JP2007119282A - Method and apparatus for preparing undiluted solution containing uranyl nitrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for preparing a stock solution containing uranyl nitrate capable of efficiently preparing the stock solution containing uranyl nitrate having highly concentrated uranium for producing ammonium diuranate particles useful for producing fuel kernels for a fuel for a high-temperature gas-cooled reactor. <P>SOLUTION: The stock solution containing uranyl nitrate is prepared by storing uranyl nitrate prepared from uranium oxide and nitric acid and a thickener in a preparation tank having a limited shape and transferring the content of the preparation tank from the lower part to the upper part of the preparation tank through a circulation channel installed at the outside of the preparation tank. The apparatus for preparing the stock solution containing uranyl nitrate by this method is also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for preparing a uranyl nitrate-containing stock solution and an apparatus for preparing a uranyl nitrate-containing stock solution, and more specifically, uranyl nitrate for producing ammonium deuterated uranate particles useful for the production of fuel nuclei for high-temperature gas reactor fuels. The present invention relates to a method capable of efficiently preparing a stock solution containing the solution in a short time under a shape-limiting condition and a stock solution preparation apparatus useful for carrying out the method.

  The core into which the fuel of the high-temperature gas reactor is charged is formed of graphite having a large heat capacity and excellent high-temperature soundness. In this high-temperature gas furnace, a gas such as helium gas, which does not cause a chemical reaction even at high temperatures and has high safety, is used as the cooling gas, so that the cooling gas can be safely taken out even when the outlet temperature is high. be able to. Therefore, even if the temperature of the core rises to about 900 ° C., the cooling gas heated to a high temperature can be used safely in a wide range of fields such as power generation, hydrogen production equipment, and other chemical plants. Yes.

  Moreover, the fuel for a high temperature gas reactor to be charged into the high temperature gas reactor generally includes a fuel core and a coating layer that covers the periphery of the fuel core. The fuel core is, for example, fine particles having a diameter of about 350 to 650 μm formed by sintering uranium dioxide into a ceramic form.

The coating layer has a four-layer structure, and has a first layer, a second layer, a third layer, and a fourth layer from the fuel core surface side. The first layer is formed of low-density pyrolytic carbon having a density of about 1 g / cm ³ , functions as a gas reservoir for gaseous fission products (FP), and serves as a buffer for absorbing fuel nuclear swelling. It also has the function of The second layer is formed of high-density pyrolytic carbon having a density of about 1.8 g / cm ³ and has a function of holding a gaseous FP. The third layer is formed of silicon carbide (SiC) having a density of about 3.2 g / cm ³ , has a function of holding a solid FP, and is a main strength member of the coating layer. The fourth layer is formed of high-density pyrolytic carbon having a density of about 1.8 g / cm ³ and has a function of holding a gaseous FP and also a function of a protective layer of the third layer. . The diameter of the coated particles forming these coating layers is usually about 500 to 1000 μm.

  The fuel nuclei (coated fuel particles) covered with the four coating layers are dispersed in a graphite matrix and molded into a fixed fuel compact shape. The fuel compact is a cylinder made of graphite. A fixed quantity is accommodated in the container and plugged up and down to form a fuel rod. Ultimately, this fuel rod is inserted into a plurality of insertion holes of the hexagonal column type graphite block, and a core is formed by arranging a plurality of the hexagonal column type graphite blocks in a honeycomb shape and stacking a plurality of stages. The

  Such a HTGR fuel can generally be manufactured through the following steps. First, a uranium nitrate solution is prepared by dissolving uranium oxide powder in nitric acid. Subsequently, water and a thickener are added to this uranyl nitrate solution and mixed by stirring to prepare a stock solution for producing ammonium biuranium particles. A thickener is a substance that is added so that droplets of a raw solution for producing ammonium heavy uranate particles dropped into an aqueous ammonia solution, which will be described later, become spherical due to its surface tension during dropping.

  Examples of the thickener include polyvinyl alcohol, tetrahydrofurfuryl alcohol, polyethylene glycol, and metroses. After the viscosity of the stock solution for producing ammonium heavy uranate particles prepared in this way is adjusted by cooling to a predetermined temperature, this nozzle is preferably removed from the nozzle with a small diameter of the stock drop device. It is dripped in the ammonia aqueous solution in the ammonia aqueous solution storage tank by vibrating.

