JPH06138277A - Controlling-element collecting device for use in high temperature gas-cooled reactor - Google Patents

Abstract

PURPOSE:To enhance the reliability of collecting operations for controlling elements by preventing the controlling elements from clogging the inlet of a collecting pipe. CONSTITUTION:A controlling-element collecting device includes a recycling pipe 22b having a recycling portion 24b which sucks helium gas in a core 2 by creating negative pressure using a blower or the like and sucks and collects controlling elements 14 in a controlling-element collecting pipe 19 by means of the flow of the helium gas and a suction nozzle 23b suspended from the lower end of the collecting portion 24b, and a winch 25 installed above the collecting portion 24b to drive the collecting pipe 22b in the vertical direction, the collecting pipe 22b having an optimum bore so that the controlling elements 14 sucked do not clog it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control element recovery device for a high temperature gas reactor, and particularly to reduce the probability that the control element will be blocked at the recovery pipe inlet, and to improve the reliability of the control element recovery operation. It is related to the configuration.

[0002]

2. Description of the Related Art Generally, a nuclear reaction of a nuclear reactor is controlled by inserting a control rod into and out of a core by a control rod driving device, and the control rod is fully inserted when the reactor is stopped. This reactor shutdown mechanism is extremely important, for example, because it must be operated reliably even when the reactor is abnormal, in a normal reactor, in addition to the main reactor shutdown system by the control rod drive device, Double- and triple-layer safety measures are implemented by installing a separate reactor shutdown system.

FIG. 3 is a schematic sectional view showing a schematic structure of a conventional high temperature gas furnace. In the figure, a reactor core 1 contains a reactor core 2, graphite blocks acting as moderators are stacked in the reactor core 2, and fuel rods 3 are loaded in these graphite blocks. Further, a gas having a large specific heat, for example, helium gas is circulated as a coolant in the reactor vessel 1.

This helium gas flows into the reactor vessel 1 through an inlet pipe 4 communicating with the bottom of the reactor vessel 1, passes through a core 2 and is heated to a high temperature, and concentrically inside the inlet tube 4. It flows out through an outlet pipe 5 which is arranged and communicates with the bottom of the core 2. The high-temperature helium gas from the outlet pipe 5 exchanges heat with the external coolant in the heat exchanger 6, and is then returned to the reactor vessel 1 again by the circulation device 7. Then, the external coolant to which the heat is transferred in the heat exchanger 6 is sent to a required place by a circulation system (not shown) and used for power generation or process heat.

In the figure, reference numeral 8 denotes a control rod driving device, and this control rod driving device 8 suspends a control rod 9 from a wire rope 10
And a drum 11 for winding and unwinding the wire rope 10 and a motor 12 for driving the drum 11. The control rod 9 is rotated relative to the core 2 by the normal rotation and the reverse rotation of the drum 11 by the motor 12. Is inserted and removed, and the output of the core 2 is controlled.

A backup reactor shutdown device 13 is installed in case the control rod drive device 8 becomes inoperable. This backup reactor stop device 13, which accommodates the control element 14 containing the neutron absorber, has a hopper 15 having a rupture disk 16 that is damaged by a predetermined pressure on the bottom surface, and is not shown in the case of an abnormality in which the reactor needs to be stopped. It is provided with a valve 17 which is opened by an emergency signal emitted by a sensor and sends hot gas from a hot gas source 18 into the hopper 15.

On the other hand, a control element accommodating pipe 19 is installed at a position directly below the hopper 15 in the core 2, and when the rupture disk 16 is destroyed by the introduction of high-pressure gas, the control element 14 in the hopper 15 accommodates the control element. It is dropped and stored in the tube 19, and the nuclear reaction of the core is stopped.

In the figure, reference numeral 20 denotes a stand pipe, and a plurality of stand pipes are projected from the upper surface of the reactor vessel 1. Control rod drive device 8
And the backup reactor shutdown device 13 is
It is installed inside. For the control element 14, the neutron absorber such as boron carbide (B ₄ C) made into a cylindrical pellet having a diameter of 13 mm and an axial length of 13 mm is used.

Although the control rod drive device 8 and the backup reactor shutdown device 13 are actually installed at a plurality of locations, only one is shown in FIG. 2 for simplification.

In the high temperature gas reactor constructed as described above, when the backup reactor shutdown device 13 is operated, the control element 14 is dropped and housed in the control element housing pipe 19. It is necessary to collect this in order to restart.

Therefore, the recovery operation will be described with reference to FIG. The same parts as those in FIG. 3 are designated by the same reference numerals. That is, FIG. 4 shows a conventional control element recovery device.
It is a typical sectional view for explaining composition and operation of 21A. In the figure, the control element recovery device 21A is attached to the stand pipe 20 of the reactor vessel 1, forms a negative pressure by a blower (not shown) or the like, sucks the helium gas in the core 2, and puts it on the flow. And a collecting section 24a for sucking and collecting the control element 14 in the control element housing tube 19 and the collecting section 24a.
The collecting pipe 22a has a suction nozzle 23a at the lower end and a hoist 25 installed above the collecting portion 24a to drive the collecting pipe 22a in the vertical direction.

Control element recovery device configured as described above
In 21A, as the recovery of the control element 14 progresses, the amount of the control element 14 in the control element housing pipe 19 decreases, and the suction nozzle 23
Since the distance between a and the upper surface of the control element deposition portion becomes large and suction becomes poor, the hoisting machine 25 is operated and the recovery pipe 22a is lowered in accordance with the lowering of the upper surface of the control element deposition portion to reduce suction efficiency. I try to prevent the decline.

Next, the recovery principle will be described. When a blower (not shown) is activated to reduce the pressure in the recovery unit 28a, the helium gas as the recovery gas in the control element housing pipe 19 is sucked through the recovery pipe 22a and is accompanied by the flow of the helium gas. The control element 14 flows upward through the collecting pipe 22a, is discharged from a discharge port (not shown), and is collected in the collecting section 24a.

At this time, when the helium gas sucked by the blower (not shown) of the control element recovery device 21A flows in the recovery pipe 22a at the flow rate u, the reaction force D received by the control element 14 by the helium gas is as follows (1) ) Is represented by a formula. D = C _D · S · ρ · u ² / 2 (1) where C _D is the resistance coefficient, S is the projected area of the control element 14 on the cross section perpendicular to the flow path, and ρ is the density of helium gas.

Therefore, the drag force D on the control element 14 is
When the value becomes larger than the weight of the control element 14, the control element
14 is sucked into the recovery pipe 22a. The equation (1) shows that when the flow velocity of the helium gas as the recovery gas is increased, the drag force D is also increased and the suction transfer of the control element 14 is facilitated. Further, the helium gas flow rate u required for floating and recovering the single control element 14 is given by the following equation (2).

[0016]

[Equation 1] Here, V is the volume of the control element 14, g is the gravitational acceleration, and ρ _l
Represents the density of the control elements 14.

When the actual recovery operation is performed, the control element
A large number of control elements instead of collecting 14 by suction
Since it is necessary to suck 14 continuously and in a stable state, a flow velocity higher than that calculated by Eq. (2) is required.

[0018]

The control element is sucked and collected by the principle described above. However, in some cases, as shown in FIG. 5, a plurality of control elements 14 may be simultaneously sucked and blocked at the inlet (nozzle 23a) of the recovery pipe 22a. If blocked, the blower must be stopped and restored. Therefore, it is possible to preliminarily increase the diameter d of the recovery pipe 22a sufficiently so that the recovery pipe 22a will not be blocked even when a plurality of suctions are simultaneously performed.

However, as described above, the control element 14
In order to suck and recover the air, a flow velocity of the floating velocity u or more is required. Therefore, if the diameter d of the recovery pipe 22a is too large, the flow rate Q required of the blower is (π / 4) d ² ×
If the blower is over the value obtained by u and the blower has an excessive capacity, it is not economically disadvantageous but wasteful energy is consumed. Further, there is a problem that the outer shape of the blower becomes large and extra space is required for installation.

Therefore, an object of the present invention is to provide a control element recovery device for a high temperature gas reactor, which is economically advantageous without clogging of the control element and which improves recovery operation reliability.

[0021]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has a suction port of a recovery pipe arranged opposite to a packed layer of control elements filled in a control element housing pipe in a core of a high temperature gas reactor. In a control element recovery device for a high temperature gas reactor in which a control gas is sucked and recovered together with the recovery gas by circulating a recovery gas through a recovery pipe, two control elements each having a cylindrical shape are in contact with each other at their plane portions. Whichever of the diameter of the circle in which the two corners of each control element are inscribed or the diameter of the circle inscribed in the state where the circumferential portions of the three cylindrical control elements are in intimate contact with each other, The diameter of the recovery pipe is larger than the larger diameter.

[0022]

The minimum limit of the diameter of the recovery pipe is set as described above by comparing the experimental results with the theoretical closing pattern. That is, using the diameter of the recovery pipe as a parameter, the size and shape of the control element having a diameter of 13 mm and a length of 13 mm as shown in the examples were used as an example, and the results of a recovery experiment were performed and a theoretical blockage pattern was plotted. It is set by comparing the obtained results. According to the experimental results, it was blocked when the diameter of the recovery pipe was 28 mm or less, and was recoverable when the diameter was 30 mm or more.

According to the theoretical closing pattern, the diameter of the inscribed circle when three control elements are lined up is the closing pattern K.
Except for those (shown in Table 2), it exceeds 30 mm. When 4 or more are lined up, all exceed 30 mm. When two pieces are lined up, the diameter of the inscribed circle may exceed 30 mm, but this condition is unstable and is extremely low. 28 mm in experimental results
From the experimental results that the blockage occurred below and the recovery was possible at 30 mm or more, the clogging pattern of 28 mm or more and less than 30 mm was the clogging pattern C in the case of 2 and the clogging pattern K in the case of 3. That is, the closing pattern C (shown in Table 2) is a state in which two control elements are arranged such that the plane portions thereof are in contact with each other and the two corner portions of each control element are inscribed, and the closing pattern K is 3 The circumferential portions of the individual control elements are in close contact with each other. If the diameter of the recovery pipe is larger than the larger diameter of the inscribed circles of these two closing patterns, it can be said that the probability of closing is extremely low. Therefore, by setting the diameter of the recovery pipe under these conditions, it is possible to select a blower having an optimum capacity, and it is economically advantageous and reliability can be improved without blocking the control element.

[0024]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a state in which an embodiment of the present invention is mounted in a high temperature gas reactor. The same parts as those in FIG. 3 are designated by the same reference numerals, and the duplicated description will be omitted.

In FIG. 1, 1 is a reactor vessel, 20 is a stand pipe, and 21B is a control element recovery device attached to this stand pipe 20. This control element recovery device 21
Similarly to the control element recovery device 21A described above, B is a negative pressure formed by a blower (not shown) or the like to suck the helium gas in the core 2, and put it on the flow to control element recovery pipe.
A collecting portion 24b for sucking and collecting the control element 14 in the collecting pipe 19, a collecting pipe 22b having a suction nozzle 23b hanging from the lower end of the collecting portion 24b, and a collecting pipe 22b installed above the collecting portion 24b. It is configured to include a hoisting machine 25 that is driven in the direction.

Therefore, the recovery pipe 22b is selected based on the experimental results whose diameter d is shown in Tables 1 and 2. Therefore, Table 1 and Table 2 will be described. First, Table 1 shows
The control element dimensions are 13 mm in diameter and 13 mm in length, and the results of recovery experiments using the recovery pipe diameter as a parameter are shown below.

[0027]

[Table 1] From this, it can be seen that when the diameter d of the recovery pipe is 28 mm or less, it is blocked and when the diameter d is 30 mm or more, the recovery is possible. Next, Table 2 shows
As an example of theoretical blockage pattern, diameter 13mm, length 13mm
The inscribed circle diameter obtained by plotting the case of the control element is shown.

