JPH038719B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention simplifies the in-reactor refueling mechanism in loop-type and tank-type fast breeder reactor (FBR) nuclear reactor structures, and improves rotation speed without reducing the size of the reactor core. This relates to a fuel handling mechanism in a fast breeder reactor with a reduced plug diameter.

Conventionally, this type of in-reactor fuel exchange mechanism will be explained based on the reactor structure of a typical tank-type fast breeder reactor (FBR), as shown in FIGS. 1 to 3.

Figure 1 is a vertical cross-sectional view of the reactor structure of a tank-type FBR, where 1 is the reactor vessel, 2 is the roof slab,
Numeral 3 is a large-rotation plug, 4 is a small-rotation plug, and 5 is an offset arm type fuel exchanger, which can draw fuel located in the furnace 6 or in the furnace relay rack 7 into a guide cylinder 5' located in the furnace.

That is, a large rotation plug 3, a small rotation plug 4,
The offset arm type fuel exchanger 5 is an in-core fuel exchange mechanism, and a double rotating plug offset arm system is adopted.

Therefore, the position of the guide tube 5' is determined by the large rotation plug 3,
This is done by a combination of the rotation angles of the small rotating plug 4 and the refueling machine 5, and spent fuel or new fuel is transferred between the reactor core 6 and the in-core relay rack 7. 8 is a chute for taking spent fuel out of the reactor and carrying new fuel into the reactor; 9 is a control rod drive mechanism; in this case, it is mounted on the small rotating plug 4;
Control rods (not shown) inserted into the reactor core 6 are moved up and down, but are separated during fuel exchange. Reference numeral 10 denotes a housing for the control rod drive mechanism 9, which is suspended from the lower end of the small rotation plug 4.

However, in a tank-type FBR, a plurality of pumps 14 and IHX (intermediate heat exchanger,
(not shown), if the diameter D _L of the large-rotation plug 3 increases, the inner diameter of the reactor vessel 1 also increases, which has the disadvantage of increasing the amount of material and increasing costs. Therefore, in order to achieve a low-cost nuclear reactor structure, it is necessary to reduce the diameter D _L of the large rotating plug 3. Although the reactor vessel 1 itself can be made smaller in the loop-type FBR by reducing the large-rotation plug diameter D _L , it is not as effective as the tank-type FBR in terms of cost.

FIG. 2 is a core plan view of a typical large FBR. Located approximately in _DC is a fuel assembly 11 including a bracket, 12 is a control rod, and 13 is a neutron shield.

Further, 7 indicates the position of the relay rack inside the furnace.

Here, since the neutron shield 13 does not need to be replaced, the guide cylinder 5 of the refueling machine shown in FIG.
The range that must be approached is within the diameter D _C and the location of the relay rack 7.

Furthermore, Fig. 3 shows the case when the conventional double-rotating plug offset arm method shown in Fig. 1 is adopted.
This is a diagram showing D _L and D _C , where a is the eccentricity of the small rotation plug 4, b is the distance inside the fuel exchanger from the center of the small rotation plug 4, and c is from the center of the fuel exchanger 5 to the guide cylinder 5'. In other words, it is the offset amount.

Further, the diameter D _R indicates the outer diameter of the control rod drive mechanism housing 10. Furthermore, d is the outer diameter of the guide tube 5', D _L ,
D _S indicates the width of the large and small rotating plug drive gear.

However, in the system described above, the basic dimensions are determined by the position (a+b+c) of the D _R and the relay rack 7.

In other words, 1/2D _R +1/2d+2c=a+b+c......b=a+c......The formula is 1/2D _R +1/2d+2c=2a
+2c Therefore, a=1/4 (D _R +d) ...... Also, D _S =2 (a+1/2D _R +L _S ) ...... D _L =2 (a+1/2D _S +L _L ) ...... Substitute and D _L = 2 (D _R + L _S + L _L ) + d In this way, the dimension of D _L is dominated by D _R , and D _R
Since it is determined by the arrangement of the control rods, it is impossible to reduce the diameter of the rotating plug unless the core is made smaller.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to reduce the plant cost of the nuclear reactor structure, and to reduce the size of the reactor core.
In order to reduce the diameter of the reactor vessel, we focused on reducing the diameter of the rotating plug, which is the dominant factor in the diameter of the reactor vessel. By mounting the rotating plug and the other components on the large rotating plug, arranging the large rotating plug eccentrically with respect to the center of the core, and using an offset arm type fuel exchanger, the diameter of the rotating plug is approximately 2 minutes smaller than that of the conventional rotating plug. The present invention provides a fuel handling mechanism in a fast breeder reactor that can be reduced in size to 1 in size.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 4 and 5. In the drawings, the same parts that correspond to the conventional structure are given the same reference numerals and their explanations will be omitted.

FIG. 4 is a diagram illustrating the concept and D _S and D _C according to the present invention.

As shown in the figure, the small rotation plug 4 is placed so as to fit inside D _C (called the envelope circle area of the control rod drive mechanism, the diameter of which corresponds to the diameter of the core fuel assembly area), and Part of 12 is attached to small rotation plug 4
Then, place the rest in the large rotation plug 3. Therefore, although not shown in the figure, the control rod drive mechanism housing 10 is also separated into the large-rotation plug 3 side and the small-rotation plug 4 side, and its cross section is crescent-shaped on the large-rotation plug 3 side and approximately half-shaped on the small-rotation plug 4 side. It has a circular shape.

In addition, in order to handle fuel in the center of the reactor core, the center of rotation of the large rotating plug 3 is offset by an amount S with respect to the core, and an offset arm type fuel exchanger 5 is used, which is mounted on the small rotating plug 4.

By doing so, the control rod drive mechanism housing 10 does not obstruct the guide tube 5' from approaching the center of the core.

Note that if the fuel exchanger 5 rotates freely, it will interfere with the control rod housing, so the rotations of the large rotation plug 3, small rotation plug 4, and fuel exchanger 5 should be controlled according to a preprogrammed procedure to avoid mutual interference. There must be.

Further, the dimensions of the eccentricities S, a, b, c, and D _S are determined to be appropriate values, taking into account the arrangement of the control rod 12.

FIG. 5 shows a longitudinal section of the concept shown in FIG. The bearing 4a of the small rotation plug 4, the drive gear 4b, and the seal structure etc., which are not shown in the figure, are
In order to be installed between the control rod drive mechanisms 9, in this embodiment, the minimum width is selected, for example, by using a bearing integrated with the components of the large and small rotating plugs.

In this embodiment, the control rod drive mechanism 9 employs a nozzle type. That is, by extending the joint between the small-diameter guide tube through which the shaft of the control rod drive mechanism 9 passes and the large-diameter drive mechanism upward through the nozzle holder 9a, 4a, 4
The structure is designed to open up space for the installation of b.

In the figure, V indicates the center of the reactor core 6, W indicates the rotation center of the large rotation plug 3, X indicates the rotation center of the small rotation plug 4, and Y indicates the rotation center of the fuel exchanger 5. Furthermore, since the control rod drive mechanism housing 10 is separated into the large-rotation plug 3 side and the small-rotation plug 4 side, there is a problem that seismic rigidity decreases during reactor operation. As shown in the figure below, it is also possible to use a key structure to achieve seismic strength.

As described in detail above, according to the fast breeder reactor fuel handling mechanism according to the present invention, the diameter of the large rotating plug can be significantly reduced.

That is, according to the present invention, in a fast breeder reactor having at least a large-rotation plug and a small-rotation plug, part of a plurality of control rod drive mechanisms and a fuel exchanger are disposed in the small-rotation plug, and the above-mentioned This is an in-core fuel handling mechanism that makes it possible to reduce the diameter of the large-rotation plug by arranging the remainder of the multiple control rod drive mechanisms in the large-rotation plug.

For example, for a core with D _R =3300 mm and L ₇ =2900 mm, in the conventional method shown in FIG. 3, D _L is approximately 9000 mm, but in the present invention shown in FIG. 4, D _L is approximately 5100 mm.

Therefore, the diameter of the furnace vessel, which was conventionally 22 m in diameter, can be reduced to about 18 m.

This not only reduces the reactor structure but also the reactor building, and the effect of reducing the amount of material is significant.
Can be constructed at low cost.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the reactor structure of a typical conventional tank-type FBR, and Figure 2 is a typical large-scale conventional tank-type FBR reactor structure.
Figure 3 is a basic conceptual diagram showing the conventional in-reactor fuel handling mechanism, Figure 4 is a basic conceptual diagram showing the in-core fuel handling mechanism according to the present invention, and Figure 5 is a core plan view of the FBR. FIG. 2 is a vertical cross-sectional view schematically showing a fuel handling mechanism. 1... Reactor vessel, 3... Large rotating plug, 4...
...Small rotation plug, 5...Fuel exchanger, 5'...Guide tube, 6...Reactor core, 7...Relay rack, 9...Control rod drive mechanism, 9a...Nozzle stand, 10...Housing, 12 ...control rod.

Claims (1)

[Claims] 1. In a fast breeder reactor having large and small rotating plugs, the large rotating plug is arranged with its center of rotation eccentric to the reactor core by a predetermined amount, and the small rotating plug is arranged so as to bite into the envelope circle area of the control rod drive mechanism of the large rotating plug. A plurality of control rod drive mechanisms are arranged in the large and small rotating plugs corresponding to the envelope circle area, and an offset arm type fuel exchanger is arranged in the small rotating plugs in other parts other than the envelope circle area. A fuel handling mechanism in a fast breeder reactor featuring: