ML18100A190

Enclosure 8 - Structural Integrity Associates, Inc. Report 130415.403, Revision 2, Assessment of Monticello Spent Fuel Canister Closure Plate Welds Based on Welding Video Records

ML18100A190
Person / Time
Site:	Monticello
Issue date:	05/22/2014
From:	Rich Smith Northern States Power Company, Minnesota, Structural Integrity Associates
To:	Office of Nuclear Material Safety and Safeguards
Shared Package
ML18100A173	List: L-MT-18-013, Response to Request for Additional Information Regarding Exemption Request for Nonconforming Dye Penetrant Examinations of Dry Shielded Canisters (Dscs) 11 Through 15 ML18100A185 ML18100A188 ML18100A190 ML18100A191 ML18100A193
References
CAC 001028, EPID L-2017-LLE-0029, L-MT-18-013 130415.403, Rev 2
Download: ML18100A190 (52)

Text

ENCLOSURE 8 STRUCTURAL INTEGRITY ASSOCIATES, INC. REPORT 130415.403, REVISION 2 ASSESSMENT OF MONTICELLO SPENT FUEL CANISTER CLOSURE PLATE WELDS BASED ON WELDING VIDEO RECORDS 51 pages follow

Assessment of Monticello Spent Fuel Canister Closure Plate Welds based on Welding Video Records Prepared for:

Xcel Nuclear Monticello Nuclear Generation Plant Monticello, MN 55362 Contract C# 1005 Release 48 Prepared by:

Structural Integrity Associates, Inc.

San Jose, California Prepared by:

~&~

Richard E. Smith Reviewed by:

Nicholas I. Mohr Approved by:

Richard E. Smith Report No. 1301415.403 Revision 2 Project No. 1301415 May 2014 Date: 05/22/2014 Date: 05/22/2014 Date: 05/22/2014 1Js1n1ctuta1 Integrity Associates. 1nc.*

REVISION CONTROL SHEET Document Number:

1301415.403.R2

Title:

Assessment of Monticello Spent Fuel Canister Closure Welds based on Welding Video Records Client:

Xcel Nuclear Monticello Nuclear Generation Plant SI Project Number:

1301415 Quality Program: [ZJ Nuclear D Commercial Section Pages Revision Date Comments 1.0 1 1-2 0

03/27/2014 Initial Issue 2.0 2-1 3.0 3 3-4 4.0 4-1 5.0 5 5-31 6.0 6 6-2 1.0 1 1-2 1

05/08/2014 Revision 1 2.0 2-1 Incorporated client comments throughout 3.0 3 3-5 4.0 4-1 5.0 5 5-32 6.0 6 6-2 1.0 1-2 2

05/22/2014 Revision 2 Clarification on Section 1.0 Introduction l;s1n1ctuta11111egr11y Associates. 1nc.*

Table of Contents Section Page

1.0 INTRODUCTION

.......................................................................................................... 1-1 2.0 TECIINICAL APPROACH.......................................................................................... 2-1 3.0 GENERAL OBSERVATIONS..................................................................................... 3-1 4.0 OVERALL EVALUATION.......................................................................................... 4-1 5.0 INDIVIDUAL WELD VIDEO RECORD ASSESSMENT........................................ 5-1 5.1 Folder "12 12"............................................................................................................. 5-1

5. 1.1 Observed Weld Surface Conditions showing Good Welding Practices......................... 5-2 5.1.2 Observed Surface Weld Conditions that May Require Mitigating Action..................... 5-5 5.1.3 General Observations.................................................................................................... 5-7 5.2 Folder "001 5 0015"..................................................................................................... 5-7 5.2.1 Observed Weld Surface Conditions showing Good Welding Practices......................... 5-8 5.2.2 Observed Surface Weld Conditions that May Require Mitigating Action..................... 5-9 5.2.3 General Observations.................................................................................................... 5-9 5.3 Folder "15 15"............................................................................................................. 5-9 5.3.1 Observed Weld Surface Conditions showing Good Welding Practices....................... 5-10 5.3.2 Observed Surface Weld Conditions that May Require Mitigating Action................... 5-11 5.3.3 General Observations.................................................................................................. 5-13 5.4 Folder "464956 012"................................................................................................. 5-14 5.4.1 Observed Weld Surface Conditions showing Good Welding Practices....................... 5-14 5.4.2 Observed Surface Weld Conditions that May Require Mitigating Action................... 5-15 5.4.3 General Observations.................................................................................................. 5-17 5.5 Folder"464956 013"................................................................................................. 5-17 5.5.1 Observed Weld Surface Conditions showing Good Welding Practices....................... 5-18 5.5.2 Observed Surface Weld Conditions that May Require Mitigating Action................... 5-19 5.5.3 General Observations.................................................................................................. 5-20 Report No. 1301415.403.R2 1ll l.;SlntclUlal Integrity Associates, Inc.*

5.6 Folder "464956 14"................................................................................................... 5-21 5.6. 1 Observed Weld Surface Conditions showing Good Welding Practices....................... 5-21 5.6.2 Observed Surface Weld Conditions that May Require Mitigating Action................... 5-23 5.6.3 General Observations.................................................................................................. 5-23 5.7 Folder "464956 DSC 013"....................................................................................... 5-23

5. 7.1 Observed Weld Surface Conditions showing Good Welding Practices....................... 5-24

5. 7.2 Observed Surface Weld Conditions that May Require Mitigating Action................... 5-25

5. 7.3 General Observations.................................................................................................. 5-25 5.8 Folder "inner 16"...................................................................................................... 5-25 5.8.1 Observed Weld Surface Conditions showing Good Welding Practices....................... 5-25 5.8.2 Observed Surface Weld Conditions that May Require Mitigating Action................... 5-26

5. 8.3 General Observations.................................................................................................. 5-26 5.9 Folder "outer 16"...................................................................................................... 5-27 5.9.1 Observed Weld Surface Conditions showing Good Welding Practices....................... 5-27 5.9.2 Observed Surface Weld Conditions that May Require Mitigating Action................... 5-29 5.9.3 General Observations.................................................................................................. 5-32

6.0 CONCLUSION

S............................................................................................................ 6-1 Report No. 1301415.403.R2 l V iJStnu:llnl lntegrlly Assocfates, Inc.*

List of Figures Figure Figure 3-1. Example of Large Weld Puddle Running Ahead of the Tungsten........................... 3-1 Figure 3-2. Examples of Contamination on the Surface of Weld Wire (a) (In some cases sparkling was observed) and Contamination from Poorly Cleaned Substrate (b )............................... 3-2 Figure 3-3. Tungsten Electrode with Unacceptable Tip Oxidation............................................ 3-3 Figure 3-4. Uneven Weld Deposit Condition where Subsequent Weld Pass Correction is attempted without the Benefit of a uniformly ground Surface............................................................. 3-4 Figure 3-5. Oxidized Surface Condition shown in the Trailing View where grinding would help to minimize the chance for trapped oxide defects on subsequent weld passes........................ 3-4 Figure 3-6. Unfused Pocket in the Weld Deposit (this location would benefit from removal prior to welding over this location with next bead) [trailing view is shown]................................... 3-5 Figure 5-1. Photo showing Filler Metal being Clipped Prior to the Start of the Next Pass (Front, OUT_ Circum_00_00005).................................................................................................... 5-2 Figure 5-2. Weld Pass with Good Sidewall Fusion, Arc Position, and Wetting........................ 5-3 (Front, OUT_ Circum _ 00 _ 00008)................................................................................................ 5-3 Figure 5-3. Presenting a Weld Pass with good Sidewall Fusion, Arc Position, and Wetting (Front, OUT_ Circum_04_00001).................................................................................................... 5-4 Figure 5-4. Weld Pass being stopped in the Correct Location................................................... 5-4 (Front, OUT_ Circum _ 00 _ 00036)................................................................................................ 5-4 Figure 5-5. Weld Pass Starting in the Correct Location to Consume the Stop of the Previous Weld Bead (Front, OUT_ Circum _ 03 _ 00000)............................................................................... 5-5 Figure 5-6. Weld Pass Starting in the Correct Location to Consume the Stop of the Previous Weld Bead and Sidewall Fusion (Rear, 02, OUT_Circum_00_04).............................. :............... 5-5 Figure 5-7. Uneven Weld Bead Profile and Uneven Sidewall Tie-in......................................... 5-6 (Front, OUT_ Circum _ 04_ 00052)................................................................................................ 5-6 Figure 5-8. Uneven Weld Bead Profile and Uneven Sidewall Tie-in......................................... 5-6 (Front, OUT_Circum_04_00052)................................................................................................ 5-6 Figure 5-9. Uneven Weld Bead Profile and Uneven Sidewall Tie-in......................................... 5-6 (Front, OUT_Circum_04_00053)................................................................................................ 5-6 Report No. 1301415.403.R2 V

