JP2012061465A - Gas refining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the refining purity of uranium hexafluoride before re-enrichment.SOLUTION: The purity of a refined objective component is improved by an adsorption process of adsorbing impurity by feeding the objective component gas to be refined and treated gas containing impurity through an adsorption tower 12 with which an adsorbent for adsorbing the impurity is filled, a condensation process of condensing the objective component by cooling the gas passing the adsorption process, and returning of the impurity discharged from the condensation process and un-condensed objective component gas to the adsorption process.

Description

  The present invention relates to a gas purification method, for example, a gas purification method suitable for converting uranium recovered by reprocessing spent nuclear fuel into a chemical form of uranium hexafluoride.

  Conventionally, for example, it has been proposed to purify gaseous uranium hexafluoride before reconcentrating uranium hexafluoride recovered by reprocessing spent nuclear reactor fuel (for example, Patent Document 1). .

  In general, uranium hexafluoride before reconcentration, that is, spent nuclear reactor fuel in nuclear power generation, contains plutonium and fission products in addition to uranium. Reprocessing is performed to remove fission products and the like. The uranium recovered by reprocessing is converted to gaseous uranium hexafluoride (UF6), and the concentration of fissile uranium isotopes is adjusted by reconcentration. used.

  For example, for the specifications of uranium hexafluoride that can be accepted by reconcentration, that is, the purity, impurity content, radiation dose, and the like, the standards established by the American Testing and Materials Association of Non-Patent Document 1 are applied. Although many impurities are removed in the reprocessing step, the reprocessed and recovered uranium after conversion to uranium hexafluoride contains a trace amount of gaseous impurities. Therefore, if the reconcentration does not meet acceptable specifications, further purification must be performed before reconcentration.

  As such a method for purifying uranium hexafluoride, the technique described in Patent Document 1 uses a gas of uranium hexafluoride containing impurities in a solid adsorbent that has a chemical adsorption action on impurities (hereinafter referred to as a target). The process gas is passed through to remove impurities fluoride, and then cooled to a temperature at which uranium hexafluoride condenses to condense and recover uranium hexafluoride.

JP 2006-46967 A

ASTM C787-06: Standard Specification for Uranium Hexafluoride for Enrichment

  However, in order to adsorb impurities to the solid adsorbent by a chemical reaction, it is necessary to make the partial pressure of the impurities in the gas to be processed higher than the equilibrium dissociation pressure. If it is lower than the equilibrium dissociation pressure, impurities cannot be removed even if the gas to be treated is passed through the solid adsorbent. Therefore, according to the technique described in Patent Document 1, in order to increase the purity of uranium hexafluoride, it is necessary to increase the amount of solid adsorbent used. The equilibrium dissociation pressure refers to an equilibrium constant when the impurity fluoride chemically adsorbed on the solid adsorbent dissociates into impurity molecules and the solid adsorbent.

  Moreover, according to the technique described in Patent Document 1, it is described that a plurality of types of solid adsorbents and a plurality of stages of adsorbers are used in order to improve purification purity. There is a problem that the amount of the used solid adsorbent increases.

  The problem to be solved by the present invention is to improve the purity of the target component to be purified in the gas purification method.

  In order to solve the above-mentioned problem, the gas purification method according to the first aspect of the present invention is configured to pass a target gas to be purified and a gas to be treated containing impurities through an adsorption tower filled with an adsorbent that adsorbs impurities. An adsorption process for adsorbing impurities, a condensation process for condensing the target component by cooling the gas that has passed through the adsorption process, and returning the impurities discharged from the condensation process and the uncondensed target component gas to the adsorption process. It is characterized by becoming.

  According to this, a part of the target component gas in the gas to be treated is condensed and recovered, and the impurities discharged from the condensation process and the non-condensed target component gas are returned to the adsorption process, so that the impurity gas in the adsorption process is recovered. The partial pressure can be increased. As a result, the dissociation equilibrium between the impurity gas and the adsorbent can be moved to the adsorption side, and the chemical adsorption reaction between the impurity gas and the adsorbent is promoted, so the degree of purification by the adsorbent can be improved and the amount of adsorbent used is reduced. it can.

  Moreover, the gas purification method of the second aspect of the present invention is a gas purification method of uranium hexafluoride, and uranium in which sodium fluoride is filled with uncondensed uranium hexafluoride gas discharged from the condensation step. It includes a uranium adsorption process for adsorbing uranium hexafluoride on sodium fluoride through an adsorption tower, and a desorption process for desorbing uranium hexafluoride from sodium fluoride as a gas by heating the uranium adsorption tower. It is characterized by.

  In the gas purification method of the third aspect of the present invention, the impurities in the gas to be treated are adsorbed on the adsorbent in the adsorption step, the gas that has passed through the adsorption step is cooled to condense the target component gas, and the impurities The uncondensed target component gas is returned to the adsorption step, and the concentration of the target component gas is reduced by lowering the concentration of the target component gas in accordance with the increased concentration of the target component gas impurity gas. When the value exceeds a set value, uncondensed impurity gas is discharged out of the system.

  According to the present invention, in the gas purification method, the purity of the target component to be purified can be improved.

1 is a conceptual diagram of a gas purification method of Embodiment 1. FIG. It is a figure which shows the ratio of the uranium hexafluoride and impurity fluoride in the to-be-processed gas of Embodiment 1. FIG. It is a conceptual diagram of the gas purification method of Embodiment 2. It is a figure which shows the temperature dependence of the saturated vapor pressure of uranium hexafluoride and NbF5. It is a figure which shows the ratio of the uranium hexafluoride and NbF5 in to-be-processed gas. It is a conceptual diagram of the gas purification method of Embodiment 4.

  Hereinafter, the present invention will be described based on embodiments. In the embodiment, uranium hexafluoride gas containing impurities supplied from a spent nuclear fuel reprocessing plant will be described as gas to be processed, and the target component will be described as uranium hexafluoride. The gas and the target component are merely illustrated, and the gas to be processed and the target component are not limited.

(Embodiment 1)
In the gas purification method of Embodiment 1, the target component gas to be purified and the gas to be treated containing impurities are cooled to condense the target component gas, and the impurities discharged from the first condensation step and uncondensed A second condensing step for cooling the target component gas at a lower temperature than the first condensing step; a heating step for heating and gasifying the condensate of the target component condensed in the second condensing step; Returning the gas to the first condensation step.

  That is, since the target component gas is condensed and recovered, a high-purity target component can be obtained. Furthermore, the non-condensed target component gas discharged from the first condensation step is cooled and condensed at a lower temperature than the first condensation step in the second condensation step, and the condensate is gasified to form the first condensation step. Therefore, the partial pressure of the target component gas in the first condensation process can be increased. As a result, the target component gas is easily condensed at the cooling temperature of the first condensing step, so that the recovery rate of the target component can be improved.

  Furthermore, since some of the impurities may be condensed in the second condensation step, the impurities in the gas generated in the heating step are adsorbed on the adsorbent in the adsorption step, and the gas that has passed through the adsorption step is the first condensation step. Return to. According to this, even if impurities are contained in the gas generated in the heating process, the impurities can be removed in the adsorption process, so that the increase in the concentration of impurities in the first condensation process can be reduced, and the target component to be purified The purity of can be further improved.

  Such a gas purification method of Embodiment 1 will be described with reference to FIG. As shown in the figure, the gas purification method of the present embodiment includes a first condenser 3 to which a gas to be treated 1 of uranium hexafluoride containing impurities is supplied, impurities discharged from the condenser 3 and uncondensed six. A second condenser 5 to which uranium fluoride gas is supplied and an adsorption tower 9 filled with an adsorbent for adsorbing impurities are included.

  The to-be-treated gas 1 is supplied from a reprocessing plant (not shown), and uranium in a chemical form such as oxide, nitrate, fluoride and the like recovered by reprocessing spent nuclear fuel is reacted with fluorine gas. It has been converted to the chemical form of uranium hexafluoride. Part of the fission product contained in the spent fuel is mixed as impurities in the recovered uranium supplied from the reprocessing plant, and the fission product that becomes a non-volatile fluoride when converted to uranium hexafluoride Things are separated. The main impurities contained in the recovered uranium are fission products that become volatile fluorides, such as technetium (Tc), ruthenium (Ru), molybdenum (Mo), antimony (Sb), tellurium (Te), niobium (Nb). , Etc., there are fluorine gas (F2) used in the conversion to uranium hexafluoride, oxygen (O2) generated during the conversion, and the like. For these impurities, since acceptance standards are set in the enrichment factory to which the purified uranium hexafluoride is supplied, if the impurities contained in the gas to be treated 1 exceed the acceptance standards, It is necessary to carry out purification. In the present embodiment, a method of removing fluorides of technetium (Tc), ruthenium (Ru), molybdenum (Mo), and antimony (Sb) as impurities from the gas to be processed 1 will be described.

  The condenser 3 into which the gas to be processed 1 is introduced is provided with a cooling means 6 so that the gas to be processed 1 can be cooled by a cooling device (not shown). The cooling temperature in the condenser 3 is selected from −30 ° C. at which 99% or more of uranium hexafluoride is condensed to 64 ° C., which is the triple point of uranium hexafluoride. In this case, from the viewpoint of the purity and recovery rate of the condensed uranium hexafluoride, it is desirable to set the recovery rate within the range of −10 ° C. to 10 ° C. at which the recovery rate is 80 to 95%. More preferably, the uranium hexafluoride contained in the gas 1 to be processed is condensed, but the impurity fluoride is difficult to condense, that is, the saturation vapor pressure of the impurity fluoride is the fraction of the impurity fluoride in the gas 1 to be processed. The temperature is smaller than the pressure. The uranium hexafluoride condensed and recovered by the condenser 3 is heated and gasified by the heating means 7 and recovered as purified uranium 8. The condenser 3 may be provided with an evaporator separately from the heating means 7, or uranium hexafluoride may be recovered as a solid without being gasified. The recovered purified uranium 8 may be discarded after being converted to intermediate storage or oxide. In this case, the purity of uranium hexafluoride can be determined in consideration of exposure at storage facilities and oxidation conversion facilities.

  The impurities fluoride and uncondensed uranium hexafluoride gas discharged from the condenser 3 are introduced into the condenser 5. The condenser 5 can cool the gas by the cooling means 6 at a cooling temperature lower than that of the condenser 3, for example, −80 ° C. As a result, most of the uncondensed uranium hexafluoride gas can be condensed and recovered. Impurity fluoride and F2 and O2 gases that are not condensed by the condenser 5 are discharged as offgas and supplied to an offgas processing system (not shown). After the off-gas is discharged, the heating means 7 heats and vaporizes the uranium hexafluoride condensate in the condenser 5, and supplies the generated gas to the adsorption tower 9. The heating temperature for vaporization can be appropriately set depending on the recovery rate of uranium hexafluoride, but is preferably 64 ° C. or higher, which is the triple point of uranium hexafluoride. In addition, you may provide heating means, such as an evaporator, without providing the heating means 7 in the condenser 5. FIG.

  The adsorption tower 9 is filled with an adsorbent that adsorbs impurity fluoride, for example, LiF, NaF, MgF2, CaF2, BaF2, UO2F2, UF5, etc., and adsorbs the impurity fluoride in the passing gas to the adsorbent. It is supposed to be removed. In the present embodiment, the adsorption tower 9 is provided with an adsorption tower heating means 10 and is adjusted to a temperature at which the impurity fluoride is easily adsorbed by the adsorbent. The temperature of the adsorption tower 9 can be appropriately selected according to the purification target component, the type and concentration of impurities, and the adsorption tower heating means 10 need not be provided. The gas of uranium hexafluoride that has passed through the adsorption tower 9 is mixed with the gas to be treated 1 and returned to the condenser 3.

  Here, the principle of the gas purification method of this embodiment will be described using an example of a fluoride volatilization type reprocessing facility. Table 1 shows the ratio of uranium hexafluoride to impurity fluoride in the gas to be treated supplied from the reprocessing facility. Reported by Argonne Laboratories, pages 68 and 89 of ANL-7583. It is based on the numerical values described. Page 68 of ANL-758 shows the flow rate when the spent fuel is fluorinated to produce gaseous uranium hexafluoride (UF6) and recovered in the condenser. Indicates the value. Since TeF6 is highly volatile, it does not condense when gaseous uranium hexafluoride is recovered in the condenser, so it is not included in the gas of uranium hexafluoride in the subsequent process. Not. From this flow rate, the number of moles of U, Nb, Mo, Tc, Ru, and Sb contained in gaseous uranium hexafluoride containing 1 mole of uranium can be calculated. The result is shown in the column. The partial pressure of each substance when this condensed and recovered uranium hexafluoride is heated and made gaseous again for purification is shown in the column Po in the table. In general, the pressure is set to 1 atm for the entire gas, but this table assumes the total pressure at which the main component uranium hexafluoride is 1 atm in consideration of easy understanding of the principle. The last two columns of Table 1 are the saturated vapor pressures of each compound at 15 ° C. and −80 ° C. as described on page 89 of ANL-7683.

Here, the processing amount of uranium hexafluoride in the gas to be processed 1 was set to 1 mol / min. In the example of ANL-7683, about 880 kg of uranium hexafluoride is processed in one day, so it is about 2.5 mol / min. However, for easy understanding of the principle, the processing amount of uranium hexafluoride is excellent. Numerical values were used. It is assumed that MoF6, TcF5, RuF6, and SbF5 are included at the ratio shown in Table 1. Shown in the column of line number 1 in FIG. 2 are the flow rate of the gas to be processed 1 (recovered U in FIG. 2) and the partial pressures (Po / Pa) of UF6, MoF6, TcF5, RuF6, and SbF5. The processing amount corresponding to 1 minute of the gas 1 to be processed is 1.00 mol for UF6, 9.96 × 10 ⁻³ mol, 2.31 × 10 ⁻³ mol, and 8.31 × 10 ⁻³ mol for MoF6, TcF5, RuF6, and SbF5, respectively. 52 × 10 ⁻³ mol and 2.91 × 10 ⁻⁴ mol are contained. Since the partial pressure of this uranium hexafluoride is defined as 1 atmosphere (1.01 × 10 ⁵ Pa), the partial pressures of MoF6, TcF5, RuF6, and SbF5 are values in the Po / Pa column by proportional calculation.

A gas (supply U in FIG. 2) obtained by adding a later-described rough purification circulation U to the gas to be treated 1 is supplied to the condenser 3. The composition of the crude recycle cycle U is shown in the line number 61 column. The composition of the supply U, the combination of both, is shown in the line number 7 column. The flow rates of MoF6, TcF5, RuF6, and SbF5 in the supply U are about 11.1%, more precisely 1/9, higher than the gas to be processed 1. When this supply U is supplied to the condenser 3 whose interior is set to 15 ° C., the saturated vapor pressure is 7.41 × 10 ³ Pa as shown in the column of VP + 15, so that the difference is 9.4 × 10 ^4. The uranium hexafluoride for Pa is condensed. Since this amount is about 93% of the original uranium hexafluoride, about 93% of the gas of uranium hexafluoride is condensed, but the partial pressures of MoF6, TcF5, RuF6, and SbF5 are each 1.04 × 10 ³ , 2.41 × 10 ² , 8.88 × 10 ² , and 3.03 × 10, all of which are smaller than the saturated vapor pressure shown in the column of VP + 15 in Table 1, and thus do not condense. The uranium hexafluoride condensed and recovered by the condenser 3 is recovered as purified uranium 8 (purified U in FIG. 2). The gases of MoF6, TcF5, RuF6, SbF5 and uncondensed uranium hexafluoride that have not been condensed in the condenser 3 are supplied to the condenser 5 and cooled to a temperature lower than that of the condenser 3, for example, −80 ° C. Most of the gas of uranium hexafluoride is condensed and recovered. The uranium hexafluoride condensate condensed and recovered by the condenser 5 is heated to a temperature at which most of the uranium hexafluoride can be gasified, for example, 64 ° C., which is the triple point of uranium hexafluoride, and is vaporized. Gas (circulation U in FIG. 2) is used.

  However, if the circulation U is added to the gas to be processed 1 as it is, MoF6, TcF5, RuF6, and SbF5 condensed by the condenser 5 will also merge with the gas to be processed 1, and the amount of impurity fluoride in the gas to be processed 1 May increase and condense with the uranium hexafluoride in the condenser 3. Therefore, before this circulation U is joined to the gas 1 to be treated, 90% of MoF6, TcF5, RuF6 and SbF5 are adsorbed and removed by the adsorbent 9 through the adsorption tower 9. For example, LiF, NaF, MgF2, CaF2, BaF2, UO2F2, and UF5 can be used as the adsorbent. The gas discharged from the adsorption tower 9 (crude refining circulation U in FIG. 2) is joined to the gas to be treated 1 and supplied to the condenser 3.

Here, we will review the movement of uranium hexafluoride. About 0.08 mol (0.0792 mol) of circulation U is added to 1.00 mol of uranium hexafluoride in the original gas 1 to be 1.08 mol. Of these, 93% is purified uranium 8, but the amount is 1.08 × 0.93 = 1.00 mol. About 0.08 mol of the amount that did not become purified uranium 8 becomes circulation U again and is added to the gas 1 to be treated. That is, even if the circulation U including MoF6, TcF5, RuF6, and SbF5 is joined to the gas 1 to be processed, uranium hexafluoride in the gas 1 to be processed is not accumulated, and uranium hexafluoride in the gas 1 to be processed is not accumulated. The flow rate and the flow rate of the purified uranium 8 are almost the same. Here, the reason is that there is 6.53 × 10 ⁻⁷ mol of uranium that is not recovered as off-gas. This unrecovered portion is an acceptable value considering that the required recovery rate of uranium hexafluoride in reprocessing is 99 to 99.5%.

  When the movement of MoF6, TcF5, RuF6, and SbF5 is observed, when the circulation U is added to the gas 1 to be processed, the amount of MoF6, TcF5, RuF6, and SbF5 that is 1/9 of the gas to be processed 1 is 1 to be processed. The amount of substance in the supply U is 10/9. However, if 90% is removed by the adsorption tower 9, the amount of the substance in the crude refining circulation U becomes 1/9, and the accumulation of impurity fluoride hardly occurs.

  According to this, since the gas of uranium hexafluoride can be condensed and recovered, high-purity uranium hexafluoride can be obtained. Further, the uncondensed uranium hexafluoride gas discharged from the condenser 3 is cooled to a lower temperature by the condenser 5 and condensed and recovered. The condensate is gasified and mixed with the gas 1 to be treated. Since it returns to the condenser 3, the partial pressure of the uranium hexafluoride gas in the condenser 3 can be increased. As a result, the uranium hexafluoride gas can be easily condensed at the cooling temperature of the condenser 3, and the uranium hexafluoride recovery rate can be improved.

  Further, even if a part of the impurity fluoride is condensed by the condenser 5, the impurity fluoride can be removed by the adsorption tower 9, so that accumulation of impurity fluoride in the system can be reduced. In this embodiment, the adsorption tower 9 is provided. However, the adsorption tower 9 may be omitted depending on the purity required for the target component, the concentration of impurities, and the like.

  Further, when the target component is uranium hexafluoride, an adsorption device filled with sodium fluoride can be used instead of the condenser 5 of the present embodiment. This utilizes the property that sodium fluoride adsorbs uranium hexafluoride at a temperature of around 100 ° C. and desorbs uranium hexafluoride at a temperature of 350 ° C. or higher. According to this, the impurity fluoride that has passed through the condenser 3 and the gas of uncondensed uranium hexafluoride are introduced into an adsorption device filled with sodium fluoride at a set temperature of about 100 ° C. to adsorb uranium hexafluoride. In addition, the purity and recovery rate of uranium hexafluoride can be improved by heating the adsorption device to 350 ° C. or higher, desorbing uranium hexafluoride as a gas, and joining the gas to be treated 1.

  Moreover, since sodium fluoride adsorbs a part of MoF6, TcF5, RuF6, and SbF5, the adsorption tower 9 can be omitted.

(Embodiment 2)
In the gas purification method of Embodiment 2, impurities in the gas to be treated are adsorbed on the adsorbent in the adsorption step, the gas that has passed through the adsorption step is cooled in the first condensation step, the target component is condensed and recovered, and uncondensed The target component gas is cooled and condensed in the second condensation step at a temperature lower than that in the first condensation step, and the condensate is heated to gasify and return to the adsorption step.

  According to this, when there is a possibility that impurities are condensed in the first condensation process, a part of the impurities in the gas to be treated can be adsorbed and removed in advance, and the partial pressure of the impurities in the first condensation process can be lowered. Thus, impurities are less likely to be condensed in the first condensation step, and a high-purity target component can be obtained. Furthermore, since it is sufficient that the adsorption process can adsorb and remove some of the impurities, the amount of adsorbent used can be reduced, and the amount of used adsorbent to be discarded can be reduced.

  Such a gas purification method of Embodiment 2 will be described with reference to FIG. The difference between the present embodiment and the first embodiment is that an adsorption tower 9 provided at the rear stage of the condenser 5 is provided at the front stage of the condenser 3, the gas 1 to be treated is passed through the adsorption tower 9, and passes through the adsorption tower 9. This is the point that the gas is cooled by the condenser 3. Furthermore, the gas generated by heating the condensate in the condenser 5 is mixed with the gas 1 to be processed, and this mixed gas is passed through the adsorption tower 9. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted. In addition, this embodiment is a gas purification method when the gas of uranium hexafluoride containing NbF5 which is easy to condense at the cooling temperature of the condenser 3 is a gas to be treated.

  Here, the principle of separation of the gas to be processed 1 of the present embodiment will be specifically described using an example of a reprocessing facility of a fluoride volatilization method type. Note that the gas to be treated is gasified again from uranium hexafluoride obtained by fluorinating spent fuel as in the above-mentioned ANL-7683. In addition, the processing amount per minute of the gas 1 to be processed is 1 mol, and uranium hexafluoride and NbF5 are included in the gas 1 to be processed at the ratio shown in Table 1 described above.

  FIG. 4 is obtained by interpolating the temperature dependence of the saturated vapor pressure of uranium hexafluoride and NbF5 in Table 1 with the following equation.

log (saturated vapor pressure) = AB / T
Where A, B ,: compound specific constant, T: absolute temperature

The gas of uranium hexafluoride heated to a temperature higher than the triple point of uranium hexafluoride includes 1.01 × 10 ⁵ Pa (1 atm), which is the value in the Po column of Table 1 (FIG. 4). Dotted line). When this gas is cooled to 15 ° C., the saturated vapor pressure is 7.41 × 10 ³ Pa as shown in the column of VP + 15. Therefore, 9.4 × 10 ⁴ Pa uranium hexafluoride that is the difference is condensed. To do. This amount is about 93% of uranium hexafluoride in 1 in the gas to be treated. At the same time, the saturated vapor pressure of NbF5 is 2.04 × 10 Pa (solid line in FIG. 4), which is the value in the Po column in Table 1, and is the difference of 3.33 × 10 ⁻¹ Pa in the column of VP + 15. Condensates with uranium fluoride. However, if about 99% of NbF5 is removed by an adsorbent such as NaF before supplying the gas to be treated 1 to the condenser 3, the vapor pressure becomes 2.05 × 10 ⁻¹ Pa (FIG. 4). Dash-dot line). At this time, if condensation is performed at 15 ° C., about 93% of uranium hexafluoride is condensed, but NbF5 is not condensed because the partial pressure of NbF5 is lower than the saturated vapor pressure. In this way, gas of uranium hexafluoride containing about 93% NbF5 and uranium hexafluoride containing about 7% NbF5 is separated.

  In this way, the mixed gas of uranium hexafluoride and impurity fluoride that has not been condensed in the condenser 3 is supplied to the condenser 5. The condenser 5 is cooled to condense and recover the mixed gas of uranium hexafluoride and impurity fluoride. The cooling temperature is desirably set to a temperature at which most of the uranium hexafluoride contained in the mixed gas is condensed, for example, −30 ° C. or lower, specifically, −80 ° C. to −50 ° C. At this time, a part of NbF5 contained in the mixed gas of uranium hexafluoride and NbF5 is condensed together with uranium hexafluoride, and an impurity fluoride having a high saturated vapor pressure at a set cooling temperature, such as Mo or Te, F2 and O2 are not condensed and are discharged as off-gas.

  On the other hand, when the uranium hexafluoride condensed and recovered by the condenser 3 is taken out, the condenser 3 is heated to a temperature at which uranium hexafluoride is gasified (64 ° C., which is the triple point of uranium hexafluoride). By doing so, uranium hexafluoride is gasified and recovered as purified uranium 8. When uranium hexafluoride condensed and recovered by the condenser 5 and a part of NbF5 are taken out, the uranium hexafluoride is heated to 64 ° C. or more at which it is gasified. The gasified uranium hexafluoride and NbF5 are mixed with the gas to be treated and circulated to the adsorption tower 9.

  Here, the recovery rate of uranium hexafluoride will be described with reference to FIG. The treatment amount of uranium hexafluoride in the gas to be treated 1 was set to 1 mol / min. In the above example of ANL-7583, about 880 kg of uranium hexafluoride is processed in one day, so it is about 2.5 mol / min. In this example, for easy understanding of the principle, uranium hexafluoride is processed. As the amount, a clear numerical value was used.

It is assumed that NbF6 is contained in the gas to be treated 1 (purification target U in FIG. 5) at the ratio shown in Table 1 described above. Shown in the column of line number 1 are the flow rate of the gas to be treated 1 (purification target U) and the partial pressure of uranium hexafluoride and NbF5. The processing amount corresponding to 1 minute of the gas 1 to be processed includes 1.00 mol of uranium hexafluoride and 2.01 × 10 −4 mol of NbF 5. Since the partial pressure of this uranium hexafluoride gas is 1 atm (1.01 × 10 5 Pa), the partial pressure of NbF 5 is 2.04 × 10 Pa by proportional calculation. NbF5 and uranium hexafluoride gas (circulation U in FIG. 5) condensed and recovered by the condenser 5 and heated and gasified are added to the gas 1 to be treated as a supply U, and this supply U is used as an adsorption tower. 9 is passed. The composition of the circulation U is shown in the column of line number 6 in FIG. 5, and the composition of the supply U is shown in the column of line number 7. The flow rate of NbF5 in the supply U is increased by about 1%, more precisely 1.01%, compared to the gas to be processed 1 before mixing by mixing the circulation U with the gas 1 to be processed. The supply U is removed 99% of NbF5 by the adsorption tower 9. The flow rate and partial pressure of NbF5 of the gas from which NbF5 has been removed (preliminary purification U in FIG. 5) are 1/100 of the supply U. This pre-purified U is supplied to the condenser 9 at 15 ° C., and as described above, about 93% of the gas of uranium hexafluoride is condensed, but the partial pressure of NbF 5 is 1.92 × 10 ⁻¹ . Since it is less than the saturated vapor pressure of 3.33 × 10 ⁻¹ , NbF5 does not condense. Therefore, uranium hexafluoride condensed and recovered by the condenser 3 is discharged as purified uranium 8. As uranium hexafluoride gas (non-condensable U in FIG. 5) which has not been condensed in the condenser 3, it is sent to the condenser 5 at −80 ° C. and condensed while containing NbF5. The condensed uranium hexafluoride and NbF5 are gasified and added to the gas 1 to be processed as a circulation U.

Here, we will review the movement of uranium hexafluoride. About 0.08 mol of circulation U is added to the original purification target U1.00 mol, resulting in a supply U of 1.08 mol. Of these, 93% is purified uranium 8, but the amount is 1.08 × 0.93 = 1.00 mol. About 0.08 mol of the amount that did not become purified uranium 8 becomes circulation U again and is added to the gas 1 to be treated. That is, even if the gas of uranium hexafluoride containing NbF5 is returned to the gas to be treated 1 in front of the adsorption tower 5, uranium hexafluoride is not accumulated in the system, and uranium hexafluoride in the gas to be treated 1 is present. The flow rate and the uranium hexafluoride flow rate of the purified uranium 8 are almost the same. Here, the reason is that there is 6.53 × 10 ⁻⁷ mol of uranium hexafluoride gas that cannot be recovered as off-gas. This unrecovered portion is an acceptable value considering that the demand for the recovery rate of uranium hexafluoride gas before the concentration step in reprocessing is 99 to 99.5%.

  According to this, a part of NbF5 in the gas to be treated 1 is adsorbed and removed in advance, and the partial pressure of NbF5 can be made lower than the saturated vapor pressure of NbF5 at the cooling temperature of the condenser 3, so Is less likely to condense and the purity of the recovered uranium hexafluoride can be improved. Furthermore, since the partial pressure of the uranium hexafluoride gas can be increased, high purity uranium hexafluoride can be obtained with a high recovery rate. Moreover, since the adsorption tower 9 is intended to reduce the partial pressure of NbF5 by adsorbing and removing a part of NbF5, the amount of adsorbent used can be reduced and the amount of adsorbent to be discarded can be reduced.

  Further, NbF5 is contained in the condensate of the condenser 5, and if it is gasified, it will be contained in the gas of uranium hexafluoride. By returning this gas to the adsorption tower 9, NbF5 can be adsorbed and removed. Therefore, an increase in NbF5 concentration due to circulation can be prevented. In this case, it is not necessary to separately provide an adsorption tower for preventing an increase in concentration, and the purification system can be miniaturized.

  Note that the condenser 5 may not be provided, and NbF5 and uncondensed uranium hexafluoride gas discharged from the condenser 3 may be circulated to the adsorption tower 9. According to this, a partial pressure of NbF5 in the gas returned to the adsorption tower 9 can be increased by condensing and recovering a part of the uranium hexafluoride gas in the gas 1 to be treated by the condenser 3. As a result, since the dissociation equilibrium between the NbF5 gas and the adsorbent can be moved to the adsorption side, the chemisorption reaction between NbF5 and the adsorbent is promoted, the degree of purification by the adsorbent can be improved, and high-purity uranium hexafluoride can be obtained. Obtainable.

  In addition, the gas obtained by heating and condensing the condensate in the condenser 5 is returned to the adsorption tower 9 through an adsorption tower filled with an adsorbent that adsorbs the impurity fluoride, and a part of the impurity fluoride is passed through. After the adsorption removal, it may be returned to the adsorption tower 9. In this case, the purpose of the adsorption tower 9 is to reduce the concentration of NbF5 in the gas 1 to be treated, so that the adsorption tower 9 can be downsized.

  Further, when the target component is uranium hexafluoride, an adsorption device filled with sodium fluoride can be used instead of the condenser 5 of the present embodiment. This utilizes the property that sodium fluoride adsorbs uranium hexafluoride at a temperature of around 100 ° C. and desorbs uranium hexafluoride at a temperature of 350 ° C. or higher. According to this, the impurity fluoride that has passed through the condenser 3 and the gas of uncondensed uranium hexafluoride are introduced into an adsorption device filled with sodium fluoride at a set temperature of about 100 ° C. to adsorb uranium hexafluoride. In addition, the purity and recovery rate of uranium hexafluoride can be improved by heating the adsorption device to 350 ° C. or higher, desorbing uranium hexafluoride as a gas, and joining the gas to be treated 1.

(Embodiment 3)
As Embodiment 3 of the present invention, among the fission products that become volatile fluorides, fluorides of niobium (Nb), technetium (Tc), ruthenium (Ru), molybdenum (Mo), and antimony (Sb) are used. A method for removal from uranium fluoride (UF6) is shown.

  Considering the configuration of the first embodiment, the adsorption tower 9 adsorbs a part of MoF6, TcF5, RuF6, and SbF5 to prevent the accumulation of impurity fluoride in the system. However, it is clear that the accumulation of impurity fluoride can be prevented even if this adsorption tower 9 is brought in front of the condenser 3, which is the position of the second embodiment. That is, a substance capable of reducing the concentration of MoF6, TcF5, RuF6, and SbF5 is selected as the adsorbent loaded in the adsorption tower 9 of Embodiment 1, or a plurality of adsorbents are loaded according to each compound, or adsorption When a plurality of columns 9 are provided for each compound, niobium (Nb), technetium (Tc), ruthenium (Ru), molybdenum (Mo), and antimony (Sb) are formed from uranium hexafluoride according to the configuration of the second embodiment. Can be removed.

(Embodiment 4)
FIG. 6 shows a conceptual diagram of Embodiment 4 of the present invention. As shown in the drawing, the gas purification method of the present embodiment condenses and recovers the uranium hexafluoride gas by cooling the adsorption tower 12 for removing the impurity fluoride in the gas to be treated and the gas passing through the adsorption tower 12. The condenser 14 is provided, and the impurity fluoride discharged from the condenser 14 and the gas of uncondensed uranium hexafluoride are mixed with the gas 1 to be treated and returned to the adsorption tower 12.

  The adsorption tower 12 is filled with an adsorbent (for example, LiF, NaF, MgF2, CaF2, BaF2, UO2F2, and UF) that adsorbs an impurity fluoride such as NbF5, MoF6, TcF5, RuF6, and SbF5. By making it flow, the impurity fluoride can be adsorbed and removed. The temperature of the adsorption tower 12 is adjusted by, for example, the temperature adjusting means 13. The temperature adjusting means may be omitted depending on the composition of the gas to be processed.

  The gas that has passed through the adsorption tower 12 is cooled to, for example, 15 ° C. by the cooling means 16 of the condenser 14 to condense uranium hexafluoride gas. The cooling temperature of the condenser 14 is not limited to 15 ° C., and is preferably a temperature at which the impurity fluoride is difficult to condense. The saturated vapor pressure of uranium hexafluoride and the impurity fluoride and uranium hexafluoride in the gas to be treated 1 And the partial pressure of the impurity fluoride. The impurity fluoride and uncondensed uranium hexafluoride gas discharged from the condenser 14 is mixed with the gas 1 to be processed, passes through the adsorption tower 12, and is cooled and condensed by the condenser 14. By this circulation, after the condenser 14 accumulates uranium hexafluoride having a predetermined concentration, if necessary, the condenser 14 is heated to a temperature higher than the triple point of uranium hexafluoride, for example, by the heating means 17 and gasified, It is recovered as purified uranium 8.

  However, if this circulation operation is repeated, the partial pressure of non-condensable gas in the system, such as impurity fluoride, F2, and O2, increases, and the recovery rate of purified uranium 8 decreases. In this case, as the concentration of the non-condensable gas increases, the cooling temperature of the condenser 14 is changed from, for example, 15 ° C. to −30 ° C. or less, specifically from −80 ° C. to −50 ° C. Most of the gas of uranium fluoride is condensed and recovered. When the partial pressure of the non-condensable gas exceeds the set value, the non-condensable gas is discharged from the condenser as an off gas. After being discharged as off-gas, the condenser 14 is heated and heated to 64 ° C. or higher, which is the triple point or more of uranium hexafluoride, by the heating means 17 such as a heater, and merged with the gas 1 to be processed.

  According to this, even if the concentration of the non-condensable gas increases and the recovery rate of the purified uranium 8 decreases, the non-condensable gas can be discharged out of the system to reduce the partial pressure of the non-condensable gas. As a result, the recovery of the purified uranium 8 can be recovered. Furthermore, the partial pressure of the impurity fluoride in the gas returned to the adsorption tower 12 can be increased by condensing and recovering part of the uranium hexafluoride gas in the gas 1 to be treated by the condenser 14. As a result, the dissociation equilibrium between the impurity fluoride gas and the adsorbent can be moved to the adsorption side, so that the chemical adsorption reaction between the impurity fluoride and the adsorbent is promoted, the purification efficiency by the adsorbent can be improved, and the use of the adsorbent The amount and the amount of waste adsorbent can be reduced. Furthermore, since the cooling temperature is set in two stages by the condenser 14, it is not necessary to provide another condenser, and facility costs and running costs can be reduced.

  When the partial pressure of the impurity fluoride contained in the gas to be treated 1 is equal to or lower than the saturated vapor pressure of the impurity fluoride in the condenser 14, the gas to be treated 1 is not directly passed through the adsorption tower 12. The gas 1 to be processed may be supplied to the condenser 14. In this case, the adsorption tower 12 only needs to remove the impurity fluoride from the impurity fluoride discharged from the condenser 14 and the uncondensed uranium hexafluoride gas, and the flow rate of the gas flowing through the adsorption tower 12 can be reduced. Therefore, the adsorption tower 12 can be reduced in size.

1 Gas to be treated 3, 5, 14 Condenser 8 Refined uranium 9, 12 Adsorption tower

Claims (4)

  The target gas to be purified and the gas to be treated containing impurities are passed through an adsorption tower filled with an adsorbent that adsorbs the impurities, and an adsorption step for adsorbing the impurities, and the gas that has passed through the adsorption step is cooled. A gas purification method comprising: condensing a target component; and returning impurities discharged from the condensation step and uncondensed target component gas to the adsorption step.   Condensation process for condensing the target component gas by cooling the target gas to be purified and the target gas containing impurities, and impurities discharged from the condensation step and uncondensed uranium hexafluoride gas, sodium fluoride A uranium adsorption step for adsorbing the uranium hexafluoride through a uranium adsorption tower packed with the uranium adsorption, and heating the uranium hexafluoride adsorbed on the sodium fluoride in the uranium adsorption step in the uranium adsorption tower A gas purification method comprising a desorption step for desorption as a gas.   The target gas to be purified and the gas to be treated containing impurities are passed through an adsorption tower filled with an adsorbent that adsorbs the impurities, and an adsorption step for adsorbing the impurities, and the gas that has passed through the adsorption step is cooled. Condensation step for condensing the target component gas, impurities discharged from the condensation step and uncondensed target component gas are returned to the adsorption step, and impurity gas of the uncondensed target component gas is returned to the condensation step. As the concentration increases, the temperature of the condensation process is lowered to condense the target component gas, and when the partial pressure of the uncondensed impurity gas exceeds a set value, the uncondensed impurity gas is not returned to the condensation process. A gas purification method comprising discharging to a gas.   The gas purification method according to claim 3, wherein the condensate of the target component condensed in the condensation step is heated to gasify and returned to the condensation step.

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