JP4785558B2 - Reactor monitoring device - Google Patents

Description

The present invention relates to a monitoring equipment of the natural circulation boiling water reactor in particular circulating coolant by natural circulation.

  In natural circulation boiling water reactors (hereinafter simply referred to as “natural circulation reactors”), chimneys are installed above the shroud that surrounds the core. A mixed flow (two-phase flow) of cooling water and water vapor (bubbles: also called voids) rises inside the core and chimney, and a water pipe is installed in the annular channel called the downcomer surrounded by the shroud outside and the pressure vessel wall. The cooling water returned from the reactor to the reactor and the cooling water flowing out from the chimney flow as a downward flow, and the cooling water circulates inside and outside the shroud. The natural circulation reactor does not have a forced circulation device such as a recirculation pump, and the density difference between the two-phase flow density in the shroud and the cooling water density outside the shroud is a source of the circulation flow.

  When starting up a natural circulation boiling water reactor, pull out the control rod from the low pressure state to make it critical, and then control the output to several percent of the rated heat output to raise the temperature and raise it to the rated pressure. Thereafter, the control rod is further pulled out while controlling the pressure to be constant, and the high pressure low output state is changed to the high pressure high output state. It is known that an instability phenomenon called natural circulation instability may occur at the initial stage of startup including a temperature rising and pressure increasing process in which a low pressure state shifts to a high pressure low output state.

  The principle of the unstable phenomenon in this state will be described. If for some reason the boiling start position in the chimney falls and the water vapor increases (the void ratio increases), the density of the mixed flow in the chimney becomes lighter, so the difference in density between the inside and outside of the shroud increases and cooling flows into the shroud. The amount of water increases. Then, the core is cooled, the cooling water temperature at the core outlet is lowered, the boiling start position in the chimney is increased, the amount of generated steam is reduced, and the void ratio is reduced. As a result, the density difference between the inside and the outside of the shroud is reduced this time, and the amount of cooling water flowing into the shroud is reduced.

  When the amount of cooling water inflow decreases, the core is heated to a higher temperature this time, the boiling start position in the chimney decreases, the void ratio increases, the density difference between the inside and outside of the shroud increases, and the amount of cooling water flowing into the shroud increases. To do. The density difference between water vapor and water is larger at low pressure than at high pressure. For example, the density ratio between water and steam is about 1000: 1 at 1 atm, whereas the density ratio at 70 atm is about 20: 1. . As a result, at low pressure, the change in natural circulation force due to the change in the void ratio in chimney becomes large, and this phenomenon is called natural circulation type instability. As described above, in a natural circulation nuclear reactor, there is a possibility that a flow instability in which the boiling start position in the chimney oscillates up and down and the core flow rate oscillates occurs at the time of startup.

  In addition, the reactor output is small at the beginning of startup, and the absolute value of the natural circulation flow rate is small compared with that at the time of high output, so the amplitude of flow fluctuations is relatively large. Even if flow instability occurs because the reactor power is small at the beginning of startup, there is no problem with the soundness of the fuel.However, due to flow fluctuations, the temperature of the coolant in the core fluctuates and the nuclear reactivity changes, and the neutron flux There is a possibility that a short period signal of the reactor period indicating a rapid rise of the reactor will be generated and the control rod pull-out operation cannot be performed.

  As a method for preventing this flow instability, for example, Patent Document 1 uses the heat of a boiler for periodic inspections to raise and boost the reactor water temperature to shift to a high pressure state where instability is unlikely to occur. The technology to increase the output is published. Patent Document 2 discloses a method for starting up a natural circulation furnace in a high-pressure state that includes a pressurizing device and is less likely to cause instability. Both are technologies that increase the output after a high pressure state where flow instability is unlikely to occur, but the former requires large-capacity boiler equipment to start up in a short time, and the latter is a pressurizing press. The equipment must be specially provided, which increases the construction cost.

  Further, in Patent Document 3, when a pressure gauge and a thermometer are installed at the upper part of the core and the lower part of the chimney, the saturation temperature of the upper part of the core and the lower part of the chimney is calculated from the pressure, and the core outlet is saturated and the lower part of the chimney is in the subcooled state. In addition, a technique for improving the stability by reducing the pressure or increasing the reactor power so that the entire chimney is saturated is disclosed. This is based on the knowledge that the flow stability is improved if the core and chimney are all in the two-phase flow state even at low pressures. Considering a realistic start-up, it is difficult to realize in the initial start-up. In addition, reducing the reactor pressure during boosting increases the startup time.

JP 59-143997 A JP-A-5-72387 JP-A-8-94793

  As described above, since the pressure in the nuclear reactor is low and the reactor power is low at the initial stage of startup of the natural circulation reactor, the natural circulation force is weakened. And since saturation temperature falls in the middle of chimney and boiling starts, natural circulation type unstable flow fluctuation is likely to occur, resulting in a problem that the reactor power fluctuates.

  The present invention is for solving the above-described problems, and monitors the saturation temperature corresponding to the chimney outlet temperature and the chimney outlet pressure, and controls the reactor power so that boiling starts at the chimney outlet. With the goal.

For purposes of resolution to the present invention the above problems, the reactor monitoring system natural circulation reactor of the present invention, the temperature measuring means for measuring the fluid temperature in Chim two by the temperature detection unit disposed below the chimney Based on the pressure measuring means for measuring the fluid pressure by the pressure detectors arranged at the upper part and the lower part of the chimney , the temperature related to the fluid temperature measured by the temperature measuring means, and the fluid pressure measured by the pressure measuring means Display means for displaying the temperature set in relation to the calculated saturation temperature on the same screen is provided.
Here, the temperature displayed by the display means is a subcool temperature or fluid temperature itself obtained by calculating the difference between the fluid temperature and the saturation temperature, and is calculated based on the fluid pressure measured by the pressure measuring means. The temperature set in relation to the temperature is a preset stability boundary subcool temperature or stability boundary temperature. Then, the subcooling temperature and the stability boundary subcooling temperature obtained by calculating the difference between the fluid temperature and the saturation temperature are displayed on the same screen, or the fluid temperature itself and the stability boundary temperature are displayed on the same screen. It is .

Further, in another form of the reactor monitoring device for a natural circulation reactor according to the present invention, temperature measuring means for measuring the fluid temperature of the chimney by the temperature detection unit disposed at the lower part of the chimney, and disposed at the upper part of the chimney and the lower part of the chimney A pressure measuring means for measuring the fluid pressure by the pressure detector, a temperature related to the fluid temperature measured by the temperature measuring means, and a saturation temperature calculated based on the fluid pressure measured by the pressure measuring means. Display means for displaying the set temperature on the same screen. The temperature related to the fluid temperature measured by the temperature measuring means is the measured chimney temperature, and the temperature set in relation to the saturation temperature calculated based on the fluid pressure measured by the pressure measuring means is: This is a preset stability boundary subcooling temperature.

  Thus, in the reactor monitoring apparatus of the present invention, the subcool temperature obtained from the fluid temperature and the subcool temperature at the preset stability limit are displayed on the same screen at the same time, so the operator can perform stable operation in real time. Confirmation can be made.

  According to the present invention, it is possible to avoid flow fluctuations in the nuclear reactor only by measuring two parameters of temperature and pressure inside the chimney of the nuclear reactor, and the operator of the nuclear reactor is always in the display device. Since it is possible to monitor the temperature rise state during startup while viewing the display screen, the reactor can be started up safely in a short time.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an output control device and a reactor monitoring device for a natural circulation reactor according to the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a nuclear reactor system in which a power control device of the present invention is applied to a natural circulation boiling water reactor according to the present invention.

As shown in FIG. 1, a nuclear reactor having a natural circulation reactor system has a core in which a fuel assembly 2 in which a plurality of fuel rods are aligned and a control rod 3 inserted in a gap between the fuel assemblies 2 is arranged. 4.
A control rod driving device 8 that drives the control rod 3 in the core 4 so as to be inserted and withdrawn in the vertical direction is provided below the reactor pressure vessel 6. A main steam pipe 12 and a water supply pipe 13 are connected to the reactor pressure vessel 6, and a cylindrical shroud 5 is disposed inside the reactor pressure vessel 6 so as to surround the reactor core 4. An ascending flow path for the coolant to rise in the direction of the arrow shown in the figure is formed inside the shroud, and the coolant descends in the gap between the shroud 5 and the reactor pressure vessel 6. A downcomer 7 is formed as a descending flow path. A cylindrical chimney 9 is disposed above the shroud 5, and an air-water separator (separator) 10 and a steam dryer (dryer) 11 are disposed above the chimney 9.

  Inside the chimney 9 in the reactor pressure vessel 6, the gas-liquid two-phase coolant boiled in the reactor core 4 passes. The gas-liquid two-phase coolant and the liquid single-phase cooling that passes through the downcomer 7 are cooled. Due to the difference in density from the material, a circulation channel is formed in which the coolant goes down the downcomer 7 and then goes to the core 4 side and passes through the core 4 and rises in the chimney 9. Then, when the mixed flow of the cooling water and water vapor that has risen in the chimney 9 passes through the steam / water separator 10, the steam is separated by the steam / water separator 10. The single-phase cooling water separated by the steam separator 10 descends the downcomer 7 again, and is sent to the core 4 in the shroud 5 through the lower part of the reactor pressure vessel 6.

