JPS62245989A - Control rod - 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 [Field of Industrial Application] The present invention relates to a control rod, and particularly to a raster type control rod which is suitable for improving fuel economy.

[Conventional technology] Surplus reactivity control and high force distribution control of light water reactors are performed using control rods,
This is done by mixing burnable poison rods and boric acid water into the coolant.

Cluster control rods used in pressurized wooden nuclear reactors consist of multiple spider arms and multiple neutron absorption rods attached to them, as described in Japanese Patent Application Laid-open No. 55-57188. The cluster is configured to be driven by a single control rod drive shaft. In addition, a cruciform control rod used in a boiling water reactor has wings made of a large number of neutron absorption rods arranged in a row attached to a drive shaft in a cruciform shape. Therefore, in these conventional control rods, all the neutron absorption rods of the control rod are driven and operated at the same time, and these neutron absorption rods cannot be operated separately.

By the way, in recent years, in order to simplify the operation of nuclear reactors, control rods are mainly used as a means of stopping the reactor, and as a means of controlling excess reactivity and power distribution, substances with large depletion of neutron absorbing material are used. A burnable poison sacrificial substance containing

There are two types of burnable poison rods: one in which a burnable poison is mixed into the fuel rod, and a burnable poison rod formed independently of the fuel rod. An example of the former is JP-A-55-70
There is a gadolinia-containing fuel rod disclosed in Japanese Patent No. 792, which is widely used in fuel assemblies of boiling water reactors. An example of the latter is a neutron absorbing rod made of a burnable poison and a moderator that does not contain a fuel substance, as disclosed in Japanese Patent Application Laid-Open No. 55-113991. These burnable poison rods are not manipulated during reactor operation and are used for at least one period from the time a fuel assembly is loaded into the core until the next time another fuel assembly is removed from the core. It remained in the furnace until the end of the operating cycle.

[Problems to be solved by the invention] To improve the fuel economy of a nuclear reactor, at the end of the operating cycle,
It is important not to allow unnecessary neutron absorbing substances such as burnable poisons to remain in the reactor core. In particular, when attempting to achieve a high burnup, the surplus reactivity of the core increases, and the amount of burnable poison waste used for surplus reactivity control also increases. For this reason, the amount of burnable poison used for control remaining increases, but in the prior art, no consideration was given to a means to remove this from outside the reactor core.

The purpose of the present invention is to remove burnable poisons used for surplus reactivity control from the reactor core at the end of the operating cycle.

The goal is to improve the fuel economy of nuclear reactors.

[Means for Solving the Problems] In order to achieve the above object, the present invention divides a plurality of neutron absorbing rods of a control rod into at least two groups, and divides the neutron absorbing rods of one group into other groups. The neutron absorbing rod is made of a neutron absorbing material that has a higher depletion loss than the neutron absorbing material that makes up the neutron absorbing rod.

The neutron absorbing materials with large depletion used in the above-mentioned group of neutron absorbing rods include mixtures of gadolinia, europium, boron, cadmium, etc. (e.g. boron-containing stainless steel) and compounds (e.g. Gd2O,
). Low depletion neutron absorbing materials used in the other groups of neutron absorbing rods mentioned above include boron carbide and hafnium, which are used in conventional control rods.

[Operation] The control rod having the above-mentioned characteristics can solve the above-mentioned problems by operating as follows.

The two groups of neutron absorbing rods are operated separately during one operating cycle of the reactor. In other words, among all the neutron absorbing rods in the two groups inserted into the reactor core, the neutron absorbing rod that has a neutron absorbing material with low m loss is pulled out from the reactor at startup, and the operating cycle period of the reactor is extended. Excess reactivity can be controlled by a neutron absorption rod containing a neutron absorption material with large depletion. Furthermore, at the end of the operating cycle, the neutron absorbing rods containing the neutron absorbing material with large depletion that had been inserted into the reactor core can be withdrawn from the reactor core.

