POSIVA OY

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Tarja Jäppinen

March 2012

Working Report 2009-101

Replicas from Surface Defects Detectedin Disposal Canister Lid Welds

March 2012

Working Reports contain information on work in progress

or pending completion.

The conclusions and viewpoints presented in the report

are those of author(s) and do not necessarily

coincide with those of Posiva.

Tar ja Jäpp inen

V T T

Work ing Report 2009 -101

Replicas from Surface Defects Detectedin Disposal Canister Lid Welds

Replicas from Surface Defects Detected in Disposal Canister Lid Welds ABSTRACT In the final disposal canister for high activity nuclear waste the copper overpack lid will be sealed using electron beam welding (EBW) or friction stir welding (FSW). The weld will be inspected by NDT-methods before the acceptation to the final disposal will be made. The replica technique is a versatile method for inspection of sensitive surfaces. By ap-plying a flexible replica material on a surface a copy (replica) of surface breaking de-fects can be produced. The purpose of this report is to give an overall description of the surface defects found in the twelve visually inspected lid welds with codes XK030 –XK041. Replicas were made of defects visible to the bare eye and the dimensions of the defects were measured from the replicas. There were one to five defects per a lid weld except on the welds no XK038 - XK040 that had no defects. The coordinates and the sizes of the surface de-fects in each lid are listed and the pictures are shown in this report. Replicas made out of the defects of the welds of twelve copper lids are reported and compared to the results of ET inspection. Replica method will be used as an aid of necessary research activities not in final disposal phase. The sizes of the defects in the replicas vary from 0.57 mm long and 0.55 wide to 6.22 mm long and 6.01 mm wide. The depths of the defects also vary from 0.15 mm to 4.17 mm. The correlation between defect sizes measured using ET and the replica method is quite good. Keywords: Replica, Surface defects, EB-weld and Disposal canister for spent nuclear fuel.

Kuparikapselin EB-sulkuhitsistä löydettyjen pintavikojen jäljenteet eli replikat TIIVISTELMÄ Korkea-aktiivisen ydinjätteen kuparisen loppusijoituskapselin kansi hitsataan EB-hitsauksella tai kitkatappihitsauksella kiinni. Kannen hitsaus tarkastetaan ainetta rikko-mattomilla menetelmillä (NDT) kannen hitsauksen jälkeen ennen kapselin hyväksymis-tä loppusijoitukseen. Arkoja pintoja pystytään monipuolisesti tarkastamaan replikoiden avulla. Pintavikojen muoto ja koko pystytään määrittämään tarkasti laittamalla juoksevan joustavaa replika-ainetta vian päälle ja ottamalla se jähmettyneenä varovasti pois. Replikamenetelmää käytetään loppusijoituskapseliin tarvittavien tutkimusten apuvälineenä, ei loppusijoitus-vaiheessa. Tässä raportissa on tehty yhteenveto 12 kuparikapselin kannen sulkuhitseistä, numerot XK030 – XK041, löytyvistä pintavioista. Paljain silmin näkyvistä vioista on tehty repli-kat ja niiden koko on mitattu mikroskoopilla. Jokaisesta kannesta löytyi yhdestä viiteen vikaa paitsi kansista XK038 - XK040, joista vikoja ei löydetty yhtään. Vikojen paikat ja koot on listattu taulukoihin ja jokaisesta replikasta on otettu kuva. Taulukot ja replika-kuvat on esitetty tässä raportissa. Kahdentoista kuparikannen pintavioista otettuja repli-koita verrataan tässä raportissa vastaavien vikojen pyörrevirta (ET) indikaatioihin. Replikoiden koko vaihtelee pienimmästä 0,57 mm pituudeltaan ja 0,55 leveydeltään ai-na 6,22 mm pitkiin ja 6,01 mm leveisiin. Vikojen syvyydet vaihtelevat 0,15 mm ja 4,17 mm välillä. Replikoista saadut mitat korreloivat melko hyvin ET- testauksella saatuja arvoja. Avainsanat: Replika, Pintavika, EB-hitsi ja loppusijoituskapseli.

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TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ FOREWORD

1 INTRODUCTION ................................................................................................... 3

2 REPLICAS ............................................................................................................. 4

3 RESULTS .............................................................................................................. 5 3.1 Weld XK030 ................................................................................................. 6 3.2 Weld XK031 ................................................................................................. 7 3.3 Weld XK032 ................................................................................................. 9 3.4 Weld XK033 ............................................................................................... 10 3.5 Weld XK034 ............................................................................................... 11 3.6 Weld XK035 ............................................................................................... 14 3.7 Weld XK036 ............................................................................................... 16 3.8 Weld XK037 ............................................................................................... 17 3.9 Welds XK038 – XK040 ............................................................................... 18 3.10 Weld XK041 ............................................................................................... 18

4 CONCLUSIONS .................................................................................................. 19

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FOREWORD This report has been prepared at VTT to the order of Posiva Oy. Replicas were made by Research Assistant Kirsti Nöjd and the analysis was made by Research Engineer Aarne Lipponen and Research Scientist Tarja Jäppinen. Subscriber and project supervisor at Posiva Oy was Jorma Pitkänen.

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1 INTRODUCTION The replica technique is a versatile method for inspection of sensitive surfaces. By ap-plying a flexible replica material on inspected surface the defects open to the surface can be identically copied. In the final disposal canister for high activity nuclear waste the copper overpack lid will be sealed using electron beam welding (EBW) or friction stir welding (FSW). This weld is inspected using nondestructive testing (NDT) methods. Ultrasonic testing (UT), ra-diographic testing (RT), eddy current testing (ET) and remote visual testing (VT) by cameras are used to verify the integrity of the EB-weld. In this document the replicas made out of the defects detected in the welds of twelve copper lids by VT are reported. NDT methods use a coordinate system to locate the pos-sible defect. The same coordinate system is used for the replicas, Figure 1. Letter C stands for the circumferential direction of the inspection while letter R denotes the di-rection from outer edge towards the middle of the canister, D is the depth of the defect.

Figure 1. The coordinate system (left) and a schematic example of a replica (right).

R

C

R C

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2 REPLICAS The objective of the replica testing is to size and locate the surface breaking defects in the weld surface on the lid. Replicas are taken from the visible defects on the weld sur-face. Replicas were made with Struers RepliSet-F5 and RepliSet-T3 replica substances. The coordinates R and C were clearly marked on the replicas, Figure 1. The identification codes of the lid welds and the number of replicas taken from each weld are listed in Table 1. In the same table also the numbers of the defects found in visible inspection and in eddy current inspection are listed. Note that there were three welds in this test serie that did not have any visible defects. Table 1. A list of lid weld identifications and the number of defects found with VT and ET.

Lid no number of replicas

number of visible defects

number of EC indica-tions

XK030 1 1 1 XK031 3 3 3 XK032 1 1 1 XK033 1 1 1 XK034 4 5 5 XK035 3 3 4 XK036 2 3 XK037 2 3 3

XK041 1 1 1

The actual coordinates of the defects were measured for the lid numbers XK031 – XK035. The distances in circumferential directions were measured simply using a met-ric measuring reel and the distance from OD in radial direction was measured with a metric measuring ruler, Figure 2.

Figure 2. A coordinate measurement scene is presented in the image. A metric ruler is placed circumferentially around the canister and another on the top of the lid.

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3 RESULTS The overall list of replicas, lid codes, defect sizes and the defect coordinates are pre-sented in Table 2. The sizes of the defects measured from the replicas vary from 0.57 mm long and 0.55 wide to 6.22 mm long and 6.01 mm wide. The depths of the defects also vary from 0.15 mm to 4.17 mm. In a couple of cases (XK031 code 211 and XK032 code 180) the tip of the replica was ripped during the replica removal. In ripped cases the defect could actually be deeper than the replica indicates. In these cases the size of the replica is medium size (see Table 2). More detailed descriptions of the defects for each lid are given in own chapters. The coordinates measured from defects on the lid correlates quite well with the replica size. An exception is made by lid no XK034 code 222 where the measured dimensions are for the horse shoe -like formation around a deeper defect, Figure 13 and XK034 code 170 where the dimensions are more complex than the two surface coordinates. Since the positioning of the defect was done visually the differences between sizes measured from replicas and the measured defect coordinates (start, end) are within a measuring accuracy ± 1 mm. Table 2. List of replicas with coordinates and the sizes of the indications. EC coordinates Size of indications in the replica Measured coordinates of the indications

Lid no Replica Code

C EC [°]

C end OD [mm]

Length R [mm]

Length C[mm]

Depth A [mm]

R start[mm]

R end [mm]

C start OD [mm]

C end OD [mm]

XK030 318 318.3 2908.2 2.77 3.39 1.7

XK031 211 211.3 1930.6 3.35 1.67 2.42 44 46 1930 1932

XK031 235 235.5 2151.7 2.57 2.87 2.43 44 46 2155 2157

XK031 286 286.1 2614.0 1.95 1.12 0.46 44 46 2613 2614

XK032 180 181 1653.8 3.95 3.68 4.17 44 46.5 1654 1657

XK033 217 217.3 1985.4 46 1996 2009

XK034 60 61.1 558.3 4.09 5.08 2.45 45.5 47 561 567

XK034 67 0.0 6.01 6.22 1.9 39.5 45.5 618 624

XK034 134 134.6 1229.8 3.4 4.18 0.32 43 47 1241 1245

XK034 170 170.8 1560.6 1.87 4.94 2.69 39.5 41 1572 1577

XK034 222 223 2037.5 0.91 0.77 0.85 46 47.5 2091 2095

XK035 4.7 4.7 42.9 1.91 2.76 0.15 46 47 53 55

XK035 78.3 715.4

XK035 85 84 767.5 4.98 7.87 1.1 42 47 781 789

XK035 316 315.3 2880.8 31 47 2900 2909

XK036 32 32.2 294.2 5.1 4.36 1.53

XK036 92.6 846.1

XK036 193 193.8 1770.7 5.08 2.78 1.32

XK037 68.7 68.7 627.7 1 0.8 0.47

XK037 68.7 68.7 627.7 1.06 1.22

XK037 348.5 3184.2 0.55 0.57 0.17

XK041 45 45.5 415.7 3.7 4.97 2.94

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3.1 Weld XK030 There was one visible defect on the weld seam on lid weld no XK030. Eddy current technique gave the circumferential position of 318˚ for this defect. A picture of the rep-lica is presented in Figure 1 with the coordinate directions along the lid surface. The measurements of the defect are (RxCxD) 2.77 x 3.39 x 1.7 mm.

Figure 3. An image of a replica XK 030 code 318.

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3.2 Weld XK031 Three defects were found in the weld no XK031 area. The coordinates and the measured sizes of the defect replicas are listed in Table 3 with the coordinates from ET. Table 3. Coordinates of the defects of the weld no XK031. EC coordinates Size of indications in the replica Measured coordinates of visual indications

Lid no Replica Code

C EC [°]

C end OD [mm]

Length R [mm]

Length C[mm]

Depth A [mm]

R start [mm]

R end [mm]

C start OD [mm]

C end OD [mm]

XK031 211 211.3 1930.6 3.35 1.67 2.42 44 46 1930 1932

XK031 235 235.5 2151.7 2.57 2.87 2.43 44 46 2155 2157

XK031 286 286.1 2614.0 1.95 1.12 0.46 44 46 2613 2614

Figures 4-6 present the replicas of the weld no XK031. The circumferential positions, measured using eddy current, are 211˚. 235˚ and 286˚.

Figure 4. An image of a replica XK031 code 211.

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Figure. 5. An image of a replica XK031 code 235.

Figure 6. An image of a replica XK031 code 286.

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3.3 Weld XK032 One visible defect was detected in the lid weld no XK032 at the circumferential position 180˚. Table 4 gives the coordinates and replica sizes for the defect. Table 4. Coordinates of the defects on the weld no XK032. EC coordinates Size of indications in the replica Measured coordinates of visual indications

Lid no Replica Code

C EC [°]

C end OD [mm]

Length R [mm]

Length C[mm]

Depth A [mm]

R start [mm]

R end [mm]

C start OD [mm]

C end OD [mm]

XK032 180 181 1653.8 3.95 3.68 4.17 44 46.5 1654 1657

The replica from the defect on this weld is ripped. It can be seen from the smooth shape of the top, Figure 7. Because of the ripped tip it is hard to say the exact depth of the de-fect. Even it is ripped, it is still the deepest one in the whole replica set. Figure 7 (right) shows an illustrative picture of the defect.

Figure 7. On the left there is an image of a replica XK032 code 180. On the right hand image there is a surface breaking defect in the weld surface beside the ruler.

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3.4 Weld XK033 Only one visible defect was found in the lid weld no XK033. The defect was a scratch in the surface. The dimensions in the replica could not be measured, Figure 8. The visi-ble scratch is about 13 mm long in the circumferential direction. There is an ET indica-tion also at the same coordinates as this scratch type defect.

Figure 8. Image shows scratches on the weld. The code of the replica is 217 on a weld no XK033.

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3.5 Weld XK034 This is a lid weld that had most defects. The sizes of the five detected defects vary and they are spread around the circumference. The sizes and the coordinates of the defects are presented in Table 5. Table 5. Coordinates of the surface defects of the weld no XK034. EC coordinates Size of indications in the replica Measured coordinates of visual indications

Lid no Replica Code

C EC [°]

C end OD [mm]

Length R [mm]

Length C[mm]

Depth A [mm]

R start [mm]

R end [mm]

C start OD [mm]

C end OD [mm]

XK034 60 61.1 558.3 4.09 5.08 2.45 45.5 47 561 567

XK034 67 * 0.0 6.01 6.22 1.9 39.5 45.5 618 624

XK034 134 134.6 1229.8 3.4 4.18 0.32 43 47 1241 1245

XK034 170 170.8 1560.6 1.87 4.94 2.69 39.5 41 1572 1577

XK034 222 223 2037.5 0.91 0.77 0.85 46 47.5 2091 2095

* Defects at the same replica with the same eddy current coordinate.

Figure 9. On the left an image of a replica XK034 code 6. The surface breaking defect is in the middle of the right hand side figure. Figure 9 shows an image of the replica of the second largest defect on the lid weld no XK034. The defect is clearly visible on the surface of the weld, Figure 9. The replicas of the four other defects on the same lid are presented in the Figures 10–13.

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Figure 10. An image of a replica XK034 code 67. In the replica with the eddy current coordinates 134˚ there are defects in a roundish shape, like a horse shoe, but the size of the defect is measured from the deepest part shown on the right.

Figure 11. An image of a replica XK034 code 134. Defect formed a horse shoe pattern as seen at the image.

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Figure 12. An image of a replica XK034 code 170.

Figure 13. An image of a replica XK034 code 222. Small scratch like defects are formed as a horse shoe patterns in the image.

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3.6 Weld XK035 Four defects were found on the lid weld no XK035 using eddy current, but one of the defects is not visible to the bare eye. One of the visible defects is not measured from the replica because of its flat shape, Figure 16. Therefore two replica measurements are left to be reported from this weld, Table 6. Table 6. Coordinates of the defects on weld no XK035 surface. EC coordinates Size of indications in the replica Measured coordinates of indications

Lid no Replica Code

C EC [°]

C end OD [mm]

Length R [mm]

Length C[mm]

Depth A [mm]

R start[mm]

R end [mm]

C start OD [mm]

C end OD [mm]

XK035 4.7 4.7 42.9 1.91 2.76 0.15 46 47 53 55

XK035 78.3 715.4 *

XK035 85 84 767.5 4.98 7.87 1.1 42 47 781 789

XK035 316 315.3 2880.8 ** 31 47 2900 2909

* not visible to the bare eye ** a scratch, no measurements from this replica

Figure 14. An image of the replica XK035 code 4.7.

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Figure 15. An image of the replica XK035 code 85.

Figure 16. Images of the replica XK035 code 316. The defect replica seen through the microscope on the left and the defect area on the weld surface in the black circle on the right.

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3.7 Weld XK036 No coordinate measurements were done for the lid welds any XK036 - XK041. All of the coordinates on the lids are eddy current coordinates.

Three replicas were taken from the lid no XK036. In two of them the size of the defect was large enough to be measured. The coordinates of the defects are in the following order: radius (R). Circumference (C) and depth (D). The sizes of the two measured de-fects are 5.1 mm * 4.36 mm * 1.53 mm and 5.08 mm * 2.78 mm * 1.32 mm.

Figure 17. An image a f the replica XK036 code 32. The dimensions of the defect are 5.1 x 4.36 x 1.53 mm (RxCxD).

Figure 18. An image of the replica XK036 code 193. The dimensions of the defect are 5.08 x 2.78 x 1.32 mm (RxCxD).

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3.8 Weld XK037 Two replicas of the weld no XK037 showed three defects. Two of them are at the same horse shoe formation. The dimensions of the defects measured from the replica with the code 68.7 are following 1.0 x 0.8 x 0.47 and 0.55 x 0.57 x 0.17. The defect seen in the other replica, code 348, was the smallest one measured in this replica set. The dimen-sions of the defect were 0.55 x 0.57 x 0.17 in mm, Figure 20.

Figure 19. An image of the replica XK037 code 68.7. The dimensions of the two defects are 1.0 x 0.8 x 0.47 mm (RxCxD) and 1.06 x 1.22 mm (RxC).

Figure 20. An image of the replica XK037 code 348, the defect is hardly seen. The di-mensions are 0.55 x 0.57 x 0.17 mm (RxCxD).

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3.9 Welds XK038 – XK040 There were no visible surface defects on the welds no XK038 -XK040. 3.10 Weld XK041 One visible defect was detected in the weld no XK041. Figure 21 shows the defect seen in replica with dimensions 3.7 x 4.97 x 2.94 [mm].

Figure 21. An image of the replica XK041 code 45. The dimensions of the defect are 3.7 x 4.97 x 2.94 mm (RxCxD).

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4 CONCLUSIONS Four NDT inspection methods (UT, RT, ET, VT) are applied between welding of the canister lid and the acceptation of the canister for final disposal. These replica studies compare the coordinates and the sizes of the indications measured by ET to the actual measured sizes of the replica and the coordinates of the defects. The purpose of this report is to give an overall description of the defects found in the welds XK030 –XK041. Replicas were made of the defects that are visible to the bare eye and the dimensions of the defects were measured from the replicas. There were 1- 5 defects per a lid except on the welds XK038 - XK040 where no defects were detected. The coordinates and the sizes of the defects are listed in this report. The coordinates measured from the weld surface correlates in most of the cases quite well to the replica sizes and to the ET indications. Two larger differences are in lid no XK034 in replica having replica code 222 where the measured dimensions are for the horse shoe -like formation around a deeper defect and in replica having replica code 170 where the di-mensions are too complex to be measured with two coordinates (C, R) on surface.