Patent Application
20090120605
1. Field of the Invention
The present application is generally drawn to nuclear steam generator examination and repair equipment.
2. Description of the Prior Art
Much of the maintenance performed in nuclear power plants is similar to that of conventional non-nuclear systems. However, nuclear systems are unique in that many components are inaccessible, due to the radiation levels.
In the early years of nuclear power, much of the maintenance was performed manually by workers entering the steam generator head. As maintenance activities and radiation levels increased, it became increasingly difficult to perform steam generator repairs manually. Because inspecting the large number of steam generator tubes is mandatory during refueling outages, this work was a logical candidate for applications of early remote technology. The first manipulator used on Once through Steam Generators (OTSG's) was positioned manually on the tubesheet, locked in place, then computer controlled from a remote location. The manipulator was then moved manually to the next location. For Recirculating Steam Generators (RSG's), an articulated arm manipulator was used having an arm for holding video and or cleaning equipment which was vertically movable into the tube bundle. Although also manually installed, it was not computer controlled. Both manipulators performed well for inspection, but they could not support the heavy tools required for plugging and other tube repair operations. For this reason and also for reduced radiation dose limits, the practice of manually installing the manipulators had to be eliminated.
Development of an advanced manipulator was based on the following criteria:
1. must be installed with no human entry in the steam generator,
2. must perform inspection and repair duties,
3. must access all tubes, and
4. must be computer controlled.
The present invention solves these problems of the prior art manipulators and others by providing a system to remotely relocate the above described manipulator with minimal support from personnel on the work platform during reactor shut down. This takes away the need for highly experienced support for manually moving the manipulator. The tube walker of the present invention consists of a movable system for reciprocally moving a body connected to the manipulator having a movable inner section and an outboard section. Both the inner and outboard sections have groups of 4 hydraulically actuated locking fingers which engage the tubes of the steam generator tube bundle. When the 4 fingers of the outboard section are locked in place, the fingers of the inner section are disengaged and the inner portion can be moved axially to an aligned position with new tube locations. Then the inner portion can be locked in place to tubes of the new location and the 4 outboard fingers can be disengaged. This allows the outboard section to be moved to a new tube location. This combination of reciprocal motion allows the walker to traverse in a straight line from one side of the generator tube bundle to the other side and back. The manipulator is attached to the walker using a pneumatic coupler.
From the foregoing it will be seen that there are two advantages with this system. The first is decreased time required to move the manipulator. The manipulator can efficiently and consistently be moved in a time comparable to that of the best moves done remotely by an individual. This system also eliminates any variation in that moving time. The second advantage is less radiation dose received by the support personnel. The need for an individual to be standing at the manway to move the manipulator no longer exists. This results in significant dose savings over the duration of an outage.
In view of the above it will be seen that one aspect of the present invention is to provide a system for easily moving the manipulator across the row of steam generator tubes from a remote location.
Another aspect is to provide a speedy movement of the manipulator to minimize radiation exposure of the personnel during reactor down time.
These and other aspects of the present invention will be more fully understood after a perusal of the following description of the preferred embodiment, when considered along with the accompanying drawings.
In the drawings wherein:
Referring now to the drawings and particularly to
This improved manipulator system (10) is composed of two main parts including the manipulator (12) and the tube walker assembly (11). Part one is the tube walker assembly (11). This assembly (11) consists of a movable inner section (18) and a two part outboard section (22a; 22b) connected by a fixed plate (23) and rods (20). Each section (18; 22a; 22b) has a pair of hydraulically actuated locking fingers (16). These fingers (16) have a collet at the end which expands to grasp a tube which locates the system (10) at a particular tube location within the bundle (16). The outboard sections (22a; 22b), while locked in place as described, now allow the inner section (18) of the tube walker assembly (11) to be moved axially along rods (20) to the position shown in
Part two is the manipulator (12) used to inspect and repair the tubes. This component is very robust, and has successfully performed the required tasks.
This improved manipulator system (10) requires much less personnel support than the standard system. The standard system requires that personnel expend dose and time to manually relocate the manipulator. This works well but in some cases can potentially cause issues. The new system can be relocated in a consistent time frame and requires almost no personnel support. The walker can not change angular orientation, it can only move via straight line motion. It does this with the use of a motor and lead screw and some guide rods (not shown), similar to the known way the known manipulator (12) moves vertically up and down.
Referring now to
It will be understood that certain details, obvious modifications and applications have been deleted h rein for the sake of conciseness and readability but are fully intended to fall within the scope of the following claims.
