JP2006143520A - Uranyl nitrate solution preparation device and uranyl nitrate solution preparation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an uranyl nitrate solution preparation device and an uranyl nitrate solution preparation method capable of promoting the dissolution of uranium oxide in nitric acid. <P>SOLUTION: The means for solving the above problem is an uranyl nitrate solution preparation device, in an uranyl nitrate solution preparation device 1 comprising a preparation tank body 2 of preparing an uranyl nitrate solution from uranium oxide and nitric acid, provided with an inert gas feeding means 3 of feeding an inert gas from the side of the lower part 2G of the preparation tank body. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a uranyl nitrate solution preparation device and a uranyl nitrate solution preparation method, and more particularly to a uranyl nitrate solution preparation device and a uranyl nitrate solution preparation method capable of promoting dissolution of uranium oxide in nitric acid.

  According to Non-Patent Documents 1 to 5, HTGR fuel is generally manufactured through the following steps. First, uranium oxide powder is dissolved in nitric acid to form a uranyl nitrate solution. Next, pure water, a thickener and the like are added to the uranyl nitrate solution and stirred to obtain a uranyl nitrate-containing stock solution. The prepared uranyl nitrate-containing stock solution is cooled to a predetermined temperature, adjusted to a viscosity, and then dropped into an aqueous ammonia solution using a small-diameter dropping nozzle.

  The droplets dropped on the aqueous ammonia solution are sprayed with ammonia gas before reaching the surface of the aqueous ammonia solution. The surface of the droplet is gelled by the ammonia gas, thereby preventing deformation when reaching the surface of the aqueous ammonia solution. Uranyl nitrate in the aqueous ammonia solution sufficiently reacts with ammonia to form ammonium heavy uranate particles (hereinafter sometimes abbreviated as “ADU particles”).

  The ammonium deuterated uranium particles are dried and then roasted in the atmosphere to contain more oxygen than uranium dioxide, resulting in uranium oxide having an oxygen: uranium molar ratio greater than 2, eg, uranium trioxide, Reduction and sintering result in high density ceramic uranium dioxide particles. The uranium dioxide particles are sieved, that is, classified to obtain fuel nuclei having a predetermined particle size.

The fuel nuclei are loaded onto a fluidized bed, and coating is performed by thermally decomposing the coating gas. The coating layer is formed by coating the first layer, the second layer, the third layer, and the fourth layer from the fuel core surface. In the case of the first layer of low density carbon, it is obtained by pyrolyzing acetylene (C ₂ H ₂ ) at about 1400 ° C. In the case of the high density pyrolytic carbon of the second layer and the fourth layer, it is obtained by pyrolyzing propylene (C ₃ H ₆ ) at about 1400 ° C. In the case of SiC of the third layer, it is obtained by thermally decomposing methyltrichlorosilane (CH ₃ SiCl ₃ ) at about 1600 ° C.

  In general fuel compacts, the coated fuel particles obtained as described above are pressed or molded into a hollow cylindrical shape or cylindrical shape together with a graphite matrix material made of graphite powder, binder, etc., and then fired. Obtained.

S. Kato "Fabrication of HTTR First Loading fuel", IAEA-TECCDOC-1210, 187 (2001) N. Kitamura "Present status of initial core fuel fabrication for the HTTR" IAEA-TECCDOC-988, 373 (1997) Kimio Hayashi, “High Temperature Engineering Test Reactor Design Policy, Manufacturability and Comprehensive Soundness Evaluation” JAERI-M 89-162 (1989) Kazuo Tsuji, “Development of Advanced Technology for HTGR Fuel Production” JAERI-Research 98-070 (1998) Hasegawa Masayoshi, Mishima Yoshimi supervision "Reactor Material Handbook", published on October 31, 1977, pages 221-247, Nikkan Kogyo Shimbun

  On the other hand, when manufacturing nuclear fuel using nuclear fuel materials such as uranium, as a method to prevent criticality accidents, in general, the "mass limit" that the amount of uranium handled is less than the critical mass, and the amount of uranium is Regardless of the shape and dimensions that do not cause criticality, the “shape restriction” handles uranium.

  In the case of “mass restriction”, the maximum handling amount for uranium of 10% by mass or less is 9.6 kg, and the maximum handling amount for uranium of 20% by mass or less is 4.0 kg. Therefore, the batch size in each manufacturing process needs to be below these values. Further, from the viewpoint of safety, considering the case of double loading by mistake, the batch size in each manufacturing process needs to be 1/2 or less of these values. Therefore, the productivity of nuclear fuel deteriorates and it cannot be said that it is suitable as a criticality management method for mass production facilities.

  On the other hand, in the case of “shape restriction”, the size defined by the enrichment and shape of uranium varies. For example, the size of the storage equipment for uranium of 10% by mass or less is 19.8 cm or less in the diameter of the cylinder when the shape of the storage equipment is cylindrical, and when the shape of the storage equipment is flat, The thickness is 8.3 cm or less.

  Further, the size of the storage facility for uranium of 20% by mass or less is 17.4 cm or less in the diameter of the cylinder when the shape of the storage facility is a cylindrical shape, and when the shape of the storage facility is a flat plate, The thickness is 6.7 cm or less.

  Since there is no limit to the amount of uranium handled in these storage facilities, “shape limitation” is preferable as a criticality management method for mass production facilities. However, as described above, since the dimensional limit value in the “shape limit” becomes smaller as the uranium becomes highly enriched, the facility for manufacturing the fuel core must be an elongated cylindrical shape or a thin flat plate shape. Absent.

  For example, in the step of dissolving uranium oxide powder in nitric acid to form a uranyl nitrate solution, stirring is performed with a propeller, fin, etc. in order to dissolve uranium oxide powder which is difficult to dissolve in nitric acid under “mass restricted” conditions. . In addition, since the container has an elongated cylindrical shape or a thin flat plate shape under the “shape restriction” condition, even if stirring is performed with a propeller or the like, the effect of stirring is limited to a part of the region. As a result, undissolved uranium oxide powder is generated, and as a result, a predetermined concentration and concentration solution cannot be obtained, which causes variations in the quality of fuel nuclei. In particular, when obtaining uranium oxide powders having two or more kinds of enrichment in order to obtain a predetermined enrichment and dissolving it in nitric acid, the undissolved residue becomes a problem.

  Furthermore, NOx gas is generated when the uranium oxide powder is dissolved in nitric acid. Most of the generated NOx is sucked into the scrubber and processed, but part of the NOx gas dissolves in nitric acid. When the NOx gas dissolved in nitric acid reaches the dissolution equilibrium, there is a problem that the dissolution rate of the uranium oxide powder becomes slow. This problem does not depend on the degree of enrichment, but it occurs, but it is a problem when uranium oxide powder is made of highly enriched uranium that becomes difficult to dissolve with nitric acid under the `` shape restriction '' condition. Becomes more important.

  An object of the present invention is to provide a uranyl nitrate solution preparation device and a uranyl nitrate solution preparation method capable of solving such conventional problems and promoting dissolution of uranium oxide in nitric acid.

As means for solving the problems,
The present invention provides an uranyl nitrate solution preparation device having a preparation tank body for preparing an uranyl nitrate solution from uranium oxide and nitric acid, and an inert gas supply means for supplying an inert gas from a lower side of the preparation tank body. An apparatus for preparing a uranyl nitrate solution,
Claim 2 is a method for preparing a uranyl nitrate solution for preparing a uranyl nitrate solution from uranium oxide and nitric acid, and mixing uranium oxide and nitric acid in a preparation tank body for preparing a uranyl nitrate solution from uranium oxide and nitric acid, An uranyl nitrate solution preparation method, wherein an inert gas is supplied from the preparation tank main body lower side.

  According to the present invention, first, when uranium oxide and nitric acid are introduced into the preparation tank body, nitric acid and uranium oxide are mixed and the reaction starts. This reaction generates NOx gas in addition to uranyl nitrate. Generation | occurrence | production of NOx gas will inhibit promotion of the reaction of uranyl nitrate. Here, since the inert gas is supplied from the lower side of the preparation tank main body so as not to reach the dissolution equilibrium of NOx gas, dissolution of uranium oxide in nitric acid can be promoted. Moreover, since the inert gas is supplied from the preparation tank main body lower side, the supplied inert gas raises the inside of the preparation tank main body. The rising inert gas can stir the liquid mixture in the preparation tank body by bubbling. Therefore, also in this respect, dissolution of uranium oxide in nitric acid can be promoted.

  Moreover, according to this invention, uranium oxide is thrown into the preparation tank main body, and nitric acid is thrown into the preparation tank main body in which the uranium oxide was accommodated. At this time, the reaction of uranium oxide and nitric acid starts, and in addition to uranyl nitrate, NOx gas is also generated. When this nitric acid is charged, a large amount of NOx gas is generated. Here, since the inert gas is supplied from the lower side of the preparation tank main body so as not to reach the dissolution equilibrium of NOx gas, dissolution of uranium oxide in nitric acid can be promoted. Moreover, since the inert gas is supplied from the preparation tank main body lower side, the supplied inert gas raises the inside of the preparation tank main body. The rising inert gas can stir the liquid mixture in the preparation tank body by bubbling. Therefore, also in this respect, dissolution of uranium oxide in nitric acid can be promoted.

  Hereinafter, a uranyl nitrate solution preparation apparatus according to an embodiment of the present invention will be described with reference to FIG. However, the uranyl nitrate solution preparation apparatus illustrated in FIG. 1 is an example of the present invention, and the uranyl nitrate solution preparation apparatus according to the present invention is not limited to the uranyl nitrate solution preparation apparatus illustrated in FIG. .

[Uranyl nitrate solution preparation equipment]
The uranyl nitrate solution preparation device 1 includes a preparation tank body 2 and an inert gas supply means 3.

  The preparation tank main body 2 only needs to be able to prepare a uranyl nitrate solution from uranium oxide and nitric acid. The preparation tank main body 2 should just be a cylindrical shape. Moreover, the cross-sectional shape in the direction perpendicular to the central axis of the preparation tank body 2 is not particularly limited, and examples thereof include a circular shape, an elliptical shape, and a polygonal shape. The material of the preparation tank body 2 is not particularly limited, and examples thereof include a stainless material having resistance to nitric acid and glass.

  An inlet 2B for introducing uranium oxide and nitric acid is formed in the preparation tank main body upper surface portion 2A. A charging pipe 2C for charging uranium oxide and nitric acid is connected to the charging port 2B. An exhaust pipe 2D that branches off from the input pipe 2C and exhausts the gas generated in the preparation tank body 2 is connected to the input pipe 2C. The input pipe 2C and the exhaust pipe 2D are provided with valves 2E and 2F, respectively. Although illustration is omitted, a gas suction means such as a scrubber is connected to the tip of the exhaust pipe 2D.

  The preparation tank main body lower part 2G is formed with a reduced diameter as it goes downward. A discharge pipe 2H and a gas supply pipe 2I branched from the discharge pipe 2H and connected to the preparation tank main body lower part 2G are connected. The discharge pipe 2H and the gas supply pipe 2I are provided with valves 2J and 2K, respectively. In addition, although illustration is abbreviate | omitted, the installation of the next process is connected to the tip of the discharge piping 2H.

  The inert gas supply means 3 supplies an inert gas from the preparation tank main body lower part 2G side. Specifically, the inert gas supply means 3 is connected to the gas supply pipe 2I. Examples of the inert gas used include nitrogen gas, argon gas, and air. Moreover, as the inert gas supply means 3, a nitrogen gas cylinder etc. can be mentioned.

  The preparation tank main body 2 is provided with a stirring flow generating means 4 and a temperature adjusting means 5.

  The stirring flow generating means 4 generates a stirring flow for stirring the mixed solution. Specifically, the stirring flow generating means 4 includes a fin 4A that rotates with respect to the central axis of the preparation tank main body 2, and a driving means that rotates the fin 4A, although not shown.

  In addition, as the stirring flow generating means 4, in addition to this, gas is supplied from the outside of the preparation tank main body 2 from the tangential direction of the preparation tank main body 2 to generate a stirring flow for stirring the mixed liquid. Good.

  The temperature adjusting means 5 adjusts the temperature of the mixed solution. The temperature control means 5 should just be provided in the part in which a liquid mixture exists at least. Examples of the temperature adjusting means 5 include an electric heater. In the present embodiment, the temperature adjusting means 5 is attached to the preparation tank main body 2 so as to cover the entire outer peripheral side of the preparation tank main body 2.

[Uranyl nitrate solution preparation method]
In the uranyl nitrate solution preparation method according to the present invention, uranium oxide and nitric acid are mixed in a preparation tank body 2 for preparing a uranyl nitrate solution from uranium oxide and nitric acid, and an inert gas is supplied from the preparation tank body lower part 2G side. It is a supply method.

  Here, uranium oxide and nitric acid to be added are in a molar ratio of uranium oxide: nitric acid = 1: 2.1 to 1: 2.5.

  Examples of uranium oxide include uranium dioxide, uranium trioxide, and uranium trioxide, and uranium octaoxide is particularly preferable.

  The specific procedure is described below. First, the valve 2E is opened, and uranium oxide is charged into the preparation tank body 2 through the charging pipe 2C. Next, nitric acid is charged into the preparation tank body 2 through the charging pipe 2C. Thus, when uranium oxide and nitric acid are put into the preparation tank main body 2, nitric acid and uranium oxide are mixed and the reaction starts. This reaction generates NOx gas in addition to uranyl nitrate. Generation | occurrence | production of NOx gas will inhibit promotion of the reaction of uranyl nitrate.

  When the nitric acid is charged, the valve 2K is opened and the valve 2J is closed. Then, the inert gas supply means 3 is operated to supply, for example, nitrogen gas as inert gas to the mixture from the preparation tank main body lower part 2G side through the gas supply pipe 2I and the discharge pipe 2H. . Then, the valve 2F is also opened, and a gas generated in the preparation tank body 2 is exhausted by operating a scrubber (not shown) or the like from the exhaust pipe 2D. Here, when nitrogen gas is supplied into the preparation tank body 2, the nitrogen gas is exhausted from the exhaust pipe 2D while introducing the generated NOx gas. Therefore, by supplying nitrogen gas from the preparation tank main body lower part 2G side, the generated NOx gas is also exhausted, so that the dissolution equilibrium of NOx gas is prevented, so that the dissolution of uranium oxide in nitric acid is promoted. Can do. Moreover, since nitrogen gas is supplied from the preparation tank main body lower part 2G side, the supplied nitrogen gas rises in the preparation tank main body 2. The rising nitrogen gas can stir the liquid mixture in the preparation tank main body 2 by bubbling. Therefore, also in this respect, dissolution of uranium oxide in nitric acid can be promoted.

  Although there is no particular limitation, after the nitric acid is added, the stirring flow generating means 4 is operated to generate a stirring flow for the mixed solution. This stirring flow further promotes dissolution of uranium oxide in nitric acid.

  Furthermore, the temperature is maintained at 90 to 100 ° C. by the temperature adjusting means 5. By maintaining in this temperature range, dissolution of uranium oxide in nitric acid further proceeds.

  When taking out the uranyl nitrate solution to the outside, first, the operation of the inert gas supply means 3, the stirring flow generation means 4 and the temperature adjustment means 5 is stopped, the valve 2J is opened, the valves 2E, 2F and Keep 2K closed. Thereafter, the uranyl nitrate solution is taken out through the discharge pipe 2H.

  In addition, a water-soluble polymer is added with respect to the obtained uranyl nitrate solution, Then, a pure water is added and it adjusts and adjusts a viscosity. The viscosity may be adjusted after the uranyl nitrate solution is taken out to the outside, or after the uranyl nitrate solution is prepared in the preparation tank body 2, a water-soluble polymer or the like is added to the uranyl nitrate solution as it is. You may do it.

  Examples of the water-soluble polymer include polyvinyl alcohol (hereinafter abbreviated as PVA), synthetic polymers such as sodium polyacrylate and polyethylene oxide, cellulose polymers such as carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, and ethyl cellulose, soluble starch, And starch-based polymers such as carboxymethyl starch, water-soluble natural polymers such as dextrin, and galactan.

  One of these various water-soluble polymers may be used alone, or two or more thereof may be used in combination. Among these, the synthetic polymer is preferable as the water-soluble polymer, and polyvinyl alcohol is particularly preferable.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications and improvements within a scope that can achieve the object of the present invention are included in the present invention.

FIG. 1 is a schematic view showing a uranyl nitrate solution preparation apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uranyl nitrate solution preparation apparatus 2 Preparation tank main body 2A Preparation tank main body upper surface part 2B Input port 2C Input pipe 2D Exhaust pipe 2E Valve 2F Valve 2G Preparation tank main body 2H Exhaust pipe 2I Gas supply pipe 2J Valve 2K Valve 3 Inert gas supply Means 4 Stirring flow generating means 5 Temperature adjusting means

Claims (2)

In a uranyl nitrate solution preparation device having a preparation tank body for preparing a uranyl nitrate solution from uranium oxide and nitric acid,
An uranyl nitrate solution preparation device comprising: an inert gas supply means for supplying an inert gas from the preparation tank main body lower side. In the uranyl nitrate solution preparation method of preparing a uranyl nitrate solution from uranium oxide and nitric acid,
A method for preparing a uranyl nitrate solution, comprising mixing uranium oxide and nitric acid in a preparation tank body for preparing a uranyl nitrate solution from uranium oxide and nitric acid, and supplying an inert gas from the lower side of the preparation tank body.

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