  Further, the steam separated by the steam separator 10 is further removed from the water droplets by the steam dryer 11 and supplied to the turbine 18 via the main steam pipe 12. The turbine 18 and the generator 21 connected to the turbine 18 are rotated by the pressure of the steam flow to generate power.

  The steam that has rotated the turbine 18 is introduced into the condenser 23 and condensed. Cooling water (condensate) condensed in the condenser 23 is returned to the reactor pressure vessel 6 from the feed water pipe 13 by the feed water pump 24. Further, the water supply pipe 13 is provided with a flow rate adjusting valve 25, and the flow rate of the cooling water flowing back into the reactor pressure vessel 6 is adjusted by the flow rate adjusting valve 25, whereby the atoms in the reactor pressure vessel 6 are adjusted. Reactor water level can be controlled. Further, the feed water pipe 13 is provided with a feed water heater 26, and steam extracted from the middle stage of the turbine 18 is guided to the feed water heater 26 through the bleed line 22, and the feed water heater 26 has a condenser. The cooling water supplied from 23 is heated to an appropriate temperature and injected into the reactor pressure vessel 6.

  Further, the main steam pipe 12 is provided with a main steam isolation valve 27 and a turbine steam flow rate adjusting valve 28 for adjusting the amount of steam introduced into the turbine 18, and an escape pipe 29 and a bypass pipe 30 are connected. When the turbine steam flow control valve 28 is throttled, the turbine bypass valve 31 provided in the bypass pipe 30 is opened, and the condenser 23 is directly connected via the bypass pipe 30 without introducing a part of the steam into the turbine 18. To be introduced to. When the main steam isolation valve 27 is closed, the safety valve 32 provided in the escape pipe 29 is opened, and the steam generated in the nuclear reactor is led into a suppression pool (not shown) in the containment vessel. Steam is condensed.

  In the embodiment of the present invention, a pressure and temperature detector 33 for measuring the fluid temperature and the fluid pressure of the coolant as a gas-liquid mixed flow is provided at the upper portion of the chimney 9 in the reactor pressure vessel 6 in particular. The pressure and temperature detected here are supplied to the pressure / temperature measuring device 34. In this pressure / temperature measurement device 34, as will be described later, an electric signal related to the pressure or temperature detected by the pressure / temperature detector 33 is converted into an actual pressure or temperature unit and sent to the output control device 35. It is done. In the output control device 34, a control signal is generated so as to obtain an output necessary for ensuring stable operation of the nuclear reactor, and is supplied to the control rod drive control device 36. The control rod drive control device 36 Controls a control rod drive 8 comprising an electric motor or a hydraulic piston for driving the control rod 3.

Hereinafter, the first embodiment of the present invention will be described in detail with reference to FIGS. FIG. 2 is a diagram showing the pressure / temperature detector 33, the pressure / temperature measuring device 34, and the output control device 35 shown in FIG. 1 in more detail. 1 are denoted by the same reference numerals, but the pressure / temperature detection unit 33 in FIG. 1 is divided into a temperature detection unit 37 and a pressure detection unit 38 in FIG. In FIG. 2, the temperature measuring device 34 is divided into a temperature measuring device 39 and a pressure measuring device 40. The description of the functions of the apparatus part already described in FIG. 1 is omitted.

First, before explaining the embodiment of the present invention of FIG. 2, an overview of the temperature change of the coolant of the natural circulation reactor will be given based on FIG.
FIG. 3 shows an example of the structure in the reactor pressure vessel 6 and the cooling water temperature distribution in the initial stage of startup. When the pressure in the steam dome 11a is, for example, 1 atm, the steam in the steam dome 11a and the cooling water temperature in the vicinity of the water surface are about 100 ° C., which is the saturation temperature. The cooling water (lower part b in FIG. 3) descending the downcomer 7 is mixed with the cold water flowing from the water supply pipe or the coolant purification system pipe and when the temperature reaches the lower plenum 6a of the pressure vessel 6, the temperature drops (for example, 95 (C to c ′ on the right side of FIG. 3). The pressure of the downcomer 7 and the lower plenum 6a is higher than that of the steam dome 11a due to the hydrostatic head. If the position is 10 m below the steam dome 11a, the pressure at that position is about 2 atm. Here, the hydrostatic head is an increase in pressure due to the weight of water, and (density) × (water height) × (gravity acceleration) ≈1 at a position 10 m below where water having a density of 1 g / cm ³ is accumulated. Atmospheric pressure, the hydrostatic head pressure increases by 1 atm from the water surface to 2 atm.

