Patent Number: 053496175
Section: claims

1. A pressurized water nuclear reactor, comprising: a. a vessel forming a first ferrule (2);  b. a second ferrule (6) contained in the vessel (2) and concentric therewith, said first and second ferrules defining an external annular compartment (3) through which primary coolant flow water circulates to provide a hairpin-shaped flow path F of said primary coolant from top to bottom of said vessel (2);  c. a central cylindrical compartment (10) containing a core (4) for heating said water, said flow path F of primary water continuing from the bottom of said vessel, through said core, to the top of cylindrical compartment;  d. an apparatus for removing residual power from the core of said reactor, said apparatus comprising a third ferrule (7) defining a complementary annular space (8) between said external annular compartment (3) and said central cylindrical compartment (10), said complementary annular space (8) including a first orifice (12) for permitting communication of flow water between a lower part of said complementary annular space (8) and a lower part of said external annular compartment (3), said complementary annular space (8) also including a second orifice (11) for permitting communication of flow water between said cylindrical compartment (10) and an upper part of said complementary annular space, said apparatus also comprising at least one self-contained auxiliary heat exchanger (9) for removing said residual power, said heat exchanger being located in said complementary annular space (8) and being supplied autonomously with a second heat transfer fluid separate from said flow water; and  e. means for increasing vacuum effect in the vicinity of the lower part of the complementary annular space, wherein said means for increasing vacuum effect comprises means for partially closing the first orifice and a series of cylindrical radial pipes (16) extending, in the vicinity of the base of the core, into the external annular compartment (3), said cylindrical radial pipes (16) issuing onto openings (15) provided on the periphery of the lower part of the intermediate ferrule in the complementary annular space and being provided on their wall with longitudinal slots (17) for communication with the external annular compartment (3).  a. a vessel forming a first ferrule (2);  b. a second ferrule (6) contained in the vessel (2) and concentric therewith, said first and second ferrules defining an external annular compartment (3) through which primary coolant flow water circulates to provide a hairpin-shaped flow path F of said primary coolant from top to bottom of said vessel (2);  c. a central cylindrical compartment (10) containing a core (4) for heating said water, said flow path F of primary water continuing from the bottom of said vessel, through said core, to the tope of said cylindrical compartment;  d. an apparatus for removing residual power from the core of said reactor, said apparatus comprising a third ferrule (7) defining a complementary annular space (8) between said external annular compartment (3) and said central cylindrical compartment (10), said complementary annular space (8) including a first orifice (12) for permitting communication of flow water between a lower part of said complementary annular space (8) and a lower part of said external annular compartment (3), said complementary annular space (8) also including a second orifice (11) for permitting communication of flow water between said cylindrical compartment (10) and an upper part of said complementary annular space, said apparatus also comprising at least one self-contained auxiliary heat exchanger (9) for removing said residual power, said heat exchanger being located in said complementary annular space (8) and being supplied autonomously with a second heat transfer fluid separate from said flow water; and  e. means for increasing vacuum effect in the vicinity of the lower part of the complementary annular space, wherein the means for increasing vacuum effect comprises means for partially closing the first orifice and in the external annular compartment (3) below the auxiliary heat exchanger (9), an annular chamber (22) linked by a series of openings (24) with the complementary annular space (8) and, by an annular slot (20), with the external annular compartment (3), said annular chamber (22) having an extension in the radial direction of the vessel (2) such that it creates, in the external annular compartment (3), a narrowing (19) which leads to an increase, at the location of the slot (20), to the flow rate of the primary flow descending into the external annular compartment (3) of the auxiliary heat exchanger (9). 2. A reactor according to claim 1, wherein there are two such longitudinal communicating slots (17) on each pipe (16) said slots being positioned azimuthly on the surface of the cylindrical pipes at an angle .phi. close to 80.degree. with the main flow path in the external annular compartment (3). 3. A pressurized water nuclear reactor, comprising: 4. A pressurized water nuclear reactor including a reactor vessel (2) having a primary water circulation in accordance with a hairpin path in the reactor vessel (2) and having two concentric ferrules (2, 6) defining an external annular compartment (3), in which cold primary water describes a downward path and a central cylindrical compartment (10) containing the actual core (4), in which the primary water flows from bottom to top, accompanied by heating, through the core, a third ferrule (7) defining a complementary annular space (8) between the two preceding compartments (3, 10), said annular space (8) being linked in this lower part by a first orifice (12) issuing into the external annular compartment (3) with the cold water of the primary circuit and in its upper part and by a second orifice (11) issuing into the central compartment (10) with the hot water of the primary circuit and an auxilliary heat exchanger (9) located in said complementary annular space (8), said auxiliary exchanger (9) being supplied autonomously by a second heat transfer fluid, which is independent of the primary cooling water of the reactor core, and means for increasing vacuum effect in the vicinity of the lower part of the complementary annular space, said means for increasing the vacuum effect incorporating means for partially closing the first orifice and a series of cylindrical radial pipes (16) extending, in the vicinity of the base of the core, into the external annular compartment (3), said cylindrical radial pipes (16) issuing onto openings (15) provided on the periphery of the lower part of the intermediate ferrule in the complementary annular space and being provided on their wall with longitudinal slots (17) for communication with the external annular compartment (3). 5. A reactor according to claim 4, wherein there are two such longitudinal communicating slots (17) on each pipe (16), said slots being positioned azimuthly on the surface of the cylindrical pipes at an angle .phi. close to 80.degree. with the main downward flow direction in the external annular compartment (3). 6. A reactor according to claim 4, wherein the means for increasing vacuum effect comprises means for partially closing the first orifice and, in the external annular compartment (3) below the auxiliary heat exchanger (9), an annular chamber (22) linked by a series of openings (24) with the complementary annular space (8) and, by an annular slot (20), with the external annular compartment (3), said annular chamber (22) having an extension in the radial direction of the vessel (2) such that it creates, in the external annular compartment (3), a narrowing (19) which leads to an increase, at the location of the slot (20), to the flow rate of the primary flow descending into the external annular compartment (3) of the auxiliary heat exchanger (9).