Patent Publication Number: US-2007104306-A1

Title: Thermal efficiency diagnosing system for nuclear power plant, thermal efficiency diagnosing program for nuclear power plant, and thermal efficiency diagnosing method for nuclear power plant

Description:
TECHNICAL FIELD  
      The present invention relates to a nuclear power plant thermal efficiency diagnostic system, a nuclear power plant thermal efficiency diagnostic program and a nuclear power plant thermal efficiency diagnostic method, and more particularly, to a nuclear power plant thermal efficiency diagnostic system, a nuclear power plant thermal efficiency diagnostic program and a nuclear power plant thermal efficiency diagnostic method for making a diagnosis on a performance of each machinery in order to specify machinery which causes deterioration of a power output from a nuclear power plant.  
     BACKGROUND ART  
      How to improve thermal efficiency in a power-generating plant such as a nuclear power plant or a thermal power plant is increasingly importance from the viewpoint of saving fuel and reducing costs of power generation.  
      However, a general power-generating plant includes plural elements such as HP (high-pressure) turbine and LP (low-pressure) turbines. Thus, if the total thermal efficiency of the power-generating plant decreases, it is difficult to accurately calculate performance of the individual elements. It is accordingly difficult to specify and determine an element that causes a drop in the thermal efficiency in the power-generating plant.  
      To that end, conventionally, a thermal efficiency diagnostic apparatus  1  for a thermal power plant as shown in  FIG. 11  has been proposed (see, for example, Japanese Patent Application (Laid-Open) No. 2002-122005). The conventional thermal efficiency diagnostic apparatus  1  for a thermal power plant includes a computer  2  and sensors  3 . The sensors  3  measure parameters such as steam flow rates, flow rates of steams extracted from turbines and pressures of the elements such as the HP turbine and the LP turbine, and the computer  2  reads measured data.  
      The computer  2  has an A/D (analog to digital) converter  4 , a CPU (Central Processing Unit)  5 , and a memory  6  built-in, and includes an input device  7  and a monitor  6 . The CPU  5  reads a program stored in the memory  6 , and the CPU  5  reading program functions as a deteriorating element specifying means  9 .  
      The measurement data read into the computer  2  are converted into digital signals by the A/D converter  4 , and the deteriorating element specifying means  9  can specify element that deteriorates thermal efficiency based on the measurement data on each element, which has been converted into the digital signal.  
      The deteriorating element specifying means  9  conducts the optimal state using several probability distributions so that a deviation of the measurement data is minimized in the entire power-generating plant while a probability is maximized, and makes low-accuracy measurement data to be converged. As a result of convergent calculation of the measurement data executed by the deteriorating element specifying means  9 , an influence of an error in the low-accuracy measurement data can be reduced.  
      Further, the deteriorating element specifying means  9  calculates thermal efficiency of each element based on the measurement data. Then, the degree of contribution of each element to the power-generating plant in the total thermal efficiency of the power-generating plant is additionally determined. The deteriorating element specifying means  9  specifies element that deteriorates thermal efficiency based on the degree of contribution of each element and the performance of each element.  
      With the conventional thermal efficiency diagnostic apparatus  1  for a thermal power plant, when the thermal efficiency of the thermal power plant decreases, the performance of each element can be accurately calculated to specify which element causes the decrease in thermal efficiency of the thermal power plant.  
      On the other hand, the nuclear power plant is configured to introduce steam generated in a reactor into a turbine equipment to generate power. Further, the turbine equipment is configured such as the HP turbine and the LP turbine are connected to a same generator through a common power transmission shaft.  
      Further, the nuclear power plant has been conventionally obliged to be operated with a constant electric power (about 1100,000 kW). However, since 2002, the plant is allowed to be operated with a constant thermal power, that is, with the constant thermal quantity supplied from the reactor to the turbine equipment. Thus, electric power of the entire nuclear power plant can be improved by improving the performance of the turbine equipment. In practice, however, as a result of operation under the condition of a constant thermal output in nuclear power plants, electric output of each power plant is various output.  
      To improve the plant output, it is important that the performance of individual elements in the turbine equipment is diagnosed in the nuclear power plant as well to thereby specify dominant elements that cause a drop in the thermal efficiency of the nuclear power plant.  
      However, steam used as a power source of the HP turbine and the LP turbine of the nuclear power plant is in a wet state unlike steam used in the thermal power plant or other such plants. Hence, the dryness of steam is different between the outlets and inlets of the HP turbine and the LP turbine, so only measuring a temperature and pressure of the steam is insufficient for precisely calculating enthalpy of the steam. As a result, it is difficult to accurately calculate internal efficiencies of the HP turbine and the LP turbine of the nuclear power plant to grasp a turbine performance.  
      Further, unlike the thermal power plant, parts of drains and steams are extracted from the HP turbine and the LP turbine of the nuclear power plant and used for heat exchanges on heaters.  
      Therefore, it is difficult to apply the conventional thermal efficiency diagnostic apparatus  1  for a thermal power plant to the nuclear power plant whose system or element is different from the thermal power plant. As a result, a technique of diagnosing thermal efficiency of each element of the nuclear power plant to thereby specify which element causes a drop in an electric power has not been yet proposed.  
     SUMMARY OF THE INVENTION  
      The present invention has been made to solve such conventional problems, and it is an object of the present invention to provide a nuclear power plant thermal efficiency diagnostic system, a nuclear power plant thermal efficiency diagnostic program and a nuclear power plant thermal efficiency diagnostic method which can specify thermal elements causing deterioration of a power output by conducting a diagnosis on a thermal efficiency of a nuclear power plant.  
      The present invention provides a nuclear power plant thermal efficiency diagnostic system comprising: a feed-and-condensate-water-flow-rate-setting-means for setting a flow rate of at least one of feedwater and condensate water in a nuclear power plant tentatively; a heat-exchange-on-heater-calculating-means for calculating heat exchange quantities of the feedwater and the condensate water on a heater arranged on a condensate and feedwater pipe of the nuclear power plant in accordance with the flow rate of at least the one of the feedwater and the condensate water, the flow rate being set by the feed-and-condensate-water-flow-rate-setting-means tentatively; a HP-turbine-power-calculating-means for acquiring a calculated power value of a high pressure turbine of the nuclear power plant by assuming a dryness on an outlet of the high pressure turbine and performing a heat balance calculation using a heat exchange quantity of either of the feedwater and the condensate water acquired by the heat-exchange-on-heater-calculating-means; a HP-turbine-power-correcting-means for making the HP-turbine-power-calculating-means correct the dryness on the outlet of the high pressure turbine to recalculate a power of the high pressure turbine when the calculated power value of the high pressure turbine is out of a threshold set on a basis of a reference power value of the high pressure turbine; a HP-turbine-internal-efficiency-calculating-means for calculating an internal efficiency of the high pressure turbine based on the calculated power value of the high pressure turbine; a steam-condition-on-LP-turbine-inlet-calculating-means for setting a condition of a steam on an inlet of a low pressure turbine of the nuclear power plant; a LP-turbine-power-calculating-means for acquiring a calculated power value of the low pressure turbine by assuming a reference expansion line of the low pressure turbine based on the condition of the steam on the inlet of the low pressure turbine and performing a heat balance calculation using a heat exchange quantity of either of the feedwater and the condensate water acquired by the heat-exchange-on-heater-calculating-means and the assumed reference expansion line of the low pressure turbine, the condition being set by the steam-condition-on-LP-turbine-inlet-calculating-means; a LP-turbine-power-correcting-means for making the LP-turbine-power-calculating-means correct the reference expansion line of the low pressure turbine to recalculate a power of the low pressure turbine when the calculated power value of the low pressure turbine is out of a threshold set on a basis of a reference power value of the low pressure turbine; a LP-turbine-internal-efficiency-calculating-means for calculating an internal efficiency of the low pressure turbine based on the calculated power value of the low pressure turbine; and a performance-deteriorating-element-specifying-means for specifying an element which causes deterioration of performance of the nuclear power plant based on the internal efficiency of the low pressure turbine calculated by the LP-turbine-internal-efficiency-calculating-means and the internal efficiency of the high pressure turbine calculated by the HP-turbine-internal-efficiency-calculating-means, as described in the claim  1  in an aspect to achieve the object.  
      The present invention also provides a nuclear power plant thermal efficiency diagnostic method comprising steps of: setting a flow rate of at least one of feedwater and condensate water in a nuclear power plant tentatively; calculating heat exchange quantities of the feedwater and the condensate water on a heater arranged on a condensate and feedwater pipe of the nuclear power plant in accordance with the flow rate of at least the one of the feedwater and the condensate water, the flow rate being set tentatively; acquiring a calculated power value of a high pressure turbine of the nuclear power plant by assuming a dryness on an outlet of the high pressure turbine and performing a heat balance calculation using a acquired heat exchange quantity of either of the feedwater and the condensate water correcting the dryness on the outlet of the high pressure turbine to recalculate a power of the high pressure turbine when the calculated power value of the high pressure turbine is out of a threshold set on a basis of a reference power value of the high pressure turbine; calculating an internal efficiency of the high pressure turbine based on the calculated power value of the high pressure turbine; setting a condition of a steam on an inlet of a low pressure turbine of the nuclear power plant; acquiring a calculated power value of the low pressure turbine by assuming a reference expansion line of the low pressure turbine based on the set condition of the steam on the inlet of the low pressure turbine and performing a heat balance calculation using an acquired heat exchange quantity of either of the feedwater and the condensate water and the assumed reference expansion line of the low pressure turbine; correcting the reference expansion line of the low pressure turbine to recalculate a power of the low pressure turbine when the calculated power value of the low pressure turbine is out of a threshold set on a basis of a reference power value of the low pressure turbine; calculating an internal efficiency of the low pressure turbine based on the calculated power value of the low pressure turbine; and specifying an element which causes deterioration of performance of the nuclear power plant based on the internal efficiency of the low pressure turbine and the internal efficiency of the high pressure turbine, as described in the claim  10  in an aspect to achieve the object.  
      The present invention also provides a nuclear power plant thermal efficiency diagnostic program allowing a computer to function as: a feed-and-condensate-water-flow-rate-setting-means for setting a flow rate of at least one of feedwater and condensate water in a nuclear power plant tentatively; a heat-exchange-on-heater-calculating-means for calculating heat exchange quantities of the feedwater and the condensate water on a heater arranged on a condensate and feedwater pipe of the nuclear power plant in accordance with the flow rate of at least the one of the feedwater and the condensate water, the flow rate being set by the feed-and-condensate-water-flow-rate-setting-means tentatively; a HP-turbine-power-calculating-means for acquiring a calculated power value of a high pressure turbine of the nuclear power plant by assuming a dryness on an outlet of the high pressure turbine and performing a heat balance calculation using a heat exchange quantity of either of the feedwater and the condensate water acquired by the heat-exchange-on-heater-calculating-means; a HP-turbine-power-correcting-means for making the HP-turbine-power-calculating-means correct the dryness on the outlet of the high pressure turbine to recalculate a power of the high pressure turbine when the calculated power value of the high pressure turbine is out of a threshold set on a basis of a reference power value of the high pressure turbine; a HP-turbine-internal-efficiency-calculating-means for calculating an internal efficiency of the high pressure turbine based on the calculated power value of the high pressure turbine; a steam-condition-on-LP-turbine-inlet-calculating-means for setting a condition of a steam on an inlet of a low pressure turbine of the nuclear power plant; a LP-turbine-power-calculating-means for acquiring a calculated power value of the low pressure turbine by assuming a reference expansion line of the low pressure turbine based on the condition of the steam on the inlet of the low pressure turbine and performing a heat balance calculation using a heat exchange quantity of either of the feedwater and the condensate water acquired by the heat-exchange-on-heater-calculating-means and the assumed reference expansion line of the low pressure turbine, the condition being set by the steam-condition-on-LP-turbine-inlet-calculating-means; a LP-turbine-power-correcting-means for making the LP-turbine-power-calculating-means correct the reference expansion line of the low pressure turbine to recalculate a power of the low pressure turbine when the calculated power value of the low pressure turbine is out of a threshold set on a basis of a reference power value of the low pressure turbine; a LP-turbine-internal-efficiency-calculating-means for calculating an internal efficiency of the low pressure turbine based on the calculated power value of the low pressure turbine; and a performance-deteriorating-element-specifying-means for specifying an element which causes deterioration of performance of the nuclear power plant based on the internal efficiency of the low pressure turbine calculated by the LP-turbine-internal-efficiency-calculating-means and the internal efficiency of the high pressure turbine calculated by the HP-turbine-internal-efficiency-calculating-means, as described in the claim  11  in an aspect to achieve the object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a functional block diagram showing a nuclear power plant thermal efficiency diagnostic system according to an embodiment of the present invention;  
       FIG. 2  is a diagram showing an example of a boiling-water nuclear power plant as a target of thermal efficiency diagnosis made by the plant diagnostic system of  FIG. 1 ;  
       FIG. 3  is a structural diagram showing an example of the HP turbine of  FIG. 2 ;  
       FIG. 4  is a bottom view showing positions of a steam extraction port and steam outlets of the HP turbine of  FIG. 3 ;  
       FIG. 5  is a structural diagram showing an example of the LP turbine of  FIG. 3 ;  
       FIG. 6  is a bottom view showing positions of steam extraction ports and steam outlets of the LP turbine of  FIG. 5 ;  
       FIG. 7  is an enlarged sectional view showing a portion near the drain catcher provided to the LP turbine of  FIG. 5 ;  
       FIG. 8  is a flowchart showing a procedure example of diagnosing thermal efficiency of the nuclear power plant in the case of applying the plant diagnostic system of  FIG. 1  to the nuclear power plant of  FIG. 2 ;  
       FIG. 9  shows an example of a reference expansion line and a corrected expansion line of the LP turbines in the h-s diagram assumed in the flowchart of  FIG. 8 ;  
       FIG. 10A  shows an example of the probability distribution of the condensate water flow rate in the optimized calculation;  
       FIG. 10B  shows an example of the probability distribution of the feedwater flow rate in the optimized calculation;  
       FIG. 10C  shows an example of the probability distribution of the internal efficiency of the LP turbines in the optimized calculation; and  
       FIG. 11  is a diagram of a conventional thermal efficiency diagnostic apparatus for a thermal power plant. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      A nuclear power plant thermal efficiency diagnostic system, a nuclear power plant thermal efficiency diagnostic program and a nuclear power plant thermal efficiency diagnostic method according to embodiments of the present invention will be described with reference to the accompanying drawings.  
       FIG. 1  is a functional block diagram showing a nuclear power plant thermal efficiency diagnostic system according to an embodiment of the present invention.  
      A nuclear power plant thermal efficiency diagnostic system  10  is constituted by reading a nuclear power plant thermal efficiency diagnostic program into an computer having an input device  11  and an output device  12  so as to function as a feed-and-condensate-water-flow-rate-setting-means  13 , a heat-exchange-on-heater-calculating-means  14 , a HP-turbine-power-calculating-means  15 , a HP-turbine-power-correcting-means  16 , a HP-turbine-internal-efficiency-calculating-means  17 , a steam-condition-on-LP-turbine-inlet-calculating-means  18 , a data-calculating-means  19 , a LP-turbine-selecting-means  20 , a LP-turbine-power-calculating-means  21 , a LP-turbine-power-correcting-means  22 , a LP-turbine-internal-efficiency-calculating-means  23 , a plant-state-optimizing-means  24  and a performance-deteriorating-element-specifying-means  25 .  
      A nuclear power plant  26  to which the nuclear power plant thermal efficiency diagnostic system  10  applies includes a shaft torque sensor  27 , a feed-and-condensate-water-flow rate sensor  28 , a generator power sensor  29  and a plant data measuring system  30 . The nuclear power plant thermal efficiency diagnostic system  10  can read data about factors measured by the shaft torque sensor  27 , the feed-and-condensate-water-flow rate sensor  28 , the generator power sensor  29  and the plant data measuring system  30 .  
      Note that, the nuclear power plant thermal efficiency diagnostic system  10  may receive data inputted to the input device  11  separately instead of reading data measured by the shaft torque sensor  27 , the feed-and-condensate-water-flow rate sensor  28 , the generator power sensor  29 , and the plant data measuring system  30  directly.  
       FIG. 2  is a diagram showing an example of a boiling-water nuclear power plant  26  as a target of thermal efficiency diagnosis made by the nuclear power plant thermal efficiency diagnostic system  10  of  FIG. 1 .  
      The nuclear power plant  26  is configured such that a reactor  40  and a turbine system  41  are connected through a main steam pipe  42  and a feed water pipe  43 . The turbine system  41  is configured such that an HP turbine  44 , a first LP turbine  45   a , a second LP turbine  45   b , and a third LP turbine  45   c  are provided to a common power transmission shaft  46 , and the power transmission shaft  46  is connected with a generator  47 . Each outlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is connected with a condenser  49  through a steam pipe  48 .  
      Incidentally, in the illustrated example of  FIG. 2 , the three LP turbines  45  are provided, but the number of LP turbines may be arbitrarily set. Further, the number of condensers  49  is not limited to 1 but may be arbitrarily set.  
      An upstream side of the main steam pipe  42  is connected with an outlet of the reactor  40 , and a downstream side of the main stream pipe  42  is connected with an inlet of the HP turbine  44  of the turbine system  41 . Further, the outlet of the HP turbine  44  is connected with one end of the steam pipe  48 , and the other end of the stream pipe  48  is branched and connected with inlets of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . A hygroscopic moisture separator  50  is provided on the steam pipe  48  provided at the outlet of the HP turbine  44 .  
      Further, an upstream side of the feed water pipe  43  is connected with the heaters  51   a ,  51   b ,  51   c ,  51   d ,  51   e  and  51   f  and the condenser  49 , and a downstream side of the feed water pipe  43  is connected with the inlet of the reactor  40  turbine system  41 . A first heater  51   a , a second heater  51   b , a reactor feedwater pump  52 , a third heater  51   c , a fourth heater  51   d , a fifth heater  51   e , a sixth heater  51   f , and a drain condenser  53  are provided onto the feed water pipe  43  in this order from the downstream side as the reactor  40  side. Further, the reactor feedwater pump  52  is provided with an RFP (reactor feedwater pump) turbine  54  for driving the reactor feedwater pump  52 .  
      Incidentally, in the illustrated example of  FIG. 2 , the number of heaters  51  is 6 but may be arbitrarily set.  
      On the other hand, the nuclear power plant  26  includes a condensate storage tank  55  that stores the condensate water and a gland steam vaporizer  56  that vaporizes the condensate water in the condensate storage tank  55  to generate steam. The condensate storage tank  55  is connected with the feed water pipe  43  between the reactor  40  and the condenser  49 , and the gland steam vaporizer  56  through a condensate water pipe  57 . The gland steam vaporizer  56  is connected with the condenser  49  through the steam pipe  48  and a drain pipe  58 . Then, the condensate water pipe  57  extending from the condensate storage tank  55  and the steam pipe  48  and the drain pipe  58  extending toward the condenser  49  are connected with one another in the gland steam vaporizer  56 .  
      Further, the HP turbine  44  of the turbine system  41  includes an extraction steam pipe  59  extending toward the first heater  51   a . The steam pipe  48  between the first heater  51   a  and the hygroscopic moisture separator  50  is connected with the extraction steam pipe  59  extending toward the second heater  51   b.    
      Furthermore, the steam pipe  48  between the hygroscopic moisture separator  50  and the LP turbines  45   a ,  45   b , and  45   c  is connected with the extraction steam pipe  59  extending toward the RFP turbine  54 . The extraction steam pipe  59  extending toward the RFP turbine  54  is guided to the condenser  49  connected with the LP turbines  45   a ,  45   b , and  45   c  by way of the RFP turbine  54 .  
      The hygroscopic moisture separator  50  is provided with a drain tank (not shown), and the drain tank of the hygroscopic moisture separator  50  is connected with the second heater  51   b  through the drain pipe  58 .  
      Further, the four extraction steam pipes  59  are connected with the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . The upstream extraction steam pipe  59  is branched and guided to the third heater  51   c  and the gland steam vaporizer  56 . The gland steam vaporizer  56  is connected with the fourth heater  51   d  through the drain pipe  58 . The extraction steam pipe  59  extending from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the gland steam vaporizer  56  is connected with the drain pipe  58  extending from the gland steam vaporizer  56  to the fourth heater  51   d.    
      The second extraction steam pipe  59  as viewed from the upstream side, which is connected with each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is guided to the fourth heater  51   d . Further, the third and fourth extraction steam pipes  59  as viewed from the upstream side, which are connected with each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are guided to the fifth heater  51   e  and the sixth heater  51   f , respectively.  
      Moreover, the drain pipes  58  are provided between the first heater  51   a  and the second heater  51   b , between the second heater  51   b  and the third heater  51   c , between the third heater  51   c  and the fourth heater  51   d , and between the fourth heater  51   d  and the fifth heater  51   e  respectively.  
      In addition, the drain pipe  58  is connected with each of the fifth heater  51   e  and the sixth heater  51   f . The other end of each drain pipe  58  is connected with a common drain tank  60 . The drain tank  60  is provided with the drain pipe  58  and the steam pipe  48 . The other end of the drain pipe  58  is guided to the condenser  49  through the drain condenser  53 , while the steam pipe  48  is guided to the sixth heater  51   f . Each drain pipe  58  and the steam pipe  48  provided in the drain tank  60  are connected with each other in the drain tank  60 .  
      Then, the extraction steam pipe  59  extending from the HP turbine  44  to the first heater  51   a  is connected with the drain pipe  58  extending toward the second heater  51   b  in the first heater  51   a . Further, the extraction steam pipe  59  extending from the midpoint between the HP turbine  44  and the hygroscopic moisture separator  50  to the second heater  51   b , the drain pipe  58  extending from the drain tank (not shown) of the hygroscopic moisture separator  50  to the second heater  51   b , and the drain pipe  58  extending from the first heater  51   a  to the second heater  51   b  are each connected with the drain pipe  58  extending from the second heater  51   b  to the third heater  51   c.    
      Further, the extraction steam pipe  59  extending from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the third heater  51   c , and the drain pipe  58  extending from the second heater  51   b  to the third heater  51   c  are each connected with the drain pipe  58  extending from the third heater  51   c  to the fourth heater  51   d . The extraction steam pipe  59  extending from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the fourth heater  51   d , the drain pipe  58  extending from the gland steam vaporizer  56  to the fourth heater  51   d , and the drain pipe  58  extending from the third heater  51   c  to the fourth heater  51   d  are connected with the drain pipe  58  extending from the fourth heater  51   d  to the fifth heater  51   e.    
      Likewise, the extraction steam pipe  59  extending from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the fifth heater  51   e , and the drain pipe  58  extending from the fourth heater  51   d  to the fifth heater  51   e  are each connected with the drain pipe  58  extending from the fifth heater  51   e  to the drain tank  60 . Further, the steam pipe  48  extending the drain tank  60  to the sixth heater  51   f  and the extraction steam pipe  59  extending from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the sixth heater  51   f  are each connected with the drain pipe  58  extending from the sixth heater  51   f  to the drain tank  60 .  
      In the nuclear power plant  26  thus configured, main steam generated in the reactor  40  is leaded to the inlet of the HP turbine  44  through the main steam pipe  42 . The main steam works in the HP turbine  44  and then the steam is lead from the outlet of the HP turbine  44  to the hygroscopic moisture separator  50  through the steam pipe  48 . Here, in the HP turbine  44 , a part of the steam which worked is lead to the first heater  51   a  as extracted steam through the extraction steam pipe  59 .  
      Moreover, a part of the steam lead from the outlet of the HP turbine  44  to the hygroscopic moisture separator  50  through the steam pipe  48  is lead to the second heater  51   b  through the extraction steam pipe  59  as extracted stream. Moisture contents of the steam lead into the hygroscopic moisture separator  50  are removed by the hygroscopic moisture separator  50 , after which the steam is lead to the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  through the branched steam pipes  48 . Further, a drain generated in the hygroscopic moisture separator  50  is lead to the second heater  51   b  through the drain pipe  58 .  
      Here, a part of the steam is lead from the steam pipe  48  between the hygroscopic moisture separator  50  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the RFP turbine  54  through the extraction steam pipe  59  as extracted steam. The extracted steam lead to the RFP turbine  54  works in the RFP turbine  54 , and is then lead to the condenser  49  and treated into a condensate water. As a result, the RFP turbine  54  is driven, and an output power of the RFP turbine  54  is used as a power for the reactor feedwater pump  52 .  
      On the other hand, the steam lead into each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  works in the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  respectively and is then condensed into a condensate water by the condenser  49 .  
      As a result, a turbine blade (not shown) is rotated together with the power transmission shaft  46  by the steam working in the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . The rotation of the power transmission shaft  46  transmits a power to the generator  47  to thereby generate electric power.  
      Here, a part of the steam working in the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is lead into the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , the sixth heater  51   f , and the gland steam vaporizer  56  through the extraction steam pipe  59  as extracted steam.  
      The extracted steam lead into the gland steam vaporizer  56  is turned into a drain through heat exchange with the condensate water lead from the condensate storage tank  55  to the gland steam vaporizer  56  and then lead to the fourth heater  51   d . A part of the condensate water lead from the condensate storage tank  55  to the gland steam vaporizer  56  is turned into steam and lead to the condenser  49  through the steam pipe  48 , while the rest is lead to the condenser  49  through the drain pipe  58  as a drain, not the steam.  
      On the other hand, condensate water generated in the condenser  49  is lead to the drain condenser  53  through the feed water pipe  43 . Heat exchange is executed between the drain lead from the drain tank  60  to the condenser  49  and the condensate water to cool the drain in the drain condenser  53 . The condensate water lead to the drain condenser  53  is led to the sixth heater  51   f , the fifth heater  51   e , the fourth heater  51   d , and the third heater  51   c  in this order. In the sixth heater  51   f , the fifth heater  51   e , the fourth heater  51   d , and the third heater  51   c , heat exchange is executed between the condensate water and the extracted steams lead from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  through the extraction steam pipes  59 , the steam lead from the drain tank  60 , and the drain lead from the second heater  51   b , the third heater  51   c , and the fourth heater  51   d  or the gland steam vaporizer  56  to heat the condensate water.  
      The drains resulting from the extracted steam or steam through the heat exchange with the condensate water in the sixth heater  51   f , the fifth heater  51   e , the fourth heater  51   d , and the third heater  51   c  are discharged from the discharge-side drain pipes  58  respectively and finally lead into the drain tank  60 .  
      Further, the condensate water passed through the third heater  51   c  is lead into the reactor feedwater pump  52  and pressurized as feedwater fed to the reactor  40 . The feedwater pressurized in the reactor feedwater pump  52  is lead into the second heater  51   b  and the first heater  51   a  in this order, and heated with the extracted steam lead from the HP turbine  44  or the steam pipe  48  through the extraction steam pipe  59  or with the drain lead from the hygroscopic moisture separator  50  or the first heater  51   a.    
      In the first heater  51   a  and the second heater  51   b , the drain resulting from the extracted steam through the heat exchange with feedwater is discharged from the discharge-side drain pipe  58  and finally lead to the third heater  51   c.    
      The feedwater heated by passing through the first heater  51   a  is lead to the reactor  40  and heated, and then lead to an inlet of the HP turbine  44  as main steam.  
       FIG. 3  is a structural diagram showing an example of the HP turbine  44  of  FIG. 2 .  FIG. 4  is a bottom view showing positions of a steam extraction port and steam outlets of the HP turbine  44  of  FIG. 3 .  
      The HP turbine  44  is configured such that plural rotor blades  70  and stationary blades  71  are alternately provided. Each rotor blade  70  is inserted to the power transmission shaft  46  rotatably with the power transmission shaft  46 . A steam X lead from the inlet side of the HP turbine  44  to the inside thereof is passed between each rotor blade  70  and each stationary blade  71  to work in the turbine. After that, the steam is discharged from a steam outlet  72 .  
      Further, an extraction port  73  is provided between the inlet and the outlet  72  of the HP turbine  44 , and a part of the steam X is lead to the first heater  51   a  from the extraction port  73  by way of the extraction steam pipe  59 .  
       FIG. 5  is a structural diagram showing an example of the LP turbine  45  of  FIG. 3 .  FIG. 6  is a bottom view showing positions of steam extraction ports and steam outlets of the LP turbine  45  of  FIG. 5 .  
      The LP turbine  45  is configured such that plural rotor blades  80  and plural stationary blades  81  are alternately provided like the HP turbine  44 . Each rotor blade  80  is inserted to the power transmission shaft  46  rotatably with the power transmission shaft  46 . The steam X lead from the inlet side of the LP turbine  45  to the inside thereof is passed between each rotor blade  80  and each stationary blade  81  and works. After that, the steam X is discharged from the discharge outlets  82 .  
      Further, a first extraction port  83 , a second extraction port  84 , third extraction ports  85 , and fifth extraction ports  86  are provided between the inlet and the outlets  82  of the LP turbine  45  in the order from the upstream side. Then, a part of the steam X in the LP turbine  45  is lead to the third heater  51   c  and the gland steam vaporizer  56  form the first extraction port  83  through the extraction steam pipe  59 . Further, parts of the steam X in the LP turbine  45  are lead to the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f  from the second extraction port  84 , the third extraction ports  85 , and the fourth extraction ports  86  through the extraction steam pipes  59 .  
      Further, the LP turbine  45  is provided with one or more drain catchers  87  for removing moisture in the steam X.  FIG. 5  shows an example of the LP turbine  45  where 5 drain catchers  87 , a first drain catcher  87   a , a second drain catcher  87   b , a third drain catcher  87   c , a fourth drain catcher  87   d , and a fifth drain catcher  87   e  are provided.  
      Further, the first drain catcher  87   a , the third drain catcher  87   c , and the fifth drain catcher  87   e  are configured such that a part of the steam is lead together with the drain to combine with the extracted steam discharged from the third extraction ports  85  and the fourth extraction ports  86  and the steam discharged from the outlets  82 . On the other hand, it is unnecessary to consider an effect of removing a part of the steam for the second drain catcher  87   b  and the fourth drain catcher  87   d.    
       FIG. 7  is an enlarged sectional view showing a portion near the drain catcher  87  provided to the LP turbine  45  of  FIG. 5 .  
      Each stationary blade  81  of the LP turbine  45  is fixed with a diaphragm  90 , while the rotor blade  80  is fixed to the power transmission shaft  46  by means of a disk  91 . The drain catcher  87  that is V-shaped grooves in section is provided on the stationary blade  81  side near the tip end of the rotor blade  80 . A steam separating chamber  92  is provided along the way of the drain catcher  87 . The moisture caught by the drain catcher  87  is lead to the steam separating chamber  92  to thereby remove moisture contents of the steam X in the LP turbine  45 .  
      In the nuclear power plant  26  as shown in  FIG. 2 , the shaft torque sensor  27  is provided to the power transmission shaft  46  that connects the HP turbine  44  with the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . The shaft torque sensor  27 A measures a shaft torque of at least one of the HP turbine  44 , the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . In this way, a measured shaft torque value F can be obtained.  
      In the case where the shaft torque sensor  27  is provided to an output shaft of the HP turbine  44 , an actual measured value of a torque of the HP turbine  44  can be obtained as a measured shaft torque value. In contrast, in the case where the shaft torque sensor  27  is provided to each output shaft of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , actual measured values of torques of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be obtained as measured shaft torque values.  
      The feed-and-condensate-water-flow rate sensor  28  is provided to the feed water pipe  43 , and configured such that flow rates of feedwater lead to the reactor  40  and the condensate water can be measured.  
      The generator power sensor  29  functions to measure the electric power generated by the generator  47 , that is, the total power of the nuclear power plant  26 .  
      The plant data measuring system  30  includes plural sensors such as temperature sensors and pressure sensors, and is configured such as data about a factor necessary for diagnosing thermal efficiency of the nuclear power plant  26  among factors such as temperatures, pressures, and flow rates of steam, feedwater, condensate water, drain, and extracted steam at required positions of each element of the nuclear power plant  26  can be obtained.  
      The feed- and-condensate-water-flow-rate-setting-means  13  of the nuclear power plant thermal efficiency diagnostic system  10  has a function of setting an assumptive flow rate of feedwater or condensate water used for diagnosing the thermal efficiency of the nuclear power plant  26  based on a flow rate of feedwater or condensate water measured by the feed-and-condensate-water-flow rate sensor  28 , and a function of informing the heat-exchange-on-heater-calculating-means  14  of the assumed flow rate of feedwater or condensate water.  
      Incidentally, the flow rate of feedwater or condensate water measured by the feed-and-condensate-water-flow rate sensor  28  may be directly used as the assumed flow rate of feedwater or condensate water. Alternatively, a value approximate to the flow rate measured by the feed-and-condensate-water-flow rate sensor  28  may be used as the assumed flow rate.  
      If receiving a request to renew a flow rate of feedwater or condensate water from the plant-state-optimizing-means  24 , the feed-and-condensate-water-flow-rate-setting-means  13  is configured to set an assumptive flow rate of feedwater or condensate water again based on the information supplied from the plant-state-optimizing-means  24 .  
      The heat-exchange-on-heater-calculating-means  14  has a function of calculating the quantities of heat exchanges of feedwater or condensate water at an inlet and an outlet of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f  provided onto the feed water pipe  43  of the nuclear power plant  26  based on the assumed value of the flow rate of feedwater or condensate water supplied from the feed-and-condensate-water-flow-rate-setting-means  13 .  
      That is, the heat-exchange-on-heater-calculating-means  14  has a function of calculating the enthalpies or specific enthalpies of feedwater or condensate water on the inlet and outlet of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f , and the enthalpy or specific enthalpy of drain at the outlet of the drain pipe  58  of each of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f , and a function of supplying necessary data out of the calculated enthalpies and specific enthalpies of the feedwater, condensate water, and drain in each of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f  to the HP-turbine-power-calculating-means  15 , the steam-condition-on-LP-turbine-inlet-calculating-means  18 , and the LP-turbine-power-calculating-means  21 .  
      Therefore, if the nuclear power plant  26  is configured as shown in  FIG. 2 , the deteriorating element specifying means  9  has the function of calculating the enthalpies or specific enthalpies of feedwater, condensate water, and drain of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f.    
      Incidentally, the heat-exchange-on-heater-calculating-means  14  is configured so as to receive data including the temperatures, pressures, and flow rates of feedwater, condensate water, and drain necessary for calculating the enthalpies or specific enthalpies from the plant data measuring system  30 .  
      The HP-turbine-power-calculating-means  15  has a function of receiving data including the temperatures, pressures, and flow rates of steam, extracted steam, drain, feedwater, and condensate water at a required position of the nuclear power plant  26  from the plant data measuring system  30 , and receiving necessary data out of the enthalpies and specific enthalpies of the feedwater, condensate water, and drain at each of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f  from the heat-exchange-on-heater-calculating-means  14  and a function of assuming dryness on the outlet  72  of the HP turbine  44 .  
      Further, the HP-turbine-power-calculating-means  15  has a function of performing a heat balance calculation, which is a balance calculation of the heat quantities of steam or extracted steam, based on assumed data or data input from the plant data measuring system  30  or the heat-exchange-on-heater-calculating-means  14  to determine a power of the HP turbine  44  and a function of supplying the calculated value of power of the HP turbine  44  obtained through the heat balance calculation to the HP-turbine-power-correcting-means  16 .  
      Further, when receiving a request to recalculate a power of the HP turbine  44  and a request to correct the dryness of steam at the outlet  72  of the HP turbine  44  from the HP-turbine-power-correcting-means  16 , the HP-turbine-power-calculating-means  15  is configured to correct the dryness of the steam to obtain the power of the HP turbine  44  again by the heat balance calculation and supply the calculated value of power of the HP turbine  44  to the HP-turbine-power-correcting-means  16 .  
      Further, the HP-turbine-power-calculating-means  15  has a function of supplying to the steam-condition-on-LP-turbine-inlet-calculating-means  18  a flow rate of steam on the outlet  72  of the HP turbine  44  which is obtained in the course of the heat balance calculation of the power of the HP turbine  44 .  
      Further, the HP-turbine-power-calculating-means  15  is configured to supply the calculated value of power of the HP turbine  44  to the plant-state-optimizing-means  24  if necessary.  
      The HP-turbine-power-correcting-means  16  has a function of receiving the calculated value of power of the HP turbine  44  from the HP-turbine-power-calculating-means  15  to compare an arbitrarily preset reference power value with the calculated value of the power of the HP turbine  44  and determine whether or not a difference or ratio between the reference power value of the HP turbine  44  and the calculated value of power is under a preset threshold value.  
      Here, as a method of setting a reference power value of the HP turbine  44 , there are a setting method using a design value, a setting method using a measured power value of the HP turbine  44 , and a setting method using an estimated value which can be obtained empirically.  
      In the case of using the measured value of the power of the HP turbine  44  as the reference power value of the HP turbine  44 , for example, a measured shaft torque value of the HP turbine  44  or the LP turbines  45   a ,  45   b , and  45   c  is inputted from the shaft torque sensor  27  to the HP-turbine-power-correcting-means  16 , and the measured value of the power of the HP turbine  44  can be obtained based on the inputted measured shaft torque value.  
      At this time, if the measured shaft torque values of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is input from the shaft torque sensor  27 , the HP-turbine-power-correcting-means  16  is configured to receive the total power of the nuclear power plant  26  measured by the generator power sensor  29  and subtract the measured shaft torque values of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  from the total power of the nuclear power plant  26  to thereby indirectly obtain the measured value of power of the HP turbine  44 .  
      The HP-turbine-power-correcting-means  16  has a function of sending the request to recalculate the power of the HP turbine  44  and the request to correct the dryness of the steam at the outlet  72  of the HP turbine  44  to the HP-turbine-power-calculating-means  15  and causing the HP-turbine-power-calculating-means  15  to execute recalculation to thereby correct the calculated value of power of the HP turbine  44  when determining that the difference or ratio between the measured value of power of the HP turbine  44  and the reference power value is not within the preset threshold value, while sending the calculated value of power of the HP turbine  44  to the HP-turbine-internal-efficiency-calculating-means  17  if determining that the difference or ratio between the measured value of power of the HP turbine  44  and the reference power value is within the preset threshold value.  
      The HP-turbine-intern al-efficiency-calculating-means  17  has a function of calculating internal efficiency of the HP turbine  44  based on the corrected calculated value of power of the HP turbine  44  received from the HP-turbine-power-correcting-means  16  and data input from the plant data measuring system  30  and a function of sending the calculated internal efficiency of the HP turbine  44  to the plant-state-optimizing-means  24 .  
      The steam-condition-on-LP-turbine-inlet-calculating-means  18  has a function of calculating each dryness of steam at the inlets of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  based on a required one of the flow rate of steam at the outlet  72  of the HP turbine  44  received from the HP-turbine-power-calculating-means  15 , the data received from the heat-exchange-on-heater-calculating-means  14 , and the data input from the plant data measuring system  30  in accordance with the structure of the nuclear power plant  26 , and a function of sending to the LP-turbine-power-calculating-means  21  the data on each calculated dryness of the steam at the inlets of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      The steam-condition-on-LP-turbine-inlet-calculating-means  18  further has a function of receiving required data in accordance with the structure of the nuclear power plant  26  based on the results of calculation made by the plant data measuring system  30  or other such functional parts in the nuclear power plant thermal efficiency diagnostic system  10 , optionally performing a heat balance calculation to determine the flow rate, temperature, pressure, and dryness of the steam at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and sending the determined data to the LP-turbine-power-calculating-means  21 .  
