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Feasibility of Upper Port Plug tube handling
Fusion Engineering and Design 86 (2011) 2060–2063
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Feasibility of Upper Port Plug tube handling J.F. Koning a,∗ , B.S.Q. Elzendoorn a , D.M.S. Ronden a , J.F.F. Klinkhamer b , W. Biel c , Y. Krasikov c , C.I. Walker d a
FOM-Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, Partner in the Trilateral Euregio Cluster and ITER-NL, P.O. Box 1207, 3430 BE Nieuwegein, The Netherlands TNO Science & Industry, Partner in ITER-NL, P.O. Box 155, 2600 AD Delft, The Netherlands Institut für Energieforschung – Plasmaphysik, Forschungszentrum Jülich Gmbh, Association EURATOM-FZJ, Member of Trilateral Euregio Cluster, 52425 Jülich, Germany d ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul-lez-Durance Cedex, France b c
a r t i c l e
i n f o
Article history: Available online 25 March 2011 Keywords: Tube Upper Port Plug Diagnostic Handling Hot Cell Facility Shut down
a b s t r a c t Central, retractable tubes are proposed in several Upper Port Plugs (UPPs) designs for ITER, to enable fast exchange of specific components of diagnostics housed in these UPPs. This paper investigates into possible designs to enable the efficient handling of tubes. The feasibility of tube handling is analysed by first reviewing the designs drivers. Several concepts for handling of the tube are proposed, exploring the limits described by the design drivers. Suggestions are presented for tube integration into the UPP design, concerning the tube mounting into the UPP, the load takeover and coping with the thermal elongation. It is found that the handling of tubes is feasible but still requires a lot of system level integration. Also, the added value of a tube as a feature in an UPP design to the availability of the subsystem the UPP is a part of, is questionable and needs further assessment on ITER system level. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Rationale for a tube in an Upper Port Plug
In the diagnostic Upper Port Plugs (UPPs) of ITER, several teams propose a removable tube as an on-vessel replaceable module. Tubes would allow more frequent maintenance than currently possible with UPP replacement or alleviate limited access conditions. Frequent maintenance is the only mitigation option left to guarantee a high availability of the system concerned to ITER operation. Currently, there is no design for the required tooling, except for the specific case of the Neutral Beam Cell (NBC) where the UPPs themselves cannot be removed. This paper reviews the rationale to design a tube in an UPP, and investigates possible design solutions at conceptual level. The time horizon for acquisition of tube handling equipment is in the distant future. However, considering that the availability of the tooling is a system design input, the design impact is imminent. The added value of the tube concept remains to be justified for each specific case. Nevertheless, they provide in the need of diagnostic designers for more frequent replacement of critical components.
The limited maintenance possibilities for UPPs, currently listed as 2 UPP maintenance actions ([1] PR1087–R) per bi-annual major shutdown [2], block the use of maintenance as a mitigation to availability problems in the design of the diagnostic concerned. With 14 UPPs (including the Electron Cyclotron Heating launchers) outside the NBC and an ITER operational lifetime of 20 years, on average each UPP can be maintained 1.5 times. Note that this includes the one time that the first wall material will be refurbished on the UPP. The limitation on maintenance interventions is essentially caused by the available time during shutdown as well as the capacity available in the maintenance systems (the Hot Cell Facility, HCF, and the Cask and Plug Remote Handling Systems, CPRHS). So, not every UPP can have maintenance at every shutdown. An option to circumvent this might be to only exchange the concerned UPP and to refurbish the used UPP during ITER operation. This will require a spare UPP to be available. The idea of a tube, as a removable module allowing frequently replacing parts having uncertain or high wear rates, was conceived to overcome the maintenance limitations. If working in parallel to other HCF operations during a shutdown, it is in principle possible to exchange every tube at every shutdown without heavy impact on the baseline maintenance schedule. The UPP and the tube are like a matryoshka doll: a smaller module designed to be removable from ITER, contained within a larger module, designed for the same purpose. Compared to an UPP, the
∗ Corresponding author. Tel.: +31 30 6096 931; fax: +31 30 6031 204. E-mail address: [email protected] (J.F. Koning). 0920-3796/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2011.02.101
J.F. Koning et al. / Fusion Engineering and Design 86 (2011) 2060–2063
tube is smaller, and probably less expensive both in terms of cost and of HCF volume consumption, but an extra set of handling equipment is necessary. Furthermore, the geometrical requirements for a tube have to be balanced with other options to increase the performance of a diagnostic [3]. In the ITER baseline, central tubes are currently accepted only in the UPPs residing within the NBC ([1] PR1087-R) but there are a number of designs considering implementation of a tube [4]. This paper qualitatively analyses the impact of a tube as a system part of the UPPs on ITER cost. For this, the design drivers must be identified, and the outline of the exchange scenario must be known. We will see that a number of design concepts is possible, depending on how wide the scope is interpreted. 3. Design drivers 3.1. Tube Exchange System (TES) requirements Avoiding cantilevered handling allows for a smaller footprint of the handling equipment, thus minimizing interference with port cell installations, and more design freedom on the tube’s flange. Using tubes has an impact on the Hot Cell operations as these are mainly serial in nature. For the on-vessel remote operations, tubes have less impact on the shutdown schedule, as these activities can to some extent be performed in parallel. Tube interfaces are to be designed for more frequent exchange than UPP interfaces. A critical point in the design is the mechanical mounting of the tube combined with design of the vacuum interface, structural mounting flange, and coolant and service connections. Worker radiological exposure is limited by the operationallifetime averaged annual worker dose limit of 500 person-mSv ([1] PR1129–R). Therefore, remote methods to disconnect the tube and clear the port cell should be considered. Port cell equipment should be designed so that most or all of it can stay during a tube exchange. 3.2. Handling sequence An outline of the installation sequence is proposed below. This ‘storyboard’ will differ depending on the mechanical concept and the system approach chosen. • Move the enclosure into the port cell • Position and align the enclosure to the UPP • Dock with the UPP and open the enclosure to the VV whilst assuring confinement • Check and refurbish the UPP-tube seal surface • Align and position the tube for insertion • Monitor insertion (clearance, forces etcetera) • Control mechanical end-stop and seal contact • Tighten flange(s) to UPP • Leak-test seal • Un-dock enclosure (assure confinement) • Re-connect cooling lines and other services These activities can be arranged in three categories. The first category contains activities that shall be performed by the TES, such as docking, moving the tube into the UPP, positioning and aligning, and structural bolting, called primary activities. Activities which the TES has to perform if the enclosure stays docked during swap are of the second category. If the enclosure undocks to store the used tube and retrieve the new tube, vessel temporary closure cap installation and removal shall be done, and additionally these activities should be done: vacuum tight bolting, cleaning of the sealing surface(s), inspection of the sealing sur-
2061
Fig. 1. UPP cask modification to handle tubes.
face(s), and polishing/refurbishing vacuum flange on UPP side. If the TES does not handle these activities, they will need to be performed by radiological workers. The third category contains these activities that are supplemental to the TES scope: cutting and welding the tubes’ cooling lines and vacuum leak testing. Note that these activities otherwise have to be performed by radiological workers prior to and after the exchange. Summarizing, there is a large number of design drivers that have to be fulfilled before the concept of a tube, supported by the TES, is a functional addition to ITER subsystems’ availability. What follows is a mechanical exploration into the extents of these design drivers. 4. System design approaches On a system level, various design approaches were formulated which are evaluated in the next paragraphs. Conventional caskbased concepts will have an extra disadvantage in that the UPP itself will need to be disconnected before the TES can dock. 4.1. Modified UPP cask A modified UPP cask as in Fig. 1 has a minimal impact on present baseline because it only requires an active converter flange mounted in the standard UPP cask. It relies on all the functionality of the UPP cask [5] to fulfil its mission, such as confinement, manoeuvring, docking and mounting. However, use of the UPP cask for tube handling might interfere with UPP maintenance operations, and an in situ exchange is not possible. A support arm could be integrated to help mounting operations and interface refurbishment. 4.2. Minimal or integrated invasive operation Respectively a customized single or multiple tube enclosure, conceptualised in Fig. 2, is dedicated to provide a small footprint to be able to leave as much equipment in the port cell as possible. The tractor/gripper travels in a dedicated axial/helical track, using the principle of a ball-screw for linear motion. If convenient, the enclosure might be guided over the ceiling or walls, rather than the floor. The multiple tube enclosure might integrate tooling for interface
Fig. 2. Integrated tube exchange chamber.
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Fig. 3. Multi-purpose TES, using a hexapod concept. Fig. 5. To separate the bag from the on-vessel part, an advanced closing mechanism is deployed.
refurbishment, but the design effort is large as all the main functions of a cask have to fulfilled by the flask-like enclosure. Rescue options are limited, due to the integrated design.
4.3. Multi-purpose exchange system Extending the scope of the TES to the full list of identified activities, but not engaging in a fully new design of the critical functions (docking, confinement), allows to take the envelope of the UPP cask. The internals are changed to a flexible tool which can perform the basic tube handling and can take care of interface refurbishment. It could include a slave system where a remote operator is able to do supplementary tasks, maybe even preparation and postinstallation tasks such as (dis)connection of pipes, pressure testing etcetera. The required high stiffness can be delivered by a parallel manipulator (also called hexapod or ‘Stewart’ platform) as sketched in Fig. 3, where six linear actuators act to position the end-effector. Note that this is the only conceptual approach which would also be able to perform maintenance operations on e.g., equatorial port cells and port plugs, and possibly it could even be used on the divertor level.
4.5. Exchange under vacuum In all concepts discussed, it is assumed that the vessel is vented. However, docking vacuum-to-vacuum allows for much more frequent tube exchanges. This benefit comes at a great potential cost, as the risk to ITER operation is deemed very high if anything would go wrong. Furthermore, the cost of such a system is likely to be higher than with other approaches. Certification by all parties involved will be difficult, especially considering that all interface refurbishment tasks have to be performed under vacuum as well – this means a welded vacuum flange is out of the question. Then, connection of cooling lines and any other pre- and post-tasks will be done in air before and after the swap, but have to be performed remotely as an exchange under vacuum will make sense only if we do not have to wait for human access to be possible after the nominal cooldown period of about 10 days. Thus, any human access as a part of a procedure, also in a rescue scenario, is impossible. 5. Tube mounting considerations The detailed design of the TES will depend on a number of important interface concepts.
4.4. Disposable single tube enclosure
5.1. Payload alignment
Taking notion that the tube will be activated, but will not stay in the confined transport volume very long, it is feasible to use a thin and maybe disposable bag as in Fig. 4, to pack the tube in during transport. As long as this bagged confinement is pumped on a sub-atmospheric pressure, tritium and (beryllium) dust are confined. Plastics are quite permeable for hydrogen isotopes, but various coatings might further reduce that effect. A slim closing mechanism as in Fig. 5, allows to separate the confinement volumes in this tight spot making use of the deformable properties of the plastic.
The diagnostic payload must be robustly aligned. Robustly means that the mounting method should avoid hysteresis effects after temporary high loads (E/M, thermal) are applied. This can only be realised by properly constraining the tube to 6 Degrees of Freedoms (DoFs). In Fig. 6, the tip of the tube is constrained tangentially at 3 different places, resulting in accurate re-mounting of the tip in X and Y.
Fig. 4. Bagged tube.
Fig. 6. Mounting concepts.
J.F. Koning et al. / Fusion Engineering and Design 86 (2011) 2060–2063
2063
Fig. 8. A compact floating flange layout.
5000 mm, and an assumed maximum T of 20 K). This means that either the back flange or the tip of the tube has to be able to move relatively to the UPP structure, respectively a ‘floating flange’ or a ‘floating tip’ as in Fig. 6. A floating flange can be implemented as illustrated in Fig. 8. 6. Conclusion and outlook
Fig. 7. Guidance concept – exaggerated view.
