JP7333917B2 - heat pipe - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law Date May 23, 2019 Conference name The 27th International Conference on Nuclear Engineering (ICONE27) Venue Tsukuba International Conference Center, Tsukuba City, Ibaraki Prefecture, Japan

TECHNICAL FIELD The present invention relates to a heat pipe suitable for a high dose environment for removing heat from molten debris in a nuclear reactor containment vessel or a nuclear reactor pressure vessel.

Core meltdown is one of the severe accidents at nuclear power plants. Core meltdown means that the fuel melts and collapses. Meltdown is the state in which fuel falls into the reactor pressure vessel during core meltdown, and meltthrough is the state in which the bottom of the reactor pressure vessel melts and falls to the containment vessel. When a meltdown or meltthrough occurs, so-called molten debris, which is a mixture of nuclear fuel and melted material from reactor structures, is generated.

Nuclear fuel generates strong radiation and high decay heat even when the nuclear reaction is stopped (subcritical state). Therefore, it takes a considerable amount of time for molten debris generated by core meltdown to dissipate heat and cool down in a high-dose environment. Therefore, various measures have been taken to improve safety by accelerating the cooling of molten debris and cooling it at an early stage.

Patent Literature 1 describes a method of removing heat from molten debris in a boiling water reactor (BWR) using a heat pipe. This heat pipe includes an evaporator (heat absorption section), a condensation section (heat radiation section), and a heat insulation section. In the heat pipe, the evaporator is embedded in the concrete horizontal inner wall of the drywell located below the nuclear reactor, and the condenser is located outside the reactor containment vessel. Furthermore, the heat insulating portion of the heat pipe communicates between the evaporating portion and the condensing portion and penetrates the containment vessel airtightly.

In Patent Document 1, the heat of the molten debris accumulated on the inner wall of the dry well is absorbed by the evaporating section of the heat pipe embedded in the inner wall and separated by concrete, and this heat is dissipated by the condensing section. It is said that the molten debris can be cooled in a short time.

JP-A-6-324178

The heat pipe has, for example, a cylindrical main body made of a material with high thermal conductivity and a small amount of working fluid (water) enclosed in the main body under reduced pressure. The evaporation-condensation cycle of the working fluid quickly transfers (transports) heat and releases it at the cooling end for cooling.

However, as in Patent Document 1, when the heat pipe is installed in a high-dose environment, the working fluid (water) is decomposed into hydrogen gas and oxygen gas by radiolysis. Furthermore, hydrogen gas does not condense (do not become liquid) when cooled. Therefore, the heat pipe loses its heat transfer function in a high dose environment, making it difficult to maintain its function of removing heat from molten debris. Note that Patent Document 1 does not describe the structure or material of the heat pipe, nor does it disclose specific specifications or performance.

In view of such problems, an object of the present invention is to provide a heat pipe that can maintain the function of removing heat from molten debris in a high dose environment.

In order to solve the above problems, a representative configuration of the heat pipe according to the present invention is a heat pipe suitable for a high radiation dose environment for removing heat from molten debris in a nuclear reactor containment vessel or a nuclear reactor pressure vessel. comprises a cylindrical body, an internal structure contained within the body and having a wick, the working fluid being water, and hydrogen gas accumulating between the internal structure and the cooling end of the body. It is characterized in that a cooling part space is formed to allow cooling.

In the above configuration, the cooling space is formed between the internal structure housed in the main body of the heat pipe and the cooling-side end of the main body. Therefore, in the heat pipe, the hydrogen gas, which is a non-condensable gas, can be stored in the cooling space, and the water vapor that can be condensed can be stored while the hydrogen gas is stored in the cooling space. Therefore, even if the working fluid (water) is decomposed by radiolysis in a high-dose environment and hydrogen gas is generated, the heat pipe can continue to circulate the working fluid, thus removing the heat of the molten debris. can be maintained.

A palladium catalyst is placed in the cooling space, which dissociatively adsorbs hydrogen gas in an atomic state, dissociatively adsorbs oxygen gas in an atomic state, and converts the atomic hydrogen gas and oxygen gas into water. should be recombined with As a result, in the heat pipe, even if the working fluid (water) is decomposed by radiolysis in a high-dose environment to generate hydrogen gas and oxygen gas, the palladium catalyst is placed in the cooling space where the hydrogen gas accumulates. Therefore, hydrogen gas, which is a non-condensable gas, is dissociated and adsorbed in atomic form. Similarly, oxygen gas is also dissociated and adsorbed atomically by contact with the palladium catalyst. Further, the atomic hydrogen gas is recombined with the atomic oxygen gas to return to water. Therefore, the heat pipe can continue to circulate the working fluid in a high radiation dose environment, thus maintaining the function of removing the heat of the molten debris.

In order to solve the above problems, another representative configuration of the heat pipe according to the present invention is a heat pipe suitable for a high dose environment for removing heat from molten debris in a nuclear reactor containment vessel or a nuclear reactor pressure vessel. comprising a cylindrical body and an internal structure housed within the body and having a wick, wherein the working fluid is water, the internal structure contains a palladium catalyst and hydrogen gas is dissociated and adsorbed in atomic form, oxygen gas is dissociated and adsorbed in atomic form, and the atomic hydrogen gas and oxygen gas are recombined with water.

In the above configuration, the palladium catalyst is arranged inside the internal structure housed in the main body of the heat pipe. For this reason, in a heat pipe, even if the working fluid (water) is decomposed by radiolysis in a high-dose environment to generate hydrogen gas and oxygen gas, the palladium catalyst converts hydrogen gas, which is a non-condensable gas, into atomic form. to dissociate and adsorb. Similarly, oxygen gas is also dissociated and adsorbed atomically by contact with the palladium catalyst. Further, the atomic hydrogen gas is recombined with the atomic oxygen gas to return to water. Therefore, the heat pipe can continue to circulate the working fluid in a high radiation dose environment, thus maintaining the function of removing the heat of the molten debris.

The above palladium catalyst is preferably chain or linear. By forming the palladium catalyst in a chain or linear form in this manner, the contact area between the palladium catalyst and hydrogen gas can be increased, and the pressure loss can be reduced. The catalyst is not limited to palladium, and other platinum group metals such as platinum may be used.

In addition, the present inventors prepared a test body containing 10% of the internal volume of the heat pipe and containing a working liquid (water), made the internal structure slightly shorter than the main body of the heat pipe, and made the non-condensable gas A cooling space was formed to accumulate (hydrogen gas). In addition, the present inventors placed the chain or linear palladium catalyst in the cooling part space of the heat pipe, and found that irradiation of up to 100 kGy as an example under a high dose environment caused heat transfer in the heat pipe. It was clarified that the function (heat transfer performance) was maintained.

ADVANTAGE OF THE INVENTION According to this invention, the heat pipe which can maintain the function which removes the heat of molten debris in a high dose environment can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining schematic structure of the nuclear reactor to which the heat pipe in embodiment of this invention is applied. It is a figure explaining the heat pipe in embodiment of this invention. It is a figure explaining the heat pipe in other embodiment of this invention. It is a table|surface which shows each condition of the performance test of each heat pipe. 5 is a graph showing the amount of heat transported under different irradiation conditions for each heat pipe of FIG. 4; It is a figure explaining the heat pipe in other embodiment of this invention.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in these embodiments are merely examples for facilitating understanding of the invention, and do not limit the invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are given the same reference numerals to omit redundant description, and elements that are not directly related to the present invention are omitted from the drawings. do.

FIG. 1 is a diagram illustrating a schematic configuration (state at the time of an accident) of a nuclear reactor to which a heat pipe according to an embodiment of the present invention is applied. A boiling water reactor (BWR) will be exemplified below for easy understanding, but the present embodiment can also be applied to an advanced boiling water reactor (ABWR).

