Patent Number: 059303204
Section: summary

FIELD OF THE INVENTION This invention relates generally to nuclear reactors and, more particularly, to assemblies for allowing expansion of a nuclear reactor pressure vessel while simultaneously mitigating effects of such expansion. BACKGROUND OF THE INVENTION Boiling water nuclear reactors typically include a reactor core located within a reactor pressure vessel (RPV). A known RPV includes a substantially cylindrical shell. The shell, for example, can be about twenty feet in diameter and about seven inches thick. The cylindrical shell is closed at its top end by a removable top head. The top head is removable so that components, such as fuel bundles, located in the RPV can be accessed. The RPV cylindrical shell is closed at its bottom end by a dome shaped bottom head assembly welded to the shell. The RPV typically is supported by a conical RPV support skirt and reactor pedestal, and extends into an upper containment. Particularly, one end of the support skirt is welded to the RPV and the other end of the support skirt is secured directly to the reactor pedestal. Known support skirts typically restrict horizontal, vertical, azimuthal and radial movement of the RPV. Particularly, such skirts are directly coupled between the RPV and the reactor pedestal, and are configured to substantially prevent any movement of the RPV during operation. Restraining vertical, horizontal and azimuthal RPV movement is, of course, desirable to maintain the stability of both the RPV and the RPV internals. During RPV operation, heat generated within the RPV causes the RPV to expand. Heat and other forces typically cause the RPV to expand radially and vertically. However, the reactor pedestal remains cool, at least with respect to the RPV, and thus typically does not expand. Accordingly, the reactor pedestal does not accommodate radial RPV expansion, i.e., resists radial movement of the support skirt, and may cause high stresses adjacent the support skirt. Over the life of the RPV, these high stresses may reduce the fatigue life of the RPV, which is undesirable. Accordingly, it would be desirable to provide a support assembly which substantially restrains azimuthal, lateral, and vertical RPV movement while allowing radial RPV expansion. It also would be desirable to provide such an assembly which is easy to install and maintain. SUMMARY OF THE INVENTION These and other objects may be attained by a nuclear reactor which, in one embodiment, includes a support assembly mitigating the effects of reactor pressure vessel (RPV) expansion while accommodating some movement of the RPV. More particularly, and in accordance with one embodiment of the present invention, the support assembly includes a support block and a guide block. The support block includes a first portion and a second portion, and the first portion is rigidly coupled to the reactor pressure vessel. The second portion of the support block is substantially "T" shaped, and is configured to movably couple to the guide block. The guide block is rigidly coupled to the reactor pedestal and includes a channel. The channel extends substantially radially with respect to the reactor pressure vessel and is sized to receive the second portion of the support block. Particularly, the channel is substantially "T" shaped having a neck portion and a head portion, and the neck portion is narrower than the head portion. The second portion of the support block is positioned within the guide block channel so that a head of the second portion is located within the head portion of the channel and so that a neck of the second portion is located within the neck portion of the channel. In operation, as the RPV expands or moves radially, e.g., because of heat and other forces, the second portion of the support block slides within the guide block channel. However, the "T" shaped second portion and the "T" shaped channel substantially restrains vertical, horizontal and azimuthal movement of the RPV. By using the above described support assembly, radial expansion of the reactor pressure vessel is substantially unrestrained, yet lateral, azimuthal and vertical movements are restrained. Such assembly is believed to facilitate providing reduced stresses in the reactor pressure vessel wall. In addition, such assembly is believed to be easy to install and maintain.