energies Article
Evaluation of Interface Defects in Inaccessible Reactor Shrink Fit Nozzle Welds Using Ultrasonic Waves Jaesun Lee 1 and Younho Cho 2, * 1 2
*
New Transportation Systems Research Center, Korea Railroad Research Institute, Uiwang 16105, Korea;
[email protected] School of Mechanical Engineering, Pusan National University, Busan 46241, Korea Correspondence:
[email protected]; Tel.: +82-51-510-2323
Academic Editor: Peter Hosemann Received: 11 January 2017; Accepted: 20 April 2017; Published: 25 April 2017
Abstract: This study proposes an effective method to inspect inaccessible nuclear power reactor head nozzles using interface waves that propagate along the shrink fit boundary of a reactor head. The reactor head is relatively thick, which makes it difficult to inspect from the outside by conventional ultrasonic testing. However, interface waves can propagate a long distance from a fixed transducer position. The inside of the nuclear reactor has limited access due to the high radiation, so the transducers are located outside the nuclear reactor head, and interface waves propagate into the nuclear reactor to detect defects. A numerical simulation and experiments were carried out to validate the method. Various defect cases that simulate field failures are also presented, and the proposed technique shows satisfactory defect classification. Keywords: nuclear facility; ultrasonic interface wave; defect detection; nondestructive testing; finite element method; inaccessible nozzle
1. Introduction For their safe operation it is very important to monitor the conditions of nuclear power plants efficiently and to detect defects. Traditionally, to prevent failures schedule-based maintenance was performed to inspect nuclear power facilities, however, inspection schemes are moving away from schedule-based maintenance toward condition-based maintenance (CBM). Condition-based maintenance is defined as maintenance when a need arises. The maintenance is performed based on a structure’s condition in which defects are identified or grow beyond some standard. Ideal condition-based maintenance allows minimizing the cost of storing spare parts, system downtime and time spent on maintenance. For condition-based maintenance inspections, a proper diagnostic method and real time data collection are needed for each component. Currently the nuclear power system industry still relies on following schedule-based maintenance, but we anticipate that CBM will be applied in nuclear power facilities sooner or later. The risk of failure due to defects has increased due to the long-term use of nuclear power plants. Proper inspection methods for defect identification and monitoring defect growth are needed for the safety diagnosis and life prediction for the main equipment in nuclear power plants. There are several ways of diagnosing plant conditions. First, diagnostic tests to classify candidate anomalies are repeated until an anomaly is identified. Second, an assumption about the nature of a detected anomaly is made, and confirmed by tests. Third, a standard set of diagnostic tests is applied, and the anomaly is diagnosed [1]. Recently, nuclear power facility safety issues have become of great concern to people. The sizes and shapes of nuclear power plant components usually do not
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follow standard commercial specifications. Standard pipes have suitable inspection methods such as long range ultrasonic testing (LRUT), ultrasonic testing (UT) and phased array ultrasonic testing (PAUT). Transducers and inspection systems based on those methods are commercialized for standard sized pipelines. Therefore, unique inspection methods and systems are required to meet the high safety demands of nuclear power plants. Currently nuclear power plant inspection is performed using regular schedule-based maintenance systems. Ultrasonic non-destructive evaluation (NDE) is employed periodically on nuclear reactors and nozzle welds to inspect any defects or defect growth during periodic overhaul periods. The need for continuous online monitoring for stability safety checks has increased. To accomplish online monitoring of a nuclear reactor, radiation hardened materials and wireless communication under high temperature and radiation condition must be developed. However, achieving the purpose of online monitoring for nuclear power plant components still has a long way to go. Recently, PAUT was employed for precise defect detection and sizing [2]. Nuclear power plant components inspection by LRUT such as nuclear power plant valves [3,4], pipes [5–10] and steam generator tubes [11–14] has been reported. Control element driving mechanism (CEDM) nozzles are attached to and penetrate through the reactor head. However, the reactor head is relatively thick, which makes it difficult to inspect it from the outside of the reactor to monitor the weld conditions inside the reactor by conventional UT due to the signal attenuation. Reactor head nozzles are generally inspected by conventional UT during the in-service inspection (ISI) period from inside of the nuclear reactor with a remote robot system due to the high radiation [15–20]. Remote robot systems are a good solution for weld inspections on reactor nozzles, but this method is only possible during ISI, so an alternative inspection method for condition-based maintenance is proposed in this paper. The penetrated nozzle on the reactor head can be inspected using pseudo interface waves, which propagate along the boundary between the nozzle and reactor head. Using this inspection technique, the defects on the weld and its interface can be identified from outside the nuclear reactor head. The characteristics of pseudo interface waves propagating in a nuclear reactor nozzle were presented in a previous study [21,22]. Previous works are however limited to experimental studies of reactor nozzle welds on simplified defect model samples using interface waves. This paper presents a numerical model analysis for fault identification using pseudo−interface waves. The pseudo-interface wave propagation characteristics and scattering from a defect and weld on a reactor nozzle were evaluated, and the method was validated experimentally for various defect locations and sizes. 2. Interface Wave Propagation Theory Rayleigh waves are one of the interface waves that travel in solid-vacuum half space. In isotropic solids, the particle motion is elliptical and retrograde for shallow depths with respect to the propagation direction. Scholte waves exist under the interface condition of fluid-solid media [23]. Most of the energy of a Scholte wave decays exponentially in solid and fluid media. Some studies using Scholte waves and quasi-Scholte waves were presented to validate the propagation characteristics [24–28]. Stoneley waves propagate at the interface between two solid media [29]. Some surface wave applications can be found in earlier papers [30–34]. Surface waves propagate on half infinite media and Stoneley waves propagate along the interface between to different solid materials. The displacement of an interface wave on a plate is defined as follows [35,36]: u = u(z)eikx , w = w(z)eikx
(1)
where u and w is the displacement in the x and z directions. The term eiωt has been omitted hereafter. The coordinate system is shown in Figure 1. The unknown amplitudes u(z) and w(z) can be defined as: u(z) = [( Ae−kαz + Bekαz ) − β(Ce−kβz − Dekβz )]eikx
(2)
w(z) = i [α( Ae−kαz − Bekαz ) − (Ce−kβz + Dekβz )]eikx
(3)
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where where
α2
c2 c2L
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= 1− , = 1 − ,
β2
= 1− =1−
c2 c2T
ω k.
,c = , = .
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where
=1−
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,
=1−
,
= .
Figure Figure 1. 1. Coordinates Coordinates of of interface interface medium medium 11 and and medium medium 2. 2.
The stress stress components componentsare: are: The + 2kβ 2 (Ce−kβz −−Dekβz )]e]ikx σz = = iµ[− [−k(1 (1 + + β2)( )( Ae−kαz + + Bekαz )) +
(4) (4)
Figure 1. Coordinates of interface medium 1 and medium 2.
= [−2 ( − ) + (1 + )( + ] σxz = µ[−2kα( Ae−kαz − Bekαz ) + k(1 + β2 )(Ce−kβz + Dekβz ]eikx
(5) (5)
The stress components are:
The at between 11and The boundary boundary conditions conditions at the the interface between media and are:] )( ) +media (1 2 = [− +interface + − 22are: = [−2
(
−
) + ((1 m1+ ))
) (m1) (m2) ( () = ) u (m2 u(m1 = ( , )w , ( )==w ( ,) ,σz
)( (m2)) +((m1)) ]
( = = σz
(4) (m2))
= σ(xz =
,, σxz
(5)
(6) (6)
The boundary conditions at the interface between media 1 and 2 are:
