JPS612094A - Aggregate of 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 [Technical Field of the Invention] The present invention relates to a control rod assembly for controlling the output of a fast breeder reactor.

[Technical background of the invention and its problems]

In general, the core of a fast breeder reactor, as shown in FIG. A large number of shields (not shown) provided to surround the outermost part of the
is formed by.

The fuel assembly 1 has a large number of fuel assembly elements 3 installed therein, and is installed in a fixed position by inserting an entrance nozzle 4 provided at the lower end into an opening in a core support plate 3. The coolant then flows from the high-pressure plenum 6 in the core support plate 5 through the coolant inlet lower of the entrance nozzle 4 and then ascends between the fuel assembly elements 3 to remove heat from the fuel assembly 1.

The control rod assembly 2 is formed by a lower guide tube 8, an upper guide tube 9, a control rod body 10, and an extension tube 11 for suspending the control rod body. The lower guide tube 8 is positioned by inserting an entrance nozzle 12 formed at the lower end into the opening of the core support plate 5.

The entrance nozzle 12 is provided with a coolant inlet 13 that communicates with the high-pressure plenum 6 and a communication hole 14 that communicates with the inside of the control rod body 10 . Further, the control rod main body 7 has a neutron absorber built therein, and when it is re-inserted, the engaging portion 15 at the lower end is inserted into the dashco pot 16 of the lower guide tube 8 to be oriented. The control rod main body 7 is suspended from the extension tube 11 by gripping the lower end of the extension tube 11 with a grip portion 18 formed at the upper end of the extension rod 17 extending upward from the upper end. By moving the extension tube 11 up and down by a control rod drive mechanism (not shown), the control rod body 10 is inserted into or withdrawn from the reactor core. This heat removal from the control rod body 10 is performed by a coolant that rises in the lower guide tube 8 from the high-pressure brenum 6 through the coolant inlet 13 of the entrance nozzle 12 and the communication hole 14.

During normal operation, the degree of insertion of the control rod body 10 into the reactor core is adjusted by vertical movement of the extension tube 11, thereby adjusting the reactor output.

Furthermore, when an abnormality occurs such as an abnormal increase in reactor power or a decrease in coolant, a scram operation is performed in which the control rod body 10 is urgently inserted into the reactor core and the reactor is stopped.

On the other hand, in a fast breeder reactor, in an emergency, the extension tube 11 cannot be lowered for some reason and the control rod body 10
Assuming a scram failure in which the reactor cannot be inserted into the reactor core, it is necessary to keep the reactivity of the reactor core below criticality even in the event of a scram failure. This is because if a scram failure occurs, the reactor power increases excessively, the coolant temperature rises, and a core damage accident may occur.

As shown in FIG. 3, when a scram fails, the positive reactivity shown in the figure a, which is higher than the criticality when the control rod reactivity is 0, is generated in the reactor core due to the Doppler effect and the coolant density effect. However, in conventional control rod assemblies,
The extension tube 11 and the extension rod 17 expand in the axial direction as the humidity of the coolant increases due to the accident, and the control rod body 10 is inserted into the reactor core, causing negative reactivity as shown in the figure. Conventionally, the safety of the nuclear reactor is ensured by maintaining the total reactivity, which is a superposition of these positive and negative reactivities, in a negative reactivity region lower than the criticality, as shown in C in the figure.

However, in conventional control rod assemblies, the total reactivity C is close to criticality, and the amount of attenuation of the reactor output is kept small.

[Purpose of the invention]

The present invention has been made in view of these points, and when the coolant temperature rises abnormally due to scram failure, etc., the temperature rise is used to automatically adjust the insertion degree of the control rod body into the reactor core. The purpose of the present invention is to provide a control rod assembly that can increase the core power and attenuate the core power to a level greater than the critical level.

[Summary of the invention]

The control rod assembly of the present invention expands and extends the length of the extension tube when the coolant temperature rises abnormally in a part of the extension tube.
It is characterized by being formed with a temperature-sensitive extension member that automatically inserts the control rod body into the reactor core.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

1 and 2 show one embodiment of the invention.

In this embodiment, a bellows-type temperature-sensitive extension member 20 is provided in the middle of the extension tube 11.

Other configurations are similar to the conventional example shown in FIG.

The temperature sensitive extension member 20 will be described with reference to FIG.

A liquid metal 22 is sealed inside the bellows 21 . This bellows 21 is provided in the middle of the extension tube 11 by fixing flanges 23 and 24 fixed to the extension tube 11 at the upper and lower sides, respectively. lower flange 24
A plurality of support rods 25.25 projecting upward from the upper flange 23 slidably pass through the opening 23a of the upper flange 23, so that the bellows 21 can expand and contract in the axial direction of the extension tube 11. This further increases the lateral strength of the extension tube 11. Further, an upper stopper 26 is fixed above the seventh flange 23 above each support rod 25 to prevent the bellows 21 from elongating excessively.
A lower stopper 27 is fixed below 3 to relieve the compressive force so that the bellows 21 does not shrink excessively due to the impact force during scramming. In addition, the liquid metal 22 in the bellows 21 may be any material that is liquid even when sealed during manufacturing and is harmless even if it leaks in the reactor core, such as Ha, which is liquid at room temperature. . Further, a skirt-shaped 7-door 28 is fixed to the lower end of the upper guide tube 9 to collect the high-temperature coolant rising from the fuel assembly 1 and introduce it into the upper guide tube 9 through the inlet 9a. .

Next, the operation of this embodiment will be explained.

Assuming that the control rod body 10 is not inserted into the reactor core during reactor scram, the amount of increase in coolant temperature will be approximately 208° C. 250 seconds after the accident occurs. This increase in coolant temperature results in a positive reactivity as shown in FIG. 3a.

The high-temperature coolant whose temperature has increased abnormally is collected by the hood 28 and flows into the upper guide pipe 9 through the inlet 9a.

For example, the stainless steel extension tube 11 with a total length of 6 m is heated by this high-temperature coolant. Extend by sci. Due to this extension of the extension tube 11 itself, the control rod body 10 is inserted into the reactor core, resulting in the negative reactivity shown in FIG. 3.

Up to this point, the operation is similar to the conventional example.

The embodiment of the present invention further operates as follows.

That is, if the natural length of the bellows 21 of the temperature-sensitive extension member 20 is 30 cm and a liquid metal 22 made of NaK is sealed inside, the amount of expansion of this liquid metal 22 is larger than that of stainless steel, so the bellows 21 is It is extended by 1.5 cm, and the extension tube 11 is extended by 3 cm as a whole. As a result, the control rod body 10 is automatically inserted 1.5011 times deeper into the reactor core than before, and a negative control rod reactivity as shown in FIG. 3d is obtained. Therefore, the reactivity of the control rods after the accident in this example is negative (not shown in Figure 3e), which is much higher than the reactivity shown in Figure 3C, which is kept slightly below the conventional criticality. Subcriticality can be ensured.

Note that instead of the bellows 21 in the above embodiment, a shape memory alloy that expands when the temperature of the coolant exceeds a certain level may be provided.

Further, the attachment position of the temperature-sensitive extension member 20 to the extension pipe 11 may be adjusted as appropriate depending on the temperature rise of the coolant.

[Effects of the Invention] As described above, the control rod assembly of the present invention is capable of moving the control rod body into the reactor core by using the temperature rise of the coolant at the time of an accident by providing a temperature-sensitive extension member in a part of the extension tube. It is possible to insert the control rods deeper than before, which allows them to apply a large negative reactivity to the reactor core.Even if a scram failure accident occurs, the reactor power is automatically attenuated, and the control rods can be inserted for a long period of time. It has the advantage of being able to ensure a subcritical state and increasing the inherent safety of the nuclear reactor.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal side view showing one embodiment of the control rod assembly of the present invention, Fig. 2 is an enlarged view of the section ■ in Fig. Fig. 4 is a longitudinal sectional side view similar to Fig. 1 showing a conventional example. 2... Control rod assembly, 8... Lower guide tube, 9.・・・
Upper guide tube, 10... Control rod body, 11... Extension tube, 17... Extension rod, 18... Gripping portion, 20... Temperature-sensitive extension member, 21... Bellows, 22... ...liquid metal. Applicant's agent Kiyoshi Inomata "Leopard 1 stitch 2nd eye funeral 3rd eye half change (sec) 64 sew procedural amendment (method) October S, 1981 Manabu Shiga, Commissioner of the Patent Office 1, of the case Indication 1981 Patent Application No. 123204 2, Name of invention Control rod assembly 3, Relationship with the case of the person making the amendment Patent applicant (307) Toshiba Corporation 4, Agent September 5, 1988 ( Date of dispatch: September 25, 1982) 6. Details subject to amendment 7. Contents of amendment

Claims (1)

[Scope of Claims] 1. A control rod body housed in a guide tube installed in the reactor core so as to be able to rise and fall freely, and a grip part provided at the top of an extension rod extending upward from the top end of the control rod body. In a control rod assembly having an extension tube that engages with the control rod body to suspend the control rod body, when the coolant temperature in a part of the extension tube rises abnormally, the control rod assembly expands to extend the length of the extension tube. A control rod assembly characterized by being provided with a temperature-sensitive extension member that automatically inserts a control rod body into a reactor core. 2. The control rod assembly according to claim 1, wherein the temperature-sensitive extension member is formed of a bellows with liquid metal sealed inside. 3. The control rod assembly according to claim 1, wherein the temperature-sensitive extension member is made of a shape memory alloy that expands at a certain temperature or higher.