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Seamless remote dismantling system for heavy and highly radioactive components of Korean nuclear power plants
Annals of Nuclear Energy 73 (2014) 39–45
Contents lists available at ScienceDirect
Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Technical note
Seamless remote dismantling system for heavy and highly radioactive components of Korean nuclear power plants Dongjun Hyun ⇑, Sung-Uk Lee, Yong-Chil Seo, Geun-Ho Kim, Jonghwan Lee, Kwan-Seong Jeong, Byung-Seon Choi, Jei-Kwon Moon Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon 305-353, Republic of Korea
a r t i c l e
i n f o
Article history: Received 31 March 2014 Received in revised form 9 June 2014 Accepted 10 June 2014
Keywords: Decommissioning Remote dismantling system Nuclear power plant
a b s t r a c t A seamless remote system for dismantling heavy and highly radioactive components during the decommissioning of a nuclear power plant is proposed. The originality of the dismantling system is in its ability to handle all the processes involved in the dismantling of major components of a nuclear power plant without external intervention. Previous types of dismantling equipment were designed for specific components or a particular process, which required time consuming and risky equipment replacement tasks between different processes. The proposed dismantling system was designed and verified by simulation of all the processes for dismantling the major components of a Korean nuclear power plant. Several challenges such as working in confined spaces and with complex movement lines as well as interference between components were overcome. The proposed system is capable of handling all the dismantling processes without equipment replacement tasks or the need to drain the reactor pool. The system is expected to considerably reduce the time and cost of the entire decommissioning process while also improving safety. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Since the commissioning of the first nuclear power plant (NPP) in Korea in 1978, 22 others have commenced operation. Although their termination licences may be revised according to government policies, the first NPP is expected to be dismantled in 10 years, and approximately 10 more would follow suit over the next 20 years. The international market of NPP decommissioning is also expected to expand dramatically. However, only a few advanced countries are presently experienced in nuclear decommissioning and have developed related technologies (Radioactive Waste Management Committee, 2011). The effective handling of the expected upsurge in the decommissioning of nuclear facilities thus requires the further development of various related technologies. The major components of an NPP, which include the reactor pressure vessel, steam generator, reactor coolant pump, and pressuriser, are very heavy and highly radioactive, and their dismantling processes are the most difficult and dangerous during decommissioning. Highlevel radiation restricts access by human workers, and this makes manual cutting of the heavy and thick structures – often made of
⇑ Corresponding author. Tel.: +82 42 868 8081; fax: +82 42 868 8062. E-mail address: [email protected] (D. Hyun). http://dx.doi.org/10.1016/j.anucene.2014.06.020 0306-4549/Ó 2014 Elsevier Ltd. All rights reserved.
carbon steel – very impractical. Remote dismantling technologies thus play an important role in NPP decommissioning. The determination of the concept of a remote dismantling system is a very important preparatory step in NPP decommissioning because a well-designed remote dismantling system would considerably reduce the total decommissioning cost and time as wells as improve the safety of the entire task. Process simulation is necessary for the design process to avoid potential problems and risks and to select an effective mechanism or equipment for managing various dismantling scenarios. A 3D graphical simulation of the dismantling process of the Korea Research Reactors 1 and 2 was performed by Kim et al. (2003), and a digital mock-up system for selecting a proper decommissioning scenario for the two reactors was also developed (Kim et al., 2006). A process simulation technology that utilises haptic rendering was used to verify the maintenance task in a PyRoprocess Integrated Inactive DEmonstration (PRIDE) digital mock-up (Park et al., 2011). The Commissariat à l‘énergie atomique et aux énergies (CEA) conducted an R&D program to develop a simulation tool that can be used to understand constraints, test different alternatives, and train workers (Chabal et al., 2011). This paper proposes a seamless remote dismantling system as a novel solution to the time consuming, costly, and risky interruptions that occur between the different dismantling processes
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D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
Fig. 1. Primary system of Korean NPP.
