- Email: [email protected]
Design and configurations for the Shielding of the Beam Dump of IFMIF DONES
Fusion Engineering and Design 153 (2020) 111475
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Design and configurations for the Shielding of the Beam Dump of IFMIF DONES
T
Daniel Sánchez-Herranza,*, Pedro Ortegob, Oriol Nomena, Beatriz Brañasc, Francisco Ogandod, Patrick Sauvand, Fernando Arranzc, Sofía Colomae a
IREC, Jardins de les Dones de Negre, 1, 2ª, 08930, Sant Adrià de Besòs, Catalonia, Barcelona, Spain Science Engineering Associates (SEA), Las Rozas, 28232, Comunidad de Madrid, Madrid, Spain c CIEMAT, Avenida Complutense, 40, 28040, Madrid, Spain d UNED, C/ Juan del Rosal 12, 28040, Madrid, Spain e Centre for Automation and Robotics UPM-CSIC, Madrid, Spain b
A R T I C LE I N FO
A B S T R A C T
Keywords: IFMIF DONES Early neutron source Remote handling Beam dump Radiation shielding
IFMIF-DONES (International Fusion Materials Irradiation Facility – DEMO Oriented Neutron Source) is currently being developed in the frame of the EUROfusion Early Neutron Source work package (WPENS). It will be an installation for fusion material testing, that will generate a flux of neutrons of 1018 m−2s−1 with a broad peak at 14 MeV by Li(d,xn) nuclear reactions thanks to a deuteron beam colliding on a liquid Li flow. The accelerator system is in charge of providing such high energy deuterons in order to produce the neutron flux expected. The objective of the Beam Dump, part of the High Energy Beam Transport Line (HEBT), is to stop the pulsed beam at low duty cycle during DONES accelerator commissioning and start-up phases. The present work explains the radiological design of the beam dump shielding and two different configuration approaches for the materialization of the design. The radiological design considers maintenance and operation, and it was done together with the building walls dimensioning so that the combined radiation attenuation by the local shield and the building leads to dose rates in the different rooms that satisfy the requirements. Activation of the materials in the HEBT line, originated by the leakage of neutrons through the beam dump entrance is evaluated and an ad-hoc solution is proposed for its minimization. Regarding the mechanical design, in the first configuration, the shielding is split into two halves horizontally, the upper-half requiring external lifting capabilities for its commission and maintenance. The second approach consists in a vertical splitting into two halves, which are self-moveable, avoiding the needs of external lifting capabilities for the remote handling of the shielding.
1. Introduction
Instrumentation and Control Systems. The Accelerator System, schematic shown in Fig. 1, is also divided into six subsystems: The ERC Ion source provides and extracts the 125 mA deuteron beam at 100 keV, the Low Energy Beam Transport line (LEBT) which guides the beam to the next stage, the Radiofrequency Quadrupole (RFQ) system whose purpose is to bunch and speed up the beam to 5 MeV, the Medium Energy Beam Transport line (MEBT) re-bunches and transports the beam to the Superconducting Radio Frequency (SRF) Linac where 40 MeV beam energy is reached and finally the High Energy Beam Transport Line (HEBT) in charge of guiding and shaping the beam with the rectangular footprint required. The HEBT will have a dedicated Beam Dump installed in a side line of the HEBT, to be used during commissioning of the facility and during
IFMIF-DONES (DEMO Oriented Neutron source) [1,2] will be a linear particle accelerator facility for fusion material study. It will generate a neutron flux with a spectrum similar to that of a (D-T) fusion reactor. This is achieved by utilizing Li(d,xn) nuclear reactions taking place in a liquid Li target when bombarded by a deuteron beam. The energy of the deuterons (40 MeV) and the current of the accelerator (125 mA) have been chosen to achieve irradiation conditions comparable to those in the first wall of a fusion power reactor. The IFMIF-DONES systems breakdown identifies five major groups of systems: 1) Site Building and Plant Systems; 2) The Test Systems; 3) The Lithium Systems; 4) The Accelerator Systems; and 5) The Central
⁎
Corresponding author. E-mail address: [email protected] (D. Sánchez-Herranz).
https://doi.org/10.1016/j.fusengdes.2020.111475 Received 16 September 2019; Received in revised form 8 January 2020; Accepted 9 January 2020 Available online 22 January 2020 0920-3796/ © 2020 Institut de Recerca en Energia de Catalunya. Published by Elsevier B.V. All rights reserved.
Fusion Engineering and Design 153 (2020) 111475
D. Sánchez-Herranz, et al.
Fig. 1. IFMIF-DONES Accelerator System Schematic.
start-up phases after a shutdown allowing beam tuning and its characterization. This will be done with a pulsed beam at low duty cycle (1 %). Once the beam has been properly tuned, it will be directed to the Lithium target with the duty cycle progressively increased up 100 %. The beam dump is composed of two subcomponents: cartridge and shielding. The aim of the cartridge is stopping the particle beam and dissipating power deposition generated, by means of a water cooling circuit. The chosen design for the cartridge is the one used for IFMIFLIPAc [3]. A mechanical analysis was performed demonstrating that this design can fulfill the needs of DONES beam dump. The interaction of the deuteron beam with the cartridge gives rise to:
-
-
-
- Prompt neutron and gamma radiation - Activation of the cartridge by deuterons and of the whole beam dump by the secondary neutrons
-
Therefore, a radiation field is generated during the operation of the beam dump and also a residual field remains after the beam disappears, due to the activated materials. The shielding surrounding the cartridge has the function of attenuating them both. DONES beam dump shield will be different from that of the LIPAc beam dump, since the neutron source produced as a consequence of the 40 MeV deuteron beam interaction with the copper cone is different from that generated by the LIPAc 9 MeV beam, and also because of the differences in the geometry of the building and dose rate limits defined in the adjacent rooms.
3. Radiological design of the Beam Dump Shield 3.1. Shield design procedure and resulting design As a starting point, a concept including cylindrical layers of light material as water or polyethylene and a heavy material as iron or lead surrounding the beam dump cartridge was considered. For the shield design the following criteria have been taken into account: - Solutions with minimum volume and total mass have been searched for. - With regard to the light material, polyethylene has been chosen because of the following reasons: - Simpler design due to the absence of water pipes for filling and emptying the shield tanks. - Also the need to monitor and control water quality is avoided. - A solid shield is easier to be handled during cartridge replacement and dismantling. - For the dimensioning of the front shield regions, an acceptable activation rate during operation in the accelerator components closer to the beam dump has been searched for.
2. Beam dump requirements General and functional beam dump requirements are listed below: -
located on Second Basement Floor (see Fig. 2). - 10 μSv/h at R201 located in First Floor (RF Source Area) (see Fig. 2). Its local shielding must allow, after a reasonable cooling time (one day is assumed), human access to the Accelerator Vault (R110) and Beam Transport Room (R113) for maintenance activities (Fig. 2). A radiation rate limit during maintenance of 1 mSv/h has been established for the project. The radiation from the beam dump received by the accelerator elements (diagnostics, quadrupoles, cavities, etc.) should be minimized as much as possible by an adequate local shield. The beam dump should be disassembled and the cartridge extracted safely at the end of its life or in case that substitution is needed during the facility lifetime. Activated cartridge should be qualified to be disposed as a waste in a near-surface repository.
Ion species: deuterons Energy: 40 MeV Max. current: 125 mA Max. instantaneous power: 5MW Max. beam pulsed duration: 2ms Max. beam frequency: 5 Hz Maximum operation time of 2000 h
Apart from the general and functional requirements, there are more specific ones related to the scope of this work, focused on radioprotection and remote handling:
The resulting design is shown in Fig. 3. For the main part of the shield (named radial shield in Fig. 3), after the analysis of several combinations of materials, an optimized design with three cylindrical layers was obtained, starting with 70 mm thickness lead, as the innermost material, followed by 650 mm of polyethylene and a 20 mm external covering of low alloy steel with low concentration in cobalt and manganese (2500 and 1000 ppm have been assumed respectively). Special configurations for the front and back shields are required. For the dimensioning of these parts conservative cases have been studied assuming possible radiation source displacements along the axial direction due to different beam focusing events. At the frontal extension of the radial shield, a thicker layer of steel is required to compensate the absence of lead and the thinner
- Average dose rates during accelerator operation on the beam dump at maximum specified power and 1 % duty cycle (50 kW) must be below limits established on each room of the building around the beam dump location. - 1000 μSv/h at R108 (Radiation Cooling Machine Room) (see Fig. 2). - 100 mSv/h at R112 (Assembly Maintenance Room) and at R109A1 (Piping and cabling penetration Space) (see Fig. 2). - 3 μSv/h at R170 (Accelerator HVAC Room) and C001 (Corridor) 2
Fusion Engineering and Design 153 (2020) 111475
D. Sánchez-Herranz, et al.
Fig. 2. Beam Dump Building Layout. Top view of the building (Top) and vertical cross section of the building (Bottom).
However, the shield performance under beam-off conditions has been found to impose stronger requirements and it has determined the final shield design consisting of an internal layer of polyethylene 150 mm thick and an external one of low alloy steel 200 mm thick. To attenuate the neutron streaming through this hole, a neutron attenuator consisting of a polyethylene disc has been located at 2.5 m before the beam dump, where the beam tube radius is the smallest. It creates a space in front of the beam dump with higher neutron reaction rate but it shields the rest of the room from the neutron stream coming through the vacuum tube from the beam dump. The internal radius of this disc is defined by the accelerator tube. Its thickness (430 mm) and external radius (660 mm) have been defined to be those required to obtain an activation rate comparable to that produced generally around the radial shield in the elements behind it.
polyethylene layer. The dimensioning of the frontal part was performed assuming the worst case which will be a defocused beam depositing its power closer to the beam dump entrance. The front shield, made also of layers of polyethylene and iron, must allow the passage of the beam tube through it. The radiation from the cartridge will escape through this shield penetration. The shield elements have been adjusted to the beam tube shape as much as possible so that the solid angle of the radiation escaping through the hole in the shield is minimized. Taking into account the reduction of the cross section of the beam tube with the distance from the beam dump aperture, the diameter of the hole in the front shield elements is 340 mm. The neutrons leaking through the frontal shield contribute to outside dose and, more importantly, activate the components around the HEBT, specially those closest to the beam dump (magnets). 3
Fusion Engineering and Design 153 (2020) 111475
D. Sánchez-Herranz, et al.
Fig. 3. Beam Dump conceptual design dimensions in mm.
During maintenance, the residual gamma radiation escaping through the opening must be stopped by a movable lead shutter blocking the shield aperture. After several calculations varying the radial overlap with the beam dump shield, a troncoconical geometry with 110 mm thickness, 200 mm minimum radius and 30° angle was chosen. The total dose behind the shutter and at the beam axis is small (less than 1 μSv/h). No dose due to the lead of the shielding is considered due to its high purity. Nevertheless, the limiting point is not the beam axis but the laterals of the shutter. The dose reduction at this location has been the objective in the shutter design and determined its troncoconical shape and the radial overlapping with the rest of the shield. The contact dose at the limiting point, which is due to the beam dump cartridge activation, is 4.9 μSv/h. With regard to the rear part of the shield, the thickness of the low alloy steel is mainly defined to limit the dose coming from the beam dump cone and cylinder, while the polyethylene thickness is defined by the limitation of activation of the low alloy steel (mainly to the production of Mn54 and secondarily to Co60 and Mn56).
Table 1 Dose rates in μSv/h of the different rooms during beam dump operation and comparison to dose rate limits. Room
Dose Limit
Max. Dose rate
Neutron Dose rate
Gamma Dose rate
R108 R170 R112 R109-A1 R201 C001
103 3 105 105 10 3
1.58 4.37 265 2.58 0.18 12.3
1.02 4.18 225 1.77 0.144 10.3
0.56 0.19 40 0.81 0.032 1.95
In the ceiling of room R109-A1, there is a large empty space required for the path of the radiofrequency conduits coming from upper floor, where the radiofrequency equipment is located, to the accelerator room where they enter through horizontal ducts. Because of its large dimension, it acts as a chimney flue for neutrons. It has been checked that the radiation coming through this opening has a negligible effect in comparison to that received directly on the second floor in the vertical of the beam dump.
3.2. Beam-on radiation analysis 3.3. Beam-off radiation analysis
Primary neutron and gamma sources resulting from the interaction of the deuteron ions with the copper of the Beam Dump cartridge have been estimated. Spectral and angular dependencies of the generated neutron source have been studied using an extended MCNPX code, called MCUNED, together with different nuclear data libraries. Large differences depending on the nuclear model used were observed, concluding that INCL4 model seems to be the most suitable, since it fits better the experimental data available. For the maximum assumed duty cycle (1 %), the total radiation intensities calculated are 1.65 × 1014 neutrons/s with an average energy of 8.5 MeV showing the origin of most neutrons in the breakup of deuteron. The intensity of prompt gamma source is 2.17 × 1014 photons/s but due to the heavy shield required for beam-off conditions the prompt gammas are never limiting. During operation of the accelerator there might be radiation leakage to the upper and lower floors. There are no direct penetrations to the upper floor in the R114 or R113, however there will be penetrations for the RF guides on the ceiling of R109-A1 (Piping and Cabling Penetration Space). This will be dealt with later. Beam dump shield has been designed taking into account wall thicknesses of the room where it is located, which are 1.5 m everywhere except at the wall separating from R110 (1 m) and at the ceiling (2.3 m). The simulations (See Table 1) show that the dose rate limits are fulfilled in four out of the six adjacent rooms, being R170 and C001 the rooms with doses higher than established limits. Thus, rooms C001 (Corridor) and R170 (Accelerator HVAC Room) classification must be reassessed accordingly from supervised area to controlled area.
When the accelerator beam is off, the existing photon radiation is due both to the residuals of the Cu(d,x) reactions and to the activation of cobalt and other elements in the Beam Dump Shielding materials by the secondary neutrons. Activation of the copper cartridge by deuterons and secondary neutrons after 2000 h of operation with 1 % duty cycle has been calculated. As the cartridge will be manufactured from Cu electrodeposition, impurity content will be very low and will contribute very slightly (0.1 %) to the total cone activation. At one-day cooling time, neutron and deuteron induced activity are comparable (7.5 T Bq each). Total activation after one-week cooling is 3 T Bq coming mainly from the deuteron activation (2 T Bq of Zn65 with a half-life of 245 days accounting for 60 % of the contact dose and 1 T Bq of Co58 with a half-life of 71 days which accounts for the 30 %). At shorter cooling times, Cu64 (half-life of 12.7 h) is also relevant. Additionally, Mn54, Mn56, Ni57, Co60 and Fe59 will be produced by neutron activation in the natural composition of the stainless-steel cylinder or in the low alloy steel used for the shielding components. The dose rate limit for maintenance in the room where the beam dump is located is 1 mSv/h. The residual dose rates (μSv/h) around the beam dump at contact have been calculated and are shown in Fig. 4 at some locations around the beam dump shielding. Around the mid region of the beam dump, the total dose rate obtained at the worst location is 7.80 μSv/h and it is due to the deuteron and neutron activation of the beam dump cone (4.6 and 0.63 μSv/h), to the activation of the steel cover (2.2 μSv/h) and to that of the cylinder 4
Fusion Engineering and Design 153 (2020) 111475
D. Sánchez-Herranz, et al.
Fig. 4. Residual dose rates (μSv/h) around the beam dump at contact. Red figures correspond to dose rates due to the activated cartridge. Black figures refer to dose rates due to the shield activation (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
(0.37 μSv/h). At the rear and front parts, the residual doses from the steel dominate, being Mn54, Co60 and Mn56 the isotopes which contribute most.
Fig. 6. DONES Beam Dump conceptual design II.
(see Fig. 6), producing a lower-half and an upper-half, the latter will require external lifting capabilities for its commission and maintenance. For both cases, the BD cartridge is assumed to be supported independently from the BD shielding. Radiation streaming outside of the beam dump will be avoided by overlapping joints with dogleg shape between adjoining pieces.
4. Beam dump configuration approaches Two different configuration approaches are under study, related to the installation, maintenance and dismantling of the Beam Dump shielding. Both options are based on LIPAc beam dump design already installed in Rokkasho (Japan) [3,4]. The first configuration consists in a vertical splitting of the shielding in two halves (see Fig. 5), which are self-moveable by means of wheels and electrical motors, not requiring external means for remote lifting of the shielding. In the second approach, the shielding is divided into two half-cylinder parts horizontally
4.1. Beam dump design I This design consists on dividing the entire body of the beam dump shield (main radial shield and frontal extension) vertically into two halves. Each of these two parts, weighting approximately 24 Tons, will be provided with wheels and electric motors to allow their transversal movement, distancing themselves from each other and leaving the internal BD cartridge uncovered, ready to be dismantled or replaced by means of remote handling. Counterweights are added on four moveable carts to properly position the center of gravity, to avoid overturning. Fig. 5 shows this design. It has been checked that integration within the HEBT line and building system is feasible. To verify this, base plates and moveable carts have been added to the 3D model. A maximum distance of 2500 mm between the internal faces of the two halves when the beam dump shielding is completely opened has been considered, allowing good access of personnel for installation and hands-on maintenance when necessary. 4.2. Beam dump design II In the second beam dump conceptual design, the shield was designed in four parts, front radial extension is divided vertically into two halves, while central part is split horizontally creating top and bottom parts. The aim of this configuration is to allow cartridge replacement and dismantling using a crane of 10 Ton lifting capacity. The two semicylindrical upper and lower parts weight 10 Tons each, whereas the frontal halves weight 6.6 Ton each. The central part of the shielding could be supported either by steel supports or alternatively with a concrete bed structure. Finally, the frontal radial extension is intended to be held by movable trolleys or steel supports. Fig. 6 shows this second conceptual approach. 4.3. Benefits and drawbacks Benefits found for design I approach are, firstly, a great reduction of the remote handling payload needed since the maximum weight expected to be lifted in this case by RH would be just an approximate weight of 960 kg belonging to the BD cartridge, and secondly, remote handling steps needed for maintenance and decommission will be eased
Fig. 5. DONES Beam Dump conceptual design I. 5
Fusion Engineering and Design 153 (2020) 111475
D. Sánchez-Herranz, et al.
and decreased. In addition, whether the final decision it is not to install bridge overhead cranes in the Beam Transport Room (BTR), this design would fit with that approach. Drawbacks identified for this design are mainly, the space needed for the moveable trolleys along the sides of the Beam Dump, and decrement of robustness due to the moveable parts composing the new design. For the second design being studied, the main benefit is lack of moveable parts which leads to an increment of the overall robustness, reducing chances of failure and consequently increasing its feasibility. However, some drawbacks have been identified, such as, the need of a 10 Ton payload overhead crane, room for the temporal storage of upper-part when disassembling or replacing BD cartridge and an increase in the number and difficulty of the remote handling operations.
Methodology, Formal analysis, Writing - review & editing. Patrick Sauvan: Methodology, Formal analysis. Fernando Arranz: Writing review & editing. Sofía Coloma: Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The radiological design of the shield has been supported by the Spanish Government in the frame of the Broader Approach Agreement. The work done by IREC has been supported by the CERCA Programme from Generalitat de Catalunya (Government of Catalonia).
5. Conclusions The radiological design of the Beam Dump Shielding of the IFMIFDONES accelerator has been detailed in this paper, demonstrating its successful performance. In addition, two Beam Dump design concepts have been analyzed, together with their benefits and drawbacks observed. Due to the short time established for maintenance activities in the facility, one short (3 days) and one long (20 days) preventive maintenance periods, the first design approach seems the most suitable to achieve these tight timeframes.
References [1] A. Ibarra, et al., The IFMIF-DONES project: preliminary engineering design, Nucl. Fus. 58 (10) (2018). [2] A. Ibarra, et al., The European approach to the fusion-like neutron source: the IFMIFDONES project, Nucl. Fus. 59 (6) (2019). [3] B. Brañas, F. Arranz, O. Nomen, et al., The LIPAc beam dump, Fus. Eng. Design 127 (2018) 127–138. [4] O. Nomen, J.I. Martinez, F. Arranz, et al., Detailed mechanical design of the LIPAc beam dump radiological shielding, Fus. Eng. Design 88 (9–10) (2013) 2723–2727, https://doi.org/10.1016/j.fusengdes.2013.01.105.
CRediT authorship contribution statement Daniel Sánchez-Herranz: Writing - original draft, Formal analysis, Visualization. Pedro Ortego: Methodology, Formal analysis, Writing review & editing. Oriol Nomen: Writing - review & editing, Supervision, Project administration. Beatriz Brañas: Writing - review & editing, Supervision, Project administration. Francisco Ogando:
6
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Design and configurations for the Shielding of the Beam Dump of IFMIF DONES
T
Daniel Sánchez-Herranza,*, Pedro Ortegob, Oriol Nomena, Beatriz Brañasc, Francisco Ogandod, Patrick Sauvand, Fernando Arranzc, Sofía Colomae a
IREC, Jardins de les Dones de Negre, 1, 2ª, 08930, Sant Adrià de Besòs, Catalonia, Barcelona, Spain Science Engineering Associates (SEA), Las Rozas, 28232, Comunidad de Madrid, Madrid, Spain c CIEMAT, Avenida Complutense, 40, 28040, Madrid, Spain d UNED, C/ Juan del Rosal 12, 28040, Madrid, Spain e Centre for Automation and Robotics UPM-CSIC, Madrid, Spain b
A R T I C LE I N FO
A B S T R A C T
Keywords: IFMIF DONES Early neutron source Remote handling Beam dump Radiation shielding
IFMIF-DONES (International Fusion Materials Irradiation Facility – DEMO Oriented Neutron Source) is currently being developed in the frame of the EUROfusion Early Neutron Source work package (WPENS). It will be an installation for fusion material testing, that will generate a flux of neutrons of 1018 m−2s−1 with a broad peak at 14 MeV by Li(d,xn) nuclear reactions thanks to a deuteron beam colliding on a liquid Li flow. The accelerator system is in charge of providing such high energy deuterons in order to produce the neutron flux expected. The objective of the Beam Dump, part of the High Energy Beam Transport Line (HEBT), is to stop the pulsed beam at low duty cycle during DONES accelerator commissioning and start-up phases. The present work explains the radiological design of the beam dump shielding and two different configuration approaches for the materialization of the design. The radiological design considers maintenance and operation, and it was done together with the building walls dimensioning so that the combined radiation attenuation by the local shield and the building leads to dose rates in the different rooms that satisfy the requirements. Activation of the materials in the HEBT line, originated by the leakage of neutrons through the beam dump entrance is evaluated and an ad-hoc solution is proposed for its minimization. Regarding the mechanical design, in the first configuration, the shielding is split into two halves horizontally, the upper-half requiring external lifting capabilities for its commission and maintenance. The second approach consists in a vertical splitting into two halves, which are self-moveable, avoiding the needs of external lifting capabilities for the remote handling of the shielding.
1. Introduction
Instrumentation and Control Systems. The Accelerator System, schematic shown in Fig. 1, is also divided into six subsystems: The ERC Ion source provides and extracts the 125 mA deuteron beam at 100 keV, the Low Energy Beam Transport line (LEBT) which guides the beam to the next stage, the Radiofrequency Quadrupole (RFQ) system whose purpose is to bunch and speed up the beam to 5 MeV, the Medium Energy Beam Transport line (MEBT) re-bunches and transports the beam to the Superconducting Radio Frequency (SRF) Linac where 40 MeV beam energy is reached and finally the High Energy Beam Transport Line (HEBT) in charge of guiding and shaping the beam with the rectangular footprint required. The HEBT will have a dedicated Beam Dump installed in a side line of the HEBT, to be used during commissioning of the facility and during
IFMIF-DONES (DEMO Oriented Neutron source) [1,2] will be a linear particle accelerator facility for fusion material study. It will generate a neutron flux with a spectrum similar to that of a (D-T) fusion reactor. This is achieved by utilizing Li(d,xn) nuclear reactions taking place in a liquid Li target when bombarded by a deuteron beam. The energy of the deuterons (40 MeV) and the current of the accelerator (125 mA) have been chosen to achieve irradiation conditions comparable to those in the first wall of a fusion power reactor. The IFMIF-DONES systems breakdown identifies five major groups of systems: 1) Site Building and Plant Systems; 2) The Test Systems; 3) The Lithium Systems; 4) The Accelerator Systems; and 5) The Central
⁎
Corresponding author. E-mail address: [email protected] (D. Sánchez-Herranz).
https://doi.org/10.1016/j.fusengdes.2020.111475 Received 16 September 2019; Received in revised form 8 January 2020; Accepted 9 January 2020 Available online 22 January 2020 0920-3796/ © 2020 Institut de Recerca en Energia de Catalunya. Published by Elsevier B.V. All rights reserved.
Fusion Engineering and Design 153 (2020) 111475
D. Sánchez-Herranz, et al.
Fig. 1. IFMIF-DONES Accelerator System Schematic.
start-up phases after a shutdown allowing beam tuning and its characterization. This will be done with a pulsed beam at low duty cycle (1 %). Once the beam has been properly tuned, it will be directed to the Lithium target with the duty cycle progressively increased up 100 %. The beam dump is composed of two subcomponents: cartridge and shielding. The aim of the cartridge is stopping the particle beam and dissipating power deposition generated, by means of a water cooling circuit. The chosen design for the cartridge is the one used for IFMIFLIPAc [3]. A mechanical analysis was performed demonstrating that this design can fulfill the needs of DONES beam dump. The interaction of the deuteron beam with the cartridge gives rise to:
-
-
-
- Prompt neutron and gamma radiation - Activation of the cartridge by deuterons and of the whole beam dump by the secondary neutrons
-
Therefore, a radiation field is generated during the operation of the beam dump and also a residual field remains after the beam disappears, due to the activated materials. The shielding surrounding the cartridge has the function of attenuating them both. DONES beam dump shield will be different from that of the LIPAc beam dump, since the neutron source produced as a consequence of the 40 MeV deuteron beam interaction with the copper cone is different from that generated by the LIPAc 9 MeV beam, and also because of the differences in the geometry of the building and dose rate limits defined in the adjacent rooms.
3. Radiological design of the Beam Dump Shield 3.1. Shield design procedure and resulting design As a starting point, a concept including cylindrical layers of light material as water or polyethylene and a heavy material as iron or lead surrounding the beam dump cartridge was considered. For the shield design the following criteria have been taken into account: - Solutions with minimum volume and total mass have been searched for. - With regard to the light material, polyethylene has been chosen because of the following reasons: - Simpler design due to the absence of water pipes for filling and emptying the shield tanks. - Also the need to monitor and control water quality is avoided. - A solid shield is easier to be handled during cartridge replacement and dismantling. - For the dimensioning of the front shield regions, an acceptable activation rate during operation in the accelerator components closer to the beam dump has been searched for.
2. Beam dump requirements General and functional beam dump requirements are listed below: -
located on Second Basement Floor (see Fig. 2). - 10 μSv/h at R201 located in First Floor (RF Source Area) (see Fig. 2). Its local shielding must allow, after a reasonable cooling time (one day is assumed), human access to the Accelerator Vault (R110) and Beam Transport Room (R113) for maintenance activities (Fig. 2). A radiation rate limit during maintenance of 1 mSv/h has been established for the project. The radiation from the beam dump received by the accelerator elements (diagnostics, quadrupoles, cavities, etc.) should be minimized as much as possible by an adequate local shield. The beam dump should be disassembled and the cartridge extracted safely at the end of its life or in case that substitution is needed during the facility lifetime. Activated cartridge should be qualified to be disposed as a waste in a near-surface repository.
Ion species: deuterons Energy: 40 MeV Max. current: 125 mA Max. instantaneous power: 5MW Max. beam pulsed duration: 2ms Max. beam frequency: 5 Hz Maximum operation time of 2000 h
Apart from the general and functional requirements, there are more specific ones related to the scope of this work, focused on radioprotection and remote handling:
The resulting design is shown in Fig. 3. For the main part of the shield (named radial shield in Fig. 3), after the analysis of several combinations of materials, an optimized design with three cylindrical layers was obtained, starting with 70 mm thickness lead, as the innermost material, followed by 650 mm of polyethylene and a 20 mm external covering of low alloy steel with low concentration in cobalt and manganese (2500 and 1000 ppm have been assumed respectively). Special configurations for the front and back shields are required. For the dimensioning of these parts conservative cases have been studied assuming possible radiation source displacements along the axial direction due to different beam focusing events. At the frontal extension of the radial shield, a thicker layer of steel is required to compensate the absence of lead and the thinner
- Average dose rates during accelerator operation on the beam dump at maximum specified power and 1 % duty cycle (50 kW) must be below limits established on each room of the building around the beam dump location. - 1000 μSv/h at R108 (Radiation Cooling Machine Room) (see Fig. 2). - 100 mSv/h at R112 (Assembly Maintenance Room) and at R109A1 (Piping and cabling penetration Space) (see Fig. 2). - 3 μSv/h at R170 (Accelerator HVAC Room) and C001 (Corridor) 2
Fusion Engineering and Design 153 (2020) 111475
D. Sánchez-Herranz, et al.
Fig. 2. Beam Dump Building Layout. Top view of the building (Top) and vertical cross section of the building (Bottom).
However, the shield performance under beam-off conditions has been found to impose stronger requirements and it has determined the final shield design consisting of an internal layer of polyethylene 150 mm thick and an external one of low alloy steel 200 mm thick. To attenuate the neutron streaming through this hole, a neutron attenuator consisting of a polyethylene disc has been located at 2.5 m before the beam dump, where the beam tube radius is the smallest. It creates a space in front of the beam dump with higher neutron reaction rate but it shields the rest of the room from the neutron stream coming through the vacuum tube from the beam dump. The internal radius of this disc is defined by the accelerator tube. Its thickness (430 mm) and external radius (660 mm) have been defined to be those required to obtain an activation rate comparable to that produced generally around the radial shield in the elements behind it.
polyethylene layer. The dimensioning of the frontal part was performed assuming the worst case which will be a defocused beam depositing its power closer to the beam dump entrance. The front shield, made also of layers of polyethylene and iron, must allow the passage of the beam tube through it. The radiation from the cartridge will escape through this shield penetration. The shield elements have been adjusted to the beam tube shape as much as possible so that the solid angle of the radiation escaping through the hole in the shield is minimized. Taking into account the reduction of the cross section of the beam tube with the distance from the beam dump aperture, the diameter of the hole in the front shield elements is 340 mm. The neutrons leaking through the frontal shield contribute to outside dose and, more importantly, activate the components around the HEBT, specially those closest to the beam dump (magnets). 3
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Fig. 3. Beam Dump conceptual design dimensions in mm.
During maintenance, the residual gamma radiation escaping through the opening must be stopped by a movable lead shutter blocking the shield aperture. After several calculations varying the radial overlap with the beam dump shield, a troncoconical geometry with 110 mm thickness, 200 mm minimum radius and 30° angle was chosen. The total dose behind the shutter and at the beam axis is small (less than 1 μSv/h). No dose due to the lead of the shielding is considered due to its high purity. Nevertheless, the limiting point is not the beam axis but the laterals of the shutter. The dose reduction at this location has been the objective in the shutter design and determined its troncoconical shape and the radial overlapping with the rest of the shield. The contact dose at the limiting point, which is due to the beam dump cartridge activation, is 4.9 μSv/h. With regard to the rear part of the shield, the thickness of the low alloy steel is mainly defined to limit the dose coming from the beam dump cone and cylinder, while the polyethylene thickness is defined by the limitation of activation of the low alloy steel (mainly to the production of Mn54 and secondarily to Co60 and Mn56).
Table 1 Dose rates in μSv/h of the different rooms during beam dump operation and comparison to dose rate limits. Room
Dose Limit
Max. Dose rate
Neutron Dose rate
Gamma Dose rate
R108 R170 R112 R109-A1 R201 C001
103 3 105 105 10 3
1.58 4.37 265 2.58 0.18 12.3
1.02 4.18 225 1.77 0.144 10.3
0.56 0.19 40 0.81 0.032 1.95
In the ceiling of room R109-A1, there is a large empty space required for the path of the radiofrequency conduits coming from upper floor, where the radiofrequency equipment is located, to the accelerator room where they enter through horizontal ducts. Because of its large dimension, it acts as a chimney flue for neutrons. It has been checked that the radiation coming through this opening has a negligible effect in comparison to that received directly on the second floor in the vertical of the beam dump.
3.2. Beam-on radiation analysis 3.3. Beam-off radiation analysis
Primary neutron and gamma sources resulting from the interaction of the deuteron ions with the copper of the Beam Dump cartridge have been estimated. Spectral and angular dependencies of the generated neutron source have been studied using an extended MCNPX code, called MCUNED, together with different nuclear data libraries. Large differences depending on the nuclear model used were observed, concluding that INCL4 model seems to be the most suitable, since it fits better the experimental data available. For the maximum assumed duty cycle (1 %), the total radiation intensities calculated are 1.65 × 1014 neutrons/s with an average energy of 8.5 MeV showing the origin of most neutrons in the breakup of deuteron. The intensity of prompt gamma source is 2.17 × 1014 photons/s but due to the heavy shield required for beam-off conditions the prompt gammas are never limiting. During operation of the accelerator there might be radiation leakage to the upper and lower floors. There are no direct penetrations to the upper floor in the R114 or R113, however there will be penetrations for the RF guides on the ceiling of R109-A1 (Piping and Cabling Penetration Space). This will be dealt with later. Beam dump shield has been designed taking into account wall thicknesses of the room where it is located, which are 1.5 m everywhere except at the wall separating from R110 (1 m) and at the ceiling (2.3 m). The simulations (See Table 1) show that the dose rate limits are fulfilled in four out of the six adjacent rooms, being R170 and C001 the rooms with doses higher than established limits. Thus, rooms C001 (Corridor) and R170 (Accelerator HVAC Room) classification must be reassessed accordingly from supervised area to controlled area.
When the accelerator beam is off, the existing photon radiation is due both to the residuals of the Cu(d,x) reactions and to the activation of cobalt and other elements in the Beam Dump Shielding materials by the secondary neutrons. Activation of the copper cartridge by deuterons and secondary neutrons after 2000 h of operation with 1 % duty cycle has been calculated. As the cartridge will be manufactured from Cu electrodeposition, impurity content will be very low and will contribute very slightly (0.1 %) to the total cone activation. At one-day cooling time, neutron and deuteron induced activity are comparable (7.5 T Bq each). Total activation after one-week cooling is 3 T Bq coming mainly from the deuteron activation (2 T Bq of Zn65 with a half-life of 245 days accounting for 60 % of the contact dose and 1 T Bq of Co58 with a half-life of 71 days which accounts for the 30 %). At shorter cooling times, Cu64 (half-life of 12.7 h) is also relevant. Additionally, Mn54, Mn56, Ni57, Co60 and Fe59 will be produced by neutron activation in the natural composition of the stainless-steel cylinder or in the low alloy steel used for the shielding components. The dose rate limit for maintenance in the room where the beam dump is located is 1 mSv/h. The residual dose rates (μSv/h) around the beam dump at contact have been calculated and are shown in Fig. 4 at some locations around the beam dump shielding. Around the mid region of the beam dump, the total dose rate obtained at the worst location is 7.80 μSv/h and it is due to the deuteron and neutron activation of the beam dump cone (4.6 and 0.63 μSv/h), to the activation of the steel cover (2.2 μSv/h) and to that of the cylinder 4
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Fig. 4. Residual dose rates (μSv/h) around the beam dump at contact. Red figures correspond to dose rates due to the activated cartridge. Black figures refer to dose rates due to the shield activation (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
(0.37 μSv/h). At the rear and front parts, the residual doses from the steel dominate, being Mn54, Co60 and Mn56 the isotopes which contribute most.
Fig. 6. DONES Beam Dump conceptual design II.
(see Fig. 6), producing a lower-half and an upper-half, the latter will require external lifting capabilities for its commission and maintenance. For both cases, the BD cartridge is assumed to be supported independently from the BD shielding. Radiation streaming outside of the beam dump will be avoided by overlapping joints with dogleg shape between adjoining pieces.
4. Beam dump configuration approaches Two different configuration approaches are under study, related to the installation, maintenance and dismantling of the Beam Dump shielding. Both options are based on LIPAc beam dump design already installed in Rokkasho (Japan) [3,4]. The first configuration consists in a vertical splitting of the shielding in two halves (see Fig. 5), which are self-moveable by means of wheels and electrical motors, not requiring external means for remote lifting of the shielding. In the second approach, the shielding is divided into two half-cylinder parts horizontally
4.1. Beam dump design I This design consists on dividing the entire body of the beam dump shield (main radial shield and frontal extension) vertically into two halves. Each of these two parts, weighting approximately 24 Tons, will be provided with wheels and electric motors to allow their transversal movement, distancing themselves from each other and leaving the internal BD cartridge uncovered, ready to be dismantled or replaced by means of remote handling. Counterweights are added on four moveable carts to properly position the center of gravity, to avoid overturning. Fig. 5 shows this design. It has been checked that integration within the HEBT line and building system is feasible. To verify this, base plates and moveable carts have been added to the 3D model. A maximum distance of 2500 mm between the internal faces of the two halves when the beam dump shielding is completely opened has been considered, allowing good access of personnel for installation and hands-on maintenance when necessary. 4.2. Beam dump design II In the second beam dump conceptual design, the shield was designed in four parts, front radial extension is divided vertically into two halves, while central part is split horizontally creating top and bottom parts. The aim of this configuration is to allow cartridge replacement and dismantling using a crane of 10 Ton lifting capacity. The two semicylindrical upper and lower parts weight 10 Tons each, whereas the frontal halves weight 6.6 Ton each. The central part of the shielding could be supported either by steel supports or alternatively with a concrete bed structure. Finally, the frontal radial extension is intended to be held by movable trolleys or steel supports. Fig. 6 shows this second conceptual approach. 4.3. Benefits and drawbacks Benefits found for design I approach are, firstly, a great reduction of the remote handling payload needed since the maximum weight expected to be lifted in this case by RH would be just an approximate weight of 960 kg belonging to the BD cartridge, and secondly, remote handling steps needed for maintenance and decommission will be eased
Fig. 5. DONES Beam Dump conceptual design I. 5
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and decreased. In addition, whether the final decision it is not to install bridge overhead cranes in the Beam Transport Room (BTR), this design would fit with that approach. Drawbacks identified for this design are mainly, the space needed for the moveable trolleys along the sides of the Beam Dump, and decrement of robustness due to the moveable parts composing the new design. For the second design being studied, the main benefit is lack of moveable parts which leads to an increment of the overall robustness, reducing chances of failure and consequently increasing its feasibility. However, some drawbacks have been identified, such as, the need of a 10 Ton payload overhead crane, room for the temporal storage of upper-part when disassembling or replacing BD cartridge and an increase in the number and difficulty of the remote handling operations.
Methodology, Formal analysis, Writing - review & editing. Patrick Sauvan: Methodology, Formal analysis. Fernando Arranz: Writing review & editing. Sofía Coloma: Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The radiological design of the shield has been supported by the Spanish Government in the frame of the Broader Approach Agreement. The work done by IREC has been supported by the CERCA Programme from Generalitat de Catalunya (Government of Catalonia).
5. Conclusions The radiological design of the Beam Dump Shielding of the IFMIFDONES accelerator has been detailed in this paper, demonstrating its successful performance. In addition, two Beam Dump design concepts have been analyzed, together with their benefits and drawbacks observed. Due to the short time established for maintenance activities in the facility, one short (3 days) and one long (20 days) preventive maintenance periods, the first design approach seems the most suitable to achieve these tight timeframes.
References [1] A. Ibarra, et al., The IFMIF-DONES project: preliminary engineering design, Nucl. Fus. 58 (10) (2018). [2] A. Ibarra, et al., The European approach to the fusion-like neutron source: the IFMIFDONES project, Nucl. Fus. 59 (6) (2019). [3] B. Brañas, F. Arranz, O. Nomen, et al., The LIPAc beam dump, Fus. Eng. Design 127 (2018) 127–138. [4] O. Nomen, J.I. Martinez, F. Arranz, et al., Detailed mechanical design of the LIPAc beam dump radiological shielding, Fus. Eng. Design 88 (9–10) (2013) 2723–2727, https://doi.org/10.1016/j.fusengdes.2013.01.105.
CRediT authorship contribution statement Daniel Sánchez-Herranz: Writing - original draft, Formal analysis, Visualization. Pedro Ortego: Methodology, Formal analysis, Writing review & editing. Oriol Nomen: Writing - review & editing, Supervision, Project administration. Beatriz Brañas: Writing - review & editing, Supervision, Project administration. Francisco Ogando:
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