ML22130A009

Duke Presentation for April 28, 2022 Public Meeting - Bolting Integrity

ML22130A009
Person / Time
Site:	Oconee
Issue date:	04/28/2022
From:	Duke Energy Carolinas
To:	Office of Nuclear Reactor Regulation
Wu A, 301-415-2995
Shared Package
ML22130A003	List: ML22130A009 ML22130A010 ML22130A011 ML22130A012
References
Download: ML22130A009 (16)

Text

ONS Subsequent License Renewal NRC Public Meeting (Bolting Integrity)

April 28, 2022

Background Information RAI B2.1.9-2 Request #2 and DE Response Request #2:

For the alternate inspection and testing methods specified in the SLRA for submerged closure bolting or closure bolting where leakage is difficult to detect, clarify what the plant- specific acceptance criteria are that will be established for the Bolting Integrity program to ensure that the intended function(s) will be maintained consistent with the current licensing basis for the subsequent period of extended operation.

Duke Energy Response:

Alternative inspections for submerged bolting include diver inspections and remote video/photo inspections. Submerged bolted connections where diver inspections are performed will include visual inspections for degraded bolts, missing or broken bolts and, where possible, the torque of bolts verified to be hand tight. Remote video and photo inspections may be performed to inspect for degraded, loose, or missing bolts. Evidence of loose or missing bolting and significant loss of material (i.e., appreciable material loss that could adversely affect intended function) identified during inspections is unacceptable and will be entered into the Corrective Action Program, if identified.

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Topics of Discussion Issue #1: Use of Remote Video and Photo as Alternative Inspection Methods It is not clear how the use of remote video and photo inspection will be sufficient to provide clear indications to detect degradations in submerged closure bolting of a pressure retaining boundary. It is noted that the GALL-SLR Report recommends detecting degradation due to crack initiation, loss of preload, or loss of material that may result in leakage from the mating surfaces or joint connections of pressure boundary components, and the use of remote video and photo inspections appear to be limited in their capability to detect some of these aging effects.

Issue #2: Use of Hand Tight Checks as Part of Alternative Inspection Methods It is not clear how the use of hand tight check will be adequate to detect loss of preload in systems requiring a specific torque value (e.g., 30 lb-ft) at their connections. It is noted that bolts and nuts that can be verified to be hand tight may still leak if the connection is not set to the specified torque value necessary to maintain the pressure boundary of the components.

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Background Information ONS SLRA Bolting Integrity Enhancement no. 4 Perform visual inspections of a representative sample of twenty percent of closure bolting where leakage is difficult to detect such as submerged connections or systems containing air/gas or a maximum of seventeen bolts for each material and environment population per unit, whichever is less, during each ten-year period. If the minimum sample size is not achieved during a ten year period, then alternative inspections may be performed. For submerged bolting, alternative inspections may include (a) diver inspections or (b) remote video inspections. For systems containing air/gas, alternative inspections may include (a) visual inspection for discoloration when leakage from inside the piping system would discolor the external surfaces of the component; (b) monitoring and trending of pressure decay when the bolted connection is located within an isolated boundary; (c) soap bubble testing on the external mating surface of the bolted component; or (d) thermography, when the temperature of the process fluid is higher than ambient conditions around the component.

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Background Information NUREG-2191 (GALL-SLR), Vol 2 XI.M18 Bolting Integrity

4. Detection of Aging Effects Submerged closure bolting is visually inspected for loss of material during maintenance activities. In this case, bolt heads are inspected when made accessible, and bolt threads are inspected when joints are disassembled. In each 10-year period during the subsequent period of extended operation a representative sample of bolt heads and threads is inspected. If opportunistic maintenance activities will not provide access to 20 percent of the population (for a material/environment combination) up to a maximum of 25 bolt heads and threads over a 10-year period, then the subsequent license renewal application (SLRA) states how integrity of the bolted joint will be demonstrated. For example: (a) periodic pump vibration measurements are taken and trended; or (b) sump pump operator walkdowns are performed demonstrating that the pumps are appropriately maintaining sump levels.

It is noteworthy that the examples of alternative inspection methods provided by GALL will not identify the specific aging effects associated with bolting materials, i.e. loss of preload, cracking or loss of material.

The examples only provide indication that there could be a problem with the component.

