Abstract:
A nuclear power plant controlling system is provided in which the thermal limit can be brought close to the full limit of operation restrictions by automatic control. The system includes a thermal limit monitor, including a receiver configured to receive a first signal, a prospective time deriving unit configured to derive a prospective time for the first signal to arrive at the full limit, a judging unit configured to judge a remaining time to the prospective time, a compensating unit configured to compensate the first signal based on a second signal, a first transmitter configured to transmit a first instruction to vary a rate factor of the first and second signals by synchronizing the compensation, and a second transmitter configured to transmit a second instruction to hold the first or second signal after arriving at the full limit or at a threshold that is just before the full limit.

Description:
TECHNICAL FIELD 
     The present invention relates to the controlling nuclear power plant technology by observing a thermal limit. 
     BACKGROUND ART 
     In the boil water type nuclear power plant, the thermal limit such as the minimum critical power ratio and maximum linear heat generation ratio which is an indicator of the soundness of fuel is operated and managed so as not to exceed the full limit. These thermal limits calculated by the power distribution based on reactor physics are made to be observable object substitute for the surface temperature of the fuel since it is difficult to measure directly. 
     These thermal limits are calculated by numerical analysis from distribution of a nuclear reaction cross section, and are calculated with the cycle of several minutes-1 hour by the reactor core performance calculation system with advanced operation throughput. 
     In advanced boiling water reactor power plant, in order to attain and adjust the target reactor power, it is automatically controlled that the drawing out/insertion operation of a control rod and the increase/decrease operation of a core flow. 
     Thus, it is necessary for the automatic control of the reactor power to observe the thermal limit continuously, but it is difficult because the calculation of the power distribution is required several minutes as mentioned above. 
     For this reason, the simple information made by an easy operation with the signal which real-time received from the sensor arranged inside the nuclear reactor is observed continuously instead of the direct observation of the thermal limit. 
     When the simple information arrives at a full limit which is the operation restrictions set up beforehand, the suspend instruction for automation is outputted and then the automatic control for the control rod and the core flow is suspended (for example, Patent Literature 1). 
     CITATION LIST 
     Patent Literatures 
     
         
         Patent Literature 1: JP1976-67898A 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     According to the simple information mentioned above, observation becomes too conservative because the simple information itself originally is lower reliability. Then it brings some subjects that the suspend instruction is outputted with a remarkable margin against the set-up full limit. 
     In many states of the reactor core, an actual thermal limit is much less than the full limit in spite of the simple information arrives at the set-up full limit. For this reason, even when the automatic control of the control rod and the core flow was suspended once, the exact thermal limit calculated by the power distribution might be far from the full limit. Then it brings some subjects that the automatic control operation are forced to resume repeatedly. 
     Thus, in order to resume the automatic control once suspended, it is necessary to reconstruct the status such as an automatic power controller, the control rod operating unit, and a recirculation flow operating unit and the like. Then that make it complicated for the process of power control of the nuclear reactor. 
     That brings some subjects such as increasing workload of the operator for checking operation and so on with resuming the automatic controls, and expanding the adjustment period for the power control of the nuclear reactor. 
     Thus, in the conventional technology, it was difficult to approach the thermal limit close to the full limit of operation restrictions by automatic control. 
     The present invention has been made in consideration of such circumstances. An object of the present invention is to provide the technique for controlling nuclear power plant in which the thermal limit can be approached close to the full limit of operation restrictions by the automatic control, using the simple information which is outputted shorter cycle than that of the thermal limit. 
     Solution to Problem 
     A nuclear power plant controlling system includes: a first signal receiver configured to receive a first signal; a prospective time deriving unit configured to derive a prospective time for the first signal to arrive at a full limit; a judging unit configured to judge a remaining time to the prospective time breaks a preset value and then request a second signal; a compensating unit configured to compensate the first signal based on the second signal received by the request; a first instruction transmitter configured to transmit a first instruction to vary a rate factor of the first signal and the second signal with synchronizing the compensation; and a second instruction transmitter configured to transmit a second instruction to hold the first signal or the second signal after arriving at the full limit or a threshold which right before the full limit. 
     Advantageous Effects of Invention 
     The present invention provides the technique for controlling nuclear power plant in which the thermal limit can be approached close to the full limit of operation restrictions by the automatic control, using the simple information outputted shorter cycle than that of the thermal limit. 
    
    
     
       BRIEF DESCRIPTION OF FIGS 
         FIG. 1  is a schematic diagram showing an embodiment of the nuclear power plant controlling system according to the present invention. 
         FIG. 2  is a horizontal sectional view of the nuclear reactor applied to the embodiment of the present invention. 
         FIG. 3  is a block diagram of the nuclear power plant controlling system concerning to an embodiment. 
         FIG. 4  is an explanatory view of the automatic control by the nuclear power plant controlling system concerning to an embodiment. 
         FIG. 5  is a flow chart explaining operation of the nuclear power plant controlling system concerning to an embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     As shown in  FIG. 1 , nuclear reactor  10  includes, a reactor core  15  for heating a furnace water held at pressure vessel  11 , a steam-water separator  14  for separating the heated furnace water into a steam and a fluid, a main steam line  12  for leading the separated steam to a turbine (not shown), a feed water line  13  for returning a feed water back to the pressure vessel  11  the feed water derives from the steam which worked and expanded in the turbine and then cooled and condensed, a recirculation pump  16  for circulating the furnace water with predetermined core flow F through a downcomer D, a lower plenum L, and a top plenum U the furnace water composed the separated fluid and the feed water joined. 
     As shown in  FIG. 2 , horizontal sectional view of the reactor core  15  is composed of multi-arranging parts such as, a fuel assembly  17  consist of plurality of fuel rods (not shown) stored in a rectangular pipe-like channel box, a control rod  18  for adjusting number of neutrons by neutron absorption and for controlling a reactor power with drawing out/insertion operation by drive  19  ( FIG. 1 ), and an instrumentation pipe  20  in which one set of four pieces of LPRM detector  21  ( FIG. 1 ) arranged in the vertical direction to detect the neutron. 
     As shown in  FIG. 1 , the control device  30  includes, a core performance calculator  31 , an automatic power controller  32 , a control rod operating unit  33 , a recirculation flow operating unit  34 , and a thermal limit monitor  40 . 
     The core performance operation part  31  calculates a thermal limit (a critical power ratio or a linear heat generation ratio) with high precision according to the power distribution based on the detection signal from various sensors set in the nuclear reactor  10 , and then transmits them to the thermal limit monitor  40  as the second signal S 2 . 
     The linear heat generation ratio means a power of per unit length of the fuel rod (not shown) in the fuel assembly  17 . The critical power ratio means a ratio of the power of the fuel assembly  17  in which boiling transition happens (marginal output), and an actual power of the fuel assembly. 
     In the core performance calculator  31 , the calculation cycle of these thermal limits (the second signal S 2 ) is a long cycle (for example, about 30 seconds) compared with the sampling interval of the first signal S 1 . 
     The thermal limit (the second signal S 2 ) is outputted fixed cycle (for example, 5-minute interval) if the value thereof is far from the full limit G (refer to  FIG. 4 ), while the thermal limit is outputted at a time when the request signal R is received from the thermal limit monitor  40  if the value thereof approached to the full limit G, as mentioned later. 
     The thermal limit (the second signal S 2 ) is high reliability and high precision value, but it is difficult for them to apply for automatic control of the reactor power because the data sampling interval thereof is long. 
     On the other hand, the LPRM signal (the first signal S 1 ) is excellent in a response because the data sampling interval thereof is short, but the LPRM signal is not reflect the thermal limit of the reactor core exactly. For this reason, it is inevitable that the automatic control of the reactor power becomes too much conservative if only based on the simple information drawn from the LPRM signal. 
     The automatic output controller  32  receives the power control instruction (the first instruction J 1 ) from thermal limit monitor  40  to very the up/down rate of the reactor power, and receives the suspend instruction (the second instructions J 2 ) to make the reactor power hold. 
     Here, the reactor power is controlled by the flow control of the core flow F in the nuclear reactor  10  and by the position adjustment of the control rod  18 . 
     The control rod operating unit  33  operates the drive  19  to move the control rod  18  for a predetermined position with the predetermined rate. 
     The recirculation flow operating unit  34  adjusts the performance of the recirculation pump  16  to operate the core flow F shows a predetermined value. 
     As shown in  FIG. 3 , the thermal limit monitor  40  includes: a first signal receiver  41  for receiving a first signal S 1 , a prospective time deriving unit  45  for deriving a prospective time f for the first signal S 1  to arrive at a full limit G ( FIG. 4 ), a judging unit  46  for judging a remaining time to the prospective time f breaks a preset value m and then request a second signal S 2  (outputs a request signal R), a compensating unit  44  for compensating the first signal S 1  based on the second signal S 2  received by the request, a first instruction transmitter  50  for transmitting a first instruction J 1  to vary a rate factor of the first signal S 1  and the second signal S 2  with synchronizing the compensation; and a second instruction transmitter  51  for transmitting a second instruction J 2  to hold the first signal S 1  or the second signal S 2  after arriving at the full limit G or a threshold K which right before the full limit G. Note that the full limits G, the threshold K, and the preset value m are accumulated in the memory  52 . 
     The first signal S 1  received at the first signal receiver  41  is a detection signal outputted from the LPRM detector  21  ( FIG. 1 ) which detects a neutron. Note that the first signal S 1  is not limited to what is outputted from LPRM detector  21 , but can use the suitable detection signal outputted from the sensor set in the nuclear reactor  10 . 
     The first signal S 1 , which is originally an analog signal, is changed into a digital signal at any timing, and then changed into the simple information imitated to the second signal S 2  by easy processing using a predetermined parameter. For this reason, the first signal S 1  is acquirable within short cycle several millisecond or less. 
     Thus the first signal S 1  is considered nearly equal to the simple information obtained by easy processes mentioned above that the first signal S 1  having an error against the second signal S 2  deemed to be a true value. Therefore, in order to secure the conservative control of a nuclear reactor plant, the first signal S 1  is processed so that the error may always distribute to the plus side. 
     The second signal S 2  received at the second signal receiver  42  is an calculation signal such as maximum linear heat generation ratio or the minimum critical power ratio transmitted from the core performance calculator  31  which calculates the power distribution in the reactor core  15  ( FIG. 1 ). Note that the second signal S 2  is not limited to such a calculation signal, but can use the suitable data whose acquisition cycle is longer than the sampling interval of the first signal S 1 . 
     The compensation formula definition unit  43  defines the compensation formula for compensating the first signal S 1  based on the newest second signal S 2  received by the newest request signal R from the judging unit  46 . Note that the same compensation formula is applied for the first signal S 1  until the next second signal S 2  is received by the next request signal R to redefine the last compensation formula. 
     Thus, the first signal S 1  and the second signal S 2  come close to the full limit G, the request signal R comes to be transmitted from the judging unit  46  and then the compensation formula comes to be redefined. While the first signal S 1  and the second signal S 2  are far from the full limit G, the second signal S 2  is transmitted at constant cycle from the core performance calculator  31 , in this case it is not necessary to redefine the compensation formula. 
     The compensating unit  44  compensates the first signal S 1  at the time of acquiring that from the first signal receiver  41 , by applying the newest compensation formula defined in the unit  43 . 
     As shown in  FIG. 4 , the prospective time deriving unit  45  derives the prospective time f (f 1 , f 2 , f 3 , f 4 ) after extrapolating the compensated first signal S 1  to arrive at the full limit G. 
     As shown by the diamond mark in  FIG. 4 , the judging unit  46  transmits the request signal R which request for the second signal S 2  to the core performance calculator  31  by judging whether the remaining time breaks the preset value m. The remaining time is the value which subtracted the receiving time of the first signal S 1  from the derived prospective time f. 
     In the core performance calculator  31  starts to calculate the thermal limit (the second signal S 2 ) after receiving the request signal R. As shown by the circle mark in  FIG. 4 , the calculated second signal S 2  is received by the second signal receiver  42 . During the period from the diamond mark to the circle mark, it is equivalent to the time adding the calculation time of the thermal limit (second signal S 2 ) in the core performance calculator  31 , and the transmission time of the request signal R and the second signal S 2 . 
     For this reason, the preset value m needs to be set for a long time than the calculation time of the thermal limit (second signal S 2 ). 
     As shown in  FIG. 4 , the rate varying unit  47  adjusts the rate factor of the first signal S 1  and the second signal S 2  to become small at the receiving time of the second signal S 2  (the circle mark) based on the latest request signal R (diamond mark). 
     The first instruction J 1  transmitted from the transmitter  50  are the power control instruction which work on the control rod operating unit  33  and the recirculation flow operating unit  34  so that the power rate of the nuclear reactor  10  may become small. 
     As shown in  FIG. 4 , the rate varying unit  47  changes the rate factor so that the thermal limit (the second signal S 2 ) to become hold at an attaining time W which is set up beforehand for the thermal limit close to the full limit G. That is, the rate varying unit  47  changes the rate factor based on the prospective time f derived from the unit  45 , and then the compensated first signal S 1  or the second signal S 2  may be attained to the full limit G or the threshold K within the attaining time W. 
     The comparing unit  48  makes the suspend instruction transmitter  51  to transmit the suspend instruction (the second instructions J 2 ) comparing the received second signal S 2  with the threshold K to find the former has arrived at the later. 
     The second instructions J 2  transmitted from the transmitter  51  encourage the control rod operating unit  33  and the recirculation flow operating unit  34  to suspend the power control of the nuclear reactor  10  to become the first signal S 1  or the second signal S 2  held in a steady value. 
     Based on the flow chart of  FIG. 5  (suitably refer to  FIG. 3  and  FIG. 4 ), operation of the nuclear plant controlling system is explained. 