      The data-calculating-means  19  has a function of receiving data about the temperature, pressure, and flow rate of each of steam, extracted steam, drain, feedwater, and condensate water measured by the plant data measuring system  30  or data about the results of calculation made by other functional parts of the nuclear power plant thermal efficiency diagnostic system  10  to calculate data necessary for diagnosing the thermal efficiency of the nuclear power plant  26  as for elements of the nuclear power plant  26  other than the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . Further, the data-calculating-means  19  has a function of sending data serving as the calculation result to the plant-state-optimizing-means  24 .  
      Examples of data calculated by the data-calculating-means  19  include the internal efficiency of the RFP turbine  54 , the heat receiving quantity of the steam in the reactor  40 , and flow rates of feedwater and condensate water lead to the reactor  40 .  
      The LP-turbine-selecting-means  20  has a function of selecting a desired one from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and sending a request to calculate a power of the selected LP turbine  45  to the LP-turbine-power-calculating-means  21 , while determining whether or not there is the LP turbine  45  of which the power has not been yet calculated in response to a notification that the calculation of the internal efficiency of the LP turbine  45  is completed, which is sent from the LP-turbine-internal-efficiency-calculating-means  23 , and selecting the LP turbine  45  of which the power calculation has not been executed if any to send a request to calculate a power to the LP-turbine-power-calculating-means  21 .  
      The LP-turbine-power-calculating-means  21  has a function of assuming a reference expansion line of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  in a h-s diagram based on the data such as the temperature, pressure, flow rate, and dryness at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , which are set by the steam-condition-on-LP-turbine-inlet-calculating-means  18 .  
      Further, the LP-turbine-power-calculating-means  21  has a function of receiving necessary data from the heat-exchange-on-heater-calculating-means  14 , inputting necessary data from the plant data measuring system  30  and obtaining a corrected expansion line and each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  through the heat balance calculation based on the input or received data, design information, and the reference expansion line of the h-s diagram.  
      Further, the LP-turbine-power-calculating-means  21  sends each calculated value of the powers of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , which is obtained through the heat balance calculation, to the LP-turbine-power-correcting-means  22  while corrects the reference expansion line of the h-s diagram to obtain the corrected expansion line and each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  through the heat balance calculation again if receiving a request to recalculate each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and a request to correct the reference expansion line of the h-s diagram from the LP-turbine-power-correcting-means  22 .  
      Further, the LP-turbine-power-calculating-means  21  has a function of calculating efficiency of each stage group obtained by dividing the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  with the first extraction port  83  to the fourth extraction port  86 , and the first drain catcher  87   a  to the fifth drain catcher  87   e , and sending the efficiency of each stage group to the LP-turbine-internal-efficiency-calculating-means  23 .  
      The LP-turbine-power-calculating-means  21  is configured to send the calculated value of each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the plant-state-optimizing-means  24  if necessary.  
      The LP-turbine-power-correcting-means  22  has a function of receiving the calculated value of each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  from the LP-turbine-power-calculating-means  21  to compare an arbitrarily preset reference power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  with the calculated value of the power and determine whether or not a difference or ratio between the reference output value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the calculated value of power is within a preset threshold.  
      Here, the reference power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be set based on data such as a design value or a measured power value similar to the reference power value of the HP turbine  44 . Hence, in the case of using the measured power value as the reference power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , the measured power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be obtained by inputting each measured shaft torque value of the HP turbine  44  or the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  from the shaft torque sensor  27 .  
      At this time, if the measured shaft torque value input from the shaft torque sensor  27  is the measured shaft torque value of the HP turbine  44 , the LP-turbine-power-correcting-means  22  configured to input the total power of the nuclear power plant  26  which is measured by the generator power sensor  29  and subtract the measured shaft torque value of the HP turbine  44  from the total power of the nuclear power plant  26  to thereby indirectly obtain the measured power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      Further, it is possible to not only input and add the measured shaft torque values of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  but also calculate the sum of the measured power values of the LP turbines  45  on the assumption that a measured shaft torque value input from one LP turbine  45  is equal to the shaft torque of another LP turbine  45 .  
      Further, the LP-turbine-power-correcting-means  22  has a function of sending a request to recalculate each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and a request to correct the reference expansion line of the h-s diagram to the LP-turbine-power-calculating-means  21  to cause the LP-turbine-power-calculating-means  21  to execute recalculation such that a difference or ratio between the measured power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the measured power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  supplied from the LP-turbine-power-calculating-means  21  is within a threshold, to thereby correct the calculated value of each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      Further, the LP-turbine-power-correcting-means  22  is configured to send an instruction to calculate each internal efficiency of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the LP-turbine-internal-efficiency-calculating-means  23  if the difference or ratio between the measured power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the calculated power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  supplied from the LP-turbine-power-calculating-means  21  is within the threshold.  
      The LP-turbine-internal-efficiency-calculating-means  23  has a function of calculating each total internal efficiency of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  based on efficiency of each stage group of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  which is supplied from the LP-turbine-power-calculating-means  21 , and sending each calculated internal efficiency of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the plant-state-optimizing-means  24 .  
      The plant-state-optimizing-means  24  has a function of receiving the calculated internal efficiencies of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  from the HP-turbine-internal-efficiency-calculating-means  17  and the LP-turbine-internal-efficiency-calculating-means  23  respectively and receiving data, e.g., the internal efficiency of the RFP turbine  54 , the heat receiving quantity of steam in the reactor  40 , or the calculated value of flow rates of feedwater or condensate water lead into the reactor  40 , necessary for diagnosing thermal efficiency of a target element of the nuclear power plant  26  from the data-calculating-means  19  to execute optimized calculation on each calculated value using an arbitrarily preset reference value, and determining whether or not the optimized calculation is completed, that is, whether or not each calculated value is optimized.  
      Here, as a reference value for the optimized calculation, data such as a design value or measured value can be used.  
      Further, the plant-state-optimizing-means  24  is configured to send a request to reset a flow rate of feedwater or condensate water to the feed-and-condensate-water-flow-rate-setting-means  13  if determining that each calculated value including a feedwater flow rate or the like is not optimized, while sends the optimized calculated values of the internal efficiency of the HP turbine  44  and the internal efficiencies of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the performance-deteriorating-element-specifying-means  25  if determining that each calculated value is optimized.  
      Further, if an accuracy of the shaft torque sensor  27  is insufficient, for example, 1% or more, the plant-state-optimizing-means  24  is configured to optionally receive the calculated value of the power of the HP turbine  44  or each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  from one or both of the HP-turbine-power-calculating-means  15  and the LP-turbine-power-calculating-means  21  to optimize the calculated value of the power.  
      The plant-state-optimizing-means  24  issues a request to correct the dryness of the steam at the outlet  72  of the HP turbine  44  to the HP-turbine-power-calculating-means  15  if determining that the calculated value of the power of the HP turbine  44  is not optimized, while issues a request to correct the reference expansion line of the h-s diagram to the LP-turbine-power-calculating-means  21  if determining that the calculated value of each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is not optimized.  
      Here, a desired method may be used for optimization. For example, there is a method of statistically optimizing each calculated value of the feedwater flow rate and the like using a probability distribution. That is, each value of the feedwater flow rate or the like is calculated several times, and thus the probability distribution can be obtained, which shows a relation between a deviation of each calculated value from the reference value and the probability. Hence, it is possible to optimize each calculated value of the feedwater flow rate or the like based on the probability distribution.  
      Since plural calculated values should be optimized, probability distributions of calculated values are integrated to obtain a probability distribution. Then, calculated values at which the deviation is smallest in the integrated probability distribution may be used as the optimized calculated values. In this case, as for a probability distribution that can be assumed as a normal distribution or a probability distribution obtained by integrating the normal distribution, the normal distribution or the probability distribution obtained by integrating the normal distribution can be used. Then, calculated values that maximize the probability about all values in consideration of each calculated value are used as the optimized calculated values.  
      In the case of statistically optimizing the calculated values of the feedwater flow rate or the like using the probability distributions, if it is determined that the calculated values of the feedwater flow rate or the like are not optimized, the plant-state-optimizing-means  24  is configured to send a request to reset a flow rate of the feedwater or condensate water to the feed-and-condensate-water-flow-rate-setting-means  13  such that the deviation is minimized.  
      Incidentally, as the optimized calculation method, it is possible to only determine whether or not each calculated value of the feedwater flow rate or the like is within a threshold based on the preset reference value. In this case, the plant-state-optimizing-means  24  may not have a function of executing the optimized calculation.  
      The performance-deteriorating-element-specifying-means  25  has a function of calculating differences between optimized calculated values of the internal efficiency of the HP turbine  44  and each internal efficiency of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  received from the plant-state-optimizing-means  24  and corresponding design values to specify a element showing the largest product of the difference between the calculated value and the design value by the preset degree of contribution. Here, the degree of contribution refers to how far each of the HP turbine  44 , and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  influences the efficiency of the nuclear power plant  26  in numeral terms.  
      The determination result from the performance-deteriorating-element-specifying-means  25  can be displayed on an output device  12  such as a monitor as appropriate.  
      Next, an operation of the nuclear power plant thermal efficiency diagnostic system  10  will be described.  
       FIG. 8  is a flowchart showing a procedure example of diagnosing thermal efficiency of the nuclear power plant  26  in the case of applying the nuclear power plant thermal efficiency diagnostic system  10  of  FIG. 1  to the nuclear power plant  26  of  FIG. 2 . In  FIG. 8 , reference numerals prefixed with “S” denote steps of the flowchart.  
      First, a flow rate GH 1  of feedwater lead to the reactor  40  is measured by the feed-and-condensate-water-flow rate sensor  28 , and the generator power sensor  29  measures electric power generated by the generator  47 , that is, the total power W TOTAL  of the nuclear power plant  26 . Further, the plant data measuring system  30  measures a factor necessary for diagnosing thermal efficiency of the nuclear power plant  26  out of the factors such as the temperature, pressure, and flow rate of each of the steam, feedwater, condensate water, drain, and extracted steam at required positions of each element of the nuclear power plant  26 .  
      Incidentally, the temperatures and pressures of the steam, feedwater, condensate water, drain, and extracted steam to be measured by the plant data measuring system  30  at each position of the nuclear power plant  26  can be measured with higher accuracy than accuracy necessary for diagnosing the thermal efficiency of the nuclear power plant  26 . On the other hand, the accuracy for measuring each flow rate of the steam, drain, extracted steam, the feedwater, and the condensate water is lower than that for each of the temperatures or pressures.  
      Therefore, all or a part of the flow rates of the steam, drain, extracted steam, feedwater, and condensate water may be measured by the plant data measuring system  30  at each point of the nuclear power plant  26 . In this example, however, measured values are used for values that are hardly calculated, and flow rates of steam and the like are obtained by calculation.  
      Further, the shaft torque sensor  27  measures the shaft torque of the HP turbine  44  for example. Thus, a measured shaft torque value F serving as an actual measured value of a power W HP  of the HP turbine  44  is obtained.  
      In step S 1 , the feed-and-condensate-water-flow-rate-setting-means  13  receives the flow rate G H 1  of feedwater lead to the reactor  40  from the feed-and-condensate-water-flow rate sensor  28 , and sets the assumptive flow rate as the feedwater flow rate G H1  used for diagnosing the thermal efficiency of the nuclear power plant  26 . That is, since accuracy of the feedwater flow rate G H1  measured by the feed-and-condensate-water-flow rate sensor  28  is about 0.7%, the assumptive value is set. Further, the feed-and-condensate-water-flow-rate-setting-means  13  sends the thus-set assumptive feedwater flow rate G H1  to the heat-exchange-on-heater-calculating-means  14 .  
      Incidentally, it is possible to input the flow rate of condensate water in place of the feedwater to set the assumptive flow rate value.  
      Next, in step S 2 , the heat-exchange-on-heater-calculating-means  14  calculates a specific enthalpy of drain resulting from the heat exchange with the extracted steam and condensate water or feedwater in each of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f.    
      The heat-exchange-on-heater-calculating-means  14  receives the temperature and pressure of the drain at the outlet of each drain pipe  58  of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f  from the plant data measuring system  30  upon calculating the specific enthalpy of the drain. Then, the heat-exchange-on-heater-calculating-means  14  calculates the specific enthalpy of the drain based on a steam table using the temperature and the pressure of the drain on the outlet of the drain pipe  58  in each of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f.    
      As the steam table, for example, a table released by the Japan Society of Mechanical Engineering may be used.  
      Further, the heat-exchange-on-heater-calculating-means  14  calculates the enthalpies of the condensate water and feedwater at the inlet and outlet of the feed water pipe  43  in each of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f  using the feedwater flow rate G H1  from the feed-and-condensate-water-flow-rate-setting-means  13 .  
      The heat-exchange-on-heater-calculating-means  14  receives from the plant data measuring system  30  the temperatures and the pressures of the condensate water and feedwater at the inlet and outlet of the feed water pipe  43  in the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f  at the time of calculating the enthalpies of the condensate water and feedwater. Then, the heat-exchange-on-heater-calculating-means  14  calculates the specific enthalpies based on the temperatures and pressures of the condensate water and feedwater at the inlet and outlet of the feed water pipe  43  in each of the first heater  51   a , the second heater  51   b , the third heater  51   c , the fourth heater  51   d , the fifth heater  51   e , and the sixth heater  51   f  to multiply this by the feedwater flow rate G H1  to thereby calculate the enthalpies of the condensate water and the feedwater.  
      Further, the heat-exchange-on-heater-calculating-means  14  sends the enthalpies of the condensate water and feedwater and the specific enthalpy of the drain in the first heater  51   a  to the HP-turbine-power-calculating-means  15 . The heat-exchange-on-heater-calculating-means  14  sends the enthalpies of the condensate water and feedwater and the specific enthalpy of the drain in the second heater  51   b  to the steam-condition-on-LP-turbine-inlet-calculating-means  18 . The heat-exchange-on-heater-calculating-means  14  sends the enthalpies of the condensate water and feedwater and the specific enthalpies of the drains in the third heater  51   c  to the fifth heater  51   f  to the LP-turbine-power-calculating-means  21 .  
      Next, in step S 3 , the HP-turbine-power-calculating-means  15  sets assumptive dryness of the steam at the outlet  72  of the HP turbine  44  based on a design value of the HP turbine  44  for heat balance calculation of the power W HP  of the HP turbine  44 .  
      Since the steam used in the nuclear power plant  26  is in a wet state, the dryness of the steam as well as the temperature and the pressure of the steam is necessary for calculating the enthalpy of the steam. To that end, the HP-turbine-power-calculating-means  15  sets assumptive dryness of the steam at the outlet  72  of the HP turbine  44  for calculating the heat quantity of the steam at the outlet  72  of the HP turbine  44 .  
      However, an inaccurate design value is used for the steam dryness at the outlet  72  of the HP turbine  44  and thus the steam dryness is set as the assumptive value.  
      Next, in step S 4 , the HP-turbine-power-calculating-means  15  calculates dryness of extracted steam at the extraction port  73  of the HP turbine  44 . That is, in the nuclear power plant  26  of  FIG. 2 , the extraction port  73  is provide to the HP turbine  44  to lead the extracted steam into the first heater  51   a . Thus, for the heat balance calculation of the power W HP  of the HP turbine  44 , the quantity of heat of the extracted steam at the extraction port  73  of the HP turbine  44  must be determined.  
      To be exact, the internal efficiency from the inlet of the HP turbine  44  to the extraction port  73  is different from that from the extraction port  73  to the outlet  72 . However, on the assumption that the HP turbine  44  operates with almost 100% load, an internal efficiency η HP  of the HP turbine  44  is set constant from the inlet to the outlet  72  of the HP turbine  44  for calculation.  
      The dryness of the extracted steam at the extraction port  73  of the HP turbine  44  can be calculated based on the assumptive dryness of steam at the outlet  72  of the HP turbine  44  set in step S 3  and the pressure at the extraction port  73 .  
      That is, in the h-s (specific entropy-specific enthalpy) diagram, points of specific enthalpies h HPin  and h HPout  and specific entropies S HPin  and S HPout  at the inlet and the outlet  72  of the HP turbine  44  are first plotted based on the pressures and temperatures at the inlet and the outlet  72  of the HP turbine  44 . Further, the point of the specific enthalpy h HPin  and specific entropy S HPin  at the inlet of the HP turbine  44  is connected with the point of the specific enthalpy h HPout  and the specific entropy S HPout  at the outlet  72  of the HP turbine  44  by straight lines. Then, an intersection between the obtained straight line and a constant-pressure line corresponding to a pressure at the extraction port  73  of the HP turbine  44  on the h-s diagram is detected, and the steam dryness at the detected intersection can be obtained as the dryness of the extracted steam at the extraction port  73  of the HP turbine  44  based on the steam table.  
      Incidentally, the temperatures and pressures of the steam at the inlet and the outlet  72  of the HP turbine  44  and the pressure of the extracted steam at the extraction port  73  of the HP turbine  44  necessary for calculating the dryness of the extracted steam at the extraction port  73  of the HP turbine  44  with the HP-turbine-power-calculating-means  15  are input from the plant data measuring system  30 .  
      Next, in step S 5 , the HP-turbine-power-calculating-means  15  calculates a flow rate G EXT  of the extracted steam for calculating the heat quantity of extracted steam necessary for executing a heat balance calculation of the power W HP  of the HP turbine  44 .  
      Here, a difference between the heat quantity of extracted steam lead to the first heater  51   a  and the heat quantity of the drain discharged from the drain pipe  58  is a loss in heat quantity of the extracted steam in the first heater  51   a . The heat quantity of the extracted steam is calculated by multiplying the specific enthalpy h EXT  of the extracted steam by the flow rate G EXT  of the extracted steam. The heat quantity of drain is calculated by multiplying the specific enthalpy h P  of the drain by the flow rate G H1D  of the drain. Further, the flow rate G H1D  of the drain can be calculated based on the flow rate G EXT  of the extracted steam.  
      Further, the heat quantity that the extracted steam loses in the first heater  51   a  is equal to the heat quantity received by the feedwater in the first heater  51   a . The heat quantity received by the feedwater in the first heater  51   a  is represented by a difference between enthalpies of feedwater at the inlet and the outlet of the first heater  51   a.    
      Hence, it is possible to execute heat balance calculation on the flow rate G EXT  of the extracted steam lead to the first heater  51   a  based on Expression (1): 
 
 G   EXT   ={G   H1 ( h   Hout   −h   Hin )+ G   H1D   h   EXT   }/h   D   (1) 
 
      Where  
      G EXT : flow rate of extracted steam lead into the first heater  
      G H1 : flow rate of feedwater in the first heater  
      G H1D : flow rate of drain discharged from first heater  
      h Hout : specific enthalpy of feedwater at the outlet of the first heater  
      h Hin : specific enthalpy of feedwater at the inlet of the first heater  
      h D : specific enthalpy of drain at the outlet of the first heater  
      h EXT : specific enthalpy of extracted steam at the inlet of the first heater  
      Here, the specific enthalpy h EXT  of the extracted steam at the inlet of the first heater  51   a  may be assumed to be equal to the specific enthalpy of the extracted stream at the extraction port  73  of the HP turbine  44  calculated in step S 4 .  
      Further, the heat quantity received by the feedwater in the first heater  51   a  can be calculated based on the enthalpies, which is supplied from the heat-exchange-on-heater-calculating-means  14 , of the feedwater at the inlet and outlet of the first heater  51   a.    
      Hence, the HP-turbine-power-calculating-means  15  calculates the flow rate G EXT  of the extracted stream using Expression (1) based on the data from the heat-exchange-on-heater-calculating-means  14  and the data from the plant data measuring system  30 .  
      Next, in step S 6 , the HP-turbine-power-calculating-means  15  calculates an exhaust loss of the steam in the HP turbine  44 , that is, a velocity energy of the steam that is not used for the rotation of a turbine blade in the HP turbine  44 .  
      Incidentally, the exhaust loss of the steam is calculated based on a flow velocity of the steam at the outlet  72  of the HP turbine  44 . The flow velocity of the steam can be calculated based on the flow rate of the steam and the sectional area of the outlet  72  in the HP turbine  44 . The flow rate of the steam at the outlet  72  of the HP turbine  44  may be calculated by subtracting the flow rate G EXT  of the exhausted steam lead to the first heater  51   a  from the flow rate G HP  of the steam at the inlet of the HP turbine  44 .  
      Next, in step S 7 , the HP-turbine-power-calculating-means  15  calculates the power of the HP turbine  44  through heat balance calculation. That is, the HP-turbine-power-calculating-means  15  receives the temperature and pressure at the inlet of the HP turbine  44  from the plant data measuring system  30  to calculate the specific enthalpy h HPin  at the inlet of the HP turbine  44 . Here, the assumptive dryness at the inlet of the HP turbine  44  may be used, as needed.  
      Further, the HP-turbine-power-calculating-means  15  receives the temperature and pressure at the outlet  72  of the HP turbine  44  to calculate the specific enthalpy h HPout  at the outlet  72  of the HP turbine  44  based on the input temperature and pressure at the outlet  72  of the HP turbine  44 , and the assumptive dryness at the outlet  72  of the HP turbine  44  set in step S 3 .  
      Next, the HP-turbine-power-calculating-means  15  multiplies the flow rate G HP  of the steam at the inlet of the HP turbine  44  by the specific enthalpy h HPin  of the steam at the inlet of the HP turbine  44  to calculate the heat quantity of the steam at the inlet of the HP turbine  44 , and multiplies the flow rate of the steam at the outlet of the HP turbine  44  by the specific enthalpy h HPout  of the steam at the outlet of the HP turbine  44  to calculate the heat quantity of the steam at the outlet of the HP turbine  44 .  
      Here, the flow rate G HP  of the steam at the inlet of the HP turbine  44  can be calculated based on the feedwater flow rate. The flow rate of the steam at the outlet  72  of the HP turbine  44  is calculated by subtracting the flow rate G EXT  of the exhausted steam calculated in step S 5  from the flow rate G HP  of the steam at the inlet of the HP turbine  44 .  
      Further, the HP-turbine-power-calculating-means  15  can calculate the heat quantity of the extracted steam by multiplying the flow rate G EXT  of the extracted steam calculated in step S 5  by the specific enthalpy of the extracted steam at the extraction port  73  of the HP turbine  44 . The specific enthalpy of the extracted steam at the extraction port  73  of the HP turbine  44  can be calculated based on the steam table in accordance with the temperature, pressure, and dryness of the extracted steam at the extraction port  73  of the HP turbine  44 .  
      Then, the HP-turbine-power-calculating-means  15  executes a energy balance calculation regarding as the heat quantities of the steam at the inlet and the outlet  72  of the HP turbine  44 , the heat quantity of the extracted steam, and the exhaust loss of the steam in the HP turbine  44  calculated in step S 6  to obtain a calculated power value W HPcal  of the HP turbine  44 .  
      The HP-turbine-power-calculating-means  15  sends the calculated power value W HPcal  of the HP turbine  44  obtained through the heat balance calculation to the HP-turbine-power-correcting-means  16 .  
      Next, in step S 8 , the HP-turbine-power-correcting-means  16  receives the measured shaft torque value F of the HP turbine  44  from the shaft torque sensor  27  and receives the calculated power value W HPcal  of the HP turbine  44  from the HP-turbine-power-calculating-means  15  to compare the measured shaft torque value F of the HP turbine  44  with the calculated power value W HPcal  of the HP turbine  44  to determine whether or not a difference or ratio between the measured shaft torque value F of the HP turbine  44  and the calculated power value W HPcal  of the HP turbine  44  is within a preset threshold value ε HP .  
      For example, the HP-turbine-power-correcting-means  16  determines whether or not the ratio between the measured shaft torque value F of the HP turbine  44  and the calculated power value W HPcal  of the HP turbine  44  is within the preset threshold value ε HP  (for example, ε HP =0.5%) based on Expression (2). 
 
 W   HPcal   /F− 1|&lt;ε HP   (2) 
 
      Then, if it is determined that the ratio between the measured shaft torque value F of the HP turbine  44  and the calculated power value W HPcal  of the HP turbine  44  is not within the preset threshold value ε HP , that is, Expression (2) is not satisfied, the HP-turbine-power-correcting-means  16  sends a request to recalculate the power W HP  of the HP turbine  44  and a request to correct the dryness of steam at the outlet  72  of the HP turbine  44  so as to satisfy Expression (2) to the HP-turbine-power-calculating-means  15 .  
      Hence, the HP-turbine-power-calculating-means  15  sets the assumptive dryness of the steam at the outlet  72  of the HP turbine  44  in step S 3  again, and the power of the HP turbine  44  is calculated from steps S 4  to S 7 . As described above, the HP-turbine-power-calculating-means  15  repeats calculating the power of the HP turbine  44  until the ratio between the measured shaft torque value F of the HP turbine  44  and the calculated power value W HPcal  of the HP turbine  44  is to be within the preset threshold value ε HP .  
      In step S 8 , when the HP-turbine-power-correcting-means  16  determines that the ratio between the measured shaft torque value F of the HP turbine  44  and the calculated power value W HPcal  of the HP turbine  44  is within the preset threshold value ε HP , the HP-turbine-power-correcting-means  16  sends the calculated power value W HPcal  of the HP turbine  44  to the HP-turbine-internal-efficiency-calculating-means  17 .  
      Next, in step S 9 , the HP-turbine-internal-efficiency-calculating-means  17  calculates the internal efficiency η HP  of the HP turbine  44  based on the calculated power value W HPcal , which is received from the HP-turbine-power-correcting-means  16 , of the HP turbine  44  after correction and the data received from the plant data measuring system  30 .  
      Here, the power W HP  of the HP turbine  44  is expressed by Expression (3). However, the extracted steam is not taken into account for simplifying calculation. Accordingly, in order to improve the calculation accuracy, the power W HP  of the HP turbine  44  may be calculated with taking account of the extracted steam. 
 
 W   HP   =Δh   HPad   ·G   HP  ·η HP   (3) 
 
      Where  
      Δh HPad : adiabatic heat drop of the HP turbine  
      G HP : steam flow rate at the inlet of the HP turbine  
      η HP : internal efficiency of the HP turbine  
      That is, the power W HP  of the HP turbine  44  can be calculated based on the product of the HP turbine adiabatic heat drop Δh HPad  by the steam flow rate G HP  at the inlet of the HP turbine  44 , that is, with correction by multiplying  
      the enthalpy change of the steam in the HP turbine  44  by the internal efficiency η HP  of the HP turbine  44  in consideration of the loss of energy consumed for the entropy change in steam. Further, modifying Expression (3) gives Expression (4). 
 
η HP   =W   HP   /Δh   HPad   ·G   HP   (4) 
 
      Here, the adiabatic heat drop Δh HPad  of the HP turbine  44  is expressed as a difference between the specific enthalpy h HPin , of the steam at the inlet of the HP turbine  44  and the specific enthalpy h HPoutad  of the steam at the outlet  72  on the assumption that the steam is subjected to the isentropic change in the HP turbine  44  as indicated by Expression (5). That is, the adiabatic heat drop Δh HPad  of the HP turbine  44  represents a work load of steam at the HP turbine  44  on the ideal state generating no energy loss. 
 
Δ h   HPad   =h   Hpin   −h   HPoutad   (5) 
 
      Hence, if the pressures of the steam at the outlet  72  and inlet of the HP turbine  44  and the temperature of the steam at the inlet of the HP turbine  44  can be acquired, the specific enthalpy h HPin , at the inlet of the HP turbine  44  and the specific enthalpy h HPoutad  at the outlet  72  on the assumption that the steam is subjected to the isentropic change based on the h-s diagram can be calculated, and the adiabatic heat drop Δh HPad  of the HP turbine  44  is calculated from Expression (5).  
      Then, the pressure of the steam at the inlet of the HP turbine  44 , the pressure of the steam at the outlet  72  of the HP turbine  44 , and the temperature of the steam at the inlet of the HP turbine  44  are measured by the plant data measuring system  30 . Here, the assumptive dryness at the inlet of the HP turbine  44  may be set if necessary. Further, the steam flow rate G HP  at the inlet of the HP turbine  44  may be a value calculated in step S 7 .  
      Then, the HP-turbine-internal-efficiency-calculating-means  17  receives the pressure of the steam at the inlet of the HP turbine  44 , the pressure of the steam at the outlet  72  of the HP turbine  44 , the temperature of the steam at the inlet of the HP turbine  44  from the plant data measuring system  30 , and also receives the calculated power value W HPcal  of the HP turbine  44  from the HP-turbine-power-correcting-means  16  to calculate the internal efficiency η HP  of the HP turbine  44  based on Expressions (4) and (5).  
      Incidentally, an accuracy of the internal efficiency η HP  of the HP turbine  44  calculated by the heat-exchange-on-heater-calculating-means  14  can be calculated using error propagation expression (6) derived from Expression (4). 
 
|δη HP /η HP   |=|W   HP   /W   HP   |+|δΔh   HPad   /Δh   HPad   |+|δG   HP   /G   HP |  (6) 
 
      Here, the accuracy of the internal efficiency η HP  of the HP turbine  44  is calculated by substituting assumptive conditions into Expression (6) and the calculation result is represented by Expression (7). 
 
|δ W   HP   /W   HP |=0.5% 
 
|δΔ h   HPad   /Δh   HPad |=0.4% 
 
|δ G   HP   /G   HP |=0.7% 
 
|δη HP /η HP |=(0.5 2 +0.4 2 +0.7 2 ) 1/2 =0.9%  (7) 
 
      Further, the HP-turbine-internal-efficiency-calculating-means  17  sends the calculated internal efficiency η HP  of the HP turbine  44  to the plant-state-optimizing-means  24 .  
      Next, the steam-condition-on-LP-turbine-inlet-calculating-means  18  calculates the flow rate of the steam at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . In general, the steam passed through the HP turbine  44  is in a wet state, so the steam is lead to the hygroscopic moisture separator  50  and the moisture of the steam are removed by the hygroscopic moisture separator  50 . Hence, the dryness of the steam lead to the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is influenced.  
      In the nuclear power plant  26  of  FIG. 2 , the extraction port is provided to the steam pipe  48  between the HP turbine  44  and the hygroscopic moisture separator  50 , and the extracted steam is lead to the second heater  51   b  and drain generated in the hygroscopic moisture separator  50  and drain at the outlet of the first heater  51   a  are also lead to the second heater  51   b  and used for heat exchange with feedwater.  
      Then, in step S 10 , the steam-condition-on-LP-turbine-inlet-calculating-means  18  calculates hygroscopic moisture separation efficiency of the hygroscopic moisture separator  50 , that is, a rate of moisture that can be separated from the moisture content of the steam, for calculating the quantity of drain that is separated in the hygroscopic moisture separator  50 .  
      The hygroscopic moisture separation efficiency of the hygroscopic moisture separator  50  can be calculated based on design information of the hygroscopic moisture separator  50  in accordance with the flow rate of the steam at the inlet of the hygroscopic moisture separator  50 . That is, the hygroscopic moisture separation efficiency is expressed as the function regarding as the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  or related with the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  in a table.  
      Further, the flow rate of the steam at the outlet  72  of the HP turbine  44  is the sum of the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  and the flow rate of the extracted steam lead to the second heater  51   b . Hence, the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  can be expressed by using the flow rate of the extracted steam lead to the second heater  51   b  indicated as a parameter and vice versa.  
      Then, the steam-condition-on-LP-turbine-inlet-calculating-means  18  calculates the hygroscopic moisture separation efficiency of the hygroscopic moisture separator  50  using the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  indicated as a parameter based on the function or table as design information of the hygroscopic moisture separator  50 .  
      Next, in step S 11 , the steam-condition-on-LP-turbine-inlet-calculating-means  18  calculates the quantity of drain separated from the steam in the hygroscopic moisture separator  50  using the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  as a parameter by multiplying the hygroscopic moisture separation efficiency of the hygroscopic moisture separator  50  calculated in step S 10  by the flow rate of the steam at the inlet of the hygroscopic moisture separator  50 .  
      Further, the steam-condition-on-LP-turbine-inlet-calculating-means  18  calculates the dryness of the steam at the outlet of the hygroscopic moisture separator  50  based on the quantity of drain separated from the steam in the hygroscopic moisture separator  50 , and the flow rate of steam at the inlet of the hygroscopic moisture separator  50  using the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  as a parameter.  
      The steam-condition-on-LP-turbine-inlet-calculating-means  18  executes a heat balance calculation regarding as the heat quantity of the drain separated from the steam in the hygroscopic moisture separator  50 , and the heat quantity of the steam at the inlet of the hygroscopic moisture separator  50  to calculate the flow rate of the steam at the outlet of the hygroscopic moisture separator  50  using the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  as a parameter.  
      At this time, the temperatures or pressures of the drain and the steam necessary for calculating the flow rate of the steam at the outlet of the hygroscopic moisture separator  50  is measured by the plant data measuring system  30  and the measured value is input to the steam-condition-on-LP-turbine-inlet-calculating-means  18 .  
      Next, in step S 12 , the steam-condition-on-LP-turbine-inlet-calculating-means  18  calculates the flow rate of the extracted steam lead to the second heater  51   b . The flow rate of the extracted steam lead to the second heater  51   b  can be calculated through the heat balance calculation using the heat quantity received by the feedwater in the second heater  51   b , the heat quantity of the drain, and the heat quantity of the extracted steam, similar to the calculation of the flow rate of the extracted steam lead to the first heater  51   a.    
      Thus, the flow rate of the extracted steam lead to the second heater  51   b , the flow rate of the steam at the inlet of the hygroscopic moisture separator  50 , the dryness of the steam at the outlet of the hygroscopic moisture separator  50 , and the flow rate of the steam at the outlet of the hygroscopic moisture separator  50  can be calculated using the flow rate of the drain at the hygroscopic moisture separator  50  which is calculated using the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  as a parameter in steps S 10  to S 12 .  
      At this time, the steam-condition-on-LP-turbine-inlet-calculating-means  18  receives data such as the temperatures or pressures of the extracted steam, feedwater, and drain necessary for calculating the flow rate of the steam at the inlet of the hygroscopic moisture separator  50  from the plant data measuring system  30 , and receives the enthalpies or specific enthalpies of the feedwater or drain from the heat-exchange-on-heater-calculating-means  14 . Further, as the specific enthalpy of the extracted steam at the inlet of the second heater  51   b , the specific enthalpy of the steam at the outlet  72  of the HP turbine  44  may be used.  
      Further, in the nuclear power plant  26  of  FIG. 2 , the extraction port is provided to the steam pipe  48  between the hygroscopic moisture separator  50  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and the extracted steam is lead to the RFP turbine  54  and used as a power source.  
      Thus, the steam-condition-on-LP-turbine-inlet-calculating-means  18  calculates the flow rate of the steam at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  using the flow rate G RFPT  of the extracted steam lead to the RFP turbine  54  as a parameter. There, the flow rate G RFPT  of the extracted steam lead to the RFP turbine  54  can be calculated through energy balance calculation at the RFP turbine  54  similar to the flow rate of the extracted steam lead to the second heater  51   b  and thus can be finally calculated by solving the energy balance calculation expression on the RFP turbine  54 .  
      Then, the steam-condition-on-LP-turbine-inlet-calculating-means  18  sends the dryness, temperature, pressure, and flow rate of the steam at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the LP-turbine-power-calculating-means  21 .  
      Next, in step S 13 , the data-calculating-means  19  calculates the internal efficiency η RFPT  of the RFP turbine  54  for a subsequent process of determining whether or not a plant state is optimized. Here, the power W RFPT  of the RFP turbine  54  is calculated by Expression (8). 
 
 W   RFPT =η RFPT   ·G   RFPT   ·Δh   RFPT   (8) 
 
      Where  
      W RFPT : Power of RFP turbine  
      η RFPT : internal efficiency of RFP turbine  
      G RFPT : flow rate of the extracted steam at the inlet of the RFP turbine  
      Δh RFPT : adiabatic heat drop of RFP turbine  
      That is, similar expression to Expression (3) of the power W HP  pf the HP turbine  44  is used. Here, the power W RFPT  of the RFP turbine  54  is considered to be equal to a power of the reactor feedwater pump  52 , that is, the pressurization energy which the feedwater acquires in the reactor feedwater pump  52 . Hence, the pressurization energy which the feedwater acquires in the reactor feedwater pump  52  is measured by the plant data measuring system  30  to calculate the power W RFPT  of the RFP turbine  54 . In addition, the internal efficiency η RFPT  of the RFP turbine  54  can be calculated using the flow rate of the extracted steam lead to the RFP turbine  54  based on Expression (8).  
      Here, as the flow rate G RFPT  of the extracted steam at the inlet of the RFP turbine  54 , a measured value or a value based on a design value of the RFP turbine  54  may be used. Further, the adiabatic heat drop Δh RFPT  of the RFP turbine  54  can be calculated based on the temperature, pressure, and dryness of the extracted steam at the inlet of the RFP turbine  54  and the pressure of the extracted steam at the outlet using the steam table.  
      The specific enthalpy of the extracted steam at the inlet of the RFP turbine  54  is equal to the specific enthalpy at the outlet of the hygroscopic moisture separator  50  calculated in step S 11 , and the temperature and pressure of the extracted steam at the inlet of the RFP turbine  54  and the pressure of the extracted steam at the outlet of the RFP turbine  54  can be calculated based on the value measured by the plant data measuring system  30 .  
      Incidentally, the power W RFPT  of the RFP turbine  54  may be a measured value or a value based on a design value of the RFP turbine  54 .  
      The data-calculating-means  19  sends the calculated internal efficiency η RFPT  of the RFP turbine  54  to the plant-state-optimizing-means  24 .  
      In step S 14 , the data-calculating-means  19  calculates the heat quantity received by the steam in the reactor  40 . The heat quantity received by the steam in the reactor  40  may be calculated as a difference between the enthalpy of the feedwater and the enthalpy of the steam based on the temperature and pressure of feedwater at the inlet of the reactor  40  and the temperature, pressure, and dryness of the steam at the outlet of the reactor  40  based on the steam table.  
      Hence, the plant data measuring system  30  measures the temperature and pressure of the feedwater at the inlet of the reactor  40  and the temperature, pressure, and dryness of the steam at the outlet of the reactor  40 , and the data-calculating-means  19  receives from the plant data measuring system  30  the temperature and pressure of feedwater at the inlet of the reactor  40  and the temperature, pressure, and dryness of the steam at the outlet of the reactor  40 .  
      The data-calculating-means  19  sends the obtained heat quantity received by the steam to the plant-state-optimizing-means  24 . The data-calculating-means  19  requests the LP-turbine-selecting-means  20  to select the LP turbine  45  of which the internal efficiency η LP  is to be calculated.  
      Next, in step S 15 , the LP-turbine-selecting-means  20  determines the LP turbine  45  of which the internal efficiency η LP  is to be calculated in response to the request from the data-calculating-means  19 , and requests the LP-turbine-power-calculating-means  21  to calculate a power of the selected LP turbine  45 . Here, the calculation is executed on the assumption that the internal efficiencies η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are equal. Thus, the LP-turbine-selecting-means  20  selects all of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      Next, in step S 16 , the LP-turbine-power-calculating-means  21  sets assumptive reference expansion line of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  in the h-s diagram in response to the request to calculate each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  from the LP-turbine-selecting-means  20 .  
      The LP-turbine-power-calculating-means  21  first calculates the specific enthalpy of the steam at the inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  based on the temperature, pressure, and dryness, which are supplied from the steam-condition-on-LP-turbine-inlet-calculating-means  18 , of the steam at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to plot points on the constant-pressure lines and the steam pressure at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the h-s diagram. Then, the LP-turbine-power-calculating-means  21  sets a reference expansion line A 1  using an arbitrary method based on the designed reference expansion line passing through the plotted points and provided as design information. For example, it is possible to set a curve similar to the designed reference expansion line or an approximate reference expansion line serving as a high-order curve.  
      For executing the calculation in steps S 17  to S 23  described below, the pressure at each point of the first extraction port  83  to the fourth extraction port  86 , and the first drain catcher  87   a , the third drain catcher  87   c , and the fifth drain catcher  87   e  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and the pressure and temperature at each outlet  82  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are measured by the plant data measuring system  30  and input to the LP-turbine-power-calculating-means  21 .  
      That is, the pressures and temperatures at the inlet and outlet of each of plural stage groups obtained by dividing each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  at the points of the first extraction port  83  to the fourth extraction port  86 , and the first drain catcher  87   a , the third drain catcher  87   c , and the fifth drain catcher  87   e  are measured.  
      Incidentally, the second drain catcher  87   b  and the fourth drain catcher  87   d  are placed near the third extraction port  85  and the fourth extraction port  86  respectively unlike the first drain catcher  87   a , the third drain catcher  87   c , and the fifth drain catcher  87   e . Hence, as for the second drain catcher  87   b  and the fourth drain catcher  87   d , the incidental steam on removing the drain may not be taken into account. Therefore, the heat balance calculations on the second drain catcher  87   b  and the fourth drain catcher  87   d  are executed together with those on the third extraction port  85  and the fourth extraction port  86  respectively.  
      Here, a method of calculating each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  using the drain quantity caught by the drain catcher  87  will be described.  
       FIG. 9  shows an example of a reference expansion line and a corrected expansion line of the LP turbines  45   a ,  45   b  and  45   c  in the h-s diagram assumed in the flowchart of  FIG. 8 .  
      In  FIG. 9 , the ordinate represents a specific enthalpy, and the abscissa represents a specific entropy. In  FIG. 9 , the dashed line represents each reference expansion line A 1  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and the solid line represents each corrected expansion line A 2  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      Further, the pressures of the steam at each inlet and outlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are denoted by p in  and p out  respectively, and the pressures at the points of the first drain catcher  87   a  to the fifth drain catcher  87   e  are denoted by p 1 , p 2 , . . . , p 5 , respectively. The point on the constant-pressure line indicating the pressure at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is denoted by pt in .  
      The LP-turbine-power-calculating-means  21  calculates the intersections pt 1 , pt 2 , . . . , pt 5 , pt out  between the reference expansion line A 1  and each constant-pressure line of the pressures p 1 , p 2 , . . . , p 5 , p out  received from the plant data measuring system  30 , by which each specific enthalpy of the steam at each point of the first drain catcher  87   a  to the fifth drain catcher  45   c  and each outlet  82  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be assumed.  
      Incidentally, the adiabatic heat drop of the steam between each inlet and outlet  82  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are calculated based on the specific enthalpy at each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the pressure Pout at each outlet  82  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  received from the plant data measuring system  30  to determine the point pt out  corresponding to the outlet  82  of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  by multiplying each design internal efficiency of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  by the adiabatic heat drop. The line connecting between the point pt in  corresponding to each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the point pt out  corresponding to each outlet  82  may be assumed as the reference expansion line A 1  by the LP-turbine-power-calculating-means  21 .  
      Next, the LP-turbine-power-calculating-means  21  divides each inside of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  based on the reference expansion line A 1  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  of  FIG. 9  into stage groups among the points pt in , pt 1 , pt 2 , . . . , pt 5 , pt out . The stage group reference turbine efficiencies η b1 , η b2 , . . . , η b6  as the respective turbine efficiencies in stage groups are calculated from Expression (9) as the general expression of the turbine efficiency by the LP-turbine-power-calculating-means  21 . 
 
η bn   =Δh   bn   /Δh   bnad   (9) 
 
      where  
      η bn : stage group reference turbine efficiency  
      Δh bn : effective heat drop of steam between points  
      Δh bnad : adiabatic heat drop of steam between points  
      Here, in the first drain catcher  87   a  to the fifth drain catcher  87   e  of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , the drain is separated from the steam, and so the dryness of the steam at downstream of each of the first drain catcher  87   a  to the fifth drain catcher  87   e  increases from that at upstream thereof. Hence, in practice, the steam expansion line is a curve having steps as indicated by the corrected expansion line A 2  of  FIG. 9 .  
      First, the dryness is increased in each of the first drain catcher  87   a  to the fifth drain catcher  87   e , so the stage-group-corrected-turbine-efficiencies η c1 , η c2 , . . . , η c6  as the turbine efficiencies in stage groups c 1 , c 2 , . . . , c 6  between the points pt in , pt 1 , pt 2 , . . . , pt 5 , pt out  based on the corrected expansion line A 2  of the steam are improved as compared with the stage-group-reference-turbine-efficiencies η b1 , η b2 , . . . , η b6  in respective stage groups.  
      Accurately, the turbine efficiency η b1  is equal to the turbine efficiencyη c1 , so pt 1  corresponds to pt clout  in  FIG. 9 .  
      Here, a regular relation based on the design information of the LP turbine  45  is established between the stage-group-corrected-turbine-efficiencies η c1 , η c2 , . . . , η c6  and the stage-group-reference-turbine-efficiencies η b1 , η b2 , . . . , η b6  in the respective stage groups c 1 , c 2 , . . . , c 6  based on the corrected expansion line A 2  of the steam. For example, a relation of Expression (10) is stabilized between the stage group corrected turbine efficiency η c3  and the stage group reference turbine efficiency η b3 . 
 
η c3 =η b3 {1 −C 1·( m   c3in   +m   c3out )/2}/{1 −C 2 ·( m   pt2   +m   pt3 )/2}  (10) 
 
      where  
      m c3in : wetness at inlet of the stage group c 3   
      m c3out : wetness at outlet of the stage group c 3   
      m pt2: wetness at point pt   2    
      m pt3 : wetness at point pt 3    
      C 1 , C 2 : constants based on design information of the LP turbine.  
      In the LP turbine  45  of  FIG. 5 , C 1 =C 2 =about 0.87.  
      In this case, m pt2  and m pt3  can be calculated based on the assumed reference expansion line A 1 . Further, provided that values of the dryness at the points pt c3out  and pt c3in  are represented by x c3out  and x c3in  respectively, the sum of x c3out  and m c3out  and the sum of x c3in  and m c3in  are equal to 1 respectively. Hence, if the dryness x c3in  at the inlet of the stage group c 3  has been known, the stage group corrected turbine efficiency η c3  is represented by the function using m c3out  as a parameter.  
      Thus, the dryness x c3out  at the outlet of the stage group c 3  and the stage group corrected turbine efficiency η c3  can be calculated by repeating the calculation of Expressions (11-1), (11-2), and (11-3) using m c3out  as a parameter. 
 
 h   c3out   =f   h ( p   3   , m   c3out )  (11-1) 
 
η c3   =f   η ( m   c3out )  (11-2) 
 
 h   c3outcal   =h   c3in −η c3  ( h   c3in   −h   c3outad )  (11-3) 
          where     h c3out : specific enthalpy of steam at outlet of stage group c 3      f h : function for calculating specific enthalpy of steam based on pressure and wetness     f η : function for calculating stage group corrected turbine efficiency based on wetness     h c3in : specific enthalpy of steam at inlet of stage group c 3      h c3outcal : calculated value of specific enthalpy of steam at outlet of stage group c 3  based on turbine efficiency calculation expression     h c3outad : specific enthalpy of steam at outlet of stage group c 3  on the assumption that the steam is subjected to isentropic change.        

      That is, m c3out  is changed to repeat calculation until the right term of Expression (11-1) equals the right term of Expression (11-3) to thereby calculate the dryness x c3out  and the stage group corrected turbine efficiency η c3 . If the specific enthalpy h c3in  at the inlet of the stage group  3  is known, h c3outad  can be derived from the h-s diagram.  
      Similar expressions are established between the stage group corrected turbine efficiencies η c1 , η c2 , . . . , η c6  and the stage group reference turbine efficiencies η b1 , η b2 , . . . , η b6  respectively. Hence, if the dryness and pressure or specific enthalpy at the inlet of each stage group is known, the dryness at the outlet can be calculated to obtain the specific enthalpy at the outlet.  
      Therefore, in order to obtain the corrected expansion line A 2 , the values of the dryness at the inlet of each of the stage groups c 1 , c 2 , . . . , c 6 , that is, each variation of the dryness at the first drain catcher  87   a  to the fifth drain catcher  87   e  should be calculated.  
      Next, in step S 17 , the LP-turbine-power-calculating-means  21  calculates the flow rate of each extracted steam lead to the gland steam vaporizer  56  and the third heater  51   c  from the first LP turbine  45   a  to the third LP turbine  45   c  through the heat balance calculation. That is, similar to the extracted steam of the HP turbine  44 , the heat quantity of each extracted steam lead from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the third heater  51   c  and the gland steam vaporizer  56  can be calculated based on the heat quantities that the condensate water receives in the third heater  51   c  and the gland steam vaporizer  56 , and the heat quantities of the drain and steam generated in the third heater  51   c  and the gland steam vaporizer  56 .  
      Next, in step S 18 , the LP-turbine-power-calculating-means  21  calculates the flow rate of each extracted steam lead from the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the fourth heater  51   d  similar to step S 17  through the heat balance calculation.  
      Next, in step S 19 , the LP-turbine-power-calculating-means  21  calculates the quantity of drain separated from the steam in the first drain catcher  87   a . Here, the hygroscopic moisture separation efficiencies in the first drain catcher  87   a  to the firth drain catcher  87   e  are organized into databases or functions serving as design information beforehand respectively.  
      For example, the hygroscopic moisture separation efficiency ε of the first drain catcher  87   a  is expressed as the function using the pressure of the stream on the downstream side of the first drain catcher  87   a , i.e. p 1  of  FIG. 9  as indicated by Expression (12). 
 
ε= f   ε ( p   1 )  (12) 
 
      Further, the flow rates of the drain and the steam separated by the first drain catcher  87   a  are expressed by Expression (13) using a constant C 3  obtained from the design information of the first drain catcher  87   a.  
 
 G   D.drain =( C 3/100) G   clout (1 −x   clout )+ G   clout (1 −x   clout ) ·ε
 
 G   D.steam =( C 3/100)· G   clout   ·x   clout  
 
 G   D   =G   D.drain   +G   D.steam   (13) 
          Where     G D.drain : flow rate of drain separated by the first drain catcher     G D.steam : flow rate of steam separated by the first drain catcher     G D : total flow rate of drain and extracted steam separated by the first drain catcher     G clout  flow rate of steam at outlet of stage group c 1      C 3 : constant derived from design information of the first drain catcher        

      Further, the flow rate G MRD  of the incidental steam generated in the first drain catcher  87   a  is expressed by Expression (14). 
 
 G   MRD =( C 3/100)· G   clout   (14) 
 
      Further, a specific enthalpy of the drain and the steam separated in the first drain catcher  87   a  is expressed by Expression (15). 
 
 h   D =( h′   clout   ·G   D.drain   +h″   clout   ·G   D.steam )/· G   D  
 
 h′   clout   =f   h′ ( p   1 ) 
 
 h″   clout   =g   h″ ( p   1 )  (15) 
          where     h D : specific enthalpy of drain and steam separated in the first drain catcher     h′ clout : specific enthalpy of saturated water at outlet of stage group c 1      h″ clout : specific enthalpy of saturated steam at outlet of stage group c 1         

      Further, the flow rate of the steam from which the drain is removed by the first drain catcher  87   a , that is, the steam at the inlet of the stage group c 2  is expressed by Expression (16). 
 
 G   c2in.drain   =G   clout ·(1 −x   clout )− G   D.drain  
 
 G   c2in.steam   =G   clout   ·x   clout   −G   D.steam  
 
 G   c2in   =G   c2in.drain   +G   c2in.steam   (16) 
          where     G c2in.drain : flow rate of drain component in steam at the inlet of the stage group c 2      G c2in.steam : flow rate of steam component in steam at the inlet of the stage group c 2      G c2in : total flow rate of steam at the inlet of the stage group c 2         

      Further, the dryness x c2in  of the steam at the inlet of the stage group c 2  is expressed by Expression (17). 
 
 x   c2in   =G   c2in.steam   /G   c2in   (17) 
 
      Further, the specific enthalpy h c2in  and specific entropy S c2in  of the steam at the inlet of the stage group c 2  are expressed as the function of the point pt 1 , that is, the pressure p 1  of the steam at the inlet of the stage group c 2  and the dryness x c2in  of the steam at the inlet of the stage group c 2 , as indicated by Expression (18). 
 
 h   c2in   =f   hC2in ( p   1   , x   c2in ) 
 
 s   c2in   =g   sC2in ( p   1   , x   c2in )  (18) 
 
