JPH053556B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a boiling water reactor (hereinafter referred to as BWR).
Regarding how to drive.

[Technical Background of the Invention] A conventional example will be described with reference to FIGS. 1 to 5. FIG. 1 is a longitudinal sectional view showing the schematic configuration of the BWR. In the figure, reference numeral 1 denotes a reactor pressure vessel, in which a reactor core 2 and a coolant 3 are housed. The reactor core 2 is composed of a plurality of fuel assemblies 4, control rods 5 shown in FIG. 2, and the like. The coolant 3 flows through the reactor core 2 from below to above, and as it does so, its temperature increases due to the heat of nuclear reaction in the reactor core 2, resulting in a two-layer flow state of water and steam. The coolant 3 in a two-layer flow state flows into a steam-water separator 6 installed above the core 2 and is separated into water and steam.
It is housed in a shroud 9 installed concentrically with the force component vessel 1, and a plurality of jet pumps 11 are installed at equal intervals in the downcomer section 10 between the shroud 9 and the reactor pressure vessel 1. There is. This jet pump 11 constitutes a recirculation system with a recirculation pipe (not shown) disposed through a recirculation system inlet nozzle 12 and a recirculation system outlet nozzle 13, and a recirculation pump (not shown) inserted into this recirculation pipe. The coolant 3 is forced to circulate through the core 2. In the figure, reference numeral 14 indicates a water supply nozzle, reference numeral 15 indicates a core spray spargeer, and reference numeral 16 indicates a control rod drive mechanism for inserting and withdrawing the control rod 5 into the reactor core 2.

The reactor core 2 is constructed as shown in FIG. FIG. 2 is a partial plan view of the reactor core 2. FIG. In other words, four fuel assemblies 4 are connected to control rods 5 having a cross-shaped cross section.
The structure is such that a unit cell 21 is arranged around the periphery of the unit cell 21, and this unit cell 21 is further arranged in a lattice shape.

In such a BWR, fissile material,
Alternatively, since the neutron absorption capacity of Zenon produced as a daughter nucleus is large, the reactivity effect contributed by Zenon is 2.5% ΔK/
Therefore, the above-mentioned xenone concentration has an important meaning when considering the operation or restart of a nuclear reactor.

In other words, if the control rods 5 are pulled out with almost no Zenon at the start of reactor startup, before the control rods 5 are pulled out to the control rod pattern required to achieve the core rated output level. The output will increase significantly. When the core power is increased in a state where the amount of control rods 5 that have been pulled out is small in this way, the proportion of control rods 5 that have been pulled out is small, so that heat generation is caused by the fuel assemblies 4 corresponding to the control rods 5 that have been pulled out.
A local over-output portion occurs in this area.

In addition, fuel is generally designed to provide an appropriate power distribution in the saturated Zenon state at the rated time, and in the absence of Zenon, the power output in the lower part of the core where voids do not occur will be significantly greater. There is a problem. In order to generally ensure the integrity of the fuel when operating a nuclear reactor, a law for core break-in (hereinafter referred to as PCIOMR standards) has been established, and a limit value (hereinafter referred to as PCIOMR standard) has been established for the fuel output. (referred to as the PC envelope). Therefore, if the output is suddenly increased without Zenon, a local increase in output will occur as described above, and the PC envelope may be exceeded. Therefore, when the core power increases, it is necessary to wait for the accumulation of Zenon and gradually increase the power.

By the way, in the BWR configured as described above, the core power is controlled in two ways: by adjusting the recirculation flow rate using the recirculation system, and by operating the control rods 5 using the control rod drive mechanism 15. It is. At startup, the control rods 5 are sequentially pulled out from the fully inserted state to obtain a control rod pattern for rated operation. However, depending on the control rod pattern implemented during this time, the local power distribution may be greatly distorted and exceed the PC envelope, so in such cases it is necessary to reduce the power by utilizing the increase in Zenone concentration. . On the other hand, when controlling the core power by controlling the recirculation flow rate using the recirculation system, the PCIOMR
If the output increase rate is below a specified value, the above applies.
Since it allows the output to rise beyond the PC envelope, it is possible to gradually increase the output, and it is possible to increase the output beyond the set value determined by the PCIOMR standard.

