Device for Removing Radioactive Particles in Moist Gas

The present invention relates to a device for removing radioactive solid particles from moistened gas and, more particularly, to a decontamination device including a filter, which device is suitable for use in the waste gas treating system of equipments for heat treatment such as drying, evaporation or the like of solution, sludges and solid matters containing radioactive substances.

Moistened gas containing radioactive solid particles is generated in the treatment of such as drying, evaporation, distillation or the like of substances containing solution, e.g. direct denitration and treatment of analytical waste liquid. In order to treat such waste gas, various methods have been used heretofore, such as scrubbing of the gas with a solution, condensation of the gas followed by re-evaporation. These conventional treating methods, however, require largescale equipment having a multiplicity of constituents. These conventional equipments require impractically large installation area when placed in a glove box for treating the radioactive substance and are difficult to handle.

It has been proposed to use a filter for removing the radioactive particles. This, however, is not preferred because the filter is soon clogged and becomes inoperative particularly when the treated gas is a moistened gas.

An object of the present invention is to provide an improved device for removing radioactive solid particles in moist gas.

Another object of the present invention is to provide the device concerned which can be installed in a glove box.

A further object of the present invention is to provide the device concerned which can be operated without substantial labor or difficulty.

Another object of the present invention is to provide the device concerned which ensures to filtrate radioactive substances to minimize clogging in a filter element.

According to the invention, a solid-gas separation filter is basically used for separating and removing radioactive particles from the moistened gas. With the knowledge that the clogging of the filter in the conventional system is mainly attributable to the condensation of moisture on the filter, according to the invention, microwave is applied to the filter to heat up the latter to evaporate and dry the moisture condensate thereby to prevent the filter from being clogged to ensure a continuous good filtration performance of the filter.

Briefly, the inventive device comprises a pipe for feeding therethrough a moist gas containing radioactive solid particles, a solid-gas separation filter disposed in the pipe, a microwave generator, a wave guide connected between the pipe and the generator so as to apply the microwave to the filter, and a shielding plate in the wave guide. The shielding plate is made of material capable of passing the microwave therethrough and preventing the spreading of contamination.

The invention will be more fully understood from the following description taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic view of a device for removing radioactive particles in moist gas according to an embodiment of the present invention.

FIG. 2 is a schematic view of a device for removing radioactive particles in moist gas according to another embodiment of the present invention.

Referring first to FIG. 1 illustrating an embodiment of the invention, an evaporator 2 disposed inside a glove box 1 and a microwave generator 3 disposed outside the glove box 1 are interconnected through a wave guide pipe 4 in which is disposed a shielding plate 5 for preventing the spreading of contamination. The shielding plate 5 is made of a material having a good microwave guiding nature and a high corrosion resistance, e.g. fluorine-containing resin, silicone resin, glass, ceramics and so forth, and is adapted to prevent radioactive substances from being diffused into the microwave generator 3, although it permits the electromagnetic wave coming from the generator 3 to pass therethrough. A filter 6 is interposed between the evaporator 2 and the shielding plate 5. The filter 6 used in this device is an HEPA filter (High Efficiency Particulate Air Filter, having performance defined in Japan Industrial Standard (JIS) Z 4812-1975) made of a material capable of passing microwave therethrough, such as, for example, asbestos containing glass. A waste gas pipe 7 is connected between the filter 6 and the shielding plate 5 and leads to a waste gas treating system (not shown).

The evaporator 2 is charged with a solution, sludge, solid matters or the like material 8 to be heated to generate a moist gas containing radioactive particles, and the microwave generator 3 is operated. The microwave having a frequency of, for examples, 915 MHz or 2450 MHz, is applied to the material 8 in the evaporator 2 through the shielding plate 5 and the filter 6. In consequence, the material 8 is evaporated to generate a moist gas which is sent through the filter 6 to the waste gas pipe 7. Namely, the portion of the wave guide pipe 4 in the vicinity of the filter 6 and extending from the evaporator 2 to the waste gas pipe 7, serves also as a gas pipe. The condensate or the like on the filter 6, which constitutes a main cause of the clogging, is heated and evaporated by the microwave so that the clogging is avoided conveniently. It is possible to employ a plurality of filteration stages in accordance with the extent of contamination of the waste gas.

The embodiment of the invention as shown in FIG. 1 offers a great advantage that the construction of the device as a whole is very much simplified because the heating of the filter 6 and the heating of the material 8 in the evaporator 2 can be made simultaneously by the single microwave generator 3.

Another embodiment of the invention as shown in FIG. 2 is suitable for use in such an equipment that the source of the moistened gas (waste gas) containing radioactive solid particles is located at a place remote from the waste gas treating system. In FIG. 2, an oven or furnace 11 is disposed at an intermediate portion of a gas pipe 10 interconnecting a waste gas generator (not shown) and a waste gas treating system (not shown). At least one filter 16 which is the same as the aforementioned HEPA filter 6 in FIG. 1 is disposed within the oven 11. The oven 11 is connected to a microwave generator 13 through a wave guide pipe 14 in which mounted is a shielding plate 15 for preventing the diffusion of the contamination.

In the embodiment of FIG. 2, two filters 16, 16 may be used with one being disposed at the waste gas inlet side and the other at the waste gas outlet side, respectively, within the oven 11, and the wave guide 14 is connected to the oven 11 at the position between the two filters 16, 16.

The condensate or the like on the HEPA filter 16 is heated and evaporated by the microwave, so that the undesirable clogging of the filter is avoided. Supply of an additional air, if necessary, can be made through air supply pipes 12. If necessary, the HEPA filter may be made of a material having also a high resistance to chemicals, such as, for example, asbestos containing relatively much glass.

As will be seen from the foregoing description, the device of the invention having the described construction can effectively remove, by means of a filter, radioactive solid particles from moistened gas in which the particles are suspended. Therefore, the apparatus and equipments can have simplified construction and reduced size suitable for installation in a glove box. In addition, the device of the invention is easy to handle and maintain.

Though the present invention has been described with reference to the preferred embodiments, many modifications and alterations can be made within the spirit of the invention.