where superscript superscript (m1) (m1) and and (m2) (m2) indicate indicate medium medium 11 and and 2, 2, respectively. respectively. To To satisfy satisfy the the boundary boundary where ( ) ( ) ( ) ( ) ( ) Equation ( ) ( )a nontrivial solution when the determinant condition,when when zz == 0, 0, the the system system (7) has is zero: zero: (6) =Equation , ( )(7) = has = ,solution = when the determinant condition, a, nontrivial is superscript (m1) where satisfy the boundary and (m2)indicate medium 1 and 2, respectively. To ((1)) − (2() ) −(1 (1 + −2 σz − σz when z = 0, the −−2 2β 2when g B1 0 −2β(7) + β21 )g solution −+ 1 + )β21Equation 0 is zero: condition, system the determinant 1 has a1nontrivial 2 2α ((1)) (2() ) (1 + 22α2 g 1 + β2)1 −−(1 1 ++β22 g) σxz D1 = 0 0 − 1 − σxz ( ) 0= . == ( ) (1 ) ) ( 1 ) ( 2 ) + −2 − −2 −(1 + u( ) − u ( ) 1 0A2 0 1 β1 − 1 β2 −1 − () () (1 +1 ) 2 2− 0 (2) α1 − 0 − − −1 −α2 −(1 + 1 )1 w((1)) − = = 0C2 (7) −w ( ) − ( ) ( )
− −
1 − −1
( )
( )
−1 −
(7) (7)
0 0
1
Figure Figure 22 shows shows wave wave amplitude amplitude distributions distributions in in the thethickness thicknessdirection. direction. The The interface interface wave wave Figure 2 shows wave amplitude distributions in the thickness direction. The interface wave amplitude distributions in the thickness direction are calculated by an analytic approach using amplitude distributions the thickness direction are calculated by an analytic approach using the the amplitude distributions inthe the finite thickness direction are calculated by an analytic using the wave ininFigure 2a2a and element numerical approach in Figure 2b. Displacement u(z) waveequation equation Figure and the finite element numerical approach inapproach Figure 2b. Displacement wave equation in Figure 2a and the finite element numerical approach in Figure 2b. Displacement is an in-plane displacement and w(z)and is anw(z) out-of-plane displacement. The out-of-plane u(z) is anu(z) in-plane displacement an out-of-plane out-of-plane displacement. Thedisplacement out-of-plane is an in-plane displacement and w(z) is is an displacement. The out-of-plane is highest at the interface and becomes zero further away from the interface. This study examines a displacement is highest at theatinterface and zerofurther further away the interface. This study displacement is highest the interface andbecomes becomes zero away from from the interface. This study examines a twomade layered made 316stainless stainless steel. two layered structure ofstructure 316 made stainless steel. examines a two layered structure ofof316 steel.
(a)
(b)
Figure 2. Wave amplitude distributions in the thickness direction, (a) theoretical analysis, and (b) Wave amplitude distributions in the thickness direction, (a) theoretical analysis, and finite element analysis. Square symbols indicate u(z), and triangle symbols represent w(z).
Figure 2. element analysis. Square symbols indicate u(z), and triangle symbols represent w(z).
(a)
(b) finite
(b)
Figure 2. Wave amplitude distributions in the thickness direction, (a) theoretical analysis, and (b) finite element analysis. Square symbols indicate u(z), and triangle symbols represent w(z).
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3. Nuclear Reactor Head Nozzle Model Energies 2017, 10, 589
3. Nuclear Reactor Head Nozzle Model
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In the small integrated nuclear reactor system illustrated in Figure 3, the control element drive In the Reactor small integrated nuclear reactor system illustrated in Figure 3, the control element drive 3. Nuclear Head Nozzle Model mechanism (CEDM) is installed through the nuclear reactor head. The reactor head and the nozzle mechanism (CEDM) is installed through the nuclear reactor head. The reactor head and the nozzle the small integrated nuclear reactor system illustrated in Figure 3, the the control element drive pipe pipe are In attached using conditions and welded at theofend shrink fit boundary. are attached usingshrink shrink fit fit conditions and welded at the end the of shrink fit boundary. The mechanism (CEDM) is installed through the nuclear reactor head. The reactor head and the nozzle The CEDM andreactor reactorhead headare areconnected connected using a J-groove weld to prevent radiation leakage. CEDM nozzle nozzle and using a J-groove weld to prevent radiation leakage. pipe are attached using shrink fit conditions and welded at the end of the shrink fit boundary. The The proposed interface wave inspection method is applied for monitoring this weld. The proposed interface wave inspection method is applied for monitoring this weld. CEDM nozzle and reactor head are connected using a J-groove weld to prevent radiation leakage. The proposed interface wave inspection method is applied for monitoring this weld.
Figure 3. Schematicofofan anintegrated integrated small reactor system. Figure 3. Schematic smallmodular modular reactor system. Figure 3. Schematic of an integrated small modular reactor system.
