JP2642372B2 - Method for producing high-purity zirconium - Google Patents

Description

The present invention relates to a method for producing high-purity zirconium from zircaloy scrap by a halide decomposition method.

(Prior Art) At present, Zircaloy-2 is used for a fuel cladding tube of a boiling water reactor, but an improved boiling water reactor (A
−BWR), high-performance fuel cladding is being developed. The burn-up of the fuel in the A-BWR will increase, and a load following operation will be performed in order to further improve economic efficiency. At this time, what is considered to be the most problem is the interaction between the pellet and the clad. In other words, the high burnup and the rapid change in burnup cause deformation such as "swelling" or "warpage" of the nuclear fuel (pellet), and the fuel comes into contact with the fuel cladding tube (cladding) to apply a load to the fuel cladding. It is possible to promote the destruction of the pipe.

As one of the measures described above, a zirconium liner tube has been developed as a fuel cladding tube. This is Zircaloy-
2. Pure zirconium having a hardness lower than that of Zircaloy-2 is lined on the inner surface of the pipe 2 to absorb the load of the pellets by a cushion effect. This cushion effect is greater as the zirconium liner layer is softer. Therefore, the higher the purity of zirconium, the greater its effect. Commercially available reactor-grade sponge zirconium has many impurities such as oxygen, and its effect is low. On the other hand, it has been already clarified that when the liner layer is formed of high-purity zirconium that further produces sponge zirconium, the cushioning effect is the largest and the cladding tube can be kept healthy. Therefore, in the future, it is considered that a zirconium liner tube lined with high-purity zirconium will be used as a high-performance fuel cladding tube,
Its demand is also expected to be considerable.

The high-purity zirconium is produced from sponge zirconium as a raw material by a purification method usually called a halide decomposition method, particularly an iodide decomposition method. The iodide decomposition method is a kind of chemical transport method and is a method used for purifying active metals such as zirconium (Zr), titanium (Ti), and hafnium (Hf). Purification is performed by the following formula (1):
The reaction is performed using the reaction of (2).

Zr + 2I ₂ → ZrI ₄ (200-500 ° C.)… (1) ZrI ₄ → Zr + 2I ₂ (1100-1500 ° C.)… (2) That is, as shown in the above formula (1), zirconium (melting point)
1857 ℃) is iodine (melting point 114 ℃, boiling point 185 ℃) and 200 ~ 500
Reacts violently at a temperature of ℃ to produce sublimable solid zirconium tetraiodide (ZrI ₄ ). Furthermore, ZrI ₄ is 1100-15
It has the property of decomposing into zirconium and iodine at a high temperature of 00 ° C. as shown in the above formula (2). Specifically, conventionally, high-purity zirconium has been manufactured using the apparatus shown in FIG. Reference numeral 1 in the figure denotes a reaction vessel that contains sponge zirconium and iodine as raw materials. This container 1 contains 200
It is fixed in a constant temperature bath (or constant temperature furnace) 2 heated to 500 ° C. Inside the container 1, for example, a U-shaped filament 3 is suspended. Both ends of the filament 3 are connected to a power source 5 via power supply jigs 4a and 4b. In such an apparatus, sponge zirconium 6 and iodine 7, which are raw materials, are accommodated in a reaction vessel 1, and the filament 3 is electrically heated from a power supply 5 through power supply jigs 4a and 4b to maintain the temperature at about 1100 to 1500 ° C. Subsequently, the entire reaction vessel 1 is heated in a thermostat 2 and maintained at 200 to 400 ° C. The raw materials, sponge zirconium 6 and iodine 7,
Zirconium tetraiodide (ZrI ₄ ) is produced by the reaction of the above formula (1) in a temperature range of 200 to 500 ° C. Generated ZrI ₄
Sublimates and decomposes into iodine (I ₂ ) and zirconium (Zr) on the high-temperature filament 3, Zr of the decomposed and purified product adheres to the filament 3, and iodine (I ₂ ) is again sponge zirconium as a raw material Reacts with 6. That is, it functions to carry zirconium onto the filament 3 using iodine as a carrier. In this way, only zirconium that reacts with iodine is carried on the filament 3 and purification is performed. By repeating this process, high-purity zirconium grows on the filament 3.

At present, sponge zirconium is industrially used as a raw material of the above-mentioned high-purity zirconium. In sponge zirconium, first, crude zirconium tetrachloride is produced from ore, and hafnium is separated into purified zirconium oxide. Subsequently, the zirconium oxide is salified to form zirconium tetrachloride, which is purified to remove impurities.
The purified zirconium tetrachloride is reduced with magnesium (Kroll method) to form sponge zirconium. Since the refining of zirconium is performed by the above complicated process, sponge zirconium itself becomes expensive. On the other hand, in the future, demand for high-purity zirconium is expected to further increase due to the spread of zirconium liner tubes, and it is necessary to produce high-purity zirconium at lower cost. To this end, it is necessary to study the manufacturing process of high-purity zirconium in more detail and reduce the manufacturing cost.However, as described above, the price of sponge zirconium, which is the raw material, is high, and the proportion of high-purity zirconium to the manufacturing cost is high large. Therefore, it is necessary to examine the raw material itself in order to greatly reduce the production cost of high-purity zirconium.

By the way, zirconium has a small thermal neutron absorption cross section and is excellent in mechanical properties and corrosion resistance. Therefore, zircaloy such as zircaloy-2 or zircaloy-4 is used as a structural material in a nuclear reactor. Zircaloy-2
Is Sn 1.20-1.79% by weight, Fe 0.07-0.20% by weight, Cr
0.05-0.15% by weight, Ni 0.03-0.08% by weight and balance Zr
Zircaloy-4 has a composition of 120 to 1.79% by weight of Sn, 0.18 to 0.24% by weight of Fe, 0.07 to 0.13% by weight of Cr, and the balance of Zr (including inevitable impurities). Each of them contains a trace amount of Sn, Fe, Cr and the like. A large amount of scrap is generated in the process of manufacturing such Zircaloy internal components. For this reason, recycling scrap is important from the viewpoint of effective use of resources. In particular, if the scrap can be used as a raw material of high-purity zirconium, it is possible to supply the raw material of high-purity zirconium at low cost and stably.

For these reasons, attempts have been made to use zircaloy-2 or zircaloy-4 scrap instead of sponge zirconium as a raw material for producing high-purity zirconium. However, Zircaloy-2 or Zircaloy-4 contains about 1.5% by weight of tin (S
Since n) is contained, a large amount of Sn remains in zirconium produced by the above-described iodide decomposition method using this scrap as a raw material. Since Sn increases the hardness of zirconium, the zirconium containing Sn cannot be used as a liner layer of a fuel cladding tube.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and aims to provide a method for producing high-purity zirconium from zircaloy scrap by a simple process. It is.

[Structure of the Invention] (Means and Action for Solving the Problems) In the method for producing high-purity zirconium according to the present invention, a scrap made of zircaloy containing tin is put into a purification tank heated with iodine, and the structure of the zircaloy is formed. A step of generating iodide composed of an element, and heating the iodide to a temperature of 100 to 400 ° C. to generate tin iodide and zirconium iodide in a gas phase, and recovering impurities connected to the purification tank. A step of cooling the tank and trapping the tin iodide in the impurity recovery tank by the vapor pressure difference between the tin iodide and the zirconium iodide in the gas phase to separate the zirconium iodide; Transporting the zirconium to a decomposition tank connected to the refining tank, decomposing the zirconium iodide and placing a high-purity zirconium material disposed in the decomposition tank; And a step of depositing zirconium on the surface of the substrate.

Hereinafter, the method for producing high-purity zirconium of the present invention will be described in the first.
This will be described in detail with reference to the manufacturing apparatus shown in FIG.

Reference numeral 11 in the drawing denotes a purification tank to which an exhaust system (not shown) is connected. The purification tank 11 is connected impurities collecting tank 13 via the pipe 12a, and the first valve 14 ₁ in the piping 12a is interposed. This recovery tank 13 is structured to be cooled by liquid nitrogen. ₂ is a second valve 14 is interposed in the said purification tank 11 is connected iodine feed tank 15 through a pipe 12b, and the pipe 12b. Further, the purification vessel 11 is connected through a piping 12c iodide zirconium supply tank 16, and the piping 12c is a third valve 14 ₃ is interposed. The supply tank 16, the fourth valve 14 ₄ is interposed in the decomposition tank 17 is connected through a pipe 12e, and the pipe 12d. The decomposition tank 17 is housed in an electric furnace 18. A U-shaped filament 19 made of pure zirconium is suspended in the decomposition tank 17, and both ends of the filament 19 are connected to a power supply 20. Furthermore, the iodide zirconium, is connected via a collecting tank 21 is a pipe 12e iodine, and the piping 12e the valve 14 ₅ of the fifth is interposed. This collection tank 21
It is connected to the exhaust system 22 via a pipe 12f. The purification tank 11, the zirconium iodide supply tank 16 and the pipe 12
a, 12c, 12d, and 12e have a structure heated by a heater.

Next, a method for producing high-purity zirconium of the present invention using the above-described production apparatus will be described. In this method, an iodide decomposition method was employed as a halide decomposition method.

First, zircaloy (for example, zircaloy-
2) Charge the scrap 23 and iodine 24. The shape of the scrap used here is desirably a cut piece having a large surface area in consideration of reactivity with iodine. Also,
It is desirable that the scrap surface be sufficiently cleaned to avoid contamination of high purity zirconium. Then,
After the inside of the purifying tank 11 is evacuated by the operation of an exhaust system (not shown), it is heated to a high temperature (200 ° C. or higher) to react the zircaloy scrap 23 with the iodine 24. At this time, in addition to SnI ₄ and ZrI ₄ , trace amounts of iodides of Fe, Ni, and Cr are generated in the purification tank 11. After the reaction has sufficiently proceeded, the temperature in the purification tank 11 is maintained at a temperature of 100 to 400 ° C., and the first valve of a pipe 12a connecting the purification tank 11 and the impurity recovery tank 13 cooled by liquid nitrogen. 14 Open ₁ . At this time, as shown in Table 1 below, which shows the equilibrium vapor pressures of SnI ₄ and ZrI ₄ , the vapor pressure of SnI ₄ is higher than that of ZrI ₄ within the temperature range of 100 to 400 ° C. (compared to other metal iodides). However, the vapor pressure is high), and since there is a large difference between the vapor pressures thereof, SnI ₄ is generated by the temperature difference between the heated purification tank 11 and the cooled impurity recovery tank 13. A trap 13 is collected through a pipe 12a. After a predetermined time has elapsed, the first closing valve 14 _1, feeds the ZrI ₄ purified by opening the third valve 14 ₃ iodide zirconium supply tank 16. By repeating these operations, a sufficient amount of purified ZrI ₄ is stored in the zirconium iodide supply tank 16. In addition, the purification tank
When the iodine in 11 is insufficient to open the second valve 14 _2, supplied into the purification tank 11 of iodine in the iodine supply tank 15 through the pipe 12b.

Next, the evacuation system 22 is operated to evacuate the inside of the decomposition tank 17 to vacuum, and the decomposition tank 17 is heated by the electric furnace 18 to a temperature at which the vapor pressure of the supplied ZrI ₄ can be maintained at a constant value. 1100 to 15 filaments 19 made of high-purity zirconium
Electric heating to 00 ° C. Then, open the fourth valve 14 ₄ is gradually supplied into the decomposition tank 17 ZrI ₄ of vapor-phase of iodide zirconium in the supply tank 16. At this time, ZrI ₄ is dissociated on the filament 19 heated to 1100 to 1500 ° C., and pure zirconium is grown on the filament 19. Also,
Iodine purified by decomposition and undecomposed ZrI ₄ are recovered by a recovery tank 21 arranged between a decomposition tank 17 and an exhaust system 22,
Reused.

By such a process, from the Zircaloy scrap to Sn
High-purity zirconium with a low concentration is produced.

Further, Fe, Ni, because iodide Cr is lower than the vapor pressure of ZrI _4, iodide zirconium supply tank 16 from the purification tank 11, in the process of moving the ZrI ₄ to decomposition vessel 17 from the supply tank 16, purified Partially remains in tank 11 and supply tank 16, and filament 19
The incorporation of Fe, Ni, and Cr into the zirconium deposited thereon is suppressed.

Furthermore, when the trap SnI ₄ impurity collection tank 13, by adjusting the holding temperature of the purification vessel 11, can be controlled content of SnI ₄ which are taken together with ZrI ₄ supplied to the supply tank 16. That is, as shown in Table 1, the difference between the vapor pressures of SnI ₄ and ZrI ₄ becomes larger as the temperature becomes lower. Therefore, the temperature of the refining tank 11 is lowered, and the temperature is maintained for a long time to be supplied to the supply tank 16 together with the ZrI _4. SnI ₄ content can be further reduced.

Therefore, according to the method of the present invention, a scrap made of tin-containing zircaloy is used as a raw material, and an impurity recovery tank 13 and a decomposition tank 17 are connected. To produce an iodide composed of the constituent elements of
Heated to a temperature of 00 ° C. to generate tin iodide and zirconium iodide in a gaseous state, and the tin iodide is stored in the impurity recovery tank 13 cooled by utilizing a vapor pressure difference between these iodides in a gaseous state. And transport the separated zirconium iodide to the decomposition tank 17, where the zirconium iodide is decomposed and the surface of the high-purity zirconium material (filament 19 made of pure zirconium) in the decomposition tank 17 By precipitating zirconium, high-purity zirconium in which the concentration of tin, which causes an increase in hardness, is kept low, can be produced at low cost.

Embodiment of the Invention Hereinafter, an embodiment of the present invention will be described with reference to FIG.

First, 10.0 kg of Zircaloy-2 scrap having the composition shown in Table 2 below and 1 kg of iodine were charged into the purification tank 11 shown in FIG. Subsequently, after the inside of the purification tank 11 was evacuated by an exhaust system, the purification tank 11 was heated to 300 ° C. to generate iodide. Subsequently, after the reaction has sufficiently proceeded, the purification tank 11
The inside temperature is maintained at a temperature of 200 ° C., and a pipe 12 for connecting an impurity recovery tank 13 and a purification tank 11 further cooled by liquid nitrogen.
first of a 1 valve 14 ₁ the collection tank 13 of SnI ₄ by opening the
Through the pipe 12a and collected. Then the first
Closing the valve 14 _1, the third a ZrI ₄ of valve 14 ₃ open purified vapor was fed to the iodide zirconium supply tank 16. By repeating such operations 20 times, about 25 kg of purified ZrI ₄ was supplied into the zirconium iodide supply tank 16.

Next, the evacuation system 22 was activated to evacuate the inside of the decomposition tank 17 to a vacuum, and the decomposition tank 17 was heated to 400 ° C. by the electric furnace 18, and the filament 19 of 2 mm in diameter made of high-purity zirconium was further heated to 1400 ° C. by the power supply 20. Electric heating was performed. Then, the fourth
Open the valve 14 _4, and gradually supplies the ZrI ₄ of gas phase in the iodide zirconium supply tank 16 into the decomposition tank 17, pure by dissociating the ZrI ₄ on the filament 19, which is energized and heated to 1400 ° C. Zirconium was grown on filament 19. When such decomposition of ZrI ₄ was performed for 120 hours, the average diameter was 25 m.
m, a high purity zirconium rod of about 2.0 kg was obtained.

The results of analyzing the components of the obtained high-purity zirconium rod are shown in Table 3 below. In Table 3, the results of analysis of zirconium rods manufactured using the zircaloy-2 scrap as a raw material by the manufacturing apparatus shown in FIG. 2 are also shown as comparative examples.

As is apparent from Table 3, the effect of reducing Sn is remarkable in the method of the present example as compared with the method of the comparative example, and a high-purity zirconium rod can be obtained.

In the above embodiment, Zircaloy was used as scrap.
The same effect as that of the example could be achieved by using Zircaloy-4 scrap consisting of 1.5% by weight of Sn, 0.15% by weight of Fe, 0.1% by weight of Cr and the balance of Zr.

[Effects of the Invention] As described in detail above, according to the present invention, zircaloy scrap is used as a raw material, and constituent elements and impurities of zircaloy are separated and removed in advance by a halide decomposition method, particularly an iodide decomposition method, to remove ZrI ₄ . By purifying, decomposing, and depositing on the surface of the zirconium material, it is possible to provide a method capable of producing high-purity zirconium at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one embodiment of a production apparatus for producing high-purity zirconium of the present invention, and FIG. 2 is a schematic view showing a conventional production apparatus for producing high-purity zirconium. 11 ... purification tank, 13 ... impurity recovery tank, 16 ... zirconium iodide supply tank, 17 ... decomposition tank, 19 ... zirconium filament.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Emiko Higashinakagawa 1 Toshiba Research Institute, Komukai, Kawasaki-shi, Kanagawa Prefecture 62-294177 (JP, A) JP-B 32-1822 (JP, B1) JP-B 33-9107 (JP, B1)

Claims (1)

(57) [Claims] 1. A step of placing a scrap made of zircaloy containing tin together with iodine in a heated purification tank to generate an iodide consisting of the constituent elements of the zircaloy, and heating the iodide to a temperature of 100 to 400 ° C. To produce tin iodide and zirconium iodide in the gas phase,
The impurity recovery tank connected to the purification tank is cooled, and the tin iodide is trapped in the impurity recovery tank by the vapor pressure difference between tin iodide and zirconium iodide in the gas phase to separate the zirconium iodide. Transporting the separated zirconium iodide to a decomposition tank connected to the purification tank, decomposing the zirconium iodide, and depositing zirconium on the surface of the high-purity zirconium material disposed in the decomposition tank. A method for producing high-purity zirconium, comprising the steps of: