JPH0631830B2 - High-concentration tritium coexisting heavy water recovery method and apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering tritium coexisting heavy water remaining in heavy water system equipment at a high concentration, and an apparatus for carrying out this method. is there.

This invention particularly reduces tritium exposure dose and recovers high-concentration heavy water during equipment open inspection work of facilities that handle high-concentration tritiated heavy water such as reactor facilities and heavy-water purification facilities that use heavy water as a moderator. Is useful for

<Prior art> Disassembly and inspection of equipment that handles high-concentration tritium coexisting heavy water is performed by drying the tritium coexisting heavy water remaining inside heavy water equipment, such as heavy water circulation pumps, to prevent work exposure due to leakage of tritium. Conventionally, a method of opening after evaporating and removing with gas or the like is used.

FIG. 4 illustrates such a conventional method.
Dry gas is sent to the heavy water system equipment 41 in the clean house 40 to evaporate the tritium coexisting heavy water 42 remaining in the equipment. Dry exhaust gas containing tritiated heavy water vapor,
It is sucked together with the outside air (air inside the clean house) by the local air blower 43 or indoor ventilation, and sent to the large-sized dehumidifier 44. In the large dehumidifier 44, heavy water vapor is adsorbed by, for example, a molecular sieve (synthetic zeolite), and only the exhaust gas 45 is discharged from the exhaust pipe 47 together with the ventilation exhaust gas sucked from the general ventilation system 46. On the other hand, the heavy water vapor coexisting with tritium that is adsorbed by the large dehumidifier 44 and then desorbed is condensed and collected, and the condensed heavy water 49 collected in the collection tank 48 is measured for the tritium concentration, taking into consideration the emission control target value. Is discharged from the outlet 50 as liquid waste.

<Problems to be Solved by the Invention> In the conventional method as described above, the dry exhaust gas containing tritium-existing heavy water vapor is combined with the outside air into a large-scale dehumidifier.
Since it is processed by 44, the recovered condensed heavy water 49 is diluted with the moisture in the outside air, and as a result, the recovered condensed heavy water has a low heavy water concentration of 0.1 to 0.01%. Therefore, it became impossible to recover and reuse heavy water and tritium from the recovered condensed heavy water containing tritium, and it had to be released to the environment. Further, when the recovered condensed heavy water 49 is processed by the heavy water purifying apparatus, the load on the apparatus is increased.

Furthermore, the amount of molecular sieve used in the large dehumidifier 44 must be sufficient to adsorb the residual heavy water in the heavy water system equipment and the moisture in the air in the clean house, so a large amount of molecular sieve is required. Becomes

In view of this, the present invention drastically reduces the amount of molecular sieve used to evaporate and remove the high-concentration tritium-rich heavy water remaining in the heavy water system equipment with a dry gas and recover it, compared with the conventional method described above. At the same time, it was made for the purpose of providing a method capable of recovering heavy water coexisting with tritium at a high concentration without diluting it.

Another object of the invention is to provide a device for effectively carrying out the method of the invention as described above.

<Means for Solving the Problems> The inventors of the present invention circulate a dry gas by sealing the inside of a heavy water system equipment to evaporate tritium coexisting heavy water remaining in the equipment, and dry gas containing this tritium coexisting heavy water vapor. The inventors have completed the present invention by finding that the above object can be achieved by passing only one through a molecular sieve.

That is, the high-concentration tritium coexisting heavy water recovery method according to the present invention, the dry water is circulated in a heavy water system equipment in a closed state to evaporate the tritium coexisting heavy water remaining in the equipment, and vaporize the tritium coexisting heavy water vapor. Adsorbing tritium coexisting heavy water vapor in the recirculating gas to the molecular sieve by passing a circulating gas containing it into the molecular sieve, then heating the molecular sieve to release the adsorbed tritium coexisting heavy water vapor, and the released vapor is condensed by a condenser. It is characterized by being condensed and collected.

Further, the apparatus according to the present invention for carrying out the above-mentioned method is provided with a circulation system pipe which is connected to a heavy water system device in which heavy water coexisting with tritium remains to form a closed circulation system, and inside and inside the device. A blower for circulating a dry gas in the system pipe, a column containing a molecular sieve arranged in the circulation system pipe, a heater for heating the molecular sieve in the column during the desorption operation, and a desorbed material from the column during the desorption operation. It is characterized in that it comprises a branch pipe for branching from the circulation system pipe to the condenser and a recovery tank for recovering the condensate from the condenser.

In a further embodiment of the device according to the invention,
The adsorption device and the regeneration recovery device can be separated and independent as separate units. That is, the separation-independent type apparatus according to the present invention is provided with a first circulation system pipe that is connected to a heavy water system device in which heavy water coexisting with tritium remains to form a closed circulation system, and inside the device and the first circulation system pipe. An adsorber unit consisting of a blower for circulating a dry gas in a circulation system pipe and a column containing a molecular sieve removably arranged in the first circulation system pipe; and a seal in which a column containing a molecular sieve can be detachably arranged A second circulation pipe forming a circulation system, a blower arranged in the second circulation pipe, and a heater for heating the molecular sieve in the column to desorb the adsorbate of the molecular sieve,
A regeneration recovery device unit comprising a condenser for condensing desorbed substances from the column and a recovery tank for recovering the condensate from the condenser; and a molecular sieve column adsorbed in the adsorption device unit is taken out and regenerated. It is characterized in that it can be mounted in the recovery unit.

<Operation> According to the present invention as described above, since the heavy water system equipment is connected to the closed circulation system piping, it is possible to pass only the dry gas containing the vapor of the heavy water coexisting with the lithium remaining in the equipment through the molecular sieve. It is possible and does not mix the outside air (air in the clean house).

As a result, it suffices to use an amount of molecular sieve that can adsorb the vapor of tritiated heavy water. Further, the condensed heavy water can be recovered in high concentration without being diluted by the moisture in the outside air.

<Examples> The present invention will be described in more detail with reference to the examples shown in the drawings. FIG. 1 shows an embodiment of the apparatus of the present invention. A circulation system pipe 1 has a blower 2 and columns 3a and 3b containing molecular sieves in the pipe, and an inlet 1a of the circulation system pipe 1 and The outlet 1b is connected to a heavy water system device (not shown) to form a closed circulation system. In this embodiment, two molecular sieve columns are installed in the circulation system pipe 1.
3a and 3b are arranged in parallel, and the circulation system piping under each column 1
Are connected by a connection pipe 4, and the flow of the circulating gas to the two columns 3a, 3b can be changed by opening / closing the valves V1, V2, V3, V4, V5. In addition, in each column 3a, 3b,
Heater 5a, which can heat the column as needed,
5b is provided. Branch pipes 6a and 6b are branched from the circulation system pipe 1 above each column, and these are joined to form a pipe 7 which is connected to a recovery tank 9 via a condenser 8. Further, in this embodiment, the dehumidifying condenser 10 is arranged in the circulation system pipe 1 upstream of the molecular sieve column, and the condensate pipe 11 from the condenser 10 joins the pipe 7 downstream of the condenser 8. Recovery tank 9
A relief valve 12 is provided at the top of the.

The operation of this device will be described. First, the inlet of the circulation system pipe 1.
1a and the outlet 1b are connected to a heavy water system device to form a closed circulation system, and dry gas is circulated in the pipe 1. As the dry gas, nitrogen gas having a low moisture concentration, instrument air in a nuclear power plant, or the like can be used. Due to the circulation of the dry gas, the tritium coexisting heavy water remaining in the heavy water system equipment is evaporated, and the vapor is circulated by the blower 2 together with the dry gas and first passes through the dehumidifying condenser 10, where the moisture in the circulating gas is condensed and removed. And molecular sieve column
Preliminarily remove the moisture in the circulating gas sent to 3a, 3b,
Reduces the load on the molecular sieve. The circulating gas is then sent to the molecular sieve columns 3a, 3b. By opening and closing the valves V1, V2, V3, V4, and V5, tritiated heavy water vapor (hereinafter abbreviated as heavy water vapor) in the circulating gas is adsorbed by molecular sieves in the column 3a, and molecular sieves are used in the column 3b. The flow of the circulating gas is controlled so that the heavy water vapor adsorbed on the is desorbed. The heater of column 3b, which is detached at this time
5b is in a heated state. The molecular sieve in column 3a adsorbs heavy water vapor to near its saturation, and column 3b
When the molecular sieve is regenerated, the valve operation is performed again to control the flow of the circulating gas so that adsorption is performed in the column 3b and desorption is performed in the column 3a. The circulation gas from which heavy water vapor has been adsorbed and removed by the molecular sieve column is circulated again as a dry gas from the circulation system piping outlet 1b to the heavy water system equipment. On the other hand, the desorbed material from the molecular sieve is branched piping
It is sent from 6a or 6b to the condenser 8 through the pipe 7, where the heavy water vapor is condensed, the condensed heavy water is stored in the recovery tank 9, and the exhaust gas is discharged from the relief valve 12. As shown in the figure, the entire apparatus can be integrated into one unit and the wheels 13 can be attached to make the apparatus portable.