IJSlnlclutal IIIIBfrlly Associates, Inc.*

Figure 5-10. Large Weld Puddle with Arc Position Away from Sidewall................................. 5-7 (Rear, (05), OUT_Circum_00_51).............................................................................................. 5-7 Figure 5-11. Tungsten Contaminated with Filler Metal that was Subsequently Replaced (Front, OUT_Tack8_00_00001)...................................................................................................... 5-8 Figure 5-12. Typical Tack Weld (Front, OUT_Tackl_03_00004)............................................ 5-8 Figure 5-13. Location where Tungsten Electrode was Stuck during Arc Initiation................... 5-9 (Front, OUT_Tack2_02_00001).................................................................................................. 5-9 Figure 5-14. Root Pass displaying good Sidewall Fusion, Arc Position, and Wetting............. 5-10 (Front, OUT_Circum_00_00051).............................................................................................. 5-10 Figure 5-15. Weld Pass with Good Sidewall Fusion, Arc Position, and Wetting.................... 5-11 (Front, OUT_ Circum _ 04 _ 00027).............................................................................................. 5-11 Figure 5-16. Area that was Ground (Front, OUT_Circum_08_00000).................................... 5-11 Figure 5-17. Filler Material Directed Into Bottom of Weld Puddle......................................... 5-12 (Front, OUT_Circum_04_00004).............................................................................................. 5-12 Figure 5-18. Filler Metal with Debris (Front, OUT_Circum_04_00058)................................ 5-12 Figure 5-19. Root Pass Area that Appears to be Unfused........................................................ 5-13 (Front, OUT_Circum_Ol_00004).............................................................................................. 5-13 Figure 5-20. Same Location of Figure 5-19 after the Welding Arc Passed over Unfused Area (Front, OUT_Circum_01_00004).................................................................................................. 5-13 Figure 5-21. Typical Root Pass (Front, OUT_Circum_03_0006)............................................ 5-15 Figure 5-22. Root Pass from the Rear Camera Showing Good Fusion.................................... 5-15 (Rear, (16), OUT_Circum_00_0035)........................................................................................ 5-15 Figure 5-23. Typical Fill Pass (Front, OUT_Circum_15_0032).............................................. 5-15 Figure 5-24. Weld Pass Showing Uneven Tie-in to the Sidewall............................................. 5-16 (Rear, (19), OUT_Circum_OO_ l3)............................................................................................ 5-16 Figure 5-25. Fill Pass Showing Undesirable Weld Bead Profile.............................................. 5-16 (Rear, (19), OUT_Circum_00_35)............................................................................................ 5-16 Figure 5-26. Wasp Entering the Welding Arc (Rear,(16), OUT_Circum_00_0038)............... 5-17 Figure 5-27. Typical Root Pass (Front, OUT_Circum_01_0014)............................................ 5-18 Figure 5-28. Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_16_0028)............................................................................ 5-18 Report No. 1301415.403.R2 VI l)Sl.rucllnl lnlegrlly Associates, Inc.*

Figure 5-29. A Later Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_25_0006).................................................................. 5-19 Figure 5-30. Burn Through During Welding of the Root Pass................................................. 5-19 (Front, OUT_ Circum _ 02 _ 00002).............................................................................................. 5-19 Figure 5-31. Wasp Entering the Welding Arc (Front, OUT_Circum_21_00001).................... 5-20 Figure 5-32. Wasp Entering the Welding Arc (Front, OUT_Circum_ l8_00004).................... 5-20 Figure 5-33. Typical Root Pass (Front, OUT_Circum_02_00008).......................................... 5-22 Figure 5-34. Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_13_00007).......................................................................... 5-22 Figure 5-35. A Later Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_l4_0001 l)................................................................ 5-22 Figure 5-36. Weld Pass Showing Uneven Tie-in to the Sidewall............................................. 5-23 (Front, OUT_ Circum _ 09 _ 00006).............................................................................................. 5-23 Figure 5-37. Typical Root Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, IN_ Circum _ 14_00011).................................................................... 5-24 Figure 5-38. Cover Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, IN_Circum_02_00083).............................................................................. 5-24 Figure 5-39. Typical Root Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, IN_Circum_Ol_00023).................................................................... 5-26 Figure 5-40. Cover Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, IN_Circum_03_00013).............................................................................. 5-26 Figure 5-41. Typical Root Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_ Circum _ 03 _ 00025)................................................................ 5-28 Figure 5-42. Typical Root Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle Looking from the Rear (Rear, OUT_Circum_00_00059)............................ 5-28 Figure 5-43. A Later Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_ l 1_00011)................................................................ 5-28 Figure 5-44. First Fill Pass with Large Amount of Oxides Preventing the Weld Puddle to Wet (Front, OUT_Circum_05_00001)...................................................................................... 5-29 Figure 5-45. Another Picture of the First Fill Pass with Large Amount of Oxides Preventing the Weld Puddle to wet the sidewall........................................................................................ 5-29 Report No. 1301415.403.R2 Vll

(Front, OUT_Circum_05_00001).............................................................................................. 5-29 Figure 5-46. Picture from the Rear Camera Showing a Sudden Puddle Shift Creating an Uneven Bead Profile (Rear, (12), OUT_Circum_00_ 44)............................................................... 5-30 Figure 5-47. Large Gap Near the Sidewall seen from Rear Camera (Rear, (12),

OUT_ Circum _ 00 _56)........................................................................................................ 5-30 Figure 5-48. Large Amount of Oxides and Undesirable Weld Profile seen from Rear............ 5-30 (Rear, (13), OUT_Circum_00_ 45)............................................................................................ 5-30 Figure 5-49. Large Amount of Oxides, Large Gap, and Undesirable Weld Profile................. 5-31 (Front, OUT_Circum_06_00001).............................................................................................. 5-31 Figure 5-50. Large Amount of Oxides and Undesirable Weld Profile (Front, OUT_Circum_06_00003).................................................................................................. 5-31 Report No. 1301415.403.R2 Vlll

1.0 INTRODUCTION

This report describes a review of the welding video records for the closure field welds on the spent fuel canisters at Monticello Nuclear Generating Plant. The first weld joins the % inch thick inner closure plate to shell wall and involves one location were the welding torch must manipulated around the periphery of the siphon and vent penetrations block. The design drawings specify a 3/16 inch single-bevel partial penetration weld that is accomplished in what appears to be two passes. Small circular Type 304 cover plates used to seal the vent and siphon penetrations. These welds were not reviewed but are most likely applied using the manual GTA W process. Next the 1 V,i inch thick outer cover plate is installed over the siphon and vent penetrations and the inner cover plate to seal to the canister vessel and to provide the final structural closure weld to the vessel. The plate is welded to the vessel shell wall completely around the canister using a Yi inch Single-J partial penetration groove. This final multipass weld is deposited using the machine GTA W process.

