JP3162516B2 - Nuclear reactor and control rod driving method for nuclear reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear reactor having a plurality of control rods and a control rod drive system for inserting or removing the control rods into or from a reactor core, and a control rod drive method for a nuclear reactor.

[0002]

2. Description of the Related Art Generally, a plurality of reactor control rods are arranged in a nuclear reactor, for example, a boiling water reactor (BW).
R) commercial power plant has an output of 1.35 million MWe,
Approximately 200 control rods are used for power control, power distribution control, or emergency shutdown of the furnace by inserting or removing these control rods into the core.

FIG. 4 is a schematic diagram showing an example of a control rod and a control rod drive system in a recent BWR plant.

In FIG. 4, a reactor 3 is equipped with a large number of control rods 4, and a control rod drive system for driving the control rods 4 includes an electric drive system 6 and a conventional hydraulic drive system 8. It consists of two systems. In order to shut down the reactor, all the control rods 4 can be inserted by the hydraulic drive system 8 and normal control rod operation enables fine adjustment of the output control by the control rods 4. The control rod 4 is designed to be driven at a low speed by using an electrically driven stepping motor 5 provided for one control rod.

Performing normal control rod operation at a low speed is as follows.
Since the power of the reactor can be finely adjusted and the thermal impact on the fuel is reduced, for example, the operation speed of the electric control rod is about 1/40 of the speed at the time of hydraulic drive, and It is designed to take about 2 minutes to pull out.

The operation speed of the control rods by the electric drive system 6 in the normal state is designed so that all the control rods 4 are at the same speed. It is controlled by the device 7.

When the control rod 4 is pulled out, the reactivity enters the core and the output increases. For this reason, in a nuclear power plant, various prevention functions or mitigation functions such as an interlock for preventing the control rod from being pulled out against an unusual increase in output and an emergency furnace stop function by a safety protection system are provided.

On the other hand, since the insertion of the control rod 4 is to add a negative reactivity to the reactor 3 and reduce the output, even if the control rod 4 is erroneously inserted, particularly, No interlock is installed in nuclear power plants.

In the case of the BWR, only a dozen or more control rods are inserted into the core during normal operation, and especially at the end of the operation cycle, when the reactivity of the core decreases,
Operating with all control rods pulled out. Therefore,
During normal operation, most control rods are withdrawn from the core.

[0010]

Incidentally, if the control rod control device 7 malfunctions during normal operation or if the operator mistakenly inserts all the control rods, for example, wholly withdrawn,
All the control rods except the inserted control rod are gradually inserted from the lower part of the core upward at the same speed.

Therefore, during the period from the start to the end of the insertion, all the control rods or almost all the control rods are inserted into the core with their axial positions coincident.
As for the power distribution of the core, only the power at the upper part of the core is large as shown by the curve B in FIG.
For example, the linear output density (output per unit length of fuel rod) may exceed a predetermined reference as shown by a curve B in FIG.

The present invention has been made in consideration of the above-described circumstances, and all the control rods are removed from a state in which all control rods are pulled out and a state in which almost all control rods are pulled out during normal operation. It is an object of the present invention to provide a reactor and a control rod driving method for a reactor that can be fully inserted while maintaining a good thermal property without increasing the power inside the reactor core even when the reactor is gradually inserted. .

[0013]

In order to solve the above-mentioned problems, a nuclear reactor according to the present invention has a plurality of control rods and a control rod drive system for inserting or removing the control rods from a core. In the nuclear reactor, the control rod drive system includes a first control rod drive system for rapidly inserting control rods for stopping the reactor, and a control rod drive system for inserting or removing control rods at a lower speed than the first control rod drive system. And a second control rod drive system for performing
Further, at least a plurality of control rods to be inserted or withdrawn by the second control rod drive system are divided into a plurality of control rod groups having different insertion speeds by the second control rod drive system. I do.

In order to solve the above-mentioned problem, a method of driving a control rod for a nuclear reactor according to the present invention comprises inserting a plurality of control rods into a nuclear reactor and rapidly inserting the control rods for reactor shutdown. A control rod drive system for a reactor having a first control rod drive system to perform insertion and withdrawal of control rods at a lower speed than the first control rod drive system. The control rod drive system according to the second aspect is characterized in that a plurality of control rods are inserted into a plurality of control rod groups having different insertion speeds by the second control rod drive system.

Further, in the method of driving a control rod for a nuclear reactor according to the present invention, the control rod which is inserted or withdrawn during normal operation is inserted at the same insertion speed by the second control rod driving system. It belongs to two groups.

[0016]

In the present invention having the above structure, the plurality of control rods to be inserted or withdrawn by the second control rod drive system are divided into a plurality of control rod groups having different insertion speeds by the second control rod drive system. During normal operation,
For example, even when all of the control rods that have been pulled out are inserted at a low speed due to a malfunction of the control rod control device or an erroneous insertion of the operator, the insertion position of each control rod group is different during the insertion. As a result, the power increase in the upper part of the core is alleviated, and the entire core can be inserted without the thermal characteristics exceeding a predetermined standard.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. In this embodiment,
Since the configuration of the control rod drive system is the same as that shown in FIG. 4, description will be made using the same reference numerals.

In FIG. 1, four fuel assemblies 1 are loaded around control rods 2a, 2b, 2c.
A unit lattice is composed of one of the fuel cells a, 2b, and 2c and the four fuel assemblies 1, and the unit lattice is arranged in a lattice to constitute a core.

The control rods 2a, 2b, and 2c are driven by two control rod drive systems, a hydraulic drive system and an electric drive system, and are rapidly driven by a hydraulic drive system 8 as a first control rod drive system for reactor shutdown. In the normal operation, the control rod operation is performed by the electric drive system 6 as the second control rod drive system provided for each control rod. Will be The insertion or withdrawal operation by the electric drive system 6 is controlled by the control rod control device 7.

The control rods 2a, 2b, and 2c are divided into a plurality of groups, for example, three groups. The control rods 2a belonging to the first group have an insertion speed of 9.0 cm / sec by the electric drive system 6, and the number thereof is Is 45. The control rod 2b belonging to the second group has an insertion speed of 6.0 cm /
sec, and the number is 52. In addition, the third
The control rods 2c belonging to the group have an insertion speed of 3.0 cm / sec by the electric drive system 6, and the number thereof is 88.
And, all the control rods 2a, 2b, 2
The total number of c is 185.

Next, the operation of this embodiment will be described.

During normal operation, the control rods 2b and 2c belonging to the second and third groups are fully drawn, and the control rods 2b and 2c belonging to the first group are adjusted to adjust the excess reactivity in the core.
a is used. That is, from the early stage to the middle stage of the cycle, 9 to 17 of the control rods 2a belonging to the first group are inserted halfway, and the remaining control rods are completely pulled out.

Consider a case where all the control rods are fully inserted by the electric drive system 6 due to a malfunction of the control rod control device 7 or an erroneous insertion of an operator at a certain time during normal operation, for example, at the end of an operation cycle.

FIG. 2 shows the axial power distribution of the nuclear reactor, the vertical axis shows the axial position of the core, and the horizontal axis shows the relative power when the average core power is set to 1. In FIG.
Curve A shows the axial power distribution in a state where the control rods 2c belonging to the third group in this embodiment are inserted from the lower end of the core to 30% of the core height, and curve B shows all the control rods having the same speed. The axial power distribution at 30% insertion when inserted at (3.0 cm / sec) is shown. Curve C shows the axial output distribution before the control rod is inserted.

In this embodiment, the control rods are not inserted at the same speed. When the control rods 2c belonging to the third group are inserted from the lower end of the core to 30% of the core height, the control rods belonging to the second group are not inserted. 2b is 60% and control rods 2a belonging to the first group are 9%.
Inserted to 0%. As a result, as compared with the case where the curve A is inserted at the same speed as shown by the curve B, the relative power at the upper part of the core becomes lower, and the distortion of the axial power distribution of the reactor is reduced.

FIG. 3 shows the time variation of the maximum linear output density,
The vertical axis indicates the maximum linear output density, and the horizontal axis indicates the time after the start of control rod insertion. In this embodiment, since the control rod is inserted at a constant speed, the horizontal axis corresponds to the control rod insertion ratio. Further, in this embodiment, since the insertion speed of the control rods 2c belonging to the third group is the slowest, all the control rods are fully inserted when the insertion percentage of the control rods 2c belonging to the third group becomes 100%. ing.

A curve D in FIG. 3 is a time change of the maximum linear output density in this embodiment, and a curve E is a maximum linear output when all the control rods are inserted at the same speed (3.0 cm / sec). It is a time change of density. Therefore, in this embodiment, the maximum linear output density does not exceed the predetermined reference from the start of insertion until all control rods are inserted.

