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The European test blanket module systems: Design and integration in ITER
Fusion Engineering and Design 81 (2006) 407–414
The European test blanket module systems: Design and integration in ITER L.V. Boccaccini a,∗ , J.-F. Salavy b , R. L¨asser c , A. Li Puma b , R. Meyder a , H. Neuberger a , Y. Poitevin c , G. Rampal b a b
Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany CEA-Saclay, Direction de l’Energie Nucl´eaire, 91191 Gif-sur-Yvette, France c EFDA Garching CSU, Boltzmannstr. 2, 85748 Garching, Germany
Received 22 February 2005; received in revised form 16 September 2005; accepted 16 September 2005 Available online 28 December 2005
Abstract The European Union proposes two different concepts of helium-cooled blanket for testing in ITER, one with ceramic breeder and beryllium, the second with lithium lead as breeder and multiplier. Test blanket modules (TBM) for both blanket concepts and their auxiliary systems have being designed in the last 2 years; this paper presents the status of this work as reached in January 2005. In particular the design of the two TBMs is discussed pointing out the common original architecture and the differences in the design choices due to different functionality, test necessities and adaptation to the ITER boundary conditions. The integration of these systems in ITER is presented in the second part of this paper. A new proposal for the integration of the TBMs inside the port plug, their replacement in the hot cell and the arrangement of the auxiliary systems in the ITER buildings is discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Test blanket; ITER; Liquid breeder; Solid breeder; Helium cooling
1. Introduction In the frame of the ITER Test Blanket Working Group activities in 2003–2004, the design and integration of the test blanket module (TBM) systems in ITER has been addressed with the mission to define ∗ Corresponding author. Tel.: +49 7247 822415; fax: +49 7247 823718. E-mail address: [email protected] (L.V. Boccaccini).
0920-3796/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2005.09.008
a coordinated test programme for the use of the three test ports, to provide a standardised system of interfaces with ITER, and to identify cooperation areas among the parties in R&D and system development. The paper presents the design and integration proposals for the blanket concepts selected in the European Union for testing in ITER, namely the helium-cooled lithium lead (HCLL) and the helium-cooled pebble bed (HCPB). The EU Testing Programme foresees the testing in succession of several TBMs (four of each line) during the first 10 years of ITER operation; each of
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these modules will be designed to cope with the related plasma phase (H–H, D–D, D–T) and perform dedicated experiments to gain information on the behaviour of the blanket concepts in the field of neutronics, thermomechanics, MHD and tritium operations in a relevant fusion environment. Each TBM is located in half of an equatorial port of ITER inside a water-cooled frame and is connected with auxiliary systems for providing helium for heat extraction and He or PbLi loop for extracting the tritium produced during the burn time.
2. Design description The description of the ongoing design of the two European TBMs has been already presented in 2004 in several posters and oral presentations of fusion meetings [1–3]; hence, for a more-detailed description of the two concepts, these papers should be considered as well. Fig. 1 shows CAD drawings of the two designs according to the status of the work as reached in January 2005. The design of the two TBMs is based on the common architecture that was developed for the HCLL and HCPB proposal for a DEMO blanket in 2003 [4,5]: a robust box (first wall (FW) and caps) reinforced by a grid and able to withstand the full pressure of the coolant helium (8 MPa) in case of in-box loss of coolant accident, a cooling with the high-pressure manifolds integrated in the back plate structure, breeder units (BU) arranged in a modular array in the space (cells) defined by the stiffening grid and cooling plates (CP) for extracting the heat from the breeder/multiplier. The main difference between the two blanket designs is the arrangement of the space inside the box (mainly BUs and grid) to accommodate the different breeder/multiplier materials. In the HCLL concept, the liquid metal fills the in-box volume and is slowly re-circulated to remove the produced tritium. As PbLi is purified outside the vacuum vessel (VV), an external loop connects the module to the extraction units. In the HCPB concept, pebble beds of lithium ceramic breeder (CB) and beryllium are contained in the box, and are purged by an independent low-pressure helium stream that extracts the tritium; an external loop leads this stream to the tritium removal units. This functional difference calls for a different design of the low-pressure distribution system neces-
sary to guide the PbLi and the He purge flow in the two concepts. In the HCLL the PbLi is fed from the top of the blanket and distributed in parallel vertical channels among pairs of cells (one cell for the radial movement towards the plasma, the other for the return); at the end the outlet stream is collected in the bottom part of the blanket [6]. The HCPB helium purge enters first a chamber at the back side of the BUs, is then distributed in parallel to the cells flowing first through the beryllium and then from the plasma side through the CB beds and exits via a collecting manifold. Other differences in the design have been intentionally introduced to investigate possible alternative structural options for the most demanding components. A typical example is the back plate: the HCLL presents a completely modular design based on reinforcement tubes (arranged in a regular grid, connecting the two thick plates that enclose the high-pressure manifold system) that provide support for the mechanical attachments and access for the helium lines in the back plate manifolds; this system provides at the same time the penetrations of the PbLi lines and instrumentation to the low-pressure in-box volume. The HCPB design is based on a few large internal cases that connect the thick plates and provide additional manifolds for the high-pressure helium flow. Selection of a common back plate design for the TBMs is targeted in a later stage of the work as result of the validation of the fabrication processes. In the design of the TBM, other differences have been introduced as a consequence of the testing strategies adopted by the two (HCLL and HCPB) European Design Teams. The strategy followed by the European Programme for the testing of DEMO concept in ITER calls for several (four for each line) test objects that should be installed in succession in ITER [1,7,8] These objects can fill up half of a port; the test volume is about 0.8 m3 and the plasma exposed surface ∼1 m2 . These dimensions represent about a quarter of a typical DEMO module [4]. The HCPB has been designed for a horizontal configuration built of 18 BUs, six in toroidal direction three in poloidal. This configuration has been chosen to keep a DEMO relevant width of the FW with respect to the length of the internal toroidal cooling channels. On the contrary, the HCLL is of a vertical configuration (three cells in toroidal × eight in poloidal direction), which is more suitable for the testing of the PbLi concept. The possibility that the two
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409
Fig. 1. TBM design with breeder unit detail: HCPB (left) and HCLL (right).
