JPS61231482A - Core for fast breeder reactor - 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 <Industrial Application Field> The present invention relates to the core of a nuclear reactor for the purpose of fuel breeding (high conversion), such as a liquid-cooled fast breeder reactor or a gas-cooled fast breeder reactor.

<Prior Art> FIGS. 7 to 10 are longitudinal sectional views of a conventional axially non-homogeneous reactor core. As shown in these figures, in the conventional axially non-homogeneous core, a disk-like or top-shaped (Fig. 10) shape is formed in the core region 1 surrounded by the radial blanket region 3 and the axial blanket region 4. The inner blanket region 2 is configured as one continuous region.

FIGS. 11 and 12 show vertical cross-sectional views of a conventional radially non-homogeneous core repaired. As shown in these figures, in a conventional radially non-homogeneous core, an open or closed annular structure or a discrete structure is formed inside the radial blanket region 3, passing through the core region 1 and the axial blanket region 4. An internal blanket area 2 is located in the area. FIG. 13 shows the structure of the assembly constituting the reactor core, with reference numeral 6 indicating a fuel assembly wrapper tube and 7 indicating a fuel pin element, and FIG. 14(a) showing its cross section. In the conventional axially non-homogeneous reactor, as shown in FIG. 14(a), the internal blanket pellets 11 are arranged in the core region height 13, so that the axial distribution of power through the internal blanket region 2 is It has the characteristic of being flattened. 8 is a fuel bottle cladding tube, 9 is a core fuel pellet, 10 is a shaft blanket pellet, 12 is a pellet pressing spring, and 14 is a shaft blanket area height.

In the conventional axially non-homogeneous core mentioned above, the disc-shaped internal blanket occupies a wide area near the core center plane.
In the event of an accident where the core fuel of the reactor melts for some reason,
Extensive internal blanket and core fuel above it may fall onto the core plane. In this case, core fuel with a large positive reactivity is substituted for the internal blanket region with a negative reactivity, which may further aggravate the accident.

Furthermore, when sodium voids (bubbles in sodium) occur, the sodium voids propagate in the axial direction because the axial direction of the aggregate is the same sodium flow path in the axially non-homogeneous core.

At the same radial position in the core fuel section where sodium voids occur, as shown in Figures 7 to 10, the core region (fuel region) 1 is widened, so sodium voids can easily propagate in the radial direction. There is a simple drawback.

On the other hand, in the conventional radially non-homogeneous core, Figs.
As shown in the figure, internal blanket regions 2 are disposed at strategic points in the radial direction, penetrating the reactor core. . For this reason,
If a sodium void occurs in the core region 1, it will be trapped in the internal blanket region 2, which has low output, and there is little possibility that the void will propagate in the radial direction. Also, when viewed in the axial direction,
As shown in FIG. 14(b), since there are no core fuel pellets 9 in the internal blanket assembly (same structure as in FIG. 13) and only internal blanket pellets 11, fuel melting occurs near the core center plane. In the event of an accident, the axially non-homogeneous core does not add as much reactivity to the reactor.

However, since the internal plunget assembly does not have core fuel which is a heat source (FIG. 14(b))', the radial power distribution in the reactor becomes low in the internal blanket region 2. □ ・As shown in Figure 6,
Compared to the core fuel assembly output 18, the output of the internal blanket assembly 19 of the conventional core is significantly lower at the beginning of the fuel cycle, causing a large difference in the outlet coolant temperature between the two at the assembly exit, and causing a thermal strain in the upper reactor mechanism.・There is a problem that causes iping (heat unevenness). 25 is the diameter blanket output.

<Problems to be Solved by the Invention> The present invention has been made in view of the above-mentioned circumstances, and is a new type of core that alleviates the drawbacks and takes advantage of the advantages of the axially non-homogeneous core and the radially non-homogeneous core. The purpose is to provide a core with an internal blanket arrangement of 1°.

Means for Solving the Problems> Therefore, in the present invention, the configuration is such that a core fuel assembly having a core fuel having a height equal to the height of the core region, an internal planket, and a an inner blanket assembly having a length shorter than the core region height, or an inner blanket assembly having a length shorter than the core region height and an inner blanket assembly having an inner blanket equal to the core region height; It is characterized in that the blankets are distributed or arranged in an annular shape in the radial direction of the core so as not to form continuous disc-shaped or segment-shaped regions.

Effects> With the above-described configuration, the core of the present invention prevents a core fuel melting accident from spreading over a wide range, and alleviates the radial distribution of sodium void reactivity and thermal striping.

<Example> Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

FIG. 1(a) is a local cross-sectional view of a core showing one embodiment of the present invention, FIG. 1(b) is a schematic cross-sectional view along A-Afa thereof, and FIG. 2(a) is a core showing another embodiment of the present invention. FIG. 3(b) is a schematic cross-sectional view of B-B#, FIG. 3(a) is a cross-sectional view of a reactor core showing still another embodiment of the present invention, and FIG.
FIG. 4 is a schematic cross-sectional view taken along line C, FIG. 4 is a schematic diagram of an assembly constituting the core of the present invention, FIGS. FIG. 2 is a diagram conceptually showing the power distribution for each assembly in the radial direction of the core for the core of the present invention and a conventional radially non-homogeneous core.

The internal blanket assembly 22 of the heterogeneous core of the present invention includes:
As shown in Figure 5(C), the internal planke, topelette 1
1 are stacked in the core region height 13, Fig. 5(a)
As shown in FIG.
), internal blanket pellets 11 are stacked alternately with core fuel pellets 9 in a plurality of stages spaced apart in the axial direction within the height of the core region to form fuel pin elements 7. An inner blanket assembly 22 is constructed from fuel pin elements 7 made up of stacks of the same fuel pellets 9 and inner blankets 11.

Note that the shaft blanket pellets 10 in the shaft blanket region 4' in the internal blanket assembly 22 may be pellets that have the same composition, structure, dimensions, etc. as the internal blanket pellets 11, or may be pellets that are different from the internal blanket pellets 11. The shaft blanket pellets in the inner shaft blanket area 4 may be the same or different. Further, the core fuel pellets 9 may be the same or different in composition, structure, size, etc. from the pellets in the core fuel assembly 21 having no internal blanket within the assembly.

The heterogeneous reactor core of the present invention has a structure in which the internal blanket assembly 22 in which the plungers, top pellets, and fuel pellets are arranged as described above is distributed in the reactor in the radial direction or arranged in an annular shape. Examples are shown in FIGS. 1 to 3. Here, 23 is a control rod assembly, and 24 is a diameter blanket assembly. As shown in the embodiments, in the core of the present invention, the position, arrangement, thickness, etc. of the internal blanket region 2 within the assembly may differ depending on the loading position in the core, but the core height is maintained at all loading positions. The inner plunket area 2 is arranged so that the entire length thereof is not occupied by the inner plunket area 2.

The position, thickness, etc. of the internal blanket region 2 in each assembly are optimally set for each assembly based on the axial/radial power distribution of the core, the breeding rate, etc.

<Effects of the Invention> As described in detail above, the present invention provides the following effects.

■ As shown in Figure 6, in the inner blanket aggregate,
Compared to the internal blanket assembly output 19 of a radially non-homogeneous core in which no core fuel is loaded, the internal blanket assembly output 20 of the reactor core of the present invention can reduce the difference between the core fuel assembly output 18 and the upper part of the reactor. Thermal striations of the mechanism can be alleviated.

■ Unlike an axially non-homogeneous core in which the internal blanket area spreads out in a radial disk shape including the core, distributing the internal blanket area in the radial direction prevents a continuous internal area, which can be a problem in the event of a core fuel melting accident. The blanket region can be divided into small sections, and the insertion reactivity can be reduced compared to conventional axially non-homogeneous cores.

■ Similar to the radially non-homogeneous core, by distributing the internal blanket regions with low heat generation density in the radial direction, the radial distribution of sodium void reactivity can be relaxed compared to the axially non-homogeneous core.

[Brief explanation of drawings]

1 to 3 are cross-sectional views of a core showing an embodiment of the present invention, No. 4rIA is a schematic diagram of an assembly constituting the core, and FIG. 5 is a longitudinal cross-sectional view showing the configuration of a fuel pin element of the present invention. Fig. 6 is a diagram conceptually showing the power distribution for each assembly in the radial direction of the core for the core of the present invention and a conventional radially non-homogeneous core, and Figs. 7 to 10 are diagrams for the conventional axially non-homogeneous core. 11 and 12 are dedicated vertical sectional views of a conventional radially non-homogeneous core, and FIG. 13 is a schematic diagram of the assembly that constitutes the core.
FIG. 4 is a longitudinal sectional view showing the configuration of a conventional fuel pin element. 1... Core region, 2... Internal blanket region, 3
... Diameter blanket area, 4... Shaft blanket area (core fuel assembly), 4'-... Shaft blanket (internal blanket assembly), 5... Central axis, 6... Assembly wrapper, 7... Fuel pin element, 8 - Fuel bottle cladding tube, 9... Core fuel pellet, 10... Shaft blanket pellet, 11... Internal blanket pellet,
12...Bellet pressing spring, 13...Core region height, 14...Shaft blanket region height, 21...Core fuel assembly, 22...Inner blanket assembly, 23
... Control rod assembly, 24 diameter blanket assembly Patent applicant Mitsubishi Atomic Crab Industry Co., Ltd. Agent Patent attorney Hideaki Sato 300? la rough 0 figures 74 figures f13 ships. 73. circle.

Claims (2)

[Claims] (1) A core fuel assembly having a core fuel equal to the core region height in the core region, and an inner blanket assembly having an internal blanket having a length shorter than the core region height or shorter than the core region height. an inner blanket assembly having a length and an inner blanket assembly having an inner blanket equal to the core region height;
A core of a fast breeder reactor characterized in that internal blankets are distributed in the radial direction of the core or arranged in an annular shape so as not to form continuous disc-shaped or segment-shaped regions. (2) Claim (1) characterized in that the internal blanket assembly having a length shorter than the height of the core region is characterized in that the internal blankets are arranged in a single layer or in multiple stages in the axial direction. The core of the fast breeder reactor described.