This review was limited to information available from canister drawings, the welding program document, welding procedure specifications, welding procedure qualification records, and the video records of the welds (including some inner cover plate welds, but primarily outer cover plate welds). Both front and rear camera views were included in some cases. Both inner and outer cover plate closure welds were recorded in some cases, but the video coverage appeared to be incomplete for all weld beads. In addition, some welds appeared to have more complete coverage than others. [It is important to note that weld data sheets were unavailable to evaluate the welding parameters used for these welds.] All of the welds reviewed are multipass partial penetration groove welds joining SA 240 Type 304 stainless steel plate (P8 material) to a similar plate or forging grade Type 304 stainless steel (P8 material). The filler metals were specified as ER308 ( dual certified ER308/ER308L permitted with 80 ksi tensile strength) solid wire filler metal. The welding of the closure welds for the inner cover plate used the machine gas tungsten arc welding (GTA W) process and included the need to steer around the siphon/vent block. There was video evidence for the machine process being steered around the block in steps. The inner cover plate joint calls for a Single-V configuration sized for a 3/32 inch weld. Two weld passes typically were required to complete the weld (root/fill and a cover pass). A companion manual Report No. 1301415.403.R2 1-1 l)Slrucllllal lnlBfrlty Assodates, 1nc.*

GTA W procedure was also available for any manual welding needed, but no manual welding was reviewed in the videos. Manual GTA W likely were used for the seal welds on the small dollar plates covering the vent and siphon ports plus and any local repairs that may have been needed. The canister weld videos reviewed were supplied by Monticello Nuclear Generation Plant personnel. No written material describing content of each video was available. The digital videos file folders were identified as follows:

1. Folder " 12 12"

2. Folder "464956 012"

3. Folder "464956 013"

4. Folder "464956 14"

5. Folder "0015 0015"

6. Folder "464956 DSC-013"

7. Folder "inner 16"

8. Folder "outer 16" It can be seen that the video record numbering scheme was inconsistent, but the number at the end of each folder name is taken to identify specific dry spent fuel canisters (DSC). There are two video folders each for DSCs #12, #13, #15, and #16. There is only one video folder identified for DSC #14. Individual files are found in each folder that stipulate specific identifying information and are tagged as "IN" or "OUT". This is taken to identify whether the videos are of the inner top cover plate (ITCP) or outer top cover plate (OTCP). Based on this information it was determined that all five of the casks reported video records of the OTCP; however, video information on the ITCP was reported only for two of the five canisters (DSC

1. 13 and DSC #16). Finally all video records displayed both front and rear views of the welding arc. Eight (8) tack welds were used on all roots to secure the assembly prior to the root pass.

The review of all video records has been completed. The following summary details coverage of the ITCP and OTCP welds reported.

DSC-12 -0TCP only DSC ITCP and OTCP DSC OTCP only DSC OTCP only DSC ITCP and OTCP Report No. 1301415.403.R2 1-2 l)Sl.nlchual lntQrlly Assoc/lJtes, Inc.*

2.0 TECHNICAL APPROACH Each video record was reviewed to document visual observations of circumstances considered by the welding community to represent conditions important to the production of a sound weld. In some cases the observed condition is not considered ideal and some action would be expected from the welding operator. The welding operator actions could range from minor tungsten position adjustment to grinding certain areas. In others the observed condition might be considered desirable thus suggesting that the weld is proceeding as planned. A number of general observations are offered. The records available for review did not provide volumetric information needed to assess the soundness of a given weld. This report describes visual surface observations that relate to both general considerations and also for specific details for each canister reviewed. Welding parameters available for examination included the Detailed Welding Procedures and the Procedure Qualification Record, but nothing of the specific welding techniques actually used except to assume that the parameters used were bounded by the welding procedures (GT AW for both manual and machine methods).

The observations made on the weld videos suggest both positive and negative welding practices

- none of which guarantee a good weld or a weld having unacceptably flawed conditions.

Accordingly, tabulation has been prepared for each weld to document visual observations of welding practices that suggest good results or conversely, results that may need to be addressed by the welding operator. If left unaddressed, the negative observation might lead to conditions where discontinuities can be produced. This assessment is subjective by nature and relies a great deal on observing the proper application of welding principles.

Austenitic stainless steel welding using machine GTA Wis considered somewhat tolerant to techniques and inconsistent conditions for stainless steel welding using ER308 filler metal. In most cases it is relatively insensitive to technique deficiencies, but not in all cases. For example, debris and oxide entrapment or non-fusion at sidewalls and weld bead interfaces can occur when good welding practices are not followed. The application of high quality inert shielding gas is also essential to prevent oxidation and volumetric discontinuities such as porosity.

Report No. 1301415.403.R2 2-1 l)siruclUlll lntegrlly Associates, Inc.*

3.0 GENERAL OBSERVATIONS It appears that the welding operators may have used relative high welding current and wire feed rate, because the molten weld puddle is large. A potential problem is that a large puddle can roll in front of the arc if the correct arc travel speed is not maintained. This condition can trap contamination and surface oxides and sometimes produces gas pockets (porosity). A second concern is that large weld puddles can be difficult to control. This condition was seen in all welds, but definitely is more pronounced periodically. The condition also can lead to fusion related defects at the sidewall, and between weld beads or layers. Visible evidence also was noted that the welding operators generally attempted to eliminate undesirable weld bead conditions by consuming them with the subsequent weld pass. This mitigating action is made more difficult when large weld puddles are in play - operator judgment is required to determine if this technique will be successful. In Figure 3-1 (below) it is seen that the molten puddle is not distributed symmetrically around the tungsten. This observed condition may suggest uneven heating and could develop into sidewall fusion issues on the side furthest away from the tungsten arc. In this case it is estimated that 75% to 80% of the molten puddle is biased to the most distant groove sidewall. In a number of cases the weld puddle was observed to roll ahead of the tungsten arc. However, it was noted that in general, the video review revealed visible evidence of good tie-in around the welds.

Figure 3-1. Example of Large Weld Puddle Running Ahead of the Tungsten Report No. 1301415.403.R2 3-1

A second general observation noted in all welds (especially in Canister video record #16) was the need for attention to maintaining clean weld wire, clean welding surfaces, and in some cases a potential degraded gas shielding (observation not shown). See Figures 3-2 (a and b)

(a) Filler wire contamination (b) Debris on substrate Figure 3-2. Examples of Contamination on the Surface of Weld Wire ( a) (In some cases sparkling was observed) and Contamination from Poorly Cleaned Substrate (b).

In general the tungsten was replaced or sharpened as needed to remove oxides formed on the tip; however, in a few cases it was observed that tungsten maintenance was not always performed in a timely manner. An oxidized tungsten tip will degrade the welding arc and make voltage control less precise. (See Figure 3-3)

Report No. 1301415.403.R2 3-2

(>SlnlclUlal lntegrlly Associates, Inc.*

Figure 3-3. Tungsten Electrode with Unacceptable Tip Oxidation A common practice observed during the review was that the welder(s) attempted to consume irregular surface conditions in the subsequent weld pass instead of removing them by grinding prior to welding. Mechanical removal is the preferred approach for large changes in surface profile (pronounced surface conditions), but in less pronounced conditions an effective mitigating action can be to proceed with subsequent weld pass( es). However, if subsequent weld passes do not correct the condition then discontinuities would remain in the weld deposit.

Best practice typically removes the condition by grinding prior to welding. Manual grinding may not be desirable due to increased radiation exposure and accumulated dose, but in some instances may be required to deposit a sound weldment. Figures 3-4, 3-5, and 3-6 provide representative examples of observations where grinding may be required in the canister welds to facilitate welding and tie-in into the previous weld bead, thus improving the probability for achieving a better weld.

Report No. 1301415.403.R2 3-3 e Strucllnl Integrity Associates, 1nc.*

Figure 3-4. Uneven Weld Deposit Condition where Subsequent Weld Pass Correction is attempted without the Benefit of a uniformly ground Surface Figure 3-5. Oxidized Surface Condition shown in the Trailing View where grinding would help to minimize the chance for trapped oxide defects on subsequent weld passes Report No. 1301415.403.R2 3-4 l)Stnlchual lnmgrlly Associates, Inc.*

Figure 3-6. Unfused Pocket in the Weld Deposit (this location would benefit from removal prior to welding over this location with next bead) [trailing view is shown]

A positive observation noted was that the tungsten was frequently repositioned to maintain proper arc location. The need for repositioning can result from out of roundness (ovality) for one or more of the following:

1. canister

2. cover plate

3. welding track setup Frequent tungsten repositioning was observed in the video tapes providing evidence that welding operator(s) were paying attention to the welding process. The root pass of the outer plate closure weld for Canister # 16 appeared to have a significant degree of surface oxidation that developed during welding - more so than with other welds. This condition may have been caused by an issue with the inert gas (argon) or uncontrolled air currents, or something else. The condition appeared to self-correct after the root and hot passes were completed.

Report No. I301415.403.R2 3-5 l)siruclUlal lnlefrlty Associates, Inc.*

4.0 OVERALL EVALUATION The reviewers conclude that a number of surface conditions observed in the video records have the potential to introduce discontinuities into the dry fuel storage canister welds unless mitigating steps are taken. In some cases the proper action is to continue welding, and in other cases to remove the surface condition prior to continuing the weld. Welding operator judgment typically will be used to determine the proper response to the observed surface condition. For example, in some cases the tungsten electrode tip will require repositioning, or the travel speed needs to be increased or slowed, or the surface needs to be brushed, or the surface needs to be ground, etc.

The idea is that some operator action may be required to mitigate the observed condition.

Unfortunately the video tapes provide very little information with which to determine if such steps actually had been taken.

Therefore, the information available from the video records was considered insufficient with which to determine whether or not unacceptable discontinuities may or may not have been introduced into the closure welds. It is possible to categorize the types of welding conditions that were observed on the tapes and this was done. The types of weld surface conditions observed were relatively consistent among canisters. What does change from canister weld to canister weld is the frequency with which specific conditions are observed and in some cases the severity. Based strictly on the video clips for each canister, it appears that Outer Top Closure Weld from Canister #16 may be the worst of the five canisters examined, because irregular surface conditions (welding anomalies) were observed more frequently in that canister top cover closure weld than for any of the other weld videos examined. Therefore, the Outer Top Closure Weld in Canister #16 is expected to have the greatest likelihood for defects. This does not imply that any of the welds is either acceptable or unacceptable, because mitigating actions by the welding operatory may have corrected the observed conditions. It is possible that all of the canister welds are acceptable, but welding surface conditions having potential to increase the likelihood for discontinuities were observed in all of the welds suggesting a potential for defects exists for any or all of the welds. However, of the five canisters evaluated, Canister #16 appears to be the most likely to have defects based on the frequency of the observations.

Report No. 1301415.403.R2 4-1 IJStnu:lu,a/ Integrity Associates, Inc.*

5.0 INDIVIDUAL WELD VIDEO RECORD ASSESSMENT The following is an observation summary for the review of DSC canister welding videos records provided by Monticello done by Nicholas Mohr and Richard Smith. The reviews of the DSC videos were conducted during the period of February 14, 2014 through February 21, 2014. It should be noted that in many instances it is unclear if the video clips represented the complete weld sequence or partial sequences (fragments). Therefore, the results reported reflect specific surface conditions observed, and comments are offered based on the content viewed and any assumptions are clearly identified. The observations and subsequent comments also have a certain degree of subjectivity so that they are intended to assist with developing insight into the potential condition of the DSC closure welds.

The DSC welding observed in all video clips had some areas of consistency and others showing inconsistency. The use of machine GT AW with bare wire being fed into the leading edge of the weld puddle and what appears to be straight current are examples of consistency across all video clips. The use of stringer beads and oscillation are permitted by the welding procedure and appear to be applied at the discretion of the welding operators. The result is that none of the outer closure canister welds appear to follow the same precise technique. The result is that significant variations were seen in weld bead heights and widths among DSC's and for any given weld. In some cases it appeared that weld bead height was mitigated by using tungsten tip oscillation to flatten the weld surface. This was considered a positive action on the part of the welding operator to adjust surface conditions to support subsequent welding.

5.1 Folder "12 12" The weldment being viewed in folder "12_12" is the outer cover plate circumferential DSC weld. The review of videos included in folder "12_12" found certain areas displaying good welding practices and others that would not be ideal for generating a defect free weld. For purposes of this video review it was assumed that this folder contains video clips for Canister 12.

As an overall assessment, the video clips showed areas of weldment where the weld was deposited with good arc placement, weld puddle wetting, side wall fusion, and weld bead profile.

Report No. 1301415.403.R2 5-1 l}StruclUlal lnlefrlly Associates, 1nc.*

In other areas of the DSC weld surface features were observed that could potentially introduce undesirable anomalies into the weld unless the welding operator implemented corrective action to mitigate the condition. Observations representing both cases have been chronicled in Subsections 5.1.1 and 5.1.2 respectively. General observations have been detailed in Subsection 5.1.3.

It should be noted that the video clips for Folder 12_12 commence after the tack welding and root pass have been completed. The reviewers are unsure if the welding technique required both a root and hot pass or a single root pass. For this reason it was assumed that root was deposited in a single pass.

5.1.1 Observed Weld Surface Conditions showing Good Welding Practices During review of the video clips one of the first good practices observed was clipping the end of the wire prior to the start of welding as shown in Figure 5-1. Each picture caption indicates the active camera for the photo (front or rear camera), and the video clip from which the picture was taken ( e.g. front, OUT_ Circum _ 00). Additional subfolders will precede the file name such as

"(12)".

Figure 5-1. Photo showing Filler Metal being Clipped Prior to the Start of the Next Pass (Front, OUT_ Circum _ 00 _ 00005)

The reviewers were also able to confirm that the welding operators were making correct arc position adjustments during DSC welding through the use of a log. Anytime the welding Report No. 1301415.403.R2 5-2 l)Slnlclutll lnlefrlly Associates. Inc.*

operator made an adjustment in arc position it was noted in the log. The log showed the welding operator made roughly 65 adjustments to the arc position during welding shown in 12_12 (Front). Arc adjustment is an important observation because it demonstrates the welding operator was observing the weld puddle and being attentive to when necessary corrections were needed. In addition, a correctly deposited weld bead makes a tie-in with subsequent weld passes much easier. Note that a log was only kept for video folder 12_12 as the reviewers satisfied themselves that the welders were paying attention to the welding process. The reviewers did observe arc adjustments being made for all welding videos even though these observations were not recorded in a log. For this reason, listing arc position adjustments as a good welding practice/observation will not be mentioned for each folder.

Figure 5-2 and 5-3 are presented below to show a weld bead being deposited with good wetting good sidewall fusion, and proper arc placement. Note the feature circled in the photo shown in Figure 5-2 is debris on the camera lens or lens protector and not porosity.

Figure 5-2. Weld Pass with Good Sidewall Fusion, Arc Position, and Wetting (Front, OUT_ Circum _ 00 _ 00008)

Edge of weld Edge of joint Report No. 1301415.403.R2 5-3 l;Slruclu,a/ lntQrlty Associates, Inc.*

Figure 5-3. Presenting a Weld Pass with good Sidewall Fusion, Arc Position, and Wetting (Front, OUT_Circum_04_00001)

Figure 5-4 is presented to show a weld bead ending and arc extinguishing after the welding operator moved the arc position away from the shell wall. This is done to prevent fusion issues at the sidewall and to permit easier cleanup/tie-in to the stop of the weld bead. Figure 5-5 (front) and 5-6 (Rear) are provided as examples representing a proper arc starting location for a subsequent weld passes. It can also be seen in Figure 5-6 that good sidewall fusion and weld bead evenness were obtained.

Figure 5-4. Weld Pass being stopped in the Correct Location (Front, OUT_Circum_00_00036)

Report No. 1301415.403.R2 5-4 l)Stmctwal lntegrlly Associates, Inc.*

Start of next weld bead Figure 5-5. Weld Pass Starting in the Correct Location to Consume the Stop of the Previous Weld Bead (Front, OUT_Circum_03_00000)

Even weld ripple/

sidewall Figure 5-6. Weld Pass Starting in the Correct Location to Consume the Stop of the Previous Weld Bead and Sidewall Fusion (Rear, 02, OUT_Circum_00_04) 5.1.2 Observed Surface Weld Conditions that May Require Mitigating Action Figures 5-7, 5-8, and 5-9 are presented to show undesirable weld bead profiles and fusion into the sidewall. These conditions are not considered desirable because they have potential to produce defects in welds unless the welding operator takes some form of mitigating action. The figures presented below are not intended to suggest that fusion was achieved, but rather is intended to describe an undesirable surface condition that can impact negatively on the likelihood for good weld. A representative picture of a large weld puddle with the arc energy applied away from the sidewall (see Figure 5-10). Overlap and/or lack of fusion at the sidewall are possible when a puddle is too large and the arc is not positioned correctly. These observations indicate a need for welding operation attention.

Report No. 1301415.403.R2 5-5

~

Struclutal Integrity Associates, Inc.*

Figure 5-7. Uneven Weld Bead Profile and Uneven Sidewall Tie-in (Front, OUT_ Circum _ 04 _ 00052)

Figure 5-8. Uneven Weld Bead Profile and Uneven Sidewall Tie-in (Front, OUT_ Circum _ 04 _ 00052)

Figure 5-9. Uneven Weld Bead Profile and Uneven Sidewall Tie-in (Front, OUT_ Circum _ 04 _ 00053)

Report No. 1301415.403.R1 5-6 l}Structwa1 lnlBfrlly Associates, Inc.*

Figure 5-10. Large Weld Puddle with Arc Position Away from Sidewall (Rear, (05), OUT_Circum_00_51) 5.1.3 General Observations In the video clips reviewed, all weld passes observed were made without oscillation.

5.2 Folder "0015 0015" The weldment being viewed in folder "0015_0015" is the tack welding portion for what appears to be the outer cover plate circumferential DSC weld. The review of videos included in folder "0015_0015" revealed visual evidence for good welding practices. Visual evidence for the need for welding operator attention was also observed. For purposes of this video review it has been assumed that this folder contains video clips for Canister 15. The tack welding shown was limited in duration and length, but a couple observations were made. Evidence of good welding practices/observations are chronicled in Subsections 5.2.1, and visual evidence of surface conditions suggesting the need for operator mitigating actions are shown in Subsection 5.2.2.

General observations are detailed in Subsection 5.2.3.

It should be noted that Folder 15_15 the video clips show the remaining tack welding, the root pass, and subsequent weld passes. Folder 0015_0015 only contains tack welding.

Report No. 1301415.403.R2 5-7 IJStruclulal Integrity Associates, Inc.*

5.2.1 Observed Weld Surface Conditions showing Good Welding Practices Figure 5-11 presents a picture of contaminated tungsten that received the appropriate response.

Specifically, the welding operator extinguished the arc and then cleaned/replaced the tungsten prior to commencement of welding. These actions are positive evidence of proper welding operator attention to a normal maintenance requirement. Figure 5-12 is representative of the tack welds on canister 15 which appear to the reviewers to be have good tie-in at the root location.

Figure 5-11. Tungsten Contaminated with Filler Metal that was Subsequently Replaced (Front, OUT_Tack8_00_00001)

Figure 5-12. Typical Tack Weld (Front, OUT_Tack1_03_00004)

Report No. 1301415.403.R2 5-8 l)StlUclulal Integrity Associates, Inc.*

5.2.2 Observed Surface Weld Conditions that May Require Mitigating Action There were a few instances where arc initiation did not occur and the tungsten tip stuck to the canister. Normally these locations should be mechanically ground to remove potential remnants of tungsten prior to reinitiating welding. Figure 5-13 provides an example of a location where the tungsten electrode was stuck and the welding operator immediately reinitiated the welding arc proceeding to weld over the location without removing tungsten tip left on the surface.

Unfortunately, tungsten remnants will not be consumed in this manner, and a tungsten inclusion will remain embedded into the tack weld. It is noted that this type of discontinuity is quite small and likely would have no impact on the serviceability of the weld.

Figure 5-13. Location where Tungsten Electrode was Stuck during Arc Initiation (Front, OUT_Tack2_02_00001) 5.2.3 General Observations Overall, the tack welding operation appears to have been successful and consistent with expectations for field tack welds.

5.3 Folder "15 15" The weldment being viewed in folder "15 _ l 5" is the outer cover plate circumferential DSC weld. The review of videos included in folder "15 _15" found certain areas of good welding practices and others that would not be ideal for generating a defect free weld. For purposes of Report No. 1301415.403.R2 5-9 l)Struclulaf lnlBfrllY Associates, inc.*

this video review it has been assumed that this folder contains video clips for Canister 15.

Similar to Canister 12, the video clips showed areas of weldment where the weld was deposited with good arc placement, weld puddle wetting, side wall fusion, and weld bead profile. In other areas of the DSC weld there were observations that could potentially be deleterious to producing a sound weldment. Evidence of good welding practices/observations are chronicled in Subsections 5.3.1, and visual evidence of surface conditions suggesting the need for operator mitigating actions are shown in Subsection 5.3.2. Any general observations are detailed in Subsection 5.3.3.

It should be noted that for Folder 15_ 15 the video clips shows the root passes and subsequent weld passes. However, there were a few tack welding clips in the folder, but it is believed the bulk of the tack welding portion is shown in folder 0015_0015.

5.3.1 Observed Weld Surface Conditions showing Good Welding Practices Good welding practices/observations were observed during the review of the video records of canister 15. Figure 5-14 and 5-15 are provided which show that good sidewall fusion, arc position, and wetting were achieved in the root and subsequent weld passes respectively.

Figure 5-14. Root Pass displaying good Sidewall Fusion, Arc Position, and Wetting (Front, OUT_Circum_00_00051)

Report No. 1301415.403.R2 5-10

Figure 5-15. Weld Pass with Good Sidewall Fusion, Arc Position, and Wetting (Front, OUT_ Circum _ 04 _ 00027)

Grinding during DSC welding is typically kept to a minimum to reduce exposure and dose.

However, in some cases it is required for welding and if necessary should be done. Figure 5-16 is a photo displaying evidence of the use of mechanical grinding.

Figure 5-16. Area that was Ground (Front, OUT_Circum_08_00000) 5.3.2 Observed Surface Weld Conditions that May Require Mitigating Action Figures 5-17, 5-18, and 5-19 are presented to show filler material feeding issues, filler material contaminated with debris, and a location appearing to have potential sidewall fusion issues. The picture shown in Figure 5-17 appears to be caused by a wire feeding issue (e.g. kink in the wire).

This was an instantaneous picture and the wire went back to feeding properly into the weld puddle. Note that there was debris on the camera lens or lens protector resulting in a speck that may appear to be porosity, but it is not. An example of this can be seen in the encircled area in Figure 5-19.

Report No. 1301415.403.R2 5-11

~

Stnu:llllal lntsgrlly Associates, Inc.*

Figure 5-17. Filler Material Directed Into Bottom of Weld Puddle (Front, OUT_Circum_04_00004)

The reviewers saw noticeable amounts of debris on the filler wire as it entered the puddle, a representative picture shown in Figure 5-18. The concern with the debris is the tendency for oxides to develop and accumulate on the surface of the weld puddle. Too much oxide accumulation on the surface can (in some cases) hinder the puddle from wetting properly into the sidewall thus leading to fusion type defects.

Figure 5-18. Filler Metal with Debris (Front, OUT Circum 04 00058)

Figure 5-19 was provided to show evidence for potential lack of fusion between the root pass and the sidewall. In such cases careful welding operator attention may be required to ensure fusion at this location during the weld root pass. It is difficult to discern if this area were properly consumed during continuation of the root pass (Figure 5-20): however, sidewall fusion definitely appears to be present immediately after the weld passed over the tacked location.

Report No. 1301415.403.R2 5-12 S)Stntclural Integrity Associates, Inc.*

Figure 5-19. Root Pass Area that Appears to be Unfused (Front, OUT_Circum_Ol_00004)

Figure 5-20. Same Location of Figure 5-19 after the Welding Arc Passed over Unfused Area (Front, OUT_Circum_Ol_00004) 5.3.3 General Observations In the video clips reviewed all weld passes were made without oscillation. The reviewers also noticed significant movement (wandering) of the wire entering the weld puddle. This could be unevenly wound filler material, wire cast issues, or liner wear. In some cases a wire spool may need to be changed. In any case, it is important for the welding operator to ensure the wire is fed into the appropriate location on the leading edge of the weld puddle at the arc.

Report No. 1301415.403.R2 5-13 e

Sll'ucllllal Integrity Associates, Inc.*

5.4 Folder "464956 012" The weldment being viewed in folder "464956_012" is the outer cover plate circumferential DSC weld. The review of videos included in folder "464956 012" revealed visible evidence of good welding practices, and other locations considered in need of welding operator attention to produce a defect free weld. For purposes of this video review it has been assumed that this folder contains video clips for Canister 12. Similar to Canister 15, the video clips provided visible evidence areas where the weld had been deposited with good arc placement, weld puddle wetting, side wall fusion, and weld bead profile. In other areas there were visible surface conditions that potentially could be lead to defective conditions and thus require welding operator judgment for taking mitigating actions to avoid discontinuities. Subsections 5.4.1 and 5.4.2 respectively chronicle these types of surface conditions. Any general observations are detailed in Subsection 5.4.3.

It should be noted that for Folder 464956_012 the video clips show the tack welds, root pass, hot passes and subsequent weld passes. The reviewers believe the remaining weld passes are shown in Folder "12 12".

5.4.1 Observed Weld Surface Conditions showing Good Welding Practices Good welding practices/observations were seen during review of canister 12.

Figure 5-21, 5-22, and 5-23 provide visual evidence showing good sidewall fusion, arc position, and wetting in the weld root and in subsequent weld passes respectively. Note that there was some debris seen on the camera lens or lens protector. This spec may appear to be porosity, but it is not. An example of this can be seen in the encircled area in Figure 5-21.

Report No. 1301415.403.R2 5-14 S)Slrucllllal lntefrlly Associates, Inc.*

Figure 5-21. Typical Root Pass (Front, OUT_Circum_03_0006)

Figure 5-22. Root Pass from the Rear Camera Showing Good Fusion (Rear, (16), OUT_Circum_00_0035)

Figure 5-23. Typical Fill Pass (Front, OUT_Circum_15_0032) 5.4.2 Observed Surface Weld Conditions that May Require Mitigating Action There was some evidence of uneven tie-in to the sidewall presented in Figure 5-24. This aspect of the weld could create difficult conditions for a subsequent weld pass to fuse that portion of the Report No. 1301415.403.R2 5-15

(>Stmclln/ lntegrlly Assaclates, Inc.*

weld. Figure 5-25 is presented to show an area were an undesirable weld profile was deposited.

A weld profile seen in Figure 5-25 would increase the difficulty for the welding operator to properly fuse the side wall and the weld bead previously deposited. Welding operator judgment is required to mitigate these types of surface conditions.

Figure 5-24. Weld Pass Showing Uneven Tie-in to the Sidewall (Rear, (19), OUT_ Circum _ 00 _ 13)

Figure 5-25. Fill Pass Showing Undesirable Weld Bead Profile (Rear, (19), OUT_Circum_00_35)

One interesting event recorded observed in this video was a wasp entered the weld groove near the welding arc as shown in Figure 5-26. It is not uncommon for flying insects, because they are attracted by light. In this case it appeared the wasp did not get incorporated into the weld puddle; however, insects incorporated into the weld deposit can create small discontinuities in the weldment due to local increases in the moisture content as well as the introduction of carbonaceous material into the weld puddle.

Report No. 1301415.403.R2 5-16 l)StluclUlal Integrity Associates, Inc.*

Figure 5-26. Wasp Entering the Welding Arc (Rear,(16), OUT_Circum_00_0038) 5.4.3 General Observations In the video clips reviewed it appears that the hot pass employed arc oscillation to assist with creating the desired weld surface profile. It was not clear if a second hot pass were used.

5.5 Folder "464956 013" The weldment being viewed in folder "464956_013" is the outer cover plate circumferential DSC weld. The review of videos included in folder "464956_013" again revealed visual evidence of good welding practices, as well as, some locations that would not be ideal for generating a discontinuity free weld and require welding operator judgment to determine if additional actions are required. For purposes of this video review it was assumed that this folder contains video clips for Canister 13. The conditions observed were similar to that seen in other folders. The video clips showed areas of weldment where the weld was deposited with good arc placement, weld puddle wetting, side wall fusion, and weld bead profile. In other areas of the DSC weld conditions were observed that could potentially lead to undesirable conditions in the weldment. For both cases the observations have been chronicled in Subsections 5.5.1 and 5.5.2 respectively. Any general observations are provided in Subsection 5.5.3.

It should be noted that for Folder 464956_013 the video clips shows the tack welds, root pass, hot passes and subsequent weld passes. It is uncertain whether or not all of the weld passes are shown.

Report No. 1301415.403.R2 5-17 IJSlruclural lnlefrlly Associates, Inc.*

5.5.1 Observed Weld Surface Conditions showing Good Welding Practices Visual surface evidence for good welding practices/observations was observed during review of canister 13. Figure 5-27, 5-28, and 5-29 are provided as visual evidence that good sidewall fusion, arc position, and wetting were achieved in the root and subsequent weld passes respectively. Note that debris was observed on the camera lens or lens protector resulting in a speck that might appear to be porosity, but is not. An example of this can be seen in the encircled area in Figure 5-27 as was described previously.

Figure 5-27. Typical Root Pass (Front, OUT_Circum_01_0014)

Figure 5-28. Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_16_0028)

Report No. 1301415.403.R2 5-18 S)Struclutal Integrity Associates, Inc.*

Figure 5-29. A Later Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_25_0006) 5.5.2 Observed Surface Weld Conditions that May Require Mitigating Action There was evidence of burn through encountered while depositing the root pass as shown in Figure 5-30. The weld puddle and tungsten can be seen to have fallen below the deposited weld bead. Once burn through was experienced the welder stopped the welding operation and took the correct mitigating action as would be expected. This observation demonstrates good welder attention to an in-process welding issue.

Figure 5-30. Burn Through During Welding of the Root Pass (Front, OUT_ Circum _ 02 _ 00002)

It was also observed that wasps entered the welding arc in Canister 13 similar to Canister 12 that was shown in Figure 5-26. Photos for Canister 13 are shown in Figures 5-31 and 5-32. It is being reemphasized that it is not uncommon for insects that are attracted by light to fly into the Report No. 1301415.403.R2 5-19 S)SlnlclUJal lntQrlly Associates, Inc.*

welding arc. For this location it appears the wasp did get into the weld puddle. In this case the welding operator stopped the welding operation as expected and made a judgment about how to proceed. No grinding or cleanup was observed prior to continuing welding, but the resulting weld deposit revealed no evidence of porosity or any other defective condition. This information provides evidence that the welding operator was attentive, correctly addressed a problem and made a knowledgeable decision regarding specific mitigation required.

Figure 5-31. Wasp Entering the Welding Arc (Front, OUT_Circum_21_00001)

Figure 5-32. Wasp Entering the Welding Arc (Front, OUT_Circum_18_00004) 5.5.3 General Observations The video clips provided visual evidence that oscillation was used for the weld root pass in certain areas and straight stringer beads for others. The hot pass also used oscillation.

Report No. 1301415.403.R2 5-20

~

Slruclutal lnlBgrlly Associates, Inc.*

5.6 Folder "464956 14" The weldment being viewed in folder "464956 _ 14" is the outer cover plate circumferential DSC weld. The review of videos included in folder "464956 14" was similar to other welds reviewed in that visual evidence was found that certain locations exhibited good welding practices and others required welding operator attention for mitigating action to achieve a sound weld. For purposes of this video review it was assumed that this folder contains video clips for Canister 14.

Similar to other folders, the video clips showed areas of weldment where the weld was deposited with good arc placement, weld puddle wetting, side wall fusion, and weld bead profile. Weld conditions were observed in other locations of the outer cover plate weld that potentially could lead to discontinuities in the final weld. Subsections 5.6.1 and 5.6.2 provide examples of surface conditions for each case respectively. Any general observations are detailed in Subsection 5.6.3.

It should be noted that for Folder 464956_ 14 the video clips show the tack welds, root pass, hot passes, and subsequent weld passes.

5.6.J Observed Weld Surface Conditions showing Good Welding Practices The following good welding practices/observations were observed during review of Canister 14.

Figure 5-33, 5-34, and 5-35 are provided which show that good sidewall fusion, arc position, and wetting was achieved in the root and subsequent weld passes respectively. Note that there was debris on the camera lens or lens protector resulting in a speck that may appear to be porosity, but it is not. An example of this can be seen in the encircled area in Figure 5-34.

Report No. 1301415.403.R2 5-21 l)StlUclutal Integrity Associates, 1nc.*

Figure 5-33. Typical Root Pass (Front, OUT_ Circum _ 02 _ 00008)

Figure 5-34. Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_ Circum _13 _ 00007)

Figure 5-35. A Later Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_14_00011)

Report No. 1301415.403.R2 5-22 l)Struclutal lnlqrlly Associates, Inc.*

5.6.2 Observed Surface Weld Conditions that May Require Mitigating Action There was some evidence of uneven tie-in to the sidewall such as presented in Figure 5-36.

Uneven tie-in is a condition known to make it difficult for a subsequent weld pass to fuse that portion of the weld. The observed condition was intermittent suggesting welding operator mitigative action was taken. While the condition is undesirable, it is considered minor, and the visual evidence suggests that proper response was taken to address the condition.

Figure 5-36. Weld Pass Showing Uneven Tie-in to the Sidewall (Front, OUT_ Circum _ 09 _ 00006)

5. 6.3 General Observations In the video clips reviewed it appears that the root pass used stringer beads and the hot pass used oscillation.

5.7 Folder "464956 DSC 013" The weldment being viewed in folder "464956_DSC_013" is the inner cover plate circumferential DSC weld. For purposes of this video review it will be assumed that this folder contains video clips for Canister 13 inner weld. Documentation of visual evidence suggesting good welding practices are chronicled in Subsections 5. 7.1, and undesirable conditions are chronicled in Subsection 5.7.2. Any general observations are detailed in Subsection 5.7.3.

Report No. 1301415.403.R2 5-23 S)StnlclUlaf Integrity Associates, Inc.*

It should be noted that for Folder 464956_DSC_013 the video clips shows the root pass and one subsequent pass.

5. 7.1 Observed Weld Surface Conditions showing Good Welding Practices Visual weld surface evidence of good welding practices/observations for Canister 13 inner weld are shown below. Figure 5-37 and 5-38 show evidence that good sidewall fusion, arc position, and wetting were achieved in the root and subsequent weld passes respectively.

Figure 5-37. Typical Root Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, IN_Circum_14_00011)

Figure 5-38. Cover Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, IN_Circum_02_00083)

Report No. 130141 5.403.R2 5-24 S)Stnlcllnl lnlegrlly Associates, Inc.*

5. 7.2 Observed Surface Weld Conditions that May Require Mitigating Action None observed.

5. 7.3 General Observations The inner weld appears to be made using two weld passes, and both appear to have been deposited without any identifiable issues.

5.8 Folder "inner 16" The weldment being viewed in folder "inner_ 16" is the inner cover plate circumferential DSC weld. For purposes of this video review it has been assumed that this folder contains video clips for Canister 16 inner cover plate weld. The observations of good welding practices/observations and other observations that may require mitigating actions are chronicled in Subsections 5.8.1 and 5.8.2 respectively. Any general observations are detailed in Subsection 5.8.3.

It should be noted that for Folder inner_ 16 the video clips shows the root pass and one subsequent pass.

5.8.J Observed Weld Surface Conditions showing Good Welding Practices Visual evidence of good welding practices was observed during review of Canister 16 inner cover plate weld. Examples of good welding practices are shown in Figure 5-39 and 5-40. These figures display that good sidewall fusion, arc position, and wetting were achieved in the root and subsequent weld pass respectively. Welder was seen adjusting the wire feeder to obtain proper angle into the weld puddle. Note that there was debris on the camera lens or lens protector resulting in a speck that may appear to be porosity, but it is not. An example of this can be seen in the encircled area in Figure 5-40.

Report No. 1301415.403.R2 5-25 e Stnu:lulal lnllfrlly Associates. Inc.*

Figure 5-39. Typical Root Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, IN_Circum_Ol_00023)

Figure 5-40. Cover Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, IN_Circum_03_00013) 5.8.2 Observed Surface Weld Conditions that May Require Mitigating Action In some locations the weld puddle appeared to be sluggish, but did not seem to cause an issue.

5.8.3 General Observations The inner weld appears to have been made using two weld passes, and both appear to have been deposited without any identifiable issues.

Report No. 1301415.403.R2 5-26

(>8'nlclUlal lntegrlly Associates, Inc.*

5.9 Folder "outer 16" The weldment being viewed in folder "outer_ 16" is the outer cover plate circumferential DSC weld. The review of videos included in folder "outer 16" found visual evidence that certain areas displayed good welding practices while other locations displayed conditions that would not be considered ideal and required welding operator attention. For purposes of this video review it was assumed that this folder contains video clips for Canister 16. Similar to other folders, the video clips displayed weld surface areas where the weld was deposited with good arc placement, good weld puddle wetting, side wall fusion, and weld bead profiles favorable to the production of sound welds. In other areas of the DSC weld there were observations which could potentially be deleterious thus indicating that welding operator judgment would be needed to determine if special mitigating actions might be required. For both cases the observations were chronicled in Sections 5.9.1 and 5.9.2 respectively. Any general observations are detailed in Subsection 5.9.3.

It should be noted that for Folder outer_16 the video clips shows the tack welds, root pass, hot passes and subsequent weld passes.

5.9.1 Observed Weld Surface Conditions showing Good Welding Practices Visual evidence for good welding practices/observations were observed during review of canister 16 outer cover plate weld and are chronicled in Figures 5-41, 5-42, and 5-43. The photos provide visual confirmation that many areas displayed good sidewall fusion, good arc positioning, and effective wetting for the root pass and subsequent weld passes.