present EU TBM concepts will be installed in one and the same port requiring a change from horizontal to vertical design or vice-versa has been envisaged; but no decision made as it depends on the future agreement of the port allocation between the six ITER parties. As consequence of the different design and testing choices, also the proposed cooling schemes and the thermo-hydraulic working points of the two concepts present some differences. Table 1 summarises the present cooling layout of the two TBMs. As the two
designs aim to test a FW DEMO relevant design, the relatively large cross-section of the FW internal channels in comparison to their length causes an insufficient helium velocity resulting in a poor heat transfer coefficient. To avoid this both concepts adopt more passes (3 or 4) of the FW channels (in the DEMO only one pass is foreseen) to increase the helium velocity to about 80 m/s and assure an adequate cooling of the surface exposed to the plasma. The drawback of this set-up is an increase of the overall pressure drop.
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Table 1 Cooling scheme and thermo-hydraulic working point for nominal conditions (270 kW/m2 surface heating and 0.78 MW/m2 neutron wall load) HCPB
HCLL
Scheme
FW surface (m2 ) He pressure (MPa) He: temperatures (◦ C)–mass flow (kg/s) 1 2 3 4 Pressure drops (MPa)
0.94 8
1.15 8
300–1.3 370–0.65 420–0.65 500–0.65
300–1.5 368–0.59
<0.3
Furthermore, it should be noted that the nominal surface heat flux for the TBM in ITER is relatively low (270 kW/m2 in comparison to 500 kW/m2 foreseen in DEMO), but the simultaneous possibility of unpredictable hot spots of 500 kW/m2 affecting 10–15% of the FW surface, necessitates the cooling of the whole FW to be dimensioned to cope with the local hot spots. A study of the transient behaviour of the first wall surface temperature due to a surface heat flux increase from 270 to 500 kW/m2 showed a local temperature rise rate of about 8 K/s with a time constant of about 10 s. As there is no way to cope with such an offset condition regulating the inlet coolant mass flow or temperature, the operational conditions required for the cooling of the first wall must be designed for the extreme heating conditions. As the He coolant flow passes first through the FW and then through breeding zone (BU and grid), the temperature of the He coolant for the chosen mass flows will be too low for almost all loading conditions of the TBM and the goal to perform DEMO relevant test will not be achieved. To cope with these conditions and assure a higher flexibility in TBM testing, a by-pass between the FW and the breeding zone has been added to inject only a small fraction of the He coolant into the breeding zone. This by-pass flow can be tuned by an external valve regulating the mass flow into the breeding zone (a time constant of about 50 s in the breeding zone makes possible this regulation).
499–0.59 <0.3
The TBM is connected to auxiliary systems that provide the coolant helium at the required conditions and the circulation of helium or PbLi for tritium extraction purposes. As the cooling requirements of the two helium coolant systems (HCS) are comparable (see Table 1), a similar system is required for the two components. At the moment two concepts of HCS are under study, a high temperature and a low temperature compressor loop (HTCL and LTCL, respectively). These two proposals differ essentially from one another in the working temperature of the helium compressor (about 300 ◦ C in the HTCL and 100 ◦ C in the other); while for the HTCL the helium coming out of the compressor can feed directly the TBM, in the LTCL it goes through a recuperator to reach the required TBM inlet temperature of 300 ◦ C; in fact, the loop is split in two parts (8-shape–configuration) by the recuperator allowing a low temperature region for the compressor (see Fig. 2). This kind of configuration is state-of-the-art for out-ofpile helium facilities; high temperature compressors for the HTCL configuration are not commercially available and necessitate dedicated R&D. An independent low-pressure loop is foreseen to extract the tritium produced in the HCPB TBM. It should supply the required purge flow at the proper mass flow and compositions (impurities should be controlled and 0.1% H2 is added to the He flow to facilitate the T extraction from the ceramic breeder). For the HCLL a PbLi circuit permits the TBM feeding and
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411
Fig. 2. Flow sheet of the helium coolant system.
the tritium extraction from the liquid metal outside the TBM. The PbLi mass flow in the circuit is adjustable in the range between 0.1 and 1 kg/s in order to allow investigation of various phenomena (lower mass flow rates to reach high tritium partial pressure in the liquid metal, higher mass flow rates to investigate MHD effects). The circuit layout is designed such that during discharge or in case of emergency the PbLi is transferred simply by gravity; all piping and components are heated in order to avoid freezing of the PbLi. Additional external equipment is also necessary to support performance measurements (e.g. tritium production, neutron fluxes, etc.) during the different tests and to monitor the systems during operation.
3. Integration in ITER As shown in Section 2, testing the two European TBMs in ITER requires integration of several systems and components. Three horizontal ports are available for allocating the TBMs (16, 18 and 2 according to the ITER numeration). In line with the strategy followed in EU, the integration of the European TBMs has been studied with the assumption that an equatorial port will contain two TBMs of different concepts; the HCPB TBM is assumed to occupy the upper position in port
16 with a horizontal configuration, and the HCLL in port 18 with a vertical configuration. An example of this integration for the HCPB TBM system is shown in [9]. The TBM is located inside a port plug (PP) that offers a standardised interface to the ITER vacuum vessel (VV) and allows the replacement of the TBMs. The frontal part of the PP (the so-called “frame”) provides a containment structure that thermally insulates and shields each TBM from the other one and from local ITER structure (see Fig. 3). The whole structure is cantilevered with a flange to the VV port extension. A thick neutron shield (about 1 m thickness) inside the PP protects the magnets, the structures and the buildings from the neutron flux. The shield constitutes also the first interface for TBM integration providing a support for the mechanical attachments and penetrations for the TBM pipes. The mechanical attachment is designed to cope with the large electromagnetic (EM) forces that are created during plasma disruptions (a radial torque of 0.72 MNm has been calculated and used as design reference for the HCPB design). The attachment consists of three shear keys capable of withstanding the EM torque and acting as the fixed point (in the middle of the TBM back plate), and four “flexibles” that locate the TBM with bolts in radial direction. Another possibility is shown in Fig. 1 for the HCLL design, where “stub
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Fig. 3. TBM integration in ITER VV and port cell.
keys” (a compact design that combines the functions of flexible and shear key) are proposed. The presence of large helium pipes caused some difficulties due to space requirements for the integration. As helium is transparent to neutrons and does not contribute to the shielding, only pipes of internal diameter (i.d.) smaller than 30 mm can be routed straight through the port plug shield; tubes of larger diameter must be bent within the shielding to reduce neutron streaming. The vacuum boundary is realised at the rear part of the shield; here the vacuum at the penetrations coming from the TBM should be ensured in relation to 0.1 MPa in the inter-space cell. To attach the TBM to the shield with screw straight holes are needed in the shield for access; to ensure the shielding function these holes should be closed by shield plugs. Flexible support (bellows) in the helium pipes to the PP must be designed in order to compensate the differential thermal expansion (e.g. up to 500 ◦ C for the hot leg in comparison to ∼150 ◦ C of the PP structure). In line with the ITER requirement each bellow must be secondarily contained with monitoring of the inter-space. The resulting interface is quite complex; this interface is one of the most critical factors and may limit the num-
ber of independent TBM systems that can be tested at the same time in ITER. Following the present philosophy adopted by ITER for the PP handling, the replacement of the TBMs is done in the hot cell after the port plug is extracted from its position in the VV, transported in the cask to the hot cell and docked to the PP refurbishment workstation. The replacement system studied in [9] is based on the use of in-bore tools and mechanical screw actuators that operate from the clean side of the docking station reaching the Interface 1 inside the PP shielding. For the helium pipes, two types of in-bore tools are required, a cutting/welding/testing device for straight pipes of 30 mm i.d., and an analogous device for bent tubes of 80 mm i.d. and bend radius not lower than 400 mm. The PbLi re-circulation pipes for the HCLL should require tools of the first type (30 mm i.d.). In addition, the electrical grounding and the instrumentation cables must be connected/disconnected as well; for these systems the design is ongoing. Several systems should be accommodated in the space in front of the VV port (the inter-space in the VV extension inside the bio-shield, and in the port cell); for both HCPB and HCLL concepts the pip-
