Patent Application
20100242660
The present invention relates to nuclear power plants, and, more particularly, to a tool to assist in mitigating stress corrosion cracking in welds in components located in nuclear reactor vessels.
Operating experience over time with nuclear power plants has shown that ineffective control of the aging degradation of reactor vessel components can jeopardize plant safety and plant life. Aging in such components needs to be effectively managed to ensure plant safety so that adequate safety margins remain, i.e., integrity and functional capability in excess of normal operating requirements.
Boiling water reactor (“BWR”) nuclear power plants have been in commercial operation in certain countries for quite some time. It has been found that, during this period, some internal reactor components made from Stainless Steel and Inconel 182 welding materials have experienced stress corrosion cracking (“SCC”), the term given to crack initiation and sub-critical crack growth of susceptible alloys under the influence of tensile stress and a “corrosive” environment, such as the BWR environment.
To proactively mitigate stress corrosion cracking in BWR internal components and welds, some BWR owners have initiated preventive maintenance programs that include the repair and replacement of SCC susceptible internal reactor components and the brushing of component welds to mitigate stress corrosion cracking of the weld areas. One concern with regard to the brushing of internal component welds is gaining access to welds that are remotely located, so as to be difficult to reach.
Differential pressure/standby liquid control (“dP/SLC”) line penetration weld joints are one example of remotely located weld joints that can benefit from stress corrosion cracking mitigation by the brushing of such welds joints and their adjacent zones. One difficulty in accessing the dP/SLC penetration weld joints is the location of the dP/SLC pipes 11, which are located at the 180° azimuth at the most peripheral region of the reactor vessel bottom head. Another difficulty in accessing the dP/SLC penetration weld joints is the obstructions to such joints caused by the presence of no longer-used vibration sensor instrument strings 13 and the clips and shrouds 15 used to hold the strings 13 onto the dP/SLC pipes, as shown, for example, in
Flow-induced vibrations of the internal components of a nuclear reactor may also cause fatigue-initiated cracking and/or failures of such components. Because of the safety hazards associated with component failure in a nuclear reactor, it is also necessary to monitor the state or condition of internal components susceptible to vibration-induced damage. One type of internal reactor component which is monitored to determine flow-induced vibrations in a reactor is in-core monitor housings (ICMH). Core power is monitored by neutron flux monitors located within in-core monitor instruments supported by in-core monitor support assemblies. Each in-core monitor support assembly includes an instrumentation guide tube and an in-core monitor housing. A vibration sensor is mounted on the outside diameter of an in-core monitor housing.
Some tool vendors have designed tools for remotely servicing boiling water reactor (“BWR”) vessels that can be used to proactively mitigate stress corrosion cracking in BWR internal components and welds. Access to the bottom of a reactor vessel is typically obstructed by various structures in the vessel. Thus, it can be challenging to fit tools past the obstructions to reach the bottom of a reactor vessel. Some tools include multi-piece manipulators that are assembled in the vessel at a location where the manipulator is to be used after the pieces of the manipulator have been inserted into the vessel at the work location. Many of these tools are manipulated by a technician using a handling pole that extends to the top of the reactor vessel. Often, however, the technicians are unable to adequately manipulate the tools with the poles to perform the activities necessary to service the reactor. A one-piece manipulator would eliminate the time needed to install and assemble the parts of a multi-part manipulator and, after use, to disassemble and remove the tool parts.
In an exemplary embodiment of the invention, a manipulator for accessing and servicing remote locations in a reactor vessel comprises a frame, an axial drive for rotating the frame, and a deployable arm mounted within the frame, the arm comprising a first rotary joint attached to the axial drive, a first pivot joint attached between the first rotation joint and a first end of an extension member, a second pivot joint attached to a second end of the extension member, a second rotary joint attached to the second pivot joint, a third pivot joint attached to the second rotary joint, and a tool mounted on the third pivot joint.
In another exemplary embodiment of the invention, a manipulator for accessing and servicing remote locations in a reactor vessel comprises a frame, an axial drive for rotating the frame, and a deployable arm mounted within the frame, the arm comprising a first rotary joint attached to the axial drive, a first pivot joint attached between the first rotation joint and a first end of an extension member, a second pivot joint attached to a second end of the extension member, a second rotary joint attached to the second pivot joint, a third pivot joint attached to the second rotary joint, and a tool mounted on the third pivot joint, the frame including an upper plate and a base plate mounted on a base that includes a plurality of latches for clamping the manipulator to various components in the reactor vessel, and having a linear dimension that allows the arm to be retracted within the frame for installation into, and removal from, the reactor vessel, the three pivot joints each being moved by a corresponding reversible servomechanism attached to a corresponding worm gear and the two rotary joints each being rotated by a corresponding reversible servomechanism.
The present invention is a manipulator tool for performing service activities in remote locations in a nuclear reactor vessel. The manipulator tool can be used to proactively mitigate stress corrosion cracking in BWR internal components and welds. The manipulator tool can also be modified to inspect and service in-core monitor housings in connection with mitigating fatigue-initiated cracking and/or component failures. The manipulator has six degrees of freedom in its ability to move so that it can fit past obstructions inside the reactor vessel to access remote locations.
Referring to
Attached to axial drive 12 is a drive shaft 14 that extends through a linear bearing 16 mounted on top of an upper plate 24 that is part of a mounting frame 22, within which is mounted arm 20 that is deployed to manipulate one of several tools used in the servicing of a reactor vessel. The proximal end 23 of shaft 14 is attached to axial drive 12, while the distal end 25 of shaft 14 is attached to arm 20. Besides upper plate 24, mounting frame 22 also includes a base plate 26 attached to a base 27. Within base 27 are a plurality of latches (
Attached to the distal end 25 of shaft 14 is a plate 17, which, in turn, is attached to a first rotary joint 18 of arm 20, which allows arm 20 to be further rotated. Rotatably attached to first rotary joint 18 through a pair of arms 54 is a first pivot joint 34. Rigidly attached to first pivot joint 34 is a cylindrical extension member 38 that extends between first pivot joint 34 and a second pivot joint 36, also rigidly attached on the opposite end of extension member 38. First and second pivot joints 34 and 36 provide the first and second degrees of pivotal freedom in the movement of deployable arm 20.
Also rotatably attached to second pivot joint 36 through a pair of arms 69 is a second rotary joint 40 that provides the second degree of rotational freedom for deployable arm 20 to perform servicing operations in a nuclear vessel. For further freedom of movement of arm 20 there is rigidly attached to second rotary joint 40 a third pivot joint 42 within which is mounted a connector 44 for attaching various tools to arm 20 for servicing a reactor vessel. One of the tools that can be used with manipulator 10 is an ultra-high pressure (“UHP”) water jet 48 that can be used to remove items, such as the vibration sensor instrument strings and clips and shrouds, discussed above. The water jet 48, which is shown in
Referring now to first pivot joint 34 and second pivot joint 36, as can be seen from
Similar to first pivot joint 34, second pivot joint 36 is moved by a third servo 58 mounted within cylinder 38 opposite second servo 56. Attached to third servo 58 is a third shaft 68 that is also shaped like screw so as to be a worm for engaging and rotating a worm gear 70 that is locked to an axis of rotation of a housing 72 that is part of second pivot joint 36. As worm 68 is caused to rotate in a first direction by the operation of third servo 58, worm gear 70 is caused to rotate in a first direction to either raise or lower second pivot joint 36. Conversely, when worm 68 is caused to rotate in the opposite direction, it causes worm gear 70 to also rotate in the opposite direction so as to move second pivot joint 36 in the opposite direction. Worm 68 and worm gear 70 are capable of rotating the second pivot joint 36 one hundred and eighty degrees (180°) about the longitudinal axis of the extension member 38.
Second rotary joint 40 includes a fourth reversible servo 76 mounted within a cylindrical extension member 78 and having a shaft 74 extending from fourth servo 76. Servo 76 rotates shaft 74 to rotate joint 40 +/−180 degrees to provide a second degree of rotational movement within arm 20.
Similar to first and second pivot joints 34 and 36, third pivot joint 42 is also rotated by a fifth reversible servo 80 mounted within the cylinder 78 containing fourth servo 76. Fifth servo 80 is positioned opposite fourth servo 76 within cylinder 78. Extending from servo 80 is a fifth shaft 82 that is shaped like a screw so as to be a worm for engaging and rotating a worm gear 84 that is locked to an axis of rotation of a housing 86 that is part of third pivot joint 42. As worm is caused to rotate in a first direction by the operation of fifth servo 80, worm gear 84 is caused to rotate in a first direction to either raise or lower third pivot joint 42. Conversely, when worm 82 is caused to rotate in the opposite direction, it causes worm gear 84 to also rotate in the opposite direction so as to move third pivot joint 42 in the opposite direction.
The manipulator 10 is designed for underwater operation in a nuclear radiation environment, such as a reactor vessel. It is designed to be remotely operated to manipulate tools to perform service activities at difficult to access regions of the reactor vessel. For illustrative purposes only, the manipulator 10 is shown in the figures as operating with an ultra-high pressure (“UHP”) water jet 48, but it should be noted that manipulator 10 is designed to handle multiple tools for specific applications, including the water jet tool 48, a camera, a gripper, a cutter and a brush. Preferably, the brush tool will be a rotary tool for rotating a plurality of bristles against a desired location within the reactor vessel to mitigate corrosion, although other brush configurations could be used with the manipulator. Such tools will be attached to one or more rotary and/or pivots joints suitable for movement of a given tool for a given application and will be capable of being controlled electrically, pneumatically and/or hydraulically to perform the movement(s) necessary for a given servicing function within the reactor vessel. Such tools will also be capable of operating underwater in a nuclear environment.
As noted above,
Once manipulator 10 has been lowered through top guide 19 and core plate 21 at a point that will locate manipulator 10 at a desired location within the reactor vessel, base 27 of manipulator 10 is positioned over a selected component within the reactor vessel. Thus, for example,
Cables (not shown) extend from the tool 10 to the top of the reactor vessel. Feedback from the servos provide the position information to a manipulator controller. Video cameras (not shown) provide an operator with a view of the position of the tool 10 within the reactor vessel. The operator controls the tool via a human interface (not shown) which assists the operator by interpreting the operator manipulation of a joystick into motion of the manipulator 10.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