A reactor containment vessel 102 is installed in the reactor building 100, and a reactor pressure vessel 104 is installed therein. Reactor pressure vessel 104 is supported within reactor containment vessel 102 by pedestal 106 . A suppression pool 108 (also called a pressure suppression chamber) is provided below the containment vessel 102 and can be depressurized by injecting excess steam into the water in the suppression pool 108 . The reactor pressure vessel 104 also accommodates a fuel assembly 110 in which fuel rods made of uranium or the like are bundled.

Note that FIG. 1 shows the state at the time of an accident such as core meltdown. In FIG. 1, water is drawn in the lower part of the containment vessel 102 and the room of the suppression pool 108, but during normal operation, the containment vessel 102 is filled with nitrogen, and the inside of the suppression pool 108 is filled with nitrogen. holds an adequate amount of water. FIG. 1 also depicts molten debris 112 deposited on the lower ends of the reactor containment vessel 102 and the reactor pressure vessel 104 .

Molten debris 112 generated by core meltdown takes a considerable amount of time to dissipate heat and cool down in a high-dose environment. Therefore, in this embodiment, the heat of the molten debris 112 is removed using heat pipes 114, 116, 118, and 120 suitable for a high dose environment.

The heat pipe 114 is installed so as to be pulled out of the reactor containment vessel 102 from the position of the fuel assembly 110 housed in the reactor pressure vessel 104 . The heat pipe 116 is installed so as to be pulled out of the reactor pressure vessel 104 from the location of the molten debris 112 deposited at the lower end of the reactor pressure vessel 104 . Heat pipes 118 , 120 rise above the location of molten debris 112 deposited under the lower end of reactor containment vessel 102 , here under pedestal 106 .

The heat pipe 120 will be described below as a representative. However, the heat pipes 114, 116, 118, and 120 have different installation positions in the reactor containment vessel 102 or the reactor pressure vessel 104 as described above, but have the same structure and function.

FIG. 2 is a diagram illustrating the heat pipe 120 in the embodiment of the invention. FIG. 2A is a diagram showing the entire heat pipe 120 and its internal structure. FIG. 2(b) is a cross-sectional view taken along the line AA of FIG. 2(a). FIG. 2(c) shows a palladium catalyst 122 (described below) disposed within the heat pipe 120. FIG.

Heat pipe 120 includes a body 124 and an internal structure 126 . The main body 124 is a cylindrical member made of, for example, a material with high thermal conductivity (SUS316 in this case), and includes a heating-side end 128 serving as an evaporating portion and a cooling-side end 130 serving as a condensing portion. have. A small amount of hydraulic fluid (water) is sealed inside the main body 124 in a decompressed state. Note that the amount of working fluid is, for example, 10% of the internal volume of the heat pipe 120 . Furthermore, the overall length of the heat pipe 120, ie, the overall length of the main body 124, is dimension L1 as shown.

The internal structure 126 is a structure housed inside the main body 124 as shown in FIG. As shown in FIG. 2(b), the internal structure 126 is a star-shaped (hexagonal) hollow structure, and the outer circumference thereof is wrapped with carbon fibers 132 (see FIG. 2(a)). ing. The internal structure 126 forms a capillary structure (wick) with carbon fibers 132 wound around its outer periphery.

Here, in a general heat pipe, when the heating side end is heated, heat is quickly transferred (transported) through the cycle of evaporation and condensation of the working fluid, and the heat is released and cooled at the cooling side end. , has the function of However, in a high-dose environment, the working fluid (water) is decomposed into hydrogen gas and oxygen gas by radiolysis. Furthermore, hydrogen gas does not condense (do not become liquid) when cooled. Therefore, in a general heat pipe, the heat transfer function is lost in a high dose environment, and it becomes difficult to maintain the function of removing heat from the molten debris 112 .

Therefore, in the heat pipe 120 of the present embodiment, a cooling space 134 is formed between the internal structure 126 and the cooling-side end 130 of the main body 124, as shown in FIG. 2(a). The cooling section space 134 is a space for accumulating hydrogen gas, which is a non-condensable gas, and can also store water vapor that can be condensed while the hydrogen gas is being accumulated. Note that the dimension L3 of the cooling space 134 shown in FIG. 2A corresponds to the difference between the dimension L1 of the main body 124 and the dimension L2 of the internal structure 126 .

In the heat pipe 120, when heat from the molten debris 112 (see FIG. 1) is input to the heating-side end 128 of the main body 124 as indicated by arrow B in FIG. (water vapor) passes through the interior of the internal structure 126 as indicated by arrow C. This water vapor accumulates in the cooling section space 134 and is further condensed to become water. As a result, in the heat pipe 120 , heat is radiated as indicated by an arrow D at the end 130 on the cooling side of the main body 124 .

Further, water is returned toward the heated end 128 of the body 124 as indicated by arrow E by capillary action utilizing the carbon fibers 132 wrapped around the inner structure 126 . The returned working fluid (water) turns into steam again and moves as shown by arrow C when the end 128 on the heating side of the main body 124 is heated.

Therefore, in the heat pipe 120, even if the working fluid (water) is decomposed by radiolysis in a high-dose environment to generate hydrogen gas, the circulation of the working fluid, that is, the cycle of evaporation and condensation, can be continued. It can maintain its ability to remove heat.

Further, in heat pipe 120 , palladium catalyst 122 is arranged inside internal structure 126 . The palladium catalyst 122, as shown in FIG. 2(c), is in the form of a chain or a line composed of a combination of thin wires and foil rings. The palladium catalyst 122 atomically dissociates and adsorbs hydrogen gas when it comes into contact with hydrogen gas, which is a non-condensable gas, and similarly, when it comes in contact with oxygen gas, it atomically dissociates and adsorbs oxygen gas.

Therefore, in the heat pipe 120, even if the working fluid (water) is decomposed by radiolysis in a high-dose environment to generate hydrogen gas and oxygen gas, the palladium catalyst 122 converts hydrogen gas, which is a non-condensable gas. It dissociatively adsorbs in atomic form, oxygen gas is dissociated and adsorbed in atomic form, and hydrogen gas in atomic form and oxygen gas in atomic form are recombined with water.

Therefore, the heat pipe 120 can continue to circulate the working fluid in a high radiation dose environment, so that the function of removing the heat of the molten debris 112 can be maintained. Furthermore, in the heat pipe 120, by making the palladium catalyst 122 chain-shaped or linear, the contact area between the palladium catalyst 122 and the hydrogen gas can be increased, and the pressure loss can be reduced. The catalyst is not limited to palladium, and other platinum group metals such as platinum may be used.

FIG. 3 is a diagram illustrating a heat pipe 120A according to another embodiment of the invention. Heat pipe 120A differs from heat pipe 120 in that palladium catalyst 122 is arranged in cooling section space 134 instead of inside internal structure 126 .

In such a heat pipe 120A, even if the working fluid (water) is decomposed by radiolysis in a high-dose environment to generate hydrogen gas and oxygen gas, the palladium catalyst 122 is placed in the cooling section space 134 for accumulating hydrogen gas. is placed. For this reason, according to the heat pipe 120A, hydrogen gas, which is a non-condensable gas, is dissociated and adsorbed into atoms, oxygen gas is dissociated and adsorbed into atoms, and hydrogen gas that is in the form of atoms and oxygen that is in the form of atoms are dissociated and adsorbed. Recombines gas with water. Therefore, in the heat pipe 120A, the working fluid can be continuously circulated in a high radiation dose environment, and the function of removing the heat of the molten debris 112 can be maintained.

FIG. 4 is a table showing each condition of the performance test of each heat pipe. As shown, in this performance test, samples S1, S5, and S8 were prepared as three specimens. In each of the samples S1, S5, and S8, the dimension L1 of the main body 124 is 50 cm, and the amount of working fluid (water) is 10% of the internal volume of the heat pipe.

In the sample S1, the dimension L2 of the internal structure 126 is "48 cm" and the catalyst is "none". That is, in the sample S1, the cooling section space 134 with the dimension L3 of "2 cm" is formed. In the sample S5, the dimension L2 of the internal structure 126 is "43 cm", so the cooling section space 134 with the dimension L3 of "7 cm" is formed. Further, the sample S5, like the sample S1, has no catalyst.

In the sample S8, since the dimension L2 of the internal structure 126 is "43 cm", the cooling section space 134 with the dimension L3 of "7 cm" is formed similarly to the sample S5. Furthermore, in sample S8, a chain or linear palladium catalyst 122 was arranged in the cooling section space 134 . That is, the sample S8 has the same configuration as the heat pipe 120A shown in FIG.

FIG. 5 is a graph showing the amount of heat transport of each heat pipe in FIG. 4 under different irradiation conditions. In the figure, the horizontal axis indicates the absorbed dose (kGy) assuming a high-dose environment, and the vertical axis indicates the amount of heat transport (W).

First, comparing the samples S1 and S5, the sample S5 has a larger cooling section space 134 for accumulating hydrogen gas, which is a non-condensable gas, than the sample S1 as described above. As a result, as shown in FIG. 5, it was found that the deterioration of performance when the absorbed dose was increased was suppressed in the sample S5 compared to the sample S1.

Next, comparing the samples S5 and S8, the samples S5 and S8 have the same size of the cooling section space 134 for accumulating hydrogen gas, which is non-condensable gas, as described above. However, in the sample S8, since the chain or linear palladium catalyst 122 is arranged in the cooling part space 134, hydrogen gas is dissociatively adsorbed in the atomic state, oxygen gas is dissociatively adsorbed in the atomic state, and The hydrogen gas and atomic oxygen gas can be recombined with water. As a result, as shown in FIG. 5, it was found that the heat transfer function (heat transfer performance) was substantially maintained in the sample S8 even after irradiation with an absorption dose of 108 (kGy) compared to the sample S5. Ta.

FIG. 6 is a diagram illustrating a heat pipe 120B in still another embodiment of the invention. The heat pipe 120B differs from the heat pipe 120 described above in that the palladium catalyst 122 is arranged not only inside the internal structure 126 but also in the cooling section space 134 .

In such a heat pipe 120B, even if the working fluid (water) is decomposed by radiolysis in a high-dose environment to generate hydrogen gas and oxygen gas, hydrogen gas is accumulated in addition to the inside of the internal structure 126. The palladium catalyst 122 is arranged in the cooling section space 134 . Therefore, according to the heat pipe 120B, the hydrogen gas, which is a non-condensable gas, is dissociated and adsorbed into atoms, and the oxygen gas is dissociated and adsorbed into atoms, and the hydrogen gas that is in the form of atoms and the oxygen that is in the form of atoms are dissociated and adsorbed. Recombines gas with water. Therefore, in the heat pipe 120B, the working fluid can be continuously circulated in a high radiation dose environment, so the function of removing the heat of the molten debris 112 can be maintained.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope described in the claims, and these also belong to the technical scope of the present invention. Understood.

INDUSTRIAL APPLICABILITY The present invention can be used as a heat pipe suitable for a high dose environment for removing heat from molten debris in a reactor containment vessel or a reactor pressure vessel.

DESCRIPTION OF SYMBOLS 100... Reactor building, 102... Reactor containment vessel, 104... Reactor pressure vessel, 106... Pedestal, 108... Suppression pool, 110... Fuel assembly, 112... Molten debris, 114, 116, 118, 120, 120A, DESCRIPTION OF SYMBOLS 120B...Heat pipe 122...Palladium catalyst 124...Main body 126...Internal structure 128...End on heating side 130...End on cooling side 132...Carbon fiber 134...Cooling space

Claims (2)

A heat pipe suitable for high-dose environments for removing heat from molten debris in a nuclear reactor containment vessel or reactor pressure vessel, comprising:
a cylindrical body;
an internal structure contained within the body and having a wick;
the working fluid is water,
A palladium catalyst is placed inside the internal structure, which dissociatively adsorbs hydrogen gas into atoms, dissociatively adsorbs oxygen gas into atoms, and converts the atomic hydrogen gas and the oxygen gas into atoms. , a heat pipe that recombines with water. 2. The heat pipe of claim 1 , wherein the palladium catalyst is chain or linear.

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