5.2. Clearance The clearance during operation is in the order of a few mm, to avoid any extra neutron tunnelling. The installation method has to account for the small space. The tube itself is stiff enough to stay within the clearance under its own weight; rather it will be the limited stiffness of the TES which will not be capable of keeping the tube within the clearance. Thus, pure cantilevered handling (handling by the back flange only), is not possible and guiding must be designed. Furthermore, even non-cantilevered handling will need an active alignment step at the end of the insertion procedure as illustrated in Fig. 7. This can be handled by the tractor [5]. Then, if there is any gap between the TES and the UPP, two sets of wheels are necessary. Finally, the difference in support stiffness of the TES and the combined UPP and Vacuum vessel means that a kind of chute is needed to handle the load transfer. 5.3. Thermal difference Thermal expansion differences between the tube and the supporting structures must be compensated. This is only an issue in the axial direction, where the length difference can be a tentative 1.6 mm (316 stainless steel with CTE = 16.2 × 10−6 K−1 , a length of
Tubes open a promising perspective to perform maintenance significantly more frequent as compared to UPP maintenance or UPP exchange. The geometrical restrictions and the additional effort arising from the installation of a tube have to be analysed and to be balanced to other means for performance enhancement. Depending on each UPP system architecture, the implementation of a tube may either enable certain risk mitigation means which need the tube, or it may make the realisation of other mitigation means more complicated. The complete system cost of UPPs will be impacted due to the necessary handling equipment. Tube handling equipment is feasible in principle but has no answer to all secondary activities (as in Section 3.2). If tubes, as an option to facilitate more frequent exchange of parts, are to be pursued, then it is imperative that dimensions and especially all handling interfaces are standardized. Furthermore, volume claims such as parking space in the HCF need to be made, and preferably the port-cell installations are designed to allow unhindered access for the equipment. Acknowledgements This work, supported by NWO, ITER-NL and the European Communities under the contract of the Association EURATOM/FOM, was carried out within the framework of the European Fusion Programme. The views and opinions expressed herein do not necessarily reflect those of the European Commission. References [1] S. Chiocchio, et al., Project Requirements, ITER D 27ZRW8, v4.6. [2] D. van Houtte, ITER machine operation availability, ITER D 34GC2G, v1.0. [3] F. Klinkhamer, et al., Optimization of the availability of the core-CXRS diagnostic for ITER, in: Proceedings of the 26th Symposium on Fusion Engineering (SOFT 2010), 2010. [4] D. Johnson, UPP Diagnostic requirements, ITER D 2FCWAJ, v1.0. [5] J.-W. Pustjens, et al., Upper port plug handling cask system assessment and design proposals, in: Proceedings of the 26th Symposium on Fusion Engineering (SOFT 2010), 2010.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Feasibility of Upper Port Plug tube handling J.F. Koning a,∗ , B.S.Q. Elzendoorn a , D.M.S. Ronden a , J.F.F. Klinkhamer b , W. Biel c , Y. Krasikov c , C.I. Walker d a
FOM-Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, Partner in the Trilateral Euregio Cluster and ITER-NL, P.O. Box 1207, 3430 BE Nieuwegein, The Netherlands TNO Science & Industry, Partner in ITER-NL, P.O. Box 155, 2600 AD Delft, The Netherlands Institut für Energieforschung – Plasmaphysik, Forschungszentrum Jülich Gmbh, Association EURATOM-FZJ, Member of Trilateral Euregio Cluster, 52425 Jülich, Germany d ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul-lez-Durance Cedex, France b c
a r t i c l e
i n f o
Article history: Available online 25 March 2011 Keywords: Tube Upper Port Plug Diagnostic Handling Hot Cell Facility Shut down
a b s t r a c t Central, retractable tubes are proposed in several Upper Port Plugs (UPPs) designs for ITER, to enable fast exchange of specific components of diagnostics housed in these UPPs. This paper investigates into possible designs to enable the efficient handling of tubes. The feasibility of tube handling is analysed by first reviewing the designs drivers. Several concepts for handling of the tube are proposed, exploring the limits described by the design drivers. Suggestions are presented for tube integration into the UPP design, concerning the tube mounting into the UPP, the load takeover and coping with the thermal elongation. It is found that the handling of tubes is feasible but still requires a lot of system level integration. Also, the added value of a tube as a feature in an UPP design to the availability of the subsystem the UPP is a part of, is questionable and needs further assessment on ITER system level. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Rationale for a tube in an Upper Port Plug
In the diagnostic Upper Port Plugs (UPPs) of ITER, several teams propose a removable tube as an on-vessel replaceable module. Tubes would allow more frequent maintenance than currently possible with UPP replacement or alleviate limited access conditions. Frequent maintenance is the only mitigation option left to guarantee a high availability of the system concerned to ITER operation. Currently, there is no design for the required tooling, except for the specific case of the Neutral Beam Cell (NBC) where the UPPs themselves cannot be removed. This paper reviews the rationale to design a tube in an UPP, and investigates possible design solutions at conceptual level. The time horizon for acquisition of tube handling equipment is in the distant future. However, considering that the availability of the tooling is a system design input, the design impact is imminent. The added value of the tube concept remains to be justified for each specific case. Nevertheless, they provide in the need of diagnostic designers for more frequent replacement of critical components.