FIG. 2 shows another embodiment of the device of the present invention, which is of a type in which the entire device is separated into an adsorption device unit 20 and a regeneration recovery unit 30. The adsorption device unit 20 has a first circulation system pipe 21, a blower 22, and a column 23 containing a molecular sieve, and has an inlet 21a and an outlet 21 of the first circulation system pipe.
The point b is connected to a heavy water system device (not shown) to form a closed circulation system, which is the same as the embodiment shown in FIG. However, in the case of the separation type device of FIG.
The molecular sieve column 23 can be detachably installed in the first circulation system pipe 21 by means of 4 and 24. On the other hand, in the regeneration / recovery device unit 30, a blower 32, a reheating drum 36 having a heater 35, a condenser 38, and a recovery tank 39 are arranged in the second circulation system pipe 31, and a reheating drum is provided. In the circulation pipe 31 between the condenser 36 and the condenser 38,
The molecular sieve column 33 can be detachably installed by 34, 34.

The operation of such a separation type device will be described.

First, the inlet 21a of the first circulation system pipe 21 of the adsorption device unit 20
And outlet 21b are connected to a heavy water system device to form a closed circulation system, and dry gas is circulated in this pipe 21 to evaporate tritium coexisting heavy water remaining in the heavy water system device, and a circulation containing this heavy water vapor. Heavy gas is adsorbed on the molecular sieve in the column 23 by passing the gas through the column 23. The circulation gas from which the heavy water vapor has been adsorbed and removed is circulated again as a dry gas from the circulation system piping outlet 21b to the heavy water system equipment. Therefore, in this adsorption device unit 20, only the adsorption operation of heavy water vapor is exclusively performed.

Thus, the molecular sieve column 23 that has adsorbed heavy water vapor
Is removed from the adsorber unit 20 and the column 33 is then placed in the second circulation system pipe in the regenerator unit 30.
The heavy water vapor adsorbed on the molecular sieve in the column 33 is desorbed and the heavy water coexisting with tritium is recovered. That is, after inserting the molecular sieve column 33 into the second circulation system pipe, the blower 32 is operated to circulate the circulating gas in the second circulation system pipe 31. This circulating gas is heated by the heater 35 when passing through the reheating drum 36, heavy water vapor is desorbed when the heated circulating gas passes through the column 33, and this heavy water vapor is condensed by the condenser 38. Only the circulating gas recovered in the recovery tank 39 circulates in the circulation system pipe 31.

As shown in FIG. 2, the regeneration / recovery device unit 30 is of a fixed type, and by attaching the wheels 26 only to the adsorption device unit 20 to make it portable, only the portable adsorption device unit 20 can be freely transported. It is also possible to recover tritiated heavy water from some of the heavy water equipment and facilities.

FIG. 3 shows a state of use of the heavy water recovery system 100 of the present invention. The heavy water system equipment 41 and the heavy water recovery system 100 are housed in the clean house 40, and the circulation system piping 101 of the heavy water recovery system is connected to the heavy water system system. 41 is connected to form a closed circulation system, and heavy water coexisting with tritium is recovered by the method of the present invention.
As can be seen from FIG. 3, according to the present invention, the required amount of molecular sieve in the heavy water recovery apparatus 100 is only the amount required to adsorb the residual heavy water 42 in the heavy water system equipment. On the other hand, when attempting to recover the residual heavy water 42 in the heavy water system equipment by the conventional method as shown in FIG. 4, the required amount of molecular sieve used in the large dehumidifier 44 is only the heavy water residual equipment 42 in the heavy water system equipment. However, in addition to that, the molecular sieve amount required to adsorb the moisture in the air in the clean house 40 is required. Specifically, comparing the amount of molecular sieves based on the results of large dehumidifiers currently in operation, the required amount of molecular sieves in the heavy water recovery device of the present invention (Fig. 3, 100) is It is about 1/10 of the required amount in Fig. 4, 44).

Further, as can be seen from FIG. 3, in the present invention, since the recovered heavy water is not diluted by the moisture in the air in the clean house 40, for example, tritium can be recovered as high-concentration heavy water with a heavy water concentration of about 10%, Even when the recovered heavy water is further purified by the heavy water purification device 200 to a high heavy water concentration of about 99.9%, the load on the heavy water purification device 200 can be reduced.

<Effects of the Invention> As can be seen from the above description, according to the present invention, a dry gas is circulated as a closed state in a heavy water system device in which tritium coexisting heavy water remains, and residual tritium coexisting heavy water is evaporated and removed. Since it is adsorbed on the molecular sieve and recovered, the amount of tritium released accompanying the recovery operation can be substantially reduced to zero, and the supply of dry gas is not required.

Further, since the moisture in the outside air is not adsorbed on the molecular sieve, the recovered tritium-rich heavy water can be recovered at the same concentration as that remaining in the heavy water system equipment without being diluted. As a result, the amount of tritium released can be reduced, and the load on a upgrading device such as a heavy water purification device can be reduced.

Further, the required amount of molecular sieve may be an amount sufficient to adsorb the tritium coexisting heavy water remaining in the heavy water system equipment, and the usage amount can be reduced. As a result, the amount of used molecular sieve that becomes radioactive waste can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the apparatus of the present invention, FIG. 2 is an explanatory view showing another embodiment of the apparatus of the present invention, and FIG. 3 is an explanatory view of a method of using the apparatus of the present invention, FIG. 4 is an explanatory view showing a conventional heavy water recovery method. 1,21,31 …… Circulation system piping, 2,22,32 …… Blower, 3
a, 3b, 23, 33 ... Molecular sieve column, 5a, 5b, 3
5 ... Heater, 6a, 6b ... Branch pipe, 8, 38 ... Condenser, 9, 39 ... Recovery tank, 20 ... Adsorption device unit,
30 Recycled recovery unit.

Claims (5)

[Claims] 1. A heavy water system device is hermetically sealed to circulate a dry gas to evaporate tritium coexisting heavy water remaining in the device, and a circulating gas containing vapor of the tritium coexisting heavy water is passed through a molecular sieve. It is characterized in that heavy water vapor coexisting with tritium in the circulating gas is adsorbed on the molecular sieve, then the molecular sieve is heated to desorb the adsorbed heavy water vapor containing tritium, and the desorbed vapor is condensed and collected by a condenser. Method for recovering heavy water containing high-concentration tritium. 2. A circulation system pipe in which heavy water coexisting with tritium is connected to a heavy water system device remaining therein to form a closed circulation system, and a blower for circulating a dry gas in the device and the circulation system pipe. A column containing molecular sieves arranged in the circulation pipe, a heater for heating the molecular sieve in the column during the desorption operation, and a desorption product from the column during the desorption operation branched from the circulation pipe to a condenser. A device for collecting heavy water containing high-concentration tritium, comprising a thin branch pipe and a recovery tank for recovering condensate from the condenser. 3. A high-concentration tritium coexisting heavy water recovery apparatus, characterized in that the apparatus according to claim 2 is integrated as one unit, and wheels can be attached for transportation. 4. A first system in which heavy water coexisting with tritium is connected to a heavy water system device remaining therein to form a closed circulation system.
Adsorber unit comprising a circulation system pipe, a blower for circulating a dry gas in the device and the first circulation system pipe, and a column including a molecular sieve detachably arranged in the first circulation system pipe. , And a second circulation system pipe forming a closed circulation system in which a column containing the molecular sieve can be removably arranged, a blower arranged in the second circulation system pipe, and the molecular sieve in the column is heated to heat the molecular sieve. Of the adsorbed material, a condenser for condensing the desorbed material from the column, and a recovery tank for recovering the condensate from the condenser. High-concentration tritium, characterized in that the molecular sieve column is removed and can be mounted in the regeneration recovery unit. Recovery unit of the presence of heavy water. 5. A high-concentration tritium coexisting heavy water recovery apparatus, wherein wheels are attached to the adsorption apparatus unit according to claim 4 for transportation.