Extraction method of tritium

An extraction method of a high purity tritium gas from tritium-containing heavy water is disclosed. Tritium-containing heavy water is led from a heavy water source into an exchange reaction column wherein the heavy water is brought into contact with a tritium-containing heavy hydrogen to thereby transfer tritium in the heavy hydrogen into the heavy water by way of the exchange reaction to obtain a tritium-enriched heavy water. The resulting tritium-enriched heavy water is then led to a heavy hydrogen gas generator such as an electrolytic cell to generate a tritium-enriched heavy hydrogen, a part of which is recycled to the exchange reaction column and the remaining part thereof is led into a hot-wire type thermal diffusion column, e.g. cascade to enrich tritium. The thus enriched tritium gas is withdrawn from the thermal diffusion column cascade. The tritium-depleted heavy hydrogen withdrawn from the exchange reaction column is burnt to produce a tritium-depleted heavy water which is then recycled to both the heavy water source and the exchange reaction column.

cl BACKGROUND OF THE INVENTION 
This invention relates to a method of extracting high purity tritium gas 
from tritium-containing heavy water. 
As a method of producing high purity tritium by extracting tritium produced 
in heavy water charged in a heavy water reactor, a Laue-Langevin Research 
Institute system is known. See D. Legsr, G. Divian, and E. Roth, 
"Deteritiation de leau lourde des reacteurs nucleaires", Energie 
Nucleaire, 12(2), 135(1970). This system comprises an exchange reaction 
column for performing the exchange reaction between vapor of heavy water 
and heavy hydrogen gas at 200.degree. C. in combination with a ultra-low 
temperature liquefied hydrogen distillation column for enriching tritium 
contained in the heavy hydrogen. According to this Laue-Langevin Research 
Institute system, however, since the vapor of the heavy water is brought 
into concurrent contact with the heavy hydrogen gas at 200.degree. C., the 
system requires an evaporator for evaporating the heavy water and a 
condensation separator for separating the vapor of the heavy water and the 
heavy hydrogen gas. In addition, since tritium is enriched and separated 
by distillation of ultra-low temperature liquefied hydrogen after it is 
transferred into the heavy hydrogen gas, the system requires also a helium 
cycle for providing the ultra-low temperature which results in 
complication and troublesome operation of the system. 
SUMMARY OF THE INVENTION 
In view of the abovementioned background, an object of the present 
invention is to provide a method of extracting high purity tritium from 
tritium-containing heavy water. 
It is another object of the present invention to provide an extraction 
method of tritium which enables to simplify the whole apparatus and to 
facilitate the radioaction control. 
These and other objects, features and advantages of the invention will be 
more apparent from the following detailed description and embodiments 
thereof. 
Briefly stated, the present invention pertains to a method of producing a 
high purity tritium gas by extracting tritium from tritium-containing 
heavy water. According to the present invention, a part of the 
tritium-containing heavy water from a heavy water source is first led to 
an exchange reaction column. In the exchange reaction column, the heavy 
water is brought into countercurrent contact with a tritium-containing 
heavy hydrogen to thereby transfer tritium in the heavy hydrogen into the 
heavy water by way of the exchange reaction. From the bottom of the 
exchange reaction column is withdrawn the heavy water having an enriched 
tritium content, and from the top of the exchange reaction column is 
withdrawn the heavy hydrogen having a reduced tritium content. The thus 
resulting tritium-enriched heavy water is led to a heavy hydrogen gas 
generator, such as an electrolytic cell, to generate a tritium-enriched 
heavy hydrogen. A part of the tritium-enriched heavy hydrogen is recycled 
to the exchange reaction column to carry out the countercurrent contact 
between the heavy water and the heavy hydrogen. The remaining part of the 
tritium-enriched heavy hydrogen is led into a hot-wire type thermal 
diffusion column e.g. cascade to enrich tritium, and the thus enriched 
tritium gas is withdrawn from the thermal diffusion column cascade as a 
product. The tritium-depleted heavy hydrogen withdrawn from the top of the 
exchange reaction column is burnt to produce a tritium-depleted heavy 
water which is then recycled to the heavy water source.

DETAILED DESCRIPTION OF THE INVENTION 
As shown in the drawing, the tritium extraction apparatus as a whole 
comprises a heavy water moderated reactor 1 as a source for obtaining 
heavy water containing tritium, a vertical exchange reaction column 2 
packed with a hydrophobic platinum catalyst, and a heavy hydrogen gas 
generator 3 such as, for example, an electrolytic cell, a hot-wire type 
thermal diffusion column cascade 4 and a burner 5 equipped with a 
condenser, and these apparatus are mutually connected by piping 
arrangement. In the drawing, full lines indicate the flow of liquid and 
broken lines indicate that of gas. 
In the heavy water inside the heavy water moderated reactor 1 is produced 
tritium which is present primarily in the form of DTO. A part of the heavy 
water containing tritium is withdrawn from the heavy water reactor 1 and 
fed to the upper portion of the exchange reaction column 2 through a line 
6. At the same time, the heavy water not containing tritium may be 
supplementally supplied to the top of the exchange reaction column 2 
through a line 7. Inside the exchange reaction column 2, the heavy water 
fed from the lines 6 and 7 together flow down and countercurrently contact 
with tritium-containing heavy hydrogen fed and flowed up from the bottom 
of the column to carry out the exchange reaction of the following formula 
in the presence of the hydrophobic platinum catalyst; 
EQU DT+D.sub.2 O.revreaction.D.sub.2 +DTO. 
This reaction proceeds to the right side at a low temperature and reversely 
to the left side at a high temperature. The separation factor at 
20.degree. C. is given by; 
##EQU1## 
wherein a symbol [] expresses a concentration in mole fraction. 
Accordingly, as the tritium-containing heavy water flows down inside the 
exchange reaction column 2 at room temperature, it deprives tritium 
contained in the heavy hydrogen gas that upwardly flows, reaches the 
bottom of the column and is withdrawn outside the column as 
tritium-enriched heavy water and then led into the electrolytic cell 3 
through a line 8. 
Inside the electrolytic cell 3, the electrolysis of the heavy water DTO, 
D.sub.2 O is carried out in accordance with the formulas; 
EQU DTO.fwdarw.DT+1/2O.sub.2 
EQU D.sub.2 O.fwdarw.D.sub.2 +1/2O.sub.2 
There is thus generated tritium-enriched heavy hydrogen gas as a mixture of 
DT and D.sub.2. The electrolytic cell 3 is equipped with a diaphragm 3a so 
that the oxygen simultaneously generated does not admix with the heavy 
hydrogen. The major portion of the tritium-enriched heavy hydrogen gas 
generated in the electrolytic cell 3 is supplied to the bottom of the 
exchange reaction column 2, and the remaining portion of the 
tritium-enriched heavy hydrogen gas is supplied to the upper portion of 
the hot-wire type thermal diffusion column cascade 4 through a line 10. 
The portion below a gas feed section 4a of the hot-wire type thermal 
diffusion column cascade 4 is a tritium enriching section 4b and the 
portion thereabove is a tritium depleting section 4c. In the hot-wire type 
thermal diffusion column of this type, a red heated hot wire (such as 
nickel-chromium alloy, tungsten, platinum, etc.) exhibits its catalytic 
action, and the following conversion reaction is constantly performed; 
EQU 2DT.fwdarw.D.sub.2 +T.sub.2. 
Accordingly, tritium gas T.sub.2 is naturally enriched at the bottom of the 
hot-wire type thermal diffusion column cascade, thereby enabling to 
withdraw a tritium gas of a purity of 99% or more from a line 11. 
On the other hand, from the depleting section 4c of the hot-wire type 
thermal diffusion column cascade 4 is recovered heavy hydrogen having a 
lower tritium content than the heavy hydrogen supplied thereto through the 
line 10, and is withdrawn from the top of the cascade 4 and recycled to a 
suitable part of the exchange reaction column 2. 
The tritium-containing heavy hydrogen supplied to the exchange reaction 
column 2 from the electrolytic cell 3 and the hot-wire type thermal 
diffusion column cascade 4 through the lines 9, 12, respectively, flows 
upward inside the exchange reaction column 3, as mentioned above. In the 
course of the up-flowing, the tritium-containing heavy hydrogen is brought 
into contact, in the presence of the hydrophobic platinum catalyst 
packaged in the column, with the heavy water which is flowing down, to 
thereby transfer tritium in the heavy hydrogen into the heavy water by way 
of the exchange reaction. Accordingly, the heavy hydrogen gas is 
substantially deprived of its tritium before it reaches the top of the 
column. The resulting tritium-depleted heavy hydrogen gas is then led from 
the top of the column to the burner 5 equipped with a condenser through a 
line 13. Due to the catalytic action of platinum or palladium, the burner 
5 is operated at ordinary temperature or below 40.degree.-50.degree. C. 
under atmospheric pressure, and the heavy hydrogen gas fed into the burner 
is oxidized by means of air or oxygen led through a line 14 and is 
condensed and liquefied into tritium-depleted heavy water. 
A part of the resulting heavy water may be recycled to the top of the 
exchange reaction column 2 through a line 15 and the rest may be fed back 
to the heavy water moderated reactor 1 through a line 16. By recycling a 
part of the resulting heavy water to the top of the exchange reaction 
column 2 through the line 15, the amount of tritium in the heavy hydrogen 
gas withdrawn from the top of the exchange reaction column, and thus in 
the heavy water fed back to the reactor 1, can significantly be reduced. 
In this manner, it is possible to produce tritium gas of a high purity from 
the tritium-containing heavy water. 
Next, the present invention will be explained with reference to definite 
numeric values in order to further facilitate the understanding of the 
invention. 
In a heavy water moderated power reactor having an output of 250,000 KWe, 
for example, about 100t of the heavy water as a moderator is charged into 
the reactor. Tritium is produced in the heavy water. If this tritium is 
not removed from the heavy water, the reactor reaches the steady state at 
a tritium concentration of about 50 Ci/l heavy water. Hence, the 
explanation will be given on the case where a tritium gas having a purity 
of not lower than 99% is produced while keeping the tritium concentration 
at 0.5 Ci/l heavy water which is 1/100 of the abovementioned 
concentration. 
From 100t of the heavy water charged into the power reactor, the heavy 
water is constantly withdrawn at a rate of 70 l/hour and fed to the 
exchange reaction column. The exchange reaction column has 20 theoretical 
plates, i.e., 15 theoretical plates for the tritium enriching section and 
5 theoretical plates for the tritium depleting section, and is packed with 
the granular hydrophobic platinum catalyst. The exchange reaction column 
is operated at 20.degree. C. In the electrolytic cell, the 
tritium-enriched heavy water is electrolyzed at a temperature below about 
60.degree. C. and the resulting tritium-enriched heavy hydrogen is 
separated from oxygen by means of the diaphragm. After the vapor of the 
heavy water is removed from the heavy hydrogen as much as possible, the 
major part of the resulting heavy hydrogen is fed back to the exchange 
reaction column, and the remaining small part, such as about 1/10,000, of 
the resulting heavy hydrogen is supplied to the thermal diffusion column 
cascade. The volume of the tritium-enriched heavy hydrogen supplied to the 
cascade may vary from about 1/1,000 to about 1/10,000 of the total volume 
of the tritium-enriched heavy hydrogen produced in the electrolytic cell, 
depending on the capacity of the thermal diffusion column cascade. 
The cascade has a separation factor of 10.sub.4 at the enriching section. 
Namely, it is a four-stage cascade consisting of a hot-wire type thermal 
diffusion column having an iron type hot-wire which has a diameter of 1.5 
mm and a length of 2,000 mm, and is heated to 700.degree.-800.degree. C. 
Since the outer wall is cooled with water, the cascade as a whole is kept 
at a temperature below 40.degree.-50.degree. C. and operated under 
atmospheric pressure. In place of the iron type hot-wire, a platinum type 
hot-wire having a diameter of 0.3 mm may be employed in the cascade. 
Using the apparatus having the above-described construction, it is possible 
to produce about 25 g (about 250,000 Ci) per annum of tritium gas having a 
purity of about 99.5%. On the other hand, the tritium-depleted heavy 
hydrogen gas flowing out from the top of the exchange reaction column is 
converted into the heavy water by the burner/condenser and fed back to 
both the heavy water moderated power reactor and the exchange reaction 
column. Its tritium concentration is 0.05 Ci/l heavy water. The heavy 
water to be supplemented to the top of the exchange reaction colum is less 
than about 100 g per annum. 
Though the abovementioned embodiment deals with the production method of 
tritium by extracting tritium contained in the heavy water inside the 
heavy water moderated reactor, the present invention is not specifically 
restricted to such an embodiment. For example, it is also possible to 
apply the method of the invention to the production of tritium by 
extracting tritium from tritium-containing light water obtained from a 
nuclear fuel reprocessing plant and the like. 
Since the present invention is constructed as mentioned above, hardly any 
turning device is required with the exception of the feeding device for 
supplying the heavy water to the exchange reaction column and the transfer 
of the fluids is enabled by the gravity or the own force of the gas 
generated. In addition, since each apparatus is substantially free from a 
high-temperature section and a low-temperature section and can be operated 
under an atmospheric pressure, the apparatus as a whole can remarkably be 
simplified and the radioaction control becomes easy. When a heavy water 
moderated reactor is used as the heavy water source, the present invention 
provides the advantage that the safety management of the reactor can 
easily be made. 
It is to be noted that while the present invention has been shown and 
described with reference to the most preferred embodiment thereof, the 
invention is not intended to be so limited, and various modifications and 
changes may be apparent to those skilled in the art without departing from 
the scope and spirit of the invention as set forth in the appended claims.