      Hence, the LP-turbine-power-calculating-means  21  can calculate the flow rates G D.drain , G D.steam , and G D  of the drain and steam separated by the first drain catcher  87   a , the total specific enthalpy h D  of the drain and steam, the flow rate G MRD  of the incidental steam generated in the first drain catcher  87   a , the flow rate G C2in , the dryness x c2in , the specific enthalpy h c2in , and the specific entropy s C2in  of the steam at the inlet of the stage group c 2 , can be calculated using the pressure p 1  on the downstream side from the first drain catcher  87   a  based on Expressions (12), (13), (14), (15), (16), (17), and (18).  
      Next, in step S 20 , the LP-turbine-power-calculating-means  21  calculates the stage group corrected turbine efficiency η c2  of the stage group c 2  through the repeated calculation of Expressions (11-1), (11-2), and (11-3) using the dryness x C2in  of the steam at the inlet of the stage group c 2 , and calculates the specific enthalpy h C2out  of the steam at the outlet of the stage group c 2 . Further, similar to steps S 18  and S 19 , the LP-turbine-power-calculating-means  21  calculates the quantity of the drain in the second drain catcher  87   b , and the flow rate of the extracted steam lead from each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the fifth heater  51   e  through the heat balance calculation. Hence, the total flow rate G C3in , the dryness x C3in , and the specific enthalpy h C3in  of the steam at the inlet of the stage group c 3  can be calculated.  
      Next, in step S 21 , similar to step S 19 , the LP-turbine-power-calculating-means  21  calculates the flow rates of the drain and steam separated by the third drain catcher  87   c , the total specific enthalpy of the drain and steam, the flow rate of the incidental steam generated in the third drain catcher  87   c , and the flow rate, the dryness, the specific enthalpy, and the specific entropy of the steam at the inlet of the subsequent stage group based on the pressure on the downstream side of the third drain catcher  87   c  in accordance with Expressions (12), (13), (14), (15), (16), (17), and (18).  
      Next, in step S 22 , similar to step S 20 , the LP-turbine-power-calculating-means  21  calculates the quantity of drain separated by the fourth drain catcher  87   d  and the flow rate of the extracted steam lead to the sixth heater  51   f  from each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  through the heat balance calculation. Here, the drain generated in each of the sixth heater  51   f  and the fifth heater  51   e  is lead to the common drain tank  60 . When the drain from the sixth heater  51   f  and drain from the fifth heater  51   e  are mixed in the drain tank  60 , the steam is generated. The steam generated in the drain tank  60  is lead to the sixth heater  51   f  and the rest drain component is lead to the drain condenser  53 .  
      Then, the data-calculating-means  19  executes the heat balance calculation on the drain tank  60 . The heat quantity of the drain lead from each of the sixth heater  51   f  and the fifth heater  51   e  to the drain tank  60  is calculated based on the specific enthalpy of the drain calculated in step S 2  by the heat-exchange-on-heater-calculating-means  14 .  
      Further, the flow rate of the drain flowing from the sixth heater  51   f  to the drain tank  60  is sufficiently lower than the flow rate of the drain flowing from the fifth heater  51   e  to the drain tank  60 , and the internal pressure of the drain tank  60  may be made approximate to the pressure of the sixth heater  51   f.    
      Then, the dryness of the steam in the drain tank  60  can be calculated based on the steam table in accordance with the heat quantity and pressure of the steam flowing into the drain tank  60 . Further, the heat quantity of the steam lead to the sixth heater  51   f  and the heat quantity of the drain lead into the drain condenser  53  can be calculated based on the dryness of the steam in the drain tank  60 .  
      Next, in step S 23 , as in step S 19 , the LP-turbine-power-calculating-means  21  can calculate the flow rates of the drain and steam separated by the fifth drain catcher  87   e , the total specific enthalpy of the drain and the steam, the flow rate of the incidental steam generated in the fifth drain catcher  87   e , and the flow rate, the dryness, the specific enthalpy, and the specific entropy of the steam at each outlet  82  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  using the pressure on the downstream side of the fifth drain catcher  87   e  based on Expressions (12), (13), (14), (15), (16), (17), and (18).  
      As a result, the corrected expansion line A 2  from the inlet to the outlet  82  of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be obtained by the LP-turbine-power-calculating-means  21 . that is, the LP-turbine-power-calculating-means  21  calculates the specific enthalpies, degrees of dryness, and flow rates of the steam at the inlet and outlet of each stage group by repeating the acquisition of the specific enthalpy and dryness of the steam at the inlet of stage groups from each inlet of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , the calculation of the stage group corrected turbine efficiency based on the stage group reference turbine efficiency, the calculation of the specific enthalpy and dryness of the steam at the outlet of the stage group, the calculation of the flow rate and the specific enthalpy of the extracted steam or drain, and the calculation of the specific enthalpy and the dryness of the steam at the inlet of the next stage group.  
      Incidentally, as a result of calculating the stage group corrected turbine efficiency η c2  on the downstream side of the first drain catcher  87   a , that is, at the stage group c 2 , the stage group corrected turbine efficiencyη c2  of the stage group c 2  shows 0.3% increase over the stage group reference turbine efficiencyη b2  of the stage group c 2 . Likewise, the stage group corrected turbine efficiencies η c3 , η c4 , η c5 , and η c6  of the stage groups c 3 , c 4 , c 5 , and c 6  show 0.8%, 1.7%, 4.0%, and 6.3% increases over the stage group reference turbine efficiencies η b3 , η b4 , η b5 , and η b6  of the stage groups c 3 , c 4 , c 5 , and c 6  respectively.  
      Hence, as in the nuclear power plant  26 , when there are the drain catchers  87  or the extraction ports  83 ,  84 ,  85 , and  86  in the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , unlike the thermal power plant, it is necessary to correct each internal efficiencyη LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  in consideration of the drain catchers  87  in order to improve the accuracy.  
      Next, in step S 24 , the LP-turbine-power-calculating-means  21  calculates each exhaust loss of the steam in the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , that is, each velocity energy of the steam not used for the rotation of the turbine blade in the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , similarly to the case of the HP turbine  44 .  
      The exhaust loss of the steam can be calculated based on the flow rate of the steam at each outlet  82  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and the sectional area at each outlet  82  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  similarly to the exhaust loss of the steam at the outlet  72  of the HP turbine  44 .  
      Next, in step S 25 , the LP-turbine-power-calculating-means  21  calculates each power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . That is, the LP-turbine-power-calculating-means  21  calculates the stage group power serving as the power of each stage group of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . Each stage group power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is calculated as the product of the effective heat drop between the outlet and inlet of each stage group by the flow rate of the steam at the inlet of each stage group. For example, the stage group power W c3  of the stage group c 3  may be derived from Expression (19). 
 
 W   c3   =G   c3in ·( h   c3in   −h   c3out )  (19) 
 
      The LP-turbine-power-calculating-means  21  calculates the stage group power in each stage group based on Expression (19) and adds the calculation results to thereby acquire the total calculated power value W LPcal  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . Then, the LP-turbine-power-calculating-means  21  sends the calculated power value W LPcal  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the LP-turbine-power-correcting-means  22 .  
      On the other hand, the stage group efficiency as efficiency of each stage group of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be expressed as a ratio between an effective heat drop and adiabatic heat drop between an output and an inlet of each stage group. For example, the stage group efficiency η c3  of the stage group c 3  can be calculated based on Expression (20) using the effective heat drop UE c3  and the adiabatic heat drop AE c3  of the stage group c 3 . 
 
η c3   =UE   c3   /AE   c3 =( h   c3in   −h   c3out )/( h   c3in   −h   c3outad )  (20) 
 
      The LP-turbine-power-calculating-means  21  calculates each stage group efficiency of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  based on Expression (20) to supply the calculation result to the LP-turbine-internal-efficiency-calculating-means  23 .  
      Next, in step S 26 , the LP-turbine-power-correcting-means  22  receives the total power W TOTAL  of the nuclear power plant  26  measured by the generator power sensor  29 , receives the measured shaft torque value F of the HP turbine  44  from the shaft torque sensor  27 , and subtracts a value, which is assumed as the power W HP  of the HP turbine  44 , obtained by multiplying the measured shaft torque value F of the HP turbine  44  by the power generation efficiency η from the total power W TOTAL  of the nuclear power plant  26  to thereby indirectly acquire the measured power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      That is, provided that the total power of the nuclear power plant  26  is represented by W TOTAL , the power of the HP turbine  44  is represented by W HP , and the power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is represented by W LP , Expression (21) is established. 
 
 W   LP   =W   TOTAL   −W   HP   (21) 
 
      Accordingly, if the power W HP  of the HP turbine  44  is equal to a value obtained by multiplying the measured shaft torque value F of the HP turbine  44  by the power generation efficiency η, Expression (22) is established. 
 
 W   LPact   =W   TOTAL    −F×η   (22) 
 
      Hence, if the measured shaft torque value F of the HP turbine  44  is measured, the measured power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be indirectly acquired. The LP-turbine-power-correcting-means  22  indirectly acquires the measured power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  based on the measured shaft torque value F of the HP turbine  44  and the total power W TOTAL  of the nuclear power plant  26  using Expression (22).  
      Further, the LP-turbine-power-correcting-means  22  determines whether or not a ratio between the measured power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the calculated power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is within the threshold value ε LP . 
 
| W   LPcal   /W   LPact −1|&lt;ε LP   (23) 
 
      Further, if it is determined that the ratio between the measured power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the calculated power value W LPcal  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is not within the threshold value ε LP , the LP-turbine-power-correcting-means  22  sends a request to correct the reference expansion line A 1  in the h-s diagram to the LP-turbine-power-calculating-means  21  and causes the LP-turbine-power-calculating-means  21  to execute recalculation to thereby correct the measured power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      In this case, in step S 16 , the LP-turbine-power-calculating-means  21  adds the variation calculated based on the Newton&#39;s method to the efficiency of the reference expansion line A 1  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to thereby correct the reference expansion line A 1 . Then, the LP-turbine-power-calculating-means  21  calculates the power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  again based on the corrected reference expansion line A 1 .  
      Thus, the LP-turbine-power-calculating-means  21  repeats calculating the power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  until the ratio between the measured power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the calculated power value W LPcal  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  becomes within the threshold value ε LP .  
      Then, the LP-turbine-power-correcting-means  22  sends an instruction to calculate one internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the LP-turbine-internal-efficiency-calculating-means  23  if it is determined that the ratio between the measured power value W LPact  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the calculated power value W LPcal  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is within the threshold value ε LP .  
      Thus, in step S 27 , the LP-turbine-internal-efficiency-calculating-means  23  calculates the corresponding total internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  based on the stage group efficiency, which is received from the LP-turbine-power-calculating-means  21 , of each stage group of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  in response to the instruction to calculate the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  from the LP-turbine-power-correcting-means  22  in step S 27 .  
      The internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  may be defined as a ratio between the total value Σ (UE) of the effective heat drops in the stage groups and the total value Σ (AE) of the adiabatic heat drops in the stage groups. Therefore, the LP-turbine-internal-efficiency-calculating-means  23  calculates the ratio between the total value Σ (UE) of the effective heat drops in the stage group and the total value Σ (AE) of the adiabatic heat drops in the stage groups based on Expression (24) to determine the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.  
 
η LP =Σ( UE )/Σ( AE )  (24) 
 
      However, the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be arbitrarily defined based on the effective heat drop UE and the adiabatic heat drop AE in each stage group instead of calculation by Expression (24).  
      The LP-turbine-internal-efficiency-calculating-means  23  sends the calculated internal efficiency nLP of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the plant-state-optimizing-means  24 , and requests the LP-turbine-selecting-means  20  to select the LP turbine  45  whose internal efficiency η LP  is next calculated.  
      Thus, in step S 28 , the LP-turbine-selecting-means  20  determines whether or not there is the LP turbine  45  whose internal efficiency η LP  should be calculated. If there is the LP turbine  45  whose internal efficiency η LP  should be calculated, the LP-turbine-selecting-means  20  selects the LP turbine  45  to request the LP-turbine-power-calculating-means  21  to calculate the power.  
      Incidentally, herein, the calculation is executed on the assumption that the internal efficiencies η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are equal to each other. Thus, the LP-turbine-selecting-means  20  determines that there is no LP turbine  45  whose internal efficiency η LP  should be calculated, and notifies the data-calculating-means  19  of the determination result.  
      Next, in step S 29 , the data-calculating-means  19  calculates the enthalpy of the condensate water at the inlet of the drain condenser  53  using the acquired heat quantity of the drain lead from the drain tank  60  to the drain condenser  53  through the heat balance calculation. At this time, necessary data such as the temperature or pressure of feedwater is input from the plant data measuring system  30  to the data-calculating-means  19 .  
      Next, in step S 30 , the data-calculating-means  19  calculates a balance of the drain and steam of the condenser  49 , and a balance of the condensate water between the condenser  49 , the gland steam vaporizer  56 , and the condensate storage tank  55  to calculate the flow rate of the condensate water at the outlet of the condenser  49 , and the flow rate G H1  of the condensate water lead to the reactor  40 , that is, the feedwater. Further, the data-calculating-means  19  executes the heat balance calculation on each heat exchanger of each condensate system (not shown).  
      Here, the flow rate of the steam lead to the condenser  49  may be calculated based on the flow rate of the steam at each outlet  82  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . Further, data that cannot be obtained through the heat balance calculation is measured by the plant data measuring system  30  and input to the data-calculating-means  19 .  
      Then, the data-calculating-means  19  sends the calculated flow rates of the condensate water and feedwater to the plant-state-optimizing-means  24 , and requests the plant-state-optimizing-means  24  to determine whether or not the plant state is optimized.  
      Next, in step S 31 , the plant-state-optimizing-means  24  executes the optimized calculation of the calculated values of the internal efficiencies η HP  and η LP  of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  received from the HP-turbine-internal-efficiency-calculating-means  17  and the LP-turbine-internal-efficiency-calculating-means  23 , the calculated values of the flow rates of the condensate water or feedwater received from the data-calculating-means  19 , the internal efficiency η RFPT  of the RFP turbine  54 , and the heat quantity received by the steam in the reactor  40  in response to the request from the data-calculating-means  19 . That is, the plant-state-optimizing-means  24  calculates probability distributions on the deviation of the calculated values from the respective reference values for the measured values in order to optimize the calculated values including the flow rate of the feedwater with a preset accuracy.  
      Here, reference values of the flow rates of the condensate water and feedwater are set to the measured values of the condensate water and the feedwater acquired by the feed-and-condensate-water-flow rate sensor  28 . A reference value of the heat quantity received by the steam in the reactor  40  is set to the measured value measured by the plant data measuring system  30 . Design values may be used as the reference values of the internal efficiencies η HP  and η LP  of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and the internal efficiency η RFPT  of the RFP turbine  54 .  
      At this time, the plant-state-optimizing-means  24  determines that optimization is impossible if the calculated values including the flow rate of the feedwater are insufficient for acquiring such probability distributions that satisfy desired accuracies. In this case, the plant-state-optimizing-means  24  requests the feed-and-condensate-water-flow-rate-setting-means  13  to reset the flow rate of the feedwater such that the deviations of the calculated values from the reference values is smaller.  
      Whether or not the calculated values including the flow rate of the feedwater are sufficient may be determined based on an arbitrary method, and more specifically, may be determined based on whether or not the data width of each deviation on the probability distributions is larger than the required accuracy ε for each probability distribution.  
      To that end, the process of steps S 1  to S 31  is repeated, and finally, deviations of the calculated values including the flow rate of the feedwater from the respective reference values are calculated to obtain the probability distributions.  
       FIGS. 10A  to  10 C show an example of the probability distribution in the optimized calculation.  
       FIG. 10A  shows the probability distribution of the condensate water flow rate,  FIG. 10B  shows the probability distribution of the feedwater flow rate, and  FIG. 10C  shows the probability distribution of the internal efficiency η LP  of the first LP turbines  45   a ,  45   b  and  45   c . In  FIGS. 10A  to  10 C, the abscissa represents the deviation of each data, and the ordinate represents the probability.  
      As shown in  FIGS. 10A  to  10 C, each probability distribution is assumed to the normal distribution or a probability distribution obtained by integrating the normal distribution statistically. Then, such calculated values that total probability obtained by multiplying the probabilities is maximal are used as the optimized calculated values.  
      Then, the plant-state-optimizing-means  24  calculates the optimized calculated values including flow rate of the feedwater and then determines that the optimized calculation is completed. Then, the optimized calculated values of the internal efficiencies η HP  and η LP  of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are supplied to the performance-deteriorating-element-specifying-means  25  from the plant-state-optimizing-means  24 .  
      Next, in step S 32 , the performance-deteriorating-element-specifying-means  25  calculates differences between calculated values, which are received from the plant-state-optimizing-means  24 , and designed values of the internal efficiency η HP  of the HP turbine  44  and the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and specifies an element having a larger value of the product of the difference between the calculated value and the designed value by the preset degree of distribution as the element that deteriorates performance of the nuclear power plant  26 .  
      That is, the performance-deteriorating-element-specifying-means  25  multiplies the internal efficiency drop as a difference between the calculated value and the designed value of the internal efficiency η HP  of the HP turbine  44  and the internal efficiency drop as a difference between the calculated value and the designed value of the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  by the respective digitalized degrees of contribution at which the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  influence the efficiency of the nuclear power plant  26 .  
      Next, the performance-deteriorating-element-specifying-means  25  compares the product of the internal efficiency drop by the degree of contribution of the HP turbine  44  with the product of the internal efficiency drop by the degree of contribution in the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to determine which product is larger. Further, the performance-deteriorating-element-specifying-means  25  displays the determination result on the output device  12  such as a monitor.  
      Incidentally, it is possible to determine whether or not elements other than the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are the elements that deteriorate performance of the nuclear power plant  26 . For example, the respective degrees of contribution of the heaters  51   a  to  51   f , the RFP turbine  54 , the reactor feedwater pump  52 , and the condenser  49  are set. Further, additionally calculated performance values and calculated values of internal efficiencies of the heaters  51   a  to  51   f , the RFP turbine  54 , the reactor feedwater pump  52 , and the condenser  49  are input. Then, the respective degrees of contribution may be multiplied by the corresponding performance drops as differences between the designed performance values and the calculated performance value, or between the designed internal efficiency and the calculated internal efficiency of the heaters  51   a  to  51   f , the RFP turbine  54 , the reactor feedwater pump  52 , and the condenser  49  to compare the products with the performance drops of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      Incidentally, the internal efficiency drop or performance drop may be a difference between a calculated value and data as a reference such as a performance experiment value as well as the designed value.  
      According to the nuclear power plant thermal efficiency diagnostic system  10 , it is possible to accurately calculate each of the internal efficiencies η HP  and η LP  of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  in the nuclear power plant  26  to diagnose the performance. Thus, according to the nuclear power plant thermal efficiency diagnostic system  10 , it is possible to apply the optimized state evaluating method to the nuclear power plant  26 , and specify the elements that deteriorate performance of the nuclear power plant  26 . As a result, it is possible to determine whether or not an element deteriorating performance of the nuclear power plant  26  is the HP turbine  44  or the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , which contributes to improvements in energy efficiency of the nuclear power plant  26 .  
      In particular, the shaft torque sensor  27  measures the powers of the HP turbine  44  and/or the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to correct the calculated power values W HPcal  and W LPcal  of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to thereby improve each calculation accuracy of the internal efficiencies η HP  and η LP  of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      In practice, the internal efficiencies η HP  and η LP  of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are calculated by using the nuclear power plant thermal efficiency diagnostic system  10  based on the designed values of elements. In this case, it is determined that the internal efficiencyη HP  of the HP turbine  44  can be acquired with the accuracy of 0.11%, and the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be acquired with the accuracy of 0.05%.  
      Incidentally, in the nuclear power plant thermal efficiency diagnostic system  10 , the shaft torque sensor  27  may be provide to each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  as well as the HP turbine  44 . In the case of providing the shaft torque sensor  27  for each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , each calculated power value W LPcal  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be obtained, while the shaft torques can be obtained as the respective measured power values thereof.  
      Further, after calculating the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , the internal efficiency η LP  of the HP turbine  44  may be calculated.  
      Further, it is possible to calculate the temperature, pressure, and flow rates and the like of the condensate water, the feedwater, the steam, the drain, and the extracted steam through the heat balance calculation and measure these values by the plant data measuring system  30 .  
      Further, a part or all of the shaft torque sensor  27 , the condensate-feedwater sensor, and the generator power sensor  29 , and the plant data measuring system  30  may be elements of the nuclear power plant thermal efficiency diagnostic system  10 .  
      On the other hand, some of the elements of the nuclear power plant thermal efficiency diagnostic system  10  may be omitted. For example, it is possible to supply the non-optimized calculated internal efficiencies η LP  and η HP  of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  to the performance-deteriorating-element-specifying-means  25  without providing the plant-state-optimizing-means  24 .  
      Further, as a method of setting a reference power value of the HP turbine  44 , the measured power value of the HP turbine  44  is used, but if the accuracy of the shaft torque sensor  27  is about 1% or more, and the measured power value of the HP turbine  44  cannot be obtained with sufficient accuracy, a value based on the designed value may be used. In this case, the plant-state-optimizing-means  24  receives the calculated power value W HPcal  of the HP turbine  44  from the HP-turbine-power-calculating-means  15 , and receives the calculated power value W LPcal  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  from the LP-turbine-power-calculating-means  21  to be optimized using the measured power values of the HP turbine  44  and the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  as reference values.  
      If it is determined that the calculated power value of the HP turbine  44  cannot be optimized, the plant-state-optimizing-means  24  sends a request to correct the dryness of the steam at the outlet  72  of the HP turbine  44  to the HP-turbine-power-calculating-means  15 , while it is determined that the calculated power value of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  cannot be optimized, the plant-state-optimizing-means  24  sends a request to correct a reference expansion line of the h-s diagram to the LP-turbine-power-calculating-means  21 .  
      Further, the nuclear power plant thermal efficiency diagnostic system  10  is not limited to be applied to a BWR (boiling water reactor) having a structure shown in  FIG. 2  but may be applied to other kinds of nuclear power plants  26  such as a BWR having a structure different from that of the above BWR or a PWR (pressurized water rector) as long as some kind of sensors acquire desired data to execute energy calculation.  
      Hence, when the nuclear power plant of which HP turbine  44  is also provided with the drain catchers  87  as shown in  FIG. 7  similarly to the LP turbine  45  is a target for applying the nuclear power plant thermal efficiency diagnostic system  10 , the HP-turbine-power-calculating-means  15  and the HP-turbine-internal-efficiency-calculating-means  17  may have the functions similar to those of the LP-turbine-power-calculating-means  21  and the LP-turbine-internal-efficiency-calculating-means  23  respectively.  
      Further, in the nuclear power plant thermal efficiency diagnostic system  10 , on calculating the power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , a change in heat quantity of each drain catcher  87  is taken into account, but the power of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  may be calculated without considering the drain catchers  87  insofar as the required accuracy is satisfied. Further, the total internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  can be defined based on other expression than Expression (24).  
      For example, in the case where two extraction ports, first and second extraction ports, are provided to each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and the a change in the heat quantity of each drain catcher  87  is not considered, the power W LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is expressed by Expression (25). 
 
