JPH01162194A - Load following operation of nuclear reactor - Google Patents

Abstract

PURPOSE:To compensate a reactivity change caused by a load following operation of a nuclear reactor, by providing a water rejecting tube in a fuel assembly and exchanging a fluid in the water rejecting tube from water to a water rejecting material. CONSTITUTION:In a fuel assembly 2 of a pressurized water nuclear reactor, its structural members consist of an upper nozzle and a lower nozzle 7 and 8, a support grid 11 and a control rod guide thimble 12. Between the nozzles 7 and 8, a number of fuel rods (only one rod is shown in the attached figure) and one or more water rejecting tubes 14 are housed. A pressurized gas or heavy water is filled in a tank 25 by closing a valve V1 of an injection device of a water rejection material. When valve V2 is opened, water in the tube 14 is flushed with a pressure decrease in the tube and the water in the tube 14 flows out from a junction tube 24. With closing the valve V2 and opening the valve V1, the water rejecting material in the tank 24 is injected into the tube 14 through an injection tubes 17a and 17b and also an injection inlet 18. Thereby, an H/U ratio changes and then compensation of a reactivity can be executed. The similar procedure can be applied for exchanging the water rejecting material with water.

Description

Detailed Description of the Invention (a) Purpose of the Invention [Field of Industrial Application] The present invention relates to a load following operation method for controlling output and reactivity during load following operation of a nuclear reactor.

[Prior Art] Generally, when the output of a nuclear reactor is changed, there are a change in reactivity A due to a change in moderator temperature, a change in Doppler reactivity B due to a change in fuel temperature, and a change in reactivity C due to a change in xenon amount. be. Figure 7 shows an example of changes in output and reactivity during load following operation of a nuclear reactor.

Reactivity control equipment must be operated to compensate for these reactivity changes.

FIG. 8 shows a cross section of the reactor vessel 22 of the pressurized water reactor. The reactor core 10 is loaded with fuel, and there are control rods 32 and boric acid 33 mixed in the primary coolant as equipment for controlling the reactivity of the reactor core.

The control rods 32 include an output control control rod with a high reactivity value used for output control, and a weak reactivity control rod with a lower reactivity value than the output control control rod used as an auxiliary to the output control control rod during load following operation. There is an absorption control rod.

[Problems to be Solved by the Invention] When boric acid is used in addition to control rods for reactivity control in a pressurized water reactor, it is necessary to frequently concentrate and dilute the boric acid. Concentration or dilution of boric acid is usually performed by injecting boric acid water or pure water into the inlet side of the primary coolant bomb in the secondary system loop, but this method changes the boric acid degree in the secondary coolant on average. Because of this, the rate of change in reactivity is small. Therefore, it is difficult to use it to control rapid changes in reactivity due to rapid changes in output; Furthermore, the amount of water to be treated increases as the boric acid concentration changes, increasing the cost of the water treatment system. Weak absorption control rods were devised as a solution to the aforementioned problems caused by the use of boric acid, and instead of concentrating or diluting boric acid, they are moved in and out of the reactor core to control reactivity, but they do not affect the power distribution. The impact is large, and a drive device and control rod guide tube are required, which also increases costs. Also, since there is a drive section, reliability and durability become issues.

Furthermore, if an attempt is made to control the output using only the control rods, the power distribution within the reactor core will deteriorate due to the insertion and withdrawal of the control rods, reducing the safety margin.

As a method of controlling the reactivity in the reactor core, in addition to the method of changing the neutron absorbing material in the core as described above, there is a method of changing the hydrogen to uranium atomic ratio (H/U). This is a method of controlling reactivity by changing the neutron energy spectrum within the reactor core by changing H/U.

As for pressurized water reactors, a nuclear reactor with a function of changing the H/Ll ratio in the core has been proposed, as shown in the invention of Japanese Patent Application No. 184390/1982. The purpose is to reduce the amount of uranium used by changing the /Ll ratio, and it is not intended to control the reactivity as the load changes.

This invention was made in view of the above circumstances, and an object of the present invention is to provide an operating method that can easily control reactivity in response to load changes without deteriorating the power distribution within the reactor core. That is.

(B) Structure of the Invention [Means for Solving the Problem] In response to this objective, the load following operation method for a nuclear reactor of the present invention provides a method for operating a nuclear reactor in which a coolant region is used in an area other than the area occupied by fuel elements in the reactor core. A light water-cooled, light water-moderated nuclear reactor separated into a water exclusion area, characterized in that the fluid in the water exclusion area is replaced between water and a water exclusion material to compensate for changes in reactivity due to load following operation. .

Hereinafter, details of the present invention will be explained with reference to the drawings showing one embodiment.

In FIG. 1, reference numeral 1 denotes a water removal material injection facility, and the water removal material injection facility 1 includes a fuel assembly 2 and a fluid supply/discharge device @3.

The fuel assembly 2 includes an upper nozzle 7, a lower nozzle 8, a support grid 11, and an i-control rod guide simple 12 as structural members, and between the upper nozzle 7 and the lower nozzle 8, a fuel rod 13 and a water drainage pipe 14 are installed. It can be paid.

There is one or more water discharge pipes 14 per fuel bundle, and the water discharge pipes 14 are hollow pipes whose upper ends are sealed. A plurality of water discharge pipes constitute one set, and the water discharge pipes in one set are connected by a connecting pipe 15 at a leg portion of the lower nozzle 8.

The connecting pipe 15 is a connection port 1 for injecting and discharging water removal material.
Has 6.

The water exclusion material injection pipe 17a on the lower core structure side has an injection port 18 to each fuel assembly, and is connected below the five-part core plate 21 to the water exclusion material injection pipe 17b on the reactor vessel 22 side. And connection position! It is connected via I23.

The water removal material injection pipe 17b penetrates the reactor vessel 22 and is connected to the water removal material injection tank 25 via the valve 1 on the upstream side of the branch pipe 24 of the fluid supply and discharge device 3. A water exclusion material injection system 27 and a water injection system 28 are connected to the water exclusion material injection tank 25 . Additionally, a pressurizing system 31 is attached, and the water removal system can be pressurized.

A valve 2 is attached to the branch pipe 24, and the end thereof is connected to the blowdown system.

In this invention, a fuel assembly is used in which a region other than the fuel elements in the core is separated into a region through which coolant flows and a region into which a water removal material or water flows.

FIG. 2 shows a horizontal sectional view of the fuel assembly 2 used in the present invention. In this embodiment, the fuel rods 13 (
That is, a control rod guide simple 12, a water discharge pipe 14, and an instrumentation guide pipe 19 are included in the fuel rod bundle. The control rod guide simple 12 is a hollow tube with an open upper end, into which a control rod is inserted from the upper side, and contains water when the control rod is pulled out.

The water discharge pipe 14 is sealed at its upper end and connected at its lower end to the fluid supply and discharge device 3 located outside the reactor vessel.

A gas such as helium or argon, or heavy water is used as the water removal material.

Because reactivity within the core must be precisely controlled, fuel assemblies are divided into multiple groups.

Figure 4 shows a cross-sectional view of the core and an example of grouping of fuel assemblies. In this example, the fuel assembly is divided into four groups from the first group to the fourth group, and the fluid in the water discharge pipes of each group can be replaced independently for each group.

[Operation] Next, a load following operation method in the nuclear reactor having the above configuration will be explained.

