JPH0833490B2 - Method and apparatus for decontaminating waste gas from a fusion reactor fuel cycle - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method and apparatus for decontaminating waste gas of a fusion reactor fuel cycle, in particular tritium and / or
OR METHOD AND DEVICE FOR DETAILING TRIGIUM AND / OR DIEUTERIUM FROM THE CHEMICAL BOND, SEPARATION FROM THE WASTE GAS, AND RETURN TO THE FUEL CYCLE FOR DECONTAMINATION OF WASTE GAS COMPONENTS CONTAINING DIUTERIUM IN A CHEMICALLY BOND Regarding

PRIOR ART The waste gas of a fusion reactor contains about 85% by volume of noble gases and about 15% by volume of pollutants and a small amount of deuterium balance. Contaminants may be argon, tritium-containing and / or deuterium-containing hydrocarbons, in particular tritium-containing and / or diuterium-containing CH ₄ , tritium-containing and / or
Or it occurs in the form of water containing diuterium and ammonia containing tritium and / or diuterium. Therefore, the exhaust gas must remove free tritium and tritium-containing pollutants or must be decontaminated to the release limit, after which the residual exhaust gas can be discharged into the atmosphere. In addition, recovery of tritium and diuterium from compounds containing tritium and diuterium and return of tritium and diuterium into the fuel cycle is desirable because it is guaranteed to keep tritium away from the ambient atmosphere in this way. Is.

A method and apparatus for decontamination according to the preamble of the claims is "Proceeding of Tritium Technology in Fusion Fusion and Isotropy Application".
s of Tritium Technology in Fission, Fusion and Isot
ropic Application ", Dayton, Ohio, April 29th (1980), pages 115-118. In this case, waste gas containing pollutants flows through the intermediate container every time. , Then passes through the catalytic reactor to reduce oxygen with hydrogen at 450 K, after which all contaminants are adsorbed and adsorbed at 75 K in the molecular sieve bed and thus separated from the waste gas. After heating to 400 K for desorption of pollutants, the pollutants are oxidized at 800 K in an oxygen-releasing fixed bed to give water containing tritium or diuterium and tritium or diuterium-free compounds, i.e. CO. _2, the N ₂ and Ar. tritium or water containing Jiyuuteriumu freezes at 160K, then periodically evaporated and fed to the hot uranium metal bed, Jiyuuteri water the metal floor at 750K Conversion to hydrogen containing um or tritium and solid UO _2. Instead of the uranium metal bed reduction, it is also possible to carry out reduction using an electrolytic cell.

The methods proposed hitherto have the following drawbacks: -many steps-risk of loss of tritium due to high temperature and thus with infiltration-oxygen release fixation at high temperature, optionally with sintering of fixed bed particles. Oxygen release (deactivation) of bed operation and loading of hot metal getters-oxidation of ammonia and hydrocarbons and re-reduction of water produced (loading of hot metal getters) -oxidation of hydrogen and reduction of water formed ( load of the thermal metal Getsuta) - often radioactive solid waste and - challenges oxygen releasing solid product invention of the NH ₃ nitrogen oxide during the oxidation in the bed it is to solve problems present invention, fuel cycle of the nuclear fusion reactor Prior art corresponding method for decontaminating waste gas components containing chemically bound tritium and / or diuterium from the waste gas of As it appears in
It is an object of the invention to provide a method and a device in which the loss of tritium and / or diuterium by osmosis and the loading of hot metal getter material and the formation of nitrogen oxides are avoided. This method should be energy-saving and easy to implement compared to the methods known in the prior art. The liberated tritium and / or diuterium should be able to be returned to the fuel cycle without any other processing means except isotope separation.

Means for Solving the Problems This problem is according to the invention: a) Tritium- and / or diuterium-containing ammonia and / or waste gases which lead together with tritium and / or diuterium-containing hydrocarbons, ammonia and hydrocarbons. Through a device for decomposing (degrading) into elements (cracking), b) liberating hydrogen isotope through the membrane, separating and discharging from the residual waste gas stream, and c) discharging decontaminated waste gas into ambient air. It will be solved.

