JPH0827361B2 - Exhaust gas treatment method for fusion reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention treats exhaust gas from a fusion reactor containing deuterium / tritium as impurities in the form of elements and chemically bound to form deuterium / tritium. The present invention relates to a method for separating tritium from these and then returning the tritium to the fuel cycle of the fusion reactor again.

[Prior Art] In the fuel cycle of a fusion reactor, the exhaust gas of the reactor is mainly deuterium and tritium in the form of unreacted fuel, helium which is a fusion reaction product, and a concentration of several percent at most. It contains many kinds of impurity gases, some of which contain hydrogen isotopes in a chemically bound form. Among these impurities, it is expected that there will be many hydrocarbons such as carbon monoxide and methane, and that there will be little ammonia, carbon dioxide, and water vapor. Since the fusion reactor exhaust gas contains tritium at a high concentration, it cannot be directly emitted to the atmosphere, and it is necessary to separate tritium in advance and reuse it as fuel.

Heretofore, several methods have been proposed for this purpose. In the method using a combination of a palladium film and a high temperature metal getter, tritium is purified with palladium, while impurities are treated by reaction with a metal. The drawback of this method is that the getter is used at 900 degrees, and the heat resistance of the material, the permeation of tritium due to the high temperature, and the dangerous operation and the generation of waste due to the regular replacement of the getter are problems. Is. A combination of a high temperature getter, an oxygen generation bed and a catalytic oxidation reactor is also possible, but problems such as generation of tritium water which is several orders of magnitude more dangerous than hydrogen gas, complicated process configuration, and oxygen generation bed of 500 degrees are problems. is there. That is, at this temperature, there is a risk of explosion due to sintering of the catalyst or generation of uncontrollable oxygen. Although combinations of oxygen evolution beds, metal getters and nickel catalysts have been proposed, the drawbacks of oxygen evolution beds are similar.

[Problems to be Solved by the Invention] The present invention does not have these drawbacks, that is, at a maximum temperature of 450 ° C. or less, does not require oxygen introduction from the oxygen generation bed or externally, or is exhausted by the reaction, and is periodically discarded. It is intended to realize a method for treating exhaust gas of a fusion reactor by a multi-stage process characterized by not using a device for generating a substance and not separating tritium in the form of water.

[Means for Solving the Problem] The present inventor has devised the following process in order to achieve this object.

(1) Most of elemental deuterium and tritium are separated by a palladium-silver permeator at 450 ° C. or lower, and at the same time, ammonia is decomposed into constituent elements in the permeator.

(2) Carbon monoxide is added to the residual gas and impurities such as carbon monoxide, nitrogen, hydrocarbons and water vapor to obtain carbon monoxide /
Set the water vapor ratio to 1.5 or more.

(3) React steam with carbon monoxide on a CuO / Cr ₂ O ₃ / ZnO catalyst at 150 to 200 degrees to generate hydrogen and carbon dioxide.

(4) The gas is further passed through a palladium / silver permeator filled with a nickel / aluminum oxide catalyst, and the hydrogen isotope generated by decomposing the hydrocarbon is merged with the hydrogen isotope of (1), while as a carbon element. To separate.

(5) Further, the remaining gas does not contain hydrogen isotopes in the form of elements or compounds, so it is released into the atmosphere, or (3)
Recycle over the catalyst.

[Operation] In step (1), the palladium / silver transmitter is 450
Used at low to low temperatures, traces of ammonia are decomposed by the catalytic action of palladium. When the partial pressure of hydrogen isotope is high, it is desirable to use the permeator at 400 to 500 degrees to prevent deterioration of permeation performance due to carbon monoxide.

In the next step the hydrogen isotope bound in the form of water is
CO over CuO / Cr ₂ O ₃ / ZnO catalysts used at 150-200 degrees
It is released by the reaction of + H ₂ O → CO ₂ + H ₂ . A CO / H ₂ O ratio of at least 1.5 is necessary to obtain a reaction rate of 100%, and in some cases carbon monoxide needs to be added to the system.

The gas leaving the CuO / Cr ₂ O ₃ / ZnO catalyst packed column in step (3) is mainly helium, and a small amount of hydrocarbons (methane, ethane, etc.), nitrogen, carbon monoxide, and carbon dioxide. In order to release deuterium and tritium in hydrocarbons, this mixed gas is passed through a palladium / silver permeator filled with a nickel / aluminum oxide catalyst to simultaneously decompose hydrocarbons and separate hydrogen isotopes. In this process, hydrogen, which is a reaction refined product, is discharged out of the system by permeation, so that a high reaction rate is achieved. The catalyst is periodically regenerated with hydrogen to prevent the catalyst from degrading activity due to carbon deposition.

[Effects of the Invention] Through the above process, all hydrogen isotopes in the form of compounds are decomposed and recovered, and a tritium-free gas is obtained at the exit of the process. That is, the removal of tritium is performed by a simple physical or catalytic reaction, and there is an effect that solid waste is not generated. In addition, since this process does not have a decomposition process of tritium compounds due to the oxidation reaction, there is no need to add oxygen from the oxygen generation bed or from the outside.
It has excellent safety.

[Example] An experimental result of the process according to the present invention will be shown as an example.

The experiment of step (4) was performed using He / CH ₄ mixed gas. When the mixed gas was circulated in a loop having a capacity of 8.8 including a permeator filled with 10 g of nickel catalyst at 460 degrees,
Methane was decomposed below the detection limit of gas chromatography, and 4.2
The methane concentration decreased with a half-life of minutes. After decomposing all methane, the nickel catalyst was regenerated at 450 to 550 degrees. This cycle was repeated 18 times, and a total of 2.2 mol of methane was decomposed, but no decrease in the activity of the catalyst was observed.

Continuation of front page (56) References JP-A-57-169696 (JP, A)

Claims (1)

[Claims] 1. A fusion reactor exhaust gas containing deuterium / tritium as an impurity in the form of elements and chemically bound, is treated, and the deuterium / tritium is separated to return to the fuel cycle of the fusion reactor. In the method of refluxing, (1) most of elemental deuterium and tritium are separated by a palladium-silver permeator at 450 ° C. or lower, and at the same time, ammonia is decomposed into constituent elements in the permeator, (2) ) Adding carbon monoxide to the residual gas and impurities such as carbon monoxide, nitrogen, hydrocarbons and water vapor, if necessary,
The carbon monoxide / steam ratio is set to 1.5 or more, and (3) steam is reacted with carbon monoxide on a CuO / Cr ₂ O ₃ / ZnO catalyst at 150 to 200 degrees to generate hydrogen and carbon dioxide, and (4) ) Further, the hydrogen isotope, which has been passed through a palladium / silver permeator filled with a nickel / aluminum oxide catalyst and decomposed hydrocarbons, is merged with the hydrogen isotope of (1), while separating carbon as an element. (5) A fusion reactor exhaust gas treatment process characterized in that a gas that does not contain residual hydrogen isotope in the form of an element or a compound is released into the atmosphere, or is recycled to the catalyst in (3).