JPH067178B2 - Fuel control Autonomous safety fast breeder reactor - Google Patents

Description

Description: FIELD OF THE INVENTION This invention relates generally to fast breeder reactors using liquid metal coolant, and more particularly to autonomously controlling fuel loading and hence reactor power. The present invention relates to a novel autonomous safe fast breeder reactor capable of performing refueling during operation.

<Conventional technology and problems> In the conventional fast breeder reactor, it is necessary to stop the reactor when refueling.Therefore, in order to improve the operation rate, efforts are made to shorten the reactor shutdown period for replacement as much as possible. However, it is indispensable to install devices such as a fuel exchanger and a fuel inlet / outlet for refueling.

In addition, its operation requires artificial output control from the outside of the furnace, and in order to prevent the release of radioactive substances to the external environment, a large amount of safety equipment such as control rods and emergency stop system In need.

As a result, the structure of the entire furnace becomes large, and once installed, it is completely impossible to move it from its installation location.

In view of this, the present invention makes it possible to perform fuel exchange during operation and to autonomously control the output, and therefore to significantly reduce the equipment conventionally required to perform the fuel exchange and the output control. The purpose of the present invention is to provide an autonomous safe fast breeder reactor which can be installed in any place such as a remote area or offshore because it can be simplified and can be made portable.

<Means for Solving Problems> In order to achieve the above object, according to the present invention, a new fuel loading tank is stacked above the core tank,
Provided is a fast breeder reactor having a tank stack structure in which a spent fuel cartridge tank is removably attached below it. The core tank has an inlet and an outlet for liquid metal coolant and has a plurality of fuel support tubes vertically extending therethrough. The new fuel loading tank has a plurality of fuel loading holes that are aligned with and aligned with the fuel support tubes of the core tank.The inside of each fuel loading hole is an inert gas atmosphere and the fuel loading holes The upper end opening is sealed by a seal plug. The spent fuel cartridge tank is provided with a plurality of bottomed spent fuel accommodating holes that are aligned with the respective fuel support tubes of the core tank.

At the upper end of each fuel support tube of the core tank, the upper shape memory alloy whose opening degree changes due to temperature change in order to control the speed at which the fuel element falls by gravity from the fuel loading hole of the new fuel loading tank into the fuel support tube A member is provided, and at the lower end of each fuel support pipe, a temperature is controlled in order to control the speed at which the spent fuel element falls by its own weight from the fuel support pipe into the spent fuel storage hole of the spent fuel cartridge tank. A lower shape memory alloy member whose opening degree changes according to the change is disposed.

<Operation> According to the fast breeder reactor of the present invention configured as described above, at the rated operating temperature, the upper shape memory alloy member moves the fuel element from the fuel loading hole of the new fuel loading tank to the core tank at a constant drop velocity. The lower shape memory alloy member also discharges the fuel element from the fuel support tube of the core tank to the spent fuel storage hole of the spent fuel cartridge tank while the lower shape memory alloy member is also loaded into the fuel support tube. As a result, the rated output is maintained.

When the operating temperature rises above the rated operating temperature, the upper shape memory alloy member reduces the opening degree to slow down the falling speed of the fuel element into the fuel support tube, while the lower shape memory alloy member increases the opening degree to increase the fuel element. Increase the speed of falling into the spent fuel storage hole of
As a result, the number of fuel elements in the fuel support tube decreases, so the core power decreases and returns to the rated power.

When the operating temperature decreases from the rated operating temperature, the upper shape memory alloy member increases the opening degree to increase the falling speed of the fuel element, while the lower shape memory alloy member reduces the opening degree to decrease the falling speed of the fuel element. As a result, the number of fuel elements in the fuel support pipe increases, so the core power rises to the rated power.

Further, in an abnormal case where the temperature rises excessively, the opening degree of the upper shape memory alloy member is significantly reduced, the loading of the fuel element on the fuel support pipe is blocked, and the opening degree of the lower shape memory alloy member is greatly increased. As a result, most of the fuel elements in the fuel support pipe are dropped into the spent fuel storage hole and discharged,
The core becomes subcritical and the power becomes zero.

As described above, the fast breeder reactor according to the present invention can autonomously control the reactor power, and thus can be referred to as a fuel control autonomous safety fast breeder reactor.

<Examples> The present invention will be further described below with reference to the examples shown in the drawings. FIG. 1 is an explanatory view showing an embodiment of a fast breeder reactor of the present invention, in which a new fuel loading tank 20 is stacked above a core tank 10 and a spent fuel cartridge tank 30 is detachably attached below the core tank 10. In addition, it has a stacked structure of three tanks as a whole.

The core tank 10 has an inlet 11 and an outlet 12 for a liquid metal coolant, for example liquid sodium, the interior is filled with a liquid sodium coolant 13, and a plurality of fuel support tubes 14 penetrate vertically. The fuel loaded in the fuel support tube 14 is in the form of a fuel element 15 in which plutonium and uranium fuel are enclosed in a cylindrical or prismatic cladding tube of a heat-resistant, radiation-resistant stainless alloy or the like. A plurality of fuel stacks are used in the fuel arrangement stacked in the fuel support tube 14.

A plurality of fuel loading holes 21 penetrate vertically through the new fuel loading tank 20, and an upper end opening of each hole is sealed by a seal plug (not shown). When the new fuel loading tank 20 is stacked on the core tank 10, each fuel loading hole 21 is aligned with each of the fuel support pipes 14, but the inside of each fuel loading hole 21 is filled with argon gas. Since the atmosphere is an inert gas atmosphere such as
The liquid sodium in 0 is prevented from coming into contact with air through the fuel loading hole 21. New fuel elements 15 are sequentially loaded and stored in the fuel loading holes 21 from the fuel loading crane 40.

The spent fuel cartridge tank 30 is provided with a plurality of bottomed spent fuel storage holes 31. This tank 3
No. 0 is detachably attached to the bottom of the core tank 10, and when it is mounted, each storage hole 31 is aligned with each of the fuel support pipes 14 of the core tank.

Each of the fuel loading hole 21, the fuel support pipe 14, and the spent fuel storage hole 31 described above has a diameter that allows the fuel element 15 to fall by its own weight.

An upper shape memory alloy member A is arranged at the upper end of each fuel support pipe 14 of the core tank 10. This member A has an opening degree set so that one fuel element is dropped by its own weight and loaded into the fuel support tube 14 from the fuel loading hole 21 at the rated operating temperature of the core in about one week (fuel element and member A The opening degree of the fuel element 15 is reduced as the temperature rises so as to send the falling velocity of the fuel element 15 and prevent the fuel element 15 from falling. On the other hand, each fuel support tube 14
A lower shape memory alloy member B is disposed at the lower end of the.
This member B has an opening degree set so that one fuel element is dropped by its own weight and discharged from the fuel support pipe 14 into the spent fuel storage hole 31 at a rated operating temperature in about one week. When the temperature rises by 10 ° C., the opening degree is expanded to increase the fuel element falling speed, and when the temperature further rises, the fuel element is immediately dropped.

The operation of the fast breeder reactor of the present invention having the above-mentioned structure will be described below. At the time of starting the furnace, the upper shape memory alloy member A is fully opened because the temperature inside the furnace is low, and the fuel element 15 drops from the new fuel loading tank 20 into each fuel support pipe 14 of the core tank 10. Lower shape memory alloy member B
Has a minimum opening degree and does not drop, a fuel element stack is formed in each fuel support tube 14, the nuclear fission reaction of the fuel becomes critical, and the temperature gradually starts to rise. As the temperature rises, the opening degree of the upper shape memory alloy member A gradually decreases, and the fuel element loading from the new fuel loading tank 20 reaches a predetermined set speed, while the opening degree of the lower shape memory alloy member B gradually increases. Then, the fuel element falls from the fuel support pipe 14 to the spent fuel cartridge tank 30 at a predetermined set speed, and the core has a rated output (see FIG. 2). Since the sodium coolant 13 has a high boiling point of about 900 ° C and is at atmospheric pressure at a furnace operating temperature of 500 to 600 ° C,
The fuel element 15 is from the new fuel loading tank 20 to the core tank 1
It can fall to 0 by its own weight.

When the output begins to become higher than the rated state, the opening degree of the lower shape memory alloy member B increases, the falling velocity of the fuel element gradually increases, the core output decreases, and the output returns to the rated state.

In addition, in an abnormal case where the core power excessively rises or the flow rate of the sodium coolant 13 decreases for some reason, the sodium temperature rises from the rated time, and the upper shape memory alloy member A has the maximum opening degree. To prevent the fuel 15 from being loaded, while the lower shape memory alloy member B has the maximum degree of opening and the fuel element 15 in each fuel support tube 14 has one uppermost fuel element (upper shape memory alloy member). All are dropped except for (held by A). As a result, the core immediately becomes subcritical and the power becomes zero (see Fig. 3). In the fast breeder reactor of the present invention, since the excess reaction is almost zero, it becomes subcritical simply by dropping a few fuel elements 15 from the core tank fuel support pipe 14 at the time of an abnormality.

In addition, the storage hole 31 of the spent fuel cartridge tank 30
When the fuel tank is full of fuel elements falling from the core, remove this cartridge tank 30 from the core tank 10 and install a new empty cartridge tank 30 '(Fig. 1) into the core tank 10 even while the reactor is operating. You can The removed cartridge tank 30 is transported to the spent fuel reprocessing site and reprocessed.

<Effects of the Invention> Since the fast breeder reactor of the present invention has the configuration as described above, the following effects can be obtained.

(1) The fuel element is loaded into the core by its own weight drop, and the fuel element drop speed is adjusted by the sodium coolant temperature, so the reactor output is autonomously controlled, and the safety is high.

(2) The control rod, the reactor emergency stop system, and the fuel exchange device, which were required in the past, are not required, and the equipment can be significantly reduced.

(3) The operation rate is improved due to the refueling during operation.

(4) Since the reactor is mainly composed of tanks, it has a simple structure, is easy to manufacture and assemble, and is a portable reactor. Therefore, it can be installed in any place such as a remote area or offshore.

(5) Maintenance-free continuous operation is possible because the fuel can be exchanged during operation and the structure is simple and the main components are highly reliable.

[Brief description of drawings]

FIG. 1 is a sectional view conceptually explaining an embodiment of the fast breeder reactor of the present invention, FIG. 2 is an explanatory view showing the arrangement of fuel elements during the operation of the reactor, and FIG. It is explanatory drawing which shows arrangement. 10 ... Core tank, 11 ... Coolant inlet, 12 ... Coolant outlet, 13 ... Liquid metal coolant, 14 ... Fuel support pipe, 15 ...
Fuel element, 20 ... New fuel loading tank, 21 ... Fuel loading hole, 30, 30 '... Spent fuel cartridge tank, 3
1 ... spent fuel storage hole, A ... upper shape memory alloy member, B
... Lower shape memory alloy member.

Claims (1)

[Claims] 1. A plurality of fuels aligned in line with a fuel support tube above a core tank having a liquid metal coolant inlet and an outlet and having a plurality of fuel support tubes vertically extending therethrough. A stack of new fuel loading tanks having loading holes penetrating therethrough, and a plurality of bottomed spent fuel storage holes that are aligned below the core tank and are aligned with the fuel support tube A fresh fuel cartridge tank is removably attached to the upper end of each fuel support tube of the core tank to control the speed at which the fuel element falls by gravity from the fuel loading hole of the new fuel loading tank into the fuel support tube. For this purpose, an upper shape memory alloy member whose opening degree changes according to temperature changes is provided, and at the lower end of each fuel support pipe, from the fuel support pipe into the spent fuel storage hole of the spent fuel cartridge tank. Spent fuel required A lower shape memory alloy member whose opening degree changes according to temperature change is arranged to control the speed at which the fuel drops by its own weight, and an inert gas atmosphere is provided in the fuel loading hole of the new fuel loading tank and the fuel loading is performed. The top opening of the hole is sealed by a seal plug, which allows
The reactor power can be controlled autonomously by adjusting the loading and discharging of fuel elements in the fuel support tube of the core tank by changing the opening degree of the upper and lower shape memory alloy members due to temperature changes, and at the same time fuel exchange during operation A fuel control autonomous safe fast breeder reactor characterized by enabling the following.