JPS59222788A - Pressure tube type 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 reactor core loaded with a pressure pipe material monitoring member loading fuel channel. The present invention relates to a pressure tube nuclear reactor that can satisfy thermal conditions for fuel without reducing the ratio of integrated amount to pressure tube maximum fast neutron flux integrated amount.

[Background of the invention]

A conventional example is shown in FIG. In this example, two channels of special fuel for pressure pipe material monitoring are loaded at positions separated from each other in the entire reactor core.

For standard fuels other than special fuels, 2.
Among these, special fuels are located in the outer standard fuel region.

The irradiation acceleration coefficient of the pressure pipe monitoring member in special fuel is set to 1.0.
In order to achieve this, the enrichment of the special fuel needs to be higher than the enrichment of the standard fuel (plutonium enrichment), but as a result, the effect of the highly enriched special fuel is less than the standard fuel surrounding the special fuel. For each fuel, the channel output of the nearest standard fuel is increased as shown in FIG. As a result, the maximum linear power density of the nearest standard fuel increases, and the thermal margin becomes almost non-existent. In addition, even in such a situation, the irradiation acceleration coefficient is only slightly above the limit value of 1.0, and the irradiation acceleration coefficient of the pressure pipe monitoring member at the time of final removal at the end of the reactor life is within the limit value of 1.0. Achieving 1 is extremely difficult.

Now consider the following case.

(1) Special fuel loading at the low channel output position, (2
) Suppression of output peaking by control rods, (3) In the conventional example, the refueling interval for special fuel is shorter than the refueling interval for standard fuel; A method of compensating for the decrease in the irradiation acceleration coefficient by increasing the enrichment of the special fuel by increasing the enrichment of the special fuel by increasing the enrichment of the special fuel. Methods (1) and (2), in which the body is replaced by taking into account its thermal integrity and irradiation acceleration coefficient, improve thermal performance, but the irradiation acceleration coefficient decreases. Regarding (3), the maximum linear power density becomes severe at the early stage of the cycle, and if the enrichment of the special fuel is further increased, the maximum linear power density will exceed the limit value. Regarding (4), this will lead to an increase in costs.

As shown above, the conventional example is considered to be very severe from the irradiation acceleration coefficient and thermal standpoint.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a pressure tube nuclear reactor that can achieve thermal integrity of the reactor without reducing the irradiation acceleration coefficient of the monitoring member.

[Summary of the invention]

The present invention utilizes the following principles.

Fast neutrons generated in one fuel assembly are absorbed and decelerated while moving within the assembly and in heavy water, so when they reach the surrounding assembly they become thermal neutrons. Therefore, most of the fast neutrons received by the pressure pipe material monitoring member in the special fuel are those generated by nuclear fission in the special fuel itself, and are not caused by the fast neutrons frequently generated by the fission of the standard fuel surrounding the special fuel. It is thought that there is little contribution. On the other hand, as mentioned above, the thermal neutrons in the special fuel that contribute to the nuclear fission of the special fuel include the fast neutrons generated by the fission of the surrounding standard fuel that are decelerated and become a thermal neutron flux. If the enrichment level of the special nearest standard fuel is reduced, it is expected that the monitoring member will deteriorate.
This is because pressure tube reactors use heavy water as a moderator, so the area where neutrons move is larger than in light water reactors, and thermal neutrons from standard fuel that is not closest to the special fuel enter the special fuel. Fuel is an absorber for neutrons, so lowering the enrichment level of the standard fuel closest to the special fuel has the effect of reducing the absorption of thermal neutrons. For these reasons, even if the enrichment level of the standard fuel closest to the special fuel is lowered, the contribution of thermal neutrons to the special fuel will still be e? f, it doesn't drop.

Therefore, as shown in FIG. 2, even if the enrichment (enrichment) of the standard fuel closest to the special fuel is lowered, the irradiation acceleration coefficient does not decrease much. On the other hand, the enrichment of the standard fuel closest to the special fuel (
Thermal margins such as maximum linear power density and minimum critical power ratio increase because the enrichment) is lowered.

[Embodiments of the invention]

A specific example will be described below.

An example is shown in FIG. The base core is a two-region core. That is, in order to flatten the power distribution, two types of standard fuel channels with different levels of plutonium enrichment are arranged in the center and periphery of the core. The inner standard fuel channel 1 has a lower cyplutonium enrichment than the outer standard fuel channel 2.

Two special fuel channels 3 are loaded in this core. Here, as shown in FIG. 3, the plutonium enrichment of the standard fuel channel 4 closest to the special fuel channel 3 is set to be lower than the plutonium enrichment of the outer standard fuel. It is assumed to be the same as channel l. By doing this, there is no need to newly manufacture standard fuel channels for surrounding special fuels with different plutonium enrichment levels.

By adopting this embodiment, the irradiation acceleration coefficient of the pressure pipe monitoring member can be increased, and at the same time, as shown in Fig. 5, the channel output of the standard fuel channel 4 surrounding the special fuel can be decreased, and therefore the maximum linear output The density also satisfies the limit value.

〔Effect of the invention〕

According to the present invention, it is possible to sufficiently monitor pressure pipes, and
The thermal margin of the fuel increases, improving the safety of the reactor.

[Brief explanation of drawings]

Figure 1 is a diagram of the fuel arrangement in the conventional example, Figure 2 is a diagram of the special fuel assembly and an enlarged view of the pressure pipe monitoring member loading gap cell, and Figure 3 is the one in which the enrichment of the standard fuel closest to the special fuel has been reduced. Fig. 4 is a diagram showing the fuel arrangement in an embodiment of the present invention, and Fig. 5 is a comparison diagram of the maximum linear power density in the conventional example and the embodiment. be. 1...Inner standard fuel channel, 2...Outer standard fuel channel, 3...Special fuel channel, 4...
Special 1st figure 2nd figure 3rd figure
tb'l) $4-ro

Claims (1)

[Claims] 1. A pressure tube nuclear reactor characterized in that the standard fuel channel closest to the special fuel channel loaded with pressure tube material monitoring components uses fuel with a lower enrichment than the standard fuel of the recycler. .