Patent Number: 052895114
Section: description

PREFERRED EMBODIMENTS OF THE INVENTION FIG. 1 shows a fast breeder reactor in which the present invention is applied to the primary sodium system. A reactor vessel 1, an intermediate heat exchanger 3, a primary sodium system pump 9 and a primary sodium system main piping 10 are all embedded and sealed in a solid sodium mass 20 solid at room temperature. High temperature liquid sodium serving as a coolant flows through the reactor vessel 1 and the piping 10. The liquid sodium coolant flowing out of the reactor vessel 1 returns to the primary sodium system pump 9 via the intermediate heat exchanger 3, and is recirculated again into the reactor vessel 1. The piping from the intermediate heat exchanger 3 to the primary sodium system pump 9 is not shown here since it is disposed in a part of the sodium mass 20 where the cutting plane of the section of this figure does not pass. In region 21 surrounding the reactor vessel 1, the pump 9 and the piping 10 through which the liquid sodium flows, the sodium stays in a molten state as its temperature is above its melting point. Although the solidified sodium mass 20 is contained in an outer container 22 with an upper cover 23, the outer container 22 does not need to have a great strength, but only needs to have water-tightness because the solidified sodium mass 20 itself has a sufficient strength. The space between the upper cover 23 and solid sodium mass 20 is filled with an inert gas. An inert gas inlet pipe 24 and a liquid sodium inlet pipe 25 are provided through the upper cover 23. A plurality of ventilation pipes 26 extend into the solid sodium mass 20 from the outside thereof in appropriate positions in the vicinity of the vessels (reactor vessel 1, intermediate heat exchanger 3 and pump 9) and the pipings (main piping 10 and pipings connecting the vessels). By controlling the temperature and velocity of ventilation air to be supplied to these ventilation pipes 26, the thickness of the molten sodium region 21 in the vicinity of the external of the vessels, and pipings can be maintained at a constant value despite transient changes in the temperature of liquid sodium flowing through the vessels and piping of the primary sodium system. Such an arrangement as described above enables the solid sodium mass 20 to actually form the coolant pressure boundary, so that the walls of the vessels and piping can be no more considered as a part of the coolant pressure boundary. Thus, the reactor vessel 1, the intermediate heat exchanger 3, the primary sodium system pump 9 and the like can be provided with sodium introducing orifices 27 through which liquid sodium can flow. By providing such sodium introducing orifices 27, both the inside and the outside of the primary sodium system can be filled with liquid sodium concurrently. That is, by supplying liquid sodium into the outer container 22 through the liquid sodium inlet pipe 25, it is filled with liquid sodium, and thereafter the reactor vessel 1, the intermediate heat exchanger 3, the primary sodium system pump 9, and further the piping 10 connecting therebetween are filled with liquid sodium through respective sodium introducing orifices 27. After the supplying of sodium is completed, by controlling the temperature and velocity of ventilation air to be supplied from the ventilation pipes 26, the liquid sodium in the region outside the primary sodium system can be solidified to create such a state as shown in FIG. 1. The sodium introducing orifices 27 may be formed in both the vessels and the piping. Further, the effects of a diffusion type cold trap can be produced by providing the sodium introducing orifices 27. Namely, impurities such as sodium oxide in the sodium coolant are transferred through the sodium introducing orifices 27 out of the primary sodium system into the molten sodium region 21 surrounding the primary sodium system, and are precipitated there in the lowest temperature portion, i.e., at the interface between the molten sodium region 21 and the solidified sodium mass 20. As can be understood from the foregoing, since the solid sodium mass surrounding the entire portion of the sodium coolant system forms the coolant pressure boundary, it is not necessary for the vessel walls or piping walls to ensure the integrity of the boundary. Therefore, it also is not necessary to install guard vessels around the respective vessels, or to dispose the main piping at higher locations. Further, it becomes possible to attach bellows to the main piping, as required. Still further, by providing sodium introducing orifices in the vessel walls and the piping walls which delimit the coolant pressure boundary, not only does it become easier to bury the sodium coolant system in the solid sodium mass, but it also becomes possible to transfer impurities in the coolant sodium to other regions outside the coolant system to allow them to precipitate there. This contributes to reducing the burden imposed on a coolant purifier system, or even allows the purifying system to be eliminated. Although the above description has been limited to the case where sodium is utilized as the liquid metal, the present invention can employ other liquid metal coolants which are solid at room temperature such as potassium, NaK, and lithium. Further, the liquid metal in the cooling system and the solid metal mass outside the cooling system may be of different kinds of metals as long as their compatibility can be maintained.