[0028]

[Table 2]

According to Table 2, in the theoretical closing pattern, the inscribed circle diameter of all four or more control elements exceeds 30 mm. In the case of three pieces, it exceeds 30 mm except for the closing pattern K. In the case of two, it is 30 mm or more. Therefore, Table 1
Compared with the experimental results shown in (1), according to the experimental results, it was possible to collect four or more pipes at the same time because it was possible to collect when the diameter of the collection pipe was 30 mm or more. Further, even in the case of three, except for the blockage pattern K, it can be said that the probability of simultaneous suction is extremely small. Further, in the case of two pieces, the inscribed circle diameter may exceed 30 mm, but from the experimental results and the closing pattern diagram shown in Table 1, the closing pattern in which the inscribed circle exceeds 30 mm is unstable in the case of two pieces. It can be said that it is a state and is a blockage pattern that exists with an extremely low probability.

Therefore, the minimum limit of the diameter d of the recovery pipe is
If the diameter of the inscribed circle in the states of the obstruction pattern C and the obstruction pattern K is larger than the larger inscribed circle diameter, the control element is not obstructed. That is, the closing pattern C
Is the two control elements lined up in contact with each other on a flat surface,
The two corner portions of each control element are inscribed, and the closing pattern K is a state where the circumferential portions of the three control elements are in close contact with each other.

For example, in the case of a cylindrical control element having a diameter of 13 mm and a length of 13 mm, the former inscribed circle diameter is 29.1 mm and the latter is 28 mm, and there is no blockage if the recovery pipe diameter d exceeds 29.1 mm. It will be. On the other hand, if the diameter d of the recovery pipe is set to 29 mm or less, the frequency of closing the control element becomes extremely high, and the blower must be stopped and recovered each time, and the recovery work efficiency is significantly reduced.

On the other hand, if the diameter of the recovery pipe becomes too large,
There is a risk that the flow rate will increase and the blower capacity will be exceeded, making recovery impossible. For example, High Temperature Engineering Test Reactor (HTTR)
Taking the above case as an example, the blower rated operating point is shown in Fig. 2. According to this figure, if the diameter of the recovery pipe exceeds 49 mm, the operating point will be outside the range of blower performance and recovery will be impossible. Therefore, it is significant to set an appropriate recovery pipe diameter for the control element size.

[0033]

As described above, according to the present invention, two control elements each having a cylindrical shape are arranged with their plane portions in contact with each other, and the diameter of a circle in which two corners of each control element are inscribed or Since the diameter of the recovery pipe is set to be larger than the larger diameter of the diameters of the inscribed circles in which the circumferential portions of the three cylindrical control elements are in intimate contact with each other, the blower capacity is increased. It is possible to provide a control element recovery device for a high temperature gas reactor in which the probability that the control element is blocked at the inlet of the recovery pipe is extremely small, and the reliability of recovery work is improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a high temperature gas furnace to which an embodiment of the present invention is applied.

FIG. 2 is a diagram showing expected blower rating performance and expected operating points related to the present invention.

FIG. 3 is a vertical cross-sectional view showing a structural example of a conventional high temperature gas furnace.

4 is a vertical cross-sectional view showing a control element recovery device mounted on the conventional high temperature gas furnace shown in FIG.

5 is an explanatory view showing a state in which a control element closes an inlet portion of a recovery pipe in the conventional high temperature gas furnace shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor vessel, 2 ... Core, 3 ... Fuel rod, 8 ... Control rod drive device, 9 ... Control rod, 14 ... Control element, 19 ... Control element accommodation pipe, 20 ... Stand pipe, 21A, 21B ... Control rod Recovery device, 22a, 22b ... Recovery pipe, 23a, 23b ... Suction nozzle,
24a, 24b ... Collection section.

Claims (1)

[Claims] 1. A suction port of a recovery pipe is arranged so as to oppose a packed layer of a control element filled in a control element housing pipe in a core of a high temperature gas reactor, and a recovery gas is circulated through the recovery pipe.
In a control element recovery device for a high temperature gas reactor, wherein the control element is sucked and recovered together with the recovery gas, two control elements each having a columnar shape are arranged so that their plane portions are in contact with each other, and each control element is arranged. Of the diameter of the circle inscribed at two corners of the circle or the diameter of the circle inscribed in the state where the circumferential portions of the three cylindrical control elements are in intimate contact with each other, whichever is larger. A control element recovery device for a high temperature gas reactor, characterized in that the diameter of the recovery pipe is increased.