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ing of the main coolant system, some component of the by-pass (valve and thermal sleeves), helium or PbLi pipes for the tritium extraction, measurement systems, etc. A further issue is the layout of the main helium pipes to the respective HCS allocated in the torus coolant water system (TCWS) vault. An example for the HCPB integration is presented in [9]; again the major requirements for the layout are the restricted space and the necessity to realise a quick exchange of the components. The use of an integrated device (the so-called piping integration cask, PIC) allows the pipes to be cut and re-welded only at the boundary interfaces, removing all the intermediate components as a block. The layout of helium pipes of 80–100 mm i.d. from the interface 2 to 3 (see Fig. 3) is dictated mainly by the necessity to compensate the thermal expansion of the pipes (maximum design values are 500 ◦ C and 8 MPa); large radius bends have been designed to accommodate this expansion. A conclusion of this study was that the space is restricted, but the accommodation of a second analogous system to support the TBM in the lower port is still possible if a common PIC is used for the integration of both systems. For the HCLL, the PbLi ancillary system has to be placed in the test port area, too, and it has to be as close as possible to the TBM in order to reduce the PbLi inventory and the tritium permeation through the pipes. Due to the space requirements for allowing the personnel to perform the maintenance operation, the PbLi circuit will be placed behind the bio-shield plug in an insulated container of 2.3 × 1.6 × 2.2 m3 (high × width × depth). As already mentioned previously, the HCSs for both EU TBMs are to be located in the TCWS vault. The pipes coming from the port cell have to be routed through vertical shafts reaching – after about 80 m length and a change of level of about +15 m – the HCSs position. The place available in the vault is insufficient to locate more than four coolant systems of a capacity to cool one TBM. Preliminary studies have been made for the HCS system in order to investigate the possibility to install it in the foreseen area of 2.5 × 7.5 m2 . The space seems to be sufficient with the exception of some additional space necessary to locate some supporting system. Several studies are ongoing to design a more compact HCS configuration or sharing some subsystems.
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Most of tritium systems will be located in the tritium building in standard glove boxes (4 × 2 × 6 m3 ), but a detailed study of integration is to be done. 4. Conclusions and future work The design of the two European TBM concepts foreseen for their testing in ITER has been almost completed. At the present, the work is focused on the detailed engineering design including the definition of fabrication routes and technologies. In future, the work will be focused on the validation of the proposed design before to install it in ITER; a large mock-up programme will address the main issue of manufacturing and performance for single components and systems. The milestone is to complete the final design in 2010 and then to start the procurement of the components to be installed in ITERs. Study of integration in ITER started already in 2004. A first proposal for the TBM integration in the Port Plug, for the TBM replacement in the hot cell and for the allocation and handling of the port cell has been presented. Studies have been already started to investigate the integration of the HCS in the TWCS vault. Acknowledgements The present work has been performed in the CEAand FZK-EURATOM associations in the frame of the European Fusion Technology Programme coordinated by EFDA Garching. Although the paper reports the work performed inside these associations and presents the opinions of the authors, a continuous exchange of information on the issue of ITER integration has been maintained with the ITER JCT in Garching and Naka. In particular, the authors thank S. Chiocchio, R. Haange, K. Ioki, K. Kataoka, M. Morimoto and A. Tesini for their valuable contributions to discussions. References [1] R. Meyder, L.V. Boccaccini, B. Dolensky, S. Hermsmeyer, M. Ilic, M.X. Jin, et al., New modular concept for the helium cooled pebble bed test blanket module for ITER, Fusion Eng. Des. 75–79 (2005) 795–799.
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[2] L.V. Boccaccini, R. Meyder, U. Fischer, Test strategy for the European HCPB test blanket module in ITER, in: Proceedings of the 16th Topical Meeting on Technology of Fusion Energy, 2004 (to be published in Fusion Sci. Technol.). [3] G. Rampal, Y. Poitevin, A. Li Puma, E. Rigal, J. Szczepanski, C. Boudot, HCLL TBM for ITER — design studies, Fusion Eng. Des. 75–79 (2005) 917–922. [4] L.V. Boccaccini, L. Giancarli, G. Janeschitz, S. Hermsmeyer, Y. Poitevin, A. Cardella, E. Diegele, Materials and design of the European DEMO blankets, J. Nucl. Mater. 329–333 (2004) 148–155. [5] A. Cardella, E. Rigal, L. Bedel, Ph. Bucci, J. Fiek, L. Forest, L.V. Boccaccini, E. Diegele, L. Giancarli, S. Hermsmeyer, et al., The manufacturing technologies of the European breeding blankets, J. Nucl. Mater. 329–333 (2004) 133–140.
