI Code Committee, Working Group Containment, Proposed Code Change IWE-3122.2, Record Number 21-1009, ASME Board Approved, which will eliminate the requirement to perform successive examinations in accordance with IWE-2420(b), (c), and (d) if the condition that caused the flaws or areas of degradation has been corrected using corrective measures (i.e. protective coatings restoration) have been performed during the current outage to prevent further degradation, and the flaws or areas of degradation are subsequently examined in accordance with Table IWE-2500-1 (E-A).
5.3.5 ASME Section XI Code Committee, Working Group Containment, Proposed Code Case, Record Number 21-1713, provides committee opinion that corrosion or erosion that has reduced the component wall thickness to less than 110% of the minimum design wall thickness, or is projected to reduce the component wall thickness to less than 110% of the minimum design wall thickness prior to the next examination may be used for defining surface areas requiring augmented examination in accordance with IWE-1241 and using the acceptance standards of IWE-3500.
Page 11 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 5.3.6 In the proposed alternative by the Owner (Duke Energy), corrosion or erosion that has reduced the component wall thickness to less than 145% of the minimum design wall thickness will be considered a relevant condition that will require evaluation or corrective measures to the extent necessary to meet the acceptance standards of IWE-3500 prior to continued service.
5.3.7 The Owner (Duke Energy) proposes that corrective action taken to restore protective coating provides reasonable assurance the submerged surfaces of the torus containment metallic liner is protected from further degradation and fully capable of performing its intended design function(s).
For the above reasons, Duke Energy requests authorization to use the proposed alternative pursuant to 10 CFR 50.55a(z)(1) on the basis that the alternative provides an acceptable level of quality and safety.
- 6. Duration of Proposed Alternative:
This alternative is requested for the duration of the Brunswick Steam Electric Plant, Units 1
& 2, Third Ten-Year Containment Inservice Inspection Interval, which is currently scheduled to end no later than May 10, 2028.
- 7. Precedents:
H.B. Robinson Steam Electric Plant, Unit 2 - Request of Alternatives to ASME Code Section XI Subsections IWE Requirements for Containment Inspections (EPID L-2021-LLR-0064)
(ML22193A212), Published: August 4, 2022
- 8.
References:
8.1 ASME Boiler and Pressure Vessel Code, Sections XI, 2001 Editions including 2003 Addenda 8.2 ASME Boiler and Pressure Vessel Code, Sections XI, 2007 Editions including 2008 Addenda 8.3 ASME Section XI Code Committee, Working Group Containment, Record Number 21-1009 and 21-1713 Page 12 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 Attachment 1 (Page 1 of 2)
Suppression Chamber (aka Torus) Detail Drawings Plan View Page 13 of 14
Relief Request Serial # RA-22-0308 Enclosure 1 Attachment 1 (Page 2 of 2)
Suppression Chamber (aka Torus) Detail Drawings Section View Page 14 of 14