JPS648319B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for encapsulating radioactive krypton gas in zeolite, and in particular to a method for obtaining a stable solidified zeolite that occludes krypton gas.

The exhaust gas emitted from spent nuclear fuel reprocessing plants and nuclear power plants contains radioactive krypton gas (krypton), which has a long half-life (half-life of 10.3 years).
85) are included. This is contained in several percent of the exhaust gas from reprocessing plants, and is emitted in trace amounts from nuclear power plants. Although the development of technology to recover radioactivity from the perspective of reducing the release of radioactivity into the environment is progressing, the technology for storing recovered krypton gas for a long period of time is still under development.

The zeolite encapsulation method, which is said to be the most developed long-term storage technology, is a method in which krypton gas is confined in the cavities of zeolite under high temperature and pressure. This encapsulation principle takes advantage of the fact that zeolite has a cage (cavity) in its crystal, and when the zeolite is heated to a high temperature, the crystal water filling the cage is removed to the outside through the pores in the crystal, and the water is replaced. The idea is to seal radioactive exhaust gas inside a cage. These pores are small at room temperature, and molecules of the radioactive exhaust gas krypton cannot pass through, but when heated to high temperatures, they become larger and can enter the cage through the pores. When the temperature is returned to room temperature in this state, the pores become smaller again and krypton molecules are sealed inside the cage. This encapsulation process is generally performed at a temperature of approximately 300 to 450°C and a gas pressure of approximately
It is carried out at high temperatures and pressures of 40,000 to 60,000 psi. Gas pressure medium is used for this high temperature and high pressure technology.
HIP is adopted. However, this equipment needs to be installed in a hot cell that is controlled at negative pressure, and in the unlikely event that the HIP container is destroyed, a large amount of gas will be blown out and the inside of the cell will be maintained at negative pressure. That is extremely difficult. Furthermore, when the container is destroyed, it is predicted that solid objects will be scattered due to the missile effect due to the accumulated energy, and in order to cope with this, it is necessary to increase the thickness of the cell wall.

This invention was made in order to eliminate such conventional drawbacks, and the pressure necessary to encapsulate krypton gas in zeolite is secured by expansion due to heating of krypton in the capsule, and the occlusion body is burned out. By tying it together, krypton gas can be immobilized safely and reliably.

That is, in this invention, zeolite is filled into a capsule, radioactive krypton gas is introduced into the capsule while the zeolite is cooled, the krypton gas is adsorbed to the zeolite, and then the capsule is surrounded so as to prevent deformation of the capsule. The krypton gas is forced into the zeolite cage by heating the zeolite and increasing the internal pressure of the capsule while being pressed with a mold, and after extracting the excess krypton gas, the zeolite is heated again and the surrounding area is released. The material is pressed and sintered.

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a capsule 1 has a heat insulating material 12 placed inside an outer plate 11 and a lid 13 attached to seal the inside, and the inside is filled with zeolite 2. Outer panel 1 of capsule 1
is made of stainless steel or ordinary carbon steel with a thickness of 1 to several mm, and the heat insulating material 12 is made of glass wool or ceramic. The zeolite 2 is filled with powder, pellets, or fibers. Heaters 3 are embedded in the zeolite 2 so as to be evenly distributed throughout the zeolite 2 in a spiral or longitudinal wave pattern, and their ends are led out to the outside through a lid 13. The lid 13 is also provided with a gas inlet 14, and a wire mesh 15 is placed at the inner end of the inlet 14 to prevent the zeolite fine powder from leaking to the outside.

Capsule 1 filled with zeolite like this
is installed on the load holder 4 of the press as shown in Fig. 2, the gas inlet 14 and the heater 3 are passed through the holder 4 as shown in Fig. 3, and the heater 3 is connected to a power source (not shown). However, the gas inlet 14 is connected to a krypton gas holder (not shown) via a joint 16, a pipe 17, and a stop valve 18.
Then, the capsule 1 is surrounded by a container 5 for liquid nitrogen, and the zeolite 2 is cooled by the liquid nitrogen to increase the adsorption performance of the zeolite. In this state, after a predetermined amount of krypton gas is introduced from the gas inlet 14, the stop valve 18 is closed. As a result, the cooled zeolite 2 adsorbs krypton gas.

Next, as shown in FIGS. 3 and 4, the liquid nitrogen container 5 is removed, the capsule 1 is surrounded by a mold 6 held by a crosshead 9, and is pressed down from above with a push rod 7. A heater 41 is arranged around the mold 6, and the push rod 7 is operated by a pressurizing cylinder 70 provided on the movable upper plate 8. Moving upper plate 8
is screwed onto a screw shaft 81, and is configured to move up and down as the screw shaft 81 is rotated by the rotation mechanism 80. Further, a cylinder 90 for raising and lowering the crosshead is attached to the movable upper plate 8. From this state, as shown in FIG. 5, the movable upper plate 8 is lowered to press the capsule 1 with a predetermined pressure.

Then, by energizing the heater 3, the inside of the capsule 1 is
For example, heat to 450-500°C. This increases the internal pressure of the capsule and the krypton gas enters the zeolite cage by diffusion. After holding for a predetermined time (for example, 1 hour), the current supply is stopped, the stop valve 18 is released, and the excess krypton gas that has not entered the cage of the zeolite 2 is collected into the gas holder. Note that since the capsule 1 has a heat insulating material 12, the heat inside the capsule does not easily flow to the mold.
In order to prevent heat dissipation as much as possible, the mold 6 is preferably heated to, for example, about 200°C.
Next, energize the heater 3 again, for example, 650 ~
Heating it to 700°C and pressurizing it with a push rod 7,
It is maintained in a heated and pressurized state for a predetermined time (for example, 1 hour). As a result, the zeolite 2 is sintered in a state in which krypton gas is captured, and the capsule 1 is shortened and reduced in volume, and is in a stable solidified state. Note that during the pressurization, the periphery of the capsule 1 is pressed by a mold to prevent deformation, so there is no problem even if the capsule itself is thin.

After the above operation, the capsule 1 is removed from the mold 6 by raising the movable upper plate 8 and raising the crosshead 9 while keeping the capsule 1 pressed by the push rod 7. Next, the push rod 7 is raised to remove the capsule 1, and the inlet port 1 protruding from the capsule 1 is removed.
4 is heated, crimped and cut, and the cut ends are sealed by welding.

FIG. 6 shows another example of the apparatus, in which the mold 6 is covered by an electric furnace 42, and the mold 6 is heated by a heater 41 arranged on the inner wall of the electric furnace 42. The mold 42 is filled with an inert gas and sealed with a gasket 43. In this configuration, the capsule 1 is heated from the outside, so there is no need to provide a heater inside the capsule 1. In addition,
The electric furnace 42 is provided with an inert gas filled pipe 45 and a shutter 44 at its lower part, and when only the mold is heated, the upper part is sealed with a push rod 7.
The lower part is for closing the shutter 44 and introducing inert gas to prevent oxidation of the mold and heat it.

FIG. 7 shows yet another example, in which a through hole is formed in the center of the capsule 1, into which a rod-shaped heater 30 is inserted in a removable manner. A heat insulating material 12 is provided inside the outer cylinder of the capsule, but no heat insulating material is provided in the inner cylinder 19 in order to introduce heat from the heater 30. Even in this configuration, there is no need to provide a heater in the capsule 1, and the heater 30 also performs heating for sintering, and after sintering, the heater 30 is removed and used repeatedly.

FIG. 8 shows yet another example, in which a wire 63 having a tensile strength of about 150 Kg/mm ² is wound around the outer periphery of a mold 61 to form a so-called wire-wound high-pressure container. This wire 63 has a rectangular cross section, and a heat insulating layer is formed on one side of the wire by thermally spraying ceramic such as zirconia or alumina to a thickness of several microns to several tens of microns. Further, a plurality of heaters 31 are embedded in the wall of the mold 61 in the axial direction. The capsule 1 is inserted into the mold 61, and the top and bottom of the capsule 1 are pressed by the push rod 7 and the receiver 4 through a heat insulating plate 69. The upper and lower parts of the mold 61 are heat insulating plates 6
A lid 62 is attached through the cap 5, and a gasket 64 seals between the lid 62, the push rod 7, and the receiver 4. With this configuration, since the plate thickness of the mold can be made thinner, there is an advantage that the production cost can be reduced and heating can be easily performed. Furthermore, since the wire 63 is formed with a ceramic layer, it is possible to effectively prevent heat from the heated mold from dissipating.

When using the apparatus shown in Figures 6, 7 and 8 above, the krypton gas filling method is as follows:
It is basically the same as shown in the figure.

As explained above, this invention mechanically presses a capsule containing zeolite from the outer periphery, heats the capsule while preventing deformation, encapsulates krypton gas in the zeolite, and stabilizes it by sintering. This makes it possible to stably encapsulate krypton gas and to reduce the thickness of the capsule.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of a capsule showing an embodiment of the capsule to which this invention is applied, Fig. 2 is a partial cross-sectional side view of the capsule installed in a press, and Fig. 3 is a longitudinal cross-section of the capsule with a mold installed. Front view, Figures 4 and 5
Each figure is a partially sectional side view of the capsule in a pressed state, and FIGS. 6, 7, and 8 are longitudinal sectional views showing other examples of the mold. 1...capsule, 2...zeolite, 3,31,4
1... Heater, 6, 61... Mold, 7... Push rod.

Claims (1)

[Claims] 1 Fill a capsule with zeolite, cool it, introduce radioactive krypton gas into the capsule to cause the krypton gas to be adsorbed to the zeolite, and then press the capsule from around it with a mold to prevent it from deforming. In this state, krypton gas is forced into the zeolite cage by heating the zeolite and increasing the internal pressure of the capsule, and then after extracting the excess krypton gas, the zeolite is heated again and pressed from the surroundings to sinter it. A method for encapsulating radioactive krypton gas in zeolite.