JPS6130794A - 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 [Technical Field of the Invention] The present invention relates to a fast breeder reactor, and particularly to the structure of its core.

"Technical Background of the Invention" Generally, the core of a fast breeder reactor has a cylindrical shape or a shape close to the cylindrical shape, and is often surrounded by a blanket. Here, the fuel loaded into the reactor core is enriched uranium or uranium enriched with plutonium, and the blanket is a parent material that absorbs neutrons leaking from the reactor core and is converted into useful fissile material. Loaded with uranium or depleted uranium.

Figure 2 shows a conventional axially non-homogeneous core. In this axially non-homogeneous core, a radial blanket portion 1 is formed at the outermost periphery, and the inner upper and lower portions of this radial blanket portion 1 are are formed with an upper shaft blanket portion 2 and a lower shaft blanket portion 3, respectively.

An outer core fuel section 4 is formed in contact with the inside of the diameter blanket section 1 and between the upper shaft blanket section 2 and the lower shaft blanket section 3. An inner core fuel section 5, an inner shaft blanket section 6, and an inner core fuel section 7 are formed between the lower shaft blanket section 2 and the lower shaft blanket section 3 in this order from the top.

[Problems with the Background Art] However, in such a conventional axially non-homogeneous core, due to the influence of the internal shaft blanket section 6 disposed near the center of the core, there is a Inner core fuel section 5 and inner shaft blanket section 6 provided
Since the neutron coupling with the inner core fuel section 7 disposed at the bottom of In a conventional axially non-homogeneous core in which the C-0 plane is not bent and is at a single level, the internal shaft blanket section 6
The output is excessively reduced in the part of the inner core fuel part 5 near the inserted control rod 8, which is disposed above the inserted control rod 8. In the inner core fuel section 7 disposed in the lower part, the degree of decrease in output is small, but there are parts where output increases greatly, and there is a problem that mismatching of output peaks often occurs.

That is, in such a case, flattening of the power within the core is lost, and it is necessary to increase the core volume more than necessary in order to obtain the same thermal output, which is economically disadvantageous.

Figure 3 shows the relationship between the axial height and power density of the inner core fuel assembly adjacent to the control rod 8 when the control rod 8 is inserted to the axial center of the inner core in Figure 2 (the plotted points are (On the line connecting ABB'A' in Figure 2) and the relationship between the axial height and power density in the inner core fuel assembly separated by one or more inner core fuel assemblies from the control rods 8 (The plot points are on the line connecting ABB'A' in Figure 2) on the line connecting D'.

The following points become clear from the figure.

The output at the inner core position DEE'D', which is separated by two fuel assemblies from the inserted control rod 8, has approximately the same peak value at the upper and lower parts of the inner core.

On the other hand, the inner core fuel assembly adjacent to the inserted control rod 8 is strongly influenced by the inserted control rod 8, and the peak output value at the upper core (AB) is significantly higher than the peak output value at the lower core (B'A').It's below.

[Object of the invention] The present invention has been made in response to such conventional circumstances,
The present invention aims to provide a fast breeder reactor that can sufficiently flatten the output within the inner core when control rods are inserted into the inner core.

[Summary of the Invention] That is, the present invention has a cylindrical reactor core loaded with enriched uranium or plutonium-enriched uranium as fuel, and has natural uranium or depleted uranium as the main material near the axial center of the core. In a fast breeder reactor with an internal shaft blanket, the axial center plane of the internal shaft blanket region included in the core fuel assembly adjacent to the operating control rod is the same as that of the internal shaft blanket region included in other core fuel assemblies. This is a fast breeder reactor characterized by being disposed below the central plane in the axial direction.

[Embodiment of the Invention] The details of the present invention will be described below with reference to an embodiment shown in the drawings.

As an example of the present invention, as shown in FIG. 1, the thermal output is 2500 MW, the core radius is approximately 3. '3m, core height approximately 1m
We consider a demonstration-class axially non-homogeneous reactor core. In this axially non-homogeneous core, a diameter blanket part 1 is formed at the outermost periphery, and an upper shaft blanket part 2 and a lower shaft blanket part 3 are formed at the upper and lower parts of the inside of this diameter blanket part 1, respectively. There is.

An outer core fuel section 4 is formed in contact with the inside of the diameter blanket section 1 and between the upper shaft blanket section 2 and the lower shaft blanket section 3. 2 and the lower shaft blanket part 3, an inner core fuel part 5, an inner shaft blanket part 6 (thickness 20-Lm in this embodiment) and an inner core fuel part 7 are formed in order from the top.

