JPS597960B2 - Radioactive waste treatment method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the treatment of low-level radioactive waste from nuclear power plants, and more specifically, to the treatment of waste ion exchange resin and radioactive crud attached to its surface by effectively peeling and separating it. The present invention relates to a method and apparatus for doing so.

A variety of radioactive wastes are emitted from nuclear power plants, but most of them are low-level radioactive wastes.

These wastes include liquid wastes such as drains from various equipment, recycled waste liquids from desalination equipment, and washing liquid from work clothes, and solid wastes such as filter fillers and ion exchange resins.

The radionuclides that contribute to the radioactivity of these wastes are
Mainly Kobal}60.

This depends on the corrosion products of the wetted parts of the primary cooling water system, including the reactor core.

In addition to cobalt, corrosion products include iron, manganese, chromium, tungsten, sodium, zinc, nickel, etc.
There are many nuclides.

These nuclides have short half-lives, except for cobal}60t.
Kobal}600 has a half-life of more than five years, which poses a problem in waste disposal.

This cobalt-60 exists in the form of ions in the cooling system, but as mentioned above, iron is a corrosion product, and this iron is in the form of fine particles of oxides or hydroxides (hereinafter referred to as cladding). Cobalt-60 exists in this porous cladding in a concentrated form, attached or adsorbed.

Therefore, the material that is actually highly radioactive is cobalt in the cladding.

These substances mix into various liquid wastes or adhere to used 6 ion exchange resins, making the waste radioactive.

In the conventional method for treating low-level liquid and solid waste, first of all, when it comes to liquids, the equipment drain is separated from the crud and stored in a storage tank, and the separated water from the crud is reused.

Floor drain, recycled waste liquid, etc. are concentrated, solidified with cement as concentrated waste liquid, and canned in drums.

Waste ion exchange resin is either stored in a storage tank or solidified with cement and canned in drums.

As described above, liquid and solid wastes are finally filled into drums and solidified with cement, and then stored in the storage warehouses of nuclear power plants or in storage tanks.

For example, the amount of drums filled with low-level radioactive waste generated by a nuclear power plant with a power generation capacity of 1 million kW is approximately 2,000 per year for a PWR (770 pressure water reactor).
The number is said to be 5,000 to 6,000 for WR (boiling water reactor), and with the expansion of nuclear power plants, it is predicted that the number will reach 10 per year in a few years, and the cumulative number will reach 620,000. .

Currently, these drum fills are not allowed to be dumped into the ocean and are all stored in hangars.

However, with regard to ocean dumping, in conjunction with the progress in the development and use of nuclear energy, consideration is being given to the environmental safety assessment of ocean dumping.

Therefore, assuming that ocean dumping is permitted, it is necessary to establish a processing method that can handle ocean dumping in addition to the current storage in drum cans.

Technical standards for dumping drum-canned waste into the ocean include regulations on the mechanical strength of the drum and radiation dose, the latter of which is heavily dependent on illegal waste disposal.

Conventionally, concentrated waste liquid has been solidified with cement and canned in drums as low-level waste, and waste ion exchange resin has been stored in storage tanks in the form of sludge.
Problems with regulatory values in the case of ocean dumping, volume reduction of these wastes, reduction of radiation doses, etc. are being focused on, and countermeasures are being considered.

For this reason, studies are being considered to solidify the concentrated waste liquid and instead of filling it with cement, which is currently the case, canning it in drums with asphalt, plastic, glass, etc.

On the other hand, waste ion exchange resin has a considerable amount of radioactive substances attached to it, so it is problematic to dispose of it in the ocean.
Currently, storage in a hangar is being considered.

In the case of solidifying concentrated waste liquid, when reviewing low-level waste, the amount of waste ion exchange resin in the waste is large, and excluding waste ion exchange resin from the list of materials subject to ocean dumping is a consideration from a storage perspective. It is disadvantageous.

The unresolved object is to eliminate the drawbacks of the prior art described above and to provide a method for effectively peeling and separating the crud from waste ion exchange resin and disposing of it.

In the present invention, the waste ion exchange resin is introduced into a freezing device in a slurry state, rapidly frozen, and then thawed. The cladding is peeled off from the ion exchange resin surface using an ultrasonic vibration device, and the cladding is separated from the ion exchange resin. The radioactivity level is further reduced by supplying the sludge containing the clasodes to a separation device, separating the clades from the ion-exchange resin based on the difference in particle size, and then dehydrating the ion-exchange resin in a dehydrator. That is.

An embodiment of the present invention will be described below with reference to the drawings.

The waste ion-exchange resin 1 with radioactive crud adhering to it once enters a slurry receiving tank 2, is transferred to a freezing device 3, and is rapidly frozen in a refrigerator using Freon as a refrigerant 30.

The ion exchange resin used in desalination equipment at nuclear power plants is in the form of granules, and the particle size is approximately 0. 5 wn.

Reddish-brown iron sesquioxide (α-Fe203) is present on the surface of this particle size.
A crud mainly composed of is attached.

By lowering the temperature of the waste ion exchange resin 1 to which the clades have adhered, a gap is created between the spherical resin surface and the clasodes due to shrinkage due to the temperature drop in the resin and volumetric expansion due to freezing of water, and the clasodes are peeled off from the resin surface. It becomes easier.

Next, the sludge containing the frozen resin is thawed by a steam heater 31.

The thawed slurry is transferred to an ultrasonic peeling device 4.

Here, the cladding is peeled off from the resin surface by applying ultrasonic vibrations at a low frequency of 20 to 30 KC with a large displacement amplitude.

The separated crud becomes fine particles.

Next, this slurry consisting of the resin and the cladding of fine particles is transferred to the sedimentation separator 5.

The particle size of the cladding is 50 μm or less compared to the resin particle size of 0.5 m.

Comparing the sedimentation speeds of both particles, it was found that resin (specific gravity = 1.
5) is approximately 7 cm/sec, cladding (specific gravity = 5.
2) is about 0. 5 cm/see or less, and the difference is about one order of magnitude.

In this way, since there is a large difference in the particle size of Clasod and resin exfoliated by freezing treatment and ultrasonic vibration, the sedimentation rates are also large and they can be easily separated using the difference in sedimentation rates. .

The sedimentation separator 5 has a structure in which clad fine particles can be extracted from the top and resin can be extracted from the bottom.

In the sedimentation separator 5, air 32 is blown from the lower part to agitate the slurry, the agitation is stopped, the resin is allowed to settle, and the upper layer of the cladding liquid 21 is extracted.

Furthermore, water 27 is supplied from the upper part, air 32 is blown from the lower part to perform stirring, and the resin and cladding are suspended, the stirring is interrupted, and the upper cladding-containing liquid 21 is drawn out in the same manner as described above.

By performing this operation at least once, the resin and Clasod are separated.

Then, the resin 22 is extracted from the bottom of the sedimentation separator 5,
Water 24 is separated by applying it to a dehydrator 6, and the resin 2 is drained.
3 is temporarily placed in the resin receiving tank 1.

Next, it is drum-canned by a drum solidification device 11 and subjected to storage 28 or future final disposal 29.

On the other hand, the crud 21 separated by the sedimentation separator 5 and the separated water 24 separated by the dehydrator 6 are combined and filtered through a filter 8, and the filtered water 25 is passed through a demineralizer 9 and put into a recovery tank 10.

This treated water 27 is reused as cooling water in the power plant, and a portion is returned to the sedimentation separator 5 to be used for separating resin and clasodes.

The clasodes 26 separated and removed by the filter 8 are stored in the storage tank 12.

In the above embodiment, a refrigerator using Freon as the refrigerant 30 of the freezing device 3 has been described, but other methods include supplying liquefied gas such as liquid air or liquid nitrogen, or adding solid matter such as dry ice. Good results can also be obtained by freezing the resin-containing slurry as a pretreatment for stripping the crud.

In addition, although steam was used in the embodiment for thawing, it is also possible to sufficiently thaw the frozen resin-containing slurry by heating with heat transfer oil, an electric heater, or the like.

As an effect of the above example, the peeling and separation removal rate of the crud mainly composed of iron sesquioxide (F e2 o3) attached to the resin surface was about 95% or more, and radioactive substances could be effectively removed from the waste ion exchange resin. reactor.

Further, in the sedimentation separation apparatus in the non-example, water is used to separate the resin and the cladding, but this water is reused after the cladding is dehydrated, and there is no need to supply a large amount of water.

As an effect of this patent, radioactive nuclides attached to waste ion exchange resin can be significantly removed and separated, so the radiation dose of the drum filling can be significantly reduced.
If ocean dumping is permitted, waste ion exchange resins can be considered ocean dumped waste.

[Brief explanation of the drawing]

The drawing is a system diagram showing an example of an apparatus implementing the present invention. 1...Waste ion exchange resin, 2...Slurry receiving tank, 3...Freezer, 4...
... Ultrasonic peeling device, 5 ... Sedimentation separation device, 6
... Dehydrator, 7 ... Resin receiving tank,
8...Filter, 9...Demineralizer, 1
0...Recovery tank, 11...Solidification device, 12...Storage tank, 21...Clad, 22.23...Resin, 24... ... Separated water, 25 ... Door water, 26 ... Clad, 27 ... Treated water.

Claims (1)

[Scope of Claims] 1. A radioactive material characterized by rapidly freezing and thawing waste ion exchange resin to which radioactive cladding is attached, peeling off the cladding from the ion exchange resin by high-frequency vibration, and then separating the ion exchange resin and the cladding. How to dispose of waste. 2. The method for treating radioactive waste according to claim 1, wherein the ion exchange resin from which the cladding has been separated is subjected to dehydration treatment. 3. Radioactive waste according to claim 2, in which the separated clades are combined with water dehydrated from an ion exchange resin and passed through a filter, the cladding is separated and stored in a tank, and the water is reused. processing method. 4 A freezing device that quickly freezes waste ion exchange resin with radioactive crud attached, a thawing device that thaws the frozen ion exchange resin, a high frequency peeling device that peels the crud from the thawed ion exchange resin, and a high frequency peeling device that peels off the crud from the thawed ion exchange resin. A radioactive waste processing device comprising: a separation device that separates exchange resin; a dehydration device that dehydrates the separated ion exchange resin; and a solidification device that solidifies the dehydrated ion exchange resin. ，