JPH06201874A - Nuclear fuel spacer - Google Patents

Abstract

(57) [Summary] [Purpose] The gap area between the channel box and the outermost fuel rod is reduced to keep the flow passage area of the coolant constant. [Structure] Leaf-shaped projections 15 and 16 having different thermal expansions are provided on two adjacent surfaces of a spacer band 14, respectively. One lobe 15 is made of Zircaloy, which has a small thermal expansion, and the other lobe 15 is
16 is made of Inconel, which has a large thermal expansion. During operation of the nuclear reactor, the gap between the spacer and the channel box is eliminated due to the difference in thermal expansion, and a predetermined coolant passage is secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear fuel spacer incorporated in a fuel assembly for a nuclear reactor to maintain fuel rods in equal intervals.

[0002]

2. Description of the Related Art Among fuel assemblies of a nuclear reactor, those used in a boiling water reactor (BWR) are shown in FIG. 7, and nuclear fuel spacers are shown in FIGS.
Description will be given with reference to (b).

A BWR fuel assembly 1 is constructed by arranging fuel rods 2 in 8 rows and 8 columns, and having an upper tie plate 3, a lower tie plate 4 and a nuclear fuel spacer 5. The fuel rod 2 is obtained by baking low-enriched uranium into pellets and inserting it into a fuel cladding tube, and a zirconium liner cladding tube is used for the fuel assembly 1.

The nuclear fuel spacer 5 is for keeping the interval between the plurality of fuel rods 2 at a specified width, and the upper tie plate 3 and the lower tie plate 4 support the upper and lower portions of the fuel rods 2 and inside the channel box 6. Inserted in. One or two of the plurality of fuel rods 2 are replaced by water rods 7.

The nuclear fuel spacer 5 is shown in FIGS.
As shown in (b), it is composed of a square spacer band 8 and a lattice plate 9 that is vertically and horizontally combined inside the spacer band 8. The grid plate 9 has a fixed support portion 11 for holding the fuel rod 2 to be inserted into the square partitioned space 10, and the fuel rod 2
The elastic support member 12 that presses the fixed support portion 11 against the grid plate 9
It is attached to the intersection of.

The spacer band 8 is provided with a plurality of leaf-shaped projections 13 projecting outward on the channel box 6 side in order to secure a space between the channel box 6 and the outermost fuel rod 2. The leaf-shaped projection 13 is generally a fixed portion having a constant height formed by plastically deforming the spacer band 8.

On the other hand, when the fuel assembly 1 is assembled, since the channel box 6 is finally inserted and assembled, the inner width of the channel box 6 is wider than the outer width of the leaf-shaped projections 13, and the fuel assembly after assembly is completed. Within the body 1 there is a small (~ 0.5 mm) gap in the fuel rod 2.

Therefore, when the reactor is operated, the designed gap (about 4 mm) between the fuel rods 2 and the channel box 6 at the outermost periphery of the fuel assembly, that is, the coolant passage area at the outermost periphery includes the manufacturing error. The coolant flow rate can be varied. When the coolant flow passage area becomes narrow, it becomes difficult for the coolant to flow, and the amount of coolant for removing heat from the fuel rods 2 facing the flow passage decreases,
Thermally becomes severe.

[0009]

Conventionally, there is a phenomenon called boiling transition as a thermo-hydraulic phenomenon that determines the limit output of a fuel assembly. When the boiling transition phenomenon occurs, the surface temperature of the fuel rod 2 at the portion where the boiling transition phenomenon occurs rapidly rises, which triggers burnout of the fuel rod. This boiling transition is likely to occur in the outer peripheral fuel rods of the fuel assembly and the high-power fuel rods.

In recent years, with the increase in burnup of nuclear reactor fuel, etc., there are many design examples of the radial peak power distribution in the initial stage of combustion of a fuel assembly, in which a high-power fuel rod is arranged around the channel box. . In other words, the coolant flow passage area changes, and the condition of higher output is added to the outermost peripheral fuel rod in which the cooling state is unstable, and the boiling transition is likely to occur.

Under such conditions, if the fuel assembly is biased to one side or the channel box is bent for some reason, and as a result the fuel assembly is biased to one side, the limit output of fuel is channeled to the fuel assembly. There is a problem that it is lower than that at the position of flow rate in the box.

The present invention has been made to solve the above-mentioned problems, and it is possible to reduce the change in the gap between the channel box and the outermost peripheral fuel rod so as to avoid a decrease in the limit output of the fuel and to avoid the fuel rod. It is to provide a nuclear fuel spacer capable of ensuring stable cooling performance.

[0013]

According to the present invention, a plurality of lattice plates are combined in a lattice shape in a square spacer band to form a square partition space having a small area, and a fixed support portion is provided on the lattice plate. In a nuclear fuel spacer in which an elastic supporting member is provided at a combination intersection of lattice plates, a plurality of leaf-shaped projections extending outward is provided in the spacer band, and a fuel rod is inserted into the compartment space, the leaf-shaped projections provided in the spacer band are The leaf-shaped projections provided on the two adjacent surfaces of the spacer band are made of a material having a higher coefficient of thermal expansion than the leaf-shaped projections on the other two adjacent surfaces and are formed to have a low height.

[0014]

In the nuclear fuel spacer according to the present invention, the leaf-shaped protrusions on two adjacent surfaces have a higher coefficient of thermal expansion and a lower height than the leaf-shaped protrusions on the other two surfaces at room temperature when the channel box is inserted. A gap required for inserting the channel box is secured between the outer diameter of the band and the inner diameter of the channel box.

On the other hand, after the fuel assembly is loaded in the reactor, the leaf-shaped projections having a large thermal expansion rise toward the channel box side due to the thermal expansion difference in the high-temperature high-pressure water under rated operation.
By filling the gap between the channel box and the lobe-like projection and pressing the fuel assembly toward the lobe-like projection side with a small thermal expansion, a predetermined outermost peripheral passage area can be secured.

[0016]

EXAMPLE A first example of the nuclear fuel spacer according to the present invention will be described with reference to FIGS. In the figure, parts having the same functions as those in FIG. 8 are designated by the same reference numerals, and overlapping description will be omitted.

Further, since the present invention is to improve the conventional leaf-shaped projections 13 in the spacer band of the nuclear fuel spacer, the lattice plate 9 and the compartment space 1 described with reference to FIGS.
The same applies to 0, the fixed support portion 11, and the elastic support member 12, and the description thereof will be omitted to avoid duplication. Similarly, the description of the second to fifth embodiments described below will be omitted, and only the main part will be described.

As shown in FIGS. 1 and 2, the spacer band 14 of the first embodiment has a low expansion leaf-shaped projection 15 on two adjacent surfaces and a high expansion leaf-shaped projection 16 on the other two adjacent surfaces. It is provided. The highly expanded leaf-shaped protrusions 16 are attached to the spacer band 14 so as to penetrate and hold the spacer band 14 as partially shown in FIG.

The low expansion leaflets 15 are made of Zircaloy,
The high expansion leaflets 16 are made of Inconel. The spacer band 14 and the channel box 6 are made of Zircaloy. The fuel rod 2 side of the high expansion leaf-shaped projection 16 is bent at a plurality of points so as to absorb the elongation of Inconel, while the channel box 6 side is bent as shown in FIGS. 1 (b) and 2 (b). It rises toward the channel box 6 side due to the difference in thermal expansion between the two.

FIG. 2 (c) illustrates the elevation height of the Inconel material due to the difference in thermal expansion between Zircaloy and Inconel. Both ends of Inconel and Zircaloy having a length of 40 mm were joined at room temperature to the reactor operating temperature. In this case, the coolant temperature t of the fuel assembly during operation of the reactor is 287 ° C, Zircaloy linear expansion coefficient α _Z = 5.7 × 10 ^-6 1 / K, Inconel X-ray expansion coefficient α _I = 12.6 × 10 ^-6 1 / K, thermal expansion difference Δl = 40 x (12.6-5.7) x 10 ^-6 x (287 ° C-
20 ° C) = 0.074 mm, θ = cos ⁻¹ (l / (l + Δl)) = 3.48 ° h = ((l + Δl) / 2) × sin θ≈1.2 mm

As is clear from the above formula, in the case of Inconel and Zircaloy having a length of 40 mm, a height of about 1.2 mm can be obtained. This value is larger than the conventional gap between the channel box and the spacer, and is sufficiently effective as the height of the protrusion of the lobule.

As described above, according to the first embodiment, the leaf-shaped projections 16 made of Inconel band expand due to the temperature rise and deform according to the difference in thermal expansion with the spacer band 14 made of Zircaloy. Since the side is bent so as to absorb thermal expansion, the height of the protrusion hardly changes.

As a result, the gap between the nuclear fuel spacer and the channel box 6 is filled, and the nuclear fuel spacer is pressed against the low expansion leaf-shaped projection 15 side. Therefore, it is possible to maintain a predetermined gap between the channel box and the fuel rod,
The flow passage area can be secured.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 shows that the zircaloy strip-shaped lobes 18 are joined at both ends to the spacer band 17 of the second embodiment.
A doglegged Inconel member 19 is provided in the inside 18.
It is characterized in that it rises toward the channel box 6 side due to the difference in thermal expansion between Inconel and Zircaloy.

A schematic drawing of this spacer band 17 is shown in FIG.
FIG. 3B shows a partial vertical cross section in FIG. Since it is difficult to join Inconel and Zircaloy, a spacer band
By providing a V-shaped Inconel member 19 in the zircaloy strip-shaped lobe 18 having both ends joined to 17, the zircaloy joint S is deformed in the direction of arrow P in FIG. 3 (c) when the temperature rises. Then, it rises to the side of the channel box 6.
Since the zircaloy strip-shaped lobe projections 18 are processed so as to be easily deformed, the zircaloy strip-shaped lobe projections 18 also rise together with the protrusion of the Inconel member 19.

As a result, the gap between the nuclear fuel spacer and the channel box 6 is filled, and the nuclear fuel spacer is pressed against the zircaloy strip-shaped lobe 18 side. Therefore, the gap between the predetermined channel box 6 and the fuel rod 2 can be maintained, and the flow passage area can be secured.

Next, a third embodiment of the present invention will be described with reference to FIG. In FIG. 4, the spacer band of the third embodiment
A zircaloy diaphragm-shaped leaf-shaped protrusion 21 is joined to the outer periphery of the spacer band 20. A gimbal-shaped Inconel member (not shown) is provided in the leaf-shaped projection 21.

The third embodiment is characterized in that, like the second embodiment, the diaphragm-shaped leaf projections 21 made of zircaloy made of zircaloy bulge toward the channel box 6 due to the difference in thermal expansion between Inconel and zircaloy.

According to the third embodiment, the cross-sectional shape, structure, action and effect are the same as those of the second embodiment, but the structure is such that the Inconel has a circular shape and the rising force is further strengthened.
When the temperature rises, it rises toward the channel box with the Zircaloy joint as the fulcrum. Since the Zircaloy strip is processed so that it can be easily deformed, the Zircaloy strip also rises along with the Inconel protrusion.

As a result, the gap between the spacer and the channel box is filled, and the spacer is more strongly pressed against the fixed gap spacer side. The flow path area can be secured by maintaining a predetermined gap between the channel box and the fuel rod.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In FIG. 5, the spacer band of the fourth embodiment
A spiral-shaped deforming portion 23 is plastically processed on 22 and a zircaloy diaphragm type leaf-shaped projection 24 is attached so as to cover the surface of the spiral-shaped deforming portion 23. An Inconel disk 26 having a spiral cut 25 is inserted between the spiral deforming portion 23 and the leaf-like projection 24.

A detent 27 is stamped on the spacer band 22 to prevent the disc 26 from rotating. The leaf-like protrusions 24 are configured to bulge as shown in FIG. 5C due to thermal expansion of the spiral portion of the disk 26.

According to the fourth embodiment, as shown in FIGS. 5 (b) and 5 (c), when the temperature rises, thermal expansion occurs in accordance with the length of the Inconel spiral portion, and the spiral provided on the spacer band 22 is increased. Thermal expansion accumulates in the central portion along the shape-deformation portion 23 and presses the diaphragm-like leaf-shaped projection 24.

As a result, the gap between the spacer and the channel box 6 is filled, the spacer is more strongly pressed against the low expansion leaf-shaped projections 15 side, and the predetermined gap between the channel box 6 and the fuel rod 2 can be maintained. The road area can be secured.

Next, a fifth embodiment of the present invention will be described with reference to FIG. In FIG. 6, the spacer band of the fifth embodiment
Two rectangular leaf-shaped projections 29 made of Inconel strips are mounted in parallel on the two adjacent sides of 28. An outward protruding portion 30 is formed at the center of the leaf-shaped projection 29. FIG. 6A is a perspective view, FIG. 6B is a top view of FIG. 6A showing a state at a low temperature, and FIG. 6C shows a state from the state of FIG.

According to the fifth embodiment, since the Inconel strip is attached along the frame of the spacer band 28, the expansion length of Inconel can be made long, so that the amount of protrusion can be made large.
In order to prevent the Inconel leaf-shaped projections 29 from biting into the channel box 6 when the channel box is inserted, a dogleg 30 is formed in the cross section.

[0037]

EFFECTS OF THE INVENTION According to the present invention, the channel box and the outermost circumference can be applied to the fuel having a peak power distribution of the outer circumference in which high-power fuel rods are arranged around the channel box as the burnup of the reactor fuel increases. Since the fuel gap, that is, the coolant flow passage area is kept constant, it is possible to avoid a situation in which the limit fuel output unexpectedly decreases, and to secure stable cooling performance of the fuel rods.

[Brief description of drawings]

FIG. 1A is a perspective view showing a spacer band portion in a first embodiment of a nuclear fuel spacer according to the present invention,
(B) is a cross-sectional view showing a state at low temperature in (a),
Similarly, (c) is a cross-sectional view showing a high temperature.

2 (a) is an elevation view at a low temperature in FIG. 1 (b),
1B is an elevation view at a high temperature in FIG. 1C, and FIG. 1C is a schematic view showing the height of the Inconel material raised by the difference in thermal expansion between Zircaloy and Inconel used in FIG. 1A.

3 (a) is a perspective view showing a spacer band portion in the second embodiment of the present invention, FIG. 3 (b) is a longitudinal sectional view showing a state at low temperature in FIG. 3 (a), and FIG. 3 (c) is also at high temperature. FIG.

FIG. 4 is a perspective view showing a spacer band portion according to a third embodiment of the present invention.

5A is a front view showing a main part of a spacer band portion in a fourth embodiment of the present invention, FIG. 5B is a longitudinal sectional view showing a state at low temperature, and FIG. FIG.

FIG. 6A is a perspective view showing a spacer band portion in a fifth embodiment of the present invention, FIG. 6B is a top view showing a state at low temperature in FIG. 6A, and FIG. The top view shown.

FIG. 7 is an elevation view showing a fuel assembly with a part thereof cut away.

8 (a) is a top view showing a conventional nuclear fuel spacer in FIG. 7, and FIG. 8 (b) is a side view showing a partial cutaway in FIG. 8 (a).

[Explanation of symbols]

1 ... Fuel assembly, 2 ... Fuel rod, 3 ... Upper tie plate,
4 ... Lower tie plate, 5 ... Nuclear fuel spacer, 6 ... Channel box, 7 ... Water rod, 8 ... Spacer band (conventional example), 9 ... Lattice plate, 10 ... Compartment space, 11 ... Fixed support part, 12 ... Elastic support Member, 13 ... Leaf-like projection, 14 ... Spacer band of the first embodiment, 15 ... Low expansion leaf-like projection, 16 ... High expansion leaf-like projection, 17 ... Spacer band of the second embodiment, 18
… Zircaloy strip-shaped lobes, 19… Inconel member, 20
... Spacer band of the third embodiment, 21 ... Diaphragm-shaped lobe protrusions, 22 ... Spacer band of the fourth embodiment, 23 ... Spiral deforming portion, 24 ... Leaf-like protrusions, 25 ... Spiral notches, 26 ...
Disk, 27 ... Rotation stop, 28 ... Spacer band of the fifth embodiment, 29 ... Rectangular leaf-shaped projection, 30 ... Projection portion.

Claims (1)

[Claims] 1. A square spacer band is formed by combining a plurality of grid plates in a grid shape to form a square partition space having a small area, a fixed support portion is provided on the grid plate, and elasticity is provided at a combination intersection of the grid plates. In a nuclear fuel spacer in which a supporting member is provided, a plurality of leaf-shaped projections extending outwardly on the spacer band, and fuel rods are inserted into the compartment space, the leaf-shaped projections provided on the spacer band are adjacent to the spacer band. A nuclear fuel spacer characterized in that the leaf-shaped projections provided on the surface are made of a material having a higher coefficient of thermal expansion than the leaf-shaped projections on the other two adjacent surfaces and are formed with a lower height.