Under such circumstances, conventionally, when starting up a nuclear reactor, priority has been given to ease of operation, and low power operation is continued for a long time so that the control rods 5 can be pulled out at a sufficiently low power level. As a result, there was a problem in that it took a long time to start up the reactor. Therefore, in order to shorten the time required for startup,
An operating method as shown in FIG. 3 has been considered.
FIG. 3 is a diagram showing time changes in core power, with time (days) plotted on the horizontal axis and core power plotted on the vertical axis.
Note that the solid thick line in the figure shows the case where the core power is increased by withdrawing the control rod 5, and the broken line shows the case where the core power is controlled by adjusting the core flow rate.
A generator is connected at point O1 in the figure, and the control rod 5 is pulled out to increase the output to point A1 in the figure. In this state, the output is maintained up to point B1 in the figure. Such output retention for a certain period of time is required at the first startup after a periodic inspection, and during this period, for example, the functional soundness of the replaced equipment is inspected. After maintaining the output for a predetermined time, the control rod 5 is pulled out and the output is rapidly increased to point C1 in the figure. An example of the control rod pattern at point C1 is shown in FIG. This fourth
The figure is a plan view schematically showing the reactor core 2, and one square represents the unit cell 21. In addition, the numbers written in each square indicate the insertion and withdrawal states of the control rods 5. The fully inserted state is indicated by O, and the fully withdrawn state is indicated by 48. The larger the number, the more the control rods 5 are pulled out. It shows that it has been removed. Note that the control rods 5 at positions without numbers in FIG. 4 are all in a fully withdrawn state. The control rod pattern at this C1 point is as described above.
It is required to be able to comply with the PCIOMR standard and to perform the reactivity compensation function due to the absence of xenone accumulation. Therefore, as shown in FIG. 4, the control rod 5 located at the center is inserted shallowly, and the control rod 5 located at the outermost periphery is fully inserted. Next, from the C1 point to the E1 point via the D1 point, the output is increased by adjusting the core flow rate (specifically, by increasing the core flow rate), and Zenon is accumulated. Thereafter, by lowering the core flow rate, the output is lowered to point F1 in the figure. The reason for reducing the output here is to prevent a situation in which the output increases locally and exceeds the PC envelope when the control rod 5 is operated to increase the output next time. After reducing the output, the shallowly inserted control rod 5 at the center and the outermost control rod 5 are pulled out to create the target control rod pattern shown in FIG. 5, and the output is increased to point G1 in the figure. After that, by adjusting the core flow rate, I
Increase the output to 1 point to obtain the rated output state.

[Problems with the background art] In the above configuration, it is necessary to lower the output from the E1 point to the F1 point and then pull out the control rod 5 as an operation before obtaining the target output state, so that the target output state is obtained. In addition, when pulling out the control rod 5 in order to increase the output from the F1 point to the G1 point, the above-mentioned
In addition to requiring sufficient monitoring based on the PCIOMR standards, there were also problems in that the xenone concentration changed in a complicated manner, and the local power distribution varied greatly with control rod operations, making operation difficult.

[Purpose of the invention]

The present invention has been made based on the above points, and its purpose is to provide a method of operating a boiling water reactor that makes it possible to obtain a target core power state in a short period of time.

[Summary of the invention]

That is, in the boiling water reactor operating method according to the present invention, when predetermined control rods are pulled out from the reactor core and the reactor is started up, the number of the outermost control rods to be pulled out, which are located at the outermost periphery of the core, is relative to the number of control rods to be pulled out. It is determined according to the xenone concentration, and when the relative xenone concentration is low, the number of the outermost control rods to be pulled out is reduced to perform startup operation, and then the outermost control rods inserted in the reactor core are gradually pulled out to perform target control. It is characterized by a bar pattern.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 6 to 9. FIG. 6 is a diagram showing time changes in core power, with time (days) on the horizontal axis and core power on the vertical axis. First, a generator is brought in at point O2 in the figure, and the control rod 5 is pulled out to increase the output to point A2 in the figure. In this state, the output is held constant up to B2 in the figure. The reason why the output is held for a certain period of time in this way is as described above. Next, the output is increased from point B2 to point C2 in the figure. At this time, the control rod 5 is pulled out so that the state of the control rod 5 at the C2 point becomes a pattern as shown in FIG. That is, B2
There is no accumulation of Zenon from point C2 to point C2, so the control rods 5 are withdrawn so that the number of inserted outermost control rods 5 located at the outermost circumference of the reactor core 2 is greater than before at point C2. , thereby attempting to compensate for the reactivity due to the lack of xenone. Further, at that time, the number of inserted outermost control rods 5 at point C2 is determined as follows. That is, as shown in FIG. 8, the outermost circumference control rods 5 located at the outermost circumference are indicated by symbols a, b, c, and d, respectively. here a
There are four outermost control rods 5 indicated by b, eight outermost control rods 5 indicated by C, eight outermost control rods 5 indicated by d, and four outermost control rods 5 indicated by d. . Then, the number of outermost control rods 5 indicated by a, b, c, and d is determined by appropriately combining them in accordance with the relative xenone concentration. Figure 9 shows the number of outermost control rods 5 that are finally inserted at point C2 on the horizontal axis and the relative xenone concentration on the vertical axis, and the relative xenone concentration and the outermost control rods that are finally inserted at point C2. It is a figure showing the relationship with the number of 5. For example, if the xenone concentration at point C2 is expected to be e, the control rod should be adjusted so that the outermost control rod 5 is finally inserted at point C2, as shown by a in FIG. Perform the extraction operation in step 5. Further, when the xenone concentration at point C2 is expected to be f, the control rod 5 is withdrawn so that the outermost control rod 5 shown by b in FIG. 8 is finally in the inserted state. Similarly, when the xenone concentrations are g, h, i, and j, the number of the outermost control rods 5 in the final inserted state is determined in the same way. In this example, the case where the xenone concentration is i is assumed. Therefore, the outermost control rods 5 corresponding to positions a, b, and c in FIG. 7 are inserted. At this time, of course, the control rod operation must be such that the PCIOMR standard can be complied with. Next, since Zenon is gradually accumulated from point C2 onwards, a margin is generated based on the PCIOMR standard, and the outermost control rod 5 that is in the inserted state is gradually pulled out and the target control rod shown in FIG. Aim to increase the output as a pattern. The amount by which the control rod 5 is withdrawn at that time is as follows. In other words, if the control rod 5 is divided into 24 parts in the axial direction, and the axial distance corresponding to one division is taken as the minimum control rod drive unit, then 3 parts per hour will be generated.
Pull out the smallest control rod drive unit one by one. This operation is also intended to increase the output while ensuring compliance with the above PCIOMR standards. Then, by operating the control rods in this manner, the output is increased to point E2 in FIG. After point E2, the output is increased to point G2 via point F2 by adjusting the core flow rate to obtain the rated output state.