Duke Energy has identified alternative inspection methods for submerged closure bolting that will specifically identify degradation of the bolting 5

Clarification of Alternative Inspection Approach Bolting Populations There are two populations of submerged bolting at ONS:

Spent Fuel Pool Cooling (SF System) Fuel Transfer Tube Isolation Valves Condenser Circulating Water (CCW System) Intake Pump Casing (Flange Seals)

The preferred inspection method for both bolting populations is direct visual inspection performed during planned maintenance (opportunistic inspections)

If opportunistic inspections do not yield the required sample size, alternative inspections methods are allowed Each bolting population has its own alternative inspection approach 6

Clarification of Alternative Inspection Approach - SF Valves Remote Video/Photo Inspections (Issue #1)

Alternative inspection of submerged bolting via remote video/photos is intended for the Spent Fuel Pool Cooling (SF) Valves Spent Fuel Pool Cooling System Fuel Transfer Tube Isolation Valves Flange and Body-to-Bonnet Bolting Stainless Steel Bolting in Treated Borated Water (External) Environment Aging effects of concern are Loss of Preload, Cracking and Loss of Material 7

Clarification of Alternative Inspection Approach - SF Valves Remote Video/Photo Inspections (Issue #1)

The SF valves bodies/bolting have a pressure boundary component level function for SLR Spent Fuel Pool treated borated water provides high visibility and the pool area is well lit High-definition cameras are available for underwater inspections 8

Clarification of Alternative Inspection Approach - SF Valves Remote Video/Photo Inspections (Issue #1)

For SLR, remote video/photo inspection of the subject bolting will demonstrate the integrity of the bolted joints by identifying degraded, loose, or missing bolts. Evidence of loose or missing bolting and significant loss of material (i.e., appreciable material loss that could adversely affect intended function) identified during inspections will be entered into the Corrective Action Program.

Bolt degradation could be evidence of loss of material or cracking Loose or missing bolts could be evidence of loss of preload or cracked/failed bolting The remote video/photo inspection method provides reasonable assurance that the integrity of the submerged bolted joints for the SF valves is maintained The remote video/photo alternative inspection methods for submerged SF valve closure bolting will specifically identify degradation of the bolting 9

Clarification of Alternative Inspection Approach -

CCW Intake Pumps Diver Inspections and Hand Tight Check (Issue #2)

Alternative inspection of submerged bolting via diver inspections (including hand tight checks) is intended for the CCW Intake Pump Casing Flange Seal Condenser Circulating Water (CCW System) Intake Pump Casings 4 pumps/unit located in the intake structure Large multi-section vertical pumps, 177K GPM (nom)

Only the top flange (flange seal) is required/designed to be leak tight Steel Bolting in Raw Water (External) Environment Aging effects of concern are Loss of Preload and Loss of Material 10

Clarification of Alternative Inspection Approach - CCW Intake Pumps Diver Inspections and Hand Tight Check (Issue #2)

The CCW Intake Pump casings and flange seal bolting have a pressure boundary component level function Diver inspections of the CCW Intake Pumps are currently performed on a once/4 year frequency as part of the pump bay and screen inspection preventative maintenance activity For SLR, diver inspections of submerged CCW Intake Pump bolted connections (casing flange seals) will include visual inspections for degraded bolts, missing or broken bolts and, where possible, the torque of bolts will be verified to be hand tight. Evidence of loose or missing bolting and significant loss of material (i.e., appreciable material loss that could adversely affect intended function) identified during inspections will be entered into the Corrective Action Program.

Bolt degradation could be evidence of loss of material Loose or missing bolts would be evidence of loss of preload Cracking is not an applicable aging effect for carbon steel bolting in raw water 11

Clarification of Alternative Inspection Approach - CCW Intake Pumps Diver Inspections and Hand Tight Check (Issue #2)

In addition to the diver visual checks, performing a check of hand tightness provides further confirmation that the bolted joint is intact Using a large torque wrench to verify bolting tightness is not a practical alternative inspection for an underwater environment The diver inspection method (including a check for hand tightness) will provide reasonable assurance that integrity of the submerged bolted joints in the CCW Intake Pump casings is maintained Degradation of the bolting will be specifically identified Due to the pump design, vibration monitoring would not accurately detect degradation of bolting in the ONS CCW Intake Pump casings Checking closure bolting to be hand tight was approved in the Peach Bottom SLRA as an acceptable method to confirm bolted joint integrity - for several different configurations 12

CCW Intake Pump 13

Clarification of Alternative Inspection Approach - CCW Intake Pumps Diver Inspections and Hand Tight Check (Issue #2)

Operating Experience (from ONS SLRA App. B):

A review of ten years (January 2011 through January 2021) of condenser circulating water system pump diver inspections was performed which identified no significant issues with the submerged bolting for these pumps. The four pumps at each of the three units have been inspected four to five times over the ten years that have been reviewed. Inspections have identified a layer of surface corrosion and corrosion nodules on the bolting and pump column which is typical in a submerged raw water environment. No significant loss of material which could impact intended functions has been detected. Marine growth and biofouling material have also been identified. No loose, missing, or broken submerged bolting has been detected in any of the inspections completed over the ten year review period.

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Conclusion The proposed alternative inspection methods for the Spent Fuel Pool Cooling System Fuel Transfer Tube Isolation Valves and the CCW Intake Pump Casing Flange Seals are capable of specifically identifying degradation of the submerged closure bolting.

With the alternative inspection methods for submerged closure bolting, the Bolting Integrity Aging Management Program (with enhancements) will provide reasonable assurance that loss of material, cracking, and loss of preload will be adequately managed so that the intended functions of components within the scope of license renewal will be maintained during the subsequent period of extended operation.

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