KR20180059399A - Sintered nuclear fuel pellet with localized burnable absorber - Google Patents

Abstract

The present invention relates to a fuel pellet including a local combustible absorber and, more specifically, to a fuel pellet in which a molded object of a combustible absorber is inserted. The fuel pellet can use a molded object of a combustible absorber and optimize self-shielding and burning velocity of combustion of the combustible absorber, thereby optimizing excess reactivity control.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a nuclear fuel sintered body including a combustible absorber,

The present invention relates to a fuel sintered body including a local combustible absorber capable of adjusting self-shielding performance.

  A reactor is a furnace for obtaining energy by using nuclear fission of nuclear fuel. In the reactor, energy is obtained by a chain reaction in which neutrons released during fission cause another fission. At this time, in order to operate the reactor more safely and economically, it is necessary to appropriately control the reactivity of the reactor core and the distribution of the reactor power.

In a typical reactor, the reactivity is controlled by mechanical insertion or withdrawal of a control rod made of a material that absorbs neutrons. Control of core reactivity by control rod has the advantage of controlling reactor core reactivity quickly. However, in general, since the control rod is locally inserted into the core, there is a problem that it is difficult to simultaneously control the reactivity and the power distribution of the core simultaneously with the control rod alone. In addition, if the surplus response is large, the mechanical motion of the control rod must also increase together with the uncertainty of the control of the response, thereby increasing the risk of accidents.

For this reason, ordinary reactors use other methods to lower the surplus reactivity and then control the reactivity using the control rod. One well-known method is to mix the coolant with the boron-containing water, a neutron absorbing material. In the case of controlling the reactivity of the core by controlling the concentration of boron contained in the cooling water, since the boron is uniformly mixed with the coolant of the reactor, it is advantageous to control the reactivity while minimizing distortion of the output distribution of the core . However, since it takes a lot of time to inject and dilute boron in the coolant, there is a problem in that it is not possible to use the reaction control of the core using boric acid when it is necessary to control the reactivity of the core rapidly, In the case of reactivity control, the process of lowering the boron concentration also generates a large amount of radioactive liquid waste. On the other hand, in order to control the concentration of water-soluble boron in the primary coolant system, an expensive and complicated device called " Chemical and Volumetric Control System (CVCS) " is required. In addition, in order to neutralize the pH of the cooling water (boric acid) containing acid which is acidic, LiH is mixed again with the coolant, and LiH reacts with the neutrons to generate a large amount of tritium. In addition, It is known to cause corrosion of structural members and fuel cladding which constitute the system, resulting in deterioration of reactor operation performance. In addition, if the concentration of boron in the coolant is very high, the coolant temperature coefficient can be very close to zero or positive. Since such a coolant temperature coefficient is not desirable from a safety point of view, It is one of safety related issues.

Considering non-boric acid or low-boric acid operation is a natural problem to improve the safety of nuclear reactors and it is common to use the so-called flammable absorber concept. The combustible absorber acts as a strong neutron absorber, but once absorbed by neutrons and converted into other nuclides, the neutron absorption cross section is greatly reduced. Gadolinium (Gd), Erbium (Er), Boron (B) and the like are used as typical combustible absorbers. In pressurized light water reactors, gadolinium (Gd) and erbium (Er) are generally used in the form of Gd ₂ O ₃ and Er ₂ O ₃ mixed properly with UO ₂ fuel. On the other hand, the void in the rare earth combustible absorber is not frequently used because it has a relatively large residual toxic effect, but can be used as a relatively efficient combustible absorber in a core having a very long cycle length. When gadolinium is mixed with nuclear fuel, the thermal conductivity of the fuel decreases, so that the fuel with mixed gadolinium is generally designed to have a very low power density There are disadvantages. Therefore, you can not use a large amount of Gadolinium when you use Gadolinium. Also, when the nuclear fuel and Gd ₂ O ₃ are mixed as in the present case, the doline is burned very quickly, so that it is difficult to apply when the cycle length of the core is long.

In the case of the boron ZrB ₂ extremely thin are often used in a so-called IFBA concept called (Integrated Fuel Burnable Absorber) used to cover the UO ₂ fuel rods. In addition, in the case of boron, a boron compound such as B ₄ C is produced in a special shape and is loaded in the control rod guide tube. As a typical concept, WABA (Wet Annular Burnable Absorber) is exemplified. In the case of boron, it absorbs neutrons and helium gas is generated. Therefore, it is difficult to mix it with nuclear fuel, so it is used in the same way as IFBA, or in the same way as WABA. In the case of boron, the neutron absorption cross-sectional area is relatively small, so when using IFBA type, a relatively large number of fuel rods must be loaded with IFBA. In addition, the use of flammable absorbers is limited in WABA, as loading of flammable absorbers into the control rod guide tube, like WABA, limits the insertion of control rods.

As described above, various types of combustible absorbers are used in fuel assemblies, but they are used in a limited manner in their use. Accordingly, the applicant of the present invention has come up with a new concept of combustible absorber concept which can more effectively control the reactivity and power distribution of the core.

The object of the present invention is to provide a nuclear fuel sintered body which can be loaded without changing a large design in a normal reactor and can optimize surplus reactivity according to the characteristics of each reactor.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

Aspects of the present invention,

And a molded body of a combustible absorber is inserted into the inside of the fuel sintered body.

According to an embodiment of the present invention, the molded article of the combustible absorber may include at least one member selected from the group consisting of a pseudo cylinder, a cylinder, a disk, a sphere, a rod, a film and a polygonal column.

According to one embodiment of the present invention, the molded article of the combustible absorber can be inserted at not more than 50% by volume based on the total volume of the nuclear fuel sintered body.

According to one embodiment of the present invention, the molded article of the combustible absorber may be inserted into the central region, the surface region, or both of the nuclear fuel sintered bodies.

According to one embodiment of the present invention, when the molded body of the combustible absorber is inserted singly or plurally, and when it is inserted in a plurality, the molded body of the combustible absorber may be inserted with the same or different shape and size.

According to one embodiment of the present invention, the molded article of the combustible absorber comprises Gd ₂ O ₃ ; Er ₂ O ₃ ; And _{CeO 2, In 2 O 3,} Y 2 O 3, ThO 2, TiO ₂ , ZrO ₂ , Al ₂ O ₃ and Y ₂ O ₃ -ZrO ₂ and Gd ₂ O ₃ and Er ₂ O ₃ stabilized with yttria-stabilized zirconia.

According to one embodiment of the present invention, the CeO ₂ , In ₂ O ₃ , Y ₂ O ₃ , ThO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O _3, and Y ₂ O ₃ -ZrO ₂ are Gd ₂ O ₃ And Er ₂ O ₃ By weight to 60% by weight.

The present invention can effectively reduce the surplus reactivity of a reactor by introducing a centrally-shielded burnable absorber (CSBA) in the center of the nuclear fuel sintered body.

The present invention can optimize the surface area of a combustible absorber to control the burning rate and self-shielding of an appropriate combustible absorber in the fuel.

The present invention can optimize the performance of the nuclear fuel by controlling the size, shape and position of the combustible absorber according to the output and the life of the fuel.

FIG. 1 is a schematic view of a nuclear fuel sintered body according to an embodiment of the present invention.
2 shows the results of the CSBA effect calculated in the first embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. Also, terminologies used herein are terms used to properly represent preferred embodiments of the present invention, which may vary depending on the user, intent of the operator, or custom in the field to which the present invention belongs. Therefore, the definitions of these terms should be based on the contents throughout this specification. Like reference symbols in the drawings denote like elements.

According to one embodiment of the present invention, the nuclear fuel sintered body effectively controls the surplus reactivity and adjusts the reaction rate and self shielding of the combustible absorber in accordance with the conditions of the reactor or the fuel. Can be adjusted.

According to one embodiment of the present invention, the fuel sintered body may be a molded body of a combustible absorber inserted in a nuclear fuel sintered body. The molded article of the combustible absorber is a molded article in which the combustible absorber is bulk-formed, can exhibit its own shielding property, and can be inserted in a freely adjustable shape in order to minimize surplus reactivity.

As an example of the present invention, the molded article of the combustible absorber may be porous, which can store the gas produced by the fission in a porous combustible absorber and prevent the combustible absorber from flowing out of the nuclear fuel even if it is melted.