Therefore, the position of the axial center plane (C'-〇' plane) of the inner shaft blanket section 6 disposed in the inner core is lower than the position of the axial center plane of the inner core <C-0 plane). It is arranged at a lower position, and its lowering is greater in the core fuel assemblies adjacent to the control rods 8 (marked 5 in this example), and smaller in the core fuel assemblies not adjacent to the control rods 8. (2.5 cm in this example).

In the fast breeder reactor configured as described above, the volume of the inner core fuel part 5 above the inner shaft blanket part 6 into which the control rods 8 are mainly inserted during operation is arranged in the lower part of the inner shaft blanket part 6. The volume of the inner core fuel section 7 is larger than that of the inner core fuel section 7. Therefore, if the influence of the control rods 8 is ignored, the power density of the inner core fuel part 5 in the upper part of the inner shaft blanket part 6, which has a large volume, is equal to the power density of the inner core fuel part 7 in the lower part of the inner shaft blanket part 6. generally higher than

During actual operation, the control rods 8 are inserted from above the core, so the power density of the inner core fuel section 5 in the upper part of the inner shaft blanket part 6 is the same as the output of the inner core fuel part 7 in the lower part of the inner shaft blanket part 6. The way the inner blanket is lowered is set to be approximately equal to the density. That is,
Since the inner shaft blanket 9 is disposed further down in the core fuel assembly where the influence of the control rods 8 is strong, the radial power distribution in the inner core fuel sections 5 and 7 can be made substantially flat.

Figure @4 shows the relationship between the power density and the axial height when the control rods 8 are inserted to the axial center plane of the inner core < C-C plane in Figure 1, and as is clear from the figure. To,
The power density of the inner core fuel part 5 at the upper part of the inner shaft blanket part 6 and the power density of the inner core fuel part 7 at the lower part of the inner shaft blanket part 6 almost match.

In addition, in FIG. 4, A, B, B'A' and ri,
E, E', and D' correspond to the positions of the same symbols shown in FIG.

And the output peaking coefficient (ratio of maximum output density to average density) ′c, which is a parameter that determines the flattening of the output distribution.
1 A comparison of these effects is as follows.

That is, in a system where the axial center plane of the internal blanket 6 is equal to the center plane of the reactor core, the power peaking coefficient is 1.83.
, and the axial center plane of the inner blanket 6 is uniformly 5
1.70 cm in the system lowered by 1.70 cm, and further lowered by 2.5 cm in the 'U 5 mark in the core fuel assembly adjacent to control rod 8 and 2.5 cm in the core fuel assembly further away as described above (Figure 1). In this case, the output peaking coefficient is 1°65. Therefore, in the fast breeder reactor of this example, the output peaking coefficient can be improved by about 11% compared to when the internal shaft blanket is not lowered at all, and about 3% compared to when the internal blanket is lowered uniformly. We were able to.

E Effects of the Invention As described above, according to the fast breeder reactor of the present invention, it is possible to suppress the output peak of the inner core fuel section disposed below the inner shaft blanket section, and achieve output flattening. can do. As a result, the power peaking coefficient of the inner core becomes smaller, the same thermal output can be obtained with a smaller fast breeder reactor, and a highly economical fast breeder reactor can be provided.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the fast breeder reactor of the present invention, FIG. 2 is a longitudinal sectional view showing a conventional axially non-homogeneous reactor core,
FIG. 3 is a graph showing the axial power density distribution of the core shown in FIG. 2, and FIG. 4 is a graph showing the axial power density distribution of the core shown in FIG. 1......Diameter blanket part 2...
......Top shaft blanket part 3...
・・・・・・Lower shaft blanket part 4・・・・・・
...Outer core fuel section 5.7...Inner core fuel section 6...Inner shaft blanket section Patent attorney Sasu Suyama - Figure 1 Figure 2 Figure 3 Figure 4 Output writing level

Claims (1)

[Claims] (1) High speed with a cylindrical reactor core loaded with enriched uranium or plutonium-enriched uranium as fuel, and an internal shaft blanket made mainly of natural uranium or depleted uranium near the axial center of the core. In a breeder reactor, the axial center plane of the internal shaft blanket area included in the core fuel assembly adjacent to the operating control rod is lower than the axial center plane of the internal shaft blanket area included in other core fuel assemblies. A fast breeder reactor characterized by the following: