Patent Number: 051125676
Section: claims

1. In a nuclear reactor system having a pressure vessel and a guide conduit for a measurement probe of elongate and generally cylindrical shape extending into said reactor vessel, a device for shutting off said conduit, said device comprising (a) a housing inserted between a lower section of the conduit in communication with the pressure vessel and an upper section of the conduit and having two means for leakproof connection to the lower section and the upper section of the conduit, respectively, and a wall bounding an inner chamber of said housing;  (b) a passage channel for the measurement probe comprising an upper part passing through the means of connection of the housing to the upper section of the conduit and a lower part passing through the means of connection of the housing to the lower section of the conduit, emerging in an inner chamber of the housing;  (c) a shutter arranged in said inner chamber and oscillating about a horizontal axis between a closed and an open position of an inner end of the upper part of the passage channel emerging in the inner chamber and comprising a closing member which cooperates with said inner end in a closed position to close the passage channel and a counterweight for returning the closing member in the closed position; and  (d) means for measuring the pressure into the inner chamber of the housing. 2. Shutoff device according to claim 1, wherein said wall of said housing comprises a body and a cover attached in a leakproof manner by virtue of a seal onto said body and clamped by a plurality of bolts. 3. Shutoff device according to claim 1, wherein said upper connection means of the housing consists of a nozzle comprising a bore with a vertical axis emerging into said inner chamber of said housing, in which bore there is fastened a seat comprising a support bearing for said closing member of said shutter. 4. Shutoff device according to claim 3, wherein said seat is fastened in said bore of said nozzle by a bolt engaged and fastened in a leakproof manner in aid bore of said nozzle and bearing on said seat, said seat and said bolt being pierced axially to form the passage channel for said measurement probe. 5. Shutoff device according to claim 3, wherein said seat is made of graphite. 6. Shutoff device according to claim 1, wherein said shutter comprises a balance arm fixed to a shaft rotatably mounted inside said housing, said shaft having a first end part to which said closing member is fastened and a second end part remote from said first end part relative to the axis of rotation of said shutter and carrying said counterweight. 7. Shutoff device according to claim 6, wherein said shaft comprises conically shaped end pivots engaged in bearings of corresponding shape, said bearings being placed in cavities arranged in the inner surface of said wall of said housing. 8. Shutoff device according to claim 7, wherein resilient return elements are inserted between said bearings and corresponding parts of said cavities in said wall of said housing. 9. Shutoff device according to claim 7, wherein said cavities receiving said bearings are machined into two components which are attached to each other to form said housing. 10. Shutoff device according to claim 1, wherein said guide conduit closed at one of its ends through which it is introduced into said pressure vessel comprises an end part remote from its closed end, said end part being open and emerging outside a vertical guide tube, by means of a leakproof passage device situated at a height above the upper level of the reactor vessel, and said housing is inserted in a vertical end part of said guide conduit above said leakproof passage device. 11. Shutoff device according to claim 10, wherein said device for measuring pressure is connected to an alarm means situated in a measuring room receiving the upper part of said guide conduit. 12. Shutoff device according to claim 11, wherein the upper end part of said guide conduit is connected to a leakproof manual closing valve.