JPH0631819B2 - Load following operation method of nuclear power plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a load following operation method for a nuclear power plant using a boiling water reactor.

(Prior art) In a conventional nuclear power plant, load follow-up operation with an output adjustment range of about 30% (for example, high output 100%, low output 70%) is adjusted only by core flow control, For such load following operation, a method has been proposed in which the power reduction that cannot be achieved by the core flow rate control is realized by inserting the control rod.

The graph of FIG. 5, in which the horizontal axis represents time and the vertical axis represents reactor power, core flow rate and control rod density, shows the time variation of reactor output, core flow rate and control rod density when operated by the conventional load following operation method. Curves 1, 2 and 3 are shown respectively.

Further, FIG. 6 shows the reactor output 1 and the core flow rate 2 shown in FIG.
The operating locus is shown by the curve 4 on the power / core flow map, and the curve 5 shows the operation limit line showing the operable range of the reactor for maintaining the soundness of the nuclear fuel and various equipment.

As shown in these figures, in the conventional load following operation method, the control rod operation is not performed as much as possible, and the reactivity is compensated for the output change and the Zenon concentration change by adjusting the core flow rate. Therefore, the core flow rate is from the minimum value indicated by the reference numeral 2a to the maximum value indicated by the reference numeral 2b in the low power operation, and from the maximum value indicated by the reference numeral 2c in the high power operation.
It greatly fluctuates to the minimum value shown by. Fig. 7 shows the power distributions when the core flow rates are 2a, 2b, 2c and 2d by curves 6, 7, 8 and 9, respectively, and Fig. 8 shows the void fraction distributions when the core flow rates are 2c and 2d. Curve 1 respectively
It is indicated by 0 and 11. As is clear from these figures, the power distribution and the void fraction distribution change depending on the core flow rate. Regarding the void fraction distribution, the void fraction increases throughout the reactor as the core flow rate decreases.

As described above, in the conventional load following operation method, priority is given to the power adjustment by the core flow rate control, but it is better to use the core flow rate control in which the variation of the local output is small from the viewpoint of fuel integrity. This is because the control rod operation is preferably restricted particularly at high output. In order to maintain the soundness of the fuel, conventionally, the operation was performed below the output distribution (PC envelope) where sufficient run-in operation was performed, and if it exceeded this, a large restriction was imposed. On the other hand, in load following operation, the xenon concentration is constantly changing, and the output distribution also changes accordingly, but if the control rod operation with a large amount of output fluctuation is used, the fluctuation of the output distribution becomes even larger, and There was a risk of violating. Therefore, the operation of the control rod, especially at the time of high output, was largely restricted.

In order to significantly relax such restrictions on fuel,
A high-performance fuel with zirconium lined inside the cladding tube was developed, and it became possible to freely change the output below a certain output (threshold value), but in the core loaded with this fuel Spectrum shift operation is required to improve the economy of the. Spectral shift operation refers to increasing the void ratio in the core by reducing the core flow rate as much as possible during most of the operation cycle.
This is a rated power operation method that increases the burn-up of fuel by increasing the production amount of Pu-239 and burning the generated Pu-239 by increasing the core flow rate at the end of the operation cycle.

(Problems to be Solved by the Invention) As described above, in the high-performance fuel core, while the constraint from the fuel integrity is greatly relaxed, the operation with the fuel economy as high as possible is required. The conventional load following operation method differs from the spectrum shift operation method in that it operates even on the high flow rate side. Therefore, in the high-performance fuel core, when the load following operation is performed by the conventional operation method although there is a sufficient margin for the fuel integrity, there is a possibility that the fuel economy may be impaired.

The present invention has been made in consideration of such a point, and an object of the present invention is to provide a load following operation method capable of improving fuel economy.

[Structure of the Invention] (Means for Solving Problems) In the load follow-up operation method for a nuclear power plant of the present invention, the core flow rate is decreased to reduce the output, and the core flow rate becomes the lower limit flow rate value at a low output level. If the output does not reach the low output target level even if it reaches, the output reduction operation in which the control rod is inserted and the output change accompanying the Zenon concentration change after this output reduction operation are compensated mainly by the control rod operation to output the output. Low power operation to maintain low power target level and power up operation to increase the core flow rate to the lower limit flow rate value at the high output level and adjust the deviation between the output at the lower limit core flow rate and the high output target level by operating the control rod. And a high-output operation for maintaining the output at the high-output target level by compensating for the output change accompanying the change in the Zenon concentration after the output-increasing operation mainly by operating the control rod. And wherein the Ranaru.

(Operation) According to the load follow-up operation method for a nuclear power plant of the present invention having the above configuration, the operation can be performed in a state where the core flow rate is low.

In general, for the same power level, the lower the core flow rate, the higher the core void fraction and the higher the amount of Pu-239 produced. Therefore, the load following operation method for a nuclear power plant of the present invention can improve fuel economy.

(Examples) Hereinafter, the details of the method of the present invention will be described with reference to the drawings.

FIG. 1 shows a load follow-up operation method according to an embodiment of the present invention. Similar to FIG. 5, curve 1 represents the reactor power, curve 2 represents the core flow rate, and curve 3 represents the control rod density with time. . As shown in this figure, the power level operation at the high power level is performed at the core flow rate 2e near the lower limit allowed at the high power level. Then, when the power reduction operation is performed, the core flow rate is reduced and the power is reduced to a target low power level. At this time, the control rod is inserted only when the output does not drop to the target level even when the core flow rate reaches the lower limit value allowed at the low output level.

After the output decreases, the Zenon concentration increases, but the output change due to this increase in Zenon concentration is compensated by pulling out the control rod,
Keep the output at the target level. At this time, when the output does not match the target level because the reactivity of the control rod is large, the core flow rate is adjusted within a predetermined range as the flow rate adjustment range A, and the output is adjusted. Also, this flow rate adjustment range A
If the output cannot be made to match the target level within, the control rod is further operated to perform the output level operation.

When the core flow rate has a margin with respect to the lower limit value, it is desirable that the flow rate adjustment range A be provided on the lower flow rate side from the core flow rate 2f at the time of power reduction. Further, the Zenon concentration changes from increasing to decreasing 5 to 6 hours after the output is reduced, and in this case also, the output is adjusted by inserting the control rod.

Next, when the power increasing operation is performed, the core flow rate is increased to the lower limit flow rate 2e at the high output level. FIG. 2 shows the locus of the reactor output 1 and the core flow rate 2 in the load following operation shown in FIG. 1 as a curve 12 on the output / flow rate map. Since the operation locus during operation is almost on the same point 13 on the output / flow rate map, when the output is increased by increasing the flow rate from this low output operation point 13, the output / flow rate is almost the same as before the output decrease. Return to the output operating point 14.

That is, when the core flow rate returns to the lower limit flow rate 2e that is allowed at the high output level, the output also returns to almost the target level. If the output deviates slightly from the target level, the output is made to match the target level by adjusting the control rod.

After returning to the high output level in this manner, the Zenon concentration sharply decreases, which is compensated by the insertion of the control rod. At this time, as in the case of the power level operation of the low power level, the reactivity value of the control rod is large, and therefore when the power does not match the target level, there is a certain range from the lower limit 2e of the core flow to the high flow The flow rate is adjusted within the adjustment range B so that the output matches the target level. If the output cannot be made to match the target level within this adjustment range B, the control rod is further operated.

As described above, in the method of this embodiment, the load following operation is performed in the state where the core flow rate is low. Therefore, the void ratio in the reactor is always kept high, the amount of Pu-239 accumulated increases, and the fuel economy is improved.

Another embodiment of the present invention is shown in FIGS. 3 and 4. Similar to FIG. 1, FIG. 3 shows changes in reactor output 1, core flow rate 2 and control rod density 3 with time, and FIG. 4 is an output / flow rate map thereof similar to FIG. This example shows the operation method when the core flow rate 2 is still lower than the lower limit even if the core flow rate 2 is decreased to lower the reactor power output 1 from the high power level to the target low power level. In this case, The core flow rate 2 is reduced to the lower limit of 2 g by pulling out the control rod.

In FIG. 4, a solid line 15 shows an operation locus when the control rod is pulled out and the core flow rate is decreased at the same time.
Reference numeral 6 shows an operation locus when the core flow rate 2 is first reduced to reduce the output, and then the core flow rate 2 is reduced to the lower limit value 2 g by pulling out the control rod. Further, the adjustment range C of the core flow rate 2 at the time of low power operation is provided with a certain width on the higher flow rate side than the lower limit value 2g.

In this load following operation method, when the furnace output is returned to the high output level again, it is necessary to insert the control rod having the reactivity value similar to that of the control rod withdrawal when the output is reduced. When only the core flow rate is increased without inserting the control rod, the output increases from the low power operation point 17 shown in FIG. Will end up. As described above, in this embodiment, the core flow rate at the low power level is lowered to the lower limit value, so that the void ratio in the reactor is further increased and the fuel economy is further improved.

〔The invention's effect〕

As is clear from the above description, according to the method of the present invention,
Since the state with a high void ratio in the reactor is always maintained during the load following operation, the load following operation can be performed without impairing the economical efficiency of the high performance fuel core. In addition, as compared with the spectrum shift operation, which is a rated output operation method that improves the fuel economy of the high performance fuel core, the void ratio in the reactor during the low output operation period of the load following operation becomes even higher. The accumulation amount of Pu-239 increases more than the case,
Economic efficiency is further improved.

[Brief description of drawings]

FIG. 1 is a graph showing changes over time in reactor power, core flow rate and control rod density in the method of one embodiment of the present invention, FIG. 2 is a graph showing the relationship between reactor power and core flow rate in FIG. 1, and FIG.
FIG. 4 is a graph showing changes over time in the reactor power, core flow rate and control rod density in the method of another embodiment of the present invention, FIG. 4 is a graph showing the relationship between the reactor power and core flow rate in FIG. 3, and FIG. Fig. 6 is a graph showing changes in reactor output, core flow rate and control rod density with time in the conventional method, Fig. 6 is a graph showing the relationship between the reactor output and core flow rate in Fig. 5, and Fig. 7 is a graph showing the conventional method during high power operation. A graph showing the output distribution at the maximum and minimum flow rates and the output distribution at the maximum and minimum flow rates during low output operation, and FIG. 8 is a graph showing the void fraction distribution at the maximum and minimum flow rates during high output operation by the conventional method. Is. 1 …… Reactor output curve 2 …… Core flow rate curve 2e …… Lower limit flow rate during high power operation 2f …… Core flow rate when output is reduced 3 …… Control rod density change over time A, B,… Flow rate adjustment range

Claims (1)

[Claims] 1. A power reduction operation in which a control rod is inserted only when a core flow rate is reduced to reduce an output and the core flow rate reaches a lower limit flow rate value at a low output level but the output does not reach a low output target level. And a low-power operation in which the output change accompanying the Zenon concentration change after the power-down operation is compensated mainly by control rod operation to maintain the output at the low-power target level, and the core flow rate is set to the lower limit flow rate value at the high-power level. Power up operation to adjust the deviation between the output at the lower limit core flow rate and the high power target level by operating the control rod, and to compensate the output change accompanying the Zenon concentration change after this power up operation mainly by operating the control rod. And a high output operation for maintaining the output at the high output target level.