involved in the decommissioning of an NPP. Because conventional remote dismantling systems are designed to handle a single process such as cutting of pipes or segmenting of cylindrical parts, interruptions are required to replace equipment between different processes. The replacement operations often involve human workers, are time intensive, and sometimes require the drainage and supply of substantial amounts of water to the reactor pool for protection against radiation. The following section presents an overview of the first Korean NPP, which is very likely to be the first to be decommissioned in the country and was the subject of the dismantling process simulated in this study. Section 3 describes how the proposed seamless remote dismantling system effectively handles the tasks of dismantling the major components of the NPP without external intervention, such as the removal of existing equipment, installation of additional equipment, and operations usually performed by human workers. The conclusion section summaries the study and states the potential contributions of the proposed system. 2. Overview of Korean NPP The primary system of the first Korean NPP is a Westinghouse two-loop pressurized water reactor that consists of a reactor pressure vessel (RPV), two steam generators (SG), two reactor coolant pumps (RCP), and a pressurizer (PZR) (see Fig. 1). The RPV composed of the reactor vessel (RV), the vessel head and reactor internals is approximately 3.4 m in diameter and 12 m in height. The RV
Fig. 2. Containment building.
weighs approximately 180 tons and has carbon steel walls with a stainless steel cladding of which thickness is 1.7 m in the cylindrical part, 1.2 m in the bottom hemispheric part, and 0.53 m in the flange. The containment building is a reinforced steel structure with a can-like shape, with the RPV at its centre (see Fig. 2). The polar crane, hand rail, and reactor pool in Fig. 2 are used to provide the proposed dismantling system with utilities because the use of existing equipment reduces the overall decommissioning cost. The polar crane is primarily used to transport heavy components within the containment building, whereas the hand rail is used to deploy the equipment and transport relatively small objects within the reactor pool. The reactor pool is situated above the RPV at a floor elevation of between +44 ft and +70 ft, and is temporarily filled with water for protection against radiation during re-fuelling. At a floor elevation of +70 ft in the containment building, the reactor pool is located at the centre and is 7.0 m long and 16.5 m wide, and includes a reactor internals storage area that is 5.5 m long and 7.2 m wide (see Fig. 3). Although the reactor internals storage area is very small for the installation of a large number of equipment, it affords the best dismantling workshop with radiation protection and isolation from contamination.
3. Seamless remote dismantling system The proposed seamless remote dismantling system has a conceptual design with specifications and operation mechanisms for components that closely interact with each other. The components of the system are yet to be developed, and only a digital mock-up designed with reasonable considerations based on existing equipment and common engineering practise is presented here. The system was designed and demonstrated using the process simulation software developed by the Korea Atomic Energy Research Institute (KAERI), which is based on DELMIA developed by Dassault Systemes. The process simulation software provides graphical tools for solving spatial problems and a unique function that can be used to flexibly simulate cutting processes. The seamless remote dismantling system consists of a circular saw, gantry manipulator, waste container, band saw, and turn table, and can be used for both dry and wet operations (see Fig. 4). The layout of the components was determined by delicate considerations such as the movement lines of heavy components from the reactor cavity area to the workshop, movement lines of segmented wastes from the cutting equipment to the waste container, and cutting of large and long cylindrical components involving slicing using a circular saw and segmenting using a band saw.
D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
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Fig. 3. Layout of reactor pool.
Fig. 4. Seamless remote dismantling system.
