JP3820503B2 - Method and apparatus for decontamination of tritium contaminated metals - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for removing tritium from metal waste contaminated with tritium generated at a nuclear power plant, a fusion development facility, or a nuclear reactor demolition site, and safely processing the tritium.
[0002]
[Prior art]
Conventionally, wastes contaminated with tritium have been generated in nuclear power plants and fusion development research facilities, and these contaminated wastes have been stored in a sealed manner. Also, in recent years, a large amount of tritium-contaminated waste is generated from the site of dismantling of nuclear reactors and the like that are becoming full-scale. Since most of these wastes are only slightly contaminated with tritium, they are disposed of after being reduced in tritium concentration, and in the future, the tritium concentration is reduced to below the limit of market release and reused. The development of appropriate tritium decontamination technology is an important issue.
[0003]
Since tritium, an isotope of hydrogen, diffuses easily inside the metal, tritium-contaminated metal materials in facilities that handle large amounts of tritium have tritium attached or adsorbed on the surface. It exists as solid solution tritium that diffuses and penetrates into the material to form a solid solution. The release rate of tritium adsorbed on the material surface gradually increases with increasing temperature. On the other hand, solid solution tritium is hardly released up to 200 ° C., and when it exceeds 200 ° C., the release rate increases. Therefore, as disclosed in Non-Patent Document 1, when the temperature of a material contaminated with tritium is increased, the amount of tritium released becomes maximum at 200 to 250 ° C., and the tritium emission at 500 to 600 ° C. Release is complete.
[0004]
At the fusion development facility, tritium is used at a fairly high concentration and for a long time under high temperature conditions. Therefore, tritium dissolved in the material is compared with the tritium adsorbed on the surface layer of the material such as piping. The amount cannot be ignored. Therefore, it has been considered that in the maintenance or dismantling work of equipment, the solid solution tritium is taken out of the material and processed by heating for a long time under a high temperature condition of several hundred degrees C. or more. Further, in order to take out solid solution tritium from contaminated piping materials even in a nuclear facility using heavy water, it has been necessary to perform a heating operation for a long time at a high temperature.
[0005]
Conventional decontamination techniques for tritium contaminated metals include wiping methods, chemical cleaning methods, etching methods, gas purge methods, water vapor purge methods, laser irradiation methods, baking methods, etc. Yes.
However, these decontamination methods remove tritium adhering to or adsorbing to the metal surface or tritium penetrating the metal surface layer, and have no ability to remove tritium that has penetrated into the metal and has become a solid solution.
In addition, if a high temperature treatment of 100 ° C. or higher is performed, not only a large-scale high temperature decontamination apparatus is obtained, but also a decontamination ancillary apparatus comprising processes such as waste liquid treatment, radioactivity confirmation, tritium recovery, and the like Equipment that strictly handles the handling and handling of wastes and the sealing during storage is indispensable. For this reason, conventionally, even in the method of decontamination by heating, low temperature heating up to about 200 ° C. has been adopted as the processing temperature.
[0006]
For example, in Patent Document 1, a dry gas is supplied to a pipe or the like installed in a facility to drive off heavy water adhering to the inside by drying, and then a low-temperature gas of 200 ° C. or lower containing light water vapor is supplied. Discloses a device in which the decontamination time is shortened by an apparatus for removing water adhering to the inner surface of a pipe or the like or tritium adsorbed on the surface. However, in the disclosed apparatus, attention is paid to the fact that the solid solution tritium is not released from the material at 200 ° C. or lower and can be confined in the material, and the solid solution tritium is left to remain in the material. However, it does not remove the solid solution tritium.
[0007]
Thus, conventionally, there has been no practical high-temperature heat treatment method that can effectively remove even solid solution tritium inside the metal material.
However, if solute tritium remains in the base metal inside the metal material, it will be regenerated on the metal surface over time, so handling of the decontaminated waste, such as transportation, and tight management during storage are required. In addition, it was necessary to confirm the tritium concentration after decontamination and to select a treatment method according to the concentration.
