Patent Number: 052232085
Section: description

OPTIMAL MODE TO REALIZE THE INVENTION This invention will now be described in more detail referring to the attached drawings. FIG. 1 is a schematic section of formations which mainly comprise permeable layers 1 and impermeable layers 2 which are faulted at fault-lines 3,4. The water is retained in the permeable layers 1, and flows along the impermeable layers 2 which forms the groundwater basin. As shown in FIGS. 1 and 2, a cutoff wall 5 is installed substantially vertical to the line of stratigraphic division of an impermeable layer. The cutoff wall 5 is built by driving a certain number of pipes into the ground, pouring in through the pipes cement grout which is a mixture of cement and water or a mixture of such cement grout and clay or water glass (sodium silicate) to fill up pores in the permeable layer. The reference numeral 6 denotes a concrete shield for biological shielding of a reactor installed on a bedrock 7 below the cutoff wall 5. A metal container 10 is placed within said concrete shielding 6, and further inside said container 10 is installed a reactor 8 which generates heat by the reaction of uranium oxide. The reactor 8 is provided with an inlet 12 for the primary cooling water for cooling the heat generated by the nuclear reaction and an outlet 14 for exhausting the primary cooling water evaporated by the heat from the reactor 8 so as to prevent the reactor 8 from being excessively heated. The steam let out from said outlet 14 of the reactor 8 is guided to a turbine 16 for generating power via piping means to actuate the turbine 16 for generation of power. It is subsequently exhausted from the turbine 16, condensed at a cooling tower 20 from gas to liquid, and recycled back to the reactor 8 via a water supply pump 18 and a cleaning apparatus 19. The primary cooling water is designed to circulate within a closed circuit as it is exposed to radiation in the reactor 8. The cooling tower 20, as shown in FIG. 3, has an air outlet port 22 at the top and an air inlet port 24 on one side thereof, and contains a spiral piping member comprising a thermally conductive tube to form a passage for the primary cooling water. A sprinkler 30 is provided above the piping member in order to sprinkle the water guided from the cutoff wall 5 via a pipe 26 and a tank 28. Further, a large-size fan 32 is installed near the air inlet port 24 for taking in the air from the surface as well as for exhausting the steam at the surface. This evaporation type cooling tower 20 is intended to absorb the energy of the primary cooling water in the form of heat by utilizing latent heat of the evaporating water, and is capable of absorbing a large amount of energy with less secondary cooling water. The reference number 34 denotes a stack which is connected to the air outlet port of the cooling tower 20 for letting out the steam to the surface, and 36 a stack connected to the air inlet port 24. The diameter of those stacks can be determined in relation to the output of the reactor 8, the amount of cooling water and the amount of air blowing, but is preferably relatively large. In FIG. 3, the reference numeral 38 denotes an overflow pipe which discharges overflow of the water caused by the difference between the amount of water seeping in the underground dam above the cutoff wall and the amount of water taken therefrom. Said overflow pipe is used to activate a turbine 40 of a hydrogenerator 41 for power generation which is installed 30-50 m below the water level of the dam. The water used for hydropower generation is discharged into a second underground dam formed with a cutoff wall 42 built in the groundwater basin located below said underground dam. The water of the second underground dam is pumped up to the first dam by a pump 43. The water is pumped up during the night by excess of the generated power. The second dam is designed to supply secondary cooling water by pumping up the water when the pondage of the first dam decreases to a level below the requirement. A water intake pipe 26 and an overflow pipe 38 for the secondary cooling water open into a water well 44 sunken near the cutoff wall 5 of the upper underground dam. Although a second dam is installed underground in this embodiment, the invention is not limited as such. Overflow of the water may be forced into the groundwater vein in the permeable layer. The reference numeral 39 denotes a repository for spent fuel installed 1,000 m or more below the surface. The amount of secondary cooling water necessary for an evaporation type cooling tower for the output of 500,000 Kw nuclear power generation is 33.6 m.sup.3 per minute loss, the heat Q.sub.2 necessary for the water of 15.degree. C. to evaporate in one day is calculated as below. ##EQU1## As the blown-in air is heated, thermal energy is further absorbed. The evaporation type cooling tower evaporates 30% of the secondary cooling water for cooling and uses 70% thereof for cooling in the form of liquid. The output of the underground nuclear power plant can be calculated from the total pondage of the groundwater, the volume of seepage and the necessary amount of water. It is preferable to set the total pondage at a level higher than necessary for safety consideration. Table 2 shows the amount of secondary cooling water required for the evaporation type cooling tower as relative to the required pondage of the underground dam at the outputs of 100,000, 500,000 and one million Kw. TABLE 2 ______________________________________ output amount of water required m.sup.3 total pondage Kw per min. per day required m.sup.3 ______________________________________ 100,000 6.7 9,677 970,000 500,000 33.6 48,384 4,830,000 1,000,000 67.2 96,768 9,670,000 ______________________________________ Required pondage is estimated as 100 times of the amount of daily intake, and the figures are obtained from formula above. If the output of the nuclear power generation is 500,000 Kw, and the amount of water seeping into an underground dam is normally 96,768 m.sup.3 per day, the hydroelectric output Q obtained by the use of this excess water would theoretically be calculated as follows: EQU Q=9.8.times.0.56 m.sup.3 /s.times.40 m (head) =219 Kw. Although in this embodiment, the overflow of the water in the underground dam is used for hydroelectric generation, use of excess groundwater is not limited to power generation but may be for irrigation for plants on the surface by pumping up the water. The plants may be used as indicator for acid rain measurement. INDUSTRIAL APPLICABILITY OF THE INVENTION As described in detail in the foregoing, the nuclear power generation system according to this invention is constructed to take in a necessary amount of groundwater which is abundant in the underground from an underground dam built nearby, and therefore the system may be installed wherever a suitable groundwater basin exists. As the system does not need pumping up of groundwater, the energy can be utilized at a higher efficiency. As the nuclear power generation system is built underground in this invention, the system is remarkably superior in earthquake resistance because the influence of S wave (transverse wave) is drastically attenuated compared to an aboveground system. As the system is built several tens meters below the surface, even if radiation is accidentally produced from the reactor, the concrete walls and impermeable layers in the formations would act as a biological shield, ensuring safety. Unlike the conventional system, as this system uses groundwater as the secondary cooling water instead of sea water, machines and equipments such as the pipings are less prone to erosion, ensuring a longer life. Moreover, this system recycles the groundwater to prevent depletion thereof without returning the same to the original groundwater vein after cooling, to prevent groundwater contamination.