JPH04296696A - Automatic output distribution adjusting device of reactor - Google Patents

Abstract

PURPOSE:To obtain an automatic output distribution adjusting device which makes the output distribution of a reactor core flat by automatically reducing the slowing down material at a high output in a reactor. CONSTITUTION:An automatic output distribution adjusting device of a reactor comprises a hollow adjusting member 1, which filled with liquid slowing down material 2 at the time of low output and the liquid slowing down material 2 of which is discharged by evaporated slowing down material 3 at the time of high output, arranged at a position near fuel rods. Therefore, since the quantity of thermal neutron which is made to slow down by the slowing down material 2 is reduced due to the discharge of the slowing down material 2, which is evaporated at a high output position in the adjusting member 1, from the adjusting member 1, local output is automatically adjusted, making the output distribution of a reactor core flat.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a nuclear reactor that uses a liquid moderator, such as a light water reactor, to automatically flatten the power distribution of the core by automatically reducing the moderator in the high-output parts. This invention relates to an automatic output distribution adjustment device.

0002

BACKGROUND OF THE INVENTION In a nuclear reactor, if a system is set up so that one or more of the neutrons released per nuclear fission survive as thermal neutrons and cause the next nuclear fission, the nuclear fission chain reaction continues. Furthermore, if just one element effectively contributes to nuclear fission, a chain reaction will proceed at a certain rate, which is called the criticality of the reactor.

Considering the path from the generation of neutrons due to nuclear fission to the time when thermal neutrons undergo a deceleration process and cause nuclear fission again, first, some of the high-speed neutrons immediately after nuclear fission are absorbed by the nuclear fuel and cause nuclear fission. wake up Neutrons must pass through a resonant absorption region before being decelerated and become thermal neutrons. The probability of escaping resonance means the proportion of neutrons that escape resonance absorption during the deceleration process and become thermal neutrons. This probability changes depending on the enrichment of the fuel, the volume ratio of fuel and moderator, the non-homogeneity of the system, etc.

[0004]Next, a factor indicating the proportion of surviving thermal neutrons that are effectively absorbed by nuclear fuel is called the thermal neutron utilization rate. When thermal neutrons are absorbed by nuclear fuel, fission causes new neutrons to be released, starting a chain reaction.

In a nuclear reactor based on the above principle, it is desirable to flatten the power distribution of the core from the viewpoint of heat removal and the like. In conventional nuclear reactors, power distribution is primarily adjusted using control rods. However, adjustments made primarily by control rods did not allow for local adjustments.

For this reason, in boiling water reactors, in order to reduce the power peaking that occurs in the fuel near the control rods and the water gap, the enrichment level of uranium is varied within one fuel assembly, and furthermore, in the early stage of the core, Improvements have been taken such as the use of boron curtains with added boron and the addition of gadolinia as a flammable poison. In addition, in pressurized water reactors, improvements such as adjusting the enrichment of uranium dioxide fuel are being taken, similar to boiling water fuels.

[0007]

[Problems to be Solved by the Invention] However, despite various improvements, it has not been possible to optimally set the fuel loading pattern from an economic point of view, it has been difficult to increase the average power density of the core, or there has been a problem in achieving sufficient power. It has been difficult to achieve flattening of the distribution. Therefore, it has been desired to develop an adjustment device that uses an output distribution flattening method that is completely different from conventional output distribution flattening methods.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic power distribution adjustment device for a nuclear reactor that flattens the power distribution of the reactor core by automatically reducing the amount of moderator in high power portions of the reactor.

[0009]

[Means for Solving the Problems] The power distribution automatic adjustment device for a nuclear reactor according to the present invention provides a power distribution for a nuclear reactor using a liquid moderator that decelerates neutrons emitted from nuclear fuel at high speed and converts them into thermal neutrons. In this adjustment device, a hollow adjustment member is installed near the fuel rod, the inside of which is filled with the liquid moderator at low power, and the liquid moderator inside is removed by vaporized moderator at high power. It is arranged at the output adjustment position.

0010

[Operation] The present invention provides a hollow adjustment member near the fuel rods, the interior of which is filled with the liquid moderator at low power, and the liquid moderator inside is removed by vaporized moderator at high power. Because it is placed at the output adjustment position, the moderator in the adjustment member placed in the high output area is vaporized and removed from the adjustment member, thereby reducing thermal neutrons that are moderated by the moderator. volume is reduced to automatically adjust local power and flatten the core power distribution.

FIG. 1 is a perspective view showing a simple construction of the adjustment member used in this method. FIG. 2 is an explanatory view showing the state in which the adjusting member of FIG. 1 is used, in which figure a shows the state at low output and figure b shows the state at high output. The inside is filled with a liquid moderator 2 at low output, and the vaporized moderator 3 is used as the liquid moderator 2 at high output.
The simplest structure of the adjustment member that eliminates and retains is shown in Figure 1.
This is a cylindrical member 1 whose upper end is closed, as shown in FIG. A preferable cylindrical member 1 is made of a material that generates heat by absorbing fuel or neutrons or γ-rays. For example, nuclear fuel material (UO2
, PuO2) or boron (B) coated with Zircaloy or the like.

As shown in FIG. 2, the moderator 2 inside the cylindrical member 1 does not vaporize in the low output portion (Figure a), so the output does not become low. In the high output section (Figure b), the heat generation of the cylindrical member 1 is large, so the moderator 2 inside the cylindrical member 1 is vaporized, the moderator 2 inside the cylindrical member 1 decreases, the moderation of neutrons decreases, and nuclear fission occurs. Thermal neutrons that tend to cause this decrease, resulting in lower output.

Note that the adjusting member is not limited to the cylindrical shape as described above, but has at least a hollow interior that can be filled with the liquid moderator, and an exhaust system for discharging the liquid moderator using the vaporized moderator. Any shape or size may be used as long as it has a configuration with an outlet, the interior is filled with liquid moderator at low output, and the vaporized moderator excludes and retains the liquid moderator at high output. It can be taken.

For example, it can be used as part of a fuel rod, or it can be attached to a channel box or support grid, or a part of the channel box or support grid can be modified to have the function of an adjustment member. You can also let Further, the upper end of the adjustment member may not only be closed, but may also be configured to have a small hole or the like, so that the moderator vaporized during high output is gradually evacuated through the small hole.

Furthermore, the material constituting the adjustment member does not need to be made of a heat-generating material as described above, as long as the material is at the position where the moderator is vaporized and the position where the vaporized moderator is held. Furthermore, the present invention is widely applicable to nuclear reactors that use a liquid moderator, and any nuclear reactor where the moderator can be vaporized within the regulating member, such as boiling water type, pressurized water type light water reactors, heavy water reactors, etc. be able to.

[0016]

Embodiment FIG. 3 is a perspective view showing the structure of an embodiment of the adjustment member used in this method. In this example, the cylindrical adjustment member with its upper end closed is used as a fuel assembly (Fig. 4) in the same way as a burnable poison rod (BPR) in a conventional pressurized water reactor.
An example is shown in which the control rod is inserted into the control rod guide tube. Figure 3
As shown in the figure, a cylindrical adjustment member 11 whose lower end is open and whose upper end is closed is attached to a mounting plate 12. This mounting plate 12 is attached to the upper nozzle of the fuel assembly by a fixed handle 13 and passes through the control rod guide tube to the adjustment member 11.
and the plug rod 14 is inserted into the interior of the fuel assembly.

FIG. 4 is an explanatory diagram showing the structure of another embodiment of the adjusting member used in this method. In this embodiment, some of the fuel rods in the fuel assembly are shortened to provide a gap without any fuel rods, and an adjustment member is installed in the gap. As shown in FIG. 4, fuel rods 2 of a pressurized water fuel assembly 20 are bundled into a bundle by a support grid 23.
A part of 2 was shortened, and a cylindrical adjustment member 21 whose upper end was closed was placed above it. In the figure, 24 is an upper nozzle, 25 is a lower nozzle, and 26 is a control rod guide tube.

FIG. 5 is a diagram showing the relationship between local output and multiplication factor change of the adjustment member portion of the fuel assembly shown in FIG. As shown in FIG. 5, the multiplication factor decreases due to the increased output and the vaporized moderator in the adjustment member.

[0019]

Effects of the Invention As explained above, the hollow adjustment member is filled with the liquid moderator when the output is low, and the liquid moderator inside is removed by the vaporized moderator when the output is high. Since it is arranged at the output adjustment position near the rod, the moderator in the adjustment member placed in the high output part is vaporized and removed from the adjustment member, so that the speed is reduced by the moderator. This has the effect of automatically adjusting the local power and flattening the power distribution of the core.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a simple configuration of an adjustment member used in the present method.

FIG. 2 is an explanatory view showing the usage state of the adjusting member in FIG. 1, in which figure a shows the state at low output and figure b shows the state at high output.

FIG. 3 is a perspective view showing the configuration of one embodiment of the adjustment member used in the present method.

FIG. 4 is an explanatory diagram showing the configuration of another example of the adjustment member used in the present method.

5 is a diagram showing the relationship between local output and multiplication factor change of the adjustment member portion of the fuel assembly shown in FIG. 4; FIG.

[Explanation of symbols]

1, 11, 21 Adjustment member 2 Liquid moderator

Claims (1)

[Claims] 1. A power distribution adjustment device for a nuclear reactor using a liquid moderator that decelerates neutrons emitted from nuclear fuel at high speed and converts them into thermal neutrons, the inside of which is filled with the liquid moderator at low output. The output of the nuclear reactor is characterized in that a hollow adjustment member is disposed at an output adjustment position near the fuel rods so that the liquid moderator inside is removed by vaporized moderator when the output is high. Distribution automatic adjustment device.