Power plant

The disclosed power plant can attain an extremely high thermal efficiency, as compared with that of the conventional power plant. The power plant comprises a steam system and a mixed medium system. The steam system comprises a heat source (1) for generating steam; a steam turbine (3) driven by the steam generated by the heat source; a steam condenser (81) for forming condensed water by condensing exhaust of the steam turbine; and a condensed water feeding pump (9) for feeding the water condensed by the steam condenser to the heat source. The mixed medium system comprises a heat exchanger (83) for exchanging heat between the exhaust of the steam turbine and a mixed medium; a separator (85) for separating the mixed medium heated by the heat exchanger (83) into liquid and vapor; a mixed medium turbine (95) driven by the mixed medium of vapor phase separated by the separator (85); a mixer (97) for mixing the exhaust of the mixed medium turbine with the mixed medium of liquid phase separated by the separator (85); a medium condenser (99) for forming condensed liquid by condensing the mixed medium mixed by the mixer; and a liquid feeding pump (102) for feeding the condensed liquid formed by the medium condenser to the heat exchanger (83).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a power plant, and more specifically to a 
power plant provided with both a steam system which uses steam (water 
vapor) to drive a turbine and a mixed medium system which uses a mixed 
medium to drive another turbine. 
2. Description of the Prior Art 
As the conventional power plants, nuclear power plants and thermal power 
plants are well known. FIG. 7 is a system diagram showing a boiling water 
reactor power plant (referred to as BWR, hereinafter). 
In FIG. 7, a conventional BWR is provided with a nuclear reactor 200 for 
heating coolant (light water) to generate steam. Here, the steam generated 
by the nuclear reactor 200 is saturated steam. The generated steam is fed 
to a high pressure steam turbine 202 through a main steam pipe 201, to 
drive the high pressure steam turbine 202. 
On the downstream side of the high pressure steam turbine 202, a moisture 
separator and reheater 203 is installed. This moisture separator and 
reheater 203 is connected to a heated steam pipe 204 branched from the 
main steam pipe 201 and to an extracted steam pipe 206 extending from the 
high pressure steam turbine 202. The steam exhausted by the high pressure 
steam turbine 202 is fed to the moisture separator and reheater 203. The 
exhausted steam fed to the moisture separator and reheater 203 is 
separated into water and vapor and further heated by high temperature 
steam fed thereto through the heated steam pipe 204 and the extracted 
steam pipe 206. The stream exhausted by the high pressure stream turbine 
202 and further heated by the moisture separator and reheater 203 becomes 
superheated steam. The obtained superheated stream is fed to two low 
pressure steam turbines 205 to drive the low pressure turbines 205. Here, 
the high pressure steam turbine 202 and the low pressure steam turbines 
205 are coupled coaxially with each other. Further, these turbines are 
coupled coaxially with an electric power generator (dynamo) 207. 
Therefore, when both the high pressure steam turbine 202 and the low 
pressure steam turbines 205 are driven by steam, it is possible to 
generate electric power by the generator 207. 
On the downstream side of the low pressure steam turbines 205, a steam 
condenser 208 is installed. To this steam condenser 208, sea (salt) water 
is supplied through a circulating water pump (not shown). The steam 
exhausted by the low pressure stream turbines 205 is fed to the steam 
condenser 208, and cooled and condensed into water by salt water 
circulating within the steam condenser 208. On the downstream side of the 
steam condenser 208, a condenser pump 209 is installed. Further, on the 
downstream side of this condenser pump 209, a plurality of low pressure 
feedwater heaters 210 are arranged in series at multistage. Further, on 
the downstream side of the low pressure feedwater heaters 210, a 
turbine-driven or motor-driven water supply pump 211 is installed. In 
addition, on the downstream side of the water supply pump 211, two high 
pressure feed-water heaters 212 are installed. To the high pressure 
feed-water heaters 212, an extracted steam pipe 213 extending from the 
high pressure steam turbine 202 and a steam pipe 214 and a drain pipe 215 
both extending from the moisture separator and reheater 203 are connected. 
Further, to the low pressure feed-water heaters 210, a drain pipe 216 
extending from the high pressure feed-water heater 212 and an extracted 
steam pipe 217 extending from the low pressure steam turbine 205 are 
connected. 
The water condensed by the steam condenser 208 is pressurized by the 
condenser pump 209, fed to the low pressure feed-water heaters 210, and 
further heated and pressurized by drain water fed through the drain pipe 
216 and steam fed through the extracted steam pipe 217, respectively. The 
heated and pressurized condensed water is further pressurized by the water 
supply pump 211, fed to the high pressure feed-water heaters 212, and 
further heated to an appropriate subcooled temperature by steam and drain 
water fed through the extracted steam pipe 213, the steam pipe 214 and the 
drain pipe 215, respectively. The condensed water heated to an appropriate 
subcooled temperature is fed to the nuclear reactor 200 through a reactor 
feed-water pipe 218, heated again to steam by the nuclear reactor 200, and 
fed again to the high pressure steam turbine 202 through the main steam 
pipe 201. 
In the above-mentioned conventional power plant, however, since electric 
power is generated in accordance with Rankin cycle by unitization of 
condensable steam, it has been difficult to increase the thermal 
efficiency. In the case of the nuclear power plant, in particular, since 
the saturated steam is used (superheated steam is difficult to use, being 
different from the thermal power plant), the thermal efficiency is lower 
than that of the thermal power plant. In other words, in the nuclear power 
plant, an improvement of the thermal efficiency is an important problem. 
However, this problem has not yet been solved sufficiently due to various 
restrictions. For instance, in the above-mentioned BWR or the pressurized 
water nuclear power plant (PWR), although the turbines are driven by use 
of steam heated to about 280.degree. C., the thermal efficiency is about 
33%, which is lower than that (40% or higher) of the thermal power plant. 
Further, in order to increase the thermal efficiency of the BWR, although 
it may be considered to increase the temperature and pressure of steam on 
the outlet side of the nuclear reactor (to increase Rankine cycle 
efficiency), when the temperature and pressure of steam are simply 
increased in the current saturated steam cycle, there inevitably arise 
some problems in that the thermal performance of the reactor core 
deteriorates or that the wall thicknesses of the pressure vessel and the 
coolant pipe must be both increased to improve the pressure resistance 
performance. 
In addition, in order to improve the thermal efficiency of the nuclear 
power plant, although it may be considered to increase only the steam 
temperature by forming superheated steam, in this case there arises 
another problem in that the reactor core must be designed in quite a 
different way from the conventional structure, with the result that the 
nuclear core structure is complicated, thus causing another problem in 
that it is difficult to control the nuclear reactor. 
Further, in the nuclear power plant, since the steam is saturated steam on 
the turbine inlet side and thereby a great amount of moisture is generated 
during the expansion process, it has been necessary to take an appropriate 
countermeasure against the generated moisture. In the case of the lower 
pressure steam turbine, in particular, in order to prevent the turbine 
from corrosion, some countermeasures of higher cost are inevitably needed. 
For instance, the following methods have been so far adopted; moisture 
separating blades with moisture removing grooves on the back blades are 
used; a mechanism for exhausting moisture effectively from the turbine 
casing is additionally provided; a pipe for exhausting moisture is formed 
of chromium molybdenum steel, etc. 
Further, in the case of the low pressure steam turbine used for the nuclear 
power plant, since the turbine is operated in a vacuum degree of about 38 
mmHg, in order to transduce the steam expansion work to the rotational 
turbine energy, a large-sized turbine is needed. In addition, since a high 
steam tightness and a high vacuum degree retention are both required for 
the steam condenser, the high costly structure has been inevitably 
adopted. 
Further, as the coolant of the nuclear reactor, it is possible to consider 
to use a medium having a boiling point which is lower than that of water, 
instead of the current light water, from the theoretical standpoint. When 
the lower boiling point medium (e.g., aqueous ammonia) is used, however, 
since the stability of the lower boiling point medium is extremely low 
against radioactive rays, the harmful substances resolved by the 
radioactive rays emitted from the nuclear core are inevitably formed, so 
that another problem arises in that a large-scaled installation for 
treating the gas resolved by the radioactive rays must be additionally 
installed. In practice, therefore, it has been impossible to use a low 
boiling point medium as the coolant of the nuclear reactor. 
