ULNRC-06479, Attachment a - Mitsubishi Responses to NRC Wjp RAIs
| ML19025A072 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 01/25/2019 |
| From: | Ameren Missouri, Mitsubishi Nuclear Energy Systems |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19025A070 | List: |
| References | |
| ULNRC-06479 | |
| Download: ML19025A072 (14) | |
Text
. MNES Mitsubishi Nuclear Energy Systems Attachment A Mitsubishi Responses to NRC WJP RAIs Question No. I Provide refueling outage and date thatthe waterjet peening was applied to the subject dissimilar metal welds.
Response to Question No. I Implementation of water jet peening (WJP) at Callaway was completed during RF22; Fall 2017 refueling outage.
Question No. 2 Section 5.2.2 of the relief request discusses peening process. Discuss deviations between the field application and the performance (mock-up) demonstration and/or peening procedure qualification.
Response to Question No. 2 With exception to one documented deviation (discussed below), all aspects of the qualification testing critical parameters, as implemented at Callaway, were achieved and stayed within the qualified acceptance criteria.
Vendor NCR SP-1Z-052 was written to document a post-calibration issue associated with the A High Pressure Pumping System (HPPS). For reactor vessel nozzle WJP, a flow rate range of 45L/min [11.89 gpmJ and 49L/min [12.94 gpm] has to be achieved to satisfy the qualification testing requirements; however, for the HPPS equipment an accuracy of +/-O.5l4%Ref 10 was established to ensure stable flow control. Prior to implementation of WJP (beginning of RF22), a pre-calibration of the HPPS flowmeters was confirmed acceptable and achieved the required accuracy of+/-O.5l4%Ref 10 Upon completion ofWJP implementation (end of RF22), a post-calibration was performed and the flowmeter accuracy was measured to be
..339%Ref. 10 which exceeded the established acceptance criteria.
A thorough review of the real time recorded parameter data files determined that with exception to the Bravo-Hot Leg (B-HL), all reactor vessel nozzles which were peened with the A HPPS achieved the minimum required flowrate of 45L/min [1 1 .89 gpm]. Based on WJP tooling position data, it was determined that this occurred only during the WJP process for this reactor vessel nozzle for only 3 seconds. Provided below is an extract of the real time recorded data applicable to the B-HL low flow instance. This particular reactor vessel nozzle required three WJP passes [called steps per the Mitsubishi WJP process] to effectively cover the dissimilar metal weld (DMW) region. As can be seen, the low flow instance occurred on the 2nd of 4 WJP scanning passes (4 scans required to effectively WJP a given location before the WJP nozzle advances to the next step) on the 3rd WJP step.
O:mes) (times) (des) (in} (psi) tga/rnin) (hi/mm) (L/mn)
Number of Data Number of times for Data ?axis V axis WJP WJP flow WJP scan Number WW flow times for step scanning number Date/Time angle position pressure rate speed CMNES) rate 3 2 13825 1124:11 172 72008 9263f3 12279 -385 138Z5 4647602 3 2 13826 11:24:12 171.7 7.2008 9286452 12.2845 3.S5 13826 46.49683 3 2 13827 11:24:13 1713 72008 9286452 122902 -3.856 13827 46.51841
- Note that due to the increased uncertainty documented from the post-calibration of the A HPPS, the allowable minimum flowrate was changed from 45Umin (11.89 gpm) to 46.526 Umin (12291 gpm) to account for the -3.39% accuracy as part of the data file evaluation process.
A visual representation of a typical reactor vessel WJP application, as it applies to the B-HL at Callaway, has been provided in Figure 1 On this figure, an overlay of the WJP process has been included and identifies the WJP steps and scans required.
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.IvIri Mitsubishi Nuclear Energy Systems Buttering (Alloy 82/1 82) Safe-end to Buttering Outside Weld (Alloy 82/1 82) rt Step (4 scans)
.j
\/ 3rd Step (4 scans) 2Step (4 scans)
I Red Line Required WJP Application Region L Blue Lines = WJP Steps (Passes) to Cover Required Region Figure 1 B-HL Reactor Vessel Nozzle WJP Application The adjusted actual lowest recorded flowrate for this occurrence by the WJP operational software, neglecting the -3.39% accuracy issue, was 46476L/min [12.278 gpm]. However, once the -3.39% accuracy is accounted for, the actual flowrate was 44.900LImin [11.861 gpm], which equates to an approximate 0.24% deviation from the required minimum 45L/min [1 1 .89 gpmJ. This deviation is considered insignificant since the other scanning passes, i.e. scans 1 3, and 4, at the 3rd step location, the adjusted flowrate was greater than the 45L/min minimum and given the 3 second duration, the region can be considered effectively peened. Furthermore, from the process qualification testing documented in DUS15O319F7 the measurement uncertainty ofthe utilized flowmeter (for process qualification) was +/-0.3% as documented in Section 1 1 .9.7 of Report NS-RPT-1 00004Ref 8 Accordingly, the reported deviation of 0.24% is less than to the 0.3% allowed uncertainty from WJP process qualification.
All other aspects ofW]P critical parameters and associated acceptance criteria were achieved at Callaway.
A full consideration and evaluation of all real time recorded data files and parameters has been performed in Report NSRPT1OOOO4Refs.
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iiriI Mitsubishi Nuclear Energy Systems Question No. 3 A) (1)
Difference in the uncertainties caused by the measurements in the calibration method and the measurements in a mockup.
Response to Question No. 3 A) (1)
There is no difference in the uncertainties of the X-ray residual stress measurements in the calibration method and the X-ray residual stress measurement in a mockup 6 The calibration contains the following two processes:
a) Determination of the X-ray Elastic Constant As described in Appendix 1 stress is calculated from lattice spacing of the diffraction plane obtained by a diffractometer. In this calculation, an X-ray elastic constant is necessary. The X-ray elastic constant is a parameter indigenous to a diffraction plane of a material. Accordingly, the X-ray elastic constant was determined in accordance with ASTM E1426-98 and JSMSSD5O2F 1 In these standards, a relationship between lattice spacing of a diffraction plane and stress is experimentally quantified by carrying out X-ray diffraction on bend specimens with known stress levels. The bend specimen was machined from the same heat of plate material used for the mockup test. The X-ray elastic constant was calculated according to the relationship between slopes of the regression lines of plots and given stress levels. All the X-ray stress measurement results for the mockup were obtained using this X-ray elastic constant.
b) Verification of the Alignment of X-ray Diffraction Instrumentation This is the verification for the X-ray instrumentation to confirm the residual stress of the ferrite powder to be zero within the band of +/-2ksi which is defined in ASTM E91 5-1 0. This verification was performed before and after measurement on each mockup.
Question No. 3 A) (2)
Difference in microstructure between the plate material and weld material that would demonstrate the residual stress in the plate is valid to represent the residual stress in the weld.
Response to Question No. 3 A) (2)
The microstructure of the plate material is different from that of the weld material. However, the two materials have similar elasto-plastic behavior (mechanical strength). Accordingly, the residual stress measured in the plate material is assumed to be a valid representation of the weld. See a) and b) below for additional descriptions of the microstructures and mechanical strength as they relate to these materials.
a) Difference in Microstructure The plate material consists of fine equiaxed grains; whereas, the weld material has columnar grains.
As mentioned above, given similarities in elasto-plastic behavior, the difference in microstructure provides that residual stress on the plate is representative of the weld material.
b) Similarities in Elasto-Plastic Behavior Room temperature yield stress and ultimate tensile strength ofAlloy 600 base metal and weld material are listed in Tables I and 2, respectively. As can be seen, the base metal and weld material yield stress values are very similar to one another. Due to this similarity, along with the consideration of an insignificant microstructure influence, the residual stress profiles of both materials after WJP are expected to be similar.
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AAI IwiI1 Mitsubishi Nuclear Energy Systems Table I Base Metal Room Temperature Yield Stress (YS) and Ultimate Tensile Ref. 2 [Table 4-6]
Strength (UTS)
Elotigation 11LS Room Lernpirature [lwrinon1cchanic1I treatment 1..s (Mla) (net 2 (MIa)
Sotirce KU(_ :l R IV F) penetrations. I ii bolt: .55)) 240 (240j 1 Figure at 3StVt i6t2F).
_(()t) ba S. Ire) \\: annealed or [fli annealed
_ C, 241 : 3))
(
- \fN) (et). pi1&rube llV or i1\V annealed 552 C, ]t)f 35
,*V){)U (Cle]e, re&tttbc ll\\ or ll\ cmnneelel ?5l7 i72
\t)t))) (eam1es Jine&ube <5) CW aiineted . :: 551 : 34)
,\hOO iseaniless ))j)et1e 5*) ( -r annealed ?551 ? 207
\nO() (p):te, )ieei. strip ) I R plate) Annealed > 552 >211 Aa)t) tIi:rglngs) Annealed . le 552 >241 Source: R(*C-M Ldnt 2)10(1. lit bolt: Fture 55t 497) , 240-400 t at 350 C. (()2 F,), 497) 40Ct rods, bars, wire) cw annealed or 11W annealed 2:556 )t)
\0)m)m e:mni)es PPetttm11e 5) 11W or l] f artnea)ed >517 > 172 > is
\t)0 eani1ess pipe&ttthc <5) Uw annealed >
586 >211
\000 real:tieaa pi1e&iuhe >5l (W anticaled >586 >2t17
,\mi() ) plaie. sheet. ti p 1 1 P ))latc) Anneale] > 586 At)tllt (Rmrnjmimi) ?58t . 2:241 30 Table 2 Weld Material Room Temperature Yield Stress (YS) and Ultimate Tensile Ref. 2 [Table 4-8]
Strength (UTS)
S
[Its (i[a) ) --
Lluntalion (4)
Room Irnipu tttiie,,, 3 0 t (6(t°i )
1
>550 d25U >3))
AI2 trated electrode 190 > it)
A 1 52 Coated electrode 550 7t) d2%O _
Question No. 3 A) (3)
Potential differences in residual stress profiles of the weld versus the plate.
Response to Question No. 3 A) (3)
Please consult the response provided to Question No. 3 A) (2).
There is no significant difference between the residual stresses at the weld and that of heat-affected zone (HAZ) in the plate. The measurement points utilized for residual stress measurements are taken in the HAZ and are considered representative of the weld itself.
In both the weld and HAZ ofthe plate, tensile residual stresses occur. Tensile residual stresses are caused by compression plastic strains which occur due to the high heat input caused by welding Ref. 3 Specifically, tensile residual stress in weld and HAZ occurs by the following described processes. During the heating caused by welding, the heated portion exhibits compressive strain because its thermal expansion is constrained by surrounding portions which received less heat input and do not significantly expand. Then Page 5 of 15 13860 Ballantyne Corporate Place, Ste. 250, Charlotte, NC 28277 Tel: (704) 945-2600 Fax: (704) 945-2601 www. mnes-us.com
.. MNES Mitsubishi Nuclear Energy Systems during the cooling that follows, the heated portions like weld metal and HAZ exhibit tensile strain, because the surrounding relatively less heated portions do not significantly shrink. This process occurs in both weld metal and the HAZ. Since the HAZ yield at first in compression and then in tensile, generally speaking, tensile residual stresses at the yield stress level are caused by welding when the strains due to compressive yielding correspond to more than twice of the yield strain of the material. As for Alloy 600, the tensile residual stresses at the yield stress level are caused when the difference between the initial temperature of itself and the maximum temperature due to welding reaches more than approximately 300CN0te 1 The difference between the initial temperature and the maximum temperature of both the weld and HAZ in the plate made ofAlloy 600 become bigger than 3000C due to welding. As a result and as mentioned above, tensile residual stresses occur as part of the cooling process. Therefore residual stresses at both the weld and the HAZ are considered to be on the same level.
Note 1:
Elastic stress a is linearly related to elastic strain by means of the Youngs modulus (Hooks law).
c=EE Where E is the Youngs modulus.
Thermal strain frøm constraining thermal expansion by the temperature difference AT is given by following relationship.
£0 AT Physical property values ofAlloy 600 are as follows:
. Linear expansion coefficient: I x I o o-1
. Yield stress: 300MPa
. Youngs modulus: 200GPa Using these relationships, the temperature difference AT which causes twice as high compressive strain as yield strain ofthe material is calculated.
2 aIE=a AT AT=2a/EIa = 2 x (300 x I 06) / (200 x I O)I (1 x I O)
= 300°C Page 6 of 15 13860 Ballantyne Corporate Place, Ste. 250, Charlotte, NC 28277 Tel: (704) 945-2600 Fax: (704) 945-2601 www.mnes-us.com
.-I;I TI Mitsubishi Nuclear Energy Systems Question No. 3 A) (4)
How is the error in the residual stress measurement on the plate as compared to the error of similar analytical residual stress values in the weld material?
Response to Question No. 3 A) (4)
The question as stated in the RAI is related to the difference between residual stress measurements actually taken in-situ, compared to those produced from analytical simulation of residual stresses. This was not the intent of the residual stress analysis documented in the Report I 001 077.401 Ref. 4 In the documentation of the acceptance of waterjet peening for Callaway, Report 1001077401Ref. 4 the analytical analysis is not performed to demonstrate an accurate analytically determined stress state versus a measured stress state. Rather, the purpose of the analytical study is to confirm that the compressive inner diameter (ID) surface stress state created by WJP is maintained following the application of plant operating cycles of pressure and temperature.
As stated in Report 1OO1O77.4O1 the finite element analytical model of the peened component is manipulated to create a residual stress state on the ID surface that matches that stress state measured during WJP qualification testing (provided by the peening vendor). As stated in lOOlOff.4OJ the analytically determined stress state is conservative relative to that actually measured in similar plates following peening. That is to say thatthe analytical stress state is less compressive in magnitude and depth than that actually measured following WJP.
As delineated in Section 4.3 of Report 1 001 077.401 Ref. 4 the approach taken analytically was to reproduce in a simulation the effects of WJP. The methodology developed for this simulation, as documented in Report 10010f7305Ref. 5 is used to determine if there is any potential of compressive residual stress relaxation (stress washout) effects due to long term operations of the plant. Moreover, when this methodology was used to simulate the effect of W]P for Callaway, a comparison to the actual achieved test data (measured residual stress values from mockups) was performed and documented in Report I 001 07f305Ref. 5 As concluded in Section 5.0 of Report 1 001 0773Q5Ref. 5 and relative to the reactor vessel nozzles (hot and cold legs), the methodology was concluded to be representative ofthe peened stress state obtained from measured testing. The magnitude ofthe surface stress achieved analytically is conservative when compared to testing results, inclusive of the general slope of the compressive stresses and achieved compressive stress depth. Thus, the manner in which the analytical stress state is achieved is not an issue, only that the calculated stress state matches the measured residual stress state following peening in magnitude and profile (stress magnitude and stress depth).
This finite element model was then subjected to the full series of plant operating transients (pressure and temperature) in an elastic plastic analysis in order to show that the operating cycles did not washout or eliminate the compressive stresses on the ID surface at plant operating conditions. There is no concern relative to the error in the residual stress methodology, as the analytical results are compared directly and validated with measured WJP results, and it is demonstrated that the analytical results which are used in the subsequent stress analysis are conservative.
Given the conservative nature of the utilized analytical methodology and type of finite element model developed for the reactor vessel nozzle and weld area, the simulated effects of WJP on both plate and weld material can be considered representative of actual WJP effects at Callaway. Accordingly, errors or uncertainties attributed to residual stress measurements are limited to X-ray diffraction techniques for obtaining actual residual stress values from the mockups. An assessment of these uncertainties was performed in Report DUS-16OO566, as summarized in Section 3.4 of Report lOOJOff.4Ol4. Based on this assessment and pursuant to ASTM standards E915 and E2860, the X-ray diffraction techniques utilized met the acceptance criteria requirements of these ASTM standards. As stated in Section 3.4 of Report I 001 077.401 Ref. 4 accounting for this acceptance criteria in the as measured residual stress values of the mockups demonstrates mitigated stresses are produced to the specified depths, and that the threshold for crack initiation is at least +1 O-ksi, thus providing margin for acceptance of the measurement uncertainties.
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Mitsubishi Nuclear Energy Systems Question No. 3 A) (5)
How do the original tensile stresses in the plate mockup compare to stresses in the weld in the field?
Response to Question No. 3 A) (5)
The original tensile stresses in the plate mockup are assumed to be equivalent or higher than the weld in the field due to the process for which the mockup is fabricated. Especially, tensile stresses of the weld surface of the plate mockup are induced by grinding, which is recognized as the method that creates extremely high tensile stress. The presence of these original residual stresses prior to WJP was confirmed in Report DUS-15O3197.
Question No. 3 B)
Provide the tabular data used to demonstrate compliance with the criteria for depth of compression in the mockup, including error associated with measurement.
Response to Question No. 3 B)
Table 3 shows the residual stress measurement results ofthe plate mockup (TP No. 47 & 48) described in the Figure 5.1.6, Test 1, of Report DUS-15O319 .
For Callaway, site implementation of WJP was conducted in a manner where the WJP application pattern was identical to that of what was utilized in for qualification testing to achieve the WJP effective range of a diameter of 40 mm [1 .57] (i.e. distance from the WJP nozzle application center is 20 mm [0.79] radially). It is important to understand that the 20 mm
[0.79] radial boundary was established as part of the qualification program by measuring the effects of wJP at three depths (0 mm [0.000], 0.5 mm [0.020] and 1.0 mm [0.039]) at six radial locations (0 mm
[0.00], 15 mm [0.59], 20 mm [O.79J, 25 mm [0.98], 30 mm [1.18], and 35 mm [1.38]). Table 3 shows that a measured WJP depth of I mm [0.039] was achieved up to 20 mm [0.79]; however, residual stress measurements beyond the 20 mm [079] location did not achieve the depth requirement of I mm [0.039]
delineated in Ameren Specification SlQ85(Q)f .
Table 3 shows that there is in fact a peening effect beyond the 20 mm [0.79] radial boundary down to a depth of 0.5 mm [0.020] and up to a radial distance of 35 mm [1.38]. Since the depth of peening effect was less than the Ameren Specification 5-1 085(Q) 1 1 required I mm [0.039] depth, the effects of peening beyond 20 mm [0.79] are not considered for qualification and demonstration ofthe Mitsubishi WJP process.
Please consult the response provided to Question No. 3 A) (1 ) to understand how measurement uncertainties have been accounted for in the WJP program.
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. Ivw1 Mitsubishi Nuclear Energy Systems Table 3 Qualification Test I (TP4Z + TP48)
Residual Stress The average of the weld line Distance direction and the from the
- The orthogonal orthogonal application Distance from The weld line direction to the direction to the center the surface direction weld line weld line (mm) (mm) (MPa) (MPA) (MPa)
Before WJP 0 [0.00] 0 [0.0001 227 902 565 n/a 0 [0.00] 0 [0.000] -486 -585 -536 0
0 [0.001 0.5 [0.020] -284 -264 -274 0 [0.00] 1.0 [0.039] -40 -26 -33 15 [0.59] 0 [0.000] -462 -556 -509 °-
15 [0.59] 0.5 [0.020] -231 -279 -255 15 [0.59] 1.0 [0.039] -30 -62 -46
- c 20 [0.79] 0 [0.000] -492 -572 -532 20 [0.79] 0.5 [0.020] -268 -271 -270
-43 a
20 [0.79] 1.0 [0.039] -1 -84 After WJP 25 [0.987 0 [0.0007 -541 -556 -549 0
25 [0.98] 0.5 [0.0207 -157 -237 -197 e Q 0 25 [0.987 1.0 [0.0397 24 -31 -4 30 [1. 18] 0 [0.0007 -457 -363 -410 30(1.187 0.510.0207 -136 -118 -127 30 [1. 187 1.0 [0.0397 20 -24 -2 .
35 [1.387 0 [0.0007 -434 -254 -344 0
3511.387 Q.5[O.0207 -136 -114 -125 3511.387 1.O[OO397 103 775 109 NOTES:
Note 1 All directions of residual stress measurements were determined to achieve a compressive state up to a depth of 1 .0 mm [0.039], thus the qualified radial boundary (from center of WJP nozzle) was established at 20 mm [079].
Note 2: Not all directions of residual stress measurements (shaded areas) were determined to achieve a compressive state up to 08fl(Q)F 11 requirements for the reactor a depth of 1 .0 mm [0.039]. Since this did not meet Ameren Specification 5-1 vessel nozzles, the effect of WJP beyond the 20 mm [0.79] radial boundary is not considered in the qualification and demonstration of the Mitsubishi WJP process.
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ivIr1 Mitsubishi Nuclear Energy Systems Question No. 3 C)
Does the number of water jet peening applications used in the mockup equal the number of applications used in the field at Callaway for the subject welds?
Response to Question No. 3 C)
Yes, the number of WJP applications are the same as WJP was applied 4 times for qualification testing and as part of implementation at Callaway, as documented in Report NS-RPT-1 00004Ref 8 Note the following:
I Qualification Testing: WJP nozzle travel speed was set at I 00 mm/mm [394 1mm], i.e. the upper limit in allowable range of96mm/min [3.78/min]to 100 mm/mm [3.94/mm], in each application ofWJP and repeated 4 times on the mockup.
. Callaway Implementation: WJP nozzle travel speed was set nominally at 98 mm/mm [3.86 1mm], i.e.,
conservatively stay within the allowable range of 96mm/mm [3.78/mini to 100 mm/mm [3.94/mm],
since higher travel speeds beyond 100 mm/mm [3.94/mm] will result in less WJP effect, in each application and repeated 4 times on the Callaway nozzles.
Question No. 3 D)
Discuss whether the peening qualification was performed on a mock up that is the same size as in the field (i.e.,
same pipe diameter and wall thickness). If not, discuss the impact of this difference on the peening applied to the mock-up specimens, and how it will provide the same results as peening on the welds in the field.
Response to Question No. 3 D)
The mockup used for qualification testing was not the same size as found in the field. As described in Report DUS-1 5031 9Ref 7 it was a flat plate with a thinner cross-section. The flat plate (200 mm [7.87] x 200 mm [7.87] x 20 mm [0.78]) was used because the diameter of the actual reactor vessel nozzle inner diameter is nominally 700 mm [27.56] and large enough to ignore the curvature when considering the size ofthe WJP effective range of 20 mm [0.78] radially (refer to the image below). As shown below in Figure 2, the comparative difference between a flat plate and the inner curvature of the reactor vessel nozzle is 0.57 mm [0.022]. The effectofthis small differences is considered insignificant since the as implemented application distance, i.e., distance between the bottom ofthe WJP nozzle and the peened surface, was set and controlled at 130 mm [5.12]; however, qualification testing as it relates to WJP effectiveness was performed atthe upper allowable limit 140 mm [5.51], as found in Report DUS15O319F7.
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. IvII MItsubishi Nuclear Energy Systems Vv)PNn7Z Distance between surfaces of pipe and flat _______,/
plateat2Omm [0.79] frornthe application center is much smaller than application distance. Application distance has an allowable range of 120mm
[4.72] to 140mm [5.51], as found in DUS 150319Ref.8. 130mm [5.11] is the Unit : mm Co established value for implementation.
_J -
In Application distance Nj Distance between surfaces of pipe and flat plate at 20 mm from the application center Surface ofpipe Surface of flat plate>
20
\J 20 dc
[0.787J /
N [0.787] C WIP effective range has a diameter of4O mm [1.57]
(i.e., distance from the application center is 20 mm [0.79]).
Figure 2 Image of WJP Application to Plate Versus Pipe with Curvature Question No. 3 E)
Page 8 of 14 of the relief request states that the test coupons are thinner than the actual pipe wall thickness, but it is thick enough. Discuss whether this statement is verified and validated based on the testing on mockup of the actual pipe wall thickness and the thinner test coupon.
Response to Question No. 3 E)
The test coupons used for qualification testing are thinner than the actual Callaway reactor vessel nozzles.
As found in Section 3.1.2.6 and 5.1.4 of Report 10010774Q1Ret4, components which are fabricated from thicker materials (greater than a few millimeters), will see a greater influence from the WJP effect. The surface compressive residual stresses are created by the WJP process when a small surface layer of the material undergoes plastic deformation. This small plastic deformation only affects the surface of the material since the unaffected material underneath works to restrain the surface deformation which results in a surface compressive surface layer. If the materials are thin (less than a few millimeters), then the induced stresses at the surface can cause the material underneath the surface layer to deform, thus reducing its ability to restrain the surface deformation.
Based on this, utilizing a test coupon which is thinner than the actual reactor vessel nozzle wall thickness is conservative. For the qualification testing performed, the thinner test coupon provides less material restraint due to lack of surrounding material, which allows the resultant compressive residual stress to partially relax at application of WJP.
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. iviFi Mitsubishi Nucear Energy Systems Question No. 4 (a)
Describe whether during qualification tests a thin layer of oxide is applied to the mockup so that qualification test is performed to mimic the field condition. If not, justify why a thin oxide layer was not removed prior to peening in the field.
Response to Question No. 4 (a)
A thin layer of oxide was not applied to the mockup given its lack of ability to influence the effects of WJP.
The reasoning for this is found in Section 3.3.2 of Report MRP-335 as quoted below:
The oxide thickness on plant materials are in the neighborhood of I pm thick, and thus are much too thin and too structurally weak to interfere with peening, which involves dimensions on the order of I mm, i.e.,
I 000 times larger.
Question No. 4 (b)
Discuss whether peening qualification tests were performed to show that the thin oxide layer does not change the peening effect on the subject weld. If not, discuss how the qualification tests are sufficient to demonstrate the compressive effect of peening in the field.
Response to Question No. 4 (b)
Please consult the response provided to Question No. 4 (a).
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. I;w4 Mitsubishi Nuclear Energy Systems References Ref. I : Standard for X-Ray Stress Measurement (2002) Iron and Steel (JSMS-SD-5-02), The Society of Materials Science, Japan Ref. 2: François Cattant, Materials Ageing in Light Water Reactors - Handbook of Destructive Assays, Editions Lavoisier, 2014 Ref. 3: T.Terasaki, Journal ofthe Japan Welding Society, Vol. 78, No. 2 P55, 2008.
Ref. 4: Report I 001 077.401 Mitigation of Reactor Vessel Hot and Cold Leg Nozzle DMWs and Reactor Vessel Bottom Mounted Nozzles and Associated DMWs by Water Jet Peening Ref. 5: Report I 001 077.305, Development of Water Jet Peening Simulation Finite Element Models Ref. 6: Report DUS-160056, Calculation Method and Uncertainties of Residual Stress by the X-rays Stress Measurement Ref. 7: Report DUS-1 5031 9, Water Jet Peening Process Qualification Test Report Ref. 8: Report NS-RPT-1 00004, WJP Implementation Final Report for Callaway Ref. 9: Report EPRI MRP-335, Revision 3-A, Materials Reliability Program Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement [PeeningJ Ref. 10: WJP Work Instruction WJP-Wl-103-A-02, High Pressure Pump System (HPPS) Flow Meter Calibration Ref. I 1 : Ameren Specification S-I 085 (Q), Specification for Mitigation of Reactor Vessel Hot and Cold Leg Nozzle Dissimilar Metal Welds and Reactor Vessel Bottom Mounted Nozzles and Associated Dissimilar Meta Welds at Callaway Energy Center Page 13 of 15 13860 Ballantyne Corporate Place, Ste. 250, Charlotte, NC 28277 Tel: (704) 945-2600 Fax: (704) 945-2601 www.mnes-us.com
. MNES Mitsubishi Nuclear Energy Systems Appendix I Principle and Method of X-ray Stress Measurement Ref. I (1) Principle In X-ray stress measurement of a crystalline material, the strain in the crystal lattice is measured and the associated residual stress is determined from the elastic constants assuming a linear elastic distortion of the appropriate crystal lattice plane (Figure 1).
When the X-ray beam reaches the surface of a crystalline material, it is diffracted by crystal lattice. The diffraction occurs only when the wavelength of X-ray, the beam angle and the lattice spacing satisfy the relationship called Braggs Law (Figure 2). By using this relationship, lattice spacing U is estimated.
Surface of specimen Lattice spacing U (example)
E1liliP Change in a lattice spacing d caused by stress Tensile stress decreases U.
Compressive stress increases U.
ISsLom Figure 1 Schematic Illustration for Effect of Stress on Lattice Spacing of a Metal Path ofX-ray beam with a wavelength A Braggaw Figure 2 Braggs Law (2) Apparatus and Method
. Figure 3 shows an example of the apparatus for X-ray stress measurement system (diffractometer). This consists of a head equipped with an X-ray emission source and a detector, a sample stage and computer system for data processing.
. To carry out X-ray stress measurements, the specimen is placed on the sample stage of the X-ray diffractometer and exposed to an X-ray beam that causes diffraction patterns depending on the beam angle and the lattice spacing of the sample. By scanning through an arc of the radius about the specimen (changing the beam angle), the intensity of diffracted X-ray is measured. As a result, the diffraction peaks can be positioned and the necessary calculations are made for quantification of stress.
. The residual stress profile in the depth direction can be determined by successive material removal by electro polishing and subsequent stress analyses.
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AIiIiI
. iviri Mitsubishi Nuclear Energy Systems X-ray emission source and detector .
Figure 3 Appearance of X-ray Stress Measurement System Page 15 of 15 13860 BaNantyne Corporate Place, Ste. 250, Charlotte, NC 28277 Tel: (704) 945-2600 Fax: (704) 945-2601 www.m nes-us.com