Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Back~round of the Invention:
(1) ~ield of the Invention:
~ his invention relates to a process for removing
tritium from tritium-containing heavy water.
(2) Description o~ the prior art:
~ he ~aue-Langevin Ins-titute process developed in
France is publicly known as one typical process for remov-
ing tritium senerated in the heavy wa-ter used in the heavy
water moderated-power reactor to rec~over tritium of high
purity. ~his ~aue-~angevin Institute process is characterized
by using a combination of an excha~e reac tion column for
effecting an exchange reaction between the vapor of heavy
water and deuterium gas in parallel flow at 200C with a
cryogenic liauified hydrogen disti]lation column for effect-
ing the concentration of the trltium in the deuterium gas~
However, since the Laue-Langevin process uses a column
wherein vapor of heavy water has to absolutely con-tact
with deuterium gas in parallel flow at 200G, several
exchange-reaction columns are required, because the apparatus
used to carry out the Laue-Langevin Institute proces~s should
be constructed countercurrently as a whole. In addition to
that, since tritium is concentrated and separated by virtue
of cryogenic liouified hydrogen distillation after moving
tritium into deuterium gas in the ~a~e-~angevin Institute
process, the Laue-Langevin Institute process requires a
helium cycle for generating cryogenic temperatures.
As stated above, the Laue-Langevin Institute process
has several defects in that the apparatus used to carry out
the process and the operation of the appara~us are very
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complicated and, also 9 high level techniques are require'd
to carry out the process.
In order to eliminate the defects of the ~aue-~angevin
Institute process as stated above, the inventors of this
invention studied and found the novel process of this
invention.
Summary of the Invention:
It is, therefore, an object of this invention to
provide a novel process for removing and recovering tritium
which eliminates the defects of the conventional art and
simplifies the apparatus used as a whole and which can be
easily controlled from the standpoint o~ radiation-pxotection.
_ief Description of Drawin~:
Fig. 1 is a schematic process flow diagram ~or
practicing the process of this invention.
Detailed Descri~tion o~ the Invention:
This invention relates to a process for removing
tritium from tritium-containing heavy water to recover
tritium gas of high purity.
~his invention is characterized b~ feeding a part
of the heav~ water containin~ tritium from a source ~or
supplying the heavy water such as heavy water moderated-
power reactor (hereinunder referred as "heavy water supply-
ing source") to an exchange reaction column wherein the
heavy water contacts with deuterium gas countercurrently,
extracting heavy water enriched in tritium ~rom ~he bottom
of the exchange reaction column and converting it to vapor
of hea~y water, passing the vapor of heavy water through
at least one packed column of two columns packed with
~0 easily oxidizable or reducible metals by steam or hydrogen
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respectively wherein the metal in the column is oxidized
to metal oxide while the vapor of heavy water is reduced
to deuterium gas, recycling most of the deuterium gas to the
exchange reaction colu~n to effect the countercurrent
contact between heavy water and deuterium gas~ extracting
the deuterium gas of reduced tritium content from the top
of the exchange reaction column, passing said deuterium
~as throu~h the other column in which the metal packed has
already been oxidized to metal oxide wherein the metal
oxide is reduced to metal while the deuterium gas is oxidized
to heavy wa-ter and rec~cling a part of the heav~ water of
reduced tritium content to the heav~ water supplying source
while recycling the resldual heavy water to the top of the
exchange reaction column. And this invention is ~urther
characterized by introducing a part of the gas obtained
after passing the vapor of heavy water through the metal-
packed column to the thermal diffusion column cascade and
concentrating the tritium to recover the tritium as tritium
gas of high purity.
Description of a Preferred Embodimen-t:
One mode contemplated for practici~g this invention
will be described in detail below in connection with the
accompanying drawing.
As can be seen from ~igo 17 one embodim~nt of the
apparatus to carr~ out this invention comprises a heavy
water moderated power reactor 1~ an exchange reaction
column 2 packed with hydrophobic platinum catal~st, a
; packed column ~, that is an oxidation-reduction column
packed with easily oxidizable or reducible metals and hot-
wire type thermal diffusion column cascade 4. ~he packed
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column 3 comprises column A and column B and is provided
with two valves 5 and 6 which can be mutually switched
over so that one of the metals charged can be reduced to
be regenerated while the other metals are being oxidized.
System components are connected with each other b~ piping.
In Fig. 1~ continuous lines represent flow of li~uid and
broken lines represent flow of gas.
Tritium is produced in heavy water used in heavy
water moderated-power reactor ~ and exists generally in
the form of D~0. A part of the heavy water containing
tritium extracted from heavy water moderated-power reactor
1 is introduced through the piping 7 into the fixed poin-t
of the exchange reaction column 2 while heavy water of
reduced tritium content is introduced into the top of the
exchange reaction column 2 through the piping 8. In the
exchange reaction column 2, the heavy waters introduced
through the piping 7 and 8 are mlxed together and subjected
to the following exchange reaction with deuterium containing
tritium coming up from the bottom of the column 2 by virtue
o~ the h~drophobic platinum catalyst packed in the column;
DT ~ D20 ~__~ D2 ~ DT0 ..~.. (1)
The exchange reaction (1) is shifted to right at low tem-
peratures and to left at high temperatures and the separation
~actor of the reaction at 20C is expressed by;
[DT0] / ~D20]
[ D-T~ - = 1.61 ... ~. (2)
[DT] / ~D2 ]
:
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~heref~re, the tritium-containing heavy water supplied in
the exchange reaction column 2 extracts tritium from the
deuterium as ~ ~roceeds up the column 2, and at the same
time the tritium-containing heavy water flows donw the
column 2 at room temperature and reaches the bottom of the
column 2 and then is extracted outside the column 2 thx~gh
piping 9 to be introduced through the change-over valve 6
and piping 10 into the column B of the oxidation-reduction
column where in accordance with the following equations
(3) and (4) the heavy water vapor containing tritium is
converted to deuterium gas containing tritium by virtue of
easily oxidazable-reducible heated metal packed thereln,
for example particles of ~ i alloy or powder of Ni - ~i
alloy supported on a carrier.
D20 + M 3 D2 ~ M0 ............ (3)
D~0 ~ M ~ DT + M0 ~OO~ (4)
M : Ni - Ti alloy
M0 : oxides of ~ i alloy
from column B of the oxidation reduction apparatus 3 the
deuterium gas passes through piplng 11, change-over valve
5 and piping 12. Most of the deuterium gas passed throùgh
piping 12 is recycled to the bottom of exchange-reaction
column 2 through piping 13 and 14 while the remainder is
introduced through piping 15 to the gas receiving section
4a of the hot-wire type thermal diffusion column cascade 4
In Fig. 1, 4b represents the txitium enriching section and
4c represents the tritium stripping section. In the hot-
wire type thermal diffusion colum~ cascade 4, the following
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xchange reacbion (5) is continuously taking place by
virtue of the catalysis of red-hot wire of, for example,
nickel, chromium alloy, tungsten, platinum and so forth
and tr.~ium gas is concentrated at the bo~om o~ ~he hot-
wire type thermal diffusion column cascade 4 to be recoveredas tritium gas of higher purity than 9~/c through piping 16
2D~ D2 + ~2 (5)
On the other hand, in tritium stripping section 4c
of the hot-wire type thermal diffusion column cascade 4,
deuterium gas having lo~er tritium content than that in the
deuterium gas introduced to said ca~cade 4 through piping
15 is recovered and extracted from the top of the cascade
4 and then is recycled to the bottom of the exchange reac-
tion column 2 through pipings 17 and 14. ~ritium-containing
_.
deuterium gas introduced into the bottom of the exchange-
reaction column 2 from the top of the packed column 3,~that
is, the oxidation-reduction column, and from the top of -the
hot-wire type thermal diffusion column cascade 4 contacts
the heavy water coming down from the top of the column 2
countercurrently through the h~drophobic platinum catalyst
bed and consequentl~ tritium contained in deuterium gas is
mov~d to the heavy water side. Therefore, when the tritium~
containing deuterium gas introduced into the column 2 reaches
. the top of the column 2, the tritium content o~ the deuterium
gas is lowe~ ~nd the gas is extracted from the top of -the
column 2 through piping 18 to be introduced into column A
of oxidation-reduction column 3 through change-over valve
5 and piping 19~ In the column A, the metal oxide is reduced
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to metal, there~y preparing for the next cycle for reduction
of vapor of heavy water to deuterium; on the other hand~
deuterium is oxidized to heavy water as shown by the following
equations (6) and ~7);
D2 ~ D20 ~ M 0.O.O ~6)
DT 1- MO -~ DTO ~ M ......... (7)
~M : Ni - ~i alloy
~MO : oxide o~ i alioyJ
The heavy water produced in the column A as stated above
passes through piping 20, change-over valve 6 and piping 21
and ~hen a part of the heavy water passed through piping 21
is recycled to the heavy water moderated-power reactor 1 while
the remainder is recycled to the top o~ the exchange reaction
column 2 through piping 23 and 8. Oxidation-reduction appara-
tus 3 comprises two columns A and B and is provided with two
valves 5 and 6 which can be mutually switched over so that
an oxidation reaction is carried out in column A while a
reduction regeneration reaction is carried out in column B7
and ~ reduction regeneration reaction is carried out in column
A while an oxidation reaction is carried out in column B.
It is, therefore, possible to remove tritium ~rom tritium-
; containing heavy water to recover tritium gas of high purity.
This m vention is further illustrated by the follow-
ing Example. However, this invention should not be limited
by the ~xample, and changes and modi~ications within the
- spirit and scope of the claim can be effected.
~- ~xample
A 25 x 104 K~ie hea~y water moderated power reactor
:
1 was employed as heavy water supplying source.
About 100 tons of heavy water are used in 25 x 104
KWe heavy water moderated power reactor as moderator and ~ri-
tium is generated in the heavy water. If the tritium is not
removed, a steady state of the tritium concentration is
about 50 Ci/l of heavy water. Therefore, this Example is
carried out in case of recovery of tritium gas 9g~ or higher
purity while maintaining the tritium concentration in heavy
water at 0.5 Ci/l.
Heavy water containing tritium is extracted at the
rate of 70Q/hour from the heavy water of 100 tons charged in
th~ 25 x 104 KWe heav~ water moderated-power reactor 1 and
supplied into exchange-reaction column 2. The exchange-reaction
column 2 comprises 20 theoretical plates -that is, 15 theo-
retical plates in the tritium enriching section and 5 theoreti-
cal plates in the tritium stripping section, and is packed with
hydrophobic pla~inum particle catalyst and operated at 20Co
The tritium-containing heavy water introduced into
the exchange-reaction column 2 extracts tritium from
deuterium gas which flows up the column 2, as the tritium-
containing heavy water flows down the column 2 and reachesthe bottom of the column 2 and then is intxoduced into the
packed column 3, that is the oxidation-reduction column.
The packed column 3 comprises two columns A and B and is
;!` operated at temperatures of 400C - 800C and the deuterium
gas produced in the step of oxidation of metal packed in
the column 3 is fed into hot-wire type thermal diffusion
cascade 4 after removing as much as possible of the vapour
of heavy water contained in the deuterium gas. The cascade
4 comprises 5 stages of hot-wire type thermal diffusion
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column having hot-wire of iron ~1~5 mm (~) x 2000 mm)
heated at temperatures of 700C to 800C and its outer
wall is cooled by water. ~he cascade 4 as a whole, is
operated at temperatures of 40a to 50C under atmospheric
pressure~ ~he separation factor in the tritlum enriching
section 4b of the cascade 4 is 104 and in the tritium
stripping section 4c of the cascade 4 it is 10. About 25g
(about 250,000 Ci) of tritium gas of 99.5% in purity are
removed and recovered per year. On the other hand, the
deuterium gas leaving from the top o~ the exchange-reaction
column 2 is introduced into the packed column ~ and is
converted to heavy water and its tritium concentration is
0.05 Ci/l. And then, a part of the heavy water is recycled
to heavy water moderated power reactor 1 and the remainder
is recycled to exchange reaction column 2. q`he amount o~
heavy water supplied through piping 24 to the top of the
exchange-reaction column 2 as replenishment is less than
about 100g per year.
The ~xample above illustrated is relating to the
removal and recovery of tritium in heav~ water charged
in a heavy water moderated power reactor;- however, this
invention is not limited thereto but is also applicable to
the removal of tritium from tritium-containing light water
produced in reprocessing of nuclear ~uel.
~he process of this invention can be operated at
atmospheric pressure and requires no rotating machine except
for means for cycling heavy water and deuterium gas. And
since a conversion of heavy water to deuterium and a con-
version of deuterium -to heavy water are carried out in -turn
in a single apparatus and the metals packed in the apparatus
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can be regenerated simultaneously in the apparatus, the
facilities to carry out this invention are very much
simplified as a whole. And further, with this invention
it is particularly easy to maintain radiation protection
control, and if a heavy water moderated power reactor is
employed as the heavy water supplying source to carry out
this invention, it is very advantageous for safety control
of power reactor. And if the process of this invention is
applied to nuclear fuel reprocessing plant, tritium can be
completely removed from tritium-containing waste water with-
out contamination of environment.