  The saturation temperature at a pressure of 2 atm is about 120 ° C., and the subcooling temperature of the cooling water at 95 ° C. (the difference between the saturation temperature and the cooling water temperature) is 25 ° C. And the cooling water which flowed into the core 4 from the lower plenum 6a is warmed by the core 4 (c-d of FIG. 3 right). For example, if the core 4 is heated to 110 ° C., boiling does not occur at the core outlet if the saturation temperature at the outlet of the core 4 is higher than 110 ° C. After that, as the cooling water rises up the chimney 9 (de in the right side of FIG. 3), when the hydrostatic head decreases, the pressure decreases and the saturation temperature decreases. When the cooling water at 110 ° C. reaches the position where the saturation temperature is as high as 110 ° C., boiling starts, and water vapor is generated from the cooling water to become a mixed flow (ea on the right in FIG. 3). When this cooling water further rises in the chimney 9, the saturation temperature also decreases due to a decrease in pressure, so the cooling water temperature decreases (e to a on the right in FIG. 3), and this difference in calorific value promotes the generation of water vapor, thereby cooling water. Promotes boiling (a to a 'on the right side of FIG. 3).

  As can be seen from FIG. 3, the temperature of the cooling water greatly changes in the reactor pressure vessel 6. Further, since there is a difference in calorific value for each fuel assembly in the core, there is a temperature distribution in the radial direction at the core outlet in the shroud. On the other hand, the pressure change in the shroud is substantially determined by the height position of the pressure vessel (distance from the water surface of the cooling water), and the pressure difference is small in the radial direction.

  Next, an embodiment of the present invention will be described in detail based on FIG. According to the present embodiment, the temperature detection unit 37 and the pressure detection unit 38 are provided above the chimney 9. There are no particular restrictions on the installation locations of the temperature detection unit 37 and the pressure detection unit 38. However, when the fuel assembly 2 is periodically replaced, the fuel assembly 2 is provided above the chimney 9 (not shown). Since it is necessary to pull it out by a refueling machine, it is appropriate to place it at a position where it does not become an obstacle during the operation, for example, at the top of a chimney partition wall (not shown) or in contact therewith.

  The temperature detection unit 37 is composed of, for example, a thermocouple, and the fluid temperature measured here is supplied to the temperature measurement device 39 as an electric signal and converted into a signal of temperature unit (° C.). Moreover, as the pressure detection part 38, the detection part of a differential pressure conduit | pipe is provided in the partition with the downcomer 7 of the outer peripheral upper part of the chimney 9, for example, and a chimney absolute pressure can be measured with the pressure gauge which has a diaphragm. The fluid pressure in the chimney detected by the pressure detection unit 38 is also sent to the pressure measuring device 40 as an electrical signal, where it is converted into a pressure unit (for example, MPa).

  The temperature signal 41 from the temperature measuring device 39 and the pressure signal 42 from the pressure measuring device 40 are supplied to the output control device 35, where the control signal is used to control insertion / extraction of the control rod 3 into the core 4. A control signal to be sent to is formed. Signals such as a subcool temperature signal generated by the output control device 35 and a target subcool signal for the stability limit are supplied to the display device 43 and displayed on the screen of the display device 43. The reactor operator can confirm the safety of the reactor operating state by viewing this display screen.

FIG. 4 shows an example of a specific block diagram of the output control device 35.
As shown in FIG. 4, the output control device 35 includes a saturation temperature calculation unit 44 to which the pressure signal 42 from the pressure measurement device 40 is supplied, and the saturation temperature and temperature measurement device 39 calculated by the saturation temperature calculation unit 44. A subcool temperature calculation unit 45 to which the temperature signal 41 from the target is supplied, and a target subcool temperature calculation unit 46 to obtain a target subcool temperature by calculation according to the pressure signal 42 supplied thereto, for example, as indicated by a dotted line. A control rod operation amount / operation timing calculation unit 47 for calculating a control rod operation amount and its operation timing based on the subcool temperature from the subcool temperature calculation unit 45 and the target subcool temperature from the target subcool temperature calculation unit 46; It is composed of

  Next, the operation of each component of the output control device 35 shown in FIG. 4 will be described. First, the saturation temperature calculation unit 44 to which the pressure signal 42 is supplied has a steam table (not shown) in which the saturation temperature corresponding to the pressure is shown in its internal memory, or the saturation temperature is calculated from the input pressure. Has a function formula to calculate. Then, the saturation temperature corresponding to the pressure signal 42 input from the steam table or the function expression is calculated and supplied to the subcool temperature calculation unit 45.

  The subcool temperature calculator 45 calculates the difference between the input saturation temperature signal and the measured temperature signal 41, and sends the difference temperature to the control rod operation amount / operation timing calculator 47 as the subcool temperature. Further, the target subcooling temperature calculation unit 46 sets the target subcooling temperature to, for example, 3 ° C. if the input pressure signal 42 is 1 atm, and sets the target subcooling temperature to, for example, 1 ° C. if the pressure signal 42 is 2 atm. A control rod that outputs a target subcooling temperature determined in advance according to the value of the input pressure signal 42 so that the target subcooling temperature is set to 0 when the natural circulation type instability becomes a problem. This is supplied to the operation amount / operation timing calculation unit 47.

  The control rod operation amount / operation timing calculation unit 47 has a function of calculating the operation amount of the control rod 3 from the input subcooling temperature signal and the target subcooling temperature signal and sending it to the control rod drive control device 36 as a control signal. It is. A detailed configuration diagram of the control rod operation amount / operation timing calculation unit 47 is as shown in FIG.

  As shown in FIG. 5, the control rod operation amount / operation timing calculator 47 is supplied with the subcool temperature from the subcool temperature calculator 45 and the target subcool temperature from the target subcool temperature calculator 46. Unit 52 and a target reactor water temperature change rate 50 of, for example, 40 (° C./h) per hour, and a target temperature change rate signal 53 calculated by the target temperature change rate calculation unit are supplied. A rate-of-change limiting unit 51, a reactor water temperature detecting unit 54 for detecting the reactor water temperature, a temperature change rate converting unit 55 for calculating the rate of change of the reactor water temperature detected by the reactor water temperature detecting unit 54, A subtractor 56 that subtracts the output 71 of the temperature change rate conversion unit 55 from the output 70 of the change rate limiting unit 51; a proportional integration circuit (PI circuit) 57 that is supplied with the output 72 of the subtractor 56; A neutron flux detector 58 for detecting a neutron flux, a subtractor 59 for subtracting the output 74 of the neutron flux detector 58 from an output 73 of the PI circuit 57, and a signal 75 for controlling the extraction and insertion (insertion / extraction) of the control rod 3 It is comprised from the control signal formation part 60 which forms.

  The PI circuit 57 includes an integration circuit 61, a proportional circuit 62, and an adder 63. A signal 72 obtained by subtracting the actual reactor water temperature change rate from the target reactor water temperature change rate is added to the PI circuit 57. Is supplied. In the PI circuit 57, the deviation signal 72 is input, the signal that has passed through the proportional circuit 62 and the signal that has passed through the integration circuit 61 are added by the adder 63 and output as a signal 73. The PI circuit 57 plays a role of calculating a neutron flux level signal 73 as a control target from a deviation signal 72 from a temperature change rate target.

  Next, the PI control operation of the control rod operation amount / operation timing calculation unit 47 having the above configuration will be described. As shown in FIG. 5, first, as the target reactor water temperature change rate 50, for example, 40 ° C./h input by the operator is set, and this is supplied to the change rate limiting unit 51. The target temperature change rate signal 53 calculated by the target temperature change rate calculator 52 is input to the change rate limiter 51. The target temperature change rate calculation unit 52 calculates the target temperature change rate from the current temperature change rate and the current subcool temperature from the stability request that becomes the target subcool temperature, and this is used as the target temperature change rate signal 53 as the change rate limiting unit. 51. Then, in the change rate limiting unit 51, the target temperature change rate 50 (for example, 40 ° C./h) that is input and the target temperature change rate 53 (from the stability request calculated by the target temperature change rate calculation unit 52 ( For example, 20 ° C./h) and the minimum value (for example, 20 ° C./h in this example) among the operation limit values (for example, 55 ° C./h) are calculated and output. Thereby, the range of the rate of change of the reactor water temperature is limited to a predetermined range by the subcooling temperature.

  As described above, when the reactor is started up, the reactor water temperature gradually rises, but the rate of change is within the operating limit (for example, 55 ° C./h) and the natural circulation type instability is not. Limited to not occur. In order to complete the temperature increase / pressure increase process at the time of reactor startup in a short time, it is necessary to keep the rate of change (increase rate) in reactor water temperature as close as possible to the limit value. In particular, in the initial stage of the temperature raising and pressure increasing process at startup, the main steam isolation valve 27 (see FIG. 1) is in a closed state, and the rate of change (increase rate) in the reactor power and the reactor water temperature is approximately proportional. Therefore, maintaining as high an output as possible within a range that does not exceed the limit value leads to a reduction in start-up time.

  The target reactor water temperature change rate 50 limited by the change rate limiting unit 51 is supplied to the subtractor 56, and is compared with the actual reactor water temperature change rate by the subtractor 56. The actual reactor water temperature change rate is obtained by calculation in the reactor water temperature change rate converter 55 from the rate of change of the reactor water temperature detected by the reactor water temperature detector 54, for example, for several minutes. In the subtracter 56, the actual reactor water temperature change rate 71 is subtracted from the limited target reactor water temperature change rate 70 from the change rate limiting unit 51, and this result is sent to the PI circuit 57 as a deviation signal 72.