As a device for decomposing ammonia, a membrane made of palladium or a palladium / silver alloy or a Ni catalyst is used, and a Ni catalyst is used for decomposing hydrocarbons.
The decomposition reaction and the separation of liberated hydrogen isotopes are carried out sequentially or in one step. In a preferred embodiment of the process according to the invention, the decomposition reaction of ammonia and hydrocarbons is carried out with a Ni catalyst on a ceramic support in a temperature range between 250 and 450 ° C., the membrane being palladium or a palladium-silver alloy. The catalyst, which consists of and surrounds the catalyst and is present inside the membrane, is heated together with the membrane to the reaction temperature.

Advantageously, the amount of component CO that uses an oxidation catalyst per
Contact with O ₂ getter metal at temperatures in the range of 200 ℃ to 300 ℃ to oxidize to CO ₂ and then to remove O ₂ and reduce water, and finally decompose ammonia and hydrocarbons Therefore, the hydrogen isotope-passing membrane and the Ni catalyst are brought into contact with each other at a temperature in the range of 300 to 450 ° C.

The device according to the invention for carrying out the process comprises a buffer vessel, a catalyst bed and a heatable metal bed, and a circulation line 21
In the flow direction of the waste gas in the inside, a buffer vessel 1 for compensating the gas pressure, a catalyst bed 2 for selectively oxidizing CO to CO ₂ , O ₂ and H ₂ O from the waste gas by a chemical reaction Contains a heatable metal bed 3 to be removed, one or several vessels 5 with a hydrogen isotope outlet 22, containing a heatable membrane selectively passing hydrogen isotopes, containing a renewable Ni catalyst 6 However, a heatable bed 10 with an inlet 7 and an outlet 8 for the regenerant and one or several pumps 23 are arranged.

In a preferred embodiment of the device, the vessel 5 and the catalyst bed
Instead of the combination with 10, in a container 11 with a gas outlet 12 for hydrogen isotope separated from waste gas, in which an externally coolable container 11 is arranged, the outer surface of which is cooled to a temperature of 200 ° C., A tubular membrane 14 made of palladium or a palladium-silver alloy containing a Ni catalyst 13 and having a supply pipe 15 for waste gas to be decontaminated and a discharge pipe 16 for waste gas decontaminated.
The container 11 has a container heating device 18 between its inner wall 17 and the tubular membrane 14. It is particularly advantageous for the tubular membrane 14 to be designed as a spiral tube.

The waste gas from the fuel cycle of the fusion reactor has approximately the following composition: 80-85 mol% He, Ar 15-20 mol% N (D, T) ₃ , C (D, T) ₄ , (D, T ) ₂ O, (D, T) ₂ , C
O, CO ₂ , N ₂ and O _{2, of} course, some of the deuterium isotopes may be replaced by light hydrogen (protium) in the corresponding compounds.

The advantages of the method according to the invention and of the device according to the invention are: a) some reduction of the steps is achieved, b) excluding the decomposition temperatures of NH ₃ and CH _{4 above} a maximum working temperature of 300 ° C. in the circulation system. No loss of tritium due to permeation of metal walls can occur, c) Minimization of radioactive waste is achieved, d) Reduction of oxygen getter (metal bed) loading to a minimum. [In-situ O ₂ formation by thermal decomposition of oxygen-releasing fixed bed (catalyst bed for selective oxidation of CO to CO ₂ );
H ₂ Oxidation and no re-reduction], e) Nitrogen oxide formation does not occur; f) Tritium-containing and / or diouterium-containing contaminants When the decomposition of ammonia and hydrocarbons and the separation of tritium or diouterium are combined: a chemical reaction The thermodynamics and the kinetics of the are found to move in a direction that favors the method.

In the case of the state-of-the-art processes, permeation losses of deuterium can occur during the catalytic oxidation of oxidizable waste gas components and during the reduction of water in the uranium bed to hydrogen.

In the process according to the invention, the waste gas is introduced as feed gas into the conduit of the circuit, flows through the buffer vessel and then at about room temperature (20 ° -25 ° C.) through a fixed bed which acts as a catalyst. The fixed bed contains, for example, hopcalite (CuO / MnO ₂ ) or perovskite. As a result, oxygen and carbon monoxide contained in the waste gas are selectively converted into CO ₂ . In the case of oxygen deficiency in the gas, the fixed bed liberates a stoichiometric amount of oxygen. The waste gas leaving this catalyst is then passed through a layer, which may contain, for example, uranium or titanium group metals, at a temperature between 200 and 300 ° C., in particular 250 ° C., and the water is decomposed under the formation of hydrogen. And, for example, uranium oxide is formed and oxygen which has not been converted to carbon dioxide is sorbed. The waste gas leaving this oxygen getter then consists of palladium or
After passing through a container having a film made of a silver alloy at a temperature between 300 and 450 ° C, especially at 400 to 450 ° C, ammonia contained in the waste gas is quantitatively decomposed by the film. The membrane may be constructed as a tube or tube bundle that is directly heated and surrounded by an outer container (tank) that is cooled.
From this vessel, deuterium produced during decomposition is discharged, and if necessary, after passing through a hydrogen isotope separation device, it is returned to the fuel cycle of the fusion reactor. The waste gas thus freed of ammonia is then passed through a fixed nickel catalyst bed heated to a temperature of 250 ° C. to 450 ° C. in order to decompose hydrocarbons, in particular methane. The decomposition is performed according to the following equation,
For simplicity in the formula, all hydrogen isotopes are represented together by H or H ₂ (this simplified notation is also maintained below): Over time, the catalyst is exhausted and must either be discarded or regenerated with light hydrogen at a sufficiently high temperature according to the formula: C ^(Ni) + 2H ₂ → CH ₄ (2) The residual gas is pure Can be discharged directly into the ambient air or circulated until the required purity is reached, in which case the residual gas once again flows through the buffer container, after which the catalyst bed, oxygen getter described And pass through the container.

The known process consists of at least seven steps, the individual working temperatures of which are sufficiently far apart from each other that the maximum temperature difference between two successive steps is 640 ° C.
The three or four steps are designed to have a significantly small temperature difference exclusively on the rising line. In the method according to the state of the art, the catalytic oxidation of all oxidizable components of the waste gas is carried out at 527 ° C.
Catalytic oxidation is only selectively applied to CO at low temperatures in the range of 20 ° C to 25 ° C. Subsequent reduction of water in the process of the invention and a suitable temperature, for example 250 ° C.
Thus, the removal of oxygen by the getter metal enables a decomposition process of ammonia and hydrocarbons. In this case, for the stationary decomposition of ammonia, a film in which the ammonia consists of palladium or a palladium-silver alloy or
Whether or not it is decomposed with a Ni catalyst is not important.

The invention will now be described in detail with reference to some figures and the description of the experiments illustrated.

The example apparatus from FIGS. 1 and 2 is generally an externally cooled vessel 5 of the embodiment of FIG. 1 with a membrane heated to 450 ° C. and an externally cooled, internally 450 ° C. The combination with the heated catalyst bed 10 is replaced by an externally cooled vessel 11 which in the embodiment of FIG. 2 has only one structure, namely a tubular membrane 14 heated to 400 ° C. They can only be distinguished by things. The spirally turning tubular membrane 14 contains the nickel catalyst 13 supported on a ceramic carrier in the latter embodiment. For regeneration of the Ni catalyst that collided with carbon, for example, a regenerant consisting of light hydrogen was used at the gas outlet
By introducing through 12 and passing through a tubular membrane 14. For this reason, the valve 24 in the conduit 21 is closed beforehand and the valve 27
open. At about the same working temperature, about 450 ° C., carbon reacts with H _{2 according} to equation (2). The resulting mixture of methane and hydrogen
28 is discharged by the regenerant outlet 26 of conduit 21. The other components of both devices are listed in the following table and need not be described further.