In this embodiment, the control rods 2a belonging to the first group having the fastest control rod insertion speed include control rods operated during normal operation. For example, the control rods 2a belonging to the first group are included.
a of the control rod control device 7 or the erroneous insertion of the operator at the time when 9 to 17 are inserted halfway,
Even when all the control rods are fully inserted by the electric drive system 6, the control rods 2a belonging to the first group are fully inserted before the control rods belonging to other groups.

Conversely, if another group has an insertion speed higher than that of the control rod 2a belonging to the first group, the insertion position of the control rod 2a belonging to the first group and the insertion position of the other group during the insertion. Matching may occur, and the effects shown in FIGS. 2 and 3 cannot be expected.

The present invention is not limited to the above embodiment, but can be variously modified. For example, the control rod group operated during normal operation needs to be included in the first control rod group having the same insertion speed, but the number of other control rod groups is 2 as in the above embodiment. Not only groups but also one or three or more groups may be provided.

That is, the control rod group only needs to include the first control rod group and the second control rod group which is different from the first control rod group in insertion speed and is formed of at least one group. The reason why the control rods operated during the normal operation are set to the same speed is to facilitate the operation of the output adjustment by the control rods.

Also, the fact that the control rods operated during operation include control rods belonging to a group of extremely high insertion speeds,
When the control rod is operated during the normal operation, the thermal effect on the fuel becomes large, which is not preferable.

Further, extremely slowing down the insertion speed of the control rod increases the operation time, which is not preferable for control rod operation. Therefore, it is preferable to set the control rod at an insertion speed of about 3 to 10 cm / sec.

The group including the control rods operated during the normal operation is preferably the group having the highest insertion speed. This is because even when all the control rods are fully inserted by the electric drive system 6 due to a malfunction of the control rod control device 7 or an erroneous insertion of the operator while some control rods are inserted during normal operation. During the period from the start to the end of insertion, the insertion position of the control rod operated during normal operation should not match the insertion position of the group that does not include the control rod operated during normal operation. is there.

[0036]

As described above, according to the nuclear reactor and the control rod driving method for a nuclear reactor according to the present invention, a plurality of control rods to be inserted or withdrawn by the second control rod drive system are used. Since the control rod drive system is divided into a plurality of control rod groups having different insertion speeds, all the control rods that are pulled out during normal operation, for example, due to a malfunction of the control rod control device or an erroneous insertion of the operator, are removed. Even when the control rods are inserted at a low speed, the insertion positions of the control rod groups are different during the insertion.

As a result, the power increase in the upper part of the core is alleviated without the power in the core fluctuating upward, and the whole can be inserted without the thermal characteristics exceeding a predetermined standard.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing a configuration of a quarter of a core in one embodiment of a nuclear reactor according to the present invention.

FIG. 2 is a graph showing axial power distributions of the reactor of the present embodiment and a conventional example.

FIG. 3 is a graph showing a time change of a maximum linear output density in the present embodiment and a conventional example.

FIG. 4 is a schematic diagram showing a control rod and a control rod drive system of a BWR plant.

[Explanation of symbols]

 Reference Signs List 1 fuel assembly 2a control rod belonging to first group (first control rod group) 2b control rod belonging to second group (second control rod group) 2c control rod belonging to third group (third control rod) Group) 6 electric drive system (second control rod drive system) 7 control rod controller 8 hydraulic drive system (first control rod drive system)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G21C 7/12 G21C 7/08 G21C 7/00

Claims (3)

(57) [Claims] In a nuclear reactor having a plurality of control rods and a control rod drive system for inserting or removing the control rods into or out of the reactor core, the control rod drive system quickly switches the control rods to shut down the reactor. A first control rod drive system to be inserted, and a second control rod drive system to insert or withdraw control rods at a lower speed than the first control rod drive system, and at least the second control rod drive system A reactor, wherein a plurality of control rods to be inserted or withdrawn by a system are divided into a plurality of control rod groups having different insertion speeds by the second control rod drive system. 2. A plurality of control rods in a nuclear reactor, a first control rod drive system for rapidly inserting the control rods for stopping the reactor, and a lower speed than the first control rod drive system. A control rod drive system for a reactor having a second control rod drive system for inserting or withdrawing control rods in the control rod drive system.
A control rod driving method for a nuclear reactor, wherein the control rod driving system is divided into a plurality of control rod groups having different insertion speeds. 3. The control rods to be inserted or withdrawn during a normal operation belong to one group inserted at the same insertion speed by the second control rod drive system. Control rod driving method for nuclear reactors.