When the load fluctuates, reactivity control during load following operation is performed using changes in the water removal rate in the control rods and core. The water removal rate is changed as follows.

a) The fuel assembly 2 is loaded into the reactor core 10 and the reactor vessel 22 is loaded.
After putting on a lid (not shown), the primary coolant is pressurized to about 157 atmospheres and heated to about 290°C. At this time, the inside of the water discharge pipe 14 is filled with water, and the water discharge system is pressurized to the same pressure as the primary coolant by closing valve (2) and opening valve (v1). In this state, the reactor output is still zero.

b) Close the valve v1 to remove the water in the water removal material injection tank 25, fill it with water removal material instead, and pressurize it to about 157 atmospheres. The water exclusion material may be a gas such as helium or argon, or heavy water, as long as it has a small neutron absorption and a neutron moderation effect smaller than that of water.

C) Next, open valve ■2. The branch fff24 is connected to the blowdown line, and the water removal pipe 14 is connected to the reactor core 1.
Since the temperature is about 290° C., which is the same as that of the coolant in the water, flushing occurs as the pressure is reduced, and the water in the water discharge pipe 14 is water and the water in the discharge material injection pipe 17a.

17b and flows out from the branch pipe 24 to the blowdown line.

d) When the water in the water drainage pipe 14 flows out, close the valve 2 and open the valve 1. Since the inside of the water removal material injection tank 25 is pressurized, the water removal material inside the water removal material is used as a water removal material. The water is injected into the water removal pipe 14 through the injection pipe 178.17b.

e) If the operation is started in this state, the inside of the water discharge pipe 14 will be filled with the water discharge material and water will be discharged. During operation, the valve 1 is opened to pressurize the water removal material injection tank 25 to the same pressure as the primary coolant, so that a large pressure difference is not applied to the water removal pipe 14.

f) To replace the water removal material in the water removal pipe 14 with water during load following operation, close the valve 1 and replace the water removal material in the water removal material injection tank 25 with water, and then ), d
), e).

FIG. 4 shows a typical example of the change m in H/U ratio versus the amount of change in reactivity. This figure changes depending on the absolute value of the H/Ll ratio, etc., but here it is shown for the case where the H/U ratio is 4.5 when water is poured into the water exclusion region.

The control reactivity m during load following operation varies depending on the range of output change, but the maximum value is approximately 3.0 when the output changes from 100% to 0%.
5% Δρ, and therefore it is necessary to change the water rejection rate by about 15% to compensate for the total reactivity control by changing the H2O ratio. Although this value varies depending on the H/U ratio, it is sufficient to consider up to 20% in a realistic H/U range.

In addition, it is only necessary to consider that the reactivity change due to xenon during load following operation is about 1%Δ at most, so only the xenon component is compensated for by the change in the H/U ratio, and other reactivity changes are compensated for by the control rod. In this case, the water removal rate should be changed by about 5%.

FIG. 5 shows an example of operation in which all reaction changes are compensated for by changes in the H/U ratio during daily load following operation for 18 hours at 100% output and 6 hours at 50% output. In this example, water removal pipes for the entire fuel assembly are used, and the maximum water removal rate is about 20%.

The fuel assembly is divided into four groups and the H/U ratio is changed in five stages. Therefore, since the water removal rate does not change continuously, the control rods are moved auxiliary to compensate for the change, keeping the output constant.

As can be seen from FIG. 5, the control rods only move slightly near the top of the core for power correction, and therefore the power distribution within the core is very stable.

FIG. 6 shows an example of operation in which xenon changes are mainly compensated for by changes in the HlU ratio. In this example, the maximum water removal rate used for load following operation is 4%.

These water exclusion areas are divided into four groups, and the H/U ratio can be changed in stages.

To reduce the power to 50%, move the control rods to 60% of the core.
Insert up to the position. After the power decreases, reactivity compensation due to the accumulation of xenon is mainly performed by changing the water rejection rate. The reason why the control rod position is moved at low power is to control the power distribution, and the reason why there is a step is to compensate for the change in reactivity that changes the water removal rate in a stepwise manner. After 6 hours, after returning the output to 100%,
Again, water is removed in stages to compensate for the change in reactivity due to xenon.

(c) Effects of the invention In this invention, most of the reactivity control during load following operation is performed using control rods and changes in the water removal rate in the core.
No additional equipment is required to implement load following operation.

