JPH0782108B2 - Flow rate adjustment mechanism for damaged fuel detector for fast reactor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a damaged fuel detection device used in a liquid metal cooled fast reactor in a nuclear power plant, and particularly for adjusting a flow rate of a coolant flowing in the device. The present invention relates to a flow rate adjusting mechanism.

[Prior Art] As a broken fuel detection device for a fast reactor used for detecting a damage of a fuel assembly, for example, a type as shown in FIG. 6 has been proposed. The damaged fuel detection device 1 shown in the drawing includes a cylindrical housing 3 extending downward from a reactor upper mechanism 2 of a reactor vessel, and a damaged fuel detection mechanism 4 is disposed in the housing 3. Damaged fuel detection mechanism 4
Is provided with cylinders 5 and 6 having various broken fuel detecting devices therein and forming a flow passage of the coolant F, and is divided into upper and lower parts. A corrosion product adsorbent 8 and a particle trap 9 for trapping a damaged fuel substance are attached in a cylindrical body 5 of a lower damaged fuel detection mechanism (hereinafter, referred to as “lower detection mechanism”) 7. Further, the cylinder body 6 of the upper damaged fuel detection mechanism (hereinafter, referred to as “upper detection mechanism”) 10 has a triple pipe structure, and the flow meter 12, the shielding material 13, and the delayed neutrons are provided in the innermost cylinder 11. A detector 14 is attached. Housing 3
An interface mechanism 18 that fits into the top opening 17 of the handling head 16 of the fuel assembly 15 is provided at the lower end portion of the fuel assembly 15. The coolant F from inside the fuel assembly 15 passes through this interface mechanism 18 and is damaged. The fuel detection mechanism 4 is guided into the cylindrical bodies 5 and 6.

In such a damaged fuel detection device 1, an irradiation rig (a kind of fuel assembly) is overloaded in a state where the reactor output is kept constant, and the damaged fuel irradiation behavior is simulated and delayed. A flow rate adjusting mechanism for adjusting the flow rate of the coolant F flowing through the damaged fuel detecting mechanism 4 is provided for the purpose of obtaining the arrival time dependency evaluation of the neutron detector count rate. The flow rate adjusting mechanism in the broken fuel detecting device 1 shown in the figure is incorporated in the upper detecting mechanism 10, and the valve body formed on the central opening 20 of the closed end plate of the intermediate cylinder 19 and the lower surface of the closed end plate of the inner cylinder 11. And a drive unit for moving the valve body 21 up and down. Inner cylinder 11
Since the intermediate portion of the valve is composed of a thin metal bellows 22, the valve element 21 can move up and down. Drive part is a lid plate
A drive motor 24 fixed to 23 is provided, and the valve body 21 can be moved up and down via a drive shaft 25 by remote control. This changes the insertion depth of the valve body 21 into the central opening 20,
The flow rate is adjusted.

[Problems to be Solved by the Invention] In the conventional flow rate adjusting mechanism as described above, a valve body is inserted into one opening and the flow rate is changed depending on the insertion depth. Since the pressure difference between the inflow side and the coolant outflow side is easily affected, there is a problem that accurate flow rate control is difficult.

In addition, since a thin metal bellows is interposed in the inner cylinder forming the primary coolant boundary, there is a possibility that metal fatigue or sodium corrosion (oxidation or carburization etc.) may occur in the metal bellows due to repeated operation. There is also a problem with high temperature structural strength.

As described above, the conventional flow rate adjusting mechanism has various problems to be solved.

[Means for Solving the Problems] Therefore, in order to solve the above-mentioned problems, a flow rate adjusting mechanism according to the present invention includes a cylindrical housing penetrating the reactor upper part mechanism of a reactor vessel and extending vertically downward toward the core. A broken fuel detection device for a fast reactor, which is vertically movable in the housing and includes a broken fuel detection device and a tubular body having a multi-tube structure that forms a coolant flow passage, A drive mechanism for vertically moving the tubular body within a predetermined range with respect to the housing, and a predetermined height on the outer surface of the tubular body for discharging the coolant flowing in the tubular body from the tubular body. When the plurality of openings provided are in slidable contact with the outer surface of the tubular body and the tubular body is located at the lower limit position, the opening is opened, and when the tubular body is located at the upper limit position, the opening is opened. The house is designed to close And a coolant leakage prevention means for preventing leakage of the coolant passing between the housing and the cylinder to the outside (upper part of the furnace). .

[Operation] In the configuration described above, the opening of the outer surface of the tubular body of the damaged fuel detection mechanism and the sliding surface of the housing constitute a slide valve, and the opening and closing of the opening is adjusted by moving the tubular body up and down. You can do it.

[Embodiment] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be denoted by the same reference numerals.

FIG. 1 is a sectional view showing a state in which a damaged fuel detecting device 30 to which the present invention is applied is attached to a reactor vessel of a fast reactor.
The damaged fuel detection device 30 is attached to penetrate the upper reactor mechanism 2 of the reactor vessel and extends vertically downward toward the core, as in the conventional mechanism described above. The housing 3 of the damaged fuel detection device 30 has an elongated cylindrical shape, and a lower damaged fuel detection mechanism (lower detection mechanism) 7 and an upper damaged fuel detection mechanism (upper detection mechanism) 31 are coaxially arranged therein. . An interface mechanism 18 connected to the handling head 16 of the fuel assembly 15 is provided at the bottom of the housing 3. The lower detection mechanism 7 includes a cylindrical tubular body 5 and a corrosion product adsorbent 8 mounted inside the tubular body 5.
And a particle trap 9 for trapping a damaged fuel substance.

The cylinder 32 of the upper detection mechanism 31 includes an inner cylinder 33, an intermediate cylinder 34, and an outer cylinder.
It has a 35-tube structure. The inner cylinder 33 constitutes a primary coolant boundary, and inside thereof, a flow meter 12, a shielding material 13, and a delayed neutron detector 14 are arranged from below. An interface mechanism 37 that fits into the top opening 36 of the lower detection mechanism 7 is provided at the lower end of the upper detection mechanism 31. The outer cylinder 35 and the intermediate cylinder 34 are integrated in the lower part thereof, and the inner cylinder 33 and the outer cylinder 35 are integrated in the upper part thereof. An annular partition plate 38 is integrally provided between the inner cylinder 33 and the outer cylinder 35 at a slight distance from the upper end of the intermediate cylinder 34.

As clearly shown in FIG. 2 which is an enlarged view of part A of FIG.
A ridge portion (also referred to as a "lower ridge portion") 39 protruding outward in the radial direction is formed on the lower portion of the outer cylinder 35 over the entire circumference, and the outer cylinder 35, the intermediate cylinder 34, and A plurality of openings (three in this embodiment) 40 that are connected to the annular space between them are formed at equal intervals in the circumferential direction. Thereby, the coolant F sent from the fuel assembly 15 through the interface mechanism 18 and the lower detection mechanism 7 flows into the inside through the interface mechanism 37 of the upper detection mechanism 31, and the inner cylinder 33 and the intermediate cylinder. 34, and the direction of the flow is changed at the lower surface of the partition plate 38, and the space between the intermediate cylinder 34 and the outer cylinder 35 descends to open the raised portion 39.
It will flow out from 40.

The upper half of the housing 3, more specifically, the portion facing the upper detection mechanism 31, has a double structure, and the lower raised portion 39 of the tubular body 32 of the upper detection mechanism 31 has an inner wall of the housing 3.
It comes in contact with the inner surface of 41 and can slide up and down.
Further, in order to vertically move the tubular body 32 in a stable state, an upper raised portion 42 having the same diameter as the lower raised portion 39 is formed on the upper portion thereof. The upper ridge 42 is provided with a labyrinth seal or a metal O-ring 43 in order to prevent leakage of the coolant rising between the housing 3 and the upper detection mechanism 31. The lower portion of the inner wall 41 of the housing 3 is thin. As can be understood from FIGS. 2 and 3, the positional relationship between the thin portion 44 and the lower raised portion 39 of the cylindrical body 32 is such that the interface mechanism 37 of the upper detection mechanism 31 is fitted to the lower detection mechanism 7. When lowered as much as possible, the opening 40 is opened to face the thin portion 44, and when the upper detection mechanism 31 is slid upward, the opening 40 is slid on the inner wall 41 of the housing 3. It is defined to be closed by the surface 45. In this way, the opening 40 and the sliding surface 45 of the housing 3 constitute a flow rate adjusting portion of the flow rate adjusting mechanism.

A so-called ball nut screw type drive mechanism is provided between the upper portion of the upper detection mechanism 31 and the housing 3. That is, at the upper end of the cylindrical body 32 of the upper detection mechanism 31, a cylindrical extension portion 46 extending vertically upward is provided coaxially. A screw is cut on the upper outer surface of the extension portion 46, and the rotating body 47 screwed with the screw portion is provided in the housing 3
By the support block 49 fixed to the upper flange 48 of
It is rotatably supported. The outer surface of the rotating body 47 has a gear 50.
Is formed, and this gear 50 meshes with the spur gear 52 of the drive motor 51 mounted on the support block 49.

In such a configuration, when the drive motor 51 is remotely operated, the drive motor 51 rotates the rotating body 47, and the extension portion 46 of the cylindrical body 32 screwed with the rotation body 47 moves upward or downward along the axis thereof. To do. As a result, the position of the opening 40 of the cylindrical body with respect to the sliding surface 45 of the housing 3 is adjusted, and the opening degree of the opening 40 is adjusted. That is, when the cylinder 32 is in the lowest position, the opening 40 is completely opened as shown in FIG. 2, and the coolant F flowing in the upper detection mechanism 31 flows out through the opening 40. Further, when the tubular body 32 is moved upward, the opening 40 is gradually covered by the sliding surface 45 of the housing 3 and the opening degree is reduced, so that the flow rate in the upper detection mechanism 31 is reduced. And
When raised to the upper limit position, open as shown in Fig. 3.
40 is closed by the sliding surface 45 of the housing 3, and the flow of the coolant F in the upper detection mechanism 31 is blocked.

Labyrinth seal or O provided on upper ridge 42
The ring 43 prevents the leakage of the coolant that rises between the housing 3 and the upper detection mechanism 31, but in order to further improve the leakage prevention performance, as shown in FIGS. 3, at an appropriate position above the lower raised portion 39 of the tubular body 32 and below the upper surface of the furnace upper mechanism 2,
It is preferable to provide a plurality of overflow holes 55. The position of the overflow hole 55 must be determined in consideration of the pressure loss of the flow rate adjusting mechanism and the shape loss such as friction loss, bending loss, and expansion loss. By providing the overflow hole 55, the coolant f rising from the opening 40 between the housing 3 and the cylindrical body 32 is returned to the furnace before reaching the labyrinth seal or the O ring 43 at the upper portion.

Further, since the sliding portion between the housing 3 and the raised portion 39 of the tubular body 32 may cause high-temperature fusion or wear deterioration, as shown in FIG. It is advisable to form a plurality of grooves 56 extending in the vertical direction that allow various leaks at appropriate intervals in the circumferential direction. By forming such a groove 56, the coolant f flowing upward is also increased. However, by providing the overflow hole 55 in the housing 3, it is possible to prevent the coolant from leaking to the outside. .

[Advantages of the Invention] As described above, since the flow rate adjusting mechanism according to the present invention constitutes the orifice type porous throttle valve, stable and highly accurate flow rate adjustment is possible, and the manufacture is easy.

In addition, since the flow rate adjusting mechanism according to the present invention does not use a metal bellows, it is extremely excellent in terms of structural soundness and safety, is easy to manufacture, and can reduce the cost.

Further, as a coolant leakage prevention means, by providing an overflow hole in the housing in addition to the labyrinth seal and the O-ring, it is possible to completely prevent the coolant from leaking to the outside.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a broken fuel detection device for a fast reactor equipped with a flow rate adjusting mechanism of the present invention, FIGS. 2 and 3 are enlarged views of part A of FIG. 1, and FIG. Fig. 3 is a diagram showing a state in which the opening of the flow rate adjusting mechanism is open, Fig. 3 is a diagram showing the state in which the opening is closed, and Fig. 4 is an enlarged vertical sectional partial view showing a damaged fuel detecting device provided with an overflow hole, Is B in FIG.
FIG. 6 is a cross-sectional view taken along the line -B, and FIG. 6 is a vertical cross-sectional view showing a conventional damaged fuel detection device. In the figure, 1,30 ... damaged fuel detection device 2 ... furnace upper mechanism, 3 ... housing 5,6,32 ... cylindrical body 7 ... lower detection mechanism (lower damaged fuel detection mechanism) 10,31 ... upper detection mechanism (upper damaged mechanism) Fuel detection mechanism) 39 ... Raised part, 40 ... Opening 41 ... Inner wall, 43 ... O-ring 45 ... Sliding surface, 51 ... Drive motor 55 ... Overflow hole 56 ... Groove

Continuation of the front page (56) References JP-A-59-214792 (JP, A) JP-A-58-122494 (JP, A) JP-A 1-163699 (JP, A) Actual development Sho-59-158096 (JP , U)

Claims (1)

[Claims] 1. A cylindrical housing penetrating an upper reactor mechanism of a nuclear reactor vessel and extending vertically downward toward a reactor core, and a vertically movable member disposed inside the housing, which includes a damaged fuel detection device and the like. A damaged fuel detection device for a fast reactor, comprising: a tubular body having a multi-tubular structure that forms a coolant flow passage; and a drive mechanism for moving the tubular body up and down within a predetermined range with respect to the housing. A plurality of openings provided at a predetermined height on the outer surface of the tubular body for discharging the coolant flowing in the tubular body from the tubular body, and slidably contacting the outer surface of the tubular body, Further, the opening is opened when the cylinder is arranged at the lower limit position, and the opening is closed when the cylinder is arranged at the upper limit position,
Damaged fuel for a fast reactor, comprising: a sliding surface formed on the inner surface of the housing; and a coolant leakage prevention means for preventing leakage of the coolant passing between the housing and the cylinder to the outside. Flow rate adjustment mechanism of the detector.