Abstract:
A rail apparatus positioned around the surface of a reactor pressure vessel surfaces (1) for carrying equipment such as a flaw detector to permit the equipment to move along the surface of a reactor pressure vessel in the vertical and circumferential directions. The rail apparatus has a plurality of vertical rails (81) and at least one circumferential rail (82) connected to the vertical rails through turn tables (83) at respective points of intersection. Each vertical rail (81) is supported by a supporting member wall fixed at its one end to a gamma-ray shielding wall (2) surrounding the reactor pressure vessel. The vertical and circumferential rails as a unit are retained by the gamma-ray shielding member (84) through oscillation prevention means (86).

Description:
BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The present invention relates to a rail apparatus around a nuclear reactor pressure vessel and, more particularly, to a rail apparatus on which a device such as an inspection device is carried to more along the surface of the reactor pressure vessel in the vertical and the circumferential directions. 
     For inspecting the surface of the reactor pressure vessel with, for example, an ultrasonic flaw detector, the ultrasonic flaw detector is movably carried on rails laid around the surface of the reactor pressure vessel to detect any flaw existing in the surface of the same. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a part of a reactor pressure vessel, showing particularly the positioning of a conventional rail apparatus around the vessel surface; 
     FIG. 2 is a perspective view of an essential part of the conventional rail apparatus; 
     FIG. 3 is a perspective view of a rail apparatus around a reactor pressure vessel surface, constructed in accordance with an embodiment of the invention; 
     FIG. 4 is a perspective view of an essential part of the rail apparatus shown in FIG. 3; 
     FIGS. 5a and 5b are a plan view and a side elevational view of an essential part of another embodiment of the invention respectively; and 
     FIG. 6 is a perspective view of a further embodiment of the invention. 
    
    
     DESCRIPTION OF THE PRIOR ART 
     FIG. 1 illustrates a conventional arrangement of a rail apparatus around the pressure vessel surface of a nuclear reactor, for inspecting flaws over the surface of the reactor pressure vessel. The nuclear reactor has a pressure vessel 1 and a gamma-ray shield wall 2. A bracket 4 is fixed at its one end to the gamma-ray shielding wall 2. A heat insulator wall 3 is supported on the other end of the bracket 4 by a support 5. A rail 6 (only a vertical rail is shown in FIG. 1) is disposed between the pressure vessel 1 and the heat insulator wall 3. 
     Referring now to FIG. 2 which shows the detail of the rail apparatus, a vertical rail 61 is constituted by a central guide 61a and side guides 61b disposed at both sides of the central guide 61a. The central guide 61a is provided with a rack adapted to be engaged with a pinion mounted on an ultrasonic flaw detector. The vertical rail 6 is supported through a thermal expansion relief section (not shown) by a rail supporting bracket 71 which projects through a hole 31 formed in the heat insulator wall 3. A circumferential rail 62 is constituted, as in the case of the vertical rail 61, by a central guide 62a and side guides 62b provided at both sides of the central guide 62a. The circumferential rail 62 is supported through a circumferential thermal expansion relief section 75 to a rail support 74. The rail support 74 is supported at its upper end by a rail support bracket 72 projecting through a hole 32 formed in the heat insulator wall 3 while the lower end thereof is carried through a vertical thermal expansion relief portion 73. 
     These rails are heated to a temperature around 300° C. during the operation of the plant. These rails, however, are cooled down almost to the room temperature while the operation of the plant is suspended for the of ultrasonic flaw detection or the like purpose. In addition, since the flaw detection has to be conducted under a radioactive circumstance, the vertical rails and the circumferential rails are supported by independent supports. This arrangement inconveniently requires an impractically large number of parts and complicated construction of the supports, in order to maintain a precise distance between adjacent rails or to preserve a constant curvature of the circumferential rail, because the rails themselves are not rigid enough. 
     It is not allowed to support the rails directly by the reactor pressure vessel, because the reactor pressure vessel is quite an important item of equipment. Insteadly, the rails are supported through brackets by the gamma-ray shielding wall disposed at the outside of the heat insulator wall. In consequence, heat leaks uneconomically at a high rate through the holes for the support brackets formed in the heat insulator wall. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the invention is to provide a rail apparatus having a simplified construction which can decrease the leakage of heat while eliminating the influence of thermal expansion, to thereby overcome the above-described problems of the prior art. 
     To this end, according to the invention, there is provided a rail apparatus for carrying a flaw detector or the like equipment around the surface of a nuclear reactor pressure vessel in the vertical and circumferential directions, the rail apparatus having an integral construction including vertical rails supported by supporting members which are fixed at their one ends to a gamma-ray shielding member surrounding the peripheral surface of the pressure vessel, and at least one circumferential rail connected to the vertical rails through turn tables, the rail apparatus as a whole being supported by the gamma-ray shielding member through an oscillation prevention means. 
     Namely, according to the invention, the aforementioned object is achieved by integrally combining, through turn tables, the vertical rails and the circumferential rails which are supported independently of each other in the conventional arrangement. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 is a perspective view of an embodiment of the invention, while FIG. 4 is a perspective view of the rail of an essential part of the embodiment shown in FIG. 3. In these Figures, the same reference numerals are used to denote the same parts or members as those in FIGS. 1 and 2. 
     This embodiment is a rail apparatus for an ultrasonic flaw detector for inspecting the welding line of the pressure vessel of a nuclear reactor. In this case, it is necessary to provide a rail for each of the welding lines. The rail apparatus, therefore, has a plurality of vertical rails and circumferential rails, which are designated at reference numerals 81 and 82 respectively. As shown in FIG. 4, each of the rails 81 and 82 is provided with a rack 81a for engaging a pinion on the ultrasonic flaw detector and grooves 81b for a chain and a roller guide. The vertical rails 81 and the circumferential rails 82 are connected at each point of intersection by a turn table 83, so that the ultrasonic flaw detector can be transferred to any point of the rail apparatus. The vertical rails 81 are disposed at such positions as to divide the circumference into four sections of an equal length. The upper end of each vertical rail is supported by one end of a supporting portion 84 which is fixed at its other end to a support 41 secured at its one end to the gamma-ray shielding wall 2, while the other end of the supporting portion 84 is extended inwardly of the heat insulator wall 3 through a hole 33 formed in the latter. The circumferential rails 82, 82 are connected to each other by a plurality of vertical reinforcement supports 85. Anti-earthquake oscillation prevention devices 86 are provided on the vertical rails 81 and retained by the support members 42 fixed to the gamma-ray shielding wall 2. 
     Thus, the rail apparatus of this embodiment has a cage-like construction consisting of circumferential rails 82 each being made integral by means of turn tables 83, and vertical rails 81 and reinforcement supports 85 connected between the circumferential rails 82. This cage-like rail apparatus as a whole is supported by supporting portions 84 and the oscillation prevention devices 86. 
     In this rail apparatus, since each circumferential rail has an integral ring-like form, the thermal expansion of the circumferential rail in the high operating temperature can be treated as a radial expansion, in contrast to the conventional arrangement in which the thermal expansion appears in the circumferential direction. Namely, according to the described arrangement of the invention, the amount of thermal expansion is decreased into 1/π of the circumferential expansion (the ratio of the radial expansion to the half of the circumferential expansion). Therefore, provided that a sufficiently large distance is preserved between the supporting portion 84 and the circumferential rail 82, it is possible to absorb the thermal expansion of the circumferential rail 82 thanks to the resiliency of the vertical rails 81 and the reinforcement supports 85, even if the supporting portion 84 is fixed. In addition, by locating the oscillation prevention devices 86 at suitable positions between the circumferential rails, the vertical elongations of the vertical rails are relieved by the similar method as the conventional method. 
     It is, therefore, possible to reduce the number of the supporting portions and the construction of the supporting structure is simplified as compared with the conventional arrangement in which a supporting portion is provided for each rail. In consequence, the number of portions penetrating the heat insulator wall is decreased to reduce the rate of leak of the heat. In addition, since the rail apparatus as a whole has an integrated construction, there is greater freedom for the selection of positions of the supporting portions and the oscillation prevention device. It is also possible to make use of the support for the temperature preservation member as a support for the rail apparatus. In consequence, the leak is advantageously decreased. 
     The portions supporting the whole of the rail apparatus are fixed perfectly so that it can maintain predetermined precision against repeated changes in the temperature and the installation is facilitated also. 
     FIGS. 5a and 5b are a plan view and a side elevational view of an essential part of another embodiment. In this embodiment, each vertical rail 81 is supported, through a pin 87, by a supporting portion 88 which is secured at its one end to the gamma-ray shielding wall 2 and projecting to the inside of the heat insulator wall 3 through a hole formed in the latter. According to this arrangement, the degree of freedom is increased to effectively suppress the stress. In the embodiment shown in FIG. 3, in which the supporting portions and the oscillation prevention means are fixed, there is a fear that the stress may undesirably exceed the limit value unless a sufficiently large distance is preserved between the thermally expansible rails and the supporting portions and the oscillation prevention means. This problem, however, is overcome by the arrangement of the embodiment shown in FIG. 5. The problem of lack of stability and precision can be overcome by decreasing the distance. This embodiment, therefore, can effectively be used in the case where the circumstances do not allow preservation of a sufficiently large distance. 
     It is possible to use, as the oscillation prevention means, a thermal expansion absorbing construction using a spring which acts rigidly against dynamic load such as that caused by an earthquake but absorbs static expansion such as thermal expansion. This arrangement facilitates the design of mounting position or the like, when a multiplicity of circumferential rails are used in stages. 
     FIG. 6 is a perspective view of another embodiment of the invention in which the same reference numerals are used to denote the same parts or members as those in FIG. 3. In this embodiment, a plurality of reinforcement supports 89 are suspended from the circumferential rail 82 and are provided at their lower ends with oscillation prevention means 86. By using such reinforcement supports, it is possible to construct the rail apparatus using only one circumferential rail. 
     In the embodiments described hereinbefore, each vertical rail is integral with the supporting member which is fixed at its one end to the gamma-ray shielding wall. This, however, is not exclusive and the supporting member fixed at its one end to the gamma-ray shielding wall may be used as a rail support which supports both the vertical rail and the circumferential rail. 
     It will be understood by those skilled in the art that rail apparatus of the described embodiments permits an easy settling of the problem caused by the thermal expansion because the whole part of the rail apparatus is held as a unit. In addition, the uneconomical leak of heat is decreased by a reduction in the number of the supporting portions. Furthermore, the design and the installation are facilitated to improve the precision. 
     As has been described, according to the invention, it is possible to obtain a rail apparatus around a reactor pressure vessel surface having a simplified construction but still capable of eliminating the unfavourable influence of thermal expansion while decreasing the rate of leakage of heat, to a great advantae in the field of industry concerned.