3.1. Finite Element Model Analyis for Reactor Nozzle
3.1. Finite Element Model Analyis for Reactor Nozzle
FiniteElement elementModel modeling was to verify the interface wave propagation pattern and 3.1. Finite Analyis for performed Reactor Nozzle
Finite element modeling wasABAQUS/CAE performed to6.12 verify the interface wave propagation reflection signal analysis using (DASSAULT SYSTEMES, Providence, RI,pattern USA). and Finite element modeling was performed to6.12 verify the interfaceSYSTEMES, wave propagation patternRI, and reflection signal analysis using ABAQUS/CAE (DASSAULT Providence, The detailed specifications of the CEDM nozzle model are shown in Figure 4, and the meshUSA). reflection signal analysis using ABAQUS/CAE 6.12 (DASSAULT SYSTEMES, Providence, RI, USA). The detailed specifications of Table the CEDM model in Figure andand the mesh information is shown in 1. Thenozzle material usedare forshown both the reactor 4, head nozzleinformation is 316 The detailed specifications of the CEDM nozzle model are shown in Figure 4, and the mesh stainless steel. The excitation frequency 1 MHz, wavelength of the interface wavestainless is 0.0027 steel. is shown in Table 1. The material used is for both and the the reactor head and nozzle is 316 information is shown in Table 1. The material used for both the reactor head and nozzle is 316 m. The mesh size is set 1/10 ofand the the wavelength for proper wave propagation inmesh the size The excitation frequency is as 1 MHz, interface wave is characteristics 0.0027wave m. The stainless steel. The excitation frequency iswavelength 1 MHz, and of thethe wavelength of the interface is 0.0027 model. The edge of the nozzlewave and propagation reactor head is set as an absorbing boundary to is setnumerical as 1/10 of the wavelength for proper characteristics in the numerical model. m. The mesh size is set as 1/10 of the wavelength for proper wave propagation characteristics in the eliminate an unexpected reflections from the boundary. The edge of themodel. nozzleThe andedge reactor head is setand as an absorbing eliminate an unexpected numerical of the nozzle reactor head isboundary set as an to absorbing boundary to eliminate an the unexpected reflections from the boundary. reflections from boundary.
Figure 4. Interface wave propagation model of the CEDM nozzle model.
Figure 4. Interface wave propagation model of the CEDM nozzle model. Figure 4. Interface wave propagation model of the CEDM nozzle model.
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Table 1. CEDM nozzle modeling specifications. Table 1. CEDM nozzle modeling specifications. Frequency Frequency Wavelength Wavelength Mesh Size Mesh Size Element Type Element Type
1 MHz 1 MHz 0.0027 m 0.0027 m 0.00027 m 0.00027 m CPE4R (plane strain conditions) CPE4R (plane strain conditions)
The interface interface waves waves propagate propagate with with strong strong directivity directivity and and less less distribution distribution in in the the circumferential circumferential The direction [22]. [22]. Figure Figure 55 shows shows the the interface interface wave wave propagation propagation and and reflection reflection from from the the finite direction finite element element model of of the the CEDM CEDM nozzle. The interface interface wave wave propagation propagation pattern pattern at at different different times times is is depicted in model nozzle. The depicted in Figure 5a–c. The excitation point is on the nozzle surface with the outside of the reactor head and the Figure 5a–c. The excitation point is on the nozzle surface with the outside of the reactor head and the weld on the the reactor reactor head headinside insidethe thereactor reactorisisinspected. inspected.The Theinterface interface wave energy concentrated weld on wave energy is is concentrated at at the interface and propagates along the axial direction. The propagation distance of the interface the interface and propagates along the axial direction. The propagation distance of the interface wave wave 430from mm the from the excitation location, it is reflected the boundary the weld andend the is 430 is mm excitation location, and itand is reflected fromfrom the boundary of theofweld and the end ofreactor the reactor head. The interface propagation velocity in this study 2.6 mm/µs. of the head. The interface wavewave propagation velocity in this study is 2.6ismm/μs.
(a)
(b)
(c) Figure 5. Interface element analysis Figure 5. Interface wave wave propagation propagation model model of of the the CEDM CEDM nozzle nozzle model model of of finite finite element analysis at at (a) initial initial moment; moment; (b) (b) 100 100 µs μs and and (c) (c) 150 150 µs. μs. (a)
The finite element model of defects in the nozzle weld is depicted in Figure 6. The J-groove weld The finite element model of defects in the nozzle weld is depicted in Figure 6. The J-groove weld is is modeled at the end of the nozzle and attached to the reactor head. The interface wave propagates modeled at the end of the nozzle and attached to the reactor head. The interface wave propagates along along the boundary of the nozzle and the reactor head. Three different defects are modeled to the boundary of the nozzle and the reactor head. Three different defects are modeled to investigate the investigate the reflection from the boundary of the weld and the end of the structure. The defect reflection from the boundary of the weld and the end of the structure. The defect locations are chosen locations are chosen based on the possibility of defect initiation in the manufacturing process and based on the possibility of defect initiation in the manufacturing process and during operation. during operation. For analysis convenience, each part of the model components is set with a different mesh type. For analysis convenience, each part of the model components is set with a different mesh type. This can help with the computation time and memory. The interface wave is generated on the outside This can help with the computation time and memory. The interface wave is generated on the outside of the reactor head and it propagates along the interface and reflects from the weld and defects. of the reactor head and it propagates along the interface and reflects from the weld and defects. The reflected signals from weld and defects are depicted on Figure 7, which shows the weld and defect reflection signal at each location.
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The reflected signals from weld and defects are depicted on Figure 7, which shows the weld and defect reflection each location. Energiessignal 2017, 10,at589 6 of 11 Energies 2017, 10, 589
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(a) Intact model (a) Intact model
(b) Anomaly #1 (b) Anomaly #1
Amplitude Amplitude
0 -1 0 -11 0 1 0
Amplitude Amplitude
0 -1 0 -11 0 1 0
0 -1 0 -1 0
100
50 100 Defect #1
150 150
200 200
250 250
300 300
350 350
400 400
Defect #1 50
100
50 100 Defect #2
150 150
200 200
250 250
300 300
350 350
400 400
Defect #2 50
100
50 100 Defect #3
150 150
200 200
250 250
300 300
350 350
400 400
Defect #3 50 50
100 100
150 150
200 250 time (us) 200 250 time (us)
300 300
350 350
400 400
0.5 0.5 0
0 -0.5 270 -0.5 0.5 270
Amplitude Amplitude
1 0
50
0.5 0
0 -0.5 270 -0.5 0.5 270
Amplitude Amplitude
Amplitude Amplitude
0 -1 0 -11 0
Intact specimen Intact specimen
0.5 0
0 -0.5 270 -0.5 0.5 270
Amplitude Amplitude
Amplitude Amplitude
1 1 0
Amplitude Amplitude
(c) Anomaly #2 (d) Anomaly #3 (c) Anomaly #2 (d) Anomaly #3 Figure 6. Nozzle weld model (a) Intact model; (b–d) anomalies. Figure 6. Nozzle weld model (a) Intact model; (b–d) anomalies. Figure 6. Nozzle weld model (a) Intact model; (b–d) anomalies.
0.5 0
Intact specimen Intact specimen 290
330
310
290
310
290 Defect #2
350
330
310
350
330
350
Defect #2 290
310
290 Defect #3
330
310
330
310 time (us) 310 time (us)
330
350 350
Defect #3 290 290
330
350 350
(b) (b)
0.30
Intact specimen Defect #1 Intact specimen Defect#1 #2 Defect Defect#2 #3 Defect
0.30 0.25
Amplitude Amplitude
350
330
Defect #1
0 -0.5 270 -0.5 270
(a) (a)
310
290 Defect #1
0.25 0.20
Defect #3
0.20 0.15 0.15 0.10 0.10 0.05 0.05 0.00 290 0.00 290
300 300
310
320
330
310 Time(us) 320 330
340 340
350 350
Time(us) (c) (d) (c) (d) Figure 7. Finite element model analysis signals. (a) Wave propagation signal of reflection from the weld Figure 7. FiniteEnlarged element model analysis signals. Wave signalregion; of reflection fromenvelop the weld and waveanalysis signal from 270 (a) μs 350propagation μs of interesting Wave of weld Figure 7. edge; Finite(b) element model signals. (a)toWave propagation signal of (c) reflection from the and edge; from (b) Enlarged signal from 270 μs to 350envelop μs of interesting region; envelop of reflection the weldwave and defects; (d) Peaks at wave of reflection from (c) theWave weld and defects. and reflection edge; (b)from Enlarged wave signal from 270 µs to 350 µs of interesting region; (c) Wave envelop of the weld and defects; (d) Peaks at wave envelop of reflection from the weld and defects.
reflection from the weld and defects; (d) Peaks at wave envelop of reflection from the weld and defects. Because two-dimensional models are used, once the interface wave is reflected from the defect, two-dimensional models are once is reflected from the defect, mostBecause of the wave energy is scattered. Theused, defects in the the interface weld areawave are the region of interest in this most of the wave energy is scattered. The defects in the weld area are the region of interest in this
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Energies 2017, 10,two-dimensional 589 7 of 11 Because models are used, once the interface wave is reflected from the defect, Energies 2017, 10, 589 7 of 11 most of the wave energy is scattered. The defects in the weld area are the region of interest in this study. Therefore,only only thewave wave signal that is reflected from the weld area is taken into account for study. from thethe weld area is taken intointo account for the study. Therefore, Therefore, onlythe the wavesignal signalthat thatisisreflected reflected from weld area is taken account for the signal analysis. The first is peak is the reflection wave from the boundary of the J-groove weld. signal analysis. The first the is reflection wave from boundary of the J-groove weld. Because the signal analysis. The peak first peak the reflection wavethe from the boundary of the J-groove weld. Because the boundary and properties material properties are discontinuous, a large reflection is measured in the boundary and material are discontinuous, a large reflection is measured in this area. Because the boundary and material properties are discontinuous, a large reflection is measured in this area. The transmitted interface wave over the weld is reflected from the boundary of defects and The transmitted interface wave over the weld is reflected from thefrom boundary of defects the and free this area. The transmitted interface wave over the weld is reflected the boundary ofand defects the free end of the specimen. end of the specimen. the free end of the specimen. The second and and third peaks peaks are from from the defect defect and free free end. The The large reflection reflection at the the defect The The second second and third third peaks are are from the the defect and and free end. end. The large large reflection at at the defect defect and free end is based on the transition of the interface boundary conditions. The numerical model is is and free end is based on the transition of the interface boundary conditions. The numerical model and free end is based on the transition of the interface boundary conditions. The numerical model is designed with with shrink shrink fit fit conditions conditions at at the the interface. However, However, the boundary boundary of of the the weld and and defects designed designed with shrink fit conditions at the interface. interface. However, the the boundary of the weld weld and defects defects shifts from shrink fit conditions to traction-free boundary conditions. This model analysis indicates shifts from shrink fit conditions to traction-free boundary conditions. This model analysis indicates shifts from shrink fit conditions to traction-free boundary conditions. This model analysis indicates the existence and and the location location of defects. defects. the the existence existence and the the location of of defects.
3.2. Experimental Experimental Setup Setup and and Specimen Specimen 3.2. 3.2. Experimental Setup and Specimen The experimental experimental setup setup is is illustrated illustrated in in Figure Figure 8. 8. The The excitation excitation frequency frequency is is 11 MHz, MHz, and and there there are are The The experimental setup is illustrated in Figure 8. The excitation frequency is 1 MHz, and there are four cycles cycles of of tone tone burst burst wave wave signals. signals. The The high-voltage high-voltage tone tone burst burst signal signal is is generated generated by by aa RPR-4000 RPR-4000 four four cycles of tone burst wave signals. The high-voltage tone burst signal is generated by a RPR-4000 (RITECInc., Inc., Warwick, Warwick,RI, RI,USA). USA).A Acommercial commercial11MHz MHzPiezoeletric Piezoeletric (PZT) (PZT) transducer transducer from from Panamatrics Panamatrics (RITEC (RITEC Inc., Warwick, RI, USA). A commercial 1 MHz Piezoeletric (PZT) transducer from Panamatrics (Waltham,MA, MA, USA) USA) was was also also used. A single (Waltham, single transducer transducerworks worksas asaatransmitter transmitterand andaareceiver. receiver. (Waltham, MA, USA) was also used. A single transducer works as a transmitter and a receiver.
Figure Figure 8. 8. CEDM CEDM nozzle nozzle inspection inspection system. system. Figure 8. CEDM nozzle inspection system.
