Patent Number: 054935911
Section: claims

1. An internal pump for a nuclear reactor, comprising: a pump unit disposed in a nuclear reactor pressure vessel, said pump unit including an axially extending pump shaft drivingly connected to a pump impeller, and  a motor unit disposed in a motor casing joined to the pressure vessel and having a motor shaft coaxial with and connected to the pumpshaft, said motor unit including:  a motor rotably driving the motor shaft,  a flywheel fixed to the motor shaft at one axial side of the motor,  a thrust disc fixed to the motor shaft at an axial side of the motor opposite the one axial side, said thrust disc serving as an auxiliary impeller, said thrust disc exhibiting a plurality of coaxial cylinder portions of different diameters including a bulging cylinder portion of large diameter and a constricted cylinder portion of smaller diameter than said bulging cylinder portion,  a large ring housing section surrounding the bulging cylinder portion with a first fixed orifice formed between the bulging cylinder portion and the large ring housing section, and  a small ring housing section surrounding the constricted cylinder portion with a second fixed orifice formed between the constricted cylinder portion and the small ring housing section,  said ring housing sections and cylinder portions defining a pressurized chamber between the first and second fixed orifices. 2. An internal pump according to claim 1, wherein said pressurized chamber is formed below the bulging cylinder portion of said thrust disc. 3. An internal pump according to claim 1, wherein said thrust disc further has cooling water circulating channel for circulating motor cooling water and pressure boosting channels for boosting pressure in said pressurized chamber, and wherein said pressurized chamber pressure boosting channels have their suction ports positioned at a discharge side of said motor cooling water circulating channels. 4. A reactor internal pump according to claim 1 wherein said thrust disc further has channels having discharge ports directed toward said pressurized chamber for boosting the pressure in said pressurized chamber, so that the pressure-boosted liquid may be fed as motor cooling circulating water into a motor chamber through the first fixed orifice. 5. A reactor internal pump according to claim 1, wherein said thrust disc further has first channels for circulating motor cooling water and for boosting the pressure in said pressurized chamber, and wherein said pressurized chamber pressure boosting channels have suction ports positioned at a suction side of said motor cooling water circulating channels. 6. A reactor internal pump according to claim 1, wherein said thrust disc further has channels having discharge ports directed toward said pressurized chamber for boosting the pressure in said pressurized chamber, so that the pressure boosted liquid may be fed as motor cooling circulating water into a motor chamber through a passage formed at a stationary side of said pressured chamber.