 W   LP   =Δh   LP1ad  ·η LP    G   LP   +Δh   LP2ad ·η LP  ·( G   LP   −G   EXT1 )+Δ h   LP3ad ·η LP  ·( G   LP   −G   EXT1   −G   EXT2 )  (25) 
          Where     Δh LP1ad : adiabatic heat drop of LP turbine (inlet-first extraction port)     Δh LP2ad : adiabatic heat drop of LP turbine (first extraction port-second extraction port)     Δh LP3ad : adiabatic heat drop of LP turbine (second extraction port-outlet)     G LP : flow rate of steam at inlet of LP turbine     G EXT1 : flow rate of extracted steam at first extraction port     G EXT2 : flow rate of extracted steam at second extraction port     η LP : internal efficiency of LP turbine        

      The powers W LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  are values corrected by multiplying the products of the LP turbine adiabatic heat drops Δh LP1ad , Δh LP2ad , and Δh LP3ad  by the flow rates of the steam by the LP turbine internal efficiencies η LP  in consideration of the energy losses consumed in the entropy changes in steam.  
      That is, each internal side of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is divided into three areas at the two extraction ports to calculate the power W LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c . That is, the first term of Expression (25) is a value obtained by multiplying the change of the specific enthalpy of the steam by the LP turbine internal efficiency η LP . The change of the specific enthalpy of the steam is expressed as a product of the LP turbine adiabatic heat drop Δh LP1ad  between each inlet and each first extraction port of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  by flow rate G LP  of the steam at the inlet of the LP turbine. In other words, the first term of Expression (25) is a work load of the steam from the inlet to the first extraction port of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c.    
      Further, a part of the steam is extracted at each first extraction port of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , and thus, the flow rate of the steam from the first extraction port to the second extraction port of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is a value obtained by subtracting the quantity G EXT1  of the extracted steam at the first extraction port from the flow rate G LP  of the steam at the inlet of the LP turbine. Thus, as indicated by the second term of Expression (25), the workload of the steam from the first extraction port to the second extraction port of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is calculated by multiplying the adiabatic heat drop Δh LP2ad  of the LP turbine between the first extraction port and the second extraction port of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the flow rate G LP -G EXT1  of the steam between the first extraction port and the second extraction port by the internal efficiency η LP  of the LP turbine.  
      Likewise, a part of the steam is extracted at each second extraction port of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c , so the flow rate of the steam between the second extraction port to the outlet of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is calculated by subtracting quantities G EXT1  and G EXT2  of the extracted steams at the first extraction port and the second extraction port from the flow rate G LP  of the steam at the inlet of the LP turbine. Hence, as indicated by the third term of Expression (25), the work load of the steam from the second extraction port to the outlet of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is calculated by multiplying the adiabatic heat drop Δh LP3ad  of the LP turbine between the second extraction port and the outlet of each of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  and the flow rate G LP -G EXT1 -G EXT2  of the steam between the second extraction port and the outlet by the internal efficiency η LP  of the LP turbine.  
      The internal efficiency η LP  of the LP turbine is expressed by Expression (26) based on Expression (25). 
 
η LP   =W   LP /{(Δ h   LP1ad   +Δh   LP2ad   +Δh   LP3ad ) G   LP −(Δ h   LP2ad   +Δh   LP3ad ) G   EXT1   −Δh   LP3ad   ·G   EXT2 }  (26) 
 
      Incidentally, the calculation accuracy for when the LP-turbine-internal-efficiency-calculating-means  23  calculates the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  based on Expression (26) can be calculated based on the error propagation expression (27) derived from Expression (26).  
                    δ   ⁢           ⁢       η   LP     /     η   LP              =            δ   ⁢           ⁢       W   LP     /     W   LP              +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad       ⁢       G   LP     /     {       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad       ⁢     G   LP       +     Δ   ⁢           ⁢       h     LP   ⁢           ⁢   2   ⁢   ad       ⁡     (       G   LP     ·     G     EXT   ⁢           ⁢   1         )         +     Δ   ⁢           ⁢       h     LP   ⁢           ⁢   3   ⁢   ad       ⁡     (         G   LP     ·     G     EXT   ⁢           ⁢   1         -     G     EXT   ⁢           ⁢   2         )           }       ⁢          δ   ⁢           ⁢   Δ   ⁢           ⁢       h     LP   ⁢           ⁢   1   ⁢   ad       /   Δ     ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad                +           Δh     LP   ⁢           ⁢   2   ⁢   ad       ⁡     (       G   LP     ·     G     EXT   ⁢           ⁢   1         )       /     {       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad       ⁢     G   LP       +     Δ   ⁢           ⁢       h     LP   ⁢           ⁢   2   ⁢   ad       ⁡     (       G   LP     ·     G     EXT   ⁢           ⁢   1         )         +     Δ   ⁢           ⁢       h     LP   ⁢           ⁢   3   ⁢   ad       ⁡     (         G   LP     ·     G     EXT   ⁢           ⁢   1         -     G     EXT   ⁢           ⁢   2         )           }       ⁢          δ   ⁢           ⁢   Δ   ⁢           ⁢       h     LP   ⁢           ⁢   2   ⁢   ad       /   Δ     ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad                +     Δ   ⁢           ⁢         h     LP   ⁢           ⁢   3   ⁢   ad       ⁡     (         G   LP     ·     G     EXT   ⁢           ⁢   1         -     G     EXT   ⁢           ⁢   2         )       /     {       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad       ⁢     G   LP       +     Δ   ⁢           ⁢       h     LP   ⁢           ⁢   2   ⁢   ad       ⁡     (       G   LP     ·     G     EXT   ⁢           ⁢   1         )         +       Δh     LP   ⁢           ⁢   3   ⁢   ad       ⁡     (         G   LP     ·     G     EXT   ⁢           ⁢   1         -     G     EXT   ⁢           ⁢   2         )         }       ⁢          δ   ⁢           ⁢   Δ   ⁢           ⁢       h     LP   ⁢           ⁢   3   ⁢   ad       /   Δ     ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad                +       (       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           )     ⁢       G   LP     /     {         (       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           )     ⁢     G   LP       -       (       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           )     ⁢     G     EXT   ⁢           ⁢   1         -     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad       ⁢     G     EXT   ⁢           ⁢   2           }       ⁢          δ   ⁢           ⁢       G   LP     /   Δ     ⁢           ⁢     G   LP              +       (       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           )     ⁢       G     EXT   ⁢           ⁢   1       /     {         (       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           )     ⁢     G   LP       -       (       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           )     ⁢     G     EXT   ⁢           ⁢   1         -     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad       ⁢     G     EXT   ⁢           ⁢   2           }       ⁢          δ   ⁢           ⁢       G     EXT   ⁢           ⁢   1       /   Δ     ⁢           ⁢     G     EXT   ⁢           ⁢   1                +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad       ⁢       G     EXT   ⁢           ⁢   2       /     {         (       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           )     ⁢     G   LP       -       (       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         +     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           )     ⁢     G     EXT   ⁢           ⁢   1         -     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad       ⁢     G     EXT   ⁢           ⁢   2           }       ⁢          δ   ⁢           ⁢       G     EXT   ⁢           ⁢   2       /   Δ     ⁢           ⁢     G     EXT   ⁢           ⁢   2                          (   27   )             
 
      Here, the accuracy of the internal efficiency η LP  of the first LP turbine  45   a , the second LP turbine  45   b , and the third LP turbine  45   c  is calculated by substituting assumptive conditions into Expression (27) and the calculation result is represented by Expression (28).  
                      δ   ⁢           ⁢       W   LP     /     W   LP              =     0.5   ⁢   %       ⁢     
     ⁢            δ   ⁢           ⁢   Δ   ⁢           ⁢       h     LP   ⁢           ⁢   1   ⁢   ad       /   Δ     ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢   ad              =     0.4   ⁢   %       ⁢     
     ⁢            δ   ⁢           ⁢   Δ   ⁢           ⁢       h     LP   ⁢           ⁢   2   ⁢   ad       /   Δ     ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad              =     0.4   ⁢   %       ⁢     
     ⁢            δ   ⁢           ⁢   Δ   ⁢           ⁢       h     LP   ⁢           ⁢   3   ⁢   ad       /   Δ     ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad              =     0.4   ⁢   %       ⁢     
     ⁢            δ   ⁢           ⁢       G   LP     /     G   LP              =     1.0   ⁢   %       ⁢     
     ⁢            δ   ⁢           ⁢       G     EXT   ⁢           ⁢   1       /     G     EXT   ⁢           ⁢   1                =     5.0   ⁢   %       ⁢     
     ⁢            δ   ⁢           ⁢       G     EXT   ⁢           ⁢   2       /     G     EXT   ⁢           ⁢   2                =     5.0   ⁢   %       ⁢     
     ⁢       G     EXT   ⁢           ⁢   1       ≈       G   LP     ·   0.1       ⁢     
     ⁢       G     EXT   ⁢           ⁢   2       ≈       G   LP     ·   0.1       ⁢     
     ⁢       Δ   ⁢           ⁢     h     LP   ⁢           ⁢   1   ⁢           ⁢   ad         ≈     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   2   ⁢   ad         ≈     Δ   ⁢           ⁢     h     LP   ⁢           ⁢   3   ⁢   ad           ⁢     
     ⁢                  δ   ⁢           ⁢       η   LP     /     η   LP              =       ⁢     {       0.5   2     +       (       1   /   2.7     ·   0.4     )     2     +       (       0.9   /   2.7     ·   0.4     )     2     +                       ⁢         (       0.8   /   2.7     ·   0.4     )     2     +       (       3   /   2.7     ·   1.0     )     2     +                       ⁢         (       0.2   /   2.7     ·   5.0     )     2     +       (       0.1   /   2.7     ·   5.0     )     2       }       1   /   2                 =       ⁢     1.3   ⁢   %                     (   28   )             
 
     INDUSTRIAL APPLICABILITY  
      The nuclear power plant thermal efficiency diagnostic system, the nuclear power plant thermal efficiency diagnostic program and the nuclear power plant thermal efficiency diagnostic method according to the invention make it possible to specify an element causing deterioration of a power output by making a diagnosis on a thermal efficiency of a nuclear power plant.