For this reason, the decontamination method which can also remove solid solution tritium is desired.
[0008]
[Patent Document 1]
JP-A-11-281792
[Non-Patent Document 1]
Holland et al. `` 3rd International Conference on the Decommissioning of Nuclear Installations, Luxembourg (1994), p445-455.
[0009]
[Problems to be solved by the invention]
Therefore, the problem to be solved by the present invention is to provide a simple decontamination method and apparatus for tritium-contaminated metals that is necessary for removing solid solution tritium and that is safe and easy to handle.
[0010]
[Means for Solving the Problems]
In the method for decontaminating tritium-contaminated metals according to the present invention, a metal material containing tritium is accommodated in a hot-air heating furnace that generates circulating hot air capable of adjusting the temperature, and is first heated with hot air at 200 ° C. or less and adhered to the material surface. Alternatively, the adsorbed tritium is expelled, and then heated and held with hot air heated from 200 ° C. to 600 ° C. to expel the solid solution tritium and collect the tritium. The metal material that is cooled and releases tritium to a safe level is taken out. In the tritium decontamination method of the present invention, the heat treatment can be easily performed with a hot air heating furnace. The tritium released from the material is cooled to about room temperature through a cooler and then recovered in its entirety by a tritium recovery device. The exhaust after cooling can be sucked with a metering pump of normal temperature specification. The exhaust gas after the tritium recovery can be released to the atmosphere through the local exhaust device and the building ventilation equipment.
[0011]
According to the tritium decontamination method of the present invention, the release to the solid solution tritium inside the metal material while suppressing the rapid release of tritium by the two-stage heating of the intermediate temperature setting of 200 ° C. or lower and the high temperature setting of 200 ° C. to 600 ° C. Thus, the tritium concentration in the metal material can be lowered to a safe level. In addition, complicated and expensive incidental equipment such as a waste liquid treatment apparatus in chemical decontamination is not required, and post-treatment such as airtight management of low-concentration contaminated materials is also unnecessary.
The local exhaust device is an exhaust device for sucking air in a decompression chamber called a green house that houses a hot air heating furnace to maintain a negative pressure. Moreover, it is preferable that the hot-air heating furnace be maintained in a closed structure at a lower pressure than the decompression chamber. Since the hot-air heating furnace is at a lower pressure than the decompression chamber and the decompression chamber is at a pressure lower than the atmospheric pressure, tritium in the hot-air heating furnace does not leak into the decompression chamber. It is safe because it does not leak out of the decompression chamber.
[0012]
Furthermore, since there is no tritium in the hot-air heating furnace after the tritium is sufficiently discharged from the material, it is safe to discharge the exhaust gas without processing it with the tritium recovery device. Therefore, at the time of cooling the hot air heating furnace, the hot air heating furnace can be efficiently cooled by switching the suction path of the local exhaust device to a path passing through the hot air heating furnace so as to take in a large amount of cooling air. .
[0013]
In the tritium decontamination method of the present invention, a contaminated metal material is placed in a basket and placed on a cart, stored in a fixed position of a hot air passage in a hot air heating furnace, and drawn out after processing and carried out by a transport cart. be able to. The basket has a large opening through which air can be vented, and a plurality of baskets can be stacked vertically. It is preferable that hot air flows through each of the stacked baskets in the same manner to cause a similar temperature transition during the process. The temperature change of the stored metal material can be directly measured by providing a temperature detection end.
As described above, the temperature in the hot air heating furnace is controlled by a program so as to have a predetermined change pattern in which it is cooled after being heated in two stages and maintained at a high temperature.
