JPH1053419A - Treatment of waste gas containing uranium hexafluoride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uranium hexafluoride in a waste gas possible of being continuously and inexpensively recovered in a form so as to be readily re-used without generating any wasted material. SOLUTION: A waste gas containing uranium hexafluoride and steam are continuously supplied into a reactor 10 heated to 200-700 deg.C and the uranium hexafluoride is reacted with the steam to produce UO2 F2 powder and a HF gas. The resultant UO2 F2 powder and the HF gas are respectively and continuously recovered. In a case of using a fluidized-bed reactor 10 filled with UO2 F2 powder as seed powder as a reactor, a waste gas containing uranium hexafluoride is supplied into the reactor from a supply nozzle 30 of the reactor and gas containing steam as a fluidizing gas is supplied into the reactor through a dispersion plate 13 of the reactor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to uranium hexafluoride (U) contained in process exhaust gas generated in a uranium enrichment plant.
F ₆ ) so that process exhaust gases can be released to uncontrolled areas. More specifically, the present invention relates to a method for treating and recovering UF _{6 in} process exhaust gas into a form that can be easily reused.

[0002]

_2. Description of the Related Art Conventionally, a method of removing UF _{6 from} exhaust gas which has been widely performed on a commercial scale is an exhaust gas passing through a container containing a solid adsorbent made of fluoride such as NaF, MgF ₂ , CoF _2. This is a method in which UF ₆ is adsorbed and removed by a solid adsorbent by providing it in a line.

[0003]

However, the above conventional method requires periodic replacement of the solid adsorbent, which is troublesome, requires a lot of time and labor, and
There is a problem that a spare adsorption vessel is required in order to continuously process the exhaust gas. In addition, the above solid adsorbent is extremely expensive, is constantly consumed in proportion to the amount of exhaust gas treated, and it is difficult to recover UF ₆ adsorbed by the adsorbent. There is a problem. An object of the present invention is to provide a method for treating uranium hexafluoride-containing exhaust gas which can continuously recover uranium hexafluoride in exhaust gas at a low cost in an easy-to-reuse form and does not generate waste. It is in.

[0004]

The invention according to claim 1 is
As shown in FIG. 1, a reactor heated to 200 to 700 ° C.
The exhaust gas containing uranium hexafluoride and steam are
Uranium hexafluoride and water vapor are supplied in the reactor 10 continuously.
UO by reacting with qi_TwoF_TwoPowder and HF gas
Generate UO_TwoF_TwoContinuous recovery of powder and HF gas separately
This is a method for treating exhaust gas containing uranium hexafluoride. this
According to the treatment method, the reaction represented by the following formula (1)
Of uranium hexafluoride generated in exhaust gas and contained in exhaust gas
UO is an easy form_TwoF_TwoContinuously and inexpensively recovered as powder
it can. UF₆ + 2H_TwoO → UO_TwoF_Two + 4HF (1) When the heating temperature of the reactor is lower than 200 ° C., UO_TwoF_TwoWhen
HF and UO_TwoF_TwoAnd H _TwoPractical due to insufficient separation of O
Not. Even when the heating temperature exceeds 700 ° C., the reaction yield is
It does not improve and wastes heat energy. Reactor for that
Is preferably 220 to 400 ° C.

[0005] The invention according to claim 2 is the invention according to claim 1, wherein the reactor 10 is a fluidized bed reactor 10 filled with UO ₂ F ₂ powder as seed powder. An exhaust gas containing uranium hexafluoride is supplied from the supply nozzle 30 into the reactor 10, and the dispersion plate 13 of the reactor 10 is supplied.
Is a method in which a gas containing water vapor is supplied as a flowing gas into the reaction apparatus 10 through the reactor. Since the UO ₂ F ₂ powder reacts with steam in a high-temperature fluidized state using the fluidized bed reactor 10, the generated UO ₂ F ₂ powder adheres to the inner wall of the reactor 10 and the inner wall of the outlet pipe, and is clogged. There is no danger that exhaust gas can be continuously processed.

The invention according to claim 3 is the invention according to claim 2, wherein the flowing gas contains water vapor and nitrogen gas. By including nitrogen gas in the flowing gas,
It is possible to adjust the amount of water vapor while keeping the amount of flowing gas constant.

A fourth aspect of the present invention is the method according to the third aspect, wherein the nitrogen gas discharged from the fluidized bed reactor 10 is reused as a flowing gas. By reusing the nitrogen gas, the cost of the carrier gas can be reduced.

The invention according to claim 5 is the invention according to claims 2 to 4
The invention according to any of the above, wherein the HF gas recovered from the fluidized bed reactor 10 is liquefied to generate hydrofluoric acid, and the amount of water vapor as a fluidizing gas is controlled in accordance with the concentration of the hydrofluoric acid. is there. By this control, the reaction efficiency in the fluidized bed reactor 10 is further improved, and the yield of the UO ₂ F ₂ powder product is increased.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fluidized bed reactor used for carrying out the method of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, a seed powder supply pipe 11 for supplying UO ₂ F ₂ powder serving as seed powder is directed obliquely upward on a side surface of a fluidized bed reactor 10 containing a fluidized bed therein. Upper extraction tubes 12 for extracting a certain UO ₂ F ₂ powder are provided diagonally downward. A dispersion plate 13 is provided near the inner bottom of the fluidized bed reactor 10 so as to partition the inside of the reactor 10. A fluidized bed 14 composed of UO ₂ F ₂ powder of seed powder is formed inside the reactor above the dispersion plate 13. The dispersing plate 13 is formed in a porous mesh so that the fluidizing gas is permeable but the seed powder does not fall off. Further, a wind box 16 for uniformly feeding steam and nitrogen gas to the fluidized bed 14 is formed inside the reactor below the dispersion plate 13. Reaction device 10
A gas supply pipe 17 for supplying steam and nitrogen gas toward the inside of the wind box 16 is provided on the bottom side wall of the fluidized bed 14. It becomes a fluidized state by nitrogen gas. Water vapor supplied to the gas supply pipe 17 is generated by heating water with a heater 40. This water vapor is sent to a mixing control valve 41, where it is mixed with nitrogen gas sent from a nitrogen tank 42, and then mixed with a gas supply pipe 17.
Sent to

A lower extraction pipe 18 for extracting UO ₂ F ₂ powder at a deep portion of the fluidized bed 14 to the outside of the reactor 10 is provided through the dispersion plate 13 and the bottom of the reactor 10. A solid-gas separation filter 1 for separating solid UO ₂ F ₂ powder generated by a fluidized bed reaction and rising from a gas body containing HF gas, unreacted steam and nitrogen gas is provided at an upper portion of the reactor 10.
9 are provided. An off-gas pipe 2 is provided above the filter 19.
3 is provided through the reactor 10. A backwash pipe 24 for blowing backwashing inert gas is connected to the upper end of the solid-gas separation filter 19. A supply nozzle 30 is provided on a side wall of the reactor 10 so as to penetrate the side wall. Supply nozzle 30
The exhaust gas containing uranium hexafluoride and nitrogen gas generated in the uranium enrichment plant is pumped to the supply nozzle 3
0 is sprayed on the fluidized bed 14.

The unreacted water vapor with the HF gas and nitrogen gas discharged from the off-gas pipe 23 is periodically sent to a condenser 32 by switching a three-way switching valve 31, where it is separated into a gas body and a condensed liquid. The separated condensate is stored in the sampling container 33 as hydrofluoric acid. The gas discharged from the condenser 32 contains nitrogen gas and a small amount of HF gas, which is sent to a washing tower 36 via a three-way switching valve 34, where it is separated into hydrofluoric acid and nitrogen gas. During normal operation, the HF gas, the nitrogen gas and the unreacted steam discharged from the off-gas pipe 23 are not sent to the condenser 32 but are sent directly to the washing tower 36 by switching the three-way switching valves 31 and 34, where the hydrofluoric acid and the nitrogen Separated into gas. The hydrofluoric acid taken out from the washing tower 36 is stored in a storage tank 37. On the other hand, the nitrogen gas taken out of the washing tower 36 is pressurized by the blower 38 and sent to the nitrogen tank 42 to be reused as a part of the flowing nitrogen gas.

A part of the hydrofluoric acid contained in the container 33 is collected for sampling, and the concentration of hydrofluoric acid is measured. As a result of the measurement, for example, when the concentration of hydrofluoric acid is too low, the ratio of water vapor to nitrogen gas is reduced by adjusting the mixing control valve 41. On the contrary, when the concentration of hydrofluoric acid is too high, the ratio of water vapor is reduced. To increase the concentration of hydrofluoric acid to a desired concentration.

In the apparatus configured as described above, a predetermined amount of UO ₂ F ₂ powder of the seed powder is supplied into the reactor 10 through the seed powder supply pipe 11, and then steam and nitrogen gas are reacted through the gas supply pipe 17. When supplied into the apparatus 10, the fluidized bed 14 is in a fluidized state. The fluidized bed is heated by a heating device (not shown) and heated to the reaction temperature. When the temperature of the fluidized bed reaches a predetermined temperature, uranium hexafluoride and nitrogen gas are sprayed onto the fluidized bed 14 from the supply nozzle 30. As a result, the sprayed gas containing uranium hexafluoride and the fluidized bed 14
Is vigorously stirred in the fluidized bed 14 and uranium hexafluoride reacts with water vapor to produce UO ₂ F ₂ and HF. The resulting UO ₂ F ₂ to form a spherical UO ₂ F ₂ powder was deposited on the UO ₂ F ₂ powder seed powder. This reaction increases the amount of UO ₂ F ₂ powder in the reactor 10. Excess UO ₂ F ₂ powder other than the seed powder is periodically extracted from the upper extraction pipe 12 as a reaction product.

[0014]

EXAMPLES Next, in order to show specific embodiments of the present invention, examples of the present invention will be described using the above fluidized bed reactor. <Example 1> UO ₂ F ₂ and HF were produced by operating the fluidized bed reactor shown in FIG. 1 under the following conditions to react uranium hexafluoride contained in exhaust gas with steam contained in the fluidized bed. . That is, 15 kg of UO ₂ F ₂ powder was supplied as seed powder into the apparatus. The area of the fluidized bed 14 is 100 mm × 100
mm and the height is 1 m. The fluidized bed was heated to 300C. A mixed gas obtained by mixing nitrogen gas at a rate of 20 L / min and steam at a rate of 5 L / min as a flowing gas is supplied to a gas supply pipe 17.
And supplied into the apparatus. Supply nozzle 3 which is a mixed gas obtained by mixing nitrogen gas at a rate of 10 L / min and UF ₆ gas at a rate of 1 L / min as a simulated exhaust gas of a process exhaust gas of a uranium enrichment plant
Sprayed from 0 to the fluidized bed 14 for 3 hours. Exhaust gas containing HF gas discharged from the off-gas pipe 23 was sent to the condenser 32, cooled with cooling water to generate hydrofluoric acid, and collected.

After completion of the test, the entire amount of UO ₂ F ₂ powder was recovered and weighed. As a result, it was confirmed that the UO ₂ F ₂ powder increased by 2.4 kg. As a result of analyzing uranium in hydrofluoric acid collected from the container 33, it was confirmed that the sensitivity was lower than the detection sensitivity. As a result of examining the state of adhesion of the UO ₂ F ₂ powder to the inner wall of the apparatus by disassembling the reactor, no adhesion that could lead to blockage was confirmed.

[0016]

As described above, according to the present invention, 2
UO ₂ F ₂ powder is obtained by continuously supplying exhaust gas containing uranium hexafluoride and steam to the reactor heated to 00 to 700 ° C. and reacting uranium hexafluoride with steam in the reactor. And HF gas are generated, and the UO ₂ F ₂ powder and the HF gas are continuously collected separately, so that uranium hexafluoride in the exhaust gas can be collected continuously and inexpensively in an easy-to-reuse form. No waste is generated.

[Brief description of the drawings]

FIG. 1 is a block diagram of a fluidized bed reactor used to carry out the method of the present invention.

[Explanation of symbols]

 Reference Signs List 10 Fluidized bed reactor 13 Dispersion plate 30 Supply nozzle

Claims (5)

[Claims] 1. A reactor heated to 200 to 700 ° C.
An exhaust gas containing uranium hexafluoride and water vapor are continuously supplied into (10), and the uranium hexafluoride and the water vapor are reacted in the apparatus (10) to thereby produce UO ₂ F ₂ powder and HF.
A method for treating an exhaust gas containing uranium hexafluoride, which generates a gas and continuously recovers the UO ₂ F ₂ powder and the HF gas separately from each other. 2. The method according to claim 1, wherein the reactor (10) is UO ₂ F ₂ as a seed powder.
A fluidized bed reactor (10) filled with powder, wherein an exhaust gas containing uranium hexafluoride is supplied into the device (10) from a supply nozzle (30) of the device (10), and the device (10) ) Dispersion plate (1
The processing method according to claim 1, wherein a gas containing water vapor is supplied as a fluidizing gas into the apparatus (10) through (3). 3. The processing method according to claim 2, wherein the flowing gas contains water vapor and nitrogen gas. 4. The process according to claim 3, wherein the nitrogen gas discharged from the fluidized bed reactor (10) is reused as a fluidizing gas. 5. HF recovered from a fluidized bed reactor (10)
5. The processing method according to claim 2, wherein the gas is liquefied to generate hydrofluoric acid, and the amount of water vapor as a flowing gas is controlled in accordance with the concentration of the hydrofluoric acid.