Patent Number: 043280714
Section: summary

This invention relates to a device for guiding ducts assigned to a rotatable component. It is known that, in certain types of liquid-metal cooled fast nuclear reactors, the reactor vessel containing the core, the liquid metal coolant (usually consisting of sodium) as well as the primary pumps and primary heat exchangers in the integrated type is closed at the top by a concrete slab or shield roof. For operations involving loading and unloading of fuel assemblies constituting the reactor core, the shield roof is in fact fitted with a large rotating shield plug whose axis coincides with the axis of the reactor vessel and the axis of the reactor core, and a small shield plug rotatably mounted with respect to the large rotating plug about an axis which is displaced off-center with respect to the axis of said large rotating plug. Moreover, a so-called "core lid" structure is suspended beneath the small rotating shield plug in the immediate vicinity of the top face of the reactor core. Moreover, in order to check the correct operation of a fast reactor, it is known that provision is made for a very large number of measuring, control or monitoring instruments placed within the reactor core lid. These instruments consist of temperature and pressure sensors, instruments for measuring neutron flux, instruments for detection and location of can failures and so forth. As will readily be apparent, the complete assembly consisting of such sensors and instruments is connected to electric conductors for supplying current to these devices and for transmitting the data recorded by these latter. In addition, provision must also be made for tubes which supply these different devices with liquids or fluids of various types. In other words, a large number of these sheathed conductor cables or tubes must be assigned to the small rotating shield plug. This is the meaning which must be given to the term "duct" which will be employed in the following description and in the appended claims and which includes both cables and tubes. The problem which arises is clearly that of guiding said tubes between the small rotating shield plug and the recording or supply devices which are placed outside the reactor vessel but are therefore rigidly fixed to the stationary portion of the shield roof. In other words, the problem to be solved lies in the need to guide said cables and tubes which start from a fixed point and must arrive at one point of the small rotating shield plug. In point of fact, this small plug is rotatable with respect to the large plug which is in turn rotatable with respect to the shield roof. This problem is clearly made even more complex by the very large number of ducts involved (tubes or electric conductors) which result in a not-negligible degree of stiffness of the complete assembly. It is clearly necessary to guide these ducts while making it possible, without any attendant risk of damage, to subject them to the very large number of operations both of the small and large rotating shield plugs during refuelling operations. In the techniques of the prior art, supply of electric current and of fluid to devices attached to the small rotating shield plug was carried out by making use of a flexible cable connection. The systems employed consisted of circular hoods located above the rotating shield plugs and having approximately the same diameter as these latter. The cables or tubes were first connected to a stationary junction of the hood so as to form a large loop within the interior of this latter, then passed through a movable junction or a stationary junction connected to a movable portion of the hood. The cables extended vertically to connectors which were rigidly fixed to the small rotating plug. The loop provided the necessary slack to ensure that the movable junction was capable of following the combination of displacements of the small and large rotating plugs, thus maintaining the downwardly extending portion of the cables or supply tubes in a vertical position. The disadvantage of this solution lies in the fact that it is highly cumbersome and takes up a large volume above the seal plugs. This is a major drawback since the small and large rotating shield plugs are already obstructed by a large number of devices related to the operation of the nuclear reactor and replacement of a duct is consequently a matter of considerable difficulty. However, the field of application of the present invention is not limited in any sense to a nuclear reactor provided with two eccentric rotating shield plugs. The invention is generally applicable to the penetration of a bundle of cables through a rotating component, the other end of the cables being stationarily fixed with respect to the rotating component. In its application to fast reactors, this invention relates to a device which serves to guide cables and tubes assigned to the small rotating shield plug and makes it possible to free almost entirely the internal space located above the small and large rotating shield plugs. In all of its embodiments, the invention relates to a device which makes it possible to carry out tens of thousands of helical rotations of cables and tubes without producing any failure at angles of rotation of the rotating component of plus or minus 220.degree. with respect to the rest position. In order to obtain this result, the invention consists of a device for guiding ducts designed to pass through a movable component which is capable of rotational motion about a vertical axis. Said device essentially comprises means for supporting said ducts between a fixed point located externally of said component and a second point located on a vertical axis which coincides with the axis of rotation of said movable component and constitutes the extremity of the supporting means. The device further comprises means for guiding those portions of ducts which are placed between the extremity of said supporting means and the center of rotation of said movable component. Said guiding means are adapted to maintain said portions of ducts in uniformly spaced relation on a ruled surface of revolution about the axis of said movable component so that said portions of ducts thus form a bundle-type assembly. Means are further provided for securing the lower extremity of said guiding means to said movable component at the center of rotation thereof. As already mentioned, the invention is applicable in particular to nuclear reactors of the double rotating shield plug type. The stationary component in that case is the small rotating shield plug. Preferably, the means for supporting the cables or ducts consist of two articulated horizontal arms. In a first embodiment, the device essentially comprises a hanger rigidly fixed to said small shield plug and comprising a vertical column and a horizontal arm, the free extremity of said hanger arm being located on the axis of said small rotating shield plug. The device further comprises a first horizontal guiding arm articulated at one end with respect to a fixed point of the reactor, and an second horizontal guiding arm having one extremity which is pivotally attached to the free extremity of said first guiding arm. Means are provided for controlling the pivotal motion of the first arm with respect to the fixed point and the pivotal motion of the two guiding arms with respect to each other in such a manner as to ensure that the free extremity of said second guiding arm is caused to remain in the axis of said small rotating shield plug. The ducts aforesaid are fixed along said two guiding arms and along the horizontal arm of the hanger. Means are also provided for guiding portions of said ducts which are located between said hanger arm and said second guiding arm so as to maintain said portions of ducts in uniformly spaced relation on a ruled surface of revolution about the axis of said small rotating shield plug so that said portions of ducts thus form a bundle-type assembly. Preferably, the guiding means aforesaid consist of a plurality of circular plates forming a bottom guide-plate rigidly fixed to the extremity of the hanger arm, a top guide-plate rotationally coupled to the free extremity of the second guiding arm but capable of free vertical translational motion with respect to this latter, and at least one intermediate guide-plate. The portions of ducts aforesaid are fixed at uniform intervals on the periphery of said guide-plates. Means are provided for maintaining said guide-plates horizontal and centered on the axis of said small rotating shield plug. Provision is also made for means whereby the angle of rotation of the top guide-plate with respect to the bottom guide-plate at the time of pivotal motion of the guiding arms and of the rotating shield plugs is uniformly distributed between the guide-plates as a function of the vertical distances between said guide-plates, a degree of slack being left in the ducts between the top guide-plate and the second guiding arm. According to another distinctive feature, said top guide-plate is rigidly fixed to the extremity of the second guiding arm by means of a variable-length unit which exerts a constant force directed along the axis of said small rotating shield plug and provides a rotational coupling. Preferably, said unit is a jack having an operating rod disposed along the axis of said small rotating shield plug and rigidly fixed to said top guide-plate, the jack body being rigidly fixed to the extremity of said second guiding arm. According to another preferred distinctive feature, the guide-plates aforesaid are connected to each other by a plurality of cables having the same length, each cable being attached at the upper end thereof to the top guide-plate and at the lower end thereof to the bottom guide-plate, said cables being so arranged as to pass through the intermediate plates aforesaid and being fixed on these latter. In an improved embodiment, the hanger aforesaid is in turn capable of rotational motion about the vertical axis of its column by means of an actuating device. In this case, the device according to the invention is distinguished by the fact that said column is stationary and that said hanger arm is pivotally mounted at the upper extremity of said column, the portions of ducts which extend along said column being attached to the periphery of the second circular guide-plates which are similar to the first guide-plates, said second top guide-plate being rigidly fixed to said arm by means of resilient devices which produce a force in the vertical direction, a degree of slack being left in the ducts between said second top guide-plate and said hanger arm generating a vertically-directed force, with some slackness in the ducts between said second upper plate and said beam. In a first alternative embodiment, the hanger is dispensed with or, in other words, the bottom guide-plate is directly fixed on the small rotating shield plug and the center of the guide-plate corresponds to the axis of rotation of the small shield plug. In a second alternative embodiment, the guiding means consist of a vertical guiding mast rigidly fixed at the lower end to the center of the small rotating shield plug and at the upper end to the free extremity of the supporting means; a horizontal top guide-plate rotationally coupled to the free extremity of said supporting means but capable of free vertical translational motion and surrounding said mast; a horizontal bottom guide-plate surrounding said mast and rigidly fixed to the lower end of said mast; and at least one intermediate guide-plate surrounding said mast and capable of free translational motion in the direction of said mast, said intermediate guide-plate being partially free for rotational motion about said mast. Each guide-plate is provided at the periphery with uniformly spaced means for fixing the cables aforesaid. The intermediate guide-plate or each intermediate guide-plate is provided with means for limiting rotational displacement about the mast so as to ensure that the angle of rotation between the top guide-plate and the bottom guide-plate is uniformly distributed between the intermediate guide-plate or plates.