Patent Number: 047145846
Section: claims

1. A device for use in a nuclear reactor which includes a pressure vessel having a vessel head, a core in the vessel, elements for controlling the reactivity of the core, drive rods which pass through the vessel head for displacing the elements, and a plurality of head adapters which pass through the vessel head, each head adapter having an inner diameter and forming part of a drive rod housing enclosing a respective drive rod, each housing enclosing a region which communicates with the interior of the vessel and which is closed at the top, said device being associated with a respective housing and constituting a housing extension including means for connecting said device to the head adapter forming part of the respective housing, said means for connecting having a substantially constant inner diameter substantially equal to that of said adapter, and means located at the lower end of said extension for forming, with the associated drive rod and within the associated housing, an annular fluid passage, said means for forming having an inner diameter less than that of said means for connecting so as to give said annular fluid passage a cross-sectional area not exceeding a selected value at least upon the occurrence of a leak in the respective housing. 2. A device as defined in claim 1, wherein said means for forming a fluid passage are carried by said connecting means. 3. A device as defined in claim 1 wherein the selected value is about 5 cm.sup.2. 4. A device as defined in claim 1, comprising a guide funnel supported by the respective housing, oriented to open toward the interior of the vessel, and defining at least part of said means for forming a fluid passage. 5. A device as defined in claim 4, wherein said means for forming a fluid passage comprise a radially inwardly extending portion of said guide funnel. 6. A device as defined in claim 4, wherein the vessel head is provided with a bore for the passage of each head adapter and further comprising means defining a radially outwardly projecting shoulder located above said funnel and having an outer diameter greater than the bore provided in the vessel head for passage of the adapter with which said device is associated, said shoulder serving to prevent ejection of said device from the vessel under the influence of the pressure within the vessel. 7. In a nuclear reactor which includes a pressure vessel having a vessel head, a core in the vessel, elements for controlling the reactivity of the core, drive rods which pass through the vessel head for displacing the elements, and a plurality of head adapters which pass through the vessel head, each head adapter having an inner diameter and forming part of a drive rod housing enclosing a respective drive rod, each housing enclosing a region which communicates with the interior of the vessel and which is closed at the top, the improvement comprising a device associated with a respective housing and constituting a housing extension located within said vessel, said device including means for connecting said device to the head adapter forming part of said respective housing, said means for connecting having a substantially constant inner diameter substantially equal to that of said adapter, and means located at the lower end of said extension and supported by said connecting means for forming, with the associated drive rod and within said associated housing, an annular fluid passage, said means for forming having an inner diameter less than that of said means for connecting so as to give said annular fluid passage a cross-sectional area not exceeding a selected value at lealst upon the occurrence of a leak in said associated housing. 8. The combination as defined in claim 7, wherein said device further comprises a guie funnel supported by said respective housing, oriented to open downwardly in said vessel, and defining at least part of said means for forming a fluid passage. 9. The combination as defined in claim 7 wherein the selected value is about 5 cm.sup.2. 10. A device for use in a nuclear reactor which includes a pressure vessel having a vessel head, a core in the vessel, elements for controlling the reactivity of the core, drive rods which pass through the vessel head for displacing the elements, and a plurality of head adapters which pass through the vessel head, each head adapter forming part of a drive rod housing enclosing a respective drive rod, each housing enclosing a region which communicates with the interior of the vessel and which is closed at the top, said device being associated with a respective housing and constituting a housing extension including means for connecting said device to the head adapter forming part of the respective housing, and means located at the lower end of said extension for forming, around the associated drive rod and within the associated housing, a fluid passage which constitutes the only path for fluid flow between the interior of the vessel and the interior of the drive rod housing above said means for forming, said means for forming comprising a flow restricting member mounted for movement relative to said connecting means from a normal position to an actuated position in response to the fluid pressure acting thereon as a result of a leak in the respective housing, and said flow restricting member being configured to cooperte with said connecting means for causing said fluid passage to have a cross-sectional area which exceeds a selected value when said flow restricting member is in said normal position and a cross-sectional area which does not exceed the selected value when said flow restricting member is in said actuated position. 11. A device as defined in claim 10 wherein the selected value is about 5 cm.sup.2. 12. A device as defined in claim 10, wherein said flow restricting member comprises a hollow cylindrical member mounted on said funnel and projecting from the narrow end of said funnel in the direction of movement of said flow restricting member from its normal position to its actuated position, said hollow cylindrical member being located within said connecting means and including a plurality of axially extending parts separated from one another by axially extending gaps and extending to the end of said hollow cylindrical member which is remote from said funnel, and said connecting means comprise an annular portion facing said hollow cylindrical member and having a camming surface positioned to deflect said axially extending parts radially inwardly when said flow restricting member moves from its normal position to its actuated position for establishing an annular gap between said parts and the drive rod which constitutes the fluid passage. 13. A device as defined in claim 10 wherein said means for forming comprises a guide funnel supported by said connecting means and oriented to open toward the interior of the vessel, said guide funnel being movable relative to said connecting means and forming a structural unit with said flow restricting member. 14. A device as defined in claim 13, wherein said flow restricting member has an upper portion enclosed by said connecting means, and said flow restricting member and said connecting means are constructed to form therebetween a portion of said fluid passage which is open when said flow restricting member is in its normal position and closed when said flow restricting member is in its actuated position. 15. A device as defined in claim 14, wherein said flow restricting member is provided with a plurality of axially extending grooves defining said portion of said fluid passage, and said connecting means comprise a flow blocking member disposed for blocking said channels when said flow restricting member is in its actuted position. 16. In a nuclear reactor which includes a pressure vessel having a vessel head, a core in the vessel, elements for controlling the reactivity of the core, drive rods which pass through the vessel head for displacing the elements, and a plurality of head adapters which pass through the vessel head, each head adapter forming part of a drive rod housing enclosing a respective drive rod, each housing enclosing a region which communicates with the interior of the vessel and which is closed at the top, the improvement comprising a device associated with a respective housing and constituting a housing extension located within said vessel, said device including means for connecting said device to the head adapter forming part of said respective housing, and means supported by said connecting means for forming, around the associated drive rod and within said associated housing, a fluid passage which constitutes the only path for fluid flow between the interior of the vessel and the interior of the drive rod housing above said means for forming, said means for forming comrpising a flow restricting member mounted for movement relative to said connecting means from a normal position to an actuated position in response to the fluid pressure acting thereon as a result of a leak in the respective housing, and said flow restricting member being configured to cooperate with said connecting means for causing said fluid passage to have a cross-sectional area which exceeds a selected value when said flow restricting member is in said normal position and a cross-sectional area which does not exceed the selected value when said flow restricting member is in said actuated position. 17. The combination as defined in claim 16 wherein the selected value is about 5 cm.sup.2.