     At the start, the full limit G, the threshold K, and the preset value m are made to acquire in the memory  52  of the computer processor (S 11 ). Then the first signal S 1  from LPRM detector  21  is received at the first signal receiver  41  (S 12 ). 
     Next, the compensating unit  44  acquires the compensation formula defined by the definition unit  43  (S 13 ), and then compensates the received first signal S 1  (S 14 ). In the prospective time deriving unit  45 , the extrapolation line is calculated based on the compensated first signal  51  (S 15 ), and then deriving the prospective time f of the compensated first signal S 1  will be arrived at the full limit G (S 16 ). 
     Next, if the receiving time t of the first signal S 1  has reached at the value which deducted preset value m from prospective time f (S 17 : Yes), the judging unit  46  judges the remaining time of the first signal S 1  arrives at the full limit G break the preset value m, and outputs the request signal R which requests the second signal S 2  from the core performance calculator  31  (S 18 ). 
     The flow S 12 -S 16  is repeated, during the period the preset value m is judged not to break by the first signal S 1  to arrive at the full limit G (S 17 : No), and the period until the second signal S 2  is received from transmission of the request signal R. (S 19 : No). 
     When the second signal S 2  is received in the second signal receiver  42  (S 19 : Yes), the compensation formula definition unit  43  redefines the compensation formula for the first signal S 1  using the second signal S 2  based on the received request signal R (S 20 ). 
     Next, it is judged whether the second received signal S 2  has arrived at the threshold K, when not having arrived (S 21 : Yes), the power control instruction (the first instruction J 1 ) which change the rate factor of the thermal limit (the first signal S 1  and the second signal S 2 ) synchronizing with redefinition of the compensation formula are transmitted to the automatic power controller  32  (S 22 ). After transmitting the first instruction J 1 , a flow of operation returns to S 12 . 
     While the received second signal S 2  has arrived at the threshold K (S 21 : No), the suspend instruction (the second instructions J 2 ) which made to suspend the power control to hold the thermal limit are transmitted to the automatic power controller  32  (S 23 ). 
     As described above, according to the embodiment of the present invention, by changing the reactor power based on the simple information like a LPRM signal, and observing the thermal limit with high reliability calculated by the core performance calculator  31  to adjust and suspend the power of the nuclear reactor automatically. 
     For this reason, the thermal limit can be adjusted close to the full limit G within a short time and without increase the workload of the operator. 
     The present invention is not limited to the embodiments disclosed. The present invention can appropriately be deformed and implemented within the scope of common technical conceptions. 
     The reactor core monitoring system can implement respective means as respective function programs by computer. The nuclear power plant controlling system can also be operated by a nuclear power plant controlling program formed by combining the respective function programs. 
     In this embodiment, although the suspend instruction of power control is transmitted when the second signal S 2  arrived at the threshold K, control can also be suitably changed so that a suspend instruction may be transmitted when the first signal S 1  arrived at a threshold or full limit G. Note that the different threshold is available for the first signal S 1  or the second signal S 2 , respectively. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  . . . nuclear reactor 
               11  . . . pressure vessel 
               12  . . . main steam line 
               13  . . . feed water line 
               14  . . . steam-water separator 
               15  . . . reactor core 
               16  . . . recirculation pump 
               17  . . . fuel assembly 
               18  . . . control rod 
               19  . . . drive 
               20  . . . instrumentation pipe 
               21  . . . LPRM detector 
               30  . . . control device 
               31  . . . core performance calculator 
               32  . . . automatic power controller 
               33  . . . control rod operating unit 
               34  . . . recirculation flow operating unit 
               40  . . . thermal limit monitor 
               41  . . . first signal receiver 
               42  . . . second signal receiver 
               43  . . . compensation formula definition unit 
               44  . . . compensating unit 
               45  . . . prospective time deriving unit 
               46  . . . judging unit 
               47  . . . rate varying unit 
               48  . . . comparing unit 
               50  . . . power control instruction transmitter (first instruction transmitter) 
               51  . . . suspend instruction transmitter (second instruction transmitter) 
               52  . . . memory 
             S 1  . . . LPRM signal (first signal) 
             S 2  . . . thermal limit, maximum linear heat generation ratio, minimum critical power ratio (second signal) 
             J 1  . . . power control instruction (first instruction) 
             J 2  . . . suspend instruction (second instructions) 
             G . . . full limit 
             K . . . threshold 
             m . . . preset value 
             f . . . prospective time 
             F . . . core flow 
             W . . . attaining time 
             R . . . request signal 
             D . . . downcomer 
             L . . . lower plenum 
             U . . . top plenum