Patent Number: 050948032
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to a steam generator utilized for a liquid-metal coolant reactor and more particularly, to a steam generator in which an electromagnetic pump is incorporated. In a fast breeder reactor utilizing a liquid-metal coolant, a primary coolant as a reactor coolant is exposed high levels of to radioactivity, so that it is necessary to isolate a primary cooling system from a steam generation system, and it is also necessary to carry out a heat exchange operation between the liquid metal and water during the steam generating process for supplying the steam to a turbine generator. However, in a fast breeder reactor utilizing a liquid-metal coolant, since an extremely large amount of heat is generally generated due to a chemical reaction based on the heat exchanging operation between the liquid metal and the water, it is necessary to disperse the heat generated. For this reason, a secondary cooling system is generally located between the primary cooling system and the steam generation system. A typical example of a cooling system of the liquid-metal coolant reactor of the conventional type described is shown in FIG. 8. Referring to FIG. 8, in a reactor vessel 1, disposed in a roof slab 8, are arranged a reactor core 2 and a primary cooling system comprising a primary main circulation pump 3 for circulating a liquid-metal coolant in the reactor vessel 1 for cooling the core 2, and an intermediate heat exchanger 4 for carrying out the heat exchanging operation between the primary coolant and the secondary coolant. On the other hand, a secondary cooling system comprises, as shown in FIG. 8, the intermediate heat exchanger 4, a steam generator 5 for generating steam to be supplied to a turbine generator, an electromagnetic pump 6 arranged inside the steam generator 5 for circulating the secondary coolant, and pipings 7 for connecting the equipment described above. The steam generator 5 is disposed outside the roof slab 8 which is surrounded by a wall structure of the reactor. The electromagnetic pump 6 is inserted into an upper portion of a liquid-metal outlet rising pipe 11 for sucking the liquid-metal from the lower portion of the rising pipe 11 and for feeding the same towards the intermediate heat exchanger 4. The electromagnetic pump 6 is generally provided with a stator coil (electromagnetic coil) wound around the outer periphery of an inner iron core in a spiral fashion, and an electric current is conducted to the stator coil from an external power source to thereby generate a magnetic field to cause the circulation of the liquid metal. During the conduction of the electric current and the operation of the electromagnetic pump 6, heat is generated from the stator coil. Accordingly, it is desired to effectively remove and disperse this heat during the operation thereof. For this purpose, various trials have been carried out for effectively absorbing the heat generated from the stator coil and recovering the same into the metal-liquid to suppress the energy loss during the operation of the reactor to a minimum. FIG. 9 shows one example of an electromagnetic pump proposed for the purpose of achieving the effect described above and disclosed in Japanese Utility Model Laid-open Publication No. 116701/1988. An electromagnetic pump 20 shown in FIG. 9 comprises an inner iron core 22 provided with an inner through hole 21 and an outer iron core 23 arranged concentrically with space around the outer periphery of the inner iron core 22. The space between the outer periphery of the inner iron core 22 and the inner periphery of the outer iron core 23 is formed as an annular passage 24 through which the liquid metal passes. A first stator coil (electromagnetic coil) 25 is embedded in an annular fashion in the outer peripheral surface of the inner iron core 22, and the outer surface of the first stator coil 25 is completely covered with a sealing member 26. Both of the vertical ends 26a of the sealing member 26 extend beyond the outer end portions of the inner iron core 22 and are connected with each other to be closed and thus define inner spaces 27 at both the ends of the iron core 22. These inner spaces 27 and the through hole 21 are filled with inert gas. A second stator coil (electromagnetic coil) 28 is embedded in an annular fashion in the inner peripheral surface of the outer iron core 23 and the outer surface of the second stator coil 28 is covered with a sealing member 29. The outer periphery of the outer iron core 23 is surrounded by an annular member 31 having its outer periphery supported by an electromagnetic pump supporting cylinder 29a. A plurality of bypass passages 32 are formed in the annular member 31 along the axial direction of the outer peripheral surface of the outer iron core 23 and the upper ends and the lower ends of the bypass passages 32 are provided with bypass passage inlets 33 and the bypass passage outlets 34, respectively. The electromagnetic pump 20 of the structure described above is secured to a flange member 35 which is secured to a flanged portion of the steam generator 5 used to install the electromagnetic pump 20 in the steam generator 5. The electromagnetic pump 20 operates to draw the liquid metal from a suction port 36 by the magnetic force caused by the first and second stator coils 25 and 28, and the drawn liquid metal flows upwardly in the annular passage 24 and is discharged through a discharge port 37. During this operation, the pressure at the inlet portion 33 of the bypass passage becomes larger than that at the outlet portion 34 of the bypass passage, so that a part of the liquid metal passes the bypass passages 32 and circulates around the outer iron core 23. The first stator coil 25 then generates heat, which is effectively recovered by the liquid metal to thereby suppress the temperature rise due to the heat generated by the first stator coil 25. The recovery of the generated heat by means of the circulating liquid metal possibly minimizes the energy loss in whole the steam generator. However, with the conventional steam generator of the character described above, the axial through hole 21 of the inner iron core 22 constituting the electromagnetic pump 20 and the spaces 27 defined by the sealing member 26a are closed and the spaces are filled with the inert gas, so that the first stator coil 25 embedded in the inner iron core 22 is cooled by only the liquid metal passing the circular passage 24. For this reason, the cooling effect for the first stator coil 25 of the inner iron core 22 decreases and the temperature rise of the inner iron core 22 is increased, whereby the characteristics of the electromagnetic pump 20 cannot be effectively utilized. SUMMARY OF THE INVENTION An object of the present invention is to substantially eliminate the defects and drawbacks encountered in the prior art described above and to provide a steam generator utilized for a liquid-metal coolant reactor provided with an electromagnetic pump capable of effectively cooling a stator coil means of the electromagnetic pump by the flow of liquid metal to thereby effectively reduce the energy loss of steam generator as a whole. This and other objects can be achieved according to the present invention by providing a steam generator utilized for a liquid-metal coolant reactor comprising an outer body shell of hollow cylindrical structure provided with a water inlet chamber disposed at a lower portion of the body shell, an outlet steam chamber disposed at an intermediate portion of the body shell and a liquid metal inlet portion disposed at an upper portion of the body shell, a heat transfer tube assembly arranged annularly along an inner wall of the body shell so as to connect the water inlet chamber and the outlet steam chamber, a liquid metal rising pipe assembly axially extending substantially a central portion of the body shell and arranged in a radial direction offset from an arrangement of the heat transfer tube assembly, and an electromagnetic pump means arranged at an upper portion inside the liquid metal outlet rising pipe means, the electromagnetic pump means comprising a hollow cylindrical iron core provided with a comb shaped portion at an outer peripheral surface thereof and an annular stator coil means assembled in said comb shaped portion of the cylindrical iron core, a main passage of liquid metal being formed on a side on which the stator coil means of the iron core is assembled, a cooling bypass passage being formed at substantially the central portion of the cylindrical iron core in a vertically penetrating fashion. In a preferred embodiment, the cylindrical iron core may be formed so as to have inner and outer iron core portions and the stator coil means may also be formed so as to have inner and outer stator coil portions in association with the inner and outer iron core portions. According to the steam generator of a liquid-metal coolant type reactor of the characters described above, the main flow passage of the liquid metal is formed on the side on which the stator coil of the cylindrical iron core is assembled and the cooling bypass passage is formed so as to penetrate the central portion of the steam generator so that the stator coil assembled in the cylindrical iron core can be cooled by the liquid metal circulating the outer peripheral surface of the stator coil, whereby the heat generated by the stator coil can be effectively absorbed and the excessive temperature rising of the stator coils and iron cores can be suppressed. Accordingly, the heat generation efficiency of the steam generator can be remarkably improved.