Patent Number: 051494906
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a typical pressurizer 10 used in a nuclear reactor coolant system. Pressurizer 10 is a vertical, cylindrical vessel with replaceable electric heaters 12 in its lower section. Heaters 12 extend through heater sleeves 14 in the vessel wall 16 into the lower portion of pressurizer 10. Heaters 12 are supported by support plate 34 inside pressurizer 10. Heater sleeves 14 extend through the vessel wall 16 which is approximately six inches thick and made of carbon steel or low alloy steel. A plurality of nozzles such as that indicated by the numeral 15 may also extend through a bore in the vessel wall at a variety of locations on the pressurizer. Only one is shown for ease of illustration. As seen in FIG. 2, a cladding 18 normally made from stainless steel is used on the interior surface of the wall 16 for corrosion protection. For ease of illustration, heater 12 is not shown in FIG. 2. For purposes of simplicity, the following description is directed to the replacement of a heater sleeve. As seen in FIG. 2, the invention is generally indicated by the numeral 20. Replacement heater sleeve 20 is formed from a tubular main body portion 22 having first or upper and second or lower ends 24, 26. The lower central section of main body portion 22 is provided with enlarged wall portion 28 having a larger outer diameter than main body portion 22. The outer circumference of enlarged wall portion 28 is provided with threads 30. Flange 32 extends radially outward from main body portion 22 immediately below and to a larger outer diameter than enlarged wall portion 28. Relief groove 36 is provided at the intersection of enlarged wall portion 28 and flange 32. Weld prep 38 is provided at lower end 26 for attaching the replacement heater or any necessary piping. Replacement of a damaged original heater sleeve 14 is carried out as follows. The electric heater 12 is removed. The damaged heater sleeve 14 is removed. Heater sleeve bore 40 is partially tapped to provide threads 42 at its lower end. Replacement heater sleeve 20 is threaded into heater sleeve bore 40 such that upper end 24 is substantially flush with the interior of pressurizer 10 and the upper face of flange 32 is against the exterior of pressurizer 10. Seal weld 44, a partial penetration weld, is then provided between upper end 24 and the interior of pressurizer 10. FIG. 3 provides a plan view of replacement heater sleeve 20 in its installed position. It should be understood that references to upper and lower ends of elements are a matter of convenience and should not be construed in a limiting fashion. Relief groove 36 serves the purpose of preventing interference between the intersection of enlarged wall portion 28 and flange 32 with threads 30 and 42 as flange 32 is caused to bear against the exterior of pressurizer 10. A replacement heater is then installed through replacement heater sleeve 20. The replacement heater is welded in place utilizing weld prep 38. The use of a replacement heater sleeve that has the same inner diameter as the original heater sleeve and can be installed in the original heater sleeve bore maintains the original heater alignment and precludes the need for special alignment procedures. The surface of flange 32 that contacts the exterior of pressurizer 10 is shaped to closely match the contour of that portion of pressurizer 10 where the work is being performed. A washer may also be used between flange 32 and the exterior of pressurizer 10 to aid in providing a sealing contact. It should be understood that the method and apparatus described and illustrated are applicable to the replacement of a heater sleeve or a nozzle. The terms heater sleeve and nozzle should be considered as interchangeable for the purposes of this description since it is common in the industry to refer to a heater sleeve as a heater nozzle. Therefore, reference to the replacement of a nozzle in the claims should be understood as being applicable to a nozzle or a heater sleeve. 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.