[0014]
The tritium-contaminated metal decontamination apparatus of the present invention includes a hot air heating furnace, an exhaust gas cooler, a tritium recovery device, and a local exhaust device, and the hot air heating furnace has an airtight can body having an air inlet and an air outlet. It has an inner box that houses the basket carriage inside, an air heater and a circulation fan are built in, the inner box is equipped with air flow rectifying plates on both sides, and the hot air generated by the air heater is sent to the inner box by the circulation fan. Circulates through the baffle plate and the air outlet is Exhaust gas cooler that exchanges heat in contact with cooling air that introduces exhaust gas from outside The tritium recovery device collects tritium in the exhaust gas while sucking air to maintain the inside of the hot air heating furnace at a negative pressure, and the local exhaust device is connected to the tritium recovery device. internal The local exhaust flow path Exhaust through the tritium recovery unit and exhaust directly to the local exhaust system When equipped with a valve that switches between the flow paths, the metal material is heated in a hot air heating furnace to expel tritium. Exhaust gas cooler When exhausting the tritium through the tritium recovery device and cooling the furnace after expelling the tritium, pass it through the hot air heating furnace. Taking outside air The furnace air is replaced with outside air.
[0015]
Tritium decontamination is performed while introducing outside air, and all the tritium released by the high temperature treatment is recovered by a tritium recovery device. As the tritium recovery apparatus, a commonly used apparatus such as a bubbler system or a refrigeration system can be used.
Note that the hot-air heating furnace is preferably installed in a decompression chamber so that tritium does not flow outside.
In addition, a separate water-cooled exhaust gas cooler may be provided in the exhaust gas passage so that the reliably cooled gas is supplied to the tritium recovery device.
In addition, a tritium monitor is further provided so that the tritium concentration in the exhaust gas is constantly monitored and managed so that there is no sudden rise in concentration that cannot be processed by the tritium recovery device. It is preferable not to release to the atmosphere.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the tritium-contaminated metal decontamination apparatus and decontamination method of the present invention will be described in detail with reference to examples.
1 is a process flow diagram of a tritium-contaminated metal decontamination apparatus of this embodiment, FIG. 2 is a perspective view of a hot air heating furnace, FIG. 3 is a cross-sectional view showing a sealing mechanism of the hot air furnace, and FIG. 4 is a decontamination basket and cart. FIG. 5 is a time chart showing the temperature management method of the hot stove.
[0017]
The tritium-contaminated metal decontamination apparatus of the present embodiment is composed mainly of a tritium expelling device 1, a tritium recovery device 2, a tritium measuring device 3 and 6, and a local exhaust device 4.
The main body of the tritium expelling apparatus 1 is a hot air heating furnace 10, which is accommodated in a negative pressure chamber called a green house 5 slightly depressurized from the atmosphere to prevent leakage of tritium, and a negative pressure further depressurized from the green house 5. Operated under pressure.
[0018]
The hot air heating furnace 10 has an inner space surrounded by a heat insulating wall, and an inner box 11 is arranged in the heating space surrounded by the heat insulating wall, so that a basket 50 for storing a metal material to be processed can be accommodated. Yes. A plate is laid on the floor of the inner box 11 and there is no air circulation, but the airflow can be distributed by a plate having a net or a large number of perforations so that temperature distribution is not possible on the object to be treated.
The space surrounding the inner box 11 forms a circulation path for high-temperature air, and is provided with an air heater 12 such as a sheathed heater and an air circulation fan 13 such as a sirocco fan in the circulation path, and flows out from one side of the inner box 11. The incoming air is heated by a heater and supplied into the inner box 11 from the other side of the inner box 11. The heating by the air heater 12 is program-controlled by the temperature regulator 14 so that the temperature in the circulation path measured at the temperature detection end provided downstream of the fan 13 follows a predetermined temperature pattern.
[0019]
A part of the air in the circulation path is sucked from the exhaust nozzle 15 and supplied to the tritium recovery device 2, the local exhaust device 4, and the like. On the other hand, an intake nozzle 16 is provided in the circulation path so that the amount sucked from the exhaust nozzle 15 can be supplemented. A relatively thin recovery pipe 17 and a thick exhaust pipe 18 are connected to the exhaust nozzle 15.
The recovery pipe 17 is connected to the tritium recovery apparatus 2 through the water cooling type cooler 19 and through the sample location of the recovery path tritium measuring apparatus 6, and the exhaust pipe 18 is a mixture that mixes the air taken in from the green house 5 and the exhaust gas. It is connected to the local exhaust device 4 through the vessel 20 and through the sample location of the tritium measuring device 3 for the exhaust passage. The exhaust pipe 18 is also provided with a suction nozzle 21 for keeping the pressure inside the green house 5 at a negative pressure. In order to manage the tritium concentration in the greenhouse, a plurality of suction nozzles for the analyzer may be provided.
[0020]
As the tritium measuring devices 3 and 6, a general device such as a bubbling method can be used. If necessary, the tritium concentration in the tritium expelling device 1 is measured to confirm the tritium release state.
The intake nozzle 16 for supplying outside air to the hot air heating furnace 10 is provided with a switching device, and a relatively small small valve 22 used for supplying air during hot air circulation and a relatively large large valve 23 for replacing the internal hot air. Can be switched.
[0021]
The tritium recovery apparatus 2 may use a general principle such as a bubbler system or a refrigeration system.
FIG. 1 shows a bubbler type recovery device. The collection device 2 is accommodated in the glove box 46. The recovery pipe sequentially passes through the two absorption tanks 41, 42 filled with water, the mist trap 43, the pump 44, and the flow meter 45, and discharges the exhaust gas after the tritium is recovered in the glove box 46. The inside of the glove box 46 is sucked by the local exhaust device 4 and is kept at a negative pressure in the same manner as the green house 5 so that the external leakage of tritium does not occur.
The tritium recovery device may be arranged in the green house. In this case, a glove box is not necessary.
[0022]
When the air in the hot-air heating furnace 10 is sucked by the pump 44, the exhaust gas is sucked into the water in the absorption tanks 41 and 42 and bubbled, and comes into contact with water while rising as fine bubbles and the tritium component is absorbed. The Next, the droplets that are discharged as fine mist from the absorption tank are dropped by the mist trap 43, and the remaining flow rate is confirmed by the flow meter 45 and discharged into the glove box 46.
All the air in the glove box 46 is sucked out by the local exhaust device 4 and diffused to the atmosphere via the building exhaust device 7 connected to the local exhaust device 4.
[0023]
FIG. 2 is a perspective view of the hot air heating furnace 10. The figure shows a state in which the main body door 24 is opened, and the inside of the inner box 11 is visible inside. The inner box 11 is provided with a side plate 25 having a large number of holes on the side surface, and a floor plate 27 on which a rail 26 on which a carriage carrying a basket 50 is laid is stretched on the floor. During operation of the hot air heating furnace 10, hot air flows from the one side plate 25 toward the other side plate inside the inner box 11 in which the basket 50 is accommodated.
The airflow that has exited the space outside the side plate 25 is heated by a heater while passing through the space below the floor plate 27, sent to a sirocco fan, and supplied to the inner box 11 again.
An exhaust nozzle 15, a mixer 20 and the like are installed on the hot air heating furnace 10, and instruments 28 are disposed on the front surface. In addition, an inspection door 29 is provided on the side surface, so that it is possible to easily inspect a control device and a motor that do not need to be constantly monitored such as a program controller.
[0024]
In order to prevent tritium from leaking into the green house 5, the hot air heating furnace 10 has an airtight structure so that it can always be kept at a lower pressure than the atmosphere in the green house. For this reason, the main body door 24 for loading and unloading waste is a packing-contact type airtight door using silicon sponge packing or the like.
[0025]
Further, in order to efficiently heat and cool the waste, the furnace body adopts a sheet metal structure having a small heat capacity and is filled with a heat insulating material between the outer casing and the inner casing, but in order to ensure airtightness, FIG. As shown in (a), a sealing material 34 such as silicon rubber coke is filled in a gap between sheet metal joining lines formed by holding the outer casings 31 with a cushioning material 32 such as ceramic paper with a rivet 33. As shown in 3 (b), the surface of the sheet metal joining portion is sealed by welding 35. The portion filled with the sealing material 34 is preferably reinforced with an adhesive tape 36 such as stainless steel foil.
The sheet metal mating portion of the inner casing 37 is not in close contact so that the gas contained in the heat insulating material 38 can breathe to prevent damage due to expansion.
[0026]
The outer casing has holes such as exhaust nozzles, intake nozzles, electric heater wires, thermocouple wells, circulation fan shaft through holes, negative pressure gauge pressure guide tubes, and the like. The exhaust nozzle and the intake nozzle are welded over the entire circumference by covering a casing opening with a housing integral with the valve body so that the outer casing does not fail. A through hole such as an electric heater is closed by filling a gap with a sealing material. Further, a shaft seal is attached to a portion where the rotating shaft of the circulation fan penetrates to seal it. Thus, since the airtight boundary is sealed, the inside of the furnace can always be kept at a negative pressure by narrowing the valve of the intake nozzle and sucking a certain amount of air by the pump 44 of the tritium recovery device 2.
[0027]
FIG. 4 is a cross-sectional view showing a state where the decontamination basket is mounted on a transport cart.
The basket 50 is loaded with a tritium-contaminated metal material, accommodated in the hot air heating furnace 10, and used to release the tritium by circulating the temperature-controlled hot air for a predetermined time.
In consideration of handling, the waste is transported and stored in a 200-liter drum or a container of about 1 cubic meter. Therefore, since the waste is cut to a size suitable for these containers, the basket 50 is preferably sized so that the contaminated metal material can be stored as it is, and has a floor area of about 1 square meter, for example. It is.
[0028]
Each basket 50 has a side plate 52 erected on the front and rear ends of the floor plate 51, and a fence is formed between the side plates 52 with beams 53 and pillars 54. A groove is provided so that the bottom surface of the basket 50 stacked on top can be fitted. In place of the fence, a highly breathable wire mesh that does not spill contents during handling may be used.
Several baskets 50 each containing a contaminated metal material are stacked and placed on a loading cart 55. The loading carriage 55 includes wheels 56 so that the basket 50 can be easily taken in and out by running on the rail 26 laid on the floor of the inner box 11 in the hot air heating furnace 10.
[0029]
The loading cart 55 on which the basket 50 is placed can be mounted on the transport cart 57 together with the cart and moved between the waste storage place and the hot air heating furnace. Rails 58 on which the wheels 56 can run are laid on the floor of the transport cart 57, and are connected to the rails 26 of the hot air heating furnace 10 so as to match the height, whereby the loading cart 55 and the hot air heating furnace 10 are connected. Can be easily transferred between.
[0030]
Next, the procedure for tritium decontamination will be described.
A metal material contaminated with tritium is stored in a dedicated decontamination basket 50 at a waste storage location not shown in the figure, and is mounted on the loading cart 55 in a pile, and the entire cart is placed on the transport cart 57. Since the metal waste is cut to a size that can be accommodated in a drum, the metal waste can be completely stored in the basket 50 of each stage.
[0031]
It is transported from the waste storage place into the green house 5, the main body door 24 of the hot air heating furnace 10 is opened, the rail 58 on the transport carriage and the rail 26 in the hot air heating furnace are brought together, and the loading cart on the transport cart 57. The stopper that has stopped 55 is released, and the loading carriage 55 is sent into the hot-air heating furnace 10 and fixed in place.
Since the completion of decontamination is determined by the processing temperature and processing time, the temperature detection end connected to the temperature indicator and the temperature recorder is set on the surface of the metal material at an appropriate position for each basket 50, and then the main body door. 24 is closed.
[0032]
In the green house 5 when performing the above storage work, air is sucked through the suction nozzle 21 by the local exhaust device 4 and the room is managed in a negative pressure state. Even if tritium leaks, It does not leak out.
Workers need to be well equipped with airline suits to prevent tritium intake. Since the work is relatively simple, a robot can be used.
Thereafter, the air in the hot-air heating furnace 10 is sucked by the pump 44 of the tritium recovery device 2 so that the pressure inside the furnace is kept lower than the negative pressure of the green house 5 so that it does not leak out of the furnace when tritium is released. To do.
[0033]
Next, the air circulation fan 13 of the hot air heating furnace 10 is operated to circulate the furnace air at a flow rate of about 1 m / s. Since air freely flows through the side plate 25 of the inner box 11 and there is only a fence on the side surface of the basket 50, the air flow circulates through the basket 50. In addition, in order to confirm the processing temperature of the metal material for each basket, a floor plate 51 through which air does not flow is stretched in the basket 50 so that independent flow paths are configured. Further, it is more preferable that the side plate 25 of the inner box 11 is used as a louver or a rectifying plate to adjust the air drift depending on the position so that air flows relatively evenly in each basket 50.
[0034]
Since the pressure in the hot air heating furnace 10 must be lower than the pressure in the greenhouse 5 even at the maximum value, a negative pressure gauge is installed near the outlet of the circulation fan 13 or in the inner box 11 in which the metal material is stored. The negative pressure is measured and managed. In order to maintain the negative pressure in the furnace from the start of the heat treatment to the end of cooling, the operation of the tritium recovery device 2 is continued during this period.
[0035]
The temperature controller 14 is attached with a program control mechanism that changes the set temperature according to the elapsed time of the heat treatment, and receives an air temperature measurement signal from a temperature detector provided in the circulation path of the furnace air, and circulates. The output of the sheathed heater 12 installed in the road is adjusted so that the air temperature has a predetermined pattern.
[0036]
FIG. 5 is a drawing showing an example of a decontamination time chart.
As the metal temperature rises, tritium adhering to or adsorbing to the surface of the metal material is released as tritium water. Its release increases with increasing temperature. On the other hand, a larger amount of tritium existing as a solid solution in the metal remains in the metal at a low temperature, but is released when the temperature of the metal material reaches 200 ° C. or more and is released from the inside as a tritium-containing hydrogen gas. come.
[0037]
The purpose of the heat treatment of this example is to completely recover tritium in the metal material including solid solution tritium, so that the heat treatment is finally continued for a necessary time at a temperature of 200 ° C. to 600 ° C. It is necessary to.
Therefore, when the temperature of the circulating air is raised from the room temperature, the release of tritium starts around 50 ° C., and the release amount increases as the temperature rises. At this time, if the transition to the target high temperature state is attempted in a short time, the tritium contained in the adsorbed water will be released in a short time, the tritium concentration in the atmosphere will rise excessively, and the tritium recovery capability will be insufficient. There is a fear.
[0038]
Therefore, the initial set temperature is set to an intermediate temperature suitably lower than 200 ° C., for example, 150 ° C., the temperature rise is temporarily held at the intermediate temperature, and the tritium water is sufficiently evaporated at an appropriate rate. It is preferable to set the temperature to 200 ° C. to 600 ° C. at which solid solution tritium is released.
The tritium inside the metal material is completely released by maintaining the temperature within a temperature range from 200 ° C. to 600 ° C. where the solid solution tritium is released for an appropriate time. The amount of tritium released can be evaluated empirically according to the heating temperature and the heating time.
The internal temperature of the metal material has a time delay with respect to the surface temperature, and this time delay is generally determined by the thickness of the metal material, and is less than one hour at a thickness of about 3 cm. However, a thick material such as a casting has a time delay of 1 hour or more. Since the time delay is proportional to the weight per surface area, the time delay is calculated by measuring the type, weight and surface area of the object to be processed in advance, and adjusted by converting it to the duration of the high temperature state. Make sure that appropriate processing is performed.
Note that the waste to be treated may be a composite material with ceramic or a non-combustible material such as ceramic.
[0039]
In the tritium expelling process, the tritium recovery device 2 is always operated, and the internal air of the hot air heating furnace 10 is continuously sucked from the exhaust nozzle 15 through the recovery pipe 17. The tritium recovery device 2 is preferably always operated at a constant flow rate in order to maintain the tritium removal performance. Further, if the tritium concentration in the furnace rises excessively, there is a risk that tritium that cannot be treated leaks out. Therefore, the opening degree of the small valve 22 attached to the furnace-side intake nozzle 16 is adjusted so as to take in outside air to replace the furnace air about 4 to 5 times per hour. Excessive replacement is not preferable because the processing amount of the tritium recovery device 2 becomes excessive and the device needs to be excessively large.
[0040]
Since the exhaust to the tritium recovery device 2 is cooled to almost room temperature through the water-cooled cooler 19, the pump 44 of the tritium recovery device 2 may be a constant-temperature metering pump, and the pump suction set based on the normal temperature Since a volume larger than the amount can be sucked from the heating furnace, there is an effect that the number of substitutions is substantially increased.
In the tritium recovery device 2, the tritium is absorbed and recovered through the exhaust gas through the absorption tanks 41 and 42 arranged in series. The atmosphere of the glove box 46 is collected and processed in the building exhaust device 7 via the local exhaust device 4.
In addition, the tritium measuring device 6 is provided in the middle of the recovery pipe 17 for transporting the exhaust gas from the hot air heating furnace 10 to the tritium recovery device 2, and the tritium content in the exhaust gas to be processed is measured and managed. The results are preferably recorded and retained.
[0041]
After the tritium in the metal material is completely expelled and recovered by the tritium recovery device 2, the hot-air heating furnace 10 is cooled to near room temperature, the internal metal material is pulled out together with the loading cart and transferred to the transport cart. Transport to storage and store.
The hot air heating furnace 10 has an intake nozzle 16 Open the two valves connected to the large-sized valve 23 and the mixer 20 of the exhaust nozzle 15, close the suction nozzle 21 of the exhaust pipe 18, and let the local exhaust device 4 suck the atmosphere in the furnace to air in the furnace. Can be rapidly cooled to about room temperature by substituting with ambient air.
[0042]
Here, the mixer 20 is used because high-temperature air in the furnace is directly sent to the local exhaust device 4 because it causes a failure unless high-temperature piping or equipment is used. And the atmosphere in the green house are mixed to lower the temperature and then sent to the local exhaust device 4. The mixer 20 is provided with several partitions inside to efficiently mix two air flows.
The exhaust pipe 18 is provided with a tritium measuring device 3 on the way, and monitors whether or not tritium is contained in the exhaust gas discharged to the atmosphere. The measurement result is preferably recorded.
[0043]
According to the decontamination method and apparatus for tritium-contaminated metals of this embodiment, high temperature treatment at 200 ° C. to 600 ° C. is performed, so that tritium can be removed almost completely including solid solution tritium inside the metal. The hot-air heating furnace that enables such high-temperature processing has a sealed structure that can withstand negative pressure by sealing the seam of the outer casing with welding, etc., forming a hot-air circulation path in the furnace and circulating Since the target metal material stored in the basket is loaded in the road, loading and unloading operations are easy.
Further, during the heat treatment of the metal material, the atmosphere in the furnace is continuously extracted at a predetermined ratio and the tritium contained in the tritium recovery device is recovered, so that the process is simple and the apparatus can be configured economically.
[0044]
Note that the metal material contaminated with tritium is usually contaminated with corrosion products (CP) and fission products (FP) at the same time. CP and FP are contaminated by adhering to the surface in contact with the contaminated fluid. If the CP or FP on the surface in contact with the fluid is removed before the tritium recovery operation, these γ rays are used during the tritium recovery process. This is preferable because the workability in tritium decontamination is improved.
[0045]
【The invention's effect】
As described above, according to the present invention, not only tritium in the vicinity of the surface but also a large amount of tritium existing as a solid solution in the inside can be removed almost completely, and a method for decontaminating tritium-contaminated metals that is simple and easy to handle and Since the equipment could be provided, it can greatly contribute to the nuclear reactor dismantling work that will become more active in the future.
[Brief description of the drawings]
FIG. 1 is a process flow diagram relating to one embodiment of a tritium-contaminated metal decontamination apparatus of the present invention.
FIG. 2 is a perspective view of a hot air heating furnace of the present embodiment.
FIG. 3 is a cross-sectional view showing a sealing mechanism in the hot air heating furnace of FIG. 2;
FIG. 4 is a side sectional view of a decontamination basket and a carriage used in the present embodiment.
FIG. 5 is a time chart showing a temperature management method of the hot air heating furnace of the present embodiment.
[Explanation of symbols]
1 Tritium expelling device
2 Tritium recovery device
3 Tritium measuring device for exhaust passage
4 Local exhaust system
5 Green House
6 Tritium measuring device for recovery path
7 Building exhaust system
10 Hot air heating furnace
11 Inner box
12 Air heater
13 Air circulation fan
14 Temperature controller
15 Exhaust nozzle
16 Intake nozzle
17 Recovery pipe
18 Exhaust pipe
19 Water-cooled cooler
20 Mixer
21 Suction nozzle
22,23 Valve
24 Body door
25 Side plate
26 rails
27 Floor board
28 Instruments
29 Inspection door
31 Outer casing
32 cushioning material
33 Rivet
34 Sealing material
35 Welding
36 Adhesive tape
37 Inner casing
38 Insulation
41, 42 Absorption tank
43 Mist Trap
44 Pump
45 Flow meter
46 Glove Box
50 baskets
51 Floor board
52 Side plate
53 Liang
54 pillars
55 Loading cart
56 wheels
57 Carriage cart
58 rails

Claims (6)

A metal material containing tritium is accommodated in a hot-air heating furnace that generates a circulating hot air capable of adjusting the temperature, and is first heated with hot air of 200 ° C. or lower to drive off the tritium adsorbed and adsorbed on the surface of the metal material, The hot air heated to 600 ° C is heated and held to drive out solid solution tritium, the tritium contained is recovered while extracting the air in the furnace, and the hot air heating furnace is heated to 100 ° C or less after a sufficient release time has elapsed. a decontamination method of tritium contamination metal to eject the cooling the metallic material to release the tritium, the hot air heating furnace is housed in a vacuum chamber, said vacuum chamber when cooling the heat air furnace A method for decontaminating tritium-contaminated metals, wherein cooling is accelerated by passing air sucked from the inside of the hot-air heating furnace .   The tritium released from the metal material is cooled to near room temperature through a cooler and then recovered by a tritium recovery device, and the exhaust gas after the tritium recovery is discharged to the atmosphere via an exhaust device. Decontamination method for tritium contaminated metals.   3. The method for decontaminating a tritium-contaminated metal according to claim 1, wherein the hot air heating furnace is operated in a state where the pressure is reduced from atmospheric pressure. The metal material containing tritium is placed in a basket and mounted on a cart, the basket is stored together with the cart in a hot air passage in the hot air heating furnace, and the cart is pulled out after heat treatment. Item 4. A method for decontaminating a tritium-contaminated metal according to any one of Items 1 to 3 . A hot-air heating furnace, an exhaust gas cooler, a tritium recovery device, a local exhaust device, and a decompression chamber that accommodates the heating furnace, the hot-air heating furnace comprising an airtight can body having an air inlet and an air outlet Is further maintained at a negative pressure from the decompression chamber , and is provided with an inner box for storing the basket carriage therein, and an air heater and a circulation fan are incorporated therein, and the inner box is provided with a rectifying plate through which air flows on both sides, Hot air generated by the air heater is circulated through the current plate of the inner box by the circulation fan, the air discharge port is connected to the tritium recovery device via the exhaust gas cooler, and the tritium recovery device is connected to the hot air heating furnace. tritium in the exhaust gas with suction air in order to maintain the internal negative pressure is recovered, said local exhaust system the flow path of the local exhaust for exhausting the interior of the furnace through the tritium recovery device Direct a flow path for the gas to a switching valve for switching between flow paths for exhausting the local exhaust system, when the cast out tritium by heating the metallic material in heat air furnace exhaust through the tritium recovery device When the inside of the furnace is cooled after the tritium is expelled, the inside air of the furnace is replaced with outside air through the hot-air heating furnace. 6. The tritium-contaminated metal decontamination apparatus according to claim 5, wherein the switching valve is provided with a mixer for mixing the gas in the hot air heating furnace and the atmosphere in the decompression chamber.

Images