Patent Number: 047864656
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 illustrates a sectional view of a typical pressurized water reactor 10. In reactor 10, coolant flows thereinto through inlet nozzle 12, downward through annulus 14, upward through core region 16, and then out of reactor 10 through outlet nozzle 18. In the original design of some reactors as described above some of the coolant flows through horizontally positioned coolant flow holes 20 adjacent the upper end of core barrel 22 as best seen in FIG. 2. As indicated by the arrows, this bypass coolant flows downwardly through vertically positioned coolant flow holes 24 in former plates 26 and then upward through core region 16 with the main coolant flow. As seen in FIG. 2, the bypass coolant flows between core barrel 22 and baffle plate 28. The method presented for converting the vertically downward flow of bypass coolant through the core barrel and former plates to a vertically upward flow is best understood by reference to FIGS. 3-5. In FIG. 3, it is seen that one of the steps in making the conversion comprises providing holes 24A in top former plate 26A which are substantially in coaxial alignment with existing holes 24 in the intermediate and lower former plates 26. Another step is plugged horizontal coolant flow holes 20 in core barrel 22 adjacent top former plate 26A. A final step comprises plugging of selected holes in lower former plate 26B. FIG. 4 illustrates a typical expander tool 30 and plug 32 which may be used for the plugging procedure. Expander tool 30 is comprised of roll expander 34, first and second tubes 36, 38, and torque shaft 40. Plug 32 is removably attached to expander tool 30 by means of left handed threads 42. First and second tubes 36, 38 form the body of expander tool 30 which serves to position and hold plug 32 and also to encase torque shaft 40. Torque shaft 40 is attached to roll expander 34 so as to cause expansion of plug 32 in response to rotation of torque shaft 40. The roll expansion process produces a tight joint between plug 32 and lower former plate 26B. Naturally, the tooling is designed for remote operation in plugging the core barrel and former plate and the tooling shown is intended only as an illustration of the type of tooling which should be acceptable for this type of operation. FIG. 5 illustrates a typical octant of lower former plate 26B with the preferred plugging pattern of coolant flow holes 24 being illustrated. Coolant flow holes which remain unplugged according to the preferred pattern are designated by the numeral 24. It is seen that the preferred plugging pattern comprises plugging alternate coolant flow holes. Coolant flow holes which are fully plugged are designated by the numeral 24B. Coolant flow holes which are partially plugged are designated by the numeral 24C. As seen in FIG. 5 a typical octant of lower former plate 26B is provided with ten (10) coolant flow holes 24, four of which are fully plugged and one of which is partially plugged. Every fifth coolant flow hole is partially plugged. Coolant flow hole 24C has forty-four (44) percent of its flow area plugged according to the preferred embodiment. It can then be seen that according to the preferred plugging pattern forty (40) percent of coolant flow holes 24 in lower former plate 26B are fully plugged and ten (10) percent are partially plugged. In operation the conversion method of the present invention is practiced as follows. Top former plate 26A is provided with coolant flow holes 24A substantially in coaxial alignment with existing coolant flow holes 24 in intermediate and lower former plates 26, 26B. Any suitable means such as drilling with remotely operated tools known in the art may be used. Coolant flow holes 20 in core barrel 22 are fully plugged using plugging techniques and equipment known in the art. Selected coolant flow holes 24B in lower former plate 26B are fully plugged while selected coolant flow holes 24C are partially plugged using techniques and equipment known in the art such as expander tool 30 described above. It is preferable to use an expander tool which can accommodate a certain minimum amount of offset between coolant flow holes 26 in adjacent former plates 26 which are not in perfect coaxial alignment. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.