[6] G. Rampal, D. Gatelet, L. Giancarli, G. Laffont, A. Li-Puma, J.F. Salavy, E. Rigal, Design approach for the main ITER test blanket modules for the EU helium cooled lithium–lead blankets, 2006, in this proceedings. [7] Y. Poitevin, L.V. Boccaccini, A. Cardella, L. Giancarli, R. Meyder, E. Diegele, R. Laesser, G. Benamati, The European breeding blankets development and the test strategy in ITER, Fusion Eng. Des. 75–79 (2005) 741–749. [8] A. Li Puma, Y. Poitevin, L. Giancarli, G. Rampal, W. Farabolini, The helium cooled lithium lead blanket test proposal in ITER and requirements on test blanket modules instrumentation, Fusion Eng. Des. 75–79 (2005) 951–955. [9] H. Neuberger, L.V. Boccaccini, R. Meyder, Integration of the EU HCPB test blanket module system in ITER, 2006, in this proceedings.
The European test blanket module systems: Design and integration in ITER L.V. Boccaccini a,∗ , J.-F. Salavy b , R. L¨asser c , A. Li Puma b , R. Meyder a , H. Neuberger a , Y. Poitevin c , G. Rampal b a b
Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany CEA-Saclay, Direction de l’Energie Nucl´eaire, 91191 Gif-sur-Yvette, France c EFDA Garching CSU, Boltzmannstr. 2, 85748 Garching, Germany
Received 22 February 2005; received in revised form 16 September 2005; accepted 16 September 2005 Available online 28 December 2005
Abstract The European Union proposes two different concepts of helium-cooled blanket for testing in ITER, one with ceramic breeder and beryllium, the second with lithium lead as breeder and multiplier. Test blanket modules (TBM) for both blanket concepts and their auxiliary systems have being designed in the last 2 years; this paper presents the status of this work as reached in January 2005. In particular the design of the two TBMs is discussed pointing out the common original architecture and the differences in the design choices due to different functionality, test necessities and adaptation to the ITER boundary conditions. The integration of these systems in ITER is presented in the second part of this paper. A new proposal for the integration of the TBMs inside the port plug, their replacement in the hot cell and the arrangement of the auxiliary systems in the ITER buildings is discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Test blanket; ITER; Liquid breeder; Solid breeder; Helium cooling
1. Introduction In the frame of the ITER Test Blanket Working Group activities in 2003–2004, the design and integration of the test blanket module (TBM) systems in ITER has been addressed with the mission to define ∗ Corresponding author. Tel.: +49 7247 822415; fax: +49 7247 823718. E-mail address: [email protected] (L.V. Boccaccini).
0920-3796/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2005.09.008
a coordinated test programme for the use of the three test ports, to provide a standardised system of interfaces with ITER, and to identify cooperation areas among the parties in R&D and system development. The paper presents the design and integration proposals for the blanket concepts selected in the European Union for testing in ITER, namely the helium-cooled lithium lead (HCLL) and the helium-cooled pebble bed (HCPB). The EU Testing Programme foresees the testing in succession of several TBMs (four of each line) during the first 10 years of ITER operation; each of
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these modules will be designed to cope with the related plasma phase (H–H, D–D, D–T) and perform dedicated experiments to gain information on the behaviour of the blanket concepts in the field of neutronics, thermomechanics, MHD and tritium operations in a relevant fusion environment. Each TBM is located in half of an equatorial port of ITER inside a water-cooled frame and is connected with auxiliary systems for providing helium for heat extraction and He or PbLi loop for extracting the tritium produced during the burn time.
2. Design description The description of the ongoing design of the two European TBMs has been already presented in 2004 in several posters and oral presentations of fusion meetings [1–3]; hence, for a more-detailed description of the two concepts, these papers should be considered as well. Fig. 1 shows CAD drawings of the two designs according to the status of the work as reached in January 2005. The design of the two TBMs is based on the common architecture that was developed for the HCLL and HCPB proposal for a DEMO blanket in 2003 [4,5]: a robust box (first wall (FW) and caps) reinforced by a grid and able to withstand the full pressure of the coolant helium (8 MPa) in case of in-box loss of coolant accident, a cooling with the high-pressure manifolds integrated in the back plate structure, breeder units (BU) arranged in a modular array in the space (cells) defined by the stiffening grid and cooling plates (CP) for extracting the heat from the breeder/multiplier. The main difference between the two blanket designs is the arrangement of the space inside the box (mainly BUs and grid) to accommodate the different breeder/multiplier materials. In the HCLL concept, the liquid metal fills the in-box volume and is slowly re-circulated to remove the produced tritium. As PbLi is purified outside the vacuum vessel (VV), an external loop connects the module to the extraction units. In the HCPB concept, pebble beds of lithium ceramic breeder (CB) and beryllium are contained in the box, and are purged by an independent low-pressure helium stream that extracts the tritium; an external loop leads this stream to the tritium removal units. This functional difference calls for a different design of the low-pressure distribution system neces-
sary to guide the PbLi and the He purge flow in the two concepts. In the HCLL the PbLi is fed from the top of the blanket and distributed in parallel vertical channels among pairs of cells (one cell for the radial movement towards the plasma, the other for the return); at the end the outlet stream is collected in the bottom part of the blanket [6]. The HCPB helium purge enters first a chamber at the back side of the BUs, is then distributed in parallel to the cells flowing first through the beryllium and then from the plasma side through the CB beds and exits via a collecting manifold. Other differences in the design have been intentionally introduced to investigate possible alternative structural options for the most demanding components. A typical example is the back plate: the HCLL presents a completely modular design based on reinforcement tubes (arranged in a regular grid, connecting the two thick plates that enclose the high-pressure manifold system) that provide support for the mechanical attachments and access for the helium lines in the back plate manifolds; this system provides at the same time the penetrations of the PbLi lines and instrumentation to the low-pressure in-box volume. The HCPB design is based on a few large internal cases that connect the thick plates and provide additional manifolds for the high-pressure helium flow. Selection of a common back plate design for the TBMs is targeted in a later stage of the work as result of the validation of the fabrication processes. In the design of the TBM, other differences have been introduced as a consequence of the testing strategies adopted by the two (HCLL and HCPB) European Design Teams. The strategy followed by the European Programme for the testing of DEMO concept in ITER calls for several (four for each line) test objects that should be installed in succession in ITER [1,7,8] These objects can fill up half of a port; the test volume is about 0.8 m3 and the plasma exposed surface ∼1 m2 . These dimensions represent about a quarter of a typical DEMO module [4]. The HCPB has been designed for a horizontal configuration built of 18 BUs, six in toroidal direction three in poloidal. This configuration has been chosen to keep a DEMO relevant width of the FW with respect to the length of the internal toroidal cooling channels. On the contrary, the HCLL is of a vertical configuration (three cells in toroidal × eight in poloidal direction), which is more suitable for the testing of the PbLi concept. The possibility that the two
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409
Fig. 1. TBM design with breeder unit detail: HCPB (left) and HCLL (right).
present EU TBM concepts will be installed in one and the same port requiring a change from horizontal to vertical design or vice-versa has been envisaged; but no decision made as it depends on the future agreement of the port allocation between the six ITER parties. As consequence of the different design and testing choices, also the proposed cooling schemes and the thermo-hydraulic working points of the two concepts present some differences. Table 1 summarises the present cooling layout of the two TBMs. As the two
designs aim to test a FW DEMO relevant design, the relatively large cross-section of the FW internal channels in comparison to their length causes an insufficient helium velocity resulting in a poor heat transfer coefficient. To avoid this both concepts adopt more passes (3 or 4) of the FW channels (in the DEMO only one pass is foreseen) to increase the helium velocity to about 80 m/s and assure an adequate cooling of the surface exposed to the plasma. The drawback of this set-up is an increase of the overall pressure drop.
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Table 1 Cooling scheme and thermo-hydraulic working point for nominal conditions (270 kW/m2 surface heating and 0.78 MW/m2 neutron wall load) HCPB
HCLL
Scheme
FW surface (m2 ) He pressure (MPa) He: temperatures (◦ C)–mass flow (kg/s) 1 2 3 4 Pressure drops (MPa)
0.94 8
1.15 8
300–1.3 370–0.65 420–0.65 500–0.65
300–1.5 368–0.59
<0.3
Furthermore, it should be noted that the nominal surface heat flux for the TBM in ITER is relatively low (270 kW/m2 in comparison to 500 kW/m2 foreseen in DEMO), but the simultaneous possibility of unpredictable hot spots of 500 kW/m2 affecting 10–15% of the FW surface, necessitates the cooling of the whole FW to be dimensioned to cope with the local hot spots. A study of the transient behaviour of the first wall surface temperature due to a surface heat flux increase from 270 to 500 kW/m2 showed a local temperature rise rate of about 8 K/s with a time constant of about 10 s. As there is no way to cope with such an offset condition regulating the inlet coolant mass flow or temperature, the operational conditions required for the cooling of the first wall must be designed for the extreme heating conditions. As the He coolant flow passes first through the FW and then through breeding zone (BU and grid), the temperature of the He coolant for the chosen mass flows will be too low for almost all loading conditions of the TBM and the goal to perform DEMO relevant test will not be achieved. To cope with these conditions and assure a higher flexibility in TBM testing, a by-pass between the FW and the breeding zone has been added to inject only a small fraction of the He coolant into the breeding zone. This by-pass flow can be tuned by an external valve regulating the mass flow into the breeding zone (a time constant of about 50 s in the breeding zone makes possible this regulation).
499–0.59 <0.3
The TBM is connected to auxiliary systems that provide the coolant helium at the required conditions and the circulation of helium or PbLi for tritium extraction purposes. As the cooling requirements of the two helium coolant systems (HCS) are comparable (see Table 1), a similar system is required for the two components. At the moment two concepts of HCS are under study, a high temperature and a low temperature compressor loop (HTCL and LTCL, respectively). These two proposals differ essentially from one another in the working temperature of the helium compressor (about 300 ◦ C in the HTCL and 100 ◦ C in the other); while for the HTCL the helium coming out of the compressor can feed directly the TBM, in the LTCL it goes through a recuperator to reach the required TBM inlet temperature of 300 ◦ C; in fact, the loop is split in two parts (8-shape–configuration) by the recuperator allowing a low temperature region for the compressor (see Fig. 2). This kind of configuration is state-of-the-art for out-ofpile helium facilities; high temperature compressors for the HTCL configuration are not commercially available and necessitate dedicated R&D. An independent low-pressure loop is foreseen to extract the tritium produced in the HCPB TBM. It should supply the required purge flow at the proper mass flow and compositions (impurities should be controlled and 0.1% H2 is added to the He flow to facilitate the T extraction from the ceramic breeder). For the HCLL a PbLi circuit permits the TBM feeding and
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Fig. 2. Flow sheet of the helium coolant system.
the tritium extraction from the liquid metal outside the TBM. The PbLi mass flow in the circuit is adjustable in the range between 0.1 and 1 kg/s in order to allow investigation of various phenomena (lower mass flow rates to reach high tritium partial pressure in the liquid metal, higher mass flow rates to investigate MHD effects). The circuit layout is designed such that during discharge or in case of emergency the PbLi is transferred simply by gravity; all piping and components are heated in order to avoid freezing of the PbLi. Additional external equipment is also necessary to support performance measurements (e.g. tritium production, neutron fluxes, etc.) during the different tests and to monitor the systems during operation.
3. Integration in ITER As shown in Section 2, testing the two European TBMs in ITER requires integration of several systems and components. Three horizontal ports are available for allocating the TBMs (16, 18 and 2 according to the ITER numeration). In line with the strategy followed in EU, the integration of the European TBMs has been studied with the assumption that an equatorial port will contain two TBMs of different concepts; the HCPB TBM is assumed to occupy the upper position in port
16 with a horizontal configuration, and the HCLL in port 18 with a vertical configuration. An example of this integration for the HCPB TBM system is shown in [9]. The TBM is located inside a port plug (PP) that offers a standardised interface to the ITER vacuum vessel (VV) and allows the replacement of the TBMs. The frontal part of the PP (the so-called “frame”) provides a containment structure that thermally insulates and shields each TBM from the other one and from local ITER structure (see Fig. 3). The whole structure is cantilevered with a flange to the VV port extension. A thick neutron shield (about 1 m thickness) inside the PP protects the magnets, the structures and the buildings from the neutron flux. The shield constitutes also the first interface for TBM integration providing a support for the mechanical attachments and penetrations for the TBM pipes. The mechanical attachment is designed to cope with the large electromagnetic (EM) forces that are created during plasma disruptions (a radial torque of 0.72 MNm has been calculated and used as design reference for the HCPB design). The attachment consists of three shear keys capable of withstanding the EM torque and acting as the fixed point (in the middle of the TBM back plate), and four “flexibles” that locate the TBM with bolts in radial direction. Another possibility is shown in Fig. 1 for the HCLL design, where “stub
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Fig. 3. TBM integration in ITER VV and port cell.
keys” (a compact design that combines the functions of flexible and shear key) are proposed. The presence of large helium pipes caused some difficulties due to space requirements for the integration. As helium is transparent to neutrons and does not contribute to the shielding, only pipes of internal diameter (i.d.) smaller than 30 mm can be routed straight through the port plug shield; tubes of larger diameter must be bent within the shielding to reduce neutron streaming. The vacuum boundary is realised at the rear part of the shield; here the vacuum at the penetrations coming from the TBM should be ensured in relation to 0.1 MPa in the inter-space cell. To attach the TBM to the shield with screw straight holes are needed in the shield for access; to ensure the shielding function these holes should be closed by shield plugs. Flexible support (bellows) in the helium pipes to the PP must be designed in order to compensate the differential thermal expansion (e.g. up to 500 ◦ C for the hot leg in comparison to ∼150 ◦ C of the PP structure). In line with the ITER requirement each bellow must be secondarily contained with monitoring of the inter-space. The resulting interface is quite complex; this interface is one of the most critical factors and may limit the num-
ber of independent TBM systems that can be tested at the same time in ITER. Following the present philosophy adopted by ITER for the PP handling, the replacement of the TBMs is done in the hot cell after the port plug is extracted from its position in the VV, transported in the cask to the hot cell and docked to the PP refurbishment workstation. The replacement system studied in [9] is based on the use of in-bore tools and mechanical screw actuators that operate from the clean side of the docking station reaching the Interface 1 inside the PP shielding. For the helium pipes, two types of in-bore tools are required, a cutting/welding/testing device for straight pipes of 30 mm i.d., and an analogous device for bent tubes of 80 mm i.d. and bend radius not lower than 400 mm. The PbLi re-circulation pipes for the HCLL should require tools of the first type (30 mm i.d.). In addition, the electrical grounding and the instrumentation cables must be connected/disconnected as well; for these systems the design is ongoing. Several systems should be accommodated in the space in front of the VV port (the inter-space in the VV extension inside the bio-shield, and in the port cell); for both HCPB and HCLL concepts the pip-
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ing of the main coolant system, some component of the by-pass (valve and thermal sleeves), helium or PbLi pipes for the tritium extraction, measurement systems, etc. A further issue is the layout of the main helium pipes to the respective HCS allocated in the torus coolant water system (TCWS) vault. An example for the HCPB integration is presented in [9]; again the major requirements for the layout are the restricted space and the necessity to realise a quick exchange of the components. The use of an integrated device (the so-called piping integration cask, PIC) allows the pipes to be cut and re-welded only at the boundary interfaces, removing all the intermediate components as a block. The layout of helium pipes of 80–100 mm i.d. from the interface 2 to 3 (see Fig. 3) is dictated mainly by the necessity to compensate the thermal expansion of the pipes (maximum design values are 500 ◦ C and 8 MPa); large radius bends have been designed to accommodate this expansion. A conclusion of this study was that the space is restricted, but the accommodation of a second analogous system to support the TBM in the lower port is still possible if a common PIC is used for the integration of both systems. For the HCLL, the PbLi ancillary system has to be placed in the test port area, too, and it has to be as close as possible to the TBM in order to reduce the PbLi inventory and the tritium permeation through the pipes. Due to the space requirements for allowing the personnel to perform the maintenance operation, the PbLi circuit will be placed behind the bio-shield plug in an insulated container of 2.3 × 1.6 × 2.2 m3 (high × width × depth). As already mentioned previously, the HCSs for both EU TBMs are to be located in the TCWS vault. The pipes coming from the port cell have to be routed through vertical shafts reaching – after about 80 m length and a change of level of about +15 m – the HCSs position. The place available in the vault is insufficient to locate more than four coolant systems of a capacity to cool one TBM. Preliminary studies have been made for the HCS system in order to investigate the possibility to install it in the foreseen area of 2.5 × 7.5 m2 . The space seems to be sufficient with the exception of some additional space necessary to locate some supporting system. Several studies are ongoing to design a more compact HCS configuration or sharing some subsystems.
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Most of tritium systems will be located in the tritium building in standard glove boxes (4 × 2 × 6 m3 ), but a detailed study of integration is to be done. 4. Conclusions and future work The design of the two European TBM concepts foreseen for their testing in ITER has been almost completed. At the present, the work is focused on the detailed engineering design including the definition of fabrication routes and technologies. In future, the work will be focused on the validation of the proposed design before to install it in ITER; a large mock-up programme will address the main issue of manufacturing and performance for single components and systems. The milestone is to complete the final design in 2010 and then to start the procurement of the components to be installed in ITERs. Study of integration in ITER started already in 2004. A first proposal for the TBM integration in the Port Plug, for the TBM replacement in the hot cell and for the allocation and handling of the port cell has been presented. Studies have been already started to investigate the integration of the HCS in the TWCS vault. Acknowledgements The present work has been performed in the CEAand FZK-EURATOM associations in the frame of the European Fusion Technology Programme coordinated by EFDA Garching. Although the paper reports the work performed inside these associations and presents the opinions of the authors, a continuous exchange of information on the issue of ITER integration has been maintained with the ITER JCT in Garching and Naka. In particular, the authors thank S. Chiocchio, R. Haange, K. Ioki, K. Kataoka, M. Morimoto and A. Tesini for their valuable contributions to discussions. References [1] R. Meyder, L.V. Boccaccini, B. Dolensky, S. Hermsmeyer, M. Ilic, M.X. Jin, et al., New modular concept for the helium cooled pebble bed test blanket module for ITER, Fusion Eng. Des. 75–79 (2005) 795–799.
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[2] L.V. Boccaccini, R. Meyder, U. Fischer, Test strategy for the European HCPB test blanket module in ITER, in: Proceedings of the 16th Topical Meeting on Technology of Fusion Energy, 2004 (to be published in Fusion Sci. Technol.). [3] G. Rampal, Y. Poitevin, A. Li Puma, E. Rigal, J. Szczepanski, C. Boudot, HCLL TBM for ITER — design studies, Fusion Eng. Des. 75–79 (2005) 917–922. [4] L.V. Boccaccini, L. Giancarli, G. Janeschitz, S. Hermsmeyer, Y. Poitevin, A. Cardella, E. Diegele, Materials and design of the European DEMO blankets, J. Nucl. Mater. 329–333 (2004) 148–155. [5] A. Cardella, E. Rigal, L. Bedel, Ph. Bucci, J. Fiek, L. Forest, L.V. Boccaccini, E. Diegele, L. Giancarli, S. Hermsmeyer, et al., The manufacturing technologies of the European breeding blankets, J. Nucl. Mater. 329–333 (2004) 133–140.
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