ML21061A089

TVA Presentation Slides for March 2, 2021, Public Meeting to Discuss Sequoyah Alternative Request

ML21061A089
Person / Time
Site:	Sequoyah
Issue date:	03/02/2021
From:	Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation
References
Download: ML21061A089 (8)

Text

TVA Request for Alternative: SQN CRDM Canopy Seal Welds March 2021

Agenda Outage activities Alternative visual examination Alternative weld repair Precedents 2

Outage Activities Planned Activities Inspection of CRDMs Failure of inspection criteria may require latch assembly replacement Contingent Activities Latch assembly replacement requires disassembly of the CRDM housing including the mid canopy seal weld A visual weld inspection would be performed after restoring the canopy seal weld Defects identified during this process may require an overlay 3

ASME Code Requirements For both units: IWA-4420 and NB-4131 provide the requirements for defect removal.

The Code of Record for the Fourth 10-Year ISI Interval is the 2007 Edition with 2008 IWA-4422.2.2(a) requires a surface Addenda of the ASME BPV Code, Section examination of the defect removal area prior XI to welding The Construction Code for 53 of the CRDM IWA-4422.2.2(e) requires examination of the housings is ASME Section III, Summer 1968 repaired area, following welding, in Edition accordance with IWA-4520 and the original Construction Code.

The Construction Code for an additional 4 CRDM housings is ASME Section III, 1971 NB-5271 requires examination of specially Edition through Winter 1972 Addenda designed seal welds by either magnetic particle or liquid penetrant methods Relief will be requested in accordance with 10 CFR 50.55a(z)(2) 4

Alternate Visual Examination To comply with ASME Section XI and the The required dye penetrant (PT) original Construction Code, a surface examinations would necessitate hands on examination must be performed on the access to the mid canopy weld completed seal weld Sequoyah will perform a remote enhanced The CRDM mid canopy seal welds are visual examination on the completed weld, in located above the Reactor Vessel Closure lieu of the surface examination required by Head, providing extremely limited access for Code workers to reach the assembled weld for examination The proposed remote enhanced visual examination would be conducted using a This highly congested area is also subject to video camera with 5X magnification high radiation levels Lighting and acuity will be verified using Most of the repair activities will be performed ASME Section XI Table IWA-2211-1 remotely using robotic equipment to the requirements for VT-1 note (2) extent practical A machinist scale will be used to ensure a 1/32-inch graduation can be distinguished 5

Alternate Weld Repair In the event a defect that can not be The modified seal weld overlay will serve as removed is identified in the seal weld or a full replacement for the secondary leakage adjoining base materials, Sequoyah will barrier replace the original CRDM housing intermediate seal weld with a modified seal It will not serve a structural function weld overlay using Code Case N-504-4 as guidance The full structural load is still carried by the threaded connection in accordance with the Contrary to the requirements of ASME original CRDM housing design Section XI and the original Construction Code, this modified seal weld may be installed without removal of the defect, and without the associated surface examination of the defect removal area prior to welding 6

Precedents NRC Letter to Exelon, Braidwood Station, NRC Letter to TVA, Relief from ASME Code Units 1 and 2 - Relief from the Requirements Repair Requirements for Canopy Seal of the American Society of Mechanical Welds Sequoyah Nuclear Power Plant, Engineers Boiler and Pressure Vessel Code Unit 1 (TAC NO. M93835), dated April 4, (EPID L-2018-LLR-0033), dated 1996 January 17, 2019 NRC Letter to TVA, Sequoyah Nuclear Plant, Unit 1 - Relief from ASME Code Repair Requirements for Canopy Seal Welds (TAC NO. MA9095), dated September 12, 2000 NRC Letter to TVA, Relief from ASME Code Repair Requirements for Canopy Seal Welds at Watts Bar Nuclear Plant (TAC NO.

MA5051), dated August 25, 1999 7