JPS6212893A - Controller for nuclear 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] [Field of Application of the Invention] The present invention relates to a nuclear reactor control device, and in particular, a nuclear reactor control device suitable for safely shutting down a fast breeder reactor in the event of an accident or core deformation. It is related to.

[Background of the invention]

Nuclear reactors are generally equipped with control rods that contain materials that absorb neutrons to allow the reactor to operate and shut down safely. These control rods can be broadly classified into adjustment rods and safety rods. To start the reactor, first withdraw the safety rod completely from the core area, then gradually withdraw the adjustment rod,
The reactor is made to be just critical at a given reactor power. During reactor operation, adjustment is performed as the operation progresses to compensate for the decrease in reactor output due to fuel consumption.
It is gradually pulled out. When shutting down a nuclear reactor, both adjustment rods and safety rods are inserted into the reactor core to create a large negative reactivity within the reactor core.In the case of a fast breeder reactor, adjustment rods and safety rods are used as control rods. In addition, it is equipped with a backup safety bar. The backup safety rod is functionally the same as the safety rod, but has a drive mechanism different from that of the safety rod and backs up the safety rod. That is, when it becomes impossible to insert the safety rod into the reactor core region, the backup safety rod is inserted into the reactor core region instead of the safety rod to stop the reactor.

In the case of a fast breeder reactor, the control rods are operated from about 10 meters above, so there is a risk of core deformation during reactor operation or during an earthquake.
Improving insertability even when the rod is deformed is one of the important issues in control rod design. Additionally, a function is required to automatically scram in the event of an accident as a back-up safety bar.

Conventionally, as a countermeasure to the former problem, Japanese Patent Laid-Open No. 57-1
As described in Japanese Patent Application Laid-open No. 36188 and Japanese Patent Application Laid-open No. 51-51697, a control rod is divided into a plurality of elements and connected with universal joints, elastic members, etc., so that each element can be bent. The control rod elements 1a''c are connected by a connecting rod 5 made of an elastic body.

Even when the guide tube 2 is bent, the control rod 1 can be moved up and down by driving the extension tube 3 up and down with a drive mechanism in the upper part of the furnace.

However, there is a problem in the reliability of the joint between the control rod elements 1a=c, and the provision of the joint reduces the amount of neutron absorbing material.

On the other hand, regarding the latter type of automatic scram function in the event of an accident, a number of effective devices are being studied to prevent coolant flow rate drop accidents and reactivity insertion accidents. Figure 3 shows a schematic diagram of a device that is effective against coolant flow rate drop accidents. In this device, the coolant flowing from the entrance nozzle 8 is transferred to the guide pipe 2.
It flows inside from the bottom to the top and flows out from the upper outlet 9. A granular neutron absorber 6 is accommodated in the guide tube 2 between perforated partition plates 10,11. The absorber 6 has a higher specific gravity than the coolant flowing in the guide tube 2, and when the flow rate of the coolant is less than a predetermined flow rate, it is deposited on the lower effective partition plate 1o due to its own weight. Further, an electromagnetic flow rate adjustment valve 7 is provided above the perforated partition plate 11, and when the nuclear reactor is shut down, the absorber 6 is deposited by restricting the flow rate with the flow rate adjustment valve 7. In the event of a coolant flow rate reduction accident, the absorber 6 is deposited and the furnace automatically shuts down. In this device, granular neutron absorber 6
Because of the use of this rod, it is highly reliable in terms of operability when the center of the road deforms, and is one of the best back-up safety rods for fast breeder reactors. However, if the electromagnetic flow control valve 7 is damaged, the absorber 6 will remain floating, potentially giving a large positive reactivity to the reactor. Furthermore, no consideration is given to automatic scrams in the event of a reactivity insertion accident.

[Purpose of the invention]

An object of the present invention is to provide a nuclear reactor control system that can reliably shut down a nuclear reactor by automatic scram in response to a coolant flow rate drop accident or a reactivity insertion accident, and that improves operability during core deformation. . [Summary of the Invention] The feature of the present invention is that during normal operation, the neutron absorber is floated by the fluid pressure of the coolant flowing in from the bottom, and in the event of a coolant flow rate drop accident, the absorber sinks due to the drop in fluid pressure. Automatic scrum and.

By installing a weight on the top of the absorber, in the event of a reactivity insertion accident, the abnormal temperature rise is detected and the weight's own weight automatically scrams.

Another feature is that insertability during core deformation is improved by configuring the neutron absorber with a granular absorber or a plurality of control rod elements.

The control rod of the present invention is operated by operating a weight via an extension tube using a drive mechanism in the upper part of the reactor, similar to conventional control rods. Although the absorbers are not mechanically connected to each other,
It follows the vertical movement of the weight as a unit due to the fluid pressure of the coolant.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 shows an embodiment in which the present invention is applied to a reactor control system for a large reactor with an electrical output of 100,100 O class. This device supplies coolant (
liquid sodium) flows in.

The coolant flows from the bottom to the top in the guide tube 2 and reaches the upper outlet 9.
flows out from. A dashpot 14 is provided at the lower part of the guide tube 2 to reduce the impact during scram.

Inside the guide tube 2, a weight 12 is housed in the upper part, a large number of granular neutron absorbers 6° are housed in the middle part, and a guide nozzle 13 is housed in the lower part. Each of the stored items 12, 6.13 has a higher specific gravity than the coolant, and when the coolant has a predetermined flow rate or less, it sinks to the lower dashbot 14 due to its own weight.

The weight 12 is made of a material with a high specific gravity, and is designed so that the neutron absorber 6 and the guide nozzle 13 alone will float due to the fluid pressure at the rated flow rate during reactor operation, but when the weight of the weight 12 is added, the engine will sink. The shape of the orifice inside the lance nozzle is designed. The guide nozzle 13 guides the absorber 6 when it floats and sinks, and when the absorber 6 sinks and is inserted into the dashbot 14, the flow path is reduced to the coolant inlet and the pressure drop there increases, so the flow rate of the coolant is reduced. decrease. Therefore, there is an effect of preventing the absorption material 6 from floating when the furnace is shut down.

The absorber 6 is made of boron carbide, tantalum, or stainless steel (hereinafter abbreviated as SUS), and the weight 12 is made of depleted uranium (specific gravity 18.9, melting point 1130°C), osmium (specific gravity 22.5, melting point 2700°C). The guide nozzle 13 is made of SUS.

The characteristics of this device are shown below using numerical examples.

The inner diameter D□ of the guide tube 2 is 132 mm, and the effective height h of the absorber 6 is 1000+n+++, which is the same as the core area A. As an absorber, boron carbide (SUS coating:
When using a ball with a cladding tube wall thickness of 0.8 mm, approximately 200
0 pieces are required, and their weight is approximately 25 kg. The total weight including the guide nozzle 13 is 30 kg or less. On the other hand, depleted uranium is used as the weight 12, and its dimensions are set to 1 in diameter.
00 mm and height 500 mm, its weight is approximately 75 kg. Therefore, the absorber 6 and the guide nozzle 1
Even if the flow rate is about 2 of the minimum floating blade for 3 (total weight 30- or less), the weight will be 3.5 times or more when combined with the weight, so it will surely sink. In addition, the sum of the weights (30 kg) of the absorber 6 and the guide nozzle 13 is calculated as the guide nozzle 1
Since the pressure loss of the combined cross-sectional area of No. 3 is approximately 5 kg/d, sufficient levitation is possible by adjusting the orifice of the entrance nozzle 8 of this device. The weight of the boron carbide in this example is approximately 12 kg, which is comparable to the approximately 13 kg weight of the boron carbide in the conventionally used back-up safety rod using pin-shaped boron carbide. The stopping function (negative reactivity effect) is equivalent.

On the other hand, the weight 12 includes the extension tube 3, the electromagnet 15, and the detachable part 16.
．． They are connected by a magnetic material 17 having a single Curie point. When the furnace is normally stopped, the electromagnet 15 and the detachable part 16 are separated by turning off the power to the electromagnet 15. When the temperature rises abnormally at the time of an accident and exceeds the single point of the magnetic body 17, the magnetic force rapidly decreases, and the magnetic body 17 and the detachable portion 16 are separated, resulting in an automatic scram. Materials with one Curie point include Fe (one Curie point 1043°K), G o (1
400°K).

N1 (631°K), etc., and by using these materials and alloys depending on the reactor design temperature, reliable reactor shutdown becomes possible.

Next, the operating method and operation of the reactor control device according to this embodiment will be explained based on FIG. 4.

When the furnace is stopped (Fig. 4-a), the weight 12, the absorber 6, and the guide nozzle 13 are sinking under their own weight. At this time,
The guide nozzle 13 is inserted into the dashbot 14. When operating the control rods for reactor startup (Figure 4-b), the extension tube 3 and the weight 12 are connected, and when the weight 12 is raised by the extension tube 3, the absorber is moved by the flow pressure of the coolant. 6
The guide nozzle 13 and the guide nozzle 13 float together. When the guide nozzle 13 exits the dashbot 14, the coolant inlet flow path widens and the flow pressure further increases. Absorber 6
However, the state in which the reactor is completely withdrawn from the core region A is the reactor operating state (Figure 4-0). In the event of a coolant flow rate drop accident (Figure 4-d), only the absorber 6 and the guide nozzle 13 sink due to the drop in fluid pressure, and the reactor is shut down by automatic scram. Extension pipe 3 and weight 12 due to abnormal rise in outlet temperature of adjacent fuel assembly due to scram signal or reactivity insertion accident.
When separated, the weight 12. The absorber 6 and the guide nozzle 13 sink together to shut down the reactor.

FIG. 5 shows another embodiment of the reactor control system.

A feature of this embodiment is that the lower diameter of the drive rod 18 for operating the weight 12 is smaller than the upper diameter. Furthermore, a flow path adjustment guide 19 is installed at the upper part of the guide tube 2, and when the weight 12 is at the upper limit position (during operation of the child furnace), the narrow diameter part of the drive rod 18 is at the position of the flow path adjustment guide 19. . When the drive rod 18 begins to descend due to scram or the like, its large diameter portion comes to the position of the flow path adjustment guide 19 and narrows the flow path.

Therefore, the flow pressure decreases and the absorber 6 sinks more rapidly, which has the effect of accelerating the scram speed.

An embodiment in which the present invention is applied to the adjustment of a fast breeder reactor will be described below. 6 Figure 6 is an embodiment of the present invention. Adjustment rods 20 made of boron are arranged. The adjustment shaft 20 is raised and lowered by operating the weight 12, and the automatic scram function in the event of an accident is provided as in the previous embodiment.

FIG. 7 shows another embodiment. For the embodiment shown in FIG.
Dividing the adjustment rod 20 into three elements 20 a = c, and dividing the weight 12 into three elements 12 a '' c,
Each element is connected by a universal joint 21. In addition to the effects of the embodiment shown in FIG. 6, since the adjustment rod can be freely deformed within the guide tube 2, the ease with which the adjustment rod can be inserted into the core during core deformation is improved. In particular, since a connecting mechanism is not required for each element 20a=c of the adjustment shaft, the density of the absorption material loaded into the reactor core is increased and there is no fear of damage to the connecting mechanism.

The scram function at abnormally high temperatures according to the present invention is constructed using an electromagnet and a magnetic material with a single Curie point, but bimetals, fused metals, and shape memory alloys may also be used.

1-8 The above explanation has been made with reference to a fast reactor using sodium as a coolant, but the present invention can be similarly applied to a gas-cooled fast reactor or a light water reactor.

In addition, if the extension tube 9 weights and control rod elements (protective tubes, cladding tubes, etc.) are made of elastic materials that are highly resistant to high temperature sodium, irradiation, and strong, they will not be inserted further when the core deforms. A nuclear reactor control system with excellent performance can be realized.

〔Effect of the invention〕

According to the present invention, it is possible to improve the ease of inserting control rods into the reactor core against core deformation during reactor operation or deformation during an earthquake, and to automatically scram in the event of a coolant drop accident or a reactivity insertion accident. It provides a nuclear reactor control system and has a great effect on the safety of nuclear reactors.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a backup safety device according to an embodiment of the present invention;
Figure 2 is a cross-sectional view of an example of a control rod with a -segment node;
The figure is a cross-sectional view of an example of a fluid differential pressure type reactor shutdown system, FIG. 4 is a cross-sectional view of a backup safety device according to an embodiment of the present invention, and FIG. FIG. 7 is a cross-sectional view of an adjustment shaft according to another embodiment of the present invention. 1...Control rod, 2...Annai tube, 3...Extension tube, 6
...neutron absorber, 7...electromagnetic flow control valve, 8...
・Entrance nozzle, 12... Weight, 13... Guide nozzle, Ji 10 Shizuka J Phantom No. 5m District 7

Claims (1)

[Claims] 1. In a reactor control system using a fluid pressure differential pressure system in which a neutron absorbing substance is floated to the upper part of the outside of the core by the action of pressurized fluid introduced from the bottom, a free float is placed above the neutron absorbing substance when the flow rate of the fluid decreases. A nuclear reactor control device characterized in that a weight to be dropped is arranged.