The specifications specifications of the CEDM nozzle specimen are marked in Figure 8. 8. TheThe thickness of the The of the theCEDM CEDMnozzle nozzlespecimen specimenare aremarked marked Figure thickness of The specifications of in in Figure 8. The thickness of the reactor head is 430 mm and the outer radius of nozzle is 170 mm and its thickness is 20 mm. The the reactor head is 430 mm and the outer radius of nozzle is 170 mm and its thickness is 20 mm. reactor head is 430 mm and the outer radius of nozzle is 170 mm and its thickness is 20 mm. The material of this specimen is 316 is SS.316 The interface on the reactor head and CEDM nozzle is connected The material ofspecimen this specimen The interface on thehead reactor and CEDM nozzle is material of this is 316 SS. TheSS. interface on the reactor andhead CEDM nozzle is connected using shrink fit conditions as part of nuclear reactor. One side of the boundary is J-groove welded connected using shrink fit conditions part ofreactor. nuclearOne reactor. side of the boundary is J-groove using shrink fit conditions as part of as nuclear side One of the boundary is J-groove welded and the other side is open. Figure 9 shows a picture of a CEDM nozzle specimen with a J-groove welded theside otherisside is open. 9 shows a picture a CEDM nozzlespecimen specimenwith withaa J-groove J-groove and theand other open. FigureFigure 9 shows a picture of aofCEDM nozzle weld. The The outside outside of of the the welded welded part part is is ground ground for for surface surface treatment. treatment. The The specimen specimen is is simplified simplified for for weld. weld. The outside of the welded part is ground for surface treatment. The specimen is simplified for the purpose of this study. A real nuclear reactor has s water cooling path inner layer in the nozzle. the of this this study. study. A A real real nuclear nuclear reactor reactor has has ss water water cooling cooling path path inner inner layer layer in in the the nozzle. nozzle. the purpose purpose of The complicated complicated inner innerstructures structuresare areexcluded excludeddue dueto tothe theinterface interfacewave wavepropagation propagationcharacteristics. characteristics. The The complicated inner structures are excluded due to the interface wave propagation characteristics.
Figure 9. CEDM nozzle specimen with a J-groove weld. Figure 9. CEDM J-groove weld. weld. Figure 9. CEDM nozzle nozzle specimen specimen with with aa J-groove
To verify the interface wave propagation, a defect was manufactured at the interface of the To verify the interface wave propagation, a defect was manufactured at the interface of the nozzle and the reactor head. Detailed information about the defects is listed in Table 2. The defect nozzle and the reactor head. Detailed information about the defects is listed in Table 2. The defect location and size are shown in Figure 10. There are four different defects located at varying locations location and size are shown in Figure 10. There are four different defects located at varying locations
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To verify the interface wave propagation, a defect was manufactured at the interface of the nozzle
on the specimen. Two defects areinformation on the same axial line and are in used thelocation interface wave and the reactor head. Detailed about the defects is listed Tableto 2. check The defect and The size are shownline in Figure 10. There are four different defects located varying locations resolution. dashed in Figure 10 indicates the boundary of theatJ-groove weld. on the specimen. Two defects are on the same axial line and are used to check the interface wave resolution. The dashed line in Figure 10 indicates the boundary of the J-groove weld.
Table 2. The defect information of the CEDM nozzle specimen.
Table 2. The defect information of the CEDM Defect Axial Size (mm) Circumferential Sizenozzle (mm)specimen. Radius Size (mm) #1 20 20 1 Defect Axial Size (mm) Circumferential Size (mm) Radius Size (mm) #2 20 20 1 #1 20 20 1 #3-1#2 3 20 5 20 1 1 #3-2#3-1 15 3 10 5 1 1 #3-2
15
10
1
Figure 10. Defect location and shape on a lateral view of specimen.
Figure 10. Defect location and shape on a lateral view of specimen. The results of the interface wave inspection experiment are shown in Figure 11. The excited
The results of the interface wave inspection experiment are shown in Figure 11. The excited interface wave is propagated along the interface between the reactor head and nozzle. The peaks below interface100wave propagated alongfrom thethe interface between reactor head and nozzle. The peaks µs areis from the banging signal transducer itself andthe the near field reflection of complicated below 100 μs areHowever, from the thenear transducer itself and the field of geometry. thebanging region of signal interest from is not the the excitation location. Thenear purpose of reflection this approach is inspection on the weld area distant from the transducer position. Therefore, the reflection complicated geometry. However, the region of interest is not the near the excitation location. The below 250 µs canis be inspection ignored in this the purpose of near from field inspection, however,position. purposesignal of this approach onstudy. the For weld area distant the transducer the reflections before approaching the weld area should be considered. The total wave propagation Therefore, the reflection signal below 250 μs can be ignored in this study. For the purpose of near signal is depicted in Figure 11a. The reflection signal of the time of flight of interest is 290 µs to 350 µs. field inspection, however, reflections approaching weldhead area should be considered. The reflection from thethe boundary of the before weld and the end of thethe reactor is included in this The totaltime wave propagation signal is depicted in Figure 11a. The reflection signal of the time of flight zone. Figure 11b, theμs. signals the weld and the end boundary of structure are clearly marked. Theend reflection of interest isIn290 μs to 350 Thefrom reflection from of the weld and the of the reactor from the defects appear at the location of the defect. The extracted peak value shows the defect location. head is included in this time zone. In the case of Defect #1 it shows a clear reflection signal of the weld boundary and the defect due to In Figure 11b, the signals from the weld and end of structure are clearly marked. The reflection the simple geometry. A large amount wave energy is reflected from the first discontinuous boundary from the defects the location of the atdefect. peakatvalue the defect at 298 µs andappear a similaratamount energy is echoed the end The of theextracted defect boundary 315 µs.shows The finite location.element In themodel case of Defect #1 itinshows clear reflectionresults signalinofFigure the weld boundary and the defect analysis results Figure a7 and experimental 11 show good agreement withsimple each other. Both of Finite Element Methodwave (FEM)energy and experimental results havethe twofirst peaksdiscontinuous from due to the geometry. A large amount is reflected from the boundary of the weld and the end of reactor head. From each defect the reflection ratio between boundary at 298 μs and a similar amount energy is echoed at the end of the defect boundary at 315 the first and second peaks are very different comparing the defective cases and the intact case. μs. The finite element model analysis results in Figure 7 and experimental results in Figure 11 show good agreement with each other. Both of Finite Element Method (FEM) and experimental results have two peaks from the boundary of the weld and the end of reactor head. From each defect the reflection ratio between the first and second peaks are very different comparing the defective cases and the intact case.
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Figure 11.11. CEDM weld specimen inspection signal. (a) Wave propagation signalsignal of reflection from the Figure CEDM weld specimen inspection signal. (a) Wave propagation of reflection from weld and edge; (b) Enlarged wave signal from 270 μs to 350 μs of interesting region; (c) Wave envelop the weld and edge; (b) Enlarged wave signal from 270 µs to 350 µs of interesting region; (c) Wave ofenvelop reflectionoffrom the weld and (d) Peaks at wave envelop of reflection the weldfrom and defects. reflection from thedefects; weld and defects; (d) Peaks at wave envelopfrom of reflection the weld and defects.
4. Discussion
4. Discussion Defect investigation was performed for the J-groove weld in a nuclear reactor nozzle by the finite element method and an experimental approach onweld interface waves. reactor The interface boundary Defect investigation was performed for the based J-groove in a nuclear nozzle by the finite was modeled by theand finite method, and the based wave propagation of the reflection element method anelement experimental approach on interface characteristics waves. The interface boundary signal were analyzed. The interface wave propagates along the interface and is reflected the was modeled by the finite element method, and the wave propagation characteristics of thefrom reflection welds and defects. The experimental numerical results show flight timeand difference in the axial signal were analyzed. The interfaceand wave propagates along thea interface is reflected from the direction propagation. The defect location can be estimated by calculating this time of flight welds and defects. The experimental and numerical results show a flight time difference in the axial difference. The reflectedThe signal pattern shows agreement between the numerical analysis and direction propagation. defect location cangood be estimated by calculating this time of flight difference. experimental It is expected thatagreement the present technique becomeanalysis a promising alternative The reflectedvalidation. signal pattern shows good between thecan numerical and experimental for inaccessible areas such as the shrink fit weld nozzles in a nuclear reactor. validation. It is expected that the present technique can become a promising alternative for inaccessible areas such as the shrink fit weld nozzles in a nuclear reactor.
Acknowledgments: The research was sponsored by a grant from the R&D Program of the Korea Railroad Research Institute and The the National Research Foundation of Korea (NRF) grant funded by the Korea government Acknowledgments: research was sponsored by a grant from the R&D Program of the Korea Railroad Research (MSIP) (No. 2016M2A2A9A03913295), Republic of Korea. The opinions expressed in this paper are those of(MSIP) the Institute and the National Research Foundation of Korea (NRF) grant funded by the Korea government (No. 2016M2A2A9A03913295), Republic of Korea. The opinions expressed in this paper are those of the authors authors and do not necessarily reflect the views of the sponsors. and do not necessarily reflect the views of the sponsors. Author Contributions: Jaesun Lee designed the methodology, implemented the simulations and experiments, and wrote the manuscript. Younho Cho prepared the specimen for the experiment, gave guidance, and helped to improve the quality of the manuscript. Conflicts of Interest: The authors declare no conflict of interest.
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Author Contributions: Jaesun Lee designed the methodology, implemented the simulations and experiments, and wrote the manuscript. Younho Cho prepared the specimen for the experiment, gave guidance, and helped to improve the quality of the manuscript. Conflicts of Interest: The authors declare no conflict of interest.
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