JPS58155396A - Load following-up method of bwr type power plant - 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 load following operation method for a boiling water nuclear power plant.

[Technical Background of the Invention] Recently, the relative importance of nuclear power plants in the electric power system has increased, and it has become necessary to perform load following operation without keeping nuclear power plants in base load operation. Core thermal output control methods for boiling water reactors include a recirculation flow rate control method that changes the core thermal output by changing the core flow rate of the neutron moderator, which changes its density, and this changes the core thermal output. There is a control rod operation method that changes the core thermal output by inserting and removing control rods from the reactor core.

On the other hand, as a result of nuclear fission in the reactor core, iodine-135 and its daughter nucleus, xenone-135, are produced, but this xenone-135 is a neutron-absorbing substance, and when the core thermal output is changed, the xenone concentration changes temporally and spatially. It fluctuates. Therefore, when transitioning from high-power operation in the daytime to low-power operation at night during load-following operation, or vice versa, the changes in the xenone concentration distribution and, therefore, the accompanying fluctuations in the power distribution should be taken into consideration when adjusting the reactor core. The flow rate must be adjusted and the control rods operated.

FIG. 1 shows the changes in core thermal output, core flow rate, iodine concentration, and xenone concentration when load following operation is performed with only core flow adjustment. In other words, in the figure, the horizontal axis is time, and the vertical axis is core thermal output, core 11 xenone concentration, and iodine concentration, where curve a is core thermal output, curve 2 is core flow rate, and curve C is xenone concentration. concentration, curve d
express the temporal fluctuations of iodine concentration.

As is clear from this figure, decreasing the core flow rate lowers the core thermal output, and increasing the core flow rate increases the core thermal output. Furthermore, in order to maintain a constant output, the core flow rate must also be increased or decreased in response to the increase or decrease in the xenone concentration. Furthermore, the Zenon concentration output distribution also changes temporally and spatially.

In addition, in boiling water reactors, the relationship between core thermal output and core flow rate is regulated in order to maintain the integrity of the nuclear fuel and various equipment, and the reactor must be operated within these limits. FIG. 2 shows such a limited range, where the horizontal axis shows the core flow I, and the vertical axis shows the core thermal output, and the shaded area is the reactor operating range. Furthermore, in order to maintain the integrity of the nuclear fuel, the output distribution when the nuclear fuel is run-in in advance is hereinafter referred to as the PC envelope.

) is allowed to change the output distribution only.

Therefore, when performing load following operation in a boiling water reactor, the above-mentioned core flow rate and core thermal power distribution must be
It is necessary to do so while adhering to certain restrictions.

However, when reducing the output during load following operation,
It is possible that the core flow rate falls below the lower limit of the core flow rate shown in FIG. Furthermore, when the core flow rate is reduced in proportion to the decrease in the xenone concentration in order to maintain the power at a high power level, the core flow rate may fall below the minimum allowable core flow rate for the high power level. Furthermore, there is a possibility that the output distribution changes during the above-mentioned flow drop at the time of output, resulting in a region where the output deviates from the PC envelope. In particular, since the power fluctuations in the lower part of the core are large, there is a high possibility that the PC envelope in the lower part of the core will deviate. However, expanding the PC envelope in the lower part of the core by running-in means that the PC envelope in the upper part of the core,
It is more difficult than the central area.

Therefore, in order to change the core thermal output within the above-mentioned two limits, a combination of core flow rate adjustment and control rod manipulation is required.

By the way, when operating control rods in order to keep the core flow rate within a limit value, it is necessary to select the control rods to be operated while fully considering the influence on the local power distribution.

In addition, if the output deviates from the PC envelope, it is possible to insert a control rod near such a part to relatively reduce the output near the control rod, but by operating the control rod, The control rods cannot be easily manipulated because the power distribution of the reactor core changes significantly.