By operating the neutron absorption rods independently in this way, while maintaining the role of the burnable poison frame and the conventional control rod,
At the end of the operating cycle, when there is no excess reactivity, it becomes possible to remove all burnable poison frames from the reactor core.

[Embodiment] A control rod which is a preferred embodiment of the present invention will be described below with reference to FIGS. 1 and 2. The control rod 1 has 16 spider arms. The four spider arms 2 are the drive shaft 4
and the remaining 12 spider arms 3 are each fixed to the drive shaft 5.

The drive shaft 4 is arranged concentrically within the drive shaft 5, as shown in FIG. The drive shafts 4 and 5 are structured so that they do not rotate relative to each other in the circumferential direction due to an axially extending groove 16 provided inside the drive shaft 5 and an axially extending protrusion 17 provided on the drive shaft 4. There is. A slight gap is formed between the drive@4 and the drive shaft 5. A shock absorber 18 is provided at the upper end of the drive shaft S, as shown in FIG. This buffer device 18 cushions the impact generated between the drive shafts 4 and 5 due to the rapid insertion of the control rod 1 during a scram of the nuclear reactor, and prevents them from being damaged.

The neutron absorption rod 10 is connected to the spider arm 3 through a spider hole 7 and a plug 8 attached to that part. There are a total of nine neutron absorption rods 9 attached to the four spider arms 2.

Neutron absorption rod 1 attached to 12 spider arms 3
0 is 16 in total. The neutron absorption rod 9 is connected to the spider arm 2 similarly to the neutron absorption rod 10.

FIG. 5 shows the structure of the part where the neutron absorption rod 9 is attached to the spider arm 2. The neutron absorption rod 9 is connected to the plug 8 by screwing. The plug 8 is inserted into the four parts 14 provided on the spider arm 2.

The upper end is held down by a sliding member 15 provided on the spider arm 2. When removing the neutron absorption rod 9 from the spider arm 2, the sliding member 15 is laterally shifted and the plug 8 and the neutron absorption rod 9 are pulled upward together. The same applies to the neutron absorption rod 10.

The neutron absorption rods 9 and 10 differ in the type of neutron absorption material contained therein. FIG. 6 shows the structure of the neutron absorption rod 9. This neutron absorption rod 9 is
Gadolinia (Gd) is placed inside the stainless steel cladding tube 11.
Neutron absorbing material 12 which is an alloy (Zr-GdSn) containing
are arranged in layers. Furthermore, the inside of the neutron absorbing material 12 is a passage 50 through which a coolant flows. As shown in FIG. 7, the neutron absorbing rod 10 has a structure in which a stainless steel cladding tube 11 is filled with a neutron absorbing material 13 made of boron carbide. The neutron absorbing material 12 contained in the neutron absorbing rod 9 is provided in layers.

Furthermore, the neutron absorbing material 12 has a greater degree of depletion than the neutron absorbing material 13 included in the neutron absorbing rod 1o.

FIG. 8 shows the control rod drive mechanism. Control rod 1 of this embodiment
In order to operate the two control rod drives 19 and 2
Requires 0. Although not shown, the control rod drive devices 19 and 20 are provided at the upper end of the child reactor vessel.The control rod drive device 19 drives the drive shaft 4, and the control rod drive device 20 drives the drive shaft. These control rod drive devices move the drive shaft up and down by electromagnetically engaging and disengaging the latch in the control rod drive device 5 from the drive shaft.For example, fM When starting up the sub-reactor, the control rod drive device 20 is activated by a signal 22, and the neutron absorption rods 10 connected to the drive shaft 5 are pulled out from the core.

