JPS62165181A - Grid spacer for nuclear fuel aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention 1] The present invention relates to a grid spacer for a nuclear fuel assembly, and particularly to a grid spacer for a nuclear fuel assembly used in a light water reactor.

[Technical background of the invention and its problems] For example, nuclear fuel assemblies currently used in light water reactors and nuclear fuel assemblies whose use is being considered house a large number of fuel bins in a channel box and connect these fuel pins. The structure is held in place by grid spacers.

As shown in FIG. 6, this grid spacer 1 constitutes a honeycomb-shaped spacer element assembly by assembling a large number of hollow hexagonal columnar spacer elements 1A that accommodate fuel pins 2. is reinforced with a hollow hexagonal columnar spacer frame 1B made of a thin plate. And this spacer frame 1B is the channel box 3
fixed to the inner wall of the

In the grid spacer of the conventional nuclear fuel assembly as described above, in order to maintain the supporting interval of the fuel pins 2, three convex portions IC are provided inside the spacer element 1A, as shown in FIG.
is provided to support the outer periphery of the fuel pin.

By the way, in light water reactors, the heat flux on the surface of the fuel rods is large, and a transition from nucleate boiling to film boiling tends to occur on the surface of the fuel rods, especially in narrow areas of the coolant flow path such as the spacer section. big. This boiling point! If a transition occurs, the fuel temperature will rise rapidly and fuel failure may occur.

[Object of the Invention] The present invention has been made to solve the conventional problems as described above, and its purpose is to widen the coolant flow path when the fuel temperature is high to reduce pressure loss, Another object of the present invention is to provide a grid spacer for a nuclear fuel assembly that reliably maintains the spacing between fuel pins and prevents the fuel pins from vibrating during low temperatures during normal operation.

[Summary of the Invention] In order to achieve the above object, the present invention presses a fuel pin against at least a part of the spacer elements of a grid spacer constituting a nuclear fuel assembly when the temperature is low during operation, that is, during normal operation, and when the temperature is high, that is, during boiling. It is characterized by the provision of a memory alloy that assumes a shape that widens the coolant flow path and reduces pressure loss when a transition occurs.

[Embodiments of the Invention] Examples of the present invention will be described in detail below with reference to the accompanying drawings.

Generally, in a nuclear reactor, a nuclear fuel assembly is supported by being inserted into a support member as shown in Fig. M2.

The nuclear fuel assembly 4 includes a channel box 3, tie plates 5.6 provided above and below the channel box 3, an entrance nozzle 7, and a grid spacer 1.
The fuel pin 2 is housed in the channel box 3 via the fuel pin 2. A plurality of grid spacers 1 are fixed to the inner wall of the channel box 3 at appropriate intervals in the longitudinal direction of the nuclear fuel assembly 4.

Further, this nuclear fuel assembly is supported by a core support plate 10.

FIGS. 1(a) and 1(b) show a first embodiment of the grid spacer according to the present invention, in which the spacer element 2
0 is made of a memory alloy, and at low temperatures during normal operation, each side surface of the spacer element 20 alternately protrudes outward and inward as shown in FIG. 1(a).

On the other hand, at high temperatures, that is, when a boiling transition occurs near the spacer, the spacer element 2
The portions that were protruding from each side of the spacer element 20 become straight, and the spacer element 20 has a hollow hexagonal column shape, and is set so that a gap is created between it and the fuel pin 2. That is, the spacer element 20 assumes its memorized shape when it reaches a certain temperature.

Further, FIG. 3 shows a second embodiment of the present invention, in which a part of the spacer element 21 is a tongue-like piece 22 (
It is formed by a presser piece). The tongue-like pieces 22 are set so that when the temperature is low, each tongue-like piece 22 bulges inward as shown in FIGS. 3(a) and 3(b), and the fuel pin 2 is pressed and fixed from three sides. Also, at high temperatures, Fig. 3 (C), (
As shown in d), the tongue-shaped piece 22 is set to be flush with the side surface of the spacer element 21.

FIG. 4 shows a third embodiment of the invention, in which the spacer element 23
Unlike the second embodiment, the tongue-shaped piece 24 (holding piece) made of a memory alloy is provided in the vertical direction, and in this embodiment as well, as in the case of the above-mentioned case, at low temperatures, the a＞
, (b) and (C), each tongue-like piece 24 bulges inward and presses the fuel pin 2 to fix it. On the other hand, at high temperatures, the tongue-shaped piece 24 is set to be flush with the side surface of the spacer element 23, as shown in FIGS. 4(d) and 4(l).

FIG. 5 shows a fourth embodiment of the present invention, in which a convex piece 26 made of a memory alloy is connected at both ends to every other side surface of a spacer element 25 having a hollow hexagonal column shape.
(holding piece) is provided. Similarly to the above, when the reactor is operating at low temperatures, this convex piece 26 also protrudes inward, as shown in FIGS. 5(a) and 5(b), and presses and fixes the fuel pin 2 from three sides.

Furthermore, at high temperatures, as shown in FIGS. 5(C) and 5(d), the protrusions of each convex piece 26 recede and become flat, causing the fuel pin 2
A certain gap is formed between the two and the flow path area can be increased.

[Effects of the Invention] As is clear from the above description, the present invention forms a gap between at least a part of the spacer element of the grid spacer that holds the fuel pin when the temperature is high, and presses the fuel pin when the temperature is low. Since we have provided a memory alloy with a shape that allows the fuel pins to maintain a certain gap during low temperatures during operation, it prevents vibration of the fuel pins and prevents damage to the cladding tube caused by vibration (fuel pins may be removed from fittings, etc.). On the other hand, at high temperatures when the boiling 111i! transition occurs, it is possible to make the coolant flow more easily to eliminate the boiling llff1 transition and lower the fuel temperature, thus improving the safety of the reactor. It has the effect of encouraging

[Brief explanation of drawings]

FIG. 1(a) is a plan view of a grid spacer according to a first embodiment of the present invention at a low temperature, FIG. 1(b) is a plan view of the same embodiment at a high temperature, and FIG. 2 shows a nuclear fuel assembly and its 3(a) is a plan view of the second embodiment of the present invention at low temperature, FIG. 3(b) is a side view of the same, and FIG. 3(C) is a partial sectional view showing a part of the surrounding area. FIG. 3(d) is a plan view of the embodiment at high temperature; FIG. 4(a) is a plan view of the third embodiment of the present invention at low temperature; FIG. 4(b) is a side view of the embodiment at high temperature. is a side view at the same low temperature, Figure 4 (C
) is a cross-sectional view taken along line 8-8 in Fig. 4(b), and Fig. 4(
d) is a plan view of the same embodiment at high temperature, FIG. 4(e) is a side view at high temperature, and FIG. Figure 5(b) is a sectional view taken along line C-C in Figure 5(a), Figure 5(C) is a plan view of the same example at high temperature, and Figure 5(d) is Figure 5(C). FIG. 6<a) is a plan view of the conventional grid spacer, and FIG. 6(b) is the III! 1
FIG. 7(a) is a partially enlarged plan view of the grid spacer, and FIG. 7(b) is a sectional view taken along line A--A in FIG. 7(a). 1...Grid spacer 2...
...Fuel pin 3...Channel box 4...
......Nuclear fuel assembly 10...Core support 1A, 20, 21.23.25......Spacer element 22.24.26...・Representative for holding piece made of memory alloy Patent attorney Nori Chika Hirofumi Mitsumata 1st mouth ((3+ (C) (e) (cll (C) (j)) (
d). +6)

Claims (1)

[Claims] (1) In a grid spacer consisting of a plurality of spacer elements each gripping a plurality of fuel pins in a channel box, each spacer element presses the fuel pin at a temperature below the normal operating temperature of the reactor, and A grid spacer for a nuclear fuel assembly, characterized in that the grid spacer is at least partially composed of a memory alloy formed into a shape that sometimes widens the coolant flow path and reduces pressure loss.