Path planning and space occupation for remote maintenance operations of transportation in DEMO

Path planning and space occupation for remote maintenance operations of transportation in DEMO

Fusion Engineering and Design 146 (2019) 325–328 Contents lists available at ScienceDirect Fusion Engineering and Design journal homepage: www.elsev...

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Fusion Engineering and Design 146 (2019) 325–328

Contents lists available at ScienceDirect

Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes

Path planning and space occupation for remote maintenance operations of transportation in DEMO

T



Alberto Vale , José Dias Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal

A R T I C LE I N FO

A B S T R A C T

Keywords: Remote maintenance Ex-vessel transportation Trajectories and occupancy DEMO

The ex-vessel Remote Maintenance Systems are responsible for the replacement and transportation of the plasma facing components. The space required to perform the ex-vessel operations of transportation, as well as the respective time duration, has a great impact in the economics of a fusion power plant. This paper provides a preliminary assessment of the volume required to perform the operations of transportation along optimized trajectories in all levels of DEMO's reactor building. The overhead systems and ground systems are considered as the possible transportation technologies. In particular to the upper level, a cask concept is compared with a hot cell concept. Computed results of occupied volumes and time duration are presented taking into account the nominal, i.e., the expected and planned operations, and the possible rescue operations.

1. Introduction The ex-vessel Remote Maintenance Systems (RMS) in the DEMOnstration Power Station (DEMO) are responsible for the replacement and transportation of the plasma facing components. The exvessel operations of transportation are performed by overhead systems or ground vehicles. The time duration of the transportation operations has to be taken into account for the reactor shutdown. The space required to perform these operations has also an impact in the economics of the power plant. The most suitable concepts to perform the operations of transportation in each level of the DEMO's reactor building were presented in [1,2] and evaluated according the criteria described in [3]. In particular, two concepts are under evaluation for the upper level: cask and hot cell [4]. The work presented in this paper provides a preliminary assessment of the volume required to perform the operations of transportation along optimized trajectories in all levels. The number of transportations per each port, in each level, has not been defined yet. Therefore, a given number was assumed to evaluate the current analysis. The travel speed is assumed constant with a maximum value of 20 cm/s (the same value assumed for Cask and Plug Remote handling System in the International Thermonuclear Experimental Reactor – ITER [5,6]) to estimate the time duration of all operations of transportation. The paper is organized as follows. Sections 2 and 3 describe the exvessel operations of transportation, the assumed technologies for



nominal, recovery and rescue operations and the expected trajectories. Section 4 describes the occupied volumes in each level and Section 5 presents the total time duration estimated for all operations of transportation. Section 6 summarizes the main results. 2. Transportation in reactor building and assumptions Three types of transportation technologies were considered for moving the heavy loads in nuclear facilities: overhead, ground and a combination of both [1]. According to [3], the selected transportation technologies are: (i) Upper – the cask and hot cell for comparison; (ii) Upper-equatorial – a radial overhead tracked-rail system; (iii) Equatorial – a radial overhead gallery crane system; a ground-based tracked railway will be used to allow for the transport of equipment and hardware between the maintenance facility and the overhead gallery cranes; (iv) Divertor – a ground vehicle automation or a ground-based track; and (v) Basement – radial tracked-rail system crane. The trajectories were evaluated in each level with the following assumptions: a CAD model of the DEMO reactor building (version of March 2017), a maximum load size specific for each level, a given number of ports in each level, a safety margin during the transportation of cranes or ground vehicles, with or without cask (the safety margin is not considered for recovery/rescue purposes), and a maximum speed for operations of transportation [7].

Corresponding author. E-mail addresses: [email protected] (A. Vale), [email protected] (J. Dias).

https://doi.org/10.1016/j.fusengdes.2018.12.057 Received 18 July 2018; Received in revised form 24 October 2018; Accepted 18 December 2018 Available online 06 January 2019 0920-3796/ © 2018 Elsevier B.V. All rights reserved.