The limited maintenance possibilities for UPPs, currently listed as 2 UPP maintenance actions ([1] PR1087–R) per bi-annual major shutdown [2], block the use of maintenance as a mitigation to availability problems in the design of the diagnostic concerned. With 14 UPPs (including the Electron Cyclotron Heating launchers) outside the NBC and an ITER operational lifetime of 20 years, on average each UPP can be maintained 1.5 times. Note that this includes the one time that the first wall material will be refurbished on the UPP. The limitation on maintenance interventions is essentially caused by the available time during shutdown as well as the capacity available in the maintenance systems (the Hot Cell Facility, HCF, and the Cask and Plug Remote Handling Systems, CPRHS). So, not every UPP can have maintenance at every shutdown. An option to circumvent this might be to only exchange the concerned UPP and to refurbish the used UPP during ITER operation. This will require a spare UPP to be available. The idea of a tube, as a removable module allowing frequently replacing parts having uncertain or high wear rates, was conceived to overcome the maintenance limitations. If working in parallel to other HCF operations during a shutdown, it is in principle possible to exchange every tube at every shutdown without heavy impact on the baseline maintenance schedule. The UPP and the tube are like a matryoshka doll: a smaller module designed to be removable from ITER, contained within a larger module, designed for the same purpose. Compared to an UPP, the
∗ Corresponding author. Tel.: +31 30 6096 931; fax: +31 30 6031 204. E-mail address: [email protected] (J.F. Koning). 0920-3796/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2011.02.101
J.F. Koning et al. / Fusion Engineering and Design 86 (2011) 2060–2063
tube is smaller, and probably less expensive both in terms of cost and of HCF volume consumption, but an extra set of handling equipment is necessary. Furthermore, the geometrical requirements for a tube have to be balanced with other options to increase the performance of a diagnostic [3]. In the ITER baseline, central tubes are currently accepted only in the UPPs residing within the NBC ([1] PR1087-R) but there are a number of designs considering implementation of a tube [4]. This paper qualitatively analyses the impact of a tube as a system part of the UPPs on ITER cost. For this, the design drivers must be identified, and the outline of the exchange scenario must be known. We will see that a number of design concepts is possible, depending on how wide the scope is interpreted. 3. Design drivers 3.1. Tube Exchange System (TES) requirements Avoiding cantilevered handling allows for a smaller footprint of the handling equipment, thus minimizing interference with port cell installations, and more design freedom on the tube’s flange. Using tubes has an impact on the Hot Cell operations as these are mainly serial in nature. For the on-vessel remote operations, tubes have less impact on the shutdown schedule, as these activities can to some extent be performed in parallel. Tube interfaces are to be designed for more frequent exchange than UPP interfaces. A critical point in the design is the mechanical mounting of the tube combined with design of the vacuum interface, structural mounting flange, and coolant and service connections. Worker radiological exposure is limited by the operationallifetime averaged annual worker dose limit of 500 person-mSv ([1] PR1129–R). Therefore, remote methods to disconnect the tube and clear the port cell should be considered. Port cell equipment should be designed so that most or all of it can stay during a tube exchange. 3.2. Handling sequence An outline of the installation sequence is proposed below. This ‘storyboard’ will differ depending on the mechanical concept and the system approach chosen. • Move the enclosure into the port cell • Position and align the enclosure to the UPP • Dock with the UPP and open the enclosure to the VV whilst assuring confinement • Check and refurbish the UPP-tube seal surface • Align and position the tube for insertion • Monitor insertion (clearance, forces etcetera) • Control mechanical end-stop and seal contact • Tighten flange(s) to UPP • Leak-test seal • Un-dock enclosure (assure confinement) • Re-connect cooling lines and other services These activities can be arranged in three categories. The first category contains activities that shall be performed by the TES, such as docking, moving the tube into the UPP, positioning and aligning, and structural bolting, called primary activities. Activities which the TES has to perform if the enclosure stays docked during swap are of the second category. If the enclosure undocks to store the used tube and retrieve the new tube, vessel temporary closure cap installation and removal shall be done, and additionally these activities should be done: vacuum tight bolting, cleaning of the sealing surface(s), inspection of the sealing sur-
2061
Fig. 1. UPP cask modification to handle tubes.
face(s), and polishing/refurbishing vacuum flange on UPP side. If the TES does not handle these activities, they will need to be performed by radiological workers. The third category contains these activities that are supplemental to the TES scope: cutting and welding the tubes’ cooling lines and vacuum leak testing. Note that these activities otherwise have to be performed by radiological workers prior to and after the exchange. Summarizing, there is a large number of design drivers that have to be fulfilled before the concept of a tube, supported by the TES, is a functional addition to ITER subsystems’ availability. What follows is a mechanical exploration into the extents of these design drivers. 4. System design approaches On a system level, various design approaches were formulated which are evaluated in the next paragraphs. Conventional caskbased concepts will have an extra disadvantage in that the UPP itself will need to be disconnected before the TES can dock. 4.1. Modified UPP cask A modified UPP cask as in Fig. 1 has a minimal impact on present baseline because it only requires an active converter flange mounted in the standard UPP cask. It relies on all the functionality of the UPP cask [5] to fulfil its mission, such as confinement, manoeuvring, docking and mounting. However, use of the UPP cask for tube handling might interfere with UPP maintenance operations, and an in situ exchange is not possible. A support arm could be integrated to help mounting operations and interface refurbishment. 4.2. Minimal or integrated invasive operation Respectively a customized single or multiple tube enclosure, conceptualised in Fig. 2, is dedicated to provide a small footprint to be able to leave as much equipment in the port cell as possible. The tractor/gripper travels in a dedicated axial/helical track, using the principle of a ball-screw for linear motion. If convenient, the enclosure might be guided over the ceiling or walls, rather than the floor. The multiple tube enclosure might integrate tooling for interface
Fig. 2. Integrated tube exchange chamber.
2062
J.F. Koning et al. / Fusion Engineering and Design 86 (2011) 2060–2063
Fig. 3. Multi-purpose TES, using a hexapod concept. Fig. 5. To separate the bag from the on-vessel part, an advanced closing mechanism is deployed.
refurbishment, but the design effort is large as all the main functions of a cask have to fulfilled by the flask-like enclosure. Rescue options are limited, due to the integrated design.
4.3. Multi-purpose exchange system Extending the scope of the TES to the full list of identified activities, but not engaging in a fully new design of the critical functions (docking, confinement), allows to take the envelope of the UPP cask. The internals are changed to a flexible tool which can perform the basic tube handling and can take care of interface refurbishment. It could include a slave system where a remote operator is able to do supplementary tasks, maybe even preparation and postinstallation tasks such as (dis)connection of pipes, pressure testing etcetera. The required high stiffness can be delivered by a parallel manipulator (also called hexapod or ‘Stewart’ platform) as sketched in Fig. 3, where six linear actuators act to position the end-effector. Note that this is the only conceptual approach which would also be able to perform maintenance operations on e.g., equatorial port cells and port plugs, and possibly it could even be used on the divertor level.
4.5. Exchange under vacuum In all concepts discussed, it is assumed that the vessel is vented. However, docking vacuum-to-vacuum allows for much more frequent tube exchanges. This benefit comes at a great potential cost, as the risk to ITER operation is deemed very high if anything would go wrong. Furthermore, the cost of such a system is likely to be higher than with other approaches. Certification by all parties involved will be difficult, especially considering that all interface refurbishment tasks have to be performed under vacuum as well – this means a welded vacuum flange is out of the question. Then, connection of cooling lines and any other pre- and post-tasks will be done in air before and after the swap, but have to be performed remotely as an exchange under vacuum will make sense only if we do not have to wait for human access to be possible after the nominal cooldown period of about 10 days. Thus, any human access as a part of a procedure, also in a rescue scenario, is impossible. 5. Tube mounting considerations The detailed design of the TES will depend on a number of important interface concepts.