Detailed descriptions of the slicing and segmenting processes are presented in Section 3.1. The circular saw and band saw of the proposed system are used as the major tools for cutting the highly radioactive and thick materials because mechanical saws are known to be the best cuttings tools for nuclear facility decommissioning owing to their large cutting capabilities, reasonable cutting speed, and nontoxic secondary waste. The size and stroke of the cutting equipment were optimised by process simulations to avoid obstruction of the cutting process. The turn table is the core component of the proposed system because it is used for all the cutting processes. The object being cut is fixed and transported by the turn table. The unique characteristic of the turn table is its translational mechanism, which connects the slicing operation using the circular saw with the
Fig. 5. Auxiliary equipment.
segmenting operation using the band saw. The mechanism considerably simplifies the dismantling processes by reducing the operations required to move and fix the object being cut. The gantry manipulator has a six degrees of freedom manipulator and an auxiliary gantry that can be used to expand the workspace, access a tool changer, and service the manipulator on the floor at +70 ft. The reach of the manipulator was determined so that its end effector could reach the centre of the turn table without singular configuration. The manipulator can thus be used to expand the workspace to the entire area of the turn table. The waste container presented in this paper is only a sample because the dimensions and specifications of the container are determined by complex considerations such as government policies, transportation, and facility capacity of the radioactive waste agency. However, the best location of the waste container in the workshop is that shown in Fig. 4, which affords the simplest movement lines of the segmented wastes coming from the cutting equipment. Auxiliary equipment such as the polar crane, pool crane, and vibrationless crane are used to support the seamless remote dismantling system. The polar crane, which is an existing equipment in the containment building, is used to transport the RV, RPV head, and reactor internals to the workshop using tripods specified for the respective components. This is done in the same way as during the re-fuelling of the NPP. The pool crane is modified by the hand rail of the containment building to transport the segmented wastes to the waste container. When a manipulator is to be deployed in the RV in the reactor cavity, the vibrationless crane, which stabilises the hung platform by means of a unique multi-wired mechanism and control algorithm, is temporarily installed on the rail of the pool crane instead of on the existing bridge, and is used to transport the manipulator mounted on the platform into the RV (see Fig. 5).
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D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
Fig. 6. RV dismantling process.
Fig. 7. Dismantling of internal upper support plates.
Fig. 8. Cutting of the CRDM guide tubes.
The following sections describe how the proposed system handles various dismantling scenarios without human intervention or equipment replacement in the workshop.
3.1. Slicing and segmenting using circular and band saws The cutting of heavy cylindrical components such as the RV, thermal shield, RCP case, and PZR require the largest places during the dismantling of an NPP. Fig. 6 shows an ideal means of dealing
with the RV, which is the most difficult owing to the size and weight of the component. The cutting process consists of slicing and segmenting operations. The slicing operation is used to cut the cylinder along the internal height of the waste container using the circular saw and turn table. During the slicing operation, the RV is hung by the polar crane through the tripod, and the joint between the tripod and the hook of the polar crane is allowed to rotate freely under an appropriate tension. After the slicing, the upper part of the cut cylinder is lifted a little, and the turn table transports the lower part to the
D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
43
Fig. 9. Cutting of the control rod guide tubes.
Fig. 10. Water jet cutting of RPV head.
band saw. The segmenting operation is used to cut the lower part of the cut cylinder into smaller pieces. Each piece is then lifted and transported into the waste container by the pool crane. For the above process, the circular saw requires a mechanism for adjusting its height and depth. The turn table also requires a rotational function, a translational function, and eight independently operated radial fixtures with external and internal teeth. The band saw should have a specific shape with specific depth, offset, and width that are determined by the dimensions of the waste container. The thick plates that are used to construct the reactor internals and the baffles that support the nuclear fuels are effectively segmented using the band saw, the translational function of the turn table, and a specially designed jig (see Fig. 7). The jig is used together with the eight radial fixtures to handle the various plates. 3.2. Application of gantry manipulator The gantry manipulator is primarily used for pipe cutting and other delicate cutting processes that the mechanical saws cannot
Fig. 11. Blade replacement process.