Furthermore, at the end of the operation cycle, the control rod drive device 19 is activated by the signal 21 to pull out the neutron absorption rods 9 connected to the drive shaft 4 from the core. Furthermore, during a reactor scram, signals 21 and 22 simultaneously turn off the power to both control rod drives and remove all latches from each drive shaft.
The control rod 1 is inserted into the reactor core by gravity. When the neutron absorption rods 10 are gradually inserted into the reactor core while the neutron absorption rods 9 are being inserted into the reactor core, the neutron absorption rods 10 can be operated by the control rod driving device [120]. However, when inserting the neutron absorption rod 10 into the reactor core with the neutron absorption rod 9 pulled out from the core, the control rod drive device 20 is powered off and then the control rod drive device 2
After removing the latch from the drive shaft 5, remove the control rod drive bag [i
! 19 to insert the neutron absorption rod 10 into the reactor core at the same time as the neutron absorption rod 9. This is the neutron absorption rod 9 and 1
The same is true when pulling 0 out of the core at the same time. In this way, there is no need to synchronize each control rod drive device, and the neutron absorption rod Operations 9 and 10 become easier.

In order to make the aforementioned control rod drive devices 19 and 2o compact, the drive shafts 4 and 5 connected to each neutron absorption rod group are concentric as described above, and have a structure that allows them to maintain mutual angles around the central axis. It is desirable that the In addition, care must be taken to ensure that parts of the control rods that are made up of highly depleted neutron absorbers do not interfere with the operation of other parts during control rod scrams.

A boiling water reactor has a core loaded with a large number of fuel assemblies 23 shown in FIG. In the fuel assembly 23, fuel rods 25 are arranged in a lattice arrangement of 15 rows and 15 columns within a rectangular tube-shaped support plate 24 that prevents floating of voids. 8 fuel rods 2
One in five control rod guide tubes 26 and 27 are provided in the fuel assembly 23. 9 control rod guide tubes 2
One neutron absorption rod 9 is inserted into each of the holes 6 . One neutron absorption rod 10 is inserted into each of the remaining 16 control rod guide tubes 27. These control rod guide tubes are
When the neutron absorption rod is pulled out, it acts as a water rod, helping to slow down neutrons. In such a fuel assembly 23.

The number of neutron absorption rods 9 inserted into the control rod guide tube 26 does not have to be nine; for example, four neutron absorption rods 9 are inserted in the center of the fuel assembly 23.
In some cases, core characteristics are better achieved by inserting neutron absorbing rods 9 into the reactor. Such a change can be easily realized by attaching only four neutron absorption rods 9 to the spider arm 2 at the center. In addition, it is easy to change the concentration of the neutron absorbing material in the neutron absorbing rods, or to change the number of neutron absorbing rods and the concentration of the neutron absorbing material depending on the number of cycles (number of operating cycles) of the fuel assembly 23 in the core. It is.

According to this embodiment, the neutron absorbing rod 9 having the neutron absorbing material 12 with large depletion can be taken out of the reactor core at the end of the operating cycle, so that no neutron absorbing material remains in the reactor core at the end of the operating cycle. Conventionally, it is not necessary to optimize the number of neutron absorbing rods and the degree of neutron absorbing material.

Using the control rods of this example, the reactor IL was overturned and extracted with a fuel assembly with an enrichment of 5% by weight, with a burnup of approximately 700 Wd/l.
An example of achieving this will be explained below.

FIG. 10 shows the change in the infinite multiplication factor from the time when a fuel assembly using conventional burnable poison fuel rods is loaded into the core (point a) to the time when it is removed from the core (point g). In FIG. 10, the period a = b is the first operation cycle, b
= Period c is the second operation cycle, period c”d is the third operation cycle.
The driving cycle, the period d - e is the fourth driving cycle, e
”= The period f is the fifth operation cycle, and the period f−g is the sixth operation cycle (the same applies to Figure 11).9 At the end of each operation cycle period, the reactor is shut down and the The spent fuel assemblies that have undergone six operating cycles are removed from the reactor core, and new fuel assemblies are loaded into the reactor core in their place.Then, the reactor is restarted and the next operating cycle begins. Ru.

Conventionally, fuel assemblies containing burnable poison have been used as new fuel assemblies to be loaded into the reactor core. The infinite multiplication factor (point a) of the new fuel assembly at the beginning of the first operating cycle is small. However, as the operation progresses and the neutron absorbing material burns, the infinite multiplication factor of the new fuel assembly increases and reaches point b at the end of the first operation cycle.

Also, the infinite multiplication factor of the fuel assembly in the second operation cycle RO changes from point b to point 0 during the operation cycle.

The infinite multiplication factor of the fuel assembly in the third operating cycle goes from point 0 to point d, the infinite multiplication factor of the fuel assembly in the fourth operating cycle goes from point d to point e, and the infinite multiplication factor of the fuel assembly in the fifth operating cycle goes from point d to point e. The infinite multiplication factor of the fuel assembly decreases from point e to point f, and the infinite multiplication factor of the fuel assembly at the beginning of the sixth operation cycle decreases from point f to point g. The infinite multiplication factor of the fuel assembly at the beginning of the cycle in the first operation cycle is adjusted by the number of fuel rods containing burnable poison and the concentration of the neutron absorbing material so that the surplus reactivity is small. Therefore, as the surplus reactivity increases, more neutron absorbing material is required, and the amount of nuclear fuel material in the fuel assembly must be reduced accordingly. This becomes a factor that reduces fuel economy.

On the other hand, if two control rods 1 of this embodiment are used, as shown in FIG.
It can be carried out by dispersing the fuel assemblies in the first operating cycle and the fuel assemblies in the second operating cycle. 11th
In the example shown in the figure, the neutron absorbing material 1 with the concentration C1 shown in FIG.
The reactor is operated by inserting N1 neutron absorption rods 9 having 2 neutron absorption rods 9 into the control rod guide tube 26 of the fuel assembly 23 in the first operation cycle, and these neutron absorption rods are controlled at the end of the operation cycle. It is pulled out from the rod guide tube 26. All neutron absorbing rods 10 are withdrawn from the fuel assembly 23 during the first operating cycle.

Furthermore, when replacing the fuel after the end of the first operation cycle, the neutron absorption rods 9 used in the first operation cycle are replaced with those of concentration C2, and the number of neutron absorption rods 9 is changed to N2, and in the next second operation cycle, These neutron absorption rods 9 are inserted into the fuel assembly 23 to operate the nuclear reactor. All neutron absorption rods 10 are withdrawn from the fuel assembly 23 even during the second operating cycle. At this time.

N1<N.

C□〉C2. By operating the control rods 1 in this manner, the fuel assembly 23 during the 1B rotation period is
The infinite multiplication factor of is uniform at point a.

Neutron absorption rod 9 before the start of the second operation cycle described above
At the beginning of the second operation cycle, the infinite multiplication factor of the fuel assembly 23 decreases to point b2 due to the replacement of
The infinite multiplication factor of the fuel assembly 23 during the operation cycle increases from point b2 to point C due to combustion of the neutron absorbing material 12.

FIG. 12 shows the output mismatch coefficient in the above operation using the control rod of this embodiment in comparison with the operation using the prior art described above. When the above operation is carried out using the control rod 1 of this embodiment, as shown in characteristic 28, it is possible to operate with the output mismatch coefficient of the fuel assembly in the first operation cycle RO, which has a high output, almost constant, and also to achieve maximum output. The value can be lowered by about 4% than the conventional case shown by characteristic 29. In order to lower this maximum value by 4% using the conventional method, it would be necessary to increase the concentration of burnable poison, and as shown by the broken line in Figure 10, more and more burnable poison would remain unburned. and reduce fuel economy. In the above operation using the control rod 1 of this embodiment, not only is there no neutron absorbing material remaining in the core at the end of the operation cycle, but also neutrons are absorbed in the fuel assemblies of the 1i-th turn cycle and the 1B-th turn cycle. Because the material 12 is dispersed, the amount of nuclear fuel material is not reduced, so the fuel economy is higher than in the past.

The structure of a control rod according to another embodiment of the present invention is shown in FIGS. 13 and 14. In this embodiment, a holding mechanism 34 for removably holding a neutron absorption rod 9A is provided at the tip of a spider arm 32 attached to one of the two drive shafts 4. The neutron absorbing rod 9A having the large neutron absorbing material 12 is separated from the control rod by this holding mechanism 34 at the beginning of the operation cycle and inserted into the reactor core. Further, at the final stage of combustion, it is grabbed by the holding mechanism 34, attached to the control rod, and taken out of the reactor core.

Even with such a configuration, the same effects as the embodiment shown in FIG. 1 can be obtained. Furthermore, although the structure becomes more complicated, it is possible to arrange three or more drive shafts, and the greater the number of groups of neutron absorption rods, the greater the degree of freedom in operation.

Although the embodiments of the present invention in so-called thermal neutron reactors have been described above, the control rods of the present invention can also be used, for example, in high conversion light water reactors. What is the structure of the control rod?

If the same as the above-described embodiment is used and a depleted uranium fuel rod is used instead of a neutron absorbing rod having a neutron absorbing material with a large depletion rate, plutonium is produced in this fuel rod and the conversion ratio is improved. Furthermore, when the fuel rods are withdrawn at the end of the operating cycle, water rods are formed as described above, thereby increasing the water-to-uranium ratio of the fuel assembly. As a result, the core reactivity increases and the operating period becomes longer. As described above, when the control rod of the present invention is used in a high conversion light water reactor, spectrum shift operation becomes possible, which is also effective in improving the fuel economy of the high conversion light water reactor.

[Effects of the Invention] As explained above, according to the present invention, the burnable poison rod, which conventionally could not be operated during reactor operation, can now be operated.
In particular, even when the required amount of neutron absorber increases due to higher burnup, the neutron absorber does not remain in the core at the end of the operating cycle, and fuel economy can be improved. Furthermore, by using the control rod of the present invention, output mismasochism can be reduced by about 4%, which is also effective in securing thermal margin.

[Brief explanation of drawings]

Figure 1 is a structural diagram of a control rod that is an embodiment of the present invention;
The figure is a plan view of the control rod in Figure 1, Figure 3 is a water Klt sectional view of the control rod drive shaft, Figure 4 is a local sectional view of the upper structure of the control rod drive shaft, and Figure 5 is a spider arm and neutron A diagram showing the connection structure of the absorption rods, FIG. 6 is a configuration diagram of the neutron absorption rod 9, a schematic diagram is a configuration diagram of the neutron absorption rod 1o, FIG. 8 is a configuration diagram of the control rod drive device, and FIG. 9 is a configuration diagram of the neutron absorption rod 9. Horizontal sectional view of the assembly, No. 10
11 is a diagram showing changes in infinite multiplication factor during operation using the control rod of FIG. 1; FIG. 12 is a diagram showing changes in infinite multiplication factor during operation using the conventional technology; 13 is a diagram showing the change in the output mismatch coefficient of the fuel assembly in the first operation cycle, FIG. 13 is a structural diagram of another embodiment of the present invention, and FIG.
The figure is a configuration diagram of the neutron absorption rod 9A. 1... Control rod, 2.3, 32... Spider arm, 4
．． 5... Control rod drive shaft, 9.9A, 10... Neutron absorption rod, 12.13... Neutron absorption material, 19.2o.
...Control rod drive device, 23...Fuel assembly, 2G, 2
7...Kaya 2 eyes Bud 1 Snake grass 4. Koko q Kol lO Koka Smokehouse (QWd/l) Koko II Eye 2' Wave 71 (cTW〆/1) Cycle η Same j\/3rd

Claims (1)

[Claims] 1. A first control rod drive shaft, a first arm provided on the first control rod drive shaft, a plurality of first neutron absorption rods attached to the first arm, and the first control rod drive shaft a second control rod disposed concentrically with the first control rod drive shaft independently of the second control rod drive shaft;
a control rod drive shaft, a second arm provided on the second control rod drive shaft, and a plurality of second arms attached to the second arm.
A control rod comprising a neutron absorption rod, wherein the first neutron absorption rod has a neutron absorption material having a larger depletion loss than the neutron absorption material contained in the second neutron absorption rod.