4.4. Disposable single tube enclosure
5.1. Payload alignment
Taking notion that the tube will be activated, but will not stay in the confined transport volume very long, it is feasible to use a thin and maybe disposable bag as in Fig. 4, to pack the tube in during transport. As long as this bagged confinement is pumped on a sub-atmospheric pressure, tritium and (beryllium) dust are confined. Plastics are quite permeable for hydrogen isotopes, but various coatings might further reduce that effect. A slim closing mechanism as in Fig. 5, allows to separate the confinement volumes in this tight spot making use of the deformable properties of the plastic.
The diagnostic payload must be robustly aligned. Robustly means that the mounting method should avoid hysteresis effects after temporary high loads (E/M, thermal) are applied. This can only be realised by properly constraining the tube to 6 Degrees of Freedoms (DoFs). In Fig. 6, the tip of the tube is constrained tangentially at 3 different places, resulting in accurate re-mounting of the tip in X and Y.
Fig. 4. Bagged tube.
Fig. 6. Mounting concepts.
J.F. Koning et al. / Fusion Engineering and Design 86 (2011) 2060–2063
2063
Fig. 8. A compact floating flange layout.
5000 mm, and an assumed maximum T of 20 K). This means that either the back flange or the tip of the tube has to be able to move relatively to the UPP structure, respectively a ‘floating flange’ or a ‘floating tip’ as in Fig. 6. A floating flange can be implemented as illustrated in Fig. 8. 6. Conclusion and outlook
Fig. 7. Guidance concept – exaggerated view.
5.2. Clearance The clearance during operation is in the order of a few mm, to avoid any extra neutron tunnelling. The installation method has to account for the small space. The tube itself is stiff enough to stay within the clearance under its own weight; rather it will be the limited stiffness of the TES which will not be capable of keeping the tube within the clearance. Thus, pure cantilevered handling (handling by the back flange only), is not possible and guiding must be designed. Furthermore, even non-cantilevered handling will need an active alignment step at the end of the insertion procedure as illustrated in Fig. 7. This can be handled by the tractor [5]. Then, if there is any gap between the TES and the UPP, two sets of wheels are necessary. Finally, the difference in support stiffness of the TES and the combined UPP and Vacuum vessel means that a kind of chute is needed to handle the load transfer. 5.3. Thermal difference Thermal expansion differences between the tube and the supporting structures must be compensated. This is only an issue in the axial direction, where the length difference can be a tentative 1.6 mm (316 stainless steel with CTE = 16.2 × 10−6 K−1 , a length of
Tubes open a promising perspective to perform maintenance significantly more frequent as compared to UPP maintenance or UPP exchange. The geometrical restrictions and the additional effort arising from the installation of a tube have to be analysed and to be balanced to other means for performance enhancement. Depending on each UPP system architecture, the implementation of a tube may either enable certain risk mitigation means which need the tube, or it may make the realisation of other mitigation means more complicated. The complete system cost of UPPs will be impacted due to the necessary handling equipment. Tube handling equipment is feasible in principle but has no answer to all secondary activities (as in Section 3.2). If tubes, as an option to facilitate more frequent exchange of parts, are to be pursued, then it is imperative that dimensions and especially all handling interfaces are standardized. Furthermore, volume claims such as parking space in the HCF need to be made, and preferably the port-cell installations are designed to allow unhindered access for the equipment. Acknowledgements This work, supported by NWO, ITER-NL and the European Communities under the contract of the Association EURATOM/FOM, was carried out within the framework of the European Fusion Programme. The views and opinions expressed herein do not necessarily reflect those of the European Commission. References [1] S. Chiocchio, et al., Project Requirements, ITER D 27ZRW8, v4.6. [2] D. van Houtte, ITER machine operation availability, ITER D 34GC2G, v1.0. [3] F. Klinkhamer, et al., Optimization of the availability of the core-CXRS diagnostic for ITER, in: Proceedings of the 26th Symposium on Fusion Engineering (SOFT 2010), 2010. [4] D. Johnson, UPP Diagnostic requirements, ITER D 2FCWAJ, v1.0. [5] J.-W. Pustjens, et al., Upper port plug handling cask system assessment and design proposals, in: Proceedings of the 26th Symposium on Fusion Engineering (SOFT 2010), 2010.