Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B4/00—Hydrogen isotopes; Inorganic compounds thereof prepared by isotope exchange, e.g. NH3 + D2 → NH2D + HD
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
  • C01B13/14—Methods for preparing oxides or hydroxides in general
  • C01B13/32—Methods for preparing oxides or hydroxides in general by oxidation or hydrolysis of elements or compounds in the liquid or solid state or in non-aqueous solution, e.g. sol-gel process
  • C01B13/322—Methods for preparing oxides or hydroxides in general by oxidation or hydrolysis of elements or compounds in the liquid or solid state or in non-aqueous solution, e.g. sol-gel process of elements or compounds in the solid state

Definitions

• the invention relates to a process for decomposing tritiated water and recovering elementary tritium in which a metal Me is used which oxidizes in the presence of water according to the formula
• tritiated water is understood to mean water in which at least certain hydrogen atoms are replaced by the tritium isotope. This isotope is very radioactive and is formed in large quantities in a nuclear fusion reactor. Several methods are known for recovering tritium.
• a first method uses the electrolysis of water in an acidic or alkaline aqueous solution.
• electrolysis separators which withstand long-term tritium. This requires frequent replacement of separators and handling of materials contaminated with tritiated water.
• the separator must not be punctured, because in this case an explosive mixture of hydrogen and oxygen is formed.
• the elementary tritium obtained there is always mixed with a non-negligible quantity of tritiated water and oxygen having passed through the separator. Even more serious is the contamination of the oxygen stream with gaseous tritium.
• a second known method uses a reaction with carbon dioxide which leads to a reduction in water and produces carbon dioxide and hydrogen.
• This reaction use of catalysts and also does not lead to total conversion of the tritiated water. It is therefore necessary to carry out a rather complicated purification of the gases leaving the reactor with a view to eliminating the tritiated water which has not reacted, and the carbon dioxide and carbon monoxide.
• the problem of permeation of reactor materials by gaseous tritium increases with temperature, which in the present case is at least 300 ° C.
• the object of the invention is therefore to propose a process and a device for the decomposition of tritiated water, which has a high yield and which does not pose any problem of permeation of tritium through the constructive materials of the reactor.
• the inner wall 3 encloses a reaction chamber 4, which is filled with a metal such as iron, zinc, cobalt and nickel.
• the space 5 between the two concentric walls 2 and 3 is connected to a device 8 for adsorbing hydrogen and its isotopes through a valve 9.
• This device constitutes a hydrogen getter which is well known to man of art.
• this space 5 can be supplied through a valve 10 by hydrogen from a source 11.
• the reaction chamber 4 is supplied with tritiated water from a reser ⁇ see 12 which is connected to it by a valve 13.
• a vacuum pump 14 can be connected by a valve 15 to this enclosure 4 when the process is started, and the enclosure has a water outlet which is connected by a valve 16 to a water collection chamber 17, this chamber which can be cooled by means not shown up to the temperature of liquid nitrogen.
• a vacuum of a few millibars is established in the enclosure 4 by means of the pump 14, the valve 15 being open.
• hydrogen is injected into space 5 by opening the valve 10.
• the hydrogen passes through the wall 3 thanks to the vacuum prevailing in the enclosure, and reacts with metal oxides possibly present in said metal bed.
• the collection chamber 17 which is at low temperature, sucks up the water vapors.
• we close valves 15 and 16, and we open valves 9 and 13. thus starts the decomposition phase.
• the tritiated water present in the reservoir 12 is sucked into the enclosure 4 and reacts there with the metal according to the formula indicated above.
• This reaction is favored by a 1' ceremonies of heating to a temperature which in the case of iron as the metal bed is chosen between 300 and 450 ⁇ C.
• a higher temperature is chosen, of the order of 650 to 1000 ° C, and for zinc a lower temperature, of the order of 250 to 400 ° C.
• This temperature defines, in combination with the morphology of the bed metal (particle size, specific surface), the reaction rate.
• the hydrogen molecules and its isotopes cross the wall 3 and are immobilized in the getter 8, which is for example based on uranium, titanium or an alloy of zirconia and titanium.
• This hydrogen migration creates a certain partial depression in the enclosure 4 thanks to which the tritiated water present in the tank is sucked towards the enclosure 4 without the aid of a pump. This phase continues until saturation. Indeed, the effective surface of the metal in the enclosure gradually oxidizes and the decomposition yield decreases.
• the valve 9 is then closed, either after fixed periods, or after reaching a predetermined saturation, and the regeneration phase is prepared by cooling the reservoir 12 with a view to inverting the flow of water and trapping in this reser ⁇ see all the tritiated water remaining in the enclosure 4. Then the valve 13 is also closed and the valves 10 and 16 are opened.
• the regeneration temperature of the metal bed in the enclosure 4 is chosen for the iron between 500 and 700 ° C, for nickel and cobalt between 800 and 1000 ° C, and for zinc between 350 and 400 ° C.
• the wall 3 is then crossed by hydrogen supplied by the source 10, and a reduction in the metal and a formation of light water is observed according to the following formula:
• the collection chamber 17 being at -196 ° C, the light water thus produced is transferred to this chamber. Simultaneously, the getter 8 can be regenerated by heating it. At a suitable temperature, the mixture of hydrogen isotopes trapped therein is released and can be treated in an unrepresented stage of separation of hydrogen isotopes to isolate the trietium.
• iron is preferably used, which is activated by a small amount of copper, chromium, calcium, potassium or manganese (up to 5%).
• copper chromium, calcium, potassium or manganese
• the sum of chromium and copper goes back to between 4 and 4.5% by weight.
• Such catalysts are obtained from an aqueous solution containing soluble iron salts (for example nitrates) as well as salts of said minority metals. Co-precipitation is carried out in the form of hydrated hydroxides or oxides under controlled acidity conditions. Then filtering, drying, shaping (pellets or grains), calcination and final reduction with hydrogen are carried out.
• the catalytic mass obtained by this process has a specific average surface area between 10 and 20 m 2 / g.
• catalytic metals on a porous alumina support for example, so that a large specific surface of the metal is obtained and simultaneously a support which is thermally and mechanically stable during the multiple transitions between the reduced state and the oxidized state.
• Activation metals have a pile effect between iron, a less noble metal, and the other, more noble metal. Another effect is that of deforming the crystal structure of the reduced iron by creating active centers for the reaction with water.
• the deposition of these metals on the porous support can be carried out by dipping the porous support in aqueous solutions of iron, chromium, manganese salts etc., for example nitrate, or else in solutions of organic salts in a solvent organic, for example acetyl acetonate. After the solvents have disappeared, the salt decomposes thermally in air and oxides are obtained which can be reduced to the metallic state by treatment with hydrogen as during the regeneration phase.
• Iron can also be deposited on zeolites, for example mordenites, starting from calcium mordenite and by means of a calcium-iron cation exchange and a subsequent reduction. Iron present in the structure of the zeolite using hydrogen.
• Other usable metals which can be deposited by the same method are zinc, nickel and cobalt.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Catalysts (AREA)

Applications Claiming Priority (3)

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ID=19731309

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• 1991
  • 1991-08-27 LU LU87994A patent/LU87994A1/fr unknown
• 1992
  • 1992-08-25 JP JP5504133A patent/JPH06510016A/ja active Pending
  • 1992-08-25 EP EP92918215A patent/EP0601009A1/de not_active Withdrawn
  • 1992-08-25 WO PCT/EP1992/001951 patent/WO1993003996A1/fr not_active Ceased
  • 1992-08-25 CA CA002116350A patent/CA2116350A1/fr not_active Abandoned
• 1994
  • 1994-02-23 US US08/199,232 patent/US5445803A/en not_active Expired - Fee Related

Non-Patent Citations (1)

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