JPS5979178A - 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 [Field of Application of the Invention] The present invention relates to a nuclear reactor in a nuclear power plant, and more particularly to the loading of fuel assemblies constituting the core of a nuclear reactor.

[Prior art]

Nuclear reactors are operated by controlling the excess reactivity of nuclear fuel, which is fissile material, in the reactor core by pulling out and pulling out the control frame, and at the end of each cycle, the control rods are completely pulled out. The burnup is maximized.

Then, when the reactor's excess reactivity is gone, the fuel is replaced, and the old, burnt-out fuel is removed from the reactor core.
In addition to loading new fuel, efforts have been made to replace the fuel position within the reactor core.

In conventional nuclear reactors, fuel exchange is carried out by removing fuel that has a high burnup and progressed combustion from the core, and then loading new fuel 1 in a uniformly distributed manner, as shown in the example shown in Figure 1. .

In conventional nuclear reactors, it has been considered to place low-reactivity fuel in the periphery of the reactor core, where output is low, in order to reduce the leakage of neutrons from the reactor core and to utilize the fuel more effectively.

Figure 2 is an example of this, where combustion progresses as a low-reactivity fuel,
The case is shown in which a fuel with a reduced infinite multiplication factor is used. In the figure,
2 is the 2nd cycle fuel, N is the N-1st cycle fuel, P
indicates peripheral area fuel. In this case, the reactor core is divided into an inner region A and a peripheral region B, and the peripheral region occupies JO ~ 20% of the volume of the entire core region, and the reactor core is kept in the inner region for N-1 cycles. In the next cycle, '1'', that is, the N-th cycle, fuel exchange is performed so that the fuel assembly, in which combustion has already progressed and the reactivity has decreased, is placed in the peripheral area where the output is low.

When such a fuel exchange is used, the period of stay of the fuel in the reactor is increased compared to when the fuel assembly with low reactivity is removed without being placed in the surrounding area. In addition, the fuel extraction burnup is increased and fuel can be used more effectively. However, because low-reactivity fuel was used, the excess reactivity of the entire core was reduced, and the operating cycle period was shortened.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a nuclear reactor in which the length of the operation cycle is increased, the fuel extraction burnup is increased, and fuel is effectively utilized.

[Summary of the invention]

In order to achieve this object, the present invention makes use of increasing the infinite multiplication factor of the fuel in the peripheral region when disposing the highly combusted fuel in the peripheral region of the reactor core.

Figure 3 shows the relationship between the infinite multiplication factor of fissile material and the burnup, and Figure 4 shows the relationship between the degree of enrichment of the fissile material. From Figures 3 and 4, infinite multiplication factor Kcy
It is understood that 3 decreases as combustion progresses and increases as enrichment increases.

For this reason, the fuel placed in the peripheral area of the reactor core is
Of the fuel taken out from the inner region of the core, the use of fuel that is relatively young in combustion or fuel with a high degree of enrichment has a higher infinite multiplication factor, making it possible to lengthen the operating cycle.

[Embodiments of the invention]

The present invention will be explained below based on examples.

Conventionally, the average enrichment of fuel assemblies in an equilibrium core has been one type, but in the present invention, this is set to two or more types for heavy equipment. FIG. 5 shows a fuel-loaded bagun as an example in which the replacement fuel is two types of fuel. In the figure, 1 and 2.3 indicate new fuel with low a sardine content, 2nd cycle fuel, and 3rd cycle fuel, and 11°12.13 indicates new fuel with high enrichment, 2nd cycle fuel phase, 3rd cycle fuel. Show me the fuel. In this example, m-
This is an example in which the fuel duty period for the 14-year Inner Head Castle is set to 3 cycles.

Replacement fuel trace density is 1, fuel assembly average enrichment is el.

It is different from C2 (C7>C2). Approximately half of the removed fuel is taken out of the reactor by leaving 3 cycles r()i in the core inner region, and the remaining half is loaded into the 110 peripheral region; The fuel is composed of highly enriched fuel, which increases the reactivity of the reactor core compared to the case of a single enrichment, making it possible to extend the operating cycle period.

In the above example, a case was explained in which there are two types of replacement fuel, but there may be two or more enrichment types υ and two or more glaze types.

In addition, when there are multiple enrichments, the fuel to be loaded around the core may be selected from those with a high content of fissile material or commercial fuels with an infinite multiplication factor.

[Effects of the Invention] As described above, in the nuclear reactor according to the present invention, the replacement fuel loaded in the inner region has a plurality of enrichments,
Among the fuel taken out from this inner region, by loading fuel NS+ with a high degree of uranium scar reduction or fuel with a high content of fissile material into the region around the core, the same amount of fission bending material f1 can be used as compared to the conventional method. Since it is possible to increase the operating period and the extraction combustion layer, it is possible to effectively utilize fissile materials such as uranium.

[Brief explanation of the drawing]

Figure 1 is a 1/4 cross-sectional view of the reactor, and Figure 2 is a 1/4 cross-sectional view of the reactor.
Figure 4 is a cross-sectional view, Figure 3 is a correlation diagram between burnup and infinite multiplication factor, Figure 4 is a correlation diagram between enrichment level and infinite multiplication factor, 'A''y Figure 5 is a quarter cross-sectional view of the reactor. 1 (11)...Low enrichment (high enrichment) new fuel, 2 (1
2)...Low enrichment (high enrichment) 2nd cycle fuel, 3
(13)...Low enrichment (high enrichment) third cycle fuel, P...peripheral area fuel. $1 Eyebrush 20 〒1U' Bamboo 3 Figure twist'i Immersed Bamboo 4z Concentration degree

Claims (1)

[Scope of Claims] (1) The furnace nozzle is divided into an inner region and a peripheral region, Nth and rth fuels are arranged in the peripheral region, and rq-i fuels are arranged in the inner region. In the small sub-reactor in which the following fuels are arranged: A nuclear reactor characterized in that it is composed of fuel assemblies with a high uranium enrichment, although there was an inner region in the mJ ff self-circle in the previous cycle. 2. The reactor core is divided into an inner region and a peripheral region, and the peripheral region Distribute the fuel of the cycle to fRL, and V to the inner area.
In a nuclear reactor in which fuel is arranged for ~-■ cycles or less, the inner region of the front 8C in each S and F cycle has a different content of fissile material on average for the fuel assembly.2 BL
A nuclear reactor comprising fuel assemblies of the same type or higher, and wherein the peripheral region is comprised of fuel assemblies with a high content of fissile material among those in the inner region in a previous cycle.