In one embodiment of the present invention, the volume fraction of the molded article of the combustible absorber relative to the nuclear fuel sintered body can be appropriately adjusted to optimize the life and output of the nuclear fuel by controlling the burning rate and the self shielding phenomenon, 50% by volume or less based on the total volume of the nuclear fuel sintered body; 2% by volume to 30% by volume; 2% by volume to 20% by volume; Or at a volume fraction of 2% to 10% by volume.

According to an embodiment of the present invention, the burning rate of the combustible absorber and the self shielding can be appropriately adjusted according to the shape, the number, the insertion position and / or the size of the molded article of the combustible absorber to optimize the surplus response.

For example, the shape of the molded article of the combustible absorber may include at least one member selected from the group consisting of irregular shape, cylinder, disk, spherical shape, rod, film and polygonal shape, Lt; / RTI > For example, depending on the shape of the molded article of the combustible absorber, the burning rate of the combustible absorber and the self-shielding phenomenon can be controlled.

In one embodiment of the present invention, the molded article of the combustible absorber may be inserted singly or plurally. For example, when inserted in a plurality, the molded body of the combustible absorber can be inserted with the same or different shape and size. For example, when inserted in a plurality, the burning rate of the combustible absorber can be adjusted.

 For example, referring to FIG. 1, FIG. 1 exemplarily shows a nuclear fuel sintered body according to an embodiment of the present invention. In order to maximize self-shielding and slow combustion of a combustible absorber, If the molded body of a combustible absorber is inserted into a spherical shape and the combustion of the combustible absorber is to be accelerated by minimizing the self shielding phenomenon, the combustible absorber of the same volume can be divided into three pieces and inserted in the form of 3 spherical balls .

In one embodiment of the present invention, the molded article of the combustible absorber may be inserted all over the nuclear fuel sintered body or inserted into the central region, the surface region, or both. This is because it is possible to control the burning rate and the self shielding phenomenon according to the insertion position of the molded article of the combustible absorber and to increase the temperature due to excessive fission at the central portion of the nuclear fuel when the molded article of the combustible absorber is inserted into the center portion of the nuclear fuel sintered body And the combustible absorber can not be released to the outside of the nuclear fuel even if the combustible absorber melts before the nuclear fuel in an extreme transient situation.

For example, referring to FIG. 1, a molded body of various types of combustible absorbers such as a spherical ball core, a cylindrical core, a surface mini-pellet, and a mini-pellet core and a molded body of a combustible absorber inserted in various positions can be applied .

In one embodiment of the present invention, the molded article of the combustible absorbent is 10 mm or less; 1 mm or less; 1 μm to 1.5 mm; Or from 1 [mu] m to 900 [mu] m, and the size may be a diameter, a radius, or a height depending on the shape of the molded body.

In one embodiment of the present invention, the combustible absorber can be applied without restriction as long as it provides a self-shielding phenomenon applicable to nuclear fuel, for example, Gd ₂ O ₃ ; Er ₂ O ₃ ; And _{CeO 2, In 2 O 3,} Y 2 O 3, ThO 2, TiO 2, ZrO 2, Al 2 O 3 and Y ₂ O ₃ -ZrO ₂ (yttria-stabilized zirconia) stabilized by at least one of Gd ₂ O _3, and Er ₂ O _3, and the like. Preferably Gd ₂ O ₃ ; And Gd ₂ O ₃ stabilized with ZrO ₂ or Y ₂ O ₃ -ZrO ₂ (yttria-stabilized zirconia).

For example, at least one of CeO ₂ , In ₂ O ₃ , Y ₂ O ₃ , ThO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O _3, and Y ₂ O ₃ -ZrO _{2 2} O ₃ and / or 1% to 70% by weight based on Er ₂ O ₃ ; 1% to 60% by weight; Or 3 to 30% by weight; Lt; / RTI > When the content is within the above range, the phase change is stabilized and the integrity of the sintered body can be improved.

As an example of the present invention, the molded article of the combustible absorber may be a structure composed of a core and a shell, and may be a structure made of, for example, Gd ₂ O ₃ , Er ₂ O ₃ Or core; And at least one of CeO ₂ , In ₂ O ₃ , Y ₂ O ₃ , ThO ₂ , A shell comprising at least one of TiO ₂ , ZrO ₂ , Al ₂ O ₃ , and Y ₂ O ₃ -ZrO ₂ (yttria-stabilized zirconia); . ≪ / RTI > For example, the shell may further comprise Gd ₂ O ₃ , Er ₂ O ₃ , or both.

For example, UO ₂ is a fuel material, and cracks due to thermal mismatch during sintering of the fuel composite sintered body can be suppressed.

According to an embodiment of the present invention, there is provided a method of manufacturing a fuel sintered body, wherein a thermal expansion and a phase transformation property are well controlled during sintering using a molded body of a combustible absorber, Size, shape, and the like of the molded article of the absorber are appropriately adjusted, so that the self-shielding phenomenon can be freely adjusted.

According to one embodiment of the present invention, a molded body of a combustible absorber can be produced by press molding the powder of the combustible absorber, and the fuel material and the combustible absorber can be mixed to produce a nuclear fuel assembly having a combustible absorber inserted into the nuclear fuel material . Next, the nuclear fuel compact is sintered to obtain a nuclear fuel sintered body having the combustible absorber inserted therein.

For example, the combustible absorber powder has a particle size of 100 mu m or less; 50 탆; Or a particle size of 100 nm to 1 占 퐉.

For example, 1% to 10% by weight, based on the total weight of the fuel material; Or 2% by weight to 4% by weight of the molded article of the combustible absorber may be mixed.

For example, the nuclear fuel compact may be heated in air, an inert gas atmosphere or a reducing gas atmosphere at a temperature of 1000 ° C to 1800 ° C; Or from 1 minute to 10 hours at a temperature of from 1300 占 폚 to 1600 占 폚; 5 minutes to 1 hour; Or for 10 minutes to 30 minutes.

For example, the sintering can be performed using a sintering furnace or a microwave sintering apparatus, and preferably a microwave sintering apparatus can be used.

The present invention is not limited thereto but may be embodied in other specific forms without departing from the spirit or scope of the present invention as set forth in the following claims, The present invention can be variously modified and changed.

Example 1

The effect of CSBA was tested through computational calculations for commercial core. A nuclear fuel assembly model used in Westinghouse's AP1000 core was considered for testing. And compared with the IFBA used in the AP1000 model and the CSBA shown in Fig. 1, and the result is shown in Fig.

Referring to FIG. 2, it can be seen that optimization of CSBA enables better control of surplus response than IFBA, and that CSBA can be optimized for core design.

The present invention can provide a nuclear fuel sintered body capable of effectively controlling surplus reactivity in the fuel by variously controlling the shape, size, and insertion position of the molded body of the combustible absorber.

Claims (8)

A molded body of a combustible absorber is inserted therein,
The molded article has a self-shielding property,
The formed body does not contain nuclear fuel,
Wherein at least one of insertion position, size and shape of the molded article of the combustible absorber is controlled to control the burning rate of the combustible absorber, the degree of self shielding,
Nuclear fuel sintered body.
The method according to claim 1,
Wherein the molded body is bulked.
The method according to claim 1,
Wherein the molded body is porous, the pores of the molded body carry a fission generating gas,
Wherein the sintered fuel body prevents melt outflow of the combustible absorber.
The method according to claim 1,
Wherein the molded article of the combustible absorber comprises at least one member selected from the group consisting of a disc, a sphere, a rod and a film.
The method according to claim 1,
Wherein the molded article of the combustible absorber is inserted at a volume of 50 vol% or less with respect to the total volume of the nuclear fuel sintered body.
The method according to claim 1,
Wherein the molded article of the combustible absorber is inserted into a central region of the nuclear fuel sintered body and is not exposed to the outside.
The method according to claim 1,
The molded article of the combustible absorber may include Gd ₂ O ₃ ; Er ₂ O ₃ ; And _{CeO 2, In 2 O 3,} Y 2 O 3, ThO 2, Gd ₂ O ₃ stabilized by at least one of TiO ₂ , ZrO ₂ , Al ₂ O ₃ and Y ₂ O ₃ -ZrO ₂ , and Er ₂ O ₃ , and mixtures thereof. Nuclear fuel sintered body.
8. The method of claim 7,
The CeO ₂ , In ₂ O ₃ , Y ₂ O ₃ , ThO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ and Y ₂ O ₃ -ZrO ₂ may be Gd ₂ O ₃ And Er ₂ O ₃ ≪ / RTI > to 30% by weight, based on the total weight of the composition. Nuclear fuel sintered body.

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