be used for owing to their bulkiness, low versatility, and the requirement of rigid cutting conditions. Miscellaneous situations, including unexpected ones, can be addressed by the gantry manipulator, which is equipped with a tool changer and various end effectors. The gantry manipulator therefore enhances the flexibility and dexterity of the remote dismantling system, and its combination with the turn table affords considerable synergy in the expansion of the workspace, as mentioned earlier. The dismantling of the RPV involves the cutting of many tubes such as the guide tubes of the control rod drive mechanism (CRDM), the control rod guide tubes of the reactor upper internals, and the bottom instrumentation guide tubes of the reactor lower internals. The gantry manipulator equipped with the hydraulic cutter as its end effector is used together with the turn table to cut all the CRDM guide tubes (see Fig. 8). To cut the control rod guide tubes, the gantry manipulator is used together with the gantry and the turn table because of the different heights of the cutting points (see Fig. 9). The gantry manipulator equipped with a high-pressure abrasive water jet can be used to manage a complicated cutting path where a mechanical saw cannot be applied. For example, the gantry manipulator equipped with a water jet nozzle can be used to cut a hemispheric surface in the tangential direction by maintaining the direction of the nozzle normal to the surface (see Fig. 10). However, despite the versatility of water jet cutting, it is necessary to minimise the use of high-pressure abrasive water jet in the dismantling of an NPP because of the accompanying increase in secondary radioactive waste. The proposed dismantling system enables the reduction of the use of high-pressure abrasive water jet because the gantry manipulator with the water jet can be used to cut hemispherical structures into simple shapes for further cutting by mechanical saws. The gantry manipulator can also be used for simple maintenance and repair tasks. For example, it can be used to replace the worn blade of the circular saw because it can climb up to the floor at +70 ft, which workers cannot easily access, and it has sufficient functions for replacing the blade (see Fig. 11). The proposed dis-
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D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
Fig. 12. Vibrationless crane with manipulator.
Fig. 13. RV nozzle cutting process.
mantling system cannot accomplish its purpose without this blade replacement process using the gantry manipulator, because human workers would have to access the highly radioactive workshop to undertake the replacement, which would also interrupt the remote dismantling process. In the case of the band saw, the worn blade can be replaced on the floor at +70 ft through the built-in elevation mechanism. 3.3. Application of vibrationless crane The vibrationless crane is used to deploy the platform equipped with the dismantling manipulator into the RV in the reactor cavity when the heads of the bolts used to fix the baffles are to be removed, or when the nozzle that connects the RV to the primary loop of the NPP has to be cut. The vibrationless crane steadily places and stabilises the platform by means of a unique multiwired mechanism and control algorithm. The platform has a radial support mechanism for rigid fastening and a positioning mechanism for adjusting the base position of the dismantling manipulator (see Fig. 12). The RV nozzle is cut to enable its extraction from the reactor cavity. The cutting from outside the RV is very difficult because of the narrow gap between the reactor cavity and the RV. A cutting process from the inner wall of the nozzle using the high-pressure abrasive water jet is thus presented in the process simulation (see Fig. 13).
4. Conclusion The simulation of the entire RPV dismantling process has demonstrated that the proposed seamless remote dismantling system can be successfully used to dismantle various components of the RPV of a Korean NPP without external intervention in the highly radioactive workshop. The components of the proposed system cooperate for mutual enhancement of their respective functions. The system is expected to improve the effectiveness and safety of the entire dismantling process by simplifying the required tasks and eliminating the need for human workers to access the workshop. Further study will be conducted to verify the proposed dismantling system, including its physical characteristics and the feasibility of the utilised equipment. The physical characteristics that require investigation include the gravity fields, mechanical strength, and friction. This is necessary because, as noted earlier, most of the components of the proposed system are yet to be developed, and the process simulation software used for the present study contained only graphical tools.
Acknowledgments This study was supported by the Nuclear R & D Program through the Ministry of Science, ICT & Future Planning.
D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
References Chabal et al., 2011. Virtual reality technologies: a way to verify and design dismantling operations. Int. J. Adv. Intell. Syst. 4, 343–356. Kim et al., 2003. The preliminary 3D dynamic simulation on the RSR dismantling process of the KRR-1&2. Ann. Nucl. Energy 30, 1487–1494.
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Kim et al., 2006. Development of a digital mock-up system for selecting a decommissioning scenario. Ann. Nucl. Energy 33, 1227–1235. Park et al., 2011. Deployment analysis and remote accessibility verification for a maintenance task in a PRIDE digital mock-up. Ann. Nucl. Energy 38, 767–774. Radioactive Waste Management Committee, 2011. Remote Handling Techniques in Decommissioning.
Contents lists available at ScienceDirect
Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Technical note
Seamless remote dismantling system for heavy and highly radioactive components of Korean nuclear power plants Dongjun Hyun ⇑, Sung-Uk Lee, Yong-Chil Seo, Geun-Ho Kim, Jonghwan Lee, Kwan-Seong Jeong, Byung-Seon Choi, Jei-Kwon Moon Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon 305-353, Republic of Korea
a r t i c l e
i n f o
Article history: Received 31 March 2014 Received in revised form 9 June 2014 Accepted 10 June 2014
Keywords: Decommissioning Remote dismantling system Nuclear power plant
a b s t r a c t A seamless remote system for dismantling heavy and highly radioactive components during the decommissioning of a nuclear power plant is proposed. The originality of the dismantling system is in its ability to handle all the processes involved in the dismantling of major components of a nuclear power plant without external intervention. Previous types of dismantling equipment were designed for specific components or a particular process, which required time consuming and risky equipment replacement tasks between different processes. The proposed dismantling system was designed and verified by simulation of all the processes for dismantling the major components of a Korean nuclear power plant. Several challenges such as working in confined spaces and with complex movement lines as well as interference between components were overcome. The proposed system is capable of handling all the dismantling processes without equipment replacement tasks or the need to drain the reactor pool. The system is expected to considerably reduce the time and cost of the entire decommissioning process while also improving safety. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Since the commissioning of the first nuclear power plant (NPP) in Korea in 1978, 22 others have commenced operation. Although their termination licences may be revised according to government policies, the first NPP is expected to be dismantled in 10 years, and approximately 10 more would follow suit over the next 20 years. The international market of NPP decommissioning is also expected to expand dramatically. However, only a few advanced countries are presently experienced in nuclear decommissioning and have developed related technologies (Radioactive Waste Management Committee, 2011). The effective handling of the expected upsurge in the decommissioning of nuclear facilities thus requires the further development of various related technologies. The major components of an NPP, which include the reactor pressure vessel, steam generator, reactor coolant pump, and pressuriser, are very heavy and highly radioactive, and their dismantling processes are the most difficult and dangerous during decommissioning. Highlevel radiation restricts access by human workers, and this makes manual cutting of the heavy and thick structures – often made of
⇑ Corresponding author. Tel.: +82 42 868 8081; fax: +82 42 868 8062. E-mail address: [email protected] (D. Hyun). http://dx.doi.org/10.1016/j.anucene.2014.06.020 0306-4549/Ó 2014 Elsevier Ltd. All rights reserved.
carbon steel – very impractical. Remote dismantling technologies thus play an important role in NPP decommissioning. The determination of the concept of a remote dismantling system is a very important preparatory step in NPP decommissioning because a well-designed remote dismantling system would considerably reduce the total decommissioning cost and time as wells as improve the safety of the entire task. Process simulation is necessary for the design process to avoid potential problems and risks and to select an effective mechanism or equipment for managing various dismantling scenarios. A 3D graphical simulation of the dismantling process of the Korea Research Reactors 1 and 2 was performed by Kim et al. (2003), and a digital mock-up system for selecting a proper decommissioning scenario for the two reactors was also developed (Kim et al., 2006). A process simulation technology that utilises haptic rendering was used to verify the maintenance task in a PyRoprocess Integrated Inactive DEmonstration (PRIDE) digital mock-up (Park et al., 2011). The Commissariat à l‘énergie atomique et aux énergies (CEA) conducted an R&D program to develop a simulation tool that can be used to understand constraints, test different alternatives, and train workers (Chabal et al., 2011). This paper proposes a seamless remote dismantling system as a novel solution to the time consuming, costly, and risky interruptions that occur between the different dismantling processes
40
D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
Fig. 1. Primary system of Korean NPP.