  In the PI circuit 57, as described above, the deviation signal 72 is integrated and output for a predetermined time. The rate of change of the reactor water temperature is the neutron flux in the core 4 portion in the reactor pressure vessel 6 and Because of the proportional relationship, the output from the PI circuit 57 corresponds to the neutron flux in the reactor pressure vessel 6, particularly near the core 4. The output signal 73 from the PI circuit 57 corresponding to the neutron flux is subtracted from the output 74 of the neutron flux detector 58 that calculates the neutron flux based on the neutrons separately detected in the core 4 of the reactor, and is actually subtracted. When the neutron flux is smaller than the value of the neutron flux obtained from the PI circuit 57, a control signal for inserting the control rod 3 inserted in the core 4 is output from the output control signal generator 60.

  If the actual neutron flux is larger than the value of the neutron flux obtained from the PI circuit 57, the output control signal generator 60 outputs a control signal for pulling out the control rod 3 inserted in the core 4 on the contrary. Like to do. This control signal is sent to the control rod drive control device 36 to select the control rod 3 to be driven by the control rod drive control device 36 and to instruct the control rod drive device 8 of the drive amount, drive start and drive stop signals. As a result, the control rod driving device 8 drives the control rod 3 and the control rod 3 is inserted into and removed from the core 4. As a result, the neutron flux in the core portion in the reactor pressure vessel 6 is always kept at the same amount, so that the nuclear fission reaction does not proceed rapidly and stable reactor operation becomes possible.

  FIG. 6 shows another embodiment of the output control device 35. The difference from that shown in FIG. 4 is that the core flow rate signal 65 is used in addition to the pressure signal 42 when setting the target subcooling temperature. The other configurations are the same as those shown in FIG.

As shown in FIG. 6, the core flow rate signal 65 is supplied from the core performance calculation device 64 to the target subcooling temperature calculation unit 46 in the output control device 35 of this example.
Here, the core performance calculation device 64 is a device that periodically calculates the power distribution of the reactor, various thermal limit values, etc. (usually every few minutes to about every hour) and launches them on a printer or the like. This is a device that calculates the various parameters based on the appropriate physical model of the core by inputting measured values such as the core flow rate, reactor pressure, control rod position, and neutron flux from the in-core neutron detector online from the reactor.

  Thus, in the core performance calculation device 64, the flow rate of the cooling water flowing through the core 4, that is, the core flow rate signal 65 is obtained by calculation. The core flow rate signal 65 and the reactor output signal 66 obtained by the core performance calculation device 64 are supplied to the target subcooling temperature calculation unit 46 together with the pressure signal 42 described with reference to FIG. Then, the target subcooling temperature calculation unit 46 calculates the target subcooling temperature from the pressure signal 42 and the core flow rate signal 65 by a predetermined calculation formula or table, and supplies it to the control rod operation amount / operation timing calculation unit 47. Here, the predetermined calculation formula indicates, for example, the relationship of the stability boundary subcooling temperature at Chimney to the calorific value of the fuel assembly with the reactor pressure as a parameter.

  The example shown in FIG. 7 is another example of the output control device 35. Unlike the example shown in FIG. 4 or FIG. 6, the target subcool temperature is not calculated by calculation in the output control device 35, but the input device 67. In this example, a predetermined value is input in advance. According to this embodiment, the target subcool temperature of a predetermined value is supplied from the input device 67 to the change rate limiting unit 51 of the control rod operation amount / operation timing calculation unit 47 described in FIG. There is no need to calculate the target subcooling temperature from a pressure signal or the like, and there is an advantage that the apparatus configuration is simplified.

Next, a second embodiment of the present invention will be described with reference to FIG. As can be seen from FIG. 8, in this embodiment, the pressure detection units 38a and 38b are provided at two locations, the upper part of the chimney and the lower part of the chimney.
Moreover, the temperature detection part 37 is provided in the chimney lower part. Since the other configuration is the same as that of the first embodiment of the present invention shown in FIG. 2, the same reference numerals are given, and the description of the configuration and operation is omitted.

  As shown in FIG. 8, different pressures are naturally detected from the pressure detector 38a arranged at the upper part of the chimney and the pressure detector 38b arranged at the lower part of the chimney, and these two different values of pressure are detected. It is supplied to the pressure measuring device 40. If the length of the chimney 9 is 10 m and the pressure at the upper part of the chimney is 1 atm, the pressure at the lower part of the chimney is 2 atm. In that case, even if the saturation temperature (boiling temperature) of the cooling water in the upper part of the chimney is 100 ° C., the saturation temperature in the lower part of the chimney is about 120 ° C. That is, an opening of 20 ° C. occurs in the saturation temperature at the top and bottom of the chimney 9.

  Since the pressure at the lower part of the chimney 9 decreases in proportion to the height position, the saturation temperature also varies depending on the position. In this case, for example, when cooling water of 110 ° C. flows from the core 4 side to the chimney 9 side, the saturation temperature at the bottom of the chimney is 120 ° C., so it does not boil at the bottom of the chimney, but reaches the top of the chimney (saturation temperature is 100 ° C.). There is always a position where the saturation temperature reaches 110 ° C. Accordingly, the cooling water at 110 ° C. at the inlet of the chimney 9 reaches a saturation temperature while rising in the chimney, boils and changes to water vapor.

  Thus, by measuring not only the fluid pressure at the outlet of the chimney 9 but also the fluid pressure and the fluid temperature at the inlet of the chimney 9, it is possible to know at which position of the chimney 9 boiling starts. As the reactor pressure increases, it stabilizes and flow instability does not occur even if some boiling occurs in the chimney. Further, the stability boundary subcooling temperature at the chimney inlet corresponding to the state can be calculated. Therefore, in the configuration of the present embodiment, when the stability boundary temperature or the stability boundary subcooling temperature depending on the pressure is given, the initial stage of startup is more than when the reactor power is controlled so that boiling does not occur at the chimney outlet. Since the reactor power can be increased, it is possible to bring it to a stable operation state in a short time.

  Next, based on FIGS. 9 to 11, contents to be displayed on the display screen of the display device 43 when performing output control at the time of starting each reactor in each embodiment of the present invention will be described. Needless to say, the display device 43 is one component of the reactor monitoring device of the present invention.

  In FIG. 9, the horizontal axis represents the reactor power (%) at the time of reactor startup, and the vertical axis represents the subcooling temperature (° C.). The solid line indicates the boundary line between the stable region and the unstable region at low pressure, and the dotted line indicates the boundary line between the stable region and the unstable region at high pressure.

  As described above, since the subcool temperature is a difference between the saturation temperature of the cooling water and the actual measured temperature, the subcool temperature is stable when the subcool temperature of the fluid is sufficiently high, and becomes unstable when the temperature is lower than a certain value. Furthermore, when the subcooling temperature is zero so that boiling starts in the core and all the inside of the chimney is saturated, stabilization is achieved.

As shown in FIG. 9, when the reactor power is about 0.1% or less of the rated value, the subcooling is normally performed at the chimney exit, so that the stable region is reached. When the reactor power becomes about 1% of the rated value, as shown by the solid line in FIG. 9, the unstable region due to the start of boiling inside the chimney increases. However, when the output increases and the steam increases, and the pressure of the steam dome increases, the stable area increases even if boiling occurs partially in the chimney as shown by the dotted line in the figure, and the stable area is extended over a wide range. . As a result, if the reactor pressure increases to some extent, it is possible to increase the output and perform stable operation without controlling the subcooling temperature, and gradually increase the reactor output to 100% of the rating.
In the operation of the reactor, the reactor power can be adjusted while adjusting the reactor output while looking at the display screen of the display device 43 as shown in FIG. Start-up operation can be performed stably without fluctuation.

  FIG. 10 shows the past subcooling temperature and stability boundary subcooling temperature displayed on the same screen with the current time (0 minutes) as a reference. It is possible to ensure stable operation by operating so that the current subcooling temperature is always higher than the subcooling temperature at the stability boundary. That is, since the subcool temperature is the difference between the saturation temperature and the current temperature, the subcool temperature at the stability boundary is set to be small. Therefore, if the operation is performed in a state where the actual subcooling temperature is higher than the subcooling temperature at the stability boundary, it can be confirmed that the operation at the time of starting is performed safely.

  FIG. 11 shows an example in which the actually measured chimney temperature and the stability boundary temperature are displayed simultaneously on the display screen of the display device 43 instead of the subcool temperature. Since the temperature inside the reactor is largely related to the power output of the reactor, the stability boundary temperature indicates the stability limit of the reactor power. If the measured temperature in the reactor (for example, the temperature at the bottom of the chimney) is lower than the safety boundary temperature indicating the stability limit, it can be confirmed that the reactor is operating safely. .

  The display screen of the display device 43 shown in FIG. 9, FIG. 10 or FIG. 11 is for the operator to constantly monitor, and these screens can always be switched on the display screen. A plurality of display windows may be provided on the screen to display a plurality of screens simultaneously.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention described in the claims. It goes without saying that the embodiment is included.

