JPH01140091A - Method of recovering tritium in fusion reactor - Google Patents

Abstract

PURPOSE:To allow tritium recovery of high efficiency by the use of an economical small-sized recovery device by permeating tritium from sweep gas containing tritium by a functionality separating film at which tritium is selectively permeated. CONSTITUTION:Spherical pellets of tritium oxide are filled as blanket material in a blanket part 2 formed on the circumference of the reactor core of a fusion reactor. Since the tritium in the blanket material is released in gas, sweep gas is fed in the breeding blanket part 2. In the case of non-volatile gas in which the sweep gas does not contain hydrogen, 90% or more of released tritium shows T2O and the residue indicates T2 less than 10%. After whole T2 is converted into T2O in an oxidation catalytic tower 12 typical of noble metal catalyst, it is passed in a T2O permeating film 4. A non-porous organic high polymer film typical of polytetrafluoroethylene and the like is proper for a functionality separating film for separating T2O. Next, T2O of 99.9% or more can be recovered by passing T2O transferred to a tritium recovery secondary system 8 in a T2O removing tower 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a tritium recovery device in a nuclear fusion reactor fueled by deuterium and tritium, and in particular to a device for recovering tritium using lithium oxide as a blanket material. This invention relates to improvements in recovery equipment using gas.

[Prior Art] There are two types of materials for the blanket formed around plasma in a nuclear fusion reactor: liquid materials such as metallic lithium, and solid materials such as lithium oxide. Recently, solid-state systems have been viewed as promising from the perspective of recovering Trichiu-11.

The present invention relates to a tritium recovery device in a nuclear fusion reactor using a solid blanket. In the blanket material, lithium reacts with neutrons to form tritium (3
T) is generated.

'Li+n-+'T+'He (1) Efficient tritium recovery is particularly important in order to reuse the generated tritium as fuel. For this purpose, it is necessary to flow a large amount of sweep gas to transfer tritium in the lithium oxide into the sweep gas.

The chemical form of tritium transferred to the sweep gas system is
When the sweep gas does not contain hydrogen, it is said that 90% or more is in the form of water (T20) and the remainder is hydrogen (T2).

When the T20a degree in the sweep gas increases, the production of LiOT in lithium oxide cannot be ignored due to the following equilibrium reaction.

Li2O+T 20 ” 2 L iOT (2)
When LiOT is generated, Li○T vapor and mist are generated at high temperatures due to its nature, and in order to remove these, new LiO
There are many problems, such as the need to install vapor traps for T. The temperature of lithium oxide in the blanket is 4
Tritium is released at a high temperature of 00 to 1000℃, but in this temperature range T2]4 degrees in the sweep gas is
It has been confirmed that keeping the amount below vppm is important in preventing the generation of L i OT. (reference
Japan Atomic Energy Research Institute Report JAERI-Mg2-194
(1982)) Conventionally, helium (, He) has been used as the sweep gas. The reason for this is that helium has an excellent cooling ability, and that due to the reaction between lithium and neutrons, trilithium has a mass number of 4, which is close to 3, and behaves similarly to hydrogen. .

In conventional systems, tritium migrated into the helium sweep gas is oxidized to the chemical form of water (T2O) by the action of a precious metal catalyst such as PT-alumina, and then adsorbed in the form of water by a molecular sieve adsorbent. and collect it. At this time, helium, which is a sweep gas, is not adsorbed and is circulated through the blanket material again. The recovery efficiency of tritium by a molecular sieve adsorption tower is mainly determined by the T and O concentrations in the molecular sieve adsorption tower. That is, when operating the molecular sieve adsorption tower at room temperature, the partial pressure at the outlet 120 is about 0.001 Torr, although it depends on the regeneration conditions. If the inlet concentration of tritium is now 50 vppm, the partial pressure of T2 is about 0.035 Torr, and the recovery efficiency η
is expressed by equation (3).

Therefore, when one stage of molecular sieve is used, the recovery efficiency remains at 97%.

As a means to improve this recovery efficiency, (1) lower the operating temperature of the molecular sieve adsorption tower below room temperature to lower the water partial pressure at the outlet; ■Add water to the inlet of the molecular sieve adsorption tower to increase the water partial pressure at the inlet. There are two possible methods. However, in case (2), a large-sized cooler is required due to the large amount of processing gas. In case (2), new problems arise, such as an increased load on the isotope separation device, which usually uses a cryogenic distillation column, to separate tritium and added hydrogen. Furthermore, since a large amount of sweep gas is used, the molecular sieve adsorption tower must be large-scale. That is, in an experimental fusion reactor class with a fusion reaction output of approximately 400 MW, the sweep gas flow rate is 200 to 30 ON/h, and in a commercial reactor of 32 o MW, the sweep gas flow rate is approximately 2000 rn'/h.
h L knee becomes.

When recovering tritiated water using an adsorbent such as a molecular sieve, a method of adding water vapor to improve the recovery efficiency is shown in, for example, Japanese Patent Publication No. 58-53760, and the closest known example to the present invention is Japanese Patent Publication No. 52-14
There is 5697.

[Problems to be Solved by the Invention] The present invention reduces the concentration of T2O in the sweep gas to 50 vppm.
Li0, which has problems in recovering tritium by using the following
The purpose is to provide a recovery device that has performance that exceeds the recovery efficiency of conventional tritium recovery devices, which is considered to be at its limit because it requires the use of a large amount of soup gas in order to prevent the generation of T. It is something.

Means for Solving the Problems The present invention achieves its objectives by using a large amount of sweep gas as a medium for recovering tritium from the blanket, and by separating tritium from the tritium-containing sweep gas. In devices that recover tritium, a separation means consisting of a functional separation membrane that selectively permeates tritium is provided, and a small amount of medium gas containing tritium that is permeated by this membrane separation means is processed to remove the medium gas from the medium gas. The main idea is to separate and recover tritium.

[Operation] The feature of the present invention is that it is composed of a primary system that circulates a large flow rate of sweep gas through a functional membrane that selectively permeates tritium, and a secondary system that contains a small flow rate of tritium to be recovered. It is in. The flow rate of the processing gas in the secondary system can be kept below the level of 1150 in the primary system, and hydrogen water containing tritium can be efficiently recovered using a small-scale getter material and cold trap.

The tritium contained in the sweep gas derived from Planchera 1- consists of a portion of T2 corresponding to hydrogen and the remainder T2O corresponding to water. The two have different separation performance with respect to a separation membrane, and in order to separate both using a separation membrane, a separation membrane suitable for each must be used. On the other hand, since it is easy to convert T2 in tritium into T2O by oxidation treatment, it is possible to use T2O as the target for membrane separation, thereby simplifying the membrane separation means.

A polymer non-porous separation membrane such as polytetrafluoroethylene is suitable as a membrane that selectively allows T2O to permeate.

To pass through this membrane, gas molecules need to be dissolved in the membrane material, and T2O has this property, but He, a low boiling point gas molecule, is difficult to dissolve, so it is difficult to dissolve the target component from the sweep gas. Only a certain T2O can be selectively transmitted. In this case, the transmission coefficient is at least 7 ×
10-S m1Lcs'rP)'C1n7 sec
, o (Hg is expected. On the other hand, the permeability coefficient of He gas is ~I Q -9'') ゛(In/sec
, ofllg, and its transmission is negligible. T2O
In this case, the partial pressure in the sweep gas is 0.04Torr
(=0.004cnHg), with a film thickness of 200μ, 4 x 10-4' (5Tp)7 mLn, ,H
The amount of permeation will be . If a hollow module with a large surface area is used, sufficient penetration can be achieved.

The tritium and some He that have permeated through the above operations are transferred to the secondary system. The secondary system is several Torr due to the action of the vacuum pump.
The recovery rate of T20 can be increased to 99.9% or more by maintaining it under the following negative pressure, guiding it to a cold trap for removing T2O, and operating it at, for example, liquid nitrogen cooling temperature.

[Embodiment 1] An embodiment of the present invention will be described with reference to FIG. A blanket section 2 is formed around a fusion reactor core section 1, and the blanket section 2 is filled with spherical pellets of lithium oxide (diameter approximately IIIfi) as a blanket material. Neutrons are generated by the D-T reaction in the fusion reactor core, and these neutrons are 6
Reacts with Li to generate 3T and 'He. A sweep gas is supplied to the breeding blanket section 2 in order to release tritium in the blanket material into gas. When the sweep gas is an inert gas that does not contain hydrogen, the chemical form of the released tritium is more than 90% T2. Yes.

The remaining less than 10% is T2. After converting the entire amount of T2 into T2O in the oxidation catalyst tower 12 represented by a noble metal catalyst, T2
Pass through the 0-permeable membrane 4. In this case, in the oxidation catalyst tower 12, 30
Since the conversion efficiency to T20 is high at high temperatures of 0 to 4oO℃,
It is provided near the exit of the growth blanket section 2, and after conversion, the temperature is lowered to around 100° C. by the action of the cooler 10, and then passed through the T20 permeable membrane 4.

On the other hand, a non-porous organic polymer membrane such as polytetrafluoroethylene is suitable as a functional separation membrane for separating T20. The transmission coefficient is 7 x 10-S"""'"7
s e c ・al of Hg, so to allow 167 mQ of T2O to permeate per minute, the surface area of the functional separation membrane will be approximately 2 I, but it is sufficient if a flat membrane module or hollow fiber membrane module is used. It is possible.

In this case, it is a sweep gas. The transmission of He can be almost ignored.

The T2O transferred to the secondary tritium recovery system 8 is passed through the T20 removal column 5, and 99.9% or more of T2O is recovered. As this T20 removal tower 5, a cold trap cooled with liquid nitrogen is used. In this cold trap, He, which is a sweep gas, is not recovered.

Only T2O is condensed and recovered.

Example 2 Another embodiment of the present invention will be described with reference to FIG.

Tritium recovery circulating in the growth blanket section 2 via the T2 permeable membrane 3 and T20 permeable membrane 4, which are functional separation membranes.
It consists of a secondary system 7 and a secondary tritium recovery system 8 that actually recovers tritium. Spherical pellets (approximately 1 mm) of lithium oxide (Li, ○) are used as blanket material for fusion reactors.
φ) is filled into the growth blanket section 2. Neutrons are generated by the DT reaction in the fusion reactor core 1, and these neutrons react with 6Li in Li2O, which is a blanket material, to generate tritium, 3T, and 'He. A sweep gas is supplied to the breeding blanket section 2 in order to release tritium in the blanket material into gas. When the sweep gas is an inert gas that does not contain hydrogen, the chemical form of the released tritium is more than 90% T2O, and the remaining 10% is T2O.
It is 2. The sweep gas may be one that has excellent separation ability from T2 with a functional separation membrane described later and does not react with the structural material at high temperatures. Further, it is not preferable to use a material that reacts nuclearly with neutrons to produce a large amount of radioactive material. From the above point of view, nitrogen NZ (molecule i28.) and argon.

Ar (molecular weight 40) is mentioned. In particular, in the case of argon gas, the molecular weight is large, and the reaction cross section with Ar neutrons is as small as several tens of mbars.
Even if it is produced, it is a beta nuclide, and compared to tritium, which is the same beta nuclide, produced in a blanket system, the amount produced is overwhelmingly smaller, and the half-life is about 1.5 hours, so there is little risk of bulking up. . The case where Ar is used as the sweep gas will be described below. In the experimental fusion reactor class, which has a nuclear reaction output of approximately 500 MW, the T20 concentration in the sweep gas is reduced to 5Q.
In order to prevent the formation of Li0T, which causes many problems in the process, by reducing the amount of Ar gas to less than vppm, approximately 20 ONrn'/h of Ar gas is vented into the growth blanket section 2 by the action of the circulation pump 10. In the breeding blanket section 2, a large number of cooling water pipes (not shown) are inserted into the lithium oxide pellet packed bed to cool the breeding blanket section 2 and turn into high-temperature water to transfer energy to the outside. In the pellet packed bed, Ar gas flows through the gaps between pellets with a diameter of about 1rrnφ.
T2O,T is desorbed from the pellet surface. At this time A
r-gas also contributes to heat transfer. The thermal conductivity of lithium oxide is more than an order of magnitude lower than that of He, but on the other hand, the thermal conductivity of lithium oxide is more than an order of magnitude higher than that of He. In a normal structure, when using Ar gas, the reduction is about 20 to 40% compared to when using He gas, but this can be sufficiently overcome by making measures such as closing the gaps between the cooling pipes. As a result, the temperature of lithium oxide is maintained at 400-1000°C. Growth blanket part 2
The Ar gas containing tritium that has exited is cooled to a temperature of about 100'C by the action of the cooler 10.

Next, it is guided to the T2 permeable membrane 3, where most of the T2 and some of the A
r is transferred from the tritium recovery secondary system 7 to the tritium recovery secondary system 8. FIG. 3 shows an example in which a porous glass membrane suitable for T2 transmission is used.

For T2 transmission, set the 12 partial pressure to 0.005 Torr.
; If T2 flow rate is 17 mQ/min,
The T2 transmission amount is 0.03 m in a glass tube with a thickness of 1 ms.
Q (STP)win.

d, the required surface area of the porous glass tube is approximately 6 OM. At this time, some Ar gas also permeates, but the amount of permeation is suppressed to 1150 compared to T2 at the same pressure. The amount of Ar gas permeated is approximately 3rd/at a pressure difference of 760mHg.
h, and the processing gas becomes 1/70. Porous separation membrane 1 For the separation of T2, for example, porous glass has small pores with a radius of 2 to 3 nm passing through it, and gas molecules permeate through these pores, but the permeation rate depends on the molecular weight of the gas molecules. The smaller the value, the larger the value; conversely, the smaller the value, the smaller the value.

Now, when argon (Ar) gas with a molecular weight of 40 is used as the sweep gas, when compared at the same partial pressure, it has been found that T2 is several tens of times more permeable than Ar, as shown in Figure 4. are doing. [Grain 3゜RADIOISOTOPE
S, 34, 207-213 (1985),
]. Since the amount of permeation is proportional to the difference in partial pressure between the primary and secondary systems of the porous membrane, the 12 partial pressure on the secondary system side should be as low as possible, and the Ar partial pressure on the secondary system should be approximately equal to that of the primary system. It is better to adjust the pressure of the next system. This is preferable because the difference in total pressure between the negative side and the secondary side becomes small, and the integrity of the membrane, which is relatively sensitive to pressure, is maintained. In order to obtain a predetermined required area, the porous glass tube 21 is formed into an ellipse in a multi-tube group as shown in FIG. flow. Note that on the inner tube side of the multi-tube group, in order to discharge the permeated T2 and lower the 12 partial pressure, the vacuum side is kept at least 10 Torr or less by the action of the vacuum pump 12. Regarding the separation of T and O, the same method as in Example 1 may be used.

On the other hand, T2 is recovered by the T2 getter 6. The T2 getter 6 may be any material that reacts with T2 at a relatively low temperature (room temperature - 200°C) to form a hydrogen compound and easily releases T2 at a high temperature, such as U powder or Ti.

A hydrogen-absorbing metal such as a Zr-Ni alloy may be used. As a result of the above, it becomes possible to recover tritium with an efficiency of 99.9% or more.

The recovered tritium is heated to a predetermined temperature in the T2 getter 6 and the T20 removal tower 5, desorbed as T, and T2O, and sent to the fuel gas purification system. For continuous operation,
A plurality of T2 getters 6 and T20 removal towers 5 may be provided and recovery and desorption operations may be performed alternately.

[Effects of the Invention] According to the present invention, due to the action of the functional separation membrane, the amount of gas processed in the secondary tritium recovery system is reduced by 115% compared to the primary system.
o or less, making it possible to apply advanced separation means such as a cold trap for T20 removal and a hydrogen absorber for T2 getter, and achieving high efficiency (99.9%) with an economical small recovery device.
(above) enables the recovery of tritium.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the basic flow of a tritium recovery device for a fusion reactor blanket system, which is an embodiment of the present invention.
The figure shows the flow of another embodiment of the present invention, and FIG. 3 is a schematic diagram of a T2 permeable membrane when the porous glass used in the embodiment of FIG. 2 is used as a multi-tube group. FIG. 4 is a diagram showing the difference in the amount of permeation of T and Ar in porous glass. Explanation of the symbols 1 is the fusion reactor core part, 2 is the breeder blanket part, 3 is T2
Permeable membrane, 4 is T2o permeable membrane, 5 is T20 removal column, 6 is T
2 a getter, 7 a tritium recovery secondary system, 8 a tritium recovery secondary system, 9 a circulation pump, 10 a cooler, 11 a vacuum pump, and 12 an oxidation catalyst tower. 21 is a porous glass tube, 22 is a primary system sweep gas inlet, 23 is a primary system sweep gas outlet, 24 is a secondary system sweep gas inlet, 25 is a secondary system sweep gas outlet, and 26 is a side part of the body.

Claims (1)

[Claims] 1. A method for recovering tritium by using a large amount of sweep gas as a medium for recovering tritium from a blanket and separating tritium from the medium gas containing tritium, which selectively permeates tritium. A method for recovering tritium in a nuclear fusion reactor, characterized in that tritium is allowed to permeate from a tritium-containing sweep gas using a functional separation membrane. 2. In a device that uses a large amount of sweep gas as a medium to recover tritium from a blanket and recovers tritium by separating tritium from the tritium-containing medium gas, a functional separation membrane that selectively permeates tritium is used. A tritium recovery device in a nuclear fusion reactor, comprising a primary system on the blanket side and a secondary system on the tritium recovery side through which tritium is transmitted through the secondary system and recovered. 3. A method that uses a large amount of sweep gas as a medium to recover tritium from the blanket and recovers tritium by separating tritium from the tritium-containing sweep gas, which selectively permeates tritium from the large amount of sweep gas. 1. A tritium recovery device for a nuclear fusion reactor, comprising a separation means made of a functional separation membrane and a means for separating tritium from a small amount of tritium-containing medium gas permeated by the membrane separation means. 4. In the invention of claim 1, the nuclear fusion is characterized in that tritium extracted from the blanket is oxidized by a sweep gas and then tritium is permeated by a membrane separation means using a functional separation membrane. Tritium recovery method in equipment. 5. A tritium recovery device in a nuclear fusion device according to the invention according to claims 2 and 3, characterized in that a porous glass membrane is used as a separation membrane for hydrogen permeation containing tritium. 6. A tritium recovery device in a nuclear fusion device according to the invention according to claims 2 and 3, characterized in that a non-porous organic functional separation membrane is used for permeation of water containing tritium. 7. In the invention of claims 2 to 3, a porous glass membrane is used as a separation membrane for hydrogen permeation containing tritium, and a non-porous organic functional separation membrane is used for permeation of water containing tritium. A tritium recovery device in a nuclear fusion device characterized by: 8. A tritium recovery device in a nuclear fusion device according to the invention according to claim 5 or 7, characterized in that a substance having a large molecular weight and hardly reacting with neutrons is used as the medium gas. 9. A tritium recovery device in a nuclear fusion device according to the invention of claim 8, characterized in that nitrogen or argon is used as the medium gas.