Patent Number: 039502201
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to recirculating pumps for nuclear reactors in general, and more particularly to improvements in internal primary pumps for recirculation of coolant in pressure vessels of boiling water reactors. It is already known to provide in a nuclear reactor plant a battery of internal recirculating pumps which extend into the bottom wall of the pressure vessel in a boiling water reactor. Such recirculating pumps are installed independently of the feed water supply lines and are driven by normal electric motors or by so-called wet or canned motors known from the art of glandless recirculating pumps. A drawback of such constructions is that the pressure vessel of the reactor must be provided with several sets of openings, namely, those for the introduction of portions of internal recirculating pumps and those for the admission of feed water. Moreover, conventional glandless recirculating pumps constitute expensive auxiliary aggregates especially since, for the reasons of safety, each such pump normally embodies a motor generator with flywheel for supplying additional energy in order to prolong the period of deceleration of the pump rotor in the event of current failure. Gradual deceleration is desirable and necessary in order to insure satisfactory cooling of the pressure vessel. In the absence of aforementioned generators, the rotor of the pump would be arrested practically immediately upon opening of the motor circuit. It was already proposed to employ in a boiling water reactor one or more internal recirculating pumps which are driven by water turbines and are mounted in such a way that feed water enters the pressure vessel by way of openings which are provided for introduction of portions of internal recirculating pumps. Reference may be had to German Offenlegungsschrift No. 1,921,903. This renders it possible to reduce the number of openings in the pressure vessel and the number of conduits for admission of feed water. However, such pressure vessels must be equipped with bypass lines. Another drawback of the just described recirculating systems is that the regulation of water turbines is extremely complex, mainly because the blades of the turbine are not readily accessible for adjustment of their angles. SUMMARY OF THE INVENTION An object of the invention is to provide the pressure vessel of a reactor, especially the pressure vessel of a boiling water reactor, with one or more novel and improved internal primary recirculating pumps which can be installed in openings for the admission of feed water and whose parts are more readily accessible than in heretofore known pressure vessels. Another object of the invention is to provide a novel and improved internal primary recirculating pump for use in the pressure vessel of a boiling water reactor. A further object of the invention is to provide an internal recirculating pump with novel and improved means for prolonging the interval of deceleration upon opening of the circuit of the pump motor. An additional object of the invention is to provide an internal recirculating pump with a novel and improved turbine. The invention is embodied in a nuclear reactor, particularly in a boiling water reactor, which comprises a pressure vessel having one or more openings for admission of feed water and an internal primary recirculating pump for each such opening. Each pump comprises a body a portion of which extends into the respective opening and is formed with an annular chamber for admission of feed water, a shaft which is rotatably mounted in the body and extends into the opening, a rotor which is directly or indirectly carried by the shaft in close proximity to the annular chamber and normally receives torque from the shaft to convey feed water from the annular opening into the pressure vessel, an electric motor mounted in the body and arranged to drive the shaft, and a single-stage or multi-stage turbine, mounted on the shaft, preferably at the suction side of the rotor, to prolong the deceleration of the rotor to zero speed and to thus lengthen the interval of cooling in the event of failure of current supply to the motor. The turbine may serve as a carrier for the pump rotor, and the pressure chamber of the turbine is preferably in communication with the pressure chamber of the rotor by way of an annular flow-restricting bypass which is defined by the pump body and the rotor. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved recirculating pump itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.