SUMMARY OF THE INVENTION 
With these various problems in mind, therefore, it is the object of the 
present invention to provide a power plant which can attain an extremely 
high thermal efficiency, as compared with that of the conventional power 
plant. 
To achieve the above-mentioned object, the present invention provides a 
power plant, comprising: a steam system having: a heat source for heating 
a water to generate a steam; a steam turbine driven by the steam generated 
by said heat source; a steam condenser for forming a condensed water by 
condensing an exhaust of said steam turbine; and condensed water feeding 
means for feeding the condensed water produced by said steam condenser to 
said heat source; and a mixed medium system having: heat exchanging means 
for exchanging heat between the exhaust of said steam turbine and a mixed 
medium; high pressure separating means for separating the mixed medium 
heated by said heat exchanging means into liquid and vapor; a mixed medium 
turbine driven by the mixed medium of vapor phase separated by said high 
pressure separating means; first medium condensing means for forming a 
condensed liquid by condensing an exhaust of said mixed medium turbine; 
first condensed liquid heating means for heating the condensed liquid 
formed by said first medium condensing means; intermediate pressure 
separating means for separating the condensed liquid heated by said first 
condensed liquid heating means into liquid and vapor; first condensed 
liquid feeding means for feeding the condensed liquid formed by said first 
medium condensing means to said intermediate pressure separating means; 
mixing means for mixing the mixed medium of liquid phase separated by said 
intermediate pressure separating means with the exhaust of said mixed 
medium turbine on upstream side of said first medium condensing means; 
second medium condensing means for forming a condensed liquid by cooling 
the mixed medium of vapor phase separated by said intermediate pressure 
separating means; second condensed liquid feeding means for feeding the 
condensed liquid formed by said second medium condensing means to said 
heat exchanging means; and first separated liquid feeding means for 
feeding the mixed medium of liquid phase separated by said high pressure 
separating means to said intermediate pressure separating means. 
Further, it is preferable that the condensed liquid formed by said first 
medium condensing means is heated at the same time that the mixed medium 
of vapor phase separated by said intermediate pressure separating means is 
cooled, by exchanging heat between the condensed liquid and the mixed 
medium of vapor phase. 
Further, it is preferable that the power plant further comprises: second 
condensed liquid heating means for heating the condensed liquid formed by 
said second medium condensing means; intermediate high pressure separating 
means for separating the condensed liquid heated by said second condensed 
liquid heating means into liquid and vapor; third medium condensing means 
for forming a condensed liquid by cooling the mixed medium of vapor phase 
separated by said intermediate high pressure separating means; and second 
separated liquid feeding means for feeding the mixed medium of liquid 
phase separated by said high pressure separating means to said 
intermediate high pressure separating means; and wherein said second 
condensed liquid feeding means feeds the condensed liquid formed by said 
third medium condensing means to said heat exchanging means; and said 
first separated liquid feeding means feeds the mixed medium of liquid 
phase separated by said intermediate high pressure separating means to 
said intermediate pressure separating means. 
Further, it is preferable that the condensed liquid formed by said second 
medium condensing means is heated at the same time that the mixed medium 
of vapor phase separated by said intermediate high pressure separating 
means is cooled, by exchanging heat between the condensed liquid and the 
mixed medium of vapor phase. 
Further, it is preferable that the power plant further comprises: a 
small-sized steam condenser for condensing the steam within said steam 
condenser which contains non-condensable gas; and non-condensable gas 
treating means for treating the non-condensable gas existing within said 
small-sized steam condenser. 
Further, it is preferable that said heat source is a nuclear reactor. 
Further, it is preferable that the mixed medium is a mixture which contains 
at least a water and an ammonia. 
Further, the present invention provides a power plant, comprising: a steam 
system having: a heat source for heating a water to generate a steam; a 
steam turbine driven by the steam generated by said heat source; a steam 
condenser for forming a condensed water by condensing an exhaust of said 
steam turbine; and condensed water feeding means for feeding the water 
condensed by said steam condenser to said heat source; and a mixed medium 
system having: heat exchanging means for exchanging heat between the 
exhaust of said steam turbine and a mixed medium; separating means for 
separating the mixed medium heated by said heat exchanging means into 
liquid and vapor; a mixed medium turbine driven by the mixed medium of 
vapor phase separated by said separating means; mixing means for mixing 
the exhaust of said mixed medium turbine with the mixed medium of liquid 
phase separated by said separating means; medium condensing means for 
forming a condensed liquid by condensing the mixed medium mixed by said 
mixing means; and condensed liquid feeding means for feeding the condensed 
liquid formed by said medium condensing means to said heat exchanging 
means. 
Further, it is preferable that said steam turbine includes: a high pressure 
steam turbine driven by the steam generated by said heat source; and a low 
pressure turbine driven by an exhaust of said high pressure steam turbine; 
and wherein said heat exchanging means exchanges heat between the exhaust 
of said low pressure steam turbine and the mixed medium. 
Further, it is preferable that the power plant further comprises: a 
small-sized steam condenser for condensing the steam within said steam 
condenser which contains non-condensable gas; and non-condensable gas 
treating means for treating the non-condensable gas existing within said 
small-sized steam condenser. 
Further, it is preferable that said heat source is a nuclear reactor. 
Further, it is preferable that the mixed medium is a mixture which contains 
at least a water and an ammonia.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
(First embodiment) 
A first embodiment of the power plant according to the present invention 
will be described hereinbelow with reference to FIG. 1. 
In this first embodiment, the power plant is provided with both a steam 
system for generating power by using steam (water vapor) and a mixed 
medium system for generating power by using a mixed medium. 
First, the steam system of the power plant will be described hereinbelow. 
In FIG. 1, the power plant 1 is provided with a nuclear reactor (heat 
source) for generating steam by heating a coolant, i.e., light water. The 
outlet side of the nuclear reactor 1 is connected to an inlet side of a 
high pressure steam turbine 3 through a main steam pipe 2. Further, the 
high pressure steam turbine 3 is coupled coaxially with an electric power 
generator 4. The outlet side of the high pressure steam turbine 3 is 
connected to the inlet side of a steam condenser 6 through an exhaust pipe 
5, and the outlet side of the steam condenser 6 is connected to the inlet 
side of a high pressure feed-water heater 8 through a condensed water pipe 
7. A turbine-driven or motor-driven type water supply pump (condensed 
water feeding means) 9 is provided midway of the condensed water pipe 7. 
The outlet side of the high pressure feed-water heater 8 is connected to 
the inlet side of the nuclear reactor 1 through a reactor feed-water pipe 
10. Further, to the high pressure feed-water heater 8, a high pressure 
turbine extracted steam pipe 11 for feeding the extracted steam from the 
high pressure steam turbine 3 and a drain pipe 12 for feeding drain water 
to the steam condenser 6 are both connected. 
Next, the mixed medium system of the power plant will be described 
hereinbelow. 
Within the steam condenser 6, an intra-condenser heat exchange element 
(heat exchanging means) 13 is provided. The mixed medium is flowing 
through at least part of the intra-condenser heat exchange element 13. 
Here, the mixed medium flowing through the inside of the intra-condenser 
heat exchange element 13 is a medium which contains two or more 
components. At least one of these components for constituting the mixed 
medium is a substance having a boiling point lower than that of water (a 
lower boiling point component). An example of the mixed medium is a 
mixture of at least water and ammonia. 
The outlet side of the intra-condenser heat exchange element 13 provided 
within the steam condenser 6 is connected to a high pressure separator 
(high pressure separating means) 15 through a pipe 14, and the high 
pressure separator 15 is connected to the inlet side of a mixed medium 
turbine 17 through a pipe 16. The mixed medium turbine 17 is coupled 
coaxially with the high pressure steam turbine 3 and the power generator 
4. The outlet side of the mixed medium turbine 17 is connected to the 
inlet side of a medium condenser (first medium condensing means) 19 
through an exhaust pipe 18. Within the medium condenser 19, a heat 
exchange element 20 is provided, and cooling salt water is flowing through 
the inside of the heat exchange element 20. The outlet side of the medium 
condenser 19 is connected to the inlet side of a triple heat exchanger 22 
through a pipe 21, and an intermediate pressure pump (first condensed 
liquid feeding means) 23 for mixed medium is provided midway of the pipe 
21. 
The outlet side of the triple heat exchanger 22 is connected to the inlet 
side of a heat exchanger 25 through a pipe 24, and the outlet side of the 
heat exchanger 25 is connected to an intermediate pressure separator 
(intermediate pressure separating means) 27 through a pipe 26. The outlet 
side of the intermediate pressure separator 27 is connected to the triple 
heat exchanger 22 through a pipe 28, and the pipe 28 is connected to an 
inlet end of a first heat exchange element (second medium condensing 
means) 29 provided within the triple heat exchanger 22. The outlet end of 
the first heat exchange element 29 is connected to the inlet end of the 
intra-condenser heat exchange element 13 provided within the steam 
condenser 6 through a pipe 30. Further, a high pressure pump (second 
condensed liquid feeding means) 31 for pressurizing the mixed medium is 
provided midway of the pipe 30. 
Further, under the intermediate pressure separator 27, an end of a pipe 32 
for feeding the condensed mixed medium to the triple heat exchanger 22 is 
connected, and the other end of this pipe 32 is connected to the inlet end 
of a second heat exchange element (first condensed liquid heating means) 
33 provided within the triple heat exchanger 22. The outlet end of the 
second heat exchange element 33 is connected to a midway portion of the 
exhaust pipe 18 through a pipe 34, and a pressure reduction valve (mixing 
means) 35 is provided midway of the pipe 34. 
Further, to the lower portion of the high pressure separator 15, an end of 
a pipe 36 for feeding the condensed mixed medium to the heat exchanger 25 
is connected, and the other end of the pipe 36 is connected to an inlet 
end of a heat exchange element 37 provided within the heat exchanger 25. 
The outlet end of the heat exchange element 37 is connected to the 
intermediate pressure separator 27 through a pipe 28, and a pressure 
reduction value (first separated liquid feeding means) 39 is provided 
midway of the pipe 38. 
The operation of the first embodiment constructed as stated above will be 
described hereinbelow. 
The coolant of light water is heated by the nuclear reactor 1 into 
saturated steam, and then fed to the high pressure steam turbine 3 through 
the main steam pipe 2. The steam fed to the high pressure steam turbine 3 
drives the high pressure steam turbine 3, so that the rotational energy of 
the turbine is transduced into electric energy by the power generator 4. 
The steam exhausted from the high pressure steam turbine 3 is fed to the 
steam condenser 6 through the exhaust pipe 5, and then cooled and 
condensed by the mixed medium flowing through the intra-condenser heat 
exchange element 13. Here, the internal pressure of the steam condenser 6 
is determined to a pressure near or beyond the atmospheric pressure. The 
condensed water formed by the steam condenser 6 is pressurized by the 
water supply pump 9, and then fed to the high pressure feed-water heater 8 
through the condenser pipe 7. The condensed water fed to the high pressure 
feed-water heater 8 is heated by the steam extracted from the high 
pressure turbine extracted steam pipe 11, and recirculated into the 
nuclear reactor 1 through the reactor feed-water pipe 10, after having 
been heated to an appropriate subcooled temperature. 
On the other hand, the mixed medium heated by the steam exhausted from the 
high pressure steam turbine 3 in the steam condenser 6 is fed to the high 
pressure separator 15 through the pipe 14, after having been boiled into a 
two-phase stream. The mixed medium fed to the high pressure separator 15 
is separated by distillation into a liquid phase portion (formed of 
liquid) and a vapor phase portion (composed of superheated vapor without 
moisture). In the superheated vapor of the mixed medium (which forms the 
vapor phase portion), the concentration (abundance ratio) of the low 
boiling point component is heightened. For instance, the mass ratio of the 
components having a low boiling point is about 0.85. The superheated vapor 
which contains the rich low boiling point components is fed to the mixed 
medium turbine 17 through the pipe 16, to drive the same turbine by its 
expansion work. Here, the conditions of the vapor existing on the inlet 
side of the mixed medium turbine 17 are 190.degree. C. in temperature and 
10,000 kPa in pressure. Since the mixed medium turbine 17 is coupled 
coaxially with the high pressure steam turbine 3 and the power generator 
4, the rotational energy of the mixed medium turbine 17 can be transduced 
into electric energy by the power generator 4. 
The mixed medium exhausted from the mixed medium turbine 17 is fed to the 
medium condenser 19 through the exhaust pipe 18. Here, when being fed, the 
exhausted mixed medium is mixed with another mixed medium which contains 
low boiling point components of an extremely low concentration (e.g., 0.16 
in mass ratio) and which is fed through the pipe 34. Therefore, the mass 
ratio of the low boiling point components is reduced from about 0.85 
(before being mixed on the inlet side of the turbine 17) to about 0.3 
(after having been mixed). Here, the mixed medium to be mixed with the 
medium exhausted by the mixed medium turbine 17 is a mixed medium of 
liquid phase portion separated by distillation in the intermediate 
pressure separator 27. In more detail, the mixed medium of liquid phase 
portion is fed from the liquid phase portion of the intermediate pressure 
separator 27 to the triple heat exchanger 22 through the pipe 32, cooled 
by the second heat exchange element 33 of the triple heat exchanger 22, 
and then mixed with the medium exhausted by the mixed medium turbine 17. 
After having been mixed with the mixed medium which contains the low 
boiling point components of an extremely low concentration, the exhausted 
medium of the mixed medium turbine 17 is fed to the medium condenser 19, 
and thereby cooled and condensed into liquid by the salt water (of the 
normal temperature) flowing through the heat exchange element 20 of the 
medium condenser 19. Here, since the exhausted medium of the mixed medium 
turbine 17 is mixed with the mixed medium which contains the low boiling 
point components of an extremely low concentration and thereby since the 
mass ratio of the low boiling point components is reduced down to about 
0.3, the internal pressure of the medium condenser 19 is about 100 kPa; 
that is, can be maintained at roughly the atmospheric pressure. Further, 
since the vapor conditions on the inlet side of the mixed medium turbine 
17 are set to 190.degree. C. and 10,000 kPa, it is possible to obtain an 
extremely high heat drop in the mixed medium turbine 17. 
The mixed medium condensed to liquid by the medium condenser 19 is 
pressurized to about 1,000 kPa by the medium pump 23, and then introduced 
into the triple heat exchanger 22. Here, vapor and liquid of the high 
temperature mixed medium fed from the intermediate pressure separator 27 
through the pipes 28 and 32 are flowing through the first heat exchange 
element 29 and the second heat exchange element 33 of the triple heat 
exchanger 22, respectively. The flowing direction of these two streams is 
opposite to that of the mixed medium introduced into the triple heat 
exchanger 22 through the pipe 21. Therefore, the condensed mixed medium 
fed through the pipe 21 can be heated effectively by the heat exchange 
through the first and second heat exchange elements 29 and 33 of the 
triple heat exchanger 22. After having been changed to a two-phase stream, 
the heated mixed medium is fed to the heat exchanger 25 through the pipe 
24. Therefore, the mixed medium is further heated by a high temperature 
mixed medium of liquid phase portion fed from the high pressure separator 
15 and flowing through the heat exchange element 37 of the heat exchanger 
25, so that it is possible to increase the proportion of the vapor for 
forming the vapor phase in the two-phase stream. 
The mixed medium of two-phase stream heated by the heat exchanger 25 is fed 
to the intermediate pressure separator 27 through the pipe 26. Further, 
after having been decompressed by the pressure reduction valve 39, the 
mixed medium passed for heat exchange through the heat exchange element 37 
of the heat exchanger 25 is introduced into the intermediate pressure 
separator 27 through the pipe 38. Here, since the inside of the 
intermediate pressure separator 27 is kept at about 135.degree. C., the 
internal mixed medium is separated by distillation to liquid phase portion 
and vapor phase portion. The mass ratio of the low boiling point 
components in vapor for forming the vapor phase is about 0.37, and the 
mass ratio of the low boiling point components in liquid for forming the 
liquid phase portion is about 0.16. 
