ML24354A199
| ML24354A199 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 12/19/2024 |
| From: | Ameren Missouri, Union Electric Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML24354A196 | List: |
| References | |
| ULNRC-06890 | |
| Download: ML24354A199 (1) | |
Text
Enclosure 2 to 10 CFR 50.55a Request IWE-02 ULNRC06890 Page 1 of 3 Proposed Alternative In accordance with 10 CFR 50.55a (z)(1)
Alternative Provides Acceptable Level of Quality and Safety
- 1. ASME Code Component Affected:
Component:
Containment Liner
Description:
Instrument Tunnel Sump (Incore Pit) Liner Component Number:
SUMPLF07DRWIT
2. Applicable Code Edition and Addenda
ASME Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2007 Edition through 2008 Addenda.
3. Applicable Code Requirement
IWA-4422, Defect Evaluation and Examination IWA-4422.2.2, Defect Removal Followed by Welding or Brazing, paragraph (a) states the following:
Surface examination of the defect removal area is required prior to welding, except as provided below.
(1) A surface examination is not required when the defect is eliminated by removing the full cross-section of the weld or base material.
(2) When surface examination of the excavation cannot be performed or will not provide meaningful results, surface examination of the excavation is not required. The acceptability of any remaining portion of the defect may be established by evaluation in accordance with IWA-4422.1(b) in lieu of the surface examination. Alternative NDE methods may be used to characterize any remaining portion of the defect.
(3) If final volumetric examination will be performed on the completed repair, the final volumetric examination method is the same as the method used to detect the defect, and the volume to be examined includes the location of the original defect, surface examination of the defect removal area is not required.
4. Reason for Request
Pursuant to 10 CFR 50.55a, "Codes and standards," paragraph (z)(1), an alternative to the Section XI, IWA-4422.2.2(a) surface examination requirement is proposed. The basis of the request is that the proposed alternative would provide an acceptable level of quality and safety.
On October 20, 2023, during Callaway's refueling outage (RFO), inservice inspection (ISI) on the Instrument Tunnel Sump (Incore Pit) was performed (Reference 1) in accordance with Callaway's Containment Pressure Boundary ISI Program procedure (Reference 2). During this inspection, Quality Control (QC) inspectors identified (25) localized pits on the liner plate wall and floor. Using a pit-to 10 CFR 50.55a Request IWE-02 ULNRC06890 Page 2 of 3 gauge, the depth measurements of the pits ranged from 0.0625" to 0.1875" and 0.250" to 1.125" in diameter (Reference 3). This condition was captured in Callaway's Corrective Action Program (Reference 4) and a job package was generated to repair the identified pits (Reference 5). Excavation was performed to get all indications (i.e., corroded, pitted, and eroded areas) to smooth base metal.
Subsequently, a pre-weld visual examination of the defect removal areas was performed. Following the base metal repairs (BMRs) to the liner, QC inspectors performed visual (VT-1) and magnetic particle (MT) surface examinations per QC examination procedures (Reference 6 and 7). However, in the Fall of 2024, it was identified during an internal oversight audit that a pre-weld surface examination of the defect removal area was not performed on the Instrument Tunnel Sump liner plate. This condition, upon identification, it was captured in Callaway's Corrective Action Program (Reference 8).
In accordance with IWA-4422.2.2(a), Callaway is required to perform a surface examination of the defect removal area prior to welding. Therefore, this relief request is proposing that the pre-weld visual examinations and the post-weld VT-1 and MT exams completed on the Instrument Tunnel Sump liner in the Fall of 2023, in addition to the pneumatic leakage test scheduled to be performed in the Spring of 2025 in accordance with IWE-5224 (bubble test-vacuum box technique), are an acceptable alternative to the IWA-4422.2.2(a) surface examination requirement. With the completion of the above-noted activities that demonstrate an intact and defect free liner, the risk of further damaging the liner does not merit re-excavation of the completed BMRs to complete pre-weld surface exams.
The technical justification for the proposed alternative is discussed in the next section of this relief request.
