JPS5855791A - Reactor - 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 The present invention relates to a nuclear reactor, and particularly to a nuclear reactor suitable for controlling the reactivity of a tank-type fast breeder reactor.

Core reactivity control of a tank-type FBFL is performed by changing the insertion depth into the core of a control rod supported via a control rod drive device installed in a reactor superstructure.

In the past, the injection of core reactivity required for increasing reactor power and core combustion was performed by withdrawing the control rods upward. Therefore, if the distance between the upper structure of the tank-type FBR reactor vessel and the reactor core changes due to some reason, such as an earthquake, during normal operation, the depth of the control rods in the reactor core will change, and the reactivity of the reactor core will change accordingly. This has unfavorable factors in terms of reactor operation control.

An object of the present invention is to provide a nuclear reactor that reduces the sensitivity of core reactivity changes to changes in the relative distance between the reactor superstructure and the reactor core, in view of the technical problems of the conventional methods described above.

The core reactivity control system of a tank-type FBH consists of approximately 30 main reactor shutdown system control rods and approximately 10 backup reactor shutdown system control rods, the former of which are inserted into the core at a depth during normal reactor operation. It is used to adjust the reactor power level by changing the reactor's power level, and when necessary, it is rapidly inserted into the reactor core to keep the reactor subcritical. On the other hand, the latter is pulled out from the core during normal reactor operation, and inserted into the core in the same way as the main reactor shutdown system control rods during an emergency shutdown, and is used when the main reactor shutdown system does not function for some reason. It is also used independently to keep the reactor subcritical. The present invention provides a control rod in which the poison distribution within the control rod is set so that the core reactivity is increased by lowering approximately half of the control rods in the main reactor shutdown system. The drive mechanism and the remaining half of the conventional main reactor shutdown system control rods and back-up reactor shutdown system control rods constitute the core reactivity control system of the tank-type FBR.

This can be expected to alleviate changes in core reactivity due to relative displacement between the reactor upper structure and the reactor core during normal reactor operation.

FIG. 1 is a conceptual diagram schematically showing the configuration of the core and core reactivity control system of a conventional tank-type FBR, and shows a normal operating state.

The tank type FBR is installed at the top of the reactor vessel, and the core 1 is
It is placed in sodium (coolant) inside the furnace vessel.

The core 1 is surrounded by an axial blanket region 2 (including gas plenum, radiation shield) and a radial blanket region 3. A large number of core fuel assemblies having blanket fuel are placed in the radial blanket region 3.A large number of blanket fuel assemblies having only blanket fuel are placed in the radial blanket region 3.Core fuel assemblies and blanket The fuel assembly is attached to a core support plate installed in the reactor vessel.A plurality of control rod guide tubes 4 are installed.

Provided between core fuel assemblies. A main reactor shutdown system control rod 5 and a backup reactor shutdown system control rod 6 are inserted into the control rod guide tube 4, and they are connected to a rotating plug (reactor upper structure) 7.
It is supported via a coupling mechanism 9 by a control rod drive device 8 installed above. Each control rod, such as the main reactor shutdown system control rod 5 and the backup reactor shutdown system control rod 6, is filled with a neutron absorbing material 10 having a length corresponding to the height of the reactor core 1.

During normal operation of the nuclear reactor, the main reactor shutdown system control rod 5 is withdrawn so as to move the neutron absorbing material 10 upward by an appropriate length in order to maintain the criticality of the reactor. Furthermore, in order to compensate for the deterioration of core reactivity due to the combustion of core fuel, it is gradually withdrawn upward. On the other hand, the neutron absorbing material 10 portion of the backup reactor shutdown system control rod 6 is completely withdrawn from the reactor core 1 and is not used for reactivity control during normal operation of the reactor core 1.

Therefore, if the distance between the one-turn plug 7, that is, the reactor cover and the reactor core 1 becomes longer due to earthquake vibration, etc., the neutron absorbing material 1 of the main reactor shutdown system control rod 5 will
0 will be withdrawn from the core 1, and it is conceivable that the core reactivity will increase.

Figure 2 schematically shows the configuration of the reactor core and core reactivity control system in one embodiment of the present invention applied to a tank-type FBR, and shows the state during normal operation of the reactor. be. Approximately half of the main reactor shutdown system control rods are control rods (referred to as lower poison control rods) 11 that contain a neutron absorbing substance 13 at the lower end of the control rod, and the remaining half are conventional control rods that contain a poison in the center. It is divided into 12 contained main reactor shutdown system control rods (referred to as middle poison control rods). The backup reactor shutdown system control rod 6 has the same function and structure as the conventional backup reactor shutdown system control rod 6. In this embodiment, core reactivity is input to compensate for reactivity deterioration due to combustion of core fuel and to increase output.

Lower the lower void/control rod 11 to reduce the length of the neutron absorbing material 13 in the lower void/control rod 11 in the core 1, or raise the middle poison control rod 12 to reduce the length of the neutron absorbing material 13 in the core 1. This is done by decreasing the length within 1. Therefore.

By adopting this embodiment, even if the relative distance between the reactor cover and the reactor core 1 changes due to some reason (for example, an earthquake), the length of the neutron absorbing material 13 inserted into the reactor core 1 will basically remain the same. does not change. That is, when the rotating P2G moves upward during an earthquake, the neutron absorbing material 13 of the middle poison control rod 12 is pulled out of the reactor core 1, but instead, the neutron absorbing material 13 of the lower poison control rod 11 is pulled out into the reactor core 1. inserted. Therefore, the change in core reactivity is extremely /J%
, it becomes a small thing.

In this embodiment, approximately half of the main reactor shutdown system control rods are divided into the lower poison control rods 11 and the middle poison control rods 12, but the same effect can be achieved even if the number of control rods is distributed according to the value of each control rod. Needless to say, you can get this.

In a tank-type FBR, it is necessary to separate the control rod and control rod drive device by separating the coupling mechanism 9 when exchanging fuel.

However, in the present invention, as shown in FIG. 3, although the neutron absorbing material 13 in the lower poison control rod 11 is extracted from the reactor core 1, the reactor is kept subcritical by the back-up reactor shutdown system control rod 6 and remains functional. There is no problem.

Similarly to the lower poison control rods 11, it is also conceivable to fill the lower portions of some of the backup reactor shutdown system control rods 6 with poison. This control rod is called the lower poison backup control rod. However, in this case, in order not to distort the power distribution of the core 1 during normal operation and to prevent a decrease in core reactivity, the neutron absorbing material in the lower poison backup control rod should be moved as far away from the core 1 as possible. It is necessary to keep it. on the other hand,
In order to shorten the insertion time during scram, the upper end of the neutron absorbing material layer of the lower poison backup control rod should be placed as close to the core 1 as possible.
A nearby stop is required. In order to satisfy these conflicting demands, it is desirable to arrange the upper end of the neutron absorbing material layer of the lower poison backup control rod 15 crn below the lower end of the reactor core 1.

This 15 crn corresponds to the allowable relative displacement between the core and control rods of approximately 1,
5 cm, and therefore, it is impossible for the lower poison backup control rod to prevent the reactivity change due to the relative displacement between the core and the control rods as expected in the present invention. In other words, if the lower and lower poison backup control rods are pulled up to just below the core 1 in order to prevent changes in reactivity due to relative displacement between the core and the control rods, the excess reactivity of the core will be reduced.

This would result in an extremely uneconomical reactor with reduced burnup.

According to the present invention, there is extremely little change in core reactivity due to relative displacement between the reactor cover and the reactor core, and therefore it is possible to provide a reactor control system that provides stable core control characteristics against disturbances such as earthquakes during plant operation. .

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of the vicinity of the core of a conventional tank-type FBR, Figure 2 is a conceptual diagram of the reactor of the tank-type FBR according to the present invention, and the vicinity of σ, and Figure 3 is a fuel exchange of the tank-type reactor of Figure 2. FIG. 1... Core, 5, 6, 11. 12... Control rod, 7.
...Hara No. 30 Continuation of page 1 0 Applicant: Central Research Institute of Electric Power Industry, Otemachi-6-1, Chiyoda-ku, Tokyo

Claims (1)

[Claims] 1. A reactor vessel, a reactor lid attached to the top of the reactor vessel, a reactor core disposed within the reactor vessel and supported by the reactor vessel, and a reactor core held by the reactor lid. In a nuclear reactor comprising a plurality of main reactor shutdown control rods and backup reactor shutdown control rods inserted into the reactor core, some of the main reactor shutdown control rods have their lower portions filled with a neutron absorbing material,
Moreover, the first main reactor shutdown control rod is inserted into the reactor core from below the reactor core, and the remaining main reactor shutdown control rods are filled with neutron absorbing material in the first main reactor shutdown control rod. A nuclear reactor characterized in that the second main reactor shutdown control rod is filled with at least a neutron absorbing material above the region and is inserted into the reactor core from above the reactor core.