involved in the decommissioning of an NPP. Because conventional remote dismantling systems are designed to handle a single process such as cutting of pipes or segmenting of cylindrical parts, interruptions are required to replace equipment between different processes. The replacement operations often involve human workers, are time intensive, and sometimes require the drainage and supply of substantial amounts of water to the reactor pool for protection against radiation. The following section presents an overview of the first Korean NPP, which is very likely to be the first to be decommissioned in the country and was the subject of the dismantling process simulated in this study. Section 3 describes how the proposed seamless remote dismantling system effectively handles the tasks of dismantling the major components of the NPP without external intervention, such as the removal of existing equipment, installation of additional equipment, and operations usually performed by human workers. The conclusion section summaries the study and states the potential contributions of the proposed system. 2. Overview of Korean NPP The primary system of the first Korean NPP is a Westinghouse two-loop pressurized water reactor that consists of a reactor pressure vessel (RPV), two steam generators (SG), two reactor coolant pumps (RCP), and a pressurizer (PZR) (see Fig. 1). The RPV composed of the reactor vessel (RV), the vessel head and reactor internals is approximately 3.4 m in diameter and 12 m in height. The RV
Fig. 2. Containment building.
weighs approximately 180 tons and has carbon steel walls with a stainless steel cladding of which thickness is 1.7 m in the cylindrical part, 1.2 m in the bottom hemispheric part, and 0.53 m in the flange. The containment building is a reinforced steel structure with a can-like shape, with the RPV at its centre (see Fig. 2). The polar crane, hand rail, and reactor pool in Fig. 2 are used to provide the proposed dismantling system with utilities because the use of existing equipment reduces the overall decommissioning cost. The polar crane is primarily used to transport heavy components within the containment building, whereas the hand rail is used to deploy the equipment and transport relatively small objects within the reactor pool. The reactor pool is situated above the RPV at a floor elevation of between +44 ft and +70 ft, and is temporarily filled with water for protection against radiation during re-fuelling. At a floor elevation of +70 ft in the containment building, the reactor pool is located at the centre and is 7.0 m long and 16.5 m wide, and includes a reactor internals storage area that is 5.5 m long and 7.2 m wide (see Fig. 3). Although the reactor internals storage area is very small for the installation of a large number of equipment, it affords the best dismantling workshop with radiation protection and isolation from contamination.
3. Seamless remote dismantling system The proposed seamless remote dismantling system has a conceptual design with specifications and operation mechanisms for components that closely interact with each other. The components of the system are yet to be developed, and only a digital mock-up designed with reasonable considerations based on existing equipment and common engineering practise is presented here. The system was designed and demonstrated using the process simulation software developed by the Korea Atomic Energy Research Institute (KAERI), which is based on DELMIA developed by Dassault Systemes. The process simulation software provides graphical tools for solving spatial problems and a unique function that can be used to flexibly simulate cutting processes. The seamless remote dismantling system consists of a circular saw, gantry manipulator, waste container, band saw, and turn table, and can be used for both dry and wet operations (see Fig. 4). The layout of the components was determined by delicate considerations such as the movement lines of heavy components from the reactor cavity area to the workshop, movement lines of segmented wastes from the cutting equipment to the waste container, and cutting of large and long cylindrical components involving slicing using a circular saw and segmenting using a band saw.
D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
41
Fig. 3. Layout of reactor pool.
Fig. 4. Seamless remote dismantling system.
