Device for shutting off a vertical conduit for supporting and guiding an element of elongate shape

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.