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Mechanical design of the JT-60SA cryogenic pipe system
Fusion Engineering and Design 146 (2019) 2214–2217
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Mechanical design of the JT-60SA cryogenic pipe system ⁎
T
Kyohei Natsume , Koji Kamiya, Kazuma Fukui, Katsumi Kawano, Haruyuki Murakami, Katsuhiko Tsuchiya, Kaname Kizu, Takaaki Isono National Institutes for Quantum and Radiological Science and Technology, Naka Ibaraki, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: JT-60SA Cryodistribution Cryogenic system Superconducting coil Cooling pipe Mechanical design
The displacement from the assemble position of several interfaces of JT-60SA cryogenic pipe system reaches to 38 mm due to the thermal contraction and electro-magnetic force of superconducting coils. The mechanical stress on the pipe or pipe support structure by the displacement difference between interfaces is critical issue to be solved. A design concept to avoid the stress concentration on the cryogenic pipe system is bending pipe without conventional flexible tubes. In order to determine the design of the system, thermal mechanical analyses have been conducted by a finite element method software ANSYS®. As results of analyses, it is confirmed that the final design of the system withstands the displacement and load due to the thermal contraction, electro-magnetic force, and seismic event.
1. Introduction
tokamak cryostat through cryoline are connected to any Valve Box (VB) or Coil Terminal Box (CTB). The temperature, pressure, and flow rate of coolant helium are measured and the flow rate is controlled in VBs or CTBs.
JT-60SA is a tokamak device using superconducting coils to be built in Naka Fusion Research Institute, Japan, as a joint international project involving Europe and Japan [1]. One design object of JT-60SA is maximization of the plasma volume and the instrumentation port availability in the condition that several buildings, diagnostics, and heating instruments of JT-60U, which is the previous device using copper coils existed at the same place, are reused. The function of JT60SA cryogenic pipe system is to transfer cryogenic helium from the helium refrigerator system (HRS) to cryogenic components: superconducting coils, diverter cryopumps (CP), thermal shield (TS) and high temperature superconducting current leads (HTSCL). The superconducting coil system for JT-60SA is composed of 18 Toroidal Field coils (TFC) and 10 Poloidal Field coils (PFC). PFC includes a Central Solenoid (CS) with 4 modules and 6 Equilibrium Field coils (EFC). The coils consist of small superconducting wires contained within a conduit through which super-critical He II flows. The current of TFC and PFC are 25.7 and 20.0 kA, respectively [2]. HRS was installed in a room next to the tokamak hall, Naka Institute in 2015 and its commissioning was completed. The cooling capacity of HRS is equivalent to about 9 kW at 4.5 K [3,4]. Fig. 1 shows a drawing of partially transparent JT-60SA tokamak body and components of the cryo-distribution. The main cryogenic transfer line which is named cryoline connects HRS and tokamak cryostat. The flow diagram of cryogenic system are shown in Fig. 2. Five cooling loops compose the cryodistribution system. All pipes which are introduced into the ⁎
2. Design concept for the cryogenic pipe system 2.1. Issue: enforced displacement on pipes JT-60SA cryogenic pipe system has two unique features. One of them is a complicated path. Relatively small 11 VBs and 5 CTBs are separately installed around the tokamak cryostat asymmetrically. The supply pipes for cryogenic helium directly go into the cryostat via cryoline. Then, they are distributed to VBs and CTBs in the tokamak cryostat. After that, VBs and CTBs control the helium flow properly. Finally, cryogenic pipes are distributed to cryogenic components such as super-conducting coils in the tokamak cryostat again. Return way is same to supply one. If we would find the space around the tokamak cryostat, a simple large distribution box was installed between the helium refrigerator and the tokamak cryostat, instead of VBs and CTBs, in order to simplify the piping path. The other is that relatively larger displacement and load which are applied to cryogenic pipes and pipe supports. The several inlets to superconducting coils, pipe supports, and control valves are placed on upper part of the tokamak. The higher support position is, the larger displacement and load are induced due to the evacuation of cryostat, cooling down cryogenic components, the electro-magnetic force, and
Corresponding author. E-mail address: [email protected] (K. Natsume).
https://doi.org/10.1016/j.fusengdes.2019.03.155 Received 8 October 2018; Received in revised form 22 March 2019; Accepted 22 March 2019 Available online 29 March 2019 0920-3796/ © 2019 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 146 (2019) 2214–2217
K. Natsume, et al.
Fig. 1. Drawing of the cryodistribution for JT-60SA. Fig. 3. Schematic of displacement by the thermal contraction.
Fig. 4. Displacement of pipe inlet for TFC operation.
Fig. 2. Flow diagram of JT-60SA cryodistribution.
the seismic load, because all gravity supports of cryogenic components are placed on the bottom of the tokamak. Fig. 3 illustrates a schematic of displacement by the thermal contraction of TFC. The displacement from assemble position causes the loads on pipes and pipe supports. For example, the cryogenic pipe interfaces of TFC are displaced about 8 mm, 11 mm and 38 mm toward radius, toroidal, and vertical direction (Fig. 4). 2.2. Solution: bending pipe without flexible tubes The excess stress on a pipe system is often observed, when the difference of enforced displacement between two adjacent support points is relatively large and the pipe are linearly connected between these two points, because the stress is only concentrated on the support points. There are two options to release the excess stress. One of them is using flexible tubes to separate the force transmission
Fig. 5. Schematic of pipe simple pipe system and the bending stress as a function of the pipe length.
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K. Natsume, et al.
between the support points. However, bellow parts of the flexible tube might be reason for a helium leak due to the vibration fatigue. The other is bending pipes to dissipate the stress. Fig. 5 displays a schematic of simple pipe system and the bending stress as a function of pipe length. The pipe connects between support point A and B through bend point O. When the displacement occurs in parallel with the AO, the pipe BO is bent by the force due to the displacement. It can be calculated from the Eq. (1)
σ=
3EID ZLOB 2
(1)
where σ, E, I, D, Z, and LOB are the bending stress, Young’s modulus, inertia moment, displacement, section modulus, and length of OB. The pipe diameter, the wall thickness, and the enforced displacement of AO are 34 mm, 1.65 mm, and 35 mm, respectively. The bending of pipe AO is ignored for simplicity in this case. The bending stress can be dissipated by increasing length of pipe in perpendicular with the displacement direction. Since the stress on pipes is combined the axial, bending, and torsional stress, the pipe design is not simple, in reality. 3. Analysis
Fig. 7. Temperature gradation of pipe support on VB09.
Structural analyses have been conducted using ANSYS® software, which is a finite element analysis tool, in order to determine the design for the cryogenic pipes. The design must satisfy that the stress for every pipes and their support structures is lower than the allowable stress of the material and avoid physical interferences with other components as a result of displacement. The definition and value of allowable stress is derived from “Code for Fusion Facilities - Rules of Superconducting Magnet Structure -, The Japan Society of Mechanical Engineers (2008)”. We have completed analyses for all cryogenic pipe configurations. Conditions and results of analysis for TFC pipes with VB09 applied the dead weight, cooling down: thermal contraction, electromagnetic, and seismic force are demonstrated in this paper.
Fig. 8. Input points of enforced displacement for analysis. Table 1 Input data of enforced displacement for analysis. Compo-nent
Input point
r: x (mm)
t: y (mm)
z (mm)
TFC
A B C D
5.3 8.2 8.1 5.1
7.8 10.8 11.2 8.4
−37.8 −36.6 −36.1 −37.3
3.1. Analysis condition Three-dimensional model drawn by CATIA® soft-ware is used for the pipe path and support structure design. Based on the 3D model, analytical models are made in a solid style using ANSYS® software. The analytical model is displayed in Fig. 6. The temperature of almost all pipe system is 4.5 K except for 300 K of the support on VB09. This VB support composes an epoxy resin plate with several holes for fixing pipes, stainless steel 80 K thermal anchors surrounding the plate, and 4 epoxy resin legs which are placed on 300 K wall. There is the temperature gradient between pipe surfaces and support legs as shown in Fig. 7. The VB support has split structure that the plate is not enable to slide in the direction of pipe axis but enable to slide in the direction of plate face. If not so, the excess stress in the legs was found by a thermal
mechanical analysis of a single VB support because the thermal contraction induces the force pulling the leg to the plate center direction. Fig. 8 shows input points for enforced displacements. Table 1 summarizes an example of the input data which are obtained by analyses of a single component such as TFC applied the dead weight, cooling down, and electromagnetic force. The seismic forces applying to pipes in analyses are 1.4 G in vertical direction and 0.6 G in 8 horizontal directions every 45 ° (case 1–8), according to a result of seismic analysis for the tokamak cryostat conducted before.
3.2. Analysis result Displacements as a result of analyses is shown in Fig. 9. The largest displacement is calculated of about 40 mm on a pipe supported by a structure on the top of TFC. The value is mainly contributed by the enforced displacement for analysis condition which is of 37.8 mm in vertical direction. The largest stress generated on the pipe system in cases of seismic force directions are shown in Fig. 10. The largest stress among them appears in case 6 in which the seismic force is parallel to the direction pointing the tokamak center. The direction is same to the displacement by the thermal contraction of superconducting coils. Fig. 11 shows the stress distribution in the case. Pipe support structures are not drawn in the figure. The maximum stress of 257 MPa appears in
Fig. 6. Analytical model for VB09 and TFC pipes. 2216
Fusion Engineering and Design 146 (2019) 2214–2217
K. Natsume, et al.
Fig. 9. Displacement of pipe system as an analysis result.
Fig. 12. Tensile stress on support legs.
Fig. 10. Maximum stress in various cases of the horizontal seismic force direction every 45°.
Fig. 13. Compressive stress on support legs.
and Fig. 13 for the compressive stress. All analysis results prove the soundness of designed pipes for TFC and VB09 in the situation with plasma operations and the seismic event. 4. Conclusion Design of all cryogenic pipes for cryogenic components of JT-60SA has been completed. It is confirmed by structural analyses using ANSYS® software that the pipes and the support structures withstand against the load and displacement by cooling down, the electro-magnetic force, and seismic event. The design that interfaces of piping are installed at the upper part of large cryogenic device can be managed without inserting conventional flexible tubes. Asymmetrical complicated piping design is not smart and need a lot of effort to confirm the soundness. However, if it is implemented, priority occupying useful space is enable to be given to other equipment such as measurement devices or heating systems.
Fig. 11. Stress distribution on a supply line for TFC.
a bent pipe connecting VB09 and the header of TFC supply line because of the large enforced displacement difference between VB09 and TFC on which the header support placed. The allowable stress of SS316 L in this condition is 350 MPa according to JSME code described before. Soundness evaluation approach of epoxy resin structure design is generally different from that of stainless steel because the mechanical strength of epoxy resin is lower than that of stainless steel. We adopt the approach that the tensile and compressive stress are calculated and compared with their allowable one, respectively. The analysis results of epoxy resin support on VB09 are shown in Fig. 12 for the tensile stress
References [1] H. Shirai, et al., Recent progress of the JT-60SA project, Nucl. Fusion 57 (2017) 10. [2] Y. Koide, et al., JT-60SA superconducting magnet system, Nucl. Fusion 55 (2015) 086001. [3] C. Hoa, et al., Installation and pre-commissioning of the cryogenic system of JT-60SA tokamak, IOP Conf. Ser.: Mater. Sci. Eng. 171 (2017) 012047. [4] K. Kamiya, et al., Commissioning of the JT-60SA helium refrigerator, IOP Conf. Ser.: J. Phys.: Conf. Ser. 897 (2017) 012015.
2217
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Mechanical design of the JT-60SA cryogenic pipe system ⁎
T
Kyohei Natsume , Koji Kamiya, Kazuma Fukui, Katsumi Kawano, Haruyuki Murakami, Katsuhiko Tsuchiya, Kaname Kizu, Takaaki Isono National Institutes for Quantum and Radiological Science and Technology, Naka Ibaraki, Japan
A R T I C LE I N FO
A B S T R A C T
Keywords: JT-60SA Cryodistribution Cryogenic system Superconducting coil Cooling pipe Mechanical design
The displacement from the assemble position of several interfaces of JT-60SA cryogenic pipe system reaches to 38 mm due to the thermal contraction and electro-magnetic force of superconducting coils. The mechanical stress on the pipe or pipe support structure by the displacement difference between interfaces is critical issue to be solved. A design concept to avoid the stress concentration on the cryogenic pipe system is bending pipe without conventional flexible tubes. In order to determine the design of the system, thermal mechanical analyses have been conducted by a finite element method software ANSYS®. As results of analyses, it is confirmed that the final design of the system withstands the displacement and load due to the thermal contraction, electro-magnetic force, and seismic event.
1. Introduction
tokamak cryostat through cryoline are connected to any Valve Box (VB) or Coil Terminal Box (CTB). The temperature, pressure, and flow rate of coolant helium are measured and the flow rate is controlled in VBs or CTBs.
JT-60SA is a tokamak device using superconducting coils to be built in Naka Fusion Research Institute, Japan, as a joint international project involving Europe and Japan [1]. One design object of JT-60SA is maximization of the plasma volume and the instrumentation port availability in the condition that several buildings, diagnostics, and heating instruments of JT-60U, which is the previous device using copper coils existed at the same place, are reused. The function of JT60SA cryogenic pipe system is to transfer cryogenic helium from the helium refrigerator system (HRS) to cryogenic components: superconducting coils, diverter cryopumps (CP), thermal shield (TS) and high temperature superconducting current leads (HTSCL). The superconducting coil system for JT-60SA is composed of 18 Toroidal Field coils (TFC) and 10 Poloidal Field coils (PFC). PFC includes a Central Solenoid (CS) with 4 modules and 6 Equilibrium Field coils (EFC). The coils consist of small superconducting wires contained within a conduit through which super-critical He II flows. The current of TFC and PFC are 25.7 and 20.0 kA, respectively [2]. HRS was installed in a room next to the tokamak hall, Naka Institute in 2015 and its commissioning was completed. The cooling capacity of HRS is equivalent to about 9 kW at 4.5 K [3,4]. Fig. 1 shows a drawing of partially transparent JT-60SA tokamak body and components of the cryo-distribution. The main cryogenic transfer line which is named cryoline connects HRS and tokamak cryostat. The flow diagram of cryogenic system are shown in Fig. 2. Five cooling loops compose the cryodistribution system. All pipes which are introduced into the ⁎
2. Design concept for the cryogenic pipe system 2.1. Issue: enforced displacement on pipes JT-60SA cryogenic pipe system has two unique features. One of them is a complicated path. Relatively small 11 VBs and 5 CTBs are separately installed around the tokamak cryostat asymmetrically. The supply pipes for cryogenic helium directly go into the cryostat via cryoline. Then, they are distributed to VBs and CTBs in the tokamak cryostat. After that, VBs and CTBs control the helium flow properly. Finally, cryogenic pipes are distributed to cryogenic components such as super-conducting coils in the tokamak cryostat again. Return way is same to supply one. If we would find the space around the tokamak cryostat, a simple large distribution box was installed between the helium refrigerator and the tokamak cryostat, instead of VBs and CTBs, in order to simplify the piping path. The other is that relatively larger displacement and load which are applied to cryogenic pipes and pipe supports. The several inlets to superconducting coils, pipe supports, and control valves are placed on upper part of the tokamak. The higher support position is, the larger displacement and load are induced due to the evacuation of cryostat, cooling down cryogenic components, the electro-magnetic force, and
Corresponding author. E-mail address: [email protected] (K. Natsume).
https://doi.org/10.1016/j.fusengdes.2019.03.155 Received 8 October 2018; Received in revised form 22 March 2019; Accepted 22 March 2019 Available online 29 March 2019 0920-3796/ © 2019 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 146 (2019) 2214–2217
K. Natsume, et al.
Fig. 1. Drawing of the cryodistribution for JT-60SA. Fig. 3. Schematic of displacement by the thermal contraction.
Fig. 4. Displacement of pipe inlet for TFC operation.
Fig. 2. Flow diagram of JT-60SA cryodistribution.
the seismic load, because all gravity supports of cryogenic components are placed on the bottom of the tokamak. Fig. 3 illustrates a schematic of displacement by the thermal contraction of TFC. The displacement from assemble position causes the loads on pipes and pipe supports. For example, the cryogenic pipe interfaces of TFC are displaced about 8 mm, 11 mm and 38 mm toward radius, toroidal, and vertical direction (Fig. 4). 2.2. Solution: bending pipe without flexible tubes The excess stress on a pipe system is often observed, when the difference of enforced displacement between two adjacent support points is relatively large and the pipe are linearly connected between these two points, because the stress is only concentrated on the support points. There are two options to release the excess stress. One of them is using flexible tubes to separate the force transmission
Fig. 5. Schematic of pipe simple pipe system and the bending stress as a function of the pipe length.
2215
Fusion Engineering and Design 146 (2019) 2214–2217
K. Natsume, et al.
between the support points. However, bellow parts of the flexible tube might be reason for a helium leak due to the vibration fatigue. The other is bending pipes to dissipate the stress. Fig. 5 displays a schematic of simple pipe system and the bending stress as a function of pipe length. The pipe connects between support point A and B through bend point O. When the displacement occurs in parallel with the AO, the pipe BO is bent by the force due to the displacement. It can be calculated from the Eq. (1)
σ=
3EID ZLOB 2
(1)
where σ, E, I, D, Z, and LOB are the bending stress, Young’s modulus, inertia moment, displacement, section modulus, and length of OB. The pipe diameter, the wall thickness, and the enforced displacement of AO are 34 mm, 1.65 mm, and 35 mm, respectively. The bending of pipe AO is ignored for simplicity in this case. The bending stress can be dissipated by increasing length of pipe in perpendicular with the displacement direction. Since the stress on pipes is combined the axial, bending, and torsional stress, the pipe design is not simple, in reality. 3. Analysis
Fig. 7. Temperature gradation of pipe support on VB09.
Structural analyses have been conducted using ANSYS® software, which is a finite element analysis tool, in order to determine the design for the cryogenic pipes. The design must satisfy that the stress for every pipes and their support structures is lower than the allowable stress of the material and avoid physical interferences with other components as a result of displacement. The definition and value of allowable stress is derived from “Code for Fusion Facilities - Rules of Superconducting Magnet Structure -, The Japan Society of Mechanical Engineers (2008)”. We have completed analyses for all cryogenic pipe configurations. Conditions and results of analysis for TFC pipes with VB09 applied the dead weight, cooling down: thermal contraction, electromagnetic, and seismic force are demonstrated in this paper.