Report No. 1301415.403.R2 5-27 IJStnlcllnl lnlQrlly Associates, Jnc.*

- -~

Figure 5-41. Typical Root Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_03_00025)

Figure 5-42. Typical Root Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle Looking from the Rear (Rear, OUT_Circum_00_00059)

Figure 5-43. A Later Fill Pass Showing Good Sidewall Fusion, Arc Position, and Wetting of the Weld Puddle (Front, OUT_Circum_ll_OOOll)

Report No. 1301415.403.R2 5-28 l)StmclUlal IIIIBgrlly Associates, Inc.*

5.9.2 Observed Surface Weld Conditions that May Require Mitigating Action An oxidation issue was observed with the outer closure weld for Canister 16. The issue appears to be related to a buildup of oxides on the weld pool surface and continue on to adjacent material as shown in Figures 5-44 and 5-45. The oxidized condition was especially prevalent with the first two fill passes and appeared to restrict the weld puddle from wetting. This condition resulted in a deposited weld bead having an irregular profile as shown from the rear camera in Figure 5-46 and 5-47. The large amount of oxide on the weld puddle presented in Figure 5-48 are also shown from the rear camera along with an undesirable weld bead. Note that there was debris on the camera lens or lens protector resulting in a speck that may appear to be porosity, but it is not. An example of this can be seen in the encircled area in Figure 5-45.

Figure 5-44. First Fill Pass with Large Amount of Oxides Preventing the Weld Puddle to Wet (Front, OUT_Circum_05_00001)

Figure 5-45. Another Picture of the First Fill Pass with Large Amount of Oxides Preventing the Weld Puddle to wet the sidewall (Front, OUT_Circum_05_00001)

Report No. 1301415.403.R2 5-29 i.>SIIUclUlal Integrity Associates, Inc.*

Figure 5-46. Picture from the Rear Camera Showing a Sudden Puddle Shift Creating an Uneven Bead Profile (Rear, (12), OUT_Circum_00_44)

Figure 5-47. Large Gap Near the Sidewall seen from Rear Camera (Rear, (12),

OUT_Circum_00_56)

Figure 5-48. Large Amount of Oxides and Undesirable Weld Profile seen from Rear (Rear, (13), OUT_ Circum_OO_ 45)

Report No. 1301415.403.R2 5-30 I_JStruclurll lntegrlly Associates, Inc.*

During the second fill pass the unevenness of the preceding weld bead was evident as shown in Figure 5-49 and 5-50. The gap to be filled in Figure 5-49 is much larger compared to Figure 5-50 which has a very narrow gap. A narrow gap can influence the weld penetration such that the penetration is less than anticipated. These conditions are undesirable and require welding operator attention to avoid areas having fusion issues. The amount of oxide remaining on the previously deposited weld bead (encircled in red in Figure 5-50) must breakdown and not be permitted to insulate the material underneath.

Figure 5-49. Large Amount of Oxides, Large Gap, and Undesirable Weld Profile (Front, OUT_Circum_06_00001)

Figure 5-50. Large Amount of Oxides and Undesirable Weld Profile (Front, OUT_ Circum _ 06 _ 00003)

Report No. 1301415.403.R2 5-31

~

StruclUJal Integrity Associates, Inc.*

5.9.3 General Observations It is uncertain if outer closure weld of Canister 16 was welded using a hot pass or if the fill passes were started directly over the root pass. In general the amount of oxides in first two fill passes did not permit proper wetting of the weld puddle and resulted in irregular weld surface profiles considered to be undesirable. This condition would have exacerbated the already difficult task for consistently depositing the weld with good sidewall fusion and good tie-in to the previously deposited weld pass. In comparison to the other canister welds the extent of these types of condition (irregular surface profiles, surface oxides, marginal wetting, etc.) was much greater for the outer closure weld of Canister 16 than with other canister welds. The reviewers believe that some level of grinding was necessary during and after the first weld pass after the root. It is understood that a large amount of grinding is not desirable due to dose concerns, but the reviewers suggest it would be the best action for this weldment.

Report No. 1301415.403.R2 5-32 lJSlnlcllllal lntefrlly Associates, Inc.*

6.0 CONCLUSION

S Available information on the inner and outer closure plate welds bas been reviewed in detail.

Particular emphasis was placed on the review of weld video records for each of the five canisters in question. The purpose of this detailed review was to carefully examine video records of the surfaces of each weld ( during welding) to determine surface conditions that assist in characterizing the weld. Examples of the types of surface conditions observed are chronicled for each weld. It is impos ible to state with certainty whether any o(the welds will be defective or not based solely on these types ofrecords. For example, it was noted that good welding practices were present in all of the welds examined, and in general, visible evidence of tie-in between the weld passes and the sidewall was present. Conversely, undesirable weld surface conditions (anomalies) were also observed, to some extent, in all of the welds examined. The presence of such undesirable weld surface conditions do not necessarily result in weld defects.

When encountered, it is required for the welding operator to stop and assess the condition and then act to mitigate as necessary.

In general, it was not possible to determine or corroborate the mitigative actions taken, except that in some cases the welding operator determined that irregular surface conditions would be fully incorporated into the weld as subsequent weld passes were placed. This was the path that appeared to be taken in most cases (based on the video review conducted). Alternatively the use of limited grinding to smooth the irregular surfaces and the use of interpass brushing to clean the weld surface could not be confirmed.

The weld designs, the materials used, and the welding processes applied are designed for quality welds. The ER308 (or ER308/308L) dual certified filler materials are correct for the Type 304 stainless steel components. In fact these material combinations tend to be quite forgiving in terms of achieving quality welds, especially with the machine GTA W welding process which is bow these structures were welded. These types of welds are generally considered to be readily weldable.

Report No. 1301415.403.R2 6-1

The probability for achieving quality welds is enhanced when good welding practices are followed. Good practices include proper and consistent fit-up, clean joint surfaces, minimizing weld surface irregularities, pure welding grade inert gas (argon), properly dressed and maintained tungsten electrode, proper electrode positioning, proven combinations of heat input (amps times volts divided by arc travel speed), and rates of filler wire additions. The written welding program controls, welding procedure specifications, welding procedure qualification records were all in order to produce sound welds. The component designs and manufacturing sequences are capable of producing quality welds. The final step is for the welding operators and their supervision to ensure that good welding practice was followed. When welding anomalies are identified corrective action should be taken to eliminate any issues.

The fabrication process called for liquid dye penetrant examinations after the root pass was completed and after the weld was completed for the inner cover plate (small weld). An intermediate inspection was added for the larger outer cover plate weld. Unfortunately these examinations (although performed) did not adhere to the qualified inspection procedure. This brings the quality of the welds into question.

All of the welds produced similar irregular weld surface conditions to some extent based strictly on the video clips for each canister closure weld. However, the outer closure weld in Canister

1. 16 appeared to exhibit a higher frequency of irregular surface conditions than any of the five canisters reviewed. As stated earlier, this does not imply that any of the welds are defective and in fact, clear evidence of sidewall and interbead tie-in is consistently observed around the entire circumference of the welds. It is entirely possible that all of the canister welds are acceptable.

However, the presence of these irregular surface features on the welds suggests that there is potential for welding discontinuities to exist in all of the canisters. Canister #16 outer closure weld appears to be the most vulnerable to potential defects, because a greater frequency of irregular surface conditions was generated in those welds during welding. Mitigating actions represent a very real part of the welding process and specific actions to mitigate the irregular surfaces could not be confirmed based on the evidence available.

Report No. 1301415.403.R2 6-2 S)Slnlcllual lntQrlly Associates, Inc.*