- 5. Propose Alternative and Basis for Use:
As an alternative, Ameren Missouri proposes, in lieu of the surface examination requirements prescribed in subparagraph IWA-4422.2.2(a), that the pre-weld visual examinations and the post-weld VT-1 and MT exams performed following the BMRs of the Instrument Tunnel Sump liner in the Fall of 2023, in addition to the pneumatic leakage test scheduled to be performed in the Spring of 2025 in accordance with IWE-5224 (bubble test-vacuum box technique), are an acceptable alternative.
With the completion of the above-noted activities that demonstrate an intact and defect-free liner, the risk of further damaging the liner does not merit re-excavation of the completed BMRs to complete pre-weld surface exams.
Justification:
A. Design Information The Instrument Tunnel Sump is a collection point for reactor coolant leakage in containment and is open to containment atmospheric pressure and temperature. Sump level instrumentation is capable of detecting reactor coolant system leakage. The minimum detectable change in level is 25 gpm.
The liner plate of the Instrument Tunnel Sump is ASME Section XI, Class MC (IWE), 1/4" thick Carbon Steel (SA-285). As a containment liner, the primary function of the Instrument Tunnel Sump liner plate is to ensure that the containment structure is leak tight. Behind the containment liner is the post-tensioned concrete containment structure. The concrete structure supports all structural loads, and no credit is taken for the liner for the pressure design of the containment structure.
to 10 CFR 50.55a Request IWE-02 ULNRC06890 Page 3 of 3 B. Visual and Magnetic Particle Surface Examinations During the IWE inspection of the Instrument Tunnel Sump liner in the Fall of 2023, there were (25) twenty-five localized pits identified on the liner wall and floor that required repair. This condition was captured in Callaway's Corrective Action Program, and a job package was generated to repair the pits.
Excavation on the defects (i.e., pitting from corrosion) was performed to get all indications to base metal so that all corroded, pitted, and eroded areas were removed. A pit depth gage was utilized before and after excavation, and pre-weld visual examinations were performed after excavation. This examination verified that all excavations were to base metal with no through-wall pitting observed.
Additionally, this examination provided reasonable assurance that no unidentified flaws were left prior to performing the weld build up.
After the BMRs were completed on the liner plate, VT-1 and MT surface examinations were completed to ensure no flaws existed that would propagate to the surface due to the new weld build-up. These post-weld examinations provide reasonable assurance that there were no surface flaws around any of the weld build-up locations and that the surface of the liner is intact (defect free).
C. Pneumatic Leakage Test In the Spring of 2025, during Callaway's next scheduled RFO, a pneumatic leakage test will be performed in accordance with IWE-5224 (bubble test-vacuum box technique). This test is being performed to meet IWE-5221(a) requirements. A successful completion of this test will provide additional assurances that the liner can perform its leak tight design function. Re-excavation of the BMRs on the Instrument Tunnel Sump liner and pre-weld surface examinations would only be performed if the pneumatic leakage test results indicate a need for such action as determined by the requirements of IWE-5250, Corrective Action.
- 6. Duration of Proposed Alternative:
The relief request will remain in effect until Callaway's end of plant life or until such a time when base metal repairs on the Instrument Tunnel Sump liner are needed at the previously repaired locations.
- 7. References:
- 1. Job 20513454.000, "Containment Pressure Boundary Inspection of Incore Sump"
- 2. ESP-ZZ-01016, "ASME Section XI IWE Containment Pressure Boundary Inspection"
- 3. Job 20513454.500, "General Visual Inspection Report"
- 6. QCP-ZZ-05040, "Visual Examination to ASME VT-1"
- 7. QCP-ZZ-05010, "Magnetic Particle Examination"
- 8. CR 202406120, " Job 20003148.496 Contains Multiple Instances of Non-Compliance with APA-ZZ-00662 and ASME Section XI"
- 9. Calculation ZZ-475, "Evaluate the Minimum Wall Thickness of the Containment Liner Required to for Conditions of Generalized and Localized Thinning"