It is a mimetic diagram showing the whole composition of one embodiment of the nuclear reactor system provided with the natural circulation type nuclear reactor concerning the present invention. It is a block block diagram which shows the 1st Example of this invention. It is a figure for demonstrating the circulation of the cooling water in the 1st Example of this invention. It is a specific block diagram of the output control device in the first embodiment of the present invention. It is a block diagram for demonstrating further in detail the control-rod operation amount and operation timing calculation part of the output control apparatus in the example of 1st Embodiment of this invention. It is a block diagram which shows the 1st modification of the output control apparatus in the 1st Example of this invention. It is a block diagram which shows the 2nd modification of the output control apparatus in the 1st Example of this invention. It is a block block diagram which shows the 2nd Example of this invention. It is an example of the 1st display screen displayed on the display apparatus used for the 1st and 2nd embodiment of this invention. It is an example of the 2nd display screen similarly displayed on the display apparatus used for the 1st and 2nd embodiment of this invention. It is an example of the 3rd display screen similarly displayed on the display apparatus used for the 1st and 2nd embodiment of this invention.

Explanation of symbols

  2 .... Fuel assembly, 3 .... Control rod, 4 .... Core, 5 .... Shroud, 6 .... Reactor pressure vessel, 7 .... Downcomer, 8 .... Control rod drive, 9 .... Chimney, 10・ ・ Air / water separator (separator), 11 ・ ・ Steam dryer (dryer), 12 ・ ・ Main steam pipe, 13 ・ ・ Water supply pipe, 18 ・ ・ Turbine, 21 ・ ・ Generator, 22 ・ ・ Bleak line, 23 .. Condenser, 24 .. Feed water pump, 25 .. Flow adjustment valve, 27 .. Steam isolation valve, 28 .. Turbine steam flow control valve, 29 .. Relief valve, 30 .. Bypass pipe, 31. Turbine bypass valve 32 safety valve 34 pressure / temperature measuring device 35 output control device 36 control rod drive control device 43 display device 44 saturation temperature calculator 45 ... Subcool temperature calculator, 46 ... Target subcool temperature calculator, 7. Control rod operation amount / operation timing calculation unit, 51 ... Change rate limiting unit, 57 ... Proportional integration circuit (PI circuit), 58 ... Neutron flux detection unit, 64 ... Core performance calculation device, 67 ...・ Input device

Claims (3)

Reactor of a natural circulation boiling water reactor in which a coolant ascending channel is formed inside a chimney disposed inside the reactor pressure vessel and a coolant descending channel is formed outside the chimney In the monitoring device,
Temperature measuring means for measuring the fluid temperature of the chimney by means of a temperature detector disposed at the lower part of the chimney;
Pressure measuring means for measuring fluid pressure by pressure detectors disposed at the upper part of the chimney and the lower part of the chimney ;
Display that displays on the same screen the temperature related to the fluid temperature measured by the temperature measuring means and the temperature set in relation to the saturation temperature calculated based on the fluid pressure measured by the pressure measuring means Means, and
The temperature related to the fluid temperature measured by the temperature measuring means is a subcool temperature obtained by calculating the difference between the fluid temperature and the saturation temperature thereof,
The temperature set in relation to the saturation temperature calculated based on the fluid pressure measured by the pressure measuring means is a preset stability boundary subcooling temperature. Reactor monitoring device for circulating boiling water reactor. Reactor of a natural circulation boiling water reactor in which a coolant ascending channel is formed inside a chimney disposed inside the reactor pressure vessel and a coolant descending channel is formed outside the chimney In the monitoring device,
Temperature measuring means for measuring the fluid temperature of the chimney by means of a temperature detector disposed at the lower part of the chimney;
Pressure measuring means for measuring fluid pressure by pressure detectors disposed at the upper part of the chimney and the lower part of the chimney ;
Display that displays on the same screen the temperature related to the fluid temperature measured by the temperature measuring means and the temperature set in relation to the saturation temperature calculated based on the fluid pressure measured by the pressure measuring means Means, and
The temperature related to the fluid temperature measured by the temperature measuring means is the measured chimney temperature,
The temperature set in relation to the saturation temperature calculated based on the fluid pressure measured by the pressure measuring means is a preset stability boundary subcooling temperature. Reactor monitoring device for circulating boiling water reactor. The pressure at an arbitrary position of the chimney is estimated from the pressure difference measured by the pressure detection unit disposed at the upper part of the chimney and the lower part of the chimney, and the saturation temperature at the arbitrary position of the chimney is estimated from the estimated pressure. 3. The natural circulation boiling water type according to claim 1, wherein the natural circulation type boiling water type is obtained by a calculation formula showing a relation with temperature or a steam table showing a relation between pressure and saturation temperature and displaying it on the display means. Reactor monitoring equipment for nuclear reactors.

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