  The aqueous ammonia solution in the ammonia aqueous solution storage tank is located above the lower side of the aqueous ammonia solution tank so that the lower droplet particles do not deform due to the load of the upper liquid droplet particles due to the accumulation of droplet particles in the aqueous ammonia solution. It is circulating towards. In this aqueous ammonia storage tank, uranyl nitrate reacts with ammonia to form ammonium heavy uranate, and ammonium heavy uranate-containing coarse particles mainly composed of ammonium heavy uranate are obtained.

  The coarse particles containing ammonium heavy uranate formed in the ammonia aqueous solution storage tank are transferred to a post-treatment device connected to the ammonia aqueous solution storage tank. The transfer of the ammonium heavy uranate-containing coarse particles to the post-treatment device is usually performed by opening a valve of a pipe connecting the aqueous ammonia solution storage tank and the post-treatment device and dropping it together with the aqueous ammonia solution by its own weight. In this post-treatment device, while rotating the post-treatment tank, by heating, the uranyl nitrate and ammonia are completely reacted to the center of the particles to produce ammonium heavy uranate (ripening treatment), heavy uranic acid with hot water, etc. It is an apparatus which performs the process (cleaning process) which wash | cleans an ammonium particle, and the process (drying process) which dries.

  Ammonium heavy uranate particles that have been aged, washed and dried are roasted in the atmosphere to form uranium trioxide particles. Further, the uranium trioxide particles are reduced and sintered to become high-density ceramic-like uranium dioxide particles. The uranium dioxide particles thus formed are classified and obtained as fuel core fine particles having a predetermined particle diameter.

  The fuel core particles obtained in this way are loaded onto a fluidized bed and coated by thermally decomposing the coating gas. For example, the first layer can be formed by pyrolyzing acetylene at about 1400 ° C., and the second and fourth layers can be formed by pyrolyzing propylene at about 1400 ° C. it can. For example, the third layer can be formed by thermally decomposing methyltrichlorosilane at about 1600 ° C. A normal fuel compact can be manufactured by press-molding or molding coated fuel particles into a hollow cylindrical shape or a medium-density cylindrical shape together with a graphite matrix material made of graphite powder and a binder, and then firing. (See Non-Patent Documents 1 and 2).

"Reactor Material Handbook" p221-p247, published October 31, 1977, published by Nikkan Kogyo Shimbun "Nuclear Power Handbook" p161-p169, issued on December 20, 1995, Ohm Corporation

  By the way, when preparing a uranyl nitrate-containing stock solution using uranium oxide containing uranium having a concentration of 5% or less, the mass limiting method is often adopted as a critical safety measure, but the concentration is reduced to 10%. When a uranyl nitrate-containing stock solution is prepared using uranium oxide containing more uranium, a safer shape limitation may be imposed.

  The preparation tank of the uranyl nitrate-containing stock solution in which the shape restriction is imposed, when using uranium with a concentration of 10% or less, when the preparation tank is a cylinder, its diameter is, for example, 19.8 cm or less, When 20% or less of uranium is used and the preparation tank is a cylinder, the diameter is, for example, 17.4 cm or less. However, since the dimensional limit value in the shape restriction becomes smaller as the uranium becomes highly enriched, the device for producing the fuel core becomes an elongated cylindrical shape.

  There is a problem that it is extremely difficult to prepare a uranyl nitrate-containing stock solution by uniformly mixing a uranyl nitrate solution and a thickener in an elongated cylindrical preparation tank. This is because, for example, when it is assumed that a stirring blade is inserted into an elongated cylindrical preparation tank to stir the liquid in the preparation tank, the stirring rotation almost reaches from one end to the other end of the elongated cylindrical preparation tank. It is conceivable to install a plurality of stirring blades on the shafts at the required locations of the stirring rotation shaft, but the stirring blades collide with the inner wall in the preparation tank by rotating the stirring rotation shaft due to the rotation of the stirring rotation shaft. If a stirrer rotating shaft with a short shaft length is adopted, the stirring by the stirring blade becomes local and smooth stirring cannot be expected in the entire preparation tank. It is clear from this.

  The present invention eliminates such conventional problems and efficiently uses a uranyl nitrate-containing stock solution having highly enriched uranium for producing ammonium heavy uranate particles useful for the production of fuel nuclei for high-temperature gas reactor fuels. It is an object of the present invention to provide a method for preparing a uranyl nitrate-containing stock solution and a uranyl nitrate-containing stock solution preparation device that can be well prepared.

As means for solving the above problems,
Claim 1 is that the uranyl nitrate solution prepared from uranium oxide and nitric acid and a thickener are housed in a shape-restricted preparation tank, and the preparation is performed by a circulation channel provided outside the preparation tank. A method for preparing a uranyl nitrate-containing stock solution, characterized in that the contents of the tank are transferred from the lower part of the preparation tank to the upper part of the preparation tank via the circulation channel,
Claim 2 is the method for preparing the uranyl nitrate-containing stock solution according to claim 1, wherein the circulation channel is equipped with a static mixer.
The third aspect of the present invention is a shape-restricted preparation tank that can contain a uranyl nitrate solution prepared from uranium oxide and nitric acid and a thickener, a lead-out opening 5 that opens at the bottom of the preparation tank, and the preparation tank An apparatus for preparing a uranyl nitrate-containing stock solution, characterized in that it comprises a circulation channel provided outside the preparation tank so as to communicate with an introduction opening that opens at the top of
A fourth aspect of the present invention provides the apparatus for preparing a uranyl nitrate-containing stock solution according to the third aspect, wherein the circulation channel is equipped with a static mixer.

  According to this invention, the uranyl nitrate solution and the thickener are accommodated in a shape-restricted preparation tank, and the contained uranyl nitrate solution and the thickener are extracted from the preparation tank and introduced into the circulation flow path. The uranyl nitrate solution and the thickener led to the passage are introduced into the preparation tank from the upper part of the preparation tank, whereby the contents contained in the preparation tank are circulated through the preparation tank and the circulation channel. A method for preparing a containing stock solution and an apparatus for preparing a stock solution containing uranyl nitrate are provided. Thus, by circulating the uranyl nitrate solution and the thickener in the preparation tank and the circulation channel, the mixing of the uranyl nitrate solution and the thickener smoothly proceeds, and the uniformly mixed uranyl nitrate-containing stock solution is obtained. It is prepared efficiently.

  In addition, if a static mixer is provided in the middle of the circulation flow path, this static mixer itself does not have a power source, and only mixes uranyl nitrate and thickener by passing through the static mixer. A method and apparatus for preparing a uranyl nitrate-containing stock solution capable of uniformly mixing uranyl nitrate and a thickener more efficiently than simply circulating and moving uranyl nitrate and a thickener. Is provided.

  FIG. 1 is a diagram showing an apparatus for preparing a uranyl nitrate-containing stock solution (hereinafter, “a device for preparing a uranyl nitrate-containing stock solution” may be simply abbreviated as “stock solution preparing apparatus”) as an example of the present invention. is there.

  As shown in FIG. 1, the stock solution preparation apparatus 1 includes a stock solution preparation tank 2 and a circulation transfer pipe 3 that is a circulation channel. The stock solution preparation tank 2 is an elongated bottomed cylindrical body whose shape is limited. A stirrer 4 that is rotated by a drive source (not shown) such as a motor is disposed inside the stock solution preparation tank 2. The stirrer 4 is not limited in its shape and structure as long as the contents of the stock solution preparation tank 2 can be stirred, and examples thereof include a propeller stirrer and a paddle stirrer. A plurality of the stirring bars 4 are usually used, but are not necessarily restricted to a plurality.

  In FIG. 1, two sets of stirrers 4 are mounted on a rotating shaft with a short rotating shaft, but in order to smoothly mix the uranyl nitrate solution and the thickener solution, the elongated stock solution is prepared. Of course, it is preferable to attach a large number of stirring bars to a long rotating shaft over the entire length of the tank 2. However, attaching a large number of stir bars to the elongated stock solution preparation tank 2 with a limited shape is extremely complicated both technically and from the work. Further, when a large number of stirring bars 4 are attached to a long rotating shaft, the stirring bars come into contact with the inner wall of the stock solution preparation tank 2 due to swinging or vibration of the rotating shaft, and the stirrer and the inner wall of the stock solution preparation tank 2 are damaged. On the other hand, the smooth mixing of the uranyl nitrate solution and the thickener solution is inhibited. For this reason, a few stirring bars must be attached to the relatively short rotating shaft, and stirring may not be performed smoothly.

  The stock solution preparation tank 2 which is the bottomed cylindrical body having a limited shape, for example, mixes a uranyl nitrate solution prepared from uranium oxide containing uranium having a concentration of 10% or less and a thickener solution. The inner diameter is 19.8 cm or less, and when the uranyl nitrate solution prepared from uranium oxide containing 20% or less of uranium and the thickener solution are mixed, the inner diameter is 17.4 cm or less. It is preferable to be designed from the viewpoint of critical safety measures. Moreover, the stock solution preparation tank 2 which is this bottomed cylindrical body has a large axial direction length, for example, 1.5-4 m can be mentioned as an example of the axial direction length.

  The circulation transfer pipe 3 includes a lead-out opening 5 that opens to the bottom surface of the stock solution preparation tank 2 and an introduction opening 6 that opens to the top of the stock solution preparation tank 2, which are external to the stock solution preparation tank 2. Is provided. It is desirable that the circulating transfer pipe 3 also has an inner diameter subjected to shape restriction. The circulating transfer pipe 3 has a static mixer 7 interposed in the middle of the pipe.

  The static mixer 7 is a static mixer that can effectively mix fluids by the action of division, conversion, and inversion, and a known static mixer can be adopted. Generally, a static mixer is a static pipe stirrer in which a plurality of elements that cause a liquid split flow are inserted into a pipe, and stirring is performed during liquid feeding by the split flow of the processing liquid and the turbulent flow generated by the action. is there. It is desirable that the pipe body forming the pipe line in the static mixer 7 has an inner diameter subjected to shape restriction. The number of elements loaded in the static mixer 7 is appropriately determined according to the scale of the stock solution preparation apparatus 1.

  On the upstream side of the static mixer 7 in the circulation transfer pipe 3, fluid forced transfer means 8 forcibly transferring the fluid existing in the circulation transfer pipe 3 in the circulation transfer pipe 3, and uranyl nitrate solution supply means 9. And the thickener solution supply means 10 are combined.

  The fluid forced transfer means 8 includes, for example, a first pump 11. When the first pump 11 is driven, the fluid in the stock solution preparation tank 2 is introduced into the circulation transfer pipe 3 from the outlet opening 5 and is forcedly transferred through the circulation transfer pipe 3. A first on-off valve 12 for opening and closing the flow path of the circulation transfer pipe 3 is interposed between the first pump 11 and the outlet opening 5 in the circulation transfer pipe 3, and the first pump 11 and the static mixer A second opening / closing valve 13 for opening / closing the flow path of the circulation transfer pipe 3 is interposed between the second opening / closing valve 13 and the circulation transfer pipe 3.

  The uranyl nitrate solution supply means 9 comprises a dissolution tank 2A for preparing uranyl nitrate by dissolving uranium oxide in nitric acid, and a uranyl nitrate solution prepared in the dissolution tank 2A. The uranyl nitrate solution transfer pipe 14 is connected upstream so as to be injected between the static mixer 7 and the second on-off valve 13, and is interposed in the middle of the uranyl nitrate solution transfer pipe 14. The uranyl nitrate solution stored in the dissolution tank 2A is caused to flow out into the uranyl nitrate solution transfer pipe 14, or the third on-off valve 15 is opened and closed to prevent the outflow, and the uranyl nitrate solution supplied from the dissolution tank 2A. Between the second pump 16 that forcibly transports the liquid toward the circulation transfer pipe 3 and the circulation transfer pipe 3 of the uranyl nitrate solution transfer pipe 14. And a fourth on-off valve 17. When the highly concentrated uranium is used, the dissolution tank 2A is preferably an apparatus having a shape limit or a mass limit. In addition, the uranyl nitrate solution transfer pipe 14 is preferably a pipe having an inner diameter having a shape restriction if a uranyl nitrate solution prepared from highly enriched uranium oxide and nitric acid is circulated.

  The thickener solution supply means 10 supplies the thickener tank 18 for preparing the thickener solution and the thickener solution stored in the thickener tank 18 to the static mixer 7 in the circulation transfer pipe 3. A thickener solution transfer pipe 19 supplied to the upstream side and the downstream side of the second on-off valve 13 and a thickener in the thickener tank 18 interposed in the middle of the thickener solution transfer pipe 19. A third pump 20 for forcibly transferring the solution to join the circulation transfer pipe 3 and a thickener solution transfer pipe 19 are provided to enable or disable the flow of the thickener solution. 5 on-off valve 21.

  A method for preparing a uranyl nitrate-containing stock solution using the stock solution preparation apparatus 1 having the above-described configuration is as follows.

  As shown in FIG. 1, first, a uranium nitrate solution is prepared by dissolving uranium oxide in nitric acid in a dissolution tank 2A. Examples of the uranyl nitrate solution include a solution obtained by dissolving uranium oxide derived from uranium having a concentration degree exceeding 10% in nitric acid.

  There is no particular limitation on the conditions for preparing a uranyl nitrate solution by dissolving highly concentrated uranium oxide in nitric acid. For example, when uranium is 4 kg, the molar ratio of uranium and nitric acid is 1: 2.5. It is prepared by mixing at 100 ° C. for 30 minutes or more.

  On the other hand, in the thickener tank 18, a thickener and a solvent are mixed to prepare a thickener solution. Examples of the thickener include polyvinyl alcohol, tetrahydrofurfuryl alcohol, polyethylene glycol, and metroses. Examples of the solvent include water such as pure water. The concentration of the thickener in the thickener solution depends on the type of thickener used and cannot be determined uniformly, but it is good in the formation process of forming ammonium deuterated uranate particles in the aqueous ammonia storage tank in the subsequent process. It is desired to adjust the concentration so that the ammonium uranate particles having a high sphericity can be formed.

For example, when the viscosity of the uranyl nitrate-containing stock solution dropped into the aqueous ammonia storage tank is 15 ° C., 4.0 × 10 ^{−2 to} 6.5 × 10 ⁻² Pa. A thickener solution is added so that it may become S, and uranium density | concentration can be made into 0.6-0.9 ml-U / l.

  Next, the third on-off valve 15 and the fourth on-off valve 17 are opened, and the first on-off valve 12, the second on-off valve 13 and the fifth on-off valve 21 are closed, and the uranyl nitrate solution prepared as described above is used. The second pump 16 is driven to flow into the circulation transfer pipe 3 through the uranyl nitrate solution transfer pipe 14. At this time, the first pump 11 and the third pump 20 are in a drive stop state. Thus, the uranyl nitrate solution is injected into the stock solution preparation tank 2. The injection of the uranyl nitrate solution into the stock solution preparation tank 2 is performed until the stock solution preparation tank 2 will become full when the thickener solution is further injected, that is, the amount of the thickener solution to be described later can be injected. The uranyl nitrate solution is poured into the stock solution preparation tank 2 at the upper limit.

  When a predetermined amount of uranyl nitrate solution is transferred to the stock solution preparation tank 2, the fifth on-off valve 21 is opened thereafter, and the first on-off valve 12, the second on-off valve 13, the third on-off valve 15, and the fourth on-off valve are opened. With the valve 17 closed, the third pump 20 is driven and the thickener solution transfer pipe 19 flows the thickener solution into the circulation transfer pipe 3. At this time, the first pump 11 and the second pump 16 are in a drive stop state. The thickener solution flowing into the circulation transfer pipe 3 passes through the static mixer 7. Although the fluid that passes through the static mixer 7 is one type of thickener solution, the residue of the uranyl nitrate solution that was previously passed is present in the static mixer 7. Mixing with the agent solution is performed. However, the mixing of the uranyl nitrate solution and the thickener solution by the static mixer 7 at this stage is not the mixing of the uranyl nitrate solution and the thickener solution which the present invention intends to achieve. Partly contributes to uniform mixing with the viscous solution. The thickener solution that has passed through the static mixer 7 further passes through the circulation transfer pipe 3 and reaches the stock solution preparation tank 2.

  The uranyl nitrate solution and the thickener solution supplied to the stock solution preparation tank 2 are stirred by rotating the stirring bar 4 in the stock solution preparation tank 2. The stirring treatment conditions at this time are not particularly limited. For example, 1 volume part of uranyl nitrate solution and 2 volume parts of thickener solution are at 5 to 25 ° C., for example, uranyl nitrate solution and thickener solution. Depending on the total amount, for example, stirring may be mentioned for 30 to 120 minutes.