Detailed descriptions of the slicing and segmenting processes are presented in Section 3.1. The circular saw and band saw of the proposed system are used as the major tools for cutting the highly radioactive and thick materials because mechanical saws are known to be the best cuttings tools for nuclear facility decommissioning owing to their large cutting capabilities, reasonable cutting speed, and nontoxic secondary waste. The size and stroke of the cutting equipment were optimised by process simulations to avoid obstruction of the cutting process. The turn table is the core component of the proposed system because it is used for all the cutting processes. The object being cut is fixed and transported by the turn table. The unique characteristic of the turn table is its translational mechanism, which connects the slicing operation using the circular saw with the
Fig. 5. Auxiliary equipment.
segmenting operation using the band saw. The mechanism considerably simplifies the dismantling processes by reducing the operations required to move and fix the object being cut. The gantry manipulator has a six degrees of freedom manipulator and an auxiliary gantry that can be used to expand the workspace, access a tool changer, and service the manipulator on the floor at +70 ft. The reach of the manipulator was determined so that its end effector could reach the centre of the turn table without singular configuration. The manipulator can thus be used to expand the workspace to the entire area of the turn table. The waste container presented in this paper is only a sample because the dimensions and specifications of the container are determined by complex considerations such as government policies, transportation, and facility capacity of the radioactive waste agency. However, the best location of the waste container in the workshop is that shown in Fig. 4, which affords the simplest movement lines of the segmented wastes coming from the cutting equipment. Auxiliary equipment such as the polar crane, pool crane, and vibrationless crane are used to support the seamless remote dismantling system. The polar crane, which is an existing equipment in the containment building, is used to transport the RV, RPV head, and reactor internals to the workshop using tripods specified for the respective components. This is done in the same way as during the re-fuelling of the NPP. The pool crane is modified by the hand rail of the containment building to transport the segmented wastes to the waste container. When a manipulator is to be deployed in the RV in the reactor cavity, the vibrationless crane, which stabilises the hung platform by means of a unique multi-wired mechanism and control algorithm, is temporarily installed on the rail of the pool crane instead of on the existing bridge, and is used to transport the manipulator mounted on the platform into the RV (see Fig. 5).
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D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
Fig. 6. RV dismantling process.
Fig. 7. Dismantling of internal upper support plates.
Fig. 8. Cutting of the CRDM guide tubes.
The following sections describe how the proposed system handles various dismantling scenarios without human intervention or equipment replacement in the workshop.
3.1. Slicing and segmenting using circular and band saws The cutting of heavy cylindrical components such as the RV, thermal shield, RCP case, and PZR require the largest places during the dismantling of an NPP. Fig. 6 shows an ideal means of dealing
with the RV, which is the most difficult owing to the size and weight of the component. The cutting process consists of slicing and segmenting operations. The slicing operation is used to cut the cylinder along the internal height of the waste container using the circular saw and turn table. During the slicing operation, the RV is hung by the polar crane through the tripod, and the joint between the tripod and the hook of the polar crane is allowed to rotate freely under an appropriate tension. After the slicing, the upper part of the cut cylinder is lifted a little, and the turn table transports the lower part to the
D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
43
Fig. 9. Cutting of the control rod guide tubes.
Fig. 10. Water jet cutting of RPV head.
band saw. The segmenting operation is used to cut the lower part of the cut cylinder into smaller pieces. Each piece is then lifted and transported into the waste container by the pool crane. For the above process, the circular saw requires a mechanism for adjusting its height and depth. The turn table also requires a rotational function, a translational function, and eight independently operated radial fixtures with external and internal teeth. The band saw should have a specific shape with specific depth, offset, and width that are determined by the dimensions of the waste container. The thick plates that are used to construct the reactor internals and the baffles that support the nuclear fuels are effectively segmented using the band saw, the translational function of the turn table, and a specially designed jig (see Fig. 7). The jig is used together with the eight radial fixtures to handle the various plates. 3.2. Application of gantry manipulator The gantry manipulator is primarily used for pipe cutting and other delicate cutting processes that the mechanical saws cannot
Fig. 11. Blade replacement process.
be used for owing to their bulkiness, low versatility, and the requirement of rigid cutting conditions. Miscellaneous situations, including unexpected ones, can be addressed by the gantry manipulator, which is equipped with a tool changer and various end effectors. The gantry manipulator therefore enhances the flexibility and dexterity of the remote dismantling system, and its combination with the turn table affords considerable synergy in the expansion of the workspace, as mentioned earlier. The dismantling of the RPV involves the cutting of many tubes such as the guide tubes of the control rod drive mechanism (CRDM), the control rod guide tubes of the reactor upper internals, and the bottom instrumentation guide tubes of the reactor lower internals. The gantry manipulator equipped with the hydraulic cutter as its end effector is used together with the turn table to cut all the CRDM guide tubes (see Fig. 8). To cut the control rod guide tubes, the gantry manipulator is used together with the gantry and the turn table because of the different heights of the cutting points (see Fig. 9). The gantry manipulator equipped with a high-pressure abrasive water jet can be used to manage a complicated cutting path where a mechanical saw cannot be applied. For example, the gantry manipulator equipped with a water jet nozzle can be used to cut a hemispheric surface in the tangential direction by maintaining the direction of the nozzle normal to the surface (see Fig. 10). However, despite the versatility of water jet cutting, it is necessary to minimise the use of high-pressure abrasive water jet in the dismantling of an NPP because of the accompanying increase in secondary radioactive waste. The proposed dismantling system enables the reduction of the use of high-pressure abrasive water jet because the gantry manipulator with the water jet can be used to cut hemispherical structures into simple shapes for further cutting by mechanical saws. The gantry manipulator can also be used for simple maintenance and repair tasks. For example, it can be used to replace the worn blade of the circular saw because it can climb up to the floor at +70 ft, which workers cannot easily access, and it has sufficient functions for replacing the blade (see Fig. 11). The proposed dis-
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D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
Fig. 12. Vibrationless crane with manipulator.
Fig. 13. RV nozzle cutting process.
mantling system cannot accomplish its purpose without this blade replacement process using the gantry manipulator, because human workers would have to access the highly radioactive workshop to undertake the replacement, which would also interrupt the remote dismantling process. In the case of the band saw, the worn blade can be replaced on the floor at +70 ft through the built-in elevation mechanism. 3.3. Application of vibrationless crane The vibrationless crane is used to deploy the platform equipped with the dismantling manipulator into the RV in the reactor cavity when the heads of the bolts used to fix the baffles are to be removed, or when the nozzle that connects the RV to the primary loop of the NPP has to be cut. The vibrationless crane steadily places and stabilises the platform by means of a unique multiwired mechanism and control algorithm. The platform has a radial support mechanism for rigid fastening and a positioning mechanism for adjusting the base position of the dismantling manipulator (see Fig. 12). The RV nozzle is cut to enable its extraction from the reactor cavity. The cutting from outside the RV is very difficult because of the narrow gap between the reactor cavity and the RV. A cutting process from the inner wall of the nozzle using the high-pressure abrasive water jet is thus presented in the process simulation (see Fig. 13).
4. Conclusion The simulation of the entire RPV dismantling process has demonstrated that the proposed seamless remote dismantling system can be successfully used to dismantle various components of the RPV of a Korean NPP without external intervention in the highly radioactive workshop. The components of the proposed system cooperate for mutual enhancement of their respective functions. The system is expected to improve the effectiveness and safety of the entire dismantling process by simplifying the required tasks and eliminating the need for human workers to access the workshop. Further study will be conducted to verify the proposed dismantling system, including its physical characteristics and the feasibility of the utilised equipment. The physical characteristics that require investigation include the gravity fields, mechanical strength, and friction. This is necessary because, as noted earlier, most of the components of the proposed system are yet to be developed, and the process simulation software used for the present study contained only graphical tools.
Acknowledgments This study was supported by the Nuclear R & D Program through the Ministry of Science, ICT & Future Planning.
D. Hyun et al. / Annals of Nuclear Energy 73 (2014) 39–45
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