Fig. 8. Input points of enforced displacement for analysis. Table 1 Input data of enforced displacement for analysis. Compo-nent
Input point
r: x (mm)
t: y (mm)
z (mm)
TFC
A B C D
5.3 8.2 8.1 5.1
7.8 10.8 11.2 8.4
−37.8 −36.6 −36.1 −37.3
3.1. Analysis condition Three-dimensional model drawn by CATIA® soft-ware is used for the pipe path and support structure design. Based on the 3D model, analytical models are made in a solid style using ANSYS® software. The analytical model is displayed in Fig. 6. The temperature of almost all pipe system is 4.5 K except for 300 K of the support on VB09. This VB support composes an epoxy resin plate with several holes for fixing pipes, stainless steel 80 K thermal anchors surrounding the plate, and 4 epoxy resin legs which are placed on 300 K wall. There is the temperature gradient between pipe surfaces and support legs as shown in Fig. 7. The VB support has split structure that the plate is not enable to slide in the direction of pipe axis but enable to slide in the direction of plate face. If not so, the excess stress in the legs was found by a thermal
mechanical analysis of a single VB support because the thermal contraction induces the force pulling the leg to the plate center direction. Fig. 8 shows input points for enforced displacements. Table 1 summarizes an example of the input data which are obtained by analyses of a single component such as TFC applied the dead weight, cooling down, and electromagnetic force. The seismic forces applying to pipes in analyses are 1.4 G in vertical direction and 0.6 G in 8 horizontal directions every 45 ° (case 1–8), according to a result of seismic analysis for the tokamak cryostat conducted before.
3.2. Analysis result Displacements as a result of analyses is shown in Fig. 9. The largest displacement is calculated of about 40 mm on a pipe supported by a structure on the top of TFC. The value is mainly contributed by the enforced displacement for analysis condition which is of 37.8 mm in vertical direction. The largest stress generated on the pipe system in cases of seismic force directions are shown in Fig. 10. The largest stress among them appears in case 6 in which the seismic force is parallel to the direction pointing the tokamak center. The direction is same to the displacement by the thermal contraction of superconducting coils. Fig. 11 shows the stress distribution in the case. Pipe support structures are not drawn in the figure. The maximum stress of 257 MPa appears in
Fig. 6. Analytical model for VB09 and TFC pipes. 2216
Fusion Engineering and Design 146 (2019) 2214–2217
K. Natsume, et al.
Fig. 9. Displacement of pipe system as an analysis result.
Fig. 12. Tensile stress on support legs.
Fig. 10. Maximum stress in various cases of the horizontal seismic force direction every 45°.
Fig. 13. Compressive stress on support legs.
and Fig. 13 for the compressive stress. All analysis results prove the soundness of designed pipes for TFC and VB09 in the situation with plasma operations and the seismic event. 4. Conclusion Design of all cryogenic pipes for cryogenic components of JT-60SA has been completed. It is confirmed by structural analyses using ANSYS® software that the pipes and the support structures withstand against the load and displacement by cooling down, the electro-magnetic force, and seismic event. The design that interfaces of piping are installed at the upper part of large cryogenic device can be managed without inserting conventional flexible tubes. Asymmetrical complicated piping design is not smart and need a lot of effort to confirm the soundness. However, if it is implemented, priority occupying useful space is enable to be given to other equipment such as measurement devices or heating systems.
Fig. 11. Stress distribution on a supply line for TFC.
a bent pipe connecting VB09 and the header of TFC supply line because of the large enforced displacement difference between VB09 and TFC on which the header support placed. The allowable stress of SS316 L in this condition is 350 MPa according to JSME code described before. Soundness evaluation approach of epoxy resin structure design is generally different from that of stainless steel because the mechanical strength of epoxy resin is lower than that of stainless steel. We adopt the approach that the tensile and compressive stress are calculated and compared with their allowable one, respectively. The analysis results of epoxy resin support on VB09 are shown in Fig. 12 for the tensile stress
References [1] H. Shirai, et al., Recent progress of the JT-60SA project, Nucl. Fusion 57 (2017) 10. [2] Y. Koide, et al., JT-60SA superconducting magnet system, Nucl. Fusion 55 (2015) 086001. [3] C. Hoa, et al., Installation and pre-commissioning of the cryogenic system of JT-60SA tokamak, IOP Conf. Ser.: Mater. Sci. Eng. 171 (2017) 012047. [4] K. Kamiya, et al., Commissioning of the JT-60SA helium refrigerator, IOP Conf. Ser.: J. Phys.: Conf. Ser. 897 (2017) 012015.
2217