The vapor separated by distillation by the intermediate pressure separator 
27 is fed to the triple heat exchanger 22 through the pipe 28, and cooled 
and condensed by heat exchange down to about 40.degree. C. by the first 
heat exchange element 29. The mixed medium of liquid phase portion is 
pressurized up to 10,000 kPa by the high pressure pump 31, and then fed to 
the steam condenser 6 through the pipe 30. The mixed medium of liquid 
phase portion fed to the steam condenser 6 is heated up to about 
190.degree. C. by the steam exhausted by the high pressure turbine 3 and 
flowing through the heat exchange element 13 of the steam condenser 6. The 
heated mixed medium is boiled into a two-phase stream, and then circulated 
into the high pressure separator 15 through the pipe 14. 
As described above, in the first embodiment of the power plant according to 
the present invention, electricity can be generated on the basis of two 
systems comprising the steam system and the mixed medium system; the mixed 
medium which contains components having a boiling point lower than that of 
water is used; a two-stage separator composed of the high pressure 
separator 15 and the intermediate pressure separator 27 is installed; and 
the concentration (abundance ratio) of the low boiling point components in 
the mixed medium is changed before and after the mixed medium turbine 17. 
Therefore, since the vapor conditions on the inlet side of the mixed 
medium turbine 17 can be optimized so as to secure a sufficient back 
pressure, the driving force of the mixed medium turbine 17 driven by the 
vapor of the mixed medium can be increased, so that it is possible to 
improve the thermal efficiency markedly in comparison with the ordinary 
Rankin cycle. In particular, since the two-state separators 15 and 27 for 
high pressure and intermediate pressure, respectively are both installed, 
it is possible to increase a difference in concentration of the low 
boiling point components between before and after the mixed medium turbine 
17. As a result, in the case where the vapor temperature on the inlet side 
of the mixed medium turbine 17 is set to 190.degree. C. and further the 
ordinary salt water is used as the cooling medium flowing through the heat 
exchange element 20 of the medium condenser 19, it is possible to increase 
the thermal efficiency of only the mixed medium system up to about 34%. 
This thermal efficiency is extremely high in comparison with that obtained 
by the conventional power plant in which the temperature of the turbine is 
set to about 190.degree. C. on the inlet side thereof. Further, as the 
whole power plant including the steam system, it is possible to attain as 
high a thermal efficiency as about 41%. Therefore, when the first 
embodiment is applied to the conventional BWR having a thermal efficiency 
of about 33%, it is possible to attain power generation of 1,350,000 kW 
class in the power plant of 1,100,000 kW class. 
Further, in the first embodiment, since the back pressure of the mixed 
medium turbine 17 can be set to or near the atmospheric pressure, the 
number of expansion stages of the mixed medium turbine 17 can be reduced 
and thereby the mixed medium turbine can be small-sized. In addition, 
since the countermeasures of the medium condenser 19 against a high vacuum 
are not required, it is possible to reduce the manufacturing cost thereof. 
Further, since being different from the conventional BWR low pressure 
steam turbine, it is unnecessary to form moisture-removing grooves on the 
back blades, to provide a structure for removing moisture effectively from 
the turbine casing, or to install moisture removing pipes formed of a 
costly chromium steel, with the result that the manufacturing cost can be 
further reduced. 
Further, since the inner pressure of the steam condenser 6 can be set to or 
near the atmospheric pressure in the same way as with the case of the 
medium condenser 19, the countermeasures of the steam condenser 6 against 
a high vacuum are not required, so that it is possible to reduce the 
manufacturing cost thereof markedly. 
Further, since electric power is generated by the steam system using light 
water as the coolant of the nuclear reactor 1 in the same way as is 
conventional and in addition by the mixed medium system (separated from 
the steam system) using the mixed medium, it is possible to avert such a 
problem that harmful substances (corrosive substances) are produced due to 
the radiolyses of the mixed medium. 
Further, although the first embodiment applied to the power plant using the 
nuclear reactor 1 as a heat source has been described above by way of 
example, without being limited only thereto, it is of course possible to 
apply the first embodiment of the present invention to various power 
plants which use thermal energy, geothermal energy, waste heat recovery 
energy, etc. as the heat source. 
(Second embodiment) 
A second embodiment of the power plant according to the present invention 
will be described hereinbelow with reference to FIG. 2, in which the same 
reference numerals have been retained for similar elements having the same 
functions as with the case of the first embodiment shown in FIG. 1, 
without repeating the similar description thereof. 
In this second embodiment, as shown in FIG. 2, a separating system 40 is 
additionally installed. The added separating system 30 is provided with a 
first heat exchanger (a third medium condensing means) 41. The inlet end 
of the first heat exchanger 41 is connected to the outlet end of the first 
heat exchange element 29 of the triple heat exchanger 22 through a pipe 
42. Further, an intermediate high pressure pump 43 is provided midway of 
the pipe 42. This intermediate high pressure pump 43 has an intermediate 
discharge pressure between those of the intermediate pressure pump 23 and 
the high pressure pump 31. 
Further, the outlet side of the first heat exchanger 41 is connected to the 
inlet side of a second heat exchanger 45 through a pipe 44, and the outlet 
side of the second heat exchanger 45 is connected to an intermediate high 
pressure separator (intermediate high pressure separating means) 47 
through a pipe 46. The lower portion of the intermediate high pressure 
separator 47 is connected to the inlet end of the heat exchanger element 
37 of the heat exchanger 25 through a pipe 48. On the other hand, the 
upper portion of the intermediate high pressure separator 47 is connected 
to an inlet end of a heat exchange element (a second condensed liquid 
heating means) 50. Further, an outlet end of the heat exchange element 50 
of the first heat exchanger 41 is connected to an inlet end of an 
intra-condenser heat exchange element 13 of the steam condenser 6 through 
a pipe 51. Further, a high pressure pump 31 is provided midway of a pipe 
51. 
Further, a heat exchange element 52 is provided within the second heat 
exchanger 45. An inlet end of the heat exchange element 52 is connected to 
the lower portion of the high pressure separator 15 through a pipe 53. On 
the other hand, an outlet end of the heat exchange element 52 is connected 
to the intermediate high pressure separator 47 through a pipe 54. Further, 
a pressure reduction valve (second separated liquid feeding means) 55 is 
provided midway of a pipe 54. 
The operation of the second embodiment will be described hereinbelow, 
without repeating the similar operation as with the case of the first 
embodiment. 
The mixed medium vapor fed from the vapor phase portion of the intermediate 
pressure separator 27 is fed to the triple heat exchanger 22 through the 
pipe 28, and cooled and condensed into liquid by heat exchange when 
flowing through the heat exchange element 29 of the triple heat exchanger 
22. The mixed medium of liquid phase portion is pressurized by the 
intermediate high pressure pump 43, introduced into the first heat 
exchanger 41 through the pipe 42, heated by the high temperature vapor of 
mixed medium fed from the intermediate high pressure separator 47 and 
flowing through the heat exchange element 50, and then introduced into the 
second heat exchanger 45 through the pipe 44 as a two-phase stream. The 
mixed medium flowing through the second heat exchanger 45 is further 
heated by the high temperature liquid portion of the mixed medium fed from 
the high pressure separator 15 and flowing through the heat exchange 
element 52, so that the proportion of vapor for forming the vapor phase 
portion of the two-phase stream can be increased. 
The mixed medium of the two-phase stream heated by the second heat 
exchanger 45 is introduced into the intermediate high pressure separator 
47 through the pipe 46. Further, the mixed medium flowing through the heat 
exchange element 52 of the second heat exchanger 45 is passed through the 
pipe 54, depressurized by a pressure reduction valve 55, and then 
introduced into the intermediate high pressure separator 47. The mixed 
medium introduced into the intermediate high pressure separator 47 is 
separated by distillation into the vapor phase portion and the liquid 
phase portion. The vapor for forming the vapor phase portion is fed to the 
first heat exchanger 41 through the pipe 49, and cooled and condensed into 
liquid by the heat exchange element 50. The liquefied mixed medium is 
pressurized by the high pressure pump 31 beyond 10,000 kPa, and then fed 
to the steam condenser 6 through the pipe 51. 
As described above, in the second embodiment, since the separating system 
40 is installed in addition to the construction of the first embodiment, 
it is possible to secure the thermal drop of the mixed medium turbine 17 
more reliably in comparison with the first embodiment. Therefore, the 
mixed medium whose condensation and boiling curves are closed to each 
other can be used more easily as the mixed medium for driving the mixed 
medium turbine 17, so that the thermal efficiency of the power plant can 
be further improved. As the practical example of the mixed medium, there 
are a mixture composed of two or more organic compounds which contain 
alcohol or ketone, a mixture composed of two or more flon-based 
substances, a mixture composed of water and two or more hydrophilic 
organic compounds (alcohol, etc.), a mixture composed of two or more 
organic compounds which contain alcohol or ketone and flon-based 
substances, etc. 
(Third embodiment) 
A third embodiment of the power plant according to the present invention 
will be described hereinbelow with reference to FIG. 3, in which the same 
reference numerals have been retained for similar elements having the same 
functions as with the case of the first and second embodiments shown in 
FIGS. 1 and 2, without repeating the similar description thereof. 
In this third embodiment, as shown in FIG. 3, means for treating 
non-condensable gas (e.g., hydrogen gas or oxygen gas) produced by the 
radiolyses due to the radiations from the nuclear reactor is installed in 
addition to the first and second embodiments. 
In FIG. 3, a non-condensable gas treating system (noncondensable gas 
treating means) 60 added to the configuration of the first or second 
embodiments is shown. The non-condensable gas treating system 60 is 
provided with a heat exchanger 61 connected to the steam condenser 6 
through a pipe 62. One end of the pipe 62 is connected to the steam 
condenser 6 at such a position a little above the liquid surface level of 
the condensed water accumulated at the bottom portion of the steam 
condenser 6. Further, the internal pressure of the steam condenser 6 is 
maintained near or above the atmospheric pressure, as already explained. 
A heat exchange element 63 is provided within the heat exchanger 61. An 
inlet end of this heat exchange element 63 is connected to the other end 
of the pipe 62. On the other hand, an outlet end of the heat exchange 
element 63 is connected to an inlet side of a small-sized steam condenser 
65 through a pipe 64. The inside of this small-sized steam condenser 65 is 
kept at a high vacuum. An outlet side of the small-sized steam condenser 
65 is connected to the heat exchanger 61 through a pipe 66, and a 
small-sized condensed water pump 67 is provided midway of the pipe 66. 
Further, an extracted steam degassing system 69 is connected to the 
small-sized steam condenser 65 through a pipe 68. The extracted steam 
degassing system 69 is provided with an ejector (not shown), a recombiner 
(not shown) for recombining radiolysis product gas, etc. Further, the heat 
exchanger 61 is connected to a water supply pump 9 and the steam condenser 
6 through a pipe 70, and the water supply pump 9 is connected to a high 
pressure feed-water heater 8 through a pipe 7. 
The operation of the third embodiment will be described hereinbelow, 
without repeating the similar function as with the case of the first and 
second embodiments. 
First, steam of less than about one % is taken out of the steam which 
contains non-condensable gas from above the liquid surface of the 
condensed water accumulated at the bottom portion of the steam condenser 
6, and then fed into the heat exchanger 61 through the pipe 62. When being 
passed through the heat exchanger 63, the steam fed to the heat exchanger 
61 through the pipe 62 is cooled by the condensed water fed from the 
small-sized steam condenser 65 through the pipe 66 and introduced into the 
heat exchanger 61. The cooled steam is introduced into the small-sized 
steam condenser 65 through the pipe 64, and then condensed into water 
under a high vacuum. On the other hand, the non-condensable gas contained 
in the steam is extracted from the small-sized steam condenser 65 through 
the pipe 68, and then treated by the extracted steam degassing system 69. 
The condensed water formed by the small-sized steam condenser 65 is 
pressurized by the small-sized condensed water pump 67, and then fed to 
the heat exchanger 61 through the pipe 66. The condensed water fed to the 
heat exchanger 61 is heated by the heat exchange element 63, and then fed 
to a suction side of the water supply pump 9 through the pipe 70. 
As described above, in the third embodiment, since the non-condensable gas 
produced by the radiolyses due to the radiations from the nuclear reactor 
can be treated by the non-condensable gas treating system considerably 
smaller than the conventional treating system installed in a nuclear power 
plant, it is possible to reduce the manufacturing cost thereof markedly. 
(Fourth embodiment) 
A fourth embodiment of the power plant according to the present invention 
will be described hereinbelow with reference to FIG. 4, in which the same 
reference numerals have been retained for similar elements having the same 
functions as with the case of the first to third embodiments shown in 
FIGS. 1 to 3, without repeating the similar description thereof. 
In this fourth embodiment, as shown in FIG. 4, a steam system for 
generating electric power by use of steam and a mixed medium system for 
generating electric power by use of a mixed medium are both provided. 
First, the steam system of the power plant will be described. 
In FIG. 4, the power plant is provided with a nuclear reactor 1 for heating 
a coolant of light water to generate steam. The outlet side of the nuclear 
reactor 1 is connected to an inlet side of the high pressure steam turbine 
3 through the main steam pipe 2. The high pressure steam turbine 3 is 
coupled coaxially with the electric power generator 4. The outlet side of 
the high pressure turbine 3 is connected to the inlet side of the steam 
condenser 81 through the exhausted steam pipe 5. The outlet side of the 
steam condenser 81 is connected to the inlet side of the high pressure 
feed-water heater 8 through the condenser pipe 7. Further, the 
turbine-driven or motor-driven type water supply pump 9 is provided midway 
of the condenser pipe 7. The outlet side of the high pressure feed-water 
heater 8 is connected to the inlet side of the nuclear reactor through the 
reactor feed-water pipe 10. Further, to the feed-water heater 8, the high 
pressure turbine extracted steam pipe 11 for feeding steam extracted from 
the high pressure steam turbine 3, and the drain pipe 12 for feeding 
drained water to the steam condenser 81 are both connected, respectively. 
Further, a valve 82 is provided midway of the drain pipe 12. 
Successively, the mixed medium system of the power plant will be described. 
In FIG. 4, an intra-condenser heat exchange element (heat exchanging means) 
83 is provided within the steam condenser 81. The mixed medium is flowing 
through at least a part of the intra-condenser heat exchange element 83. 
Here, the mixed medium flowing through the intra-condenser heat exchange 
element 83 contains two or more components, and at least one component of 
these components for constituting the mixed medium is a substance having a 
boiling point lower than that of water. As an example of the mixed medium, 
there is a mixture of water and ammonia. 
The outlet side of the intra-condenser heat exchange element 83 of the 
steam condenser 81 is connected to a separator (separating means) 85 
through a pipe 84, and the separator 85 is connected to the inlet side of 
a heat exchanger 87 through a pipe 86. Within the heat exchanger 87, a 
first heat exchange element 88 and a second heat exchange element 89 are 
provided. An inlet end of the first heat exchange element 88 is connected 
to a midway portion of the main steam pipe 2 through a main extracted 
steam pipe 90, and an inlet end of the second heat exchange element 89 is 
connected to the high pressure steam turbine 3 through an extracted steam 
pipe 91. Further, two outlet ends of the first and second heat exchange 
elements 88 and 89 are connected to the steam condenser 81 through two 
pipes 92 and 93, respectively. 
An outlet side of the heat exchanger 87 is connected to an inlet side of a 
mixed medium turbine 95 through a pipe 94. The mixed medium turbine 95 is 
coupled coaxially with a high pressure steam turbine 3 and the electric 
power generator 4. The outlet side of the mixed medium turbine 95 is 
connected to an inlet side of a mixer (mixing means) 97 through an 
exhausted steam pipe 96. An outlet side of the mixer 97 is connected to an 
inlet side of a medium condenser (medium condensing means) 99 through a 
pipe 98. A heat exchange element (not shown) is provided within the medium 
condenser 99, and salt water is flowing through the inside of the heat 
exchange element. An outlet side of the medium condenser 99 is connected 
to an inlet side of a heat exchanger 101, and a liquid supply pump 
(condensed liquid feeding means) 102 is provided midway of a pipe 100. An 
outlet side of the heat exchanger 101 is connected to the inlet end of the 
intra-condenser heat exchange element 83 of the steam condenser 81 through 
a pipe 103. Further, a heat exchange element 104 is provided within the 
heat exchanger 101. An outlet end of the heat exchange element 104 is 
connected to the mixer 97 through a pipe 105. A pressure reduction valve 
(mixing means) 106 is provided midway of the pipe 105. Further, the 
pressure reduction valve 106 can be replaced with an orifice. An inlet end 
of the heat exchange element 104 is connected to the lower portion of the 
separator 85 through a pipe 107. 
The operation of the fourth embodiment constructed as described above will 
be described hereinbelow. 
The coolant of light water is heated by the nuclear reactor 1 into 
saturated steam, and then fed to the high pressure steam turbine 3 through 
the main steam pipe 2. The steam fed to the high pressure steam turbine 3 
drives the high pressure steam turbine 3, so that the rotational energy of 
the steam turbine 3 can be transduced into electric energy by the power 
generator 4. The steam exhausted from the high pressure steam turbine 3 is 
fed to the steam condenser 81 through the exhaust pipe 5, and then cooled 
and condensed by the mixed medium flowing through the intra-condenser heat 
exchange element 83. Here, the internal pressure of the steam condenser 81 
is determined to a pressure near or beyond the atmospheric pressure. The 
condensed water formed by the steam condenser 81 is pressurized by the 
water supply pump 9, and then fed to the high pressure feed-water heater 8 
through the condenser pipe 7. The condensed water fed to the high pressure 
feed-water heater 8 is heated by the steam fed through the high pressure 
turbine extracted steam pipe 11, and then recirculated into the nuclear 
reactor 1 through the reactor feed-water pipe 10, after having been heated 
to an appropriate subcooled temperature. 
On the other hand, the mixed medium flowing through the intra-condenser 
heat exchange element 83 of the steam condenser 81 is heated by the steam 
flowing from the high pressure steam turbine 3 to the steam condenser 81 
through the exhaust pipe 5, by the extracted main steam flowing into the 
steam condenser 81 through the pipe 92, and by the steam extracted from 
the high pressure steam turbine 3 and fed into the steam condenser 81 
through the pipe 93. After having been boiled into a two-phase stream, the 
mixed medium heated by the steam condenser 81 is fed to the separator 85 
through the pipe 84. 
The mixed medium fed to the separator 85 is separated by distillation using 
gravity into a liquid phase portion (formed of liquid) and a vapor phase 
portion (formed of vapor). In the vapor of the mixed medium (which forms 
the vapor phase portion), the concentration (abundance ratio) of the low 
boiling point component is heightened. The vapor which contains a large 
quantity of low boiling point components is fed to the heat exchanger 87 
through the pipe 86. The vapor of the mixed medium fed to the heat 
exchanger 87 is heated to superheated vapor by the main steam extracted 
from the nuclear reactor 1 and flowing through the first heat exchange 
element 88 and by the steam extracted from the high pressure steam turbine 
3 and flowing through the second heat exchange element 89 of the heat 
exchanger 87. The superheated vapor of the mixed medium is fed to the 
mixed medium turbine 95 through the pipe 94, to drive the turbine by its 
expansion work. Here, since the mixed medium turbine 95 is coupled 
coaxially with the high pressure steam turbine 3 and the power generator 
4, the rotational energy of the mixed medium turbine 95 can be transduced 
into electric energy by the power generator 4. 
The mixed medium exhausted by the mixed medium turbine 95 is fed to the 
mixer 97 through the exhaust pipe 96, and then mixed with the mixed medium 
fed from the liquid phase portion of the separator 85 and flowing into the 
mixer 97 through the pipe 105. Here, before being mixed, the mixed medium 
fed from the separator 85 is cooled by the mixed medium condensed by the 
medium condenser 99 when flowing through the heat exchange element 104 of 
the heat exchanger 101. Further, since the separator 85 is maintained at a 
pressure higher than that of the mixer 97, the mixed medium fed from the 
separator 85 is depressurized by the pressure reduction valve 106 before 
being mixed. Further, in order to increase the mixing efficiency, the 
mixed medium of liquid phase portion fed from the separator 85 is jetted 
into the mixer 97. 
As described above, although the vapor extracted from the mixed medium 
turbine 95 is mixed with the mixed medium fed from the liquid phase 
portion of the separator 85, since the concentration (abundance ratio) of 
the low boiling point components of the mixed medium forming the liquid 
phase portion of the separator 85 is low, after having been mixed, the 
concentration of the low boiling point components of the mixed medium can 
be reduced. Further, the vapor extracted from the mixed medium turbine 95 
and the mixed medium of liquid phase fed from the separator 85 are mixed 
by the mixer 97 into a two-phase stream. The mixed medium of two-phase 
stream is fed to the medium condenser 99. Here, a heat exchange element 
(not shown) is provided within the medium condenser 99, and further salt 
water of the normal temperature is flowing through the heat exchange 
element. Therefore, the mixed medium of two-phase stream fed to the medium 
condenser 99 is cooled and condensed into liquid by the salt water flowing 
through the heat exchange element. Here, since the concentration of the 
low boiling point components of the mixed medium of two-phase stream 
introduced into the medium condenser 99 is previously lowered, when cooled 
by the salt water of the normal temperature, it is possible to maintain 
the internal pressure of the medium condenser 99 at about the atmospheric 
pressure. As described above, since the mixed medium turbine 95 is driven 
by the mixed medium having a high concentration of the low boiling point 
components and since the vapor extracted from the mixed medium turbine 95 
is condensed after the concentration of the low boiling point components 
thereof has been reduced, it is possible to increase the pressure on the 
inlet side and to decrease the back pressure on the outlet side of the 
mixed medium turbine 95, so that the thermal drop of the mixed medium 
turbine 95 can be increased. 
The mixed medium condensed into liquid by the medium condenser 99 is 
pressurized to a high pressure by the liquid supply pump 102, and then fed 
to the heat exchanger 101 through the pipe 100. The mixed medium 
(condensed liquid) introduced into the heat exchanger 101 is heated by the 
heat exchange element 104 of the heat exchanger 101, and then fed to the 
steam condenser 81 through the pipe 103. The mixed medium fed to the steam 
condenser 81 is further heated and boiled by the steam extracted from the 
high pressure steam turbine 3 flowing through the intra-condenser heat 
exchange element 83, into a two-phase stream. The boiled two-phase stream 
is recirculated into the separator 85 through the pipe 84. 
As described above, in the fourth embodiment of the power plant according 
to the present invention, electricity can be generated on the basis of two 
systems of the steam system and the mixed medium system; the mixed medium 
which contains components having a boiling point lower than that of water 
is used; and the concentration (abundance ratio) of the low boiling point 
components in the mixed medium is changed by use of the separator 85 
before and after the mixed medium turbine 95. Therefore, since the vapor 
conditions on the inlet side of the mixed medium turbine 95 can be 
optimized so as to secure a sufficient back pressure, the driving force of 
the mixed medium turbine 95 driven by the mixed medium stream can be 
increased, with the result that it is possible to improve the thermal 
efficiency of the turbine 95 markedly, in comparison with the ordinary 
Rankin cycle. For instance, when the fourth embodiment is applied to the 
conventional BWR, it is possible to improve the thermal efficiency by 
about 1 to 2%. 
Further, in the fourth embodiment, since the back pressure of the mixed 
medium turbine 95 can be set to or near the atmospheric pressure, the 
number of expansion stages of the mixed medium turbine 95 can be reduced 
and thereby the turbine can be small-sized. In addition, since the 
countermeasures of the medium condenser 99 against a high vacuum are not 
required, it is possible to reduce the manufacturing cost thereof. 
Further, being different from the conventional BWR low pressure steam 
turbine, it is unnecessary to form moisture-removing grooves on the back 
blades, to provide a structure for removing moisture effectively from the 
turbine casing, or to install moisture removing pipes formed of a costly 
chromium steel, with the result that the manufacturing cost can be further 
reduced. 
Further, since the inner pressure of the steam condenser 81 can be set to 
or near the atmospheric pressure, in the same way as with the case of the 
medium condenser 99, the countermeasures of the steam condenser 81 against 
a high vacuum are not required, so that it is possible to reduce the 
manufacturing cost thereof markedly. 
Further, since electric power is generated by the steam system by using 
light water as the coolant of the nuclear reactor 1 in the same way as is 
conventional, and by the mixed medium system (separated from the steam 
system) by using the mixed medium, it is possible to avert such a problem 
that harmful substances (corrosive substances) are produced due to the 
radiolyses of the mixed medium. 
Further, although the fourth embodiment applied to the power plant using 
the nuclear reactor 1 as a heat source has been described by way of 
example, without being limited only thereto, it is of course possible to 
apply the embodiment of the present invention to various power plants 
which use thermal energy, geothermal energy, waste heat recovery energy, 
etc. as the heat source. 
(Fifth embodiment) 
A fifth embodiment of the power plant according to the present invention 
will be described hereinbelow with reference to FIG. 5, in which the same 
reference numerals have been retained for similar elements having the same 
functions as with the case of the first to fourth embodiments shown in 
FIGS. 1 to 4, without repeating the similar description thereof. 
In this fifth embodiment, as shown in FIG. 5, in addition to the high 
pressure steam turbine, a low pressure steam turbine is provided. Further, 
the mixed medium is heated by steam exhausted from the low pressure steam 
turbine. 
In FIG. 5, the power plant is provided with the nuclear reactor 1 as a heat 
source. A coolant of light water is heated by the nuclear reactor 1 to 
generate steam. The generated steam is fed to the high pressure turbine 3 
through the main steam pipe 2, to drive the high pressure steam turbine 3. 
On the downstream side of the high pressure steam turbine 3, a moisture 
separator and reheater 111 is installed. The moisture separator and 
reheater 111 is connected to a heated steam pipe 112 branched from the 
main steam pipe 2 and to an exhausted steam pipe 113 extending from the 
high pressure steam turbine 3. The steam exhausted from the high pressure 
steam turbine 3 is fed to the moisture separator and reheater 111, 
separated into vapor and liquid, and further heated by high temperature 
steam which is fed to the moisture separator and reheater 111 through both 
the heated steam pipe 112 and the extracted steam pipe 113. The 
superheated steam heated by the moisture separator and reheater 111 is fed 
to a low pressure steam turbine 115 through a pipe 114, to drive the low 
pressure steam turbine 115. Here, the low pressure steam turbine 115 is 
constructed at a relatively high pressure stage in such a way that the 
temperature of the exhausted steam becomes 100.degree. C. or higher. The 
high pressure steam turbine 2 and the low pressure steam turbine 115 are 
coupled coaxially with each other and also coupled coaxially with the 
electric power generator 4. 
The outlet side of the high pressure steam turbine 115 is connected to the 
inlet side of the steam condenser 81 through an exhaust pipe 116. The 
outlet side of the steam condenser 81 is connected to a low pressure 
feed-water heater 118 through a condenser pipe 117. A turbine-driven or 
motor-driven condenser water pump 119 is provided midway of the condenser 
pipe 117. The outlet side of the low pressure feed-water heater 118 is 
connected to one of the two high pressure feed-water heaters 8 through a 
pipe 120. A water supply pump 9 is provided midway of the pipe 120. The 
outlet side of the other of the two high pressure feed-water heaters 8 is 
connected to the inlet side of the nuclear reactor through a reactor 
feed-water pipe 10. Further, to the two high pressure feed-water heaters 
8, both the high pressure turbine extracted steam pipe 11 for feeding 
steam extracted from the high pressure steam turbine 3 and a drain pipe 
112 for feeding drain water to the low pressure feed-water heater 118 are 
connected, respectively. Further, to the low pressure feed-water heater 
118, a drain pipe 122 for feeding drain water to the steam condenser 81 is 
connected. 
Further, the intra-condenser heat exchange element 83 is provided within 
the steam condenser 81, and the mixed medium is flowing at least a part of 
the intra-condenser heat exchange element 83. Here, the mixed medium 
flowing through the intra-condenser heat exchange element 83 is a mixed 
medium which contains two or more components, and at least one component 
of a plurality of components for constituting the mixed medium is a 
substance having a boiling point lower than that of water. As the 
practical example of the mixed medium, there are a mixture composed of 
water and ammonia; a mixture composed of two or more organic compounds 
which contain hydrocarbon, alcohol or ketone; a mixture composed of two or 
more flon-based substances; a mixture composed of water and two or more 
hydrophilic organic compounds (alcohol, etc.); a mixture composed of two 
or more organic compounds which contain hydrocarbon, alcohol or ketone and 
flon-based substances, etc. 
The outlet side of the intra-condenser heat exchange element 83 provided 
within the steam condenser 81 is connected to the separator 85 through the 
pipe 84, and the separator 85 is connected to the inlet side of the heat 
exchanger 87 through the pipe 86. Within the heat exchanger 87, a first 
heat exchange element 88 and a second heat exchange element 89 are 
provided. The inlet end of the first heat exchange element 88 is connected 
to a midway portion of the pipe 114 through a superheated steam extracting 
pipe 123, and the second heat exchange element 89 is connected to the low 
pressure steam turbine 115 through an extracted steam pipe 91. Further, 
the outlet ends of both the first and second heat exchange elements 88 and 
89 are connected to the steam condenser 81 through two pipes 92 and 93, 
respectively. 
The outlet side of the heat exchanger 87 is connected to the inlet side of 
the mixed medium turbine 95 through the pipe 94. The mixed medium turbine 
95 is coupled coaxially with the high pressure steam turbine 3, the low 
pressure steam turbine 115, and further the electric power generator 4. 
The outlet side of the mixed medium turbine 95 is connected to the inlet 
side of the mixer 97 through the exhaust pipe 96, and the outlet side of 
the mixer 97 is connected to the inlet side of the medium condenser 99 
through the pipe 98. A heat exchange element (not shown) is provided 
within the medium condenser 99, and salt water is flowing through the heat 
exchange element. The outlet side of the medium condenser 99 is connected 
to the inlet side of the heat exchanger 101 through a pipe 100, and a 
liquid supply pump 102 is provided midway of the pipe 100. The outlet side 
of the heat exchanger 101 is connected to the inlet end of the 
intra-condenser heat exchange element 83 of the steam condenser 81 through 
a pipe 103. Further, a heat exchange element 104 is provided within the 
heat exchanger 101, and the outlet end of the heat exchange element 104 is 
connected to the mixer 97 through a pipe 105. A pressure reduction valve 
106 is provided midway of the pipe 105. The inlet end of the heat exchange 
element 104 is connected to the lower portion of the separator 85 through 
a pipe 107. 
The operation of the fifth embodiment constructed as described above will 
be described hereinbelow. 
The coolant of light water is heated by the nuclear reactor 1 into 
saturated steam, and then fed to the high pressure steam turbine 3 through 
the main steam pipe 2. The steam fed to the high pressure steam turbine 3 
drives the high pressure steam turbine 3, so that the rotational energy of 
the turbine is transduced into electric energy by the power generator 4. 
The steam exhausted from the high pressure steam turbine 3 is heated by 
the moisture separator and reheater 111 into superheated steam, and then 
fed to the low pressure steam turbine 115 through the pipe 114. The steam 
fed to the low pressure steam turbine 115 drives the low pressure steam 
turbine 115, so that the rotational energy of the turbine is transduced 
into electric energy by the power generator 4. 
The temperature of the steam exhausted from the low pressure steam turbine 
115 is 100.degree. C. or higher. The exhausted steam is fed to the steam 
condenser 81 through the pipe 116, and cooled and condensed by the mixed 
medium flowing through the intra-condenser heat exchange element 83. Here, 
the internal pressure of the steam condenser 81 can be set to a pressure 
near or beyond the atmospheric pressure. The condensed water formed by the 
steam condenser 81 is fed to the low pressure feed-water heater 118 by the 
condenser pump 119 and heated, and further pressurized by the water supply 
pump 9, and then fed to the high pressure feed-water heaters 8 through the 
pipe 120. The condensed water fed to the high pressure feed-water heaters 
8 is heated by the steam fed through the high pressure turbine exhausted 
steam pipe 11 and the other pipes extending from the moisture separating 
reheater 111, and then recirculated into the nuclear reactor 1 through the 
reactor feed-water pipe 10, after having been heated to an appropriate 
subcooled temperature. 
On the other hand, the mixed medium flowing through the intra-condenser 
heat exchange element 83 of the steam condenser 81 is heated by the steam 
exhausted from the low pressure steam turbine 115 and fed to the steam 
condenser 81 through the exhaust pipe 116, the extracted superheated steam 
fed into the steam condenser 81 through the pipe 92, the steam extracted 
from the low pressure steam turbine 115 and fed into the steam condenser 
81 through the pipe 93, and water drained from the low pressure feed-water 
heater 118 and fed into the steam condenser 81 through the drain pipe 122. 
After having been boiled into a two-phase stream, the mixed medium heated 
by the steam condenser 81 is fed to the separator 85 through the pipe 84. 
The mixed medium fed to the separator 85 is separated by distillation using 
gravity into a liquid phase portion (formed of liquid) and a vapor phase 
portion (formed of vapor). In the vapor of the mixed medium (which forms 
the vapor phase portion), the concentration (abundance ratio) of the low 
boiling point component thereof is heightened. The vapor which contains 
much low boiling point components is fed to the heat exchanger 87 through 
the pipe 86. The vapor of the mixed medium fed to the heat exchanger 87 is 
heated to superheated vapor by the superheated steam flowing through the 
second heat exchange element 89 and by the steam extracted from the low 
pressure steam turbine 115 and flowing through the first heat exchange 
element 88 of the heat exchanger 87. The superheated vapor of the mixed 
medium is fed to the mixed medium turbine 95 through the pipe 94, to drive 
the turbine by its expansion work. Here, since the mixed medium turbine 95 
is coupled coaxially with the high pressure steam turbine 3, the low 
pressure steam turbine 115, and further the power generator 4, the 
rotational energy of the mixed medium turbine 95 can be transduced into 
electric energy by the power generator 4. 
The mixed medium exhausted from the mixed medium turbine 95 is fed to the 
mixer 97 through the exhaust pipe 96, and then mixed with the mixed medium 
fed from the liquid phase portion of the separator 85 and introduced into 
the mixer 97 through the pipe 105. Here, before being mixed, the mixed 
medium fed from the separator 85 is cooled by the mixed medium condensed 
by the medium condenser 99 when flowing through the heat exchange element 
104 of the heat exchanger 101. Further, since the separator 85 is 
maintained at a pressure higher than that of the mixer 97, the mixed 
medium fed from the separator 85 is depressurized by the pressure 
reduction valve 106 before being mixed. Further, in order to increase the 
mixing efficiency, the mixed medium of liquid phase fed from the separator 
85 is jetted into the mixer 97. 
As described above, although the vapor extracted from the mixed medium 
turbine 95 is mixed with the mixed medium fed from the liquid phase 
portion of the separator 85, since the concentration (abundance ratio) of 
the low boiling point components is low in the mixed medium for forming 
the liquid phase portion of the separator 85, after having been mixed, the 
concentration of the low boiling point components is reduced. Further, the 
vapor extracted from the mixed medium turbine 95 and the mixed medium of 
liquid phase fed from the separator 85 are mixed by the mixer 97 into a 
two-phase stream. The mixed medium of two-phase stream is fed to the 
medium condenser 99 through the pipe 98. Here, a heat exchange element 
(not shown) is provided within the medium condenser 99, and further salt 
water of the normal temperature is flowing through the heat exchange 
element. Therefore, the mixed medium of two-phase stream fed to the medium 
condenser 99 is cooled and condensed into liquid by the salt water flowing 
through the heat exchange element. Here, since the concentration of the 
low boiling point components of the mixed medium of two-phase stream 
introduced into the medium condenser 99 is previously lowered by the mixer 
97, when cooled by the salt water of the normal temperature, it is 
possible to set the internal pressure of the medium condenser 99 to about 
the atmospheric pressure. As described above, since the mixed medium 
turbine 95 is driven by the mixed medium having a high concentration of 
the low boiling point components and since the vapor extracted from the 
mixed medium turbine 95 is condensed after the concentration of the low 
boiling point components thereof has been reduced, it is possible to 
increase the pressure on the inlet side and to decrease the back pressure 
on the outlet side of the mixed medium turbine 95, so that the thermal 
drop of the mixed medium turbine 95 can be increased. 
The mixed medium condensed into liquid by the medium condenser 99 is 
pressurized to a high pressure by the liquid supply pump 102, and then fed 
to the heat exchanger 101 through the pipe 100. The mixed medium 
(condensed liquid) introduced into the heat exchanger 101 is heated by the 
heat exchange element 104 of the heat exchanger 101, and then fed to the 
steam condenser 81 through the pipe 103. The mixed medium fed to the steam 
condenser 81 is further heated and boiled into a two-phase stream by the 
steam extracted from the high pressure steam turbine 3 and flowing through 
the intra-condenser heat exchange element 83. The boiled two-phase stream 
is recirculated into the separator 85 through the pipe 84. 
As described above, in the fifth embodiment of the power plant according to 
the present invention, electricity can be generated by use of three 
systems of the high pressure steam system, the low pressure steam system, 
and the mixed medium system; the mixed medium which contains components 
having a boiling point lower than that of water is used; and the 
concentration (abundance ratio) of the low boiling point components of the 
mixed medium is changed by use of the separator 85 before and after the 
mixed medium turbine 95. Therefore, since the vapor conditions on the 
inlet side of the mixed medium turbine 95 can be optimized so as to secure 
a sufficient back pressure, the driving force of the mixed medium turbine 
95 driven by the mixed medium stream can be increased, so that it is 
possible to improve the thermal efficiency markedly in comparison with the 
ordinary Rankin cycle. 
Further, in the low pressure steam turbine 115, being different from the 
low pressure steam turbine of the conventional BWR, since the lower 
pressure stages are not used, the countermeasures against moisture are not 
required, so that the manufacturing cost can be reduced markedly. 
Further, in the fifth embodiment, since the back pressure of the mixed 
medium turbine 95 can be set to or near the atmospheric pressure, the 
number of expansion stages of the mixed medium turbine 95 can be reduced 
and thereby the turbine can be small-sized. In addition, since the 
countermeasures of the medium condenser 99 against a high vacuum are not 
required, it is possible to reduce the manufacturing cost thereof. 
Further, since the inner pressure of the steam condenser 81 can be set to 
or near the atmospheric pressure, in the same way as with the case of the 
medium condenser 99, the countermeasures of the steam condenser 81 against 
a high vacuum are not required, so that it is possible to reduce the 
manufacturing cost thereof markedly. 
Further, since electric power can be generated by the two steam systems of 
high and low pressures by using light water as the coolant of the nuclear 
reactor 1 in the same way as is conventional, and by the mixed medium 
system (separated from the steam system) by using the mixed medium, it is 
possible to avert such a problem that harmful substances (corrosive 
substances) are produced due to the radiolyses of the mixed medium. 
Further, although the fifth embodiment applied to the power plant which 
uses the nuclear reactor 1 as a heat source has been described by way of 
example, without being limited only thereto, it is of course possible to 
apply the fifth embodiment of the present invention to various power 
plants which use thermal energy, geothermal energy, waste heat recovery 
energy, etc. as the heat source. 
(Sixth embodiment) 
A sixth embodiment of the power plant according to the present invention 
will be described hereinbelow with reference to FIG. 6, in which the same 
reference numerals have been retained for similar elements having the same 
functions as with the case of the first to fifth embodiments shown in 
FIGS. 1 to 5, without repeating the similar description thereof. 
In this sixth embodiment, as shown in FIG. 6, the non-condensable gas 
treating system 60 (shown in FIG. 3) of the third embodiment is applied to 
the fourth and fifth embodiments. In more detail, 1% or less steam which 
contains non-condensable gas is extracted from above the liquid surface of 
the condensed water accumulated at the bottom portion of the steam 
condenser 81, and the extracted non-condensable gas is treated by the 
non-condensable gas treating system 60. 
In this sixth embodiment, in the same way as with the case of the third 
embodiment, since the non-condensable gas produced by the radiolyses due 
to the radiations from the nuclear reactor can be treated by a system 
considerably smaller than the conventional treating system installed in 
the nuclear power plant, it is possible to reduce the manufacturing cost 
markedly. 
As described above, in the power plant according to the present invention, 
since the steam system including the steam turbine and the mixed medium 
system including the mixed medium turbine are installed; since the mixed 
medium is heated by the steam exhausted from the steam turbine; and 
further since the concentration (abundance ratio) of the low boiling point 
components of the mixed medium is increased or decreased before and after 
the mixed medium turbine, it is possible to increase the thermal 
efficiency markedly, as compared with the conventional power plant.