As described above, according to the operating method according to this embodiment, there is no need for the conventional operation of once increasing the output, lowering it, and then increasing the output again by operating the control rods, so the operation is simplified and the rated output state is obtained. The time required for this can be shortened. This can be explained by comparing Figures 3 and 6. Conventionally, approximately 65% of the output was obtained in two days and a few hours, whereas in the case of this example, it took two days and a few hours. Approximately 80% output can be obtained, and the rated output state can be obtained in approximately 3 days thereafter. This conventionally required approximately 4 days, but this can be reduced to approximately 1 day. Shortening the time required to obtain the rated output state in this way is extremely effective in improving the operating rate of the plant. In addition, at point C2 in Figure 6, the core 2
The control rod pattern near the center matches the target control rod pattern, so there is no need to operate those control rods 5 when increasing the output from point C2 to point E2. The operation of the control rods 5 in the center has a large effect on the core output, so not operating the control rods 5 in the center means
This is extremely effective in complying with the PCIOMR standards. Although the above embodiment has been explained assuming a situation where there is no Zenon at all, the present invention is not limited to this, but the number of outermost control rods 5 may be determined and operated according to the situation, such as when a certain amount of Zenon is present. Bye.

[Effects of the Invention] As described in detail above, according to the present invention, when a predetermined control rod is pulled out from the core and a reactor is started up, the outermost control rod located at the outermost periphery of the core is pulled out. The number of bottles is determined according to the relative xenone concentration,
When the relative xenone concentration is low, startup operation is performed by reducing the number of outermost control rods that are pulled out, and then the outermost control rods inserted into the reactor core are gradually pulled out to maintain the core output as before. Since there is no need to perform startup operation while adjusting the core flow rate so that the reactor does not exceed the PC envelope, the time from startup to rated power operation can be shortened, and the target output level can be reached in a short time. It is possible to provide a method for operating a boiling water reactor that allows

[Brief explanation of the drawing]

Figures 1 to 5 are diagrams showing conventional examples. Figure 1 is a vertical sectional view showing the schematic configuration of a boiling water reactor, and Figure 2
The figure is a partial plan view of the reactor core, FIG. 3 is a line diagram showing changes in core power over time, FIGS. 4 and 5 are schematic plan views of the core showing control rod patterns, and FIGS. 6 to 9 The figures are diagrams showing one embodiment of the present invention, in which Fig. 6 is a diagram showing temporal changes in core output, Figs. 7 and 8 are schematic plan views of the reactor core showing control rod patterns, and Fig. 9 The figure is a diagram showing the relationship between the relative xenone concentration and the number of outermost control rods inserted. 2...Reactor core, 4...Fuel assembly, 5...Control rod, 21...Unit cell.

Claims (1)

[Claims] 1. When a predetermined control rod is pulled out from the reactor core to perform startup operation of the reactor, the number of the outermost control rods located at the outermost periphery of the core to be pulled out is determined according to the relative xenone concentration, and the relative xenone concentration is When the temperature is low, a startup operation is performed by reducing the number of the outermost control rods to be pulled out, and then the outermost control rods inserted into the reactor core are gradually pulled out to form a target control rod pattern. How to operate a furnace.