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3. Trajectories and occupied area The trajectories were optimized in a Software tool developed by IST for ITER purposes, to minimize the distance and the risk of collision [5]. The algorithm provides a single path between two points and it can include maneuvers. However, the load is assumed to be transported in the properly configuration to the target point, and hence, no maneuvers are considered. There is an exception in the equatorial level, where a vertical rotation might be required. In upper, divertor and equatorial levels, the trajectories are assumed to start in the same initial point, where in equatorial level, there are two possible entrances to this level, and hence, two different initial points. A single transportation solution is used for each level, with exception for the upper level, where two concepts are addressed and compared: the cask concept (the load is transported horizontally by a ground vehicle) and the hot cell concept (the load is transported vertically by a crane system). Each trajectory has its respective length and time duration of execution, assuming a constant velocity. The occupied area corresponds to the footprint, i.e., the 2D space occupied by the casks/cranes transporting the largest load, while following the respective trajectory. The occupied area with a safety margin is the original occupied area enlarged with 0.3 m only for safety purposes and not for recovery or rescue. The volume results from an extrusion along the vertical axis of the occupied area. The following sections present the results for each level.

Fig. 2. Trajectories for all ports in the upper level (cask concept), the resulted occupied area and volume (top images). The occupied volume in Upper-equatorial, equatorial, divertor and basement levels are in bottom images.

occupied area is similar to the upper level and assuming the cask concept. Finally, in the basement level, the occupied area is similar to the upper-equatorial level, but with six connections to the ports. The top images of Fig. 2 illustrate the poses along all the trajectories in the upper level (cask concept), the occupied area and the respective volume, that results from the extrusion of the occupied area along the height of the vehicle with the largest load. The bottom images illustrate the occupied volumes for the other levels. 3.2. Recovery and rescue operations During recovery operations, the failed crane/cask follows a trajectory already evaluated for a nominal operation and no additional space is required. If the recovery operation is not successfully completed, the deployment of additional/external system is required for rescue operations, as the proposed approaches described in [8]. When an overhead transportation system performs the nominal operations, there are two possible solutions for rescue operations: a rescue crane using the same overhead system or a ground rescue vehicle. A rescue crane using the same overhead system is confined to operate along the overhead railway or conveyor, which may difficult or even compromise the rescue operations. In addition, a failure may occur during the transportation of heavy loads, i.e., the crane may fail and stop its motion, hanging and tilting the load in the middle of the galleries. Besides the risk of dealing with activated material during the rescue operations, a heavy load hung from the ceiling is an additional risk. A ground system is the proposed rescue solution to keep the load or the failed equipment as much as possible on the floor. Therefore, the proposed strategy is the following:

3.1. Nominal operations The nominal operations are the expected and planned operations of transportation. The occupied area required by the nominal operations are evaluated combining all the expected trajectories in each level and following the procedure depicted in Fig. 1. The dimension of the load plays an important role in the occupied area. Taking into account the example of the cask concept in the upper level, the results illustrated in Fig. 2 were achieved with a load of 17.4 m × 3.5 m × 5.7 m and with a safety margin of 0.3 m. If the load is 1 m wider or 1 m longer, the occupied area would increase 20% and 7%, respectively. In the upper level and with the cask concept, the shape of the occupied area is similar to a ring with equally spaced branches to several ports. In a previous design of reactor, the number of ports was 18, but the actual design considers 16 ports. The studies performed in this paper considered 14 ports and the resulted must be assumed as a lower bound of the total occupied value for a number of ports larger than 14. The cask has access to each port by the shortest or by the longest path. Still in the upper level, but with the hot cell concept, the occupied area is defined by two interconnected and concentric rings, where the inner one has access to the ports. In the upper-equatorial level, the occupied area has two interconnected and concentric rings, with 5 connections to the ports, each one with a “trident” shape. The equatorial level resembles the upper-equatorial, with a slight change: the occupied area depends if the load is transported vertically or horizontally. However, at the end, the occupied volume is the same. In the divertor level, the

• In levels where a ground system performs the nominal operations of •

transportation, the rescue operations are only performed by ground rescue vehicles, which may take advantage of the same ground transportation system or, when necessary, switch to an independent wheeled system. In levels where an overhead system performs the nominal operations of transportation, a hybrid approach is the proposed solution, i.e., a rescue crane, which shares the same overhead transportation system, in cooperation with ground rescue vehicles, performs the rescue operations.

The proposed strategy requires a ground rescue system available in all levels, but provides the following advantages:

• a single rescue technology that can be shared in all levels, • a single or multiple rescue vehicles can operate in simultaneous for a rescue operation, • a rescue ground vehicle provides free roaming capability to take the best profit of moving in cluttered scenarios, and • a more stable and controllable solution for failure and seismic

Fig. 1. Methodology to estimate the occupied area from trajectories. 326

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Fig. 4. Example of the occupied volume, assuming the cask concept, inserted in the CAD models of DEMO reactor building (version of March 2017).

space for the nominal operations in case of overhead systems might never be used. However, a failure may occur anywhere along the expected trajectories and in any moment of the ex-vessel operations of transportation, and that space must be available. Assuming the CAD model of the DEMO reactor building (version of March 2017), the additional volume for rescue operations is minimal in upper level with the cask concept, in the equatorial and divertor levels. In the upper level with the hot cell concept and in the upper-equatorial level, the volumes increase 49% and 72%, respectively. In the basement level, the additional volume for rescue operations is 533%, since the height of the load is 2 m, while the height of the level is 18.8 m. A possible ground system solution for nominal operations in the basement level would adopt an identical layout to the tracked-rail system crane and with a similar building structure, as described in [3]. The volume occupied by the nominal operations is similar, which would be also enough to accommodate the rescue operations, i.e., no additional volume would be required for rescue operations in the basement level. Fig. 4 provides a first shot of these volumes integrated in the CAD model of the reactor building. For simplicity of perception, the results are compared to the volume of an Olympic swimming pool, which dimensions are 50 m × 25 m × 2 m (length, width and depth), corresponding to 2500 m3 of water. Fig. 5 shows the comparison results for the volume occupied in each level considering the vehicle, load and rescue volume.

Fig. 3. Occupied volume required by the RMS in all levels, assuming the two concepts for the upper level (top images) and how the rescue space depends to the height of the level (bottom images).

conditions. In addition, no substantial requirements are expected in the building to support the ground rescue system, such as the available space for navigation, docking, charging, anchoring and parking places for the rescue vehicles.

4. Occupied volume The occupied volumes performed by the RMS during the nominal and rescue operations of transportation are evaluated by the 3D shapes resulted from the extrusion along the vertical axis of the occupied areas, as illustrated in Fig. 2. The amount of extrusion is given by the height of the load. Additional 3D shapes are evaluated corresponding to the ground vehicles or cranes, in case of ground or overhead transportation, respectively, as illustrated in the top images of Fig. 3. The cask concept in the upper level assumes two intermediate levels: one for the equipment cask and another for the hardware cask. The volume occupied by the equipment cask can be significantly lower if assuming smaller loads and without an additional ground vehicle. Even though, the cask concept for the upper level is, by far, the largest occupied volume, where the maintenance cask tackles the critical point (more than 55% of the upper level occupied volume). For the cask concept, the occupied volume of the upper level is so large as the occupied volume of the other levels together. In levels where a ground system is already available for nominal operations, the additional space required for rescue operations is not substantial high, since the rescue vehicles are able to share the same space reserved for the nominal operations. In levels where an overhead transportation system is available for the nominal operations, the total occupied volume with the additional space required for a hybrid approach with a ground vehicle corresponds to the total height of the level. Therefore, the space required for rescue operations is strongly dependent on the height of the level, as depicted in the bottom image of Fig. 3. The minimum space required for rescue operations corresponds to the height of the load plus the height of the rescue ground vehicle plus the height of the overhead system (when applicable), which is closer to the volume of nominal operations. In summary, the space required for rescue operations corresponds to the space required for nominal operations plus the additional space given the height of a ground system, which can be something below 1 m. If the height of the level is significantly higher than the height of the load, the space required for rescue operations increases dramatically, since the space in the middle must be also reserved to support the rescue operations, including the exchange of loads between the overhead system and the ground system. The space between the rescue ground system and the

5. Time duration The expected time duration for each ex-vessel operation of transportation is given by (1), with the following assumptions:

time = speed × #operations × length of trajectory × #ports × 2

(1)

• The travel speed is assumed constant with a maximum value of 20 cm/s. With accelerations, the estimated time duration increases. • The length of trajectory is measured between the initial point and the destination port. • The number of operations is the number of casks/cranes with dif-

ferent load configurations expected at the same port. The used values are just indicative for assessment purposes, without any reference found in the literature. It is expected two times more

Fig. 5. Occupied volumes required by the vehicles (with/without load) and rescue operations in amount of Olympic swimming pools. 327

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388 h (16 days), similar to cask and hot cell. This estimation does not include docking, accelerations neither operations that are not transportation. The amount of time required for transportations leads to the necessity of addressing strategies with multiple vehicles in simultaneous operation. The results achieved in this preliminary assessment will help the design process to optimize the time duration of the reactor shutdown and the layout of the DEMO power plant.

Fig. 6. Expected time duration of ex-vessel operations of transportation in the reactor building.

Acknowledgments

operations using a single crane, since the cask is able to transport additional tools or part of the equipment can be temporarily placed inside the maintenance cask in the cask concept. The number of ports were achieved from the CAD models, and it is assumed that all ports are accessed with the same number of times. The result is multiplied by 2, since each operation is assumed that the cask/crane has to move to the target port and thus return to its base.Fig. 6 presents the comparison results between the total time assuming the shortest and the longest paths for each level.

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 under grant agreement no. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

• •

References [1] A. Vale, D. Fonte, F. Valente, I. Ribeiro, Trajectory optimization for autonomous mobile robots in ITER, Robot. Auton. Syst. 62 (2014) 871–888. [2] D. Iglesias, R. Bastow, D. Cooper, R. Crowe, D. Middleton-Gear, R. Sibois, D. Carloni, Z. Vizvary, O. Crofts, J. Harman, A. Loving, Remote handling assessment of attachment concepts for DEMO blanket segments, Fusion Eng. Des. 98–99 (2015) 1500–1504. [3] I. Clargo, Final report on deliverable ex-vessel remote maintenance concept designs, EUROfusion DEMO Work Program of Remote Maintenance, 2N3H37 v1.1, (2017). [4] A. Vale, Transport system path planning and space occupation, EUROfusion DEMO Work Program of Remote Maintenance, 2MS7PQ v1.0, (2017). [5] A. Vale, R. Ventura, P. Lopes, I. Ribeiro, Assessment of navigation technologies for automated guided vehicle in nuclear fusion facilities, Fusion Eng. Des. 97 (2017) 153–170. [6] J. Davies, Concept design description for the DEMO upper port maintenance system, EUROfusion DEMO Work Program of Remote Maintenance, 2MMR6P v1.0, (2015). [7] O. Crofts, A. Loving, D. Iglesias, M. Coleman, M. Siuko, M. Mittwollen, V. Queral, A. Vale, E. Villedieu, Overview of progress on the European DEMO remote maintenance strategy, Fusion Eng. Des. 109–111 (Part B) (2015) 1392–1398. [8] M. Irving, C. Damiani, J.C. Morey, G. Puccini, G. Brang, E. Fassy, Remote handling and assembly engineering support – rescue of a failed transfer cask system, Framework Contract ESC-04, Task Agreement No. 006, (2008).

6. Conclusions This paper presented a preliminary assessment of the required volume and time duration of ex-vessel operations of transportation, in all levels of the DEMO's reactor building. A total of 87 trajectories were evaluated, with a total length of approximately 3 km. The total occupancy volume for nominal operations is, comparatively, between 21 and 45 Olympic swimming pools, where the hot cell concept is the best option in the upper level of the reactor building. A ground system is the proposed rescue solution to keep the load or the failed equipment as much as possible on the floor. However, the required space for rescue operations is strongly dependent to the height of each level of the building and, thus, shall be considered as an issue for the building design. The total time duration estimated for all ex-vessel operations of transportation in the reactor building are between 166 h (7 days) and

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