  As explained in the section of the prior art, it is difficult to uniformly mix the uranyl nitrate solution and the thickener solution in a short time only by rotating the stirring bar 4 in the stock solution preparation tank 2. is there. In the stock solution preparation apparatus 1 according to an embodiment of the present invention, the contents 22 in the stock solution preparation tank 2 are forcibly introduced into the circulation transfer pipe 3 and formed by the stock solution preparation tank 2 and the circulation transfer pipe 3. By circulating the contents 22 of the stock solution preparation tank 2 through the circulation path, uniform mixing of the uranyl nitrate solution and the thickener solution is achieved within a short time.

  That is, the contents 22 in the stock solution preparation tank 2 are circulated as follows.

  The first on-off valve 12 and the second on-off valve 13 are opened, the third on-off valve 15, the fourth on-off valve 17 and the fifth on-off valve 21 are closed, and the second pump 16 and the third pump 20 are stopped. When the first pump 11 is driven in the state, the contents 22 of the stock solution preparation tank 2 in which the uranyl nitrate solution and the thickener solution are stirred open to the lower part of the stock solution preparation tank 2. 5 into the circulating transfer pipe 3. When the contents 22 are taken out from the lower part of the stock solution preparation tank 2 and the contents 22 are put into the stock solution preparation tank 2 from the introduction opening 6 of the circulation transfer pipe 3 located at the upper part of the stock solution preparation tank 2, Since the mixing effect is exerted by the impact of time, the uranyl nitrate solution and the thickener solution are mixed in a uniform solution in a short time in combination with the stirring effect by the stirring bar 4. In the stock solution preparation apparatus 1 shown in FIG. 1, since the static mixer 7 is interposed in the circulation transfer pipe 3, the mixing of the uranyl nitrate solution and the thickener solution is further promoted. That is, the content 22 introduced into the circulation transfer pipe 3 is further mixed by the static mixer 7 and reaches the stock solution preparation tank 2 again from the introduction opening 6. When such circulation is repeated, the uranyl nitrate solution and the thickener solution are mixed to form a uniform uranyl nitrate-containing stock solution within a short time.

  As a specific example of the stock solution preparation apparatus of the present invention, not only the stock solution preparation apparatus 1 having the device configuration shown in FIG. 1 but also a stock solution preparation apparatus 1A shown in FIG.

  2 differs from the stock solution preparation apparatus 1 shown in FIG. 1 in that the stock solution preparation tank 2 shown in FIG. 1 has a thickener solution connected to the circulation transfer pipe 3. There is no thickener solution supply means 10 having the transfer pipe 19, and the thickener solution transfer pipe opened at the upper part of the stock solution preparation tank 2 so that the thickener solution can be supplied directly to the stock solution preparation tank 2. The thickener solution supply means 10A provided with 19 is provided. In FIG. 2, the same members or means as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

  In this stock solution preparation apparatus 1A, a uranyl nitrate-containing stock solution is prepared as follows.

  First, a highly concentrated uranium oxide is dissolved in nitric acid in a dissolution tank 2A to prepare a uranyl nitrate solution. The conditions at this time are the same as described above. Next, the third on-off valve 15 and the fourth on-off valve 17 are opened, and the second on-off valve 13 is closed, and the uranyl nitrate solution prepared as described above is driven by the second pump 16 to drive the uranyl nitrate solution. The uranyl nitrate solution poured into the circulating transfer pipe 3 through the transfer pipe 14 passes through the static mixer 7 and is transferred to the stock solution preparation tank 2.

  After the uranyl nitrate solution is poured into the stock solution preparation tank 2 or while the uranyl nitrate solution is poured into the stock solution preparation tank 2, the thickener solution is supplied from the thickener solution supply means 10A to the stock solution preparation tank 2. It is supplied to the preparation tank 2.

  In the stock solution preparation tank 2, the stirring element 4 is rotated to stir the uranyl nitrate solution and the thickener solution. The stirring conditions at this time are the same as described above. The contents 22 of the stock solution preparation tank 2 obtained by stirring the uranyl nitrate solution and the thickener solution are transferred to the circulation transfer pipe 3 as follows. That is, when driving of the first pump 11 is started with the first on-off valve 12 and the second on-off valve 13 opened, and the third on-off valve 15 and the fourth on-off valve 17 closed, the lower part of the stock solution preparation tank 2 The contents 22 of the stock solution preparation tank 2 are extracted from the outlet opening 5 of the circulation transfer pipe 3 to the circulation transfer pipe 3 and are transferred through the circulation transfer pipe 3 by driving the first pump 11.

  The contents 22 moving in the circulation transfer pipe 3 are further sufficiently mixed by the static mixer 7, and the liquid that has passed through the static mixer 7 is introduced to the upper part of the stock solution preparation tank 2. 6 is returned to the stock solution preparation tank 2. The uranyl nitrate solution and the thickener solution supplied to the stock solution preparation tank 2 are introduced into the stock solution preparation tank 2 from the upper part of the stock solution preparation tank 2 by the circulation transfer pipe 3, and the introduced liquid is supplied to the circulation transfer pipe 3. By repeating the circulation such as being led out, the uranyl nitrate solution and the thickener solution are mixed to form a uniform solution within a short time.

  In the present invention, the circulation channel is provided in spite of the provision of the stirrer 4 capable of stirring a part of the content liquid at a predetermined position in the stock solution preparation tank whose shape is limited. In comparison, a uranyl nitrate-containing stock solution can be uniformly prepared in a stock solution preparation tank having a larger axial length.

  The uranyl nitrate-containing stock solution prepared by the stock solution preparation apparatus according to the present invention is dropped into an aqueous ammonia solution, and the uranyl nitrate and ammonia in the dropped droplets react to form ammonium deuterated uranate particles. The

  Ammonium heavy uranate particles thus formed are aged, washed and dried to become ammonium heavy uranate particles, and the ammonium heavy uranate particles are roasted in the air to become uranium trioxide particles. . Further, the uranium trioxide particles are reduced and sintered to become high-density ceramic-like uranium dioxide particles. The uranium dioxide particles are classified and obtained as fuel core fine particles having a predetermined particle diameter.

  An experimental operation using uranium cannot be carried out arbitrarily and in a short period of time for a patent application under circumstances where permission from the supervisory authority must be obtained. For this reason, the mixability of the uranyl nitrate solution and the thickener solution was evaluated by a simulation experiment using the stock solution preparation apparatus 1 shown in FIG. At this time, water was used as the uranyl nitrate solution and a polyvinyl alcohol aqueous solution (hereinafter referred to as “PVA aqueous solution”) was used as the thickener solution.

(Simulation 1)
This simulation 1 corresponds to the first embodiment. First, water (viscosity 1 cP) stored in the dissolution tank 2A is opened to the third on-off valve 15 and the fourth on-off valve 17, and the first on-off valve 12, the second on-off valve 13 and the fifth on-off valve 21 are In the closed state, the second pump 16 was driven and transferred to the stock solution preparation tank 2 (inner diameter 150 mm, height 2000 mm, bottomed cylindrical shape) through the uranyl nitrate solution transfer pipe 14. At this time, the stirring bar 4 is not driven.

  Next, the fifth on-off valve 21 is opened, and the third pump 20 is driven with the first on-off valve 12, the second on-off valve 13, the third on-off valve 15 and the fourth on-off valve 17 closed. The PVA aqueous solution was supplied to the stock solution preparation tank 2 through the thickener solution transfer pipe 19, and the total amount of water and the PVA aqueous solution was 24L. At this time, the PVA aqueous solution contained 300 g of polyvinyl alcohol and 10.8 L of tetrahydrofurfuryl alcohol.

  Water and PVA aqueous solution supplied to the stock solution preparation tank 2 are fed into the stock solution preparation tank 2 at 150 rpm by means of a stirrer 4 having a propeller-like stirring blade at a rotational drive mechanism, for example, a motor (not shown). The mixture was rotated and mixed at 15 ° C., and water and an aqueous PVA solution were stirred.

  Subsequently, the mixture of the prepared water and the PVA aqueous solution is a stock solution preparation tank in a state where the first on-off valve 12 and the second on-off valve 13 are opened and the fourth on-off valve 17 and the fifth on-off valve 21 are closed. 2 is extracted from the lead-out opening 5 that opens at the lower part of 2 and the first pump 11 is driven to supply the static mixer 7 (the number of elements is 21) by the circulating transfer pipe 3 at a liquid feeding speed of 3 L / min. Then, the mixing state in the mixture of water and the aqueous PVA solution is further enhanced, and further, the contents 22 in the stock solution preparation tank 2 are repeatedly circulated through the stock solution preparation tank 2 and the circulation transfer pipe 3 to obtain a uranyl nitrate-containing stock solution. A corresponding aqueous solution was prepared.

  From the initial mixing process in the stock solution preparation tank 2 to the circulating mixing process of the mixed solution of water and PVA aqueous solution, the first pump 11 is stopped and the feeding is stopped, and then the stock solution preparation tank 2 is stopped. Three samples of the mixed solution were taken from the lower part of the sample every 20 minutes, the viscosity of each sample was measured, and the quality of the mixed state was evaluated by the change in the viscosity. As a result, when 20 minutes passed after the start of the initial mixing process, it was visually confirmed that the mixed solution was very homogeneous and there was no inhomogeneous phase. From the result, it was confirmed that the above state was observed.

(Simulation 2)
This simulation 2 corresponds to the second embodiment. The same operation as in the simulation 1 was performed except that the static mixer 7 was not interposed in the circulation transfer pipe 3 in the simulation 1. As a result, although a slight heterogeneous phase is observed when 20 minutes have elapsed after the start of the initial mixing process, it is visually confirmed that the mixed solution is almost homogeneous, and even when 40 minutes have elapsed. From the result of the viscosity measurement, it was confirmed that the above state was obtained.

(Simulation 3)
This simulation 3 corresponds to a comparative example. In the stock solution preparation apparatus 1 shown in FIG. 1, the first on-off valve 12 and the second on-off valve 13 are closed all the time until the preparation of the mixed solution of water and the PVA aqueous solution is completed, and the first pump 11 is also always on-hand. Without being driven, the liquid mixture of the water and the PVA aqueous solution supplied to the stock solution preparation tank 2 was continuously stirred with the stirring bar 4.

  The water in the dissolution tank 2A and the PVA aqueous solution in the thickener tank 18 were prepared in the same manner as in the simulation 1. Further, the rotation speed of the stirring bar 4 in the stock solution preparation tank 2 is the same as in the simulation 1.

  By visual observation and viscosity measurement similar to those of simulation 1, the quality of the mixed state of the mixed solution of water and the aqueous PVA solution was evaluated. As a result, it took about 5 hours until a homogeneous mixed solution equivalent to simulation 2 was prepared.

FIG. 1 is a view showing a stock solution preparation apparatus which is an example of the present invention. FIG. 2 is a view showing a stock solution preparation apparatus which is another example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stock solution preparation apparatus 1A Stock solution preparation apparatus 2 Stock solution preparation tank 2A Dissolution tank 3 Circulation transfer pipe 4 Stirrer 5 Outlet opening 6 Introduction opening 7 Static mixer 8 Fluid forced transfer means 9 Uranyl nitrate solution supply means 10 Thickener solution supply Means 10A Thickener solution supply means 11 First pump 12 First on-off valve 13 Second on-off valve 14 Uranyl nitrate solution transfer pipe 15 Third on-off valve 16 Second pump 17 Fourth on-off valve 18 Thickener tank 19 Thickening Agent solution transfer pipe 20 Third pump 21 Fifth on-off valve 22 Contents

Claims (4)

  A uranyl nitrate solution prepared from uranium oxide and nitric acid and a thickener are housed in a shape-restricted preparation tank body, and the circulation path provided outside the preparation tank body allows the preparation tank body to A method for preparing a uranyl nitrate-containing stock solution, wherein the contents are transferred from the lower part of the preparation tank body to the upper part of the preparation tank body through the circulation channel.   The method for preparing a uranyl nitrate-containing stock solution according to claim 1, wherein the circulation channel is equipped with a static mixer.   A shape-restricted preparation tank body capable of containing a uranyl nitrate solution prepared from uranium oxide and nitric acid and a thickener, a lead-out opening opening at the bottom of the preparation tank body, and an upper part of the preparation tank body An apparatus for preparing a uranyl nitrate-containing stock solution, comprising: a circulation channel provided outside the preparation tank main body so as to communicate with an introduction opening that opens.   4. The apparatus for preparing a uranyl nitrate-containing stock solution according to claim 3, wherein the circulation channel is equipped with a static mixer.

Images