Patent Number: 048790877
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear power plant, and more particularly to a nuclear power plant suitably employing a nuclear reactor in which the core flow-rate is controlled by feed water. 2. Statement of the Related Art At present, reduction in construction expenses is a major task in a nuclear power plant. With respect to a boiling water reactor (hereafter referred to as the BWR power plant), for instance, development is under way of a new type of power plant which is provided with internal pumps. In this new type of power plant, since a recirculation system used in an existing BWR power plant is not required, the overall size of a reactor container becomes compact. However, it is desirable to make the reactor container even more compact. Examples in which the reactor container can be made compact are disclosed, though not directly referred to therein, in Japanese Patent Examined Publication No. 43-23117 (U.S. patent Ser. No. 497,787; application date: Oct. 19, 1965) and Japanese Patent Examined Publication No. 49-16920 (U.S. Pat. No. 3,621,926). In a BWR power plant disclosed in Japanese Patent Examined Publication No. 43-23117, a portion of the feed water is supplied to a reactor pressure vessel via a feed water sparger, while the remaining portion of the feed water is used as the driving water for jet pumps so as to supply cooling water to the core. The feed water introduced into the feed water sparger is used for controlling the water level in the reactor pressure vessel. Furthermore, in this BWR power plant, the cooling water discharged from the feed water sparger and the cooling water separated by a steam separator above the core (the two kinds of cooling water are in a mixed state) is cooled by the feed water used as the jet pump driving water, and is subsequently sucked into jet pumps. The cooling of the jet pump suction water by this heat exchanger is aimed at preventing the occurrence of cavitation in the jet pumps due to the boiling of the cooling water in the jet pumps. Japanese Patent Examined Publication No. 49-16920 discloses a BWR power plant which has jet pumps using as their driving water the cooling water discharged from a recirculation pipe and jet pumps using as their driving water a portion of the feed water, the remaining portion of the feed water being supplied from the feed water sparger into the reactor pressure vessel. In this publication as well, it is disclosed (column 6, lines 37-44) that the cooling water which is sucked from the feed water sparger into the jet pumps through an annular descending flow passage is cooled, as in the case of Japanese Patent Examined Publication No. 43-23117. Each of the foregoing examples of the prior art is arranged such that a heat exchanger is installed in a reactor pressure vessel, and the cooling water sucked into the jet pumps is cooled by the jet pump driving water, i.e., part of the feed water, by using this heat exchanger. However, the temperature difference between the cooling water sucked into the jet pumps and the jet pump driving water, both being allowed to flow into the heat exchanger, in the order of 5.degree.-60.degree. C., which the flow rate at the side, of the heat exchanger, to be cooled is 10 times as much as the flow rate at cooling side thereof. For this reason, the heat exchange efficiency of the cooling water sucked into the jet pumps and the jet pump driving water is very poor, so that the temperature of the cooling water sucked into the jet pumps does not decline appreciably. Accordingly, in these conventional examples, the range which makes it possible to prevent the occurrence of cavitation in the jet pumps is narrow, so that a reactor output through the core flow-rate control cannot be altered substantially. In particular, it is difficult to effect a load following operation in the conventional examples. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a nuclear power plant which is capable of simplifying the structure of a nuclear reactor. Another object of the present invention is to provide a nuclear power plant which is capable of preventing the occurrence of cavitation in jet pumps and of substantially altering a reactor power through core flow-rate control. Still another object of the present invention is to provide a nuclear power plant which is capable of preventing a decline in the water level of a reactor during a trip. A further object of the present invention is to provide a nuclear power plant which is capable of altering outputs with small amplitude and short cycles. A characteristic feature of the present invention lies in that there is provided feed water supplying means for introducing a portion of the feed water into jet pumps in a reactor container as driving water and introducing the remaining portion of the feed water into a feed water sparger in the reactor container at a temperature lower than that of the portion of the feed water introduced into the jet pumps. In accordance with the present invention, since it is not necessary to install in a reactor container a heat exchanger for heating the feed water used as the driving water for the jet pumps, the structure of the reactor can be simplified.