JPH01155295A - Self-actuating nuclear reactor shut-off mechanism - Google Patents

Abstract

PURPOSE:To prevent a malfunction of a mechanism, by providing a plurality of grooves through which a reactor core coolant flows, at peripheries of an armature or an electromagnet or both, to get a large difference of an electromagnetic coercive force between a normal operating condition and an abnormal one. CONSTITUTION:An armature 4 of a nuclear reactor shut-off mechanism is composed of a magnetic material having its Curie point to be the same temperature to which a sodium flow temperature rises at an abnormal operating condition, and with a phenomena which a sodium temperature at an outlet of a fuel assembly 9 in the abnormal operating condition rises and the temperature of the armature 4 reaches to the Curie point, a magnetic attraction between the armature and an electromagnet 8 is weakened. Therewith, the armature 4 is separated from the electromagnet 8 and a control rod 3 falls into a reactor core. In case that numerous grooves are provided at peripheries of not only the armature 4 but also a magnetic core 33 of the electromagnet 8, the sodium 10 touches the whole part where lines of magnetic force 17 run in the armature 4. Therefore, a thermal transfer to the armature 4 is improved and a difference in electromagnetic coercive force between a standard rate operation and an abnormal condition can be set with rather large amount of value and therewith a possibility of a malfunction is much more lessened.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a nuclear reactor shutdown system, and particularly relates to an electromagnetic type 5ASS suitable for preventing the occurrence of ATWS (scram failure during abnormal temperature change). (Self-actuated reactor shutdown mechanism).

[Prior art] When rationalizing fast breeder reactors, a hypothetical core collapse accident (H
There is a growing international trend to treat CDA as a non-design basis event. There are several accident sequences that lead to HCDA, but the most important sequence among them is ATWS. Therefore, as a method of preventing the occurrence of ATWS, it is considered to improve the reliability of the nuclear reactor shutdown system and reduce the probability of occurrence of ATWS to a negligible value.

However, during regular inspections at the AHL reactor (West Germany), almost all scram relays were found to be malfunctioning (1985).
, failure to insert half of the control rods in Browns Ferry-3 (USA) (1980), and Salem-1
Failure of trip breaker during unit trip (198
3 years ago), and these are a type of common cause failure in which redundant equipment fails simultaneously due to the same cause.

In order to prevent such common cause failures and improve the reliability of the reactor shutdown system, unlike conventional methods, control rods can be inserted by directly detecting physical phenomena occurring in the reactor core without relying on reactor scram signals. A self-actuated reactor shutdown system (SASS) is being considered. The 5ASS type uses the Curie point of a magnetic material that detects the rise in sodium temperature at the outlet of the reactor core when an abnormality occurs (Japanese Patent Laid-Open No. 56
-137271), those that utilize fluid pressure,
There are some that use molten metal.

A conventional example of 5ASS using the Curie point of the magnetic material mentioned above is shown in Fig. 2.A control rod 3 containing a neutron absorber is inserted into a lower guide tube 1 provided in the core of a fast breeder reactor. It has become so. An armature 4 made of a magnetic material having a Curie point in a temperature range of 600° C. to 800° C. is provided at the upper end of the control rod 3, and the magnetic force of this armature 4 decreases at the Curie point. Directly above the lower guide tube 1 is supported a core upper guide tube 6 in which a hanging tube 2 is disposed.

An electromagnet 8 that attracts the armature 4 is fixed to the lower end of the hanging tube 2. During normal operation, the control rods 3 are pulled upward from the core, but if the temperature of the core fuel 9 rises due to an abnormality, the armature 4 reaches the Curie point due to the high-temperature coolant, and the magnetic force decreases, causing control. stick 3
will fall under its own weight and the reactor will shut down.

[Problems to be solved by the invention] However, when the above-mentioned 5ASS structure is introduced into a nuclear reactor plant, there is a possibility that control rods may fall during normal operation due to malfunction etc., affecting plant operation. It is necessary to prevent such malfunctions. To this end, it is important to maintain a large difference between the holding force of the electromagnet during normal operation and the holding force of the electromagnet at abnormal operating temperatures. It is necessary to improve the heat transfer effect and increase the difference between the armature temperature under normal conditions and the armature temperature increase due to the rise in core coolant temperature during abnormal conditions. The conventional technology is
No special efforts were made regarding this matter.

The present invention is an electromagnet-type self-actuated nuclear reactor shutdown mechanism that utilizes a magnetic material having a Curie point, which improves the heat transfer effect from the core coolant to the magnetic material, and improves the holding force of the electromagnet during normal operation. It is an object of the present invention to provide an improvement that makes it possible to make a large difference from that in an abnormal state, thereby preventing malfunctions.

[Means for Solving the Problems] The self-actuating nuclear reactor shutdown mechanism according to the present invention includes a magnetic armature attached to the upper part of a control rod and an electromagnet that magnetically attracts the armature. The armature or the magnetic core of the electromagnet, or both, has a Curie point corresponding to the temperature rise of the reactor core coolant during an abnormality, and the reactor core coolant flows around the armature, the electromagnet, or both. It is characterized by having a plurality of grooves.

[Function] By providing the above-mentioned grooves, the core coolant flows through the grooves, so heat transfer from the coolant to the armature and electromagnets is improved, thereby reducing the temperature during normal and abnormal conditions. Therefore, the difference in holding force of the electromagnet between normal and abnormal conditions can be increased, and malfunctions can be prevented.

[Example] An example in which the present invention is applied to a fast breeder reactor will be described below.

Figure 3 shows an example of a control rod in a fast breeder reactor. Third
As shown in FIG. 3(b), the control rod 3 is constructed by collecting a plurality of control rod elements 15 containing neutron absorbing material pellets 14 as shown in FIG. 3(b). It is designed to be inserted into a lower guide tube 1 which serves as a passage for insertion into the lower guide tube 1. 5 is a control rod connecting pipe.

FIG. 4 is a cross-sectional view of the arrangement inside the reactor, in which 3 is a control rod inserted into the lower guide tube, 5 is a control rod connecting pipe,
9 is a fuel assembly arranged around the control rod 3, 13 is a fuel assembly introduction pipe, 30 is an upper guide pipe, 8 is an electromagnet provided at the lower end of the control rod suspension pipe 31, and 4 is a fuel assembly arranged around the control rod 3. Connecting pipe 5
It is an armature attached to the upper end of the control rod 3
From the fuel assembly 9 existing around the fuel assembly introduction pipe 1
A portion of the hot liquid sodium stream 10 collected at 3 is directed to an electromagnet 8 as shown by the arrow. The control rod 3 is normally suspended by the armature 4 being magnetically attracted to the electromagnet 8, and is pulled up to the upper part of the reactor core during normal operation of the reactor. When making an emergency shutdown of the reactor, by stopping the excitation of the electromagnet 8, the armature 4 is separated from the electromagnet 8, and the control rod 3 can be dropped into the reactor core. Control rod falling ffl! In order to alleviate I,
As shown in FIG. 3(b), a shock absorber 1 is installed at the bottom of the lower guide pipe 1.
6 is provided.

The armature 4 is made of a magnetic material whose Curie point is the temperature at which the temperature of the sodium flow 10 rises during an abnormality, and when the temperature of the outlet sodium of the fuel assembly 9 rises during an abnormality, the temperature of the armature 4 rises to the Curie point. By reaching this point, the magnetic adsorption force with the electromagnet 8 weakens, the armature 4 separates from the electromagnet 8, and the control rod 3 falls into the reactor core.

Now, in the above configuration, several embodiments of the armature 4 and electromagnet 8 having the above-mentioned Curie point will be described below based on the present invention.

FIG. 5 shows an example of this, where 32 is the winding of the electromagnet 8, 33 is its magnetic core, and 17 is the magnetic flux. The armature 4 is provided with a plurality of vertical grooves 11 around its circumference, so that the sodium 10 led from the fuel assembly 9 flows as shown by the arrow in the figure, and its temperature is effectively controlled by the armature 4. Make sure that it is conveyed to the people. By doing this, it is possible to increase the difference between the temperature of the armature 4 during normal operation and the temperature of the armature 4 when the temperature of the sodium fuel assembly 9 rises during an abnormality, and the temperature of the electromagnet 8 during normal operation and abnormality can be increased. The difference in holding force increases, and the possibility of malfunction can be reduced.

However, in the embodiment in which the groove 11 is provided only in the armature 4 as shown in FIG. 5, the outlet sodium 10 is deflected to the outside midway, so that the temperature rise in the portion of the armature 4 near the electromagnet 8 is reduced.

Therefore, in order to properly drop the product in response to an abnormality, it must be dropped before the temperature rises much from the temperature at rated operation, and the difference between the holding force at rated operation and the holding force at which the drop should be made is necessary. becomes smaller, leaving the possibility of malfunction during rated operation.

Therefore, in the embodiment shown in FIG. 1, not only the armature 4 but also the magnetic core 33 of the electromagnet 8 are provided with a large number of grooves 11 around the circumference. In this way, the sodium 10 touches the entire part of the armature 4 where the lines of magnetic force 17 pass, so the temperature is transferred to the armature 4 well, and the difference in holding force during rated operation and abnormality can be made large. The possibility of errors in attendance can be further reduced.

By the way, when the grooves 11 are provided in both the electromagnet 8 and the armature 4, if the two grooves 11 are not brought into contact with each other so that they match, the contact area will be reduced, the holding force will be reduced, and there is a possibility of malfunction. remain. Therefore, in the embodiment shown in FIGS. 6 to 8, a groove 11 is formed between the electromagnet 8 and the armature 4.
In addition, a protrusion 18 is provided on the electromagnet 8 side so that the grooves 11 of both are always aligned, and a recess 12 is provided in the armature 4, so that these can be fitted together. In addition, a rotary joint structure 19 is provided between the armature 4 side and the control rod connecting pipe 5 so that it can always correspond to the attitude of the electromagnet 8 side, so that the armature 4 can always correspond to the groove 11 on the electromagnet 8 side. Make it. FIG. 7 is a bottom view of the electromagnet 8, and FIG. 8 is a top view of the armature 4. When the electromagnet 8 and the armature 4 are brought close to each other, the protrusion 18 fits into the recess 12, and the armature 4 naturally rotates due to the rotary joint 19, and the grooves 11 of both sides are at an angle that coincides with each other. It is adsorbed. In addition, in order to align the centers, a convex portion is provided at the center of the protrusion 18 and a recessed portion is provided at the center of the recess 12.

In each of the above embodiments, the armature 4 attached to the control rod
is a magnetic material having a Curie point, but a magnetic material having a Curie point may be used for the magnetic core of the electromagnet 8, or
A magnetic material having a Curie point may be used for both the armature 4 and the electromagnet 8. Furthermore, the present invention is applicable not only to fast breeder reactors but also to nuclear reactors in general.

[Effects of the Invention] According to the present invention, the temperature of the coolant at the exit of the reactor core can be well transmitted to the magnetic body of the electromagnetic type 5ASS that utilizes a magnetic body having a Curie point that captures the temperature rise of the coolant at the exit of the reactor core in the event of an abnormality. Therefore, it is possible to provide a highly reliable ATWS prevention means that can provide a large difference in the holding force of the three magnets during rated operation and during abnormal operation, has a small error one-motion difference, and operates reliably during abnormal conditions.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the present invention, Fig. 2 shows a conventional example, Fig. 3(a) shows a control rod element, and Fig. 3(a) shows a control rod element.
b) is a diagram showing the control rod inserted into the lower guide tube, FIG. 4 is a diagram showing the arrangement in the fast breeder reactor according to the embodiment of the present invention, and FIG.
6 is a diagram showing still another embodiment of the present invention, and FIGS. 7 and 8 are diagrams showing another embodiment of the present invention, respectively.
FIG. 3 is a bottom view of the electromagnet and a top view of the armature in the figure. 1... Lower guide pipe 3... Control rod 4... Armature 5... Connecting pipe 9... Fuel assembly 10... (Outlet) Sodium 1100. Groove 12...Dent 13...
Fuel assembly introduction pipe 14...Absorber pellet 15...Control rod element 16
...) Jt impactor 18... protrusion 19...
Rotating joint 32...Winding 33...Magnetic core Fig. 1 4--Armature Fig. 3 (b) (α) Outline Fig. 6

Claims (1)

[Scope of Claims] 1. Consisting of a magnetic armature attached to the upper part of a control rod and an electromagnet that magnetically attracts the armature, the armature, the magnetic core of the electromagnet, or both are capable of cooling the reactor core in the event of an abnormality. A self-actuated atom having a Curie point corresponding to the temperature rise of the nuclear reactor, and characterized in that a plurality of grooves are provided around the armature, the electromagnet, or both, through which a reactor core coolant flows. Furnace shutdown mechanism. 2. The self-actuating atom according to claim 1, wherein the groove is provided on both the armature and the electromagnet, and the electromagnet and the armature are provided with positioning fitting means for aligning the grooves of both. Furnace shutdown mechanism. 3. A self-actuating nuclear reactor shutdown mechanism according to claim 1, wherein a rotating joint is provided between the armature and the control rod.