Table: 1. Buffer vessel 2. Catalyst bed with eg hopcalite 3. Metal bed with eg uranium 4. Metal bed eg with palladium 6. Nickel catalyst 7. Regenerant inlet to catalyst bed 8. From catalyst bed 10 Regenerant outlet of 9. Regenerant, for example H ₂ 12. Gas outlet of hydrogen isotope from vessel 11. 15. Supply pipe for waste gas from metal bed at vessel 11 (joined with conduit 21) 16. For decontaminated waste gas,
Exhaust pipe from container 11. Inner wall of container 11. Heating device for tubular membrane 14. Cooling device for container 11 21. Circulation conduit 22. Gas outlet for hydrogen isotope from container 5 23. Pump The method of the present invention , In the experimental apparatus schematically shown in FIG.
I investigated its effectiveness. For this reason, the process gases to be treated can be replaced with ammonia and / or methane, respectively, as an alternative to genuine waste gas from the fusion reactor fuel cycle.
A gas mixture consisting of helium with up to mol% was simulated by using it with or without the addition of small amounts of other important gases. This gas mixture was produced in the laboratory by feeding gas, helium by inlet valve 31, ammonia by inlet valve 32, methane by inlet valve 33 and other gases by inlet valve 30. The gas mixture was passed through the Nickel catalyst bed 36 at a high throughput, ie a high flow rate, ie 150 l / h. The catalyst present in the quartz tube is
It is heated to the desired temperature in an externally openable tube furnace (not shown in the drawing, but suggested by the heating device 37). The tube furnace is connected to an all-electronic control unit (not shown in the drawing). The gas mixture was then passed through a Pd / Ag membrane 41 which was heated by the heating device 38.
The hydrogen used at a temperature of 450 ° C. and produced from the catalytic cracking of methane or ammonia was separated off continuously via outlet 42. The catalyst container 36 as well as the Pd / Ag film 41 can each encircle one bypass. in this case,
The composition of the obtained gas was measured by using a gas chromatograph 43 connected to a self-recording integrator 44 for evaluation.
rapak) Q, Pola Park R or Morequiller Sieve 5A
Analyzed using a column. In addition, a quadrupole mass spectrometer 46
Is directly connected to the circulation path 52 via the gas suction system 45. High pressure (eg atmospheric pressure) using gas suction system 45
Can be fed to a mass spectrometer used in high vacuum without changing the percentage composition.
The gas suction system was heated to avoid condensation effects (not shown). A calculator 48 connected to a quadrupole mass spectrometer 46 via a coupler 47 was used for data evaluation. Due to the high sensitivity of mass spectrometry, each analysis requires only a very small amount of sample. Thus, it is possible to withdraw the sample from the circuit in a continuous manner over a period of several hours without any pressure drop. A very high throughput was chosen for the test. As a result, the conversion per pass becomes small, and the measurement results can be easily interpreted according to the principle of the batch reactor. The experimental setup is still composed of several pressure regulators 34, manometers 35, expansion vessels 49, flow meters 50 and several pumps 51,
And a valve.

Experiment A: Catalytic decomposition of methane into elements In the above experimental apparatus, a gas mixture consisting of helium and 14.5 mol% methane was pumped at 450 ° C through a nickel catalyst on a ceramic carrier having the trade name BASF type G1-22. Circulated in. Circulating flow volume is 6 l, catalyst volume is 5 ml
It was.

Part 1 of Experiment The temperature of the vessel with the palladium membrane was kept at 25 ° C. The detection of the decomposition of methane in helium as a carrier gas was verified by analyzing the methane and hydrogen contents by mass spectrometry. FIG. 4 shows the results in the left part of the curve (up to 4 hours). Decomposition of methane was indicated at the beginning of the experiment but stagnated after about 2 hours. XPS on catalyst surface
Analysis (XPS = photoelectron spectrometer) revealed that the carbon produced was present in elemental form and not in carbide form.

Second part of the experiment: However, when the palladium membrane is heated to 400 ° C., the hydrogen produced by the decomposition reaction of methane is continuously taken out from the system. This results in a shift of the chemical equilibrium towards the product hydrogen, which results in a quantitative conversion (see FIG. 4, right part of the curve, between 4 and 6 hours).

Part 3 of the experiment: The regeneration of the Nickel catalyst is carried out by introducing light hydrogen into helium as a carrier gas in the temperature range between 250 ° C and 450 ° C to remove the elemental carbon deposited on the Nickel catalyst. , Was converted to methane by supplying hydrogen, and was discharged from the experimental device. The production of methane was proven.

Experiment B: Catalytic decomposition of ammonia into elements A gas mixture consisting of helium and about 15 mol% ammonia was passed through the experimental apparatus at a flow rate of 18 l / h. In this case, ammonia is 400% in a container with Pd / Ag membrane (surface area 1.2 m ² ).
Decomposed at ° C. FIG. 5 shows the decomposition rate as a function of four ammonia source concentrations, determined by mass spectrometry. The raw ammonia partial pressure was 87.10 mbar * for 35.48 mbar for △, 14.14 mbar for 9.34 mbar for 9.34 mbar.

The reaction rate constant confirmed from ammonia decomposition is 1
There were 4 × 10 ¹³ molecules per cm ² · 1 second. The conversion rate is quantitative.

Comparative example for helium / methane mixture: avoid nickel catalyst, helium and methane about 15 mol%
The mixture consisting of was pumped through a palladium membrane in the circuit for 4 hours at a flow rate of 18 l / h. The temperature of the palladium film was 400 ° C. No decrease in methane concentration could be detected by mass spectrometry. This means that the palladium film decomposes ammonia exclusively, but methane does not. In contrast to this, the Nickel catalyst decomposes not only methane but also ammonia.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the device according to the invention, in which the decomposition of ammonia and the decomposition of hydrocarbons are carried out in two different component parts of the device, and FIG. FIG. 3 is a schematic sectional view showing another embodiment of the device according to the invention, in which hydrogen is simultaneously carried out in the same component part of the device, and FIG. 3 is a schematic sectional view of an experimental device examining the effectiveness of the method according to the invention. FIG. 4 is a curve diagram showing the effectiveness of the decomposition reaction in the case of methane, and FIG. 5 is a curve diagram showing the effectiveness of the decomposition reaction in the case of ammonia. 1 ... Buffer, 2 ... Catalyst bed, 3 ... Metal bed, 4 ...
Membrane, 5 ... Container, 6 ... Nickel catalyst, 7 ... Regenerant inlet, 8 ... Regenerant outlet, 9 ... Regenerant, 10 ... Catalyst bed,
11 …… Container, 12 …… Gas outlet, 13 …… Nickel catalyst, 14
...... Tubular membrane, 15 …… Supply pipe, 16 …… Exhaust pipe, 17 …… Inner wall, 18 …… Heating device, 19 …… Cooling device, 21 …… Conduit, 22
…… Gas outlet, 23 …… Pump, 24 …… Valve, 25 …… Regenerant, 26 …… Regenerant outlet, 27 …… Valve, 28 …… Methane / hydrogen mixture, 30 …… Inlet valve, 31 …… Inlet valve, 32 ... Inlet valve,
33 ... Inlet valve, 34 ... Pressure regulator, 35 ... Manometer, 36 ... Catalyst container, 37 ... Heating device, 38 ... Heating device, 39 ... Bypass, 40 ... Bypass, 41 ... Membrane , 42 ...
… Outlet, 43 …… Gas chromatograph, 44 …… Self-integrator, 45 …… Gas inlet system, 46 …… Rotating mass spectrometer, 47…
… Coupler, 48 …… Calculator, 49 …… Expansion vessel, 50 …… Flowmeter, 51 …… Pump

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Bernd Schuster Karlsruhe Bonnell Strasse 4 (56) Reference JP-A-54-102500 (JP, A)

Claims (7)

[Claims] 1. Decontamination of tritium and / or deuterium from waste gas of a fusion reactor fuel cycle to decontaminate waste gas components containing tritium and / or deuterium in chemically bound form. And separating it from the waste gas and returning it into the fuel cycle: a) the waste gas with which tritium and / or deuterium-containing ammonia and / or tritium and / or deuterium-containing hydrogenated carbon is derived together with ammonia and carbonization. Passing through a device that decomposes hydrogen into elements, b) releasing free hydrogen isotopes through the membrane, separating and discharging from the residual waste gas stream, and c) discharging decontaminated waste gas into the ambient atmosphere. A method for decontaminating waste gas of a fuel cycle of a fusion reactor, characterized by: 2. A membrane made of palladium or a palladium-silver alloy or a Ni catalyst is used as a decomposing device for ammonia, and a Ni catalyst is used for decomposing hydrocarbons, and a decomposition reaction and separation of released hydrogen isotopes are performed. The method according to claim 1, wherein the steps are carried out sequentially or in one step. 3. A decomposition reaction of ammonia and hydrocarbons,
Conducted in a temperature range of 250 ° C to 450 ° C using a Ni catalyst on a ceramic support, the membrane is made of palladium or a palladium-silver alloy, and surrounds the catalyst, and the catalyst present inside the membrane reacts with the membrane. The method of claim 1 wherein the method comprises heating to a temperature. 4. A temperature in the range of 200 ° C. to 300 ° C. for the selective oxidation of the component CO to CO ₂ using an oxidation catalyst in the waste gas, followed by the removal of O ₂ and the reduction of water. At O ₂
At a temperature in the range of 300 ° C to 450 ° C for contact with the getter metal and finally to decompose ammonia and hydrocarbons,
The method of claim 1 wherein the hydrogen isotope is passed through the membrane and the Ni catalyst is contacted. 5. A buffer vessel, a catalyst bed and a heatable metal for decontaminating waste gas components containing chemically bound tritium and / or deuterium from the waste gas of a fusion reactor fuel cycle. In an apparatus having a bed, a buffer container (1) for compensating the gas pressure, a catalyst bed (2) for selectively oxidizing CO to CO ₂ , and an exhaust gas O A metal bed (3) for removing ₂ and H ₂ O by chemical reaction, one or several heatable membranes (4) selectively passing hydrogen isotopes and containing a product outlet of hydrogen isotopes (22 (5) having a), a heatable catalyst bed (10) containing a renewable Ni catalyst (6) and having an inlet (7) and an outlet (8) for a regenerant (9),
And an apparatus for decontaminating the waste gas of the fuel cycle of a fusion reactor, characterized in that one or several pumps (23) are arranged and connected to each other by a circulation conduit (21). 6. A container (11) containing a tubular membrane, which can be externally cooled, is arranged in place of the combination of the container (5) containing the membrane selectively passing hydrogen isotopes and the catalyst bed (10). The Ni catalyst (13) is placed inside a vessel (11) containing a tubular membrane, the outer surface of which is cooled to a temperature of 200 ° C and which has a gas outlet (12) of hydrogen isotope separated from waste gas. contains,
A tubular membrane (14) made of palladium or an alloy of palladium / silver and having a supply pipe (15) for the waste gas to be decontaminated and a discharge pipe (16) for the decontaminated waste gas is arranged, and a container ( Device according to claim 5, wherein 11) has a heating device (18) for the tubular membrane between its inner wall (17) and the tubular membrane (14). 7. Device according to claim 6, characterized in that the tubular membrane (14) is constructed as a spiral tube.