[Object of the Invention 1 The present invention has been made in response to such conventional circumstances,
When performing load following operation of a boiling water reactor, the operation limiting conditions and power distribution regulated by the core flow rate and core thermal output described above (1 [limiting condition, that is, P
It is an object of the present invention to provide a load following operation method for a boiling water nuclear power plant that can execute load following operation without deviating from the C envelope or the like.

In general, when performing load following operation, the possibility of deviating from the operational limit conditions is the lowest, and the most difficult to deal with is when the core flow rate is reduced to ensure a reduction in the xenone concentration during high power operation. At this point, there is a risk that the core flow rate may fall below the lower limit or the power output at the bottom of the core may exceed the PC envelope.

Therefore, in the present invention, the minimum flow part is kept above the lower limit value especially in high power operation, and the power in the lower part of the core is
The present invention aims to provide a load following operation method for a boiling water nuclear power plant that allows sufficient margin for the envelope.

[Summary of the Invention] That is, the present invention provides a load following operation method for a boiling water nuclear power plant in which low power operation and high power operation are performed alternately by adjusting the core flow rate and operating control rods. A PC in which all inserted control rods are fully inserted when the maximum allowable core flow occurs.
Control for low power operation in which a PC envelope is created in advance by performing the high power operation according to a control rod pattern for creating an envelope, and almost all of the control rods are inserted in the control rod turn for creating the PCC envelope. When the low power operation is carried out using the bar pattern and the a control of the high power operation is carried out by adjusting the core flow, the minimum core flow value is approximately equal to the allowable minimum core flow value. This is a load following operation method for a boiling water nuclear power plant characterized by an output operation restriction in which the control rods inserted in the control rod pattern for creating the PC envelope are withdrawn.

[Embodiment of the Invention] The details of the present invention will be described below with reference to an embodiment shown in the drawings.

According to the load following operation method of a boiling water nuclear power plant shown in this example, the reactor is first operated with a control rod pattern for creating a PC envelope, and then the control rod pattern for low power operation is used to create a PC envelope. Low output operation is performed for a certain period of time in the rod pattern, then high output operation is performed for a constant FR11 in the control rod pattern for high output operation, and by repeating this low output operation and high output operation, the load following operation becomes II. be exposed. That is, for example, perform 100% high output operation for 14 fi and 50% low output operation for 8 hours,
When performing a load following operation in which output fluctuations are performed for one hour each, the upper limit value of the core flow rate is set to 105%, and the lower limit value for high power operation is set to 86%.The control rod pattern for creating the PC envelope is the third one. The result will be as shown in the figure.

In FIG. 3, the symbols in the grid indicate the degree of insertion of the control rod, with 0 indicating full insertion and 48 indicating full withdrawal.

In addition, control rods that are completely withdrawn in the figure are left blank without reference numerals. In other words, in Figure 3, the number of control rods inserted is determined so that almost all the control rods are inserted when the core flow rate is 105% of the upper limit in high power operation, and the insertion positions are determined at high power operation. It is adjusted to the rated output during operation.

Here, the reason why the core flow rate is set to the maximum allowable flow rate is to make it possible to pull out the control rods that have been inserted nearly to the full insertion point in the high-power operation control rod pattern as described later.

Moreover, by doing this, the control rods are inserted deeply into the core, so the power distribution is shifted to the lower part of the core, and the PC envelope in the lower part of the core is expanded. Therefore, by performing high-power operation for a certain period of time using this tilll rod pattern for creating a PCC envelope, a PC envelope at the lower part of the core having a shape as shown as curve e in FIG. 4 is created. Furthermore, as will be described later, the control rods inserted in this PC envelope creation control rod pattern are not fully withdrawn even in the IIJ m rod pattern for low power operation, but only the insertion position is changed. .

The control rod pattern for low power operation is formed by inserting all the control rods in the control rod pattern for creating the PC■C vent loop shown in FIG.

Then, iJ is applied to the control rod pattern for high-power operation, which will be described later.
If there is an outermost control rod that has not been fully inserted, this outermost control rod will be fully inserted. Note that the outermost control rod inserted here is the outermost control rod that is inserted deeply in the control rod pattern for high-power operation (described later) (the outermost control rod is placed on the outer periphery of the reactor core and is designated by the reference numeral 10 in Fig. 5). ) is the same as the control rod. By fully inserting the control rods in this manner, the power distribution during low power operation can be made to have a bottom peak, that is, a power distribution having a peak at the bottom of the core.

Therefore, the patent application No. 56-868 already filed by the present applicant
As is clear from No. 87, it is possible to reduce the increase in power in the lower part of the core after a slow return to high power operation.

The control rod pattern for high-power operation is shown in FIG. In other words, the control rod pattern for high-power operation at this point is shown in Figure 3, where the deeply inserted control rods are withdrawn and at the same time the outermost control rods are deeply inserted so that the core flow rate almost matches the lower limit of 86%. In addition, the insertion position of the deep insertion control rod and the selection and insertion position of the outermost IIJ Ill rod are determined so that the output in the lower part of the core is the lowest.

In addition, the insertion position of the deeply inserted control rod is recalculated by fully inserting the outermost control rod selected here during low power operation, so that the minimum flow rate during high power operation almost matches the lower limit value. It can be decided.

The reason why the outermost control rods are deeply inserted is that, as is clear from Japanese Patent Application No. 136539/1983 filed by the present applicant, deep insertion of the outermost control rods increases the power output in the lower part of the core. By inserting the outermost control rod in this way, the control rod shown in FIG. 3 can be further pulled out. The number of outermost control rods to be inserted should be as small as possible, since increasing the number of outermost control rods inserted will cause the output to shift toward the center of the core, and conversely, the output at the bottom of the core will increase. It can be determined as follows.

When performing high-output operation using such a control rod pattern for high-output operation, the output distribution as shown by curve f in Fig. 4 is compared to the control rod pattern for PC envelope creation shown by curve 1e. , the power distribution can be shifted to the upper part of the core, and the power in the lower part of the core can be lowered. Therefore, even if the power in the lower part of the core increases during the minimum flow rate of high-power operation in load following operation, there is little chance of exceeding the PC envelope in the lower part of the core created by control rods forming the PCC envelope. 0.3kW allowed for output increase due to Zenon concentration change
/ft.

[Effects of the Invention] As described above, according to the load following operation method for a boiling water nuclear power plant of the present invention, the operation limit conditions regulating the core style and core thermal output, the PC envelope regarding the power distribution, etc. Load following operation can be performed without deviation, and load following operation can be performed while sufficiently ensuring the soundness of the fuel.

[Brief explanation of the drawing]

Fig. 1 is a graph showing temporal changes in core thermal output, core flow rate, xenone concentration, and iodine concentration during load following operation, Fig. 2 is a graph showing the reactor operating range, and Fig. 3 is an example of an implementation of the present invention. An explanatory diagram showing a control rod pattern for creating a PCC engine used in the example, Figure 4 shows the output when high output operation and low output operation are performed by the load following operation method of a boiling water nuclear power plant of the present invention. A graph showing the distribution, and FIG. 5 is an explanatory diagram showing a control rod pattern for high output operation. Representative patent attorney Satoshi Suyama - 11th hour Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In a load following operation method for a boiling water nuclear power plant in which low power operation and high power operation are performed alternately by adjusting the core flow rate and operating control rods, the maximum core flow allowed in the high power operation is A PC envelope is created in advance by performing the high-output operation using the control rod pattern for creating a PCC envelope in which all the control rods inserted are almost completely inserted when the control rods are inserted, and the control rod pattern for creating the PC envelope is created. The low power operation is performed using a control rod pattern for low power operation in which almost all of the control rods are inserted in the control rod pattern, and the minimum core flow rate when the high power operation is controlled by adjusting the core flow. The high power operation is performed using a high power operation control rod pattern in which the control rods inserted in the PC envelope creation control rod pattern are pulled out so that the value almost matches the value of the minimum allowable core flow rate. A load following operation method for a boiling water nuclear power plant characterized by: