JPS6145995A - Boiling water type reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a boiling water nuclear reactor equipped with a recirculation system that controls output by varying the flow rate of core coolant.

[Technical Background of the Invention] A conventional example will be explained with reference to FIG. FIG. 4 is a diagram showing a schematic configuration of a control mechanism for a recirculation system of a conventional boiling water reactor. Reference numeral 1 in the figure indicates a reactor pressure vessel, in which a coolant 2 and a reactor core 3 are accommodated. This core 3 is composed of a plurality of fuel assemblies, control rods, etc. (not shown). The coolant 2 flows upward through the reactor core 3, and its temperature increases due to the heat of nuclear reaction in the reactor core 3. The heated coolant 2 enters a two-layer flow state of water and steam, and is separated into water and steam by the steam separator 4 installed above the core 3, and the separated steam flows through the steam separator 4. It is dried in a steam dryer 5 installed above to become dry steam,
It is transferred to the steam turbine 7 via the main steam pipe 6-+ connected to the reactor pressure vessel 1. On the other hand, the separated water flows downward through the reactor core 3 via the downcomer section 9 between the shroud 8 that accommodates the reactor core 3 and the reactor pressure vessel 1, and flows upward through the reactor core 3 again. The same cycle is repeated thereafter.

The steam transferred to the steam turbine 7 performs work there, is condensed in a condenser 10 installed below the steam turbine 7, and is condensed by a condensate pump 11, a demineralizer (not shown), and a feed water heater 12.
, and is returned into the reactor pressure vessel 1 through a water supply pipe 14 in which a water supply pump 13 is inserted. A main steam control valve 25 is inserted in the main steam pipe 6, and a bypass steam pipe 26 is provided between the condenser 10 and the main steam pipe 6. A turbine bypass valve 27 is inserted therein.

In a boiling water reactor having such a configuration, its output is controlled by the following two methods. The first method is to control the output by changing the degree of insertion of the neutron absorber, that is, the aforementioned control rod, into the core 3. This method performs output control by changing the .

In addition to coolant flow rate, other factors that affect the neutron balance without manipulating control rods or other absorbers include in-core coolant pressure and coolant core inlet temperature. These will be briefly described below.

First, let's talk about the coolant pressure in the core. When the coolant pressure in the core changes, the steam volume fraction (hereinafter referred to as void fraction) in the core 3 changes, and as a result, it has a subtle effect on changes in the output of the reactor. For example, as the coolant pressure in the core increases, the void fraction decreases, resulting in an increase in core power and pressure. As described above, since the increase in the core coolant pressure has a positive feedback effect, output control based on the core coolant pressure is not normally performed.

In addition, the method of controlling output by changing the coolant core inlet temperature, that is, the subcooling degree of the fluid, was adopted in so-called dual-cycle boiling water reactors, and is not a very common method at present. .

As mentioned above, the three factors, the inner core coolant pressure and the coolant core inlet temperature, cannot be said to be appropriate as a method for controlling the core output, and the general method is to change the coolant flow rate. It can be said that there is. Core power control based on changes in coolant flow rate will be explained below. The flow rate of coolant in the core is usually changed by changing the recirculation flow rate using a recirculation system. That is, as shown in the figure, a plurality of jet pumps 21 are installed in the downcomer section 9, while a recirculation pump 22 is installed outside the reactor pressure vessel 1. These jet pumps 21
A recirculation system piping 23 is disposed between the recirculation pump 22 and the recirculation pump 22 . With the recirculation system having such a configuration, the output is controlled by changing the recirculation amount. Therefore, the principle of output control by changing the recirculation flow rate will be explained.

In other words, in steady state, an equilibrium state is maintained between the reactor power (neutron side density) and the amount of voids in the reactor.
The amount of voids generated in the furnace and the amount of outflow are equal. In such a steady state, when the recirculation flow rate is increased, the income and expenditure balance of the voids in the furnace is temporarily disrupted due to the increase in flow rate, the amount of voids flowing out increases, and the amount of voids in the furnace decreases.

This decrease in the amount of voids in the reactor increases the neutron moderation effect, and as a result, the negative void reactivity coefficient inherent in the BWR core temporarily adds positive reactivity to the reactor, and therefore the reactor The neutron side density, ie the heat output, increases. Due to this increase in thermal output, the amount of voids generated within the reactor increases again, and at this time, the flow rate at the core inlet also increases, and as a result, the core output is increased. In addition, when reducing the core power, it is done based on the opposite logic to that described above.

Further, the recirculation flow rate can be changed by the following method. That is, the recirculation flow rate is adjusted by changing the frequency of the induction transmission 24 connected to the recirculation pump 22 and changing the pump rotation speed. This will be explained in detail below.

Reference numeral 31 in the figure indicates a pressure control system, and this pressure control system 31
is a variable frequency power generation unit connected to the steam turbine 7.
A rotation speed signal (Sl) is input from 1128. For example, a request signal for reactor pressure change is output to the main controller 32 manually (indicated by 82 in the figure) or as a load change signal (S3) from the pressure control system 31. Main controller 3
2 processes the input signal with an appropriate PID operation and outputs it to the speed controller 33 as a speed request signal (S4).

The speed controller 33 outputs a control signal (S5) to the scoop pipe position adjuster 34 so that the rotational speed of the variable frequency generator 28 matches the input speed request signal (S4), and adjusts the speed inside the fluid reader 35. Adjust the position of the scoop pipe (not shown) as an oil level regulator. Note that this fluid reader 35 causes the electric motor 36 to
The power from the AC generator 37 is transmitted to the AC generator 37 side. Such action adjusts the amount of oil within the fluid reader 35 and changes the bonding force within the fluid reader 35. As a result, the frequency of the generator 37 changes and, via the induction motor 1I24, the speed of the recirculation pump 22 changes.

If the speed of the recirculation pump 22 changes, the recirculation flow rate changes and the amount of steam generated changes. As a result, the balance with the turbine steam amount is disrupted and a pressure change occurs. Due to this pressure change, the main steam control valve 2
5 is adjusted, and the amount of turbine steam changes until it matches the amount of steam generated by the reactor. In this way, the turbine output changes and follows the initially given load command.

[Problems with the background art] According to the above configuration, the plant's load followability through recirculation flow rate control is performed through many devices as described above, resulting in poor responsiveness and a certain amount of time delay. . In addition, a large cooler for the fluid reader 36 is required, and the variable frequency power generator consisting of the AC generator VA 37, the fluid reader 35, and the drive motor 36 is
(referred to as "G set") has become larger in size and has a more complicated configuration, resulting in problems in terms of cost.

[Purpose of the invention]

The present invention has been made based on the above points, and its purpose is to improve load response, simplify the configuration, downsize the device, and reduce costs. An object of the present invention is to provide a boiling water nuclear reactor equipped with a system.

[Summary of the Invention] That is, a boiling water nuclear reactor according to the present invention includes a plurality of jet pumps arranged between a reactor pressure vessel and a shroud, and a plurality of jet pumps arranged outside the reactor pressure vessel and connected to the jet pumps. In a boiling water reactor equipped with a recirculation system consisting of a recirculation pump connected via circulation system piping, the recirculation pump performs output control by changing the flow rate of core coolant using the recirculation system. The blades of the recirculating pump have a variable pitch, and when a reactor output request signal is output by the control mechanism, the pitch angle of the blades of the recirculation pump is changed to change the core coolant flow rate and perform output control. It is something to do.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a diagram showing a schematic configuration of a boiling water nuclear reactor, and reference numeral 101 in the figure indicates a reactor pressure vessel. Inside this reactor pressure vessel 101, there is a coolant 102 and a reactor core 1.
03 is accommodated.

The reactor core 103 is composed of a plurality of fuel assemblies, control rods, etc. (not shown), and is installed within a shroud 104. The coolant 102 is the reactor pressure vessel 101
Reactor pressure vessel 10 via water supply pipe 105 connected to
1 and flows upward through the core 1'03. At this time, the temperature rises due to the heat of nuclear reaction in the core 103, resulting in a two-layer flow of water and steam. The two-layer flow coolant 102 is separated into water and steam in a steam separator 113 installed above the core 1°3, and the separated steam is transferred to the steam separated further above. Dry steam is dried in the dryer 114 and is supplied to the steam turbine 107 via the main steam pipe 106 connected to the reactor pressure vessel 101. On the other hand, the separated water is transferred to the reactor core 103 via a downcomer section 108 formed between the reactor pressure vessel 101 and the shroud 104.
It flows downward and flows upward through the core 103 again. Then, the cycle is repeated. The steam supplied to the steam turbine 107 performs work there, and the steam turbine 1
The water becomes condensed in the condenser 108 installed below 07, is pressurized by the condensate pump 110, is pre-pressurized by the feed water heater 111, is further pressurized by the feed water pump 112, and then 105 and is returned into the reactor pressure vessel 101. A main steam control valve 121 is inserted into the main steam pipe 106 . Further, a bypass steam pipe 122 is disposed between the main steam pipe 105 and the condenser 107, and a turbine bypass valve 123 is inserted into the bypass steam pipe 122. Further, a variable frequency generator 124 is connected to the steam turbine 107.

A boiling water reactor with the above configuration is equipped with a recirculation system. The configuration of this recirculation system will be explained below.

That is, a plurality of jet pumps 131 are installed inside the downcomer section 104, while a recirculation pump 132 is installed outside the reactor pressure vessel 101. These jet pump 131 and recirculation pump 132 are connected via recirculation system piping 133. The recirculation pump 132 includes an induction type engine 134.
are connected. The blades of the recirculation pump 132 are of a variable pitch type, and by appropriately changing the pitch angle by the control device 141, the recirculation flow rate is changed and the core output is controlled.

Next, the configuration of the control device 141 will be explained. First, a rotation speed signal S11 is output from the variable frequency generator 124 to the pressure control system 142, and the pressure control system 142 outputs a load deviation signal 812 to the main controller 143 based on this rotation speed signal 811.

Note that the pressure control system 142 includes the main steam control valve 121
and a control signal (S13
) and <814). In addition, the main controller 14
3 includes a load deviation signal (S12) from the pressure control system 142.
), a manual signal S15 can also be input. The main controller 143 outputs a recirculation flow rate control signal 816 to the recirculation flow rate controller 144 based on the load deviation signal 312. Note that this recirculation flow rate controller 144 is installed corresponding to each of the recirculation pumps 132. Further, a recirculation flow meter device 45 is installed in the recirculation system piping 133, and a recirculation flow rate signal S17 is input from the recirculation flow meter device 45 to the recirculation flow rate controller 144. Recirculation flow controller 144 This recirculation flow signal S17
and the recirculation flow rate deviation control signal 318 based on the recirculation flow rate control signal 816.
46. This propeller pitch angle controller S”19
The variable pitch controller 146 outputs this pitch angle instruction signal S1'-'9 based on the pitch
change the pitch angle of the blades. In this way, the recirculation flow rate is appropriately changed to increase the core output.

The operation will be explained based on the above configuration. First, the load deviation signal S12 from the pressure control system 142 or the manual signal S
15 is input to the main controller 143, the main controller 143
calculates the optimum coolant recirculation flow rate according to the input signal, and outputs a recirculation flow rate control signal S16 to the recirculation flow rate controller 144 installed corresponding to each recirculation loop. .

Note that this recirculation flow rate control signal S16 is the load deviation signal S
It is also possible to set it as a function of 12.

The recirculation flow rate controller 144 also includes a coolant recirculation meter device 4.
A recirculation flow rate signal S17 is input from 5. Recirculation flow controller 144 compares these recirculation flow control signal S16 and recirculation flow signal S17. For example, when (S16-817) is negative, it is determined that the reactor is overpowered with respect to the load request, and in order to reduce the coolant recirculation flow rate, the recirculation flow rate deviation control signal 318 is set to the propeller pitch angle. Output to controller 146. The propeller pitch controller 146 receives the recirculation flow deviation control signal 818.
is converted into a propeller pitch angle instruction signal 819 based on a set program, and the variable pitch controller 147
Output to.

Note that the propeller pitch angle instruction signal 819 can also be set as a function of the recirculation flow rate deviation control signal S18. The variable pitch controller 147 then controls the recirculation pump 1 based on the propeller pitch angle instruction signal 319.
The pitch angle of the 32 blades is changed. This reduces the coolant recirculation flow rate. As the coolant recirculation flow rate decreases, the coolant flow rate at the inlet of the reactor core 103 also decreases, and as a result, the void ratio within the reactor core 103 increases and the core power decreases. By repeating this operation, the reactor output is reduced to a predetermined value, and the deviation from the load is eliminated.

Next, the case where (816-817) is positive will be explained. In this case, the reactor is determined to be underpowered relative to the load request. and recirculation flow controller 144
outputs a recirculation flow deviation control signal 818 to propeller pitch angle controller 146 to increase the coolant recirculation flow rate. The propeller pitch angle controller 146 receives the input recirculation flow rate deviation control signal S18, processes it based on a set program, converts it into a propeller pitch angle instruction signal S19, and outputs it to the variable pitch controller 147. The variable pitch controller 147 receives the input propeller pitch angle instruction signal S.
19, the pitch angle of the blades of the recirculation pump 132 is changed. Such operation increases the coolant recirculation flow rate. This increase in coolant recirculation flow rate allows the core 10
The coolant flow rate at the inlet of reactor 103 also increases, resulting in a decrease in void fraction within the reactor core 103 and an increase in reactor power.

By repeating such operations, the reactor output increases to a predetermined load, and the deviation from the load is eliminated.

Next, a case where (816-817) is zero will be explained.

In this way, if there is no deviation between the recirculation flow rate control signal S16 and the recirculation flow rate signal 817, the recirculation flow rate controller 144 does not output any control signal, and the reactor remains in the operating state. Continue.

As described above, according to this embodiment, unlike the conventional method in which the rotational speed of the recirculation pump is changed to change the coolant recirculation flow rate, the blades of the recirculation pump 132 are of a variable pitch type and the pitch angle is changed. As a result, the response to the control signal is quick, and the coolant flow rate of the core 103 can be controlled at high speed. Also, conventional M-
Compared to the case of the G set, the configuration is simpler and smaller, and as a result, it is possible to reduce costs.

In particular, there is no longer a need for a large cooler that was required when using a conventional fluid reader, and only a small cooler (not shown) is required for the variable pitch controller 147. Of course, this is extremely effective in improving plant thermal efficiency. This will be explained with reference to the diagrams in FIGS. 2 and 3. Figure 2 shows the conventional case, and Figure 3 shows the case of this embodiment, with time plotted on the horizontal axis.
The vertical axis shows the percentage (%) of the rated time, which is 95% of the rated value.
Main parameters (reactor main steam flow rate and core inlet flow rate) when a step disturbance equivalent to 10% core flow mountain width is input to the main controller 143 as a load deviation signal 812 during steady operation with output and core flow rate of 185% FIG. 2 is a diagram showing changes over time. Line A in the figure is the reactor main steam flow rate,
Diagram B is the core inlet flow rate. In Figure 2, the core inlet flow rate hardly changes for about 2 seconds after the transient starts, and the response to subsequent changes is slow, and it takes about 12 seconds to finally reach the target value. Therefore, it takes approximately 25 seconds to establish the reactor main steam flow rate.In contrast, in the case of this embodiment, as shown in Figure 3, The final target value was reached in about 2 seconds, and the reactor main steam flow rate was established in about 10 seconds.The broken line in Figure 3 is a diagram showing the conventional case. be.

As described above, in the case of this embodiment, the response is extremely fast compared to the conventional one, and it becomes possible to control the core flow rate at high speed.

(Effects of the Invention) As detailed above, the boiling water reactor according to the present invention includes a plurality of jet pumps arranged between a reactor pressure vessel and a shroud, and a plurality of jet pumps arranged outside the reactor pressure vessel. In a boiling water reactor equipped with a recirculation system consisting of the above-mentioned jet pump and a recirculation pump connected via recirculation system piping, the recirculation system controls output by changing the flow rate of core coolant. , the blades of the recirculation pump have a variable pitch, and when a reactor output request signal is output by the mm control mechanism, the blade pitch angle of the recirculation pump is changed to change the core coolant flow rate and output control. It is characterized by the following.

Therefore, the load response of the reactor can be greatly improved and the reliability of the device can be greatly improved, and the configuration can be simplified and the device can be made smaller, which is an effective way to reduce costs. This is extremely effective.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing one embodiment of the present invention.
The figure shows a schematic configuration of a boiling water reactor, Figures 2 and 3 are line diagrams for explaining effects, and Figure 4 shows a schematic configuration of a conventional boiling water reactor. . 101... Reactor pressure vessel, 102... Coolant, 1
03...core, 104...shroud, 131...
・Jet pump, 132...Recirculation pump, 133
...Recirculation system piping, 141...Control device.

Claims (2)

[Claims] (1) A plurality of jet pumps arranged between the reactor pressure vessel and the shroud, and a recirculation pump arranged outside the reactor pressure vessel and connected to the jet pumps via recirculation system piping. In a boiling water reactor, the output is controlled by changing the flow rate of core coolant using the recirculation system, the blades of the recirculation pump have a variable pitch, and the control mechanism controls the A boiling water nuclear reactor characterized in that when a reactor output request signal is output, the blade pitch angle of the recirculation pump is changed to change the core coolant flow rate to perform output control. (2) The above control mechanism compares the main controller that outputs a signal when the reactor output change request signal is output, and the signal from this main controller and the recirculation flow rate measurement value to control the recirculation pump. a recirculation flow rate controller that outputs a signal for controlling the pitch angle of the blade; and a blade pitch angle controller that outputs a signal for changing the pitch angle of the blade of the recirculation pump based on the signal from the recirculation flow rate controller. A boiling water nuclear reactor according to claim 1, characterized in that the boiling water nuclear reactor comprises: