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Aerial work robot for a nuclear power plant with a pressurized heavy water reactor
Annals of Nuclear Energy 92 (2016) 284–288
Contents lists available at ScienceDirect
Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Technical note
Aerial work robot for a nuclear power plant with a pressurized heavy water reactor Hocheol Shin ⇑, Changhoi Kim, Yongchil Seo, Kyungmin Jeong, Youngsoo Choi, Byungseon Choi, Jeikwon Moon Korea Atomic Energy Research Institute, Daedeok-daero 989-111, Yuseong-gu, Daejeon 305-353, Republic of Korea
a r t i c l e
i n f o
Article history: Received 31 August 2015 Received in revised form 12 January 2016 Accepted 15 January 2016
Keywords: Aerial work robot Nuclear power plant Pressurized heavy water reactor Fuel handling machine Manual operation Delayed neutron tubes
a b s t r a c t This paper presents an aerial work robot for a nuclear power plant (NPP) with a pressurized heavy water reactor (PHWR). The aerial work robot provides measurements by teleoperating a fuel handling machine placed at a high location in front of the PHWR. The robot can detect a leak from pipes such as delayed neutron (DN) monitoring tubes, which are also placed at a high place. The robot is equipped with radiation-hardened controllers, radiation-hardened cameras, and a noise robust communication system. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The systems and components of a nuclear power plant age with its operation. Since a fuel-handling machine, one of the major components of a PHWR NPP, also ages, at the end of the design life of the NPP, the machine may be stuck to the pressure tube in front of the PHWR Calandria. Even though the machine has a troubleshooting measure of a manual drive mechanism at its rear side and the workers make the machine operate normally by handling the manual drive mechanism, it is still a difficult problem to access the manual drive mechanism. When the machine is stuck, the NPP is being operated so that the radiation level is extremely high and the machine can be located at a high position of up to nine meters. Therefore, a human worker cannot approach the mechanism and the mechanism should be handled remotely. When the machine is stuck to the pressure tube, the workers go down to the basement, disassemble the concrete plug which is under the manual drive mechanism from the ceiling of the basement and try to manipulate the mechanism with a long poleshaped manually operated device. Choi made a motorized device with a telescopic mast to handle this mechanism (Choi et al., 2006). Because these devices are operated in the basement of the reactor room, the concrete plug should be removed from the ceiling of the basement and the pole or the mast should be extended ⇑ Corresponding author. http://dx.doi.org/10.1016/j.anucene.2016.01.017 0306-4549/Ó 2016 Elsevier Ltd. All rights reserved.
up to 15 m. The pole or mast can be deformed largely due the flexibility. This flexibility makes it difficult to engage the tool attached to the end of the pole with the manual drive mechanism. To avoid any difficulties, Seo developed a mobile robot that accesses the manual drive mechanism on the ground floor (Seo et al., 2007). The mobile robot can extended to 8 m high which is too low to inspect the DN monitor tubes. This paper shows the aerial work robot, which can raise a tool to a height of 12 m with a telescopic mast. Thus, the robot can teleoperate the fuel handling machine and inspect the DN monitor tubes. The robot equips with radiation-hardened controllers, radiationhardened cameras, and a noise robust communication system.
2. Working environment in front of the Calandria A PHWR should be refueled everyday while the reactor is working. For this purpose, there is a fuel exchange machine, as shown in Fig. 1. Since the fuel refueling takes place within a 9 m height, there is large space in front of the Calandria, which is a reactor room. In addition, the radiation level is so high during the on-power state that maintenance is carried out behind the shelter wall. The wall moves on the guide rail in the ditch with a width of 75 cm and depth of 25 cm, as shown in Fig. 1. It was noted that there is a service area with a passing gate with a height of 2 m and width of 1.5 m.
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Fig. 3. Crossing the guide rail ditch. Fig. 1. Working environment in front of the Calandria.
Table 1 Design criteria of the aerial work robot. Min height Max height Width Obstacle ditch
<2 m >9 m <1.5 m 75 cm 25 cm (w d)
and reconfigurable mechanisms should stand the weight of the aerial work robot, which is about 500 kg. Fig. 3 shows the passage of the guide rail ditch. The robot changes the direction using the skid steering method. The robot has two omni-wheels at the rear side, which reduces the turning torque to a third that of the robot with all rubber wheels (Shin et al., 2013).
From the investigation of the working environment, the design criteria can be determined for an aerial work robot which teleoperates the fuel handling machine and inspects the DN monitor tubes as follows (see Table 1). 3. Robot system 3.1. Mobile platform The width of the mobile platform is designed to be 0.89 m to easily pass through the gate. To access the Calandria face area, the monitoring robot should cross over the guide rail ditch. Thus we designed a flipper and a reconfigurable mechanism for the monitoring robot. Fig. 2 shows the mobile platform with four reconfigurable flippers. The flippers have an active small wheel at the end of them. When the aerial work robot crosses over the guide rail ditch, the robot pulls down the flippers for the small wheels to touch the ground and rolls the small and main wheels. The small wheel is driven synchronously with a main wheel by a chain. The flippers
Fig. 2. Mobile platform.
Fig. 4. Telescopic mast.
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initial height of the telescopic mast is 1.1 m so that the height of the robot is 1.8 m, which satisfies the min height constraint. And the robot can reach up to 12 m with an emergency operation device of a fuel exchange machine when the mast is fully extended. The first frame of the mast is driven by an electrical motor through a chain and a screw. The mast design was refined from our previous telescopic mast design, which reached up to 9 m and adapted a chain-driven mechanism. Thus, the robot can observe a higher area and lose weight. The weight of the mast is 230 kg and the payload is 50 kg. Fig. 4 shows the mast installed on the mobile platform.
ram driving tool clutch driving tool camera
clutch driving motor
3.3. Tele-ram-operating device of fuel exchange machine
clutch part rotating motor clutch part lifting motor helical gear engaging motor ram driving motor
Fig. 5. Tele-ram-operating device of fuel exchange machine.
3.2. Telescopic mast The telescopic mast is composed of the same shaped aluminum frames sliding synchronously with a cable driven mechanism. The
As described above, the fuel exchange machine can be stuck to the pressure tube. For this case, a manual drive mechanism exists at the rear side of the fuel exchange machine. However, human workers cannot approach the front of the Calandria due to the radiation during normal operation. Thus, human workers should go to the basement of the reactor room, remove the around 200 kg concrete plug that closes the plug hole penetrating the floor of the reactor room from the ceiling of the basement, and push a long stick to drive the manual ram drive mechanism to withdraw the fuel handling machine. This is very hard work and takes a long time to achieve. If the withdraw fails, the reactor should be shut down. We developed a compact ram operating device to handle the manual ram drive mechanism. The monitoring robot with a telescopic mast can locate the device under the manual ram drive mechanism, and lift the device to the mechanism. Fig. 5 shows the ram operating device. Because the total height of the robot is restricted to the height of the service area door of 2 m, the ram operating tool cannot be installed directly on the top of the mast. Therefore, the installer mechanism of the ram operating device was designed to fold the device down at the side of the mast initially. After the robot goes into the reactor room, the installer unfolds the device in an up-standing position.
Fig. 6. Radiation hardened DSP motor controller and emergency controller.
Fig. 7. Radiation hardened camera.
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H. Shin et al. / Annals of Nuclear Energy 92 (2016) 284–288
auxiliary driving line -front camera
virtual target - tool, wing and rear cameras
virtual tool trace - tool and wing camera Fig. 8. Reference coordinates and augmented reality images.
4. Control system
4.2. Radiation hardened camera
4.1. Radiation hardened motor controller
The main task of the monitoring robot is visually inspecting the status of a high radiation aerial working environment. However, commercial CCD cameras cannot survive for a long time in a high radiation environment because electric parts fail from the radiation. Commercial CCD cameras work under a total accumulated dose of 300–500 Gy. We developed a radiation hardened camera with a head separated HAD (Hole Accumulation Diode) type camera. The camera can endure radiation of up to 1 kGy by separating an image sensor and a driving circuit which is shielded with a tungsten case. The camera head is enclosed with a plastic case. Fig. 7 shows the developed radiation hardened camera.
The robots working in NPPs are exposed to severe radiation. This high radiation level damages and changes the characteristics of the materials that make up the robots. Damage to a semiconductor is critical because the controllers of the robots are mostly composed of them. Many researches have been performed to construct a radiation-hardened controller for a high radiation region using commercial off-the-shelf (COTS) semiconductor devices. The radiation dosage at the rear of the fuel magazine housing is 122 krad for a single fuel exchange (Lee et al., 2004). The manual drive mechanism is 3–4 m away from the fuel magazine housing. Thus, the radiation level at the mechanism drops to one-tenth. Thus, a motor controller was developed to stand radiation of up to 1 kGy using DSP. In addition, an emergency controller was also developed, which is composed of mechanical relays that are stronger to the irradiation than the semiconductors. Fig. 6 shows the DSP motor controller and the emergency controller.
4.3. Guiding program with augmented images Since the worker operates the robot in the service area, he cannot directly see the robot in the reactor room. He controls the robot with the image information from the cameras. Six cameras are attached to the robot. We calibrated the cameras and augmented guide objects on the camera images, which are an auxiliary driving
Fig. 9. Mockup test crossing the guide rail ditch.
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Fig. 10. Mockup test driving the manual ram drive mechanism.
line, a virtual target, and a virtual tool trace. The operators can easily control the robot with the augmented reality images. Fig. 8 shows reference coordinates and augmented reality images. 5. Conclusion This paper describes the development of aerial work robot monitoring the environment in a high radiation area such as the place in front of the Calandria face. The analysis of the working environment in front of the Calandria face results in the design criteria of the robot. The initial height of the developed monitoring robot is 1.8 m with the telescopic mast, the width is 0.89 m, and the weight is about 500 kg. The mobile platform was designed to have active wheel-attached flippers so that the robot can cross a 75 cm width guide rail ditch. Fig. 9 shows the mockup test crossing the guide rail ditch. As expected, the flippers and reconfigurable mechanisms endured the weight of the aerial work robot well. When the telescopic mast fully extends, the robot can reach to a height of 12 m with a mission device to closely inspect an aerial working environment. A radiation hardened motor controller and a radiation hardened camera and a ram operating device for the manual ram drive mechanism are also developed. An image guiding program is also developed to help operators to control the
robot. Fig. 10 shows the mockup test driving the manual ram drive mechanism. Before the robot extended the mast, the robot pulled down the flippers and the side bars to secure the stable horizontal pose. First the ram driving tool was inserted to the target, and then the clutch driving tool inserted. The tools were operated in accordance with a given order. Acknowledgments This work was supported by the Nuclear Research and Development Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning. References Choi, C., Seo, Y.C., Jung, S.H., Kim, S.H., 2006. Tele-operated fuel handling machine manipulation robot for the nuclear power plants. Proc. ASCC, 983–987. Lee, N.H., Kim, S.H., Kim, Y.M., 2004. Radiation monitoring on a fuel handling machine with semiconductor sensors. J. Control, Automat. Syst. Eng. 10 (3), 249–253. Seo, Y.C., Kim, C.H., Shin, H., Jung, S.H., Choi, C., 2007. A mobile robot for emergency operation of fuel exchange machine. Trans. Korean Nucl. Soc. Spring Meeting. Shin, H.W., Lee, S.G., Kim, B., Moon, C., Kim, H., 2013. Dynamic modeling and analysis of omni-directional wheel type heavy-water reactor robot. In: Proc. of KSPE 2013 Spring Conference, pp. 43–44.
Contents lists available at ScienceDirect
Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Technical note
Aerial work robot for a nuclear power plant with a pressurized heavy water reactor Hocheol Shin ⇑, Changhoi Kim, Yongchil Seo, Kyungmin Jeong, Youngsoo Choi, Byungseon Choi, Jeikwon Moon Korea Atomic Energy Research Institute, Daedeok-daero 989-111, Yuseong-gu, Daejeon 305-353, Republic of Korea
a r t i c l e
i n f o
Article history: Received 31 August 2015 Received in revised form 12 January 2016 Accepted 15 January 2016
Keywords: Aerial work robot Nuclear power plant Pressurized heavy water reactor Fuel handling machine Manual operation Delayed neutron tubes
a b s t r a c t This paper presents an aerial work robot for a nuclear power plant (NPP) with a pressurized heavy water reactor (PHWR). The aerial work robot provides measurements by teleoperating a fuel handling machine placed at a high location in front of the PHWR. The robot can detect a leak from pipes such as delayed neutron (DN) monitoring tubes, which are also placed at a high place. The robot is equipped with radiation-hardened controllers, radiation-hardened cameras, and a noise robust communication system. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction The systems and components of a nuclear power plant age with its operation. Since a fuel-handling machine, one of the major components of a PHWR NPP, also ages, at the end of the design life of the NPP, the machine may be stuck to the pressure tube in front of the PHWR Calandria. Even though the machine has a troubleshooting measure of a manual drive mechanism at its rear side and the workers make the machine operate normally by handling the manual drive mechanism, it is still a difficult problem to access the manual drive mechanism. When the machine is stuck, the NPP is being operated so that the radiation level is extremely high and the machine can be located at a high position of up to nine meters. Therefore, a human worker cannot approach the mechanism and the mechanism should be handled remotely. When the machine is stuck to the pressure tube, the workers go down to the basement, disassemble the concrete plug which is under the manual drive mechanism from the ceiling of the basement and try to manipulate the mechanism with a long poleshaped manually operated device. Choi made a motorized device with a telescopic mast to handle this mechanism (Choi et al., 2006). Because these devices are operated in the basement of the reactor room, the concrete plug should be removed from the ceiling of the basement and the pole or the mast should be extended ⇑ Corresponding author. http://dx.doi.org/10.1016/j.anucene.2016.01.017 0306-4549/Ó 2016 Elsevier Ltd. All rights reserved.
up to 15 m. The pole or mast can be deformed largely due the flexibility. This flexibility makes it difficult to engage the tool attached to the end of the pole with the manual drive mechanism. To avoid any difficulties, Seo developed a mobile robot that accesses the manual drive mechanism on the ground floor (Seo et al., 2007). The mobile robot can extended to 8 m high which is too low to inspect the DN monitor tubes. This paper shows the aerial work robot, which can raise a tool to a height of 12 m with a telescopic mast. Thus, the robot can teleoperate the fuel handling machine and inspect the DN monitor tubes. The robot equips with radiation-hardened controllers, radiationhardened cameras, and a noise robust communication system.
2. Working environment in front of the Calandria A PHWR should be refueled everyday while the reactor is working. For this purpose, there is a fuel exchange machine, as shown in Fig. 1. Since the fuel refueling takes place within a 9 m height, there is large space in front of the Calandria, which is a reactor room. In addition, the radiation level is so high during the on-power state that maintenance is carried out behind the shelter wall. The wall moves on the guide rail in the ditch with a width of 75 cm and depth of 25 cm, as shown in Fig. 1. It was noted that there is a service area with a passing gate with a height of 2 m and width of 1.5 m.
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H. Shin et al. / Annals of Nuclear Energy 92 (2016) 284–288
Fig. 3. Crossing the guide rail ditch. Fig. 1. Working environment in front of the Calandria.
Table 1 Design criteria of the aerial work robot. Min height Max height Width Obstacle ditch
<2 m >9 m <1.5 m 75 cm 25 cm (w d)
and reconfigurable mechanisms should stand the weight of the aerial work robot, which is about 500 kg. Fig. 3 shows the passage of the guide rail ditch. The robot changes the direction using the skid steering method. The robot has two omni-wheels at the rear side, which reduces the turning torque to a third that of the robot with all rubber wheels (Shin et al., 2013).
From the investigation of the working environment, the design criteria can be determined for an aerial work robot which teleoperates the fuel handling machine and inspects the DN monitor tubes as follows (see Table 1). 3. Robot system 3.1. Mobile platform The width of the mobile platform is designed to be 0.89 m to easily pass through the gate. To access the Calandria face area, the monitoring robot should cross over the guide rail ditch. Thus we designed a flipper and a reconfigurable mechanism for the monitoring robot. Fig. 2 shows the mobile platform with four reconfigurable flippers. The flippers have an active small wheel at the end of them. When the aerial work robot crosses over the guide rail ditch, the robot pulls down the flippers for the small wheels to touch the ground and rolls the small and main wheels. The small wheel is driven synchronously with a main wheel by a chain. The flippers
Fig. 2. Mobile platform.
Fig. 4. Telescopic mast.
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H. Shin et al. / Annals of Nuclear Energy 92 (2016) 284–288
initial height of the telescopic mast is 1.1 m so that the height of the robot is 1.8 m, which satisfies the min height constraint. And the robot can reach up to 12 m with an emergency operation device of a fuel exchange machine when the mast is fully extended. The first frame of the mast is driven by an electrical motor through a chain and a screw. The mast design was refined from our previous telescopic mast design, which reached up to 9 m and adapted a chain-driven mechanism. Thus, the robot can observe a higher area and lose weight. The weight of the mast is 230 kg and the payload is 50 kg. Fig. 4 shows the mast installed on the mobile platform.
ram driving tool clutch driving tool camera
clutch driving motor
3.3. Tele-ram-operating device of fuel exchange machine
clutch part rotating motor clutch part lifting motor helical gear engaging motor ram driving motor
Fig. 5. Tele-ram-operating device of fuel exchange machine.
3.2. Telescopic mast The telescopic mast is composed of the same shaped aluminum frames sliding synchronously with a cable driven mechanism. The
As described above, the fuel exchange machine can be stuck to the pressure tube. For this case, a manual drive mechanism exists at the rear side of the fuel exchange machine. However, human workers cannot approach the front of the Calandria due to the radiation during normal operation. Thus, human workers should go to the basement of the reactor room, remove the around 200 kg concrete plug that closes the plug hole penetrating the floor of the reactor room from the ceiling of the basement, and push a long stick to drive the manual ram drive mechanism to withdraw the fuel handling machine. This is very hard work and takes a long time to achieve. If the withdraw fails, the reactor should be shut down. We developed a compact ram operating device to handle the manual ram drive mechanism. The monitoring robot with a telescopic mast can locate the device under the manual ram drive mechanism, and lift the device to the mechanism. Fig. 5 shows the ram operating device. Because the total height of the robot is restricted to the height of the service area door of 2 m, the ram operating tool cannot be installed directly on the top of the mast. Therefore, the installer mechanism of the ram operating device was designed to fold the device down at the side of the mast initially. After the robot goes into the reactor room, the installer unfolds the device in an up-standing position.
Fig. 6. Radiation hardened DSP motor controller and emergency controller.
Fig. 7. Radiation hardened camera.
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H. Shin et al. / Annals of Nuclear Energy 92 (2016) 284–288
auxiliary driving line -front camera
virtual target - tool, wing and rear cameras
virtual tool trace - tool and wing camera Fig. 8. Reference coordinates and augmented reality images.
4. Control system
4.2. Radiation hardened camera
4.1. Radiation hardened motor controller
The main task of the monitoring robot is visually inspecting the status of a high radiation aerial working environment. However, commercial CCD cameras cannot survive for a long time in a high radiation environment because electric parts fail from the radiation. Commercial CCD cameras work under a total accumulated dose of 300–500 Gy. We developed a radiation hardened camera with a head separated HAD (Hole Accumulation Diode) type camera. The camera can endure radiation of up to 1 kGy by separating an image sensor and a driving circuit which is shielded with a tungsten case. The camera head is enclosed with a plastic case. Fig. 7 shows the developed radiation hardened camera.
The robots working in NPPs are exposed to severe radiation. This high radiation level damages and changes the characteristics of the materials that make up the robots. Damage to a semiconductor is critical because the controllers of the robots are mostly composed of them. Many researches have been performed to construct a radiation-hardened controller for a high radiation region using commercial off-the-shelf (COTS) semiconductor devices. The radiation dosage at the rear of the fuel magazine housing is 122 krad for a single fuel exchange (Lee et al., 2004). The manual drive mechanism is 3–4 m away from the fuel magazine housing. Thus, the radiation level at the mechanism drops to one-tenth. Thus, a motor controller was developed to stand radiation of up to 1 kGy using DSP. In addition, an emergency controller was also developed, which is composed of mechanical relays that are stronger to the irradiation than the semiconductors. Fig. 6 shows the DSP motor controller and the emergency controller.
4.3. Guiding program with augmented images Since the worker operates the robot in the service area, he cannot directly see the robot in the reactor room. He controls the robot with the image information from the cameras. Six cameras are attached to the robot. We calibrated the cameras and augmented guide objects on the camera images, which are an auxiliary driving
Fig. 9. Mockup test crossing the guide rail ditch.
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H. Shin et al. / Annals of Nuclear Energy 92 (2016) 284–288
Fig. 10. Mockup test driving the manual ram drive mechanism.
line, a virtual target, and a virtual tool trace. The operators can easily control the robot with the augmented reality images. Fig. 8 shows reference coordinates and augmented reality images. 5. Conclusion This paper describes the development of aerial work robot monitoring the environment in a high radiation area such as the place in front of the Calandria face. The analysis of the working environment in front of the Calandria face results in the design criteria of the robot. The initial height of the developed monitoring robot is 1.8 m with the telescopic mast, the width is 0.89 m, and the weight is about 500 kg. The mobile platform was designed to have active wheel-attached flippers so that the robot can cross a 75 cm width guide rail ditch. Fig. 9 shows the mockup test crossing the guide rail ditch. As expected, the flippers and reconfigurable mechanisms endured the weight of the aerial work robot well. When the telescopic mast fully extends, the robot can reach to a height of 12 m with a mission device to closely inspect an aerial working environment. A radiation hardened motor controller and a radiation hardened camera and a ram operating device for the manual ram drive mechanism are also developed. An image guiding program is also developed to help operators to control the
robot. Fig. 10 shows the mockup test driving the manual ram drive mechanism. Before the robot extended the mast, the robot pulled down the flippers and the side bars to secure the stable horizontal pose. First the ram driving tool was inserted to the target, and then the clutch driving tool inserted. The tools were operated in accordance with a given order. Acknowledgments This work was supported by the Nuclear Research and Development Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning. References Choi, C., Seo, Y.C., Jung, S.H., Kim, S.H., 2006. Tele-operated fuel handling machine manipulation robot for the nuclear power plants. Proc. ASCC, 983–987. Lee, N.H., Kim, S.H., Kim, Y.M., 2004. Radiation monitoring on a fuel handling machine with semiconductor sensors. J. Control, Automat. Syst. Eng. 10 (3), 249–253. Seo, Y.C., Kim, C.H., Shin, H., Jung, S.H., Choi, C., 2007. A mobile robot for emergency operation of fuel exchange machine. Trans. Korean Nucl. Soc. Spring Meeting. Shin, H.W., Lee, S.G., Kim, B., Moon, C., Kim, H., 2013. Dynamic modeling and analysis of omni-directional wheel type heavy-water reactor robot. In: Proc. of KSPE 2013 Spring Conference, pp. 43–44.