Specifically, during load following operation, boric acid is not concentrated or diluted, so there is no need to strengthen equipment for boric acid concentration or dilution.

Furthermore, since there is no need to use weakly absorbing control rods, cost increases can also be avoided.

Next, since the H2O ratio can be changed uniformly in the axial direction, changes in the axial power distribution can be suppressed to a smaller extent than in the case of using control rods. Therefore, the safety margin does not decrease due to load following operation.

In this way, this invention compensates for changes in reactivity due to changes in load by replacing the fluid in the water exclusion region, thereby significantly reducing movement of the control rods and reducing the concentration of boric acid in the secondary coolant. It can be reduced to almost zero.

In the conventional load follow-up method, xenon compensation was performed using boric acid, so the period during which load follow-up was possible was limited due to limitations in the dilution ability of boric acid. Furthermore, since boric acid cannot respond to rapid changes in reactivity, the ability to quickly return to 100% output is limited. The present invention can solve these problems all at once without increasing equipment, and the ability to respond to load following operation is greatly improved.

Furthermore, there is no need for a control rod for load following, making it possible to significantly reduce costs.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the configuration showing the water removal equipment of the reactor, Figure 2 is an explanatory cross-sectional diagram of the fuel assembly of the reactor, Figure 3 is an explanatory diagram of the configuration of the reactor core, and Figure 4 is an explanatory diagram of the configuration showing the reactor core. A graph showing the relationship between the amount of change in the H/U ratio and the amount of change in reactivity. Figure 15 is a graph showing the time change in output, control rod position, and water removal rate.
The figure is a graph showing changes in output, control rod position, and water removal rate over time, and Figure 7 is a graph showing an example of changes in output and reactivity.
and FIG. 8 is an explanatory longitudinal cross-sectional view of the reactor vessel. 1...Water removal material injection equipment 2...Fuel assembly 3.
...Fluid supply and discharge device 4...Fluid recovery tank 5...
Gas surge tank 6...Water supply pump 7...Upper nozzle 8...5 part nozzle 10...Reactor core
11...Support grid 12...Control rod guide simple 13...Fuel rod 14...Water removal pipe 15.
...Connecting pipe 16... Connection port 17a. 17b... Water removal material injection pipe 18... Inlet 19
...Instrumentation guide tube 21...Lower core plate 22...
・Reactor vessel 23... Connection position 24... Branch pipe 25... Water removal material injection tank 27...
Water removal material injection system 28... Water injection system 31...
Pressure system Figure 2 + 1ft Jichi v1 Ite Figure 7 Time Time

Claims (4)

[Claims] (1) In a light water-cooled light water-moderated nuclear reactor that is separated into a coolant region and a water exclusion region in an area other than the area occupied by the fuel elements in the core, the fluid in the water exclusion area is transferred between the water and the water exclusion material. A method for load following operation of a nuclear reactor, characterized by compensating for changes in reactivity due to load following operation by replacing the parts. (2) Load tracking of a nuclear reactor according to claim 1, characterized in that the water exclusion area is divided into a plurality of water exclusion area sections, and the replacement is performed for each of the water exclusion area sections. how to drive (3) For the portions of the water exclusion area where the water removal rate is equal to or less than 20%, the water exclusion area is divided into multiple groups and the fluid in the groups is sequentially replaced with water and water removal material. A method for load following operation of a nuclear reactor according to claim 1 or 2, further comprising performing reactivity compensation using control rods in an auxiliary manner (4) For the portions of the water removal area where the water removal rate is equal to or less than 5%, the water removal area is divided into multiple groups to compensate for changes in reactivity due to changes in xenon amount due to load following operation. Claims 1, 2 or 3, characterized in that the fluid in the water exclusion region is sequentially replaced with water and a water exclusion material for each group as an aid to reactivity compensation by the control rod for output changes. Load following operation method of nuclear reactor described in Section 3