JPS58100800A - Treatment of radioactive waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for disposing of radioactive waste, and in particular, it is an object of the present invention to provide a method for purposefully reducing the volume of radioactive waste generated in a boiling water reactor power plant.

Combustible miscellaneous solids (paper, cloth, plastic, etc.) generated at nuclear power plants with boiling water reactors are incinerated to reduce their volume and stored in the form of incinerated ash on the power plant premises. However, since incineration ash is a powder, there is a risk of scattering and difficulty in handling. Father, nuclear power plants continue to operate for quite a long time, and as nuclear power plants continue to operate, the cumulative amount of radioactive incinerated ash that must be managed and stored continues to increase. The apparent density was small, ranging from 0.4 to 0.82Xrn3, and incineration alone was still insufficient to reduce the volume.

As a result of intensive research to provide a method for purposefully reducing the volume of radioactive waste generated from boiling water reactor power plants, the inventors of the present invention have developed a method for evaporating and solidifying the concentrated waste liquid generated at the same power plants. It was confirmed that the compound itself has excellent properties as a binder, and the present invention was completed based on this knowledge. That is, the present invention combines incineration ash of combustible miscellaneous solids generated in a boiling water reactor power plant with evaporated solidified powder of concentrated waste liquid generated in the same power plant to a weight ratio of 40% or more to form a pellet solid. The gist of this paper is a method for disposing of radioactive waste, which is characterized by its oxidation.

Specific examples will be explained in detail below.

In order to obtain a simulant of combustible miscellaneous solid incineration ash, a mixture of paper, cloth, and polyethylene in equal amounts by weight was incinerated.

Nuclear power plants with boiling water reactors generate large amounts of waste liquid whose main component is sodium sulfate. In order to reduce the volume, the sodium sulfate is concentrated to about 18% by volume using a condenser, and then evaporated using a centrifugal thin film evaporator to form a solid powder. The main component of this powder is sodium sulfate, and in this case, sodium sulfate was used to simulate this evaporated solidified powder, and incinerated ash alone was used as a comparative example, and sodium marrow acid was mixed with it as an example. Pellets were prepared by tabletting. The shape of the pellet is approximately 20φ×8.

If the incineration ash is 0, it cannot be formed into pellets at all. Therefore, an attempt was made to create pellets by adding a cellulose-based binder. FIG. 1 shows the condition of the pellets depending on the amount of binder added.

In this figure, region I indicates a region where pellets cannot be molded at all and remains in a disjointed state, region ■ indicates a region where pellets can be molded but there are cracks, and only pellets that peel or break easily can be created, and region ■ It shows the area where perfect pellets can be molded without cracking or peeling. As is clear from this figure, complete pellets can be made by adding 30 parts or more of the binder. However, the addition of such a large amount of binder has the effect of offsetting volume reduction, which is one of the main objectives of pellet molding, and is not desirable from this point of view.

Therefore, we focused on the fact that sodium sulfate alone can be molded into perfect pellets without cracks, etc., and added it to incineration ash to create pellets. The state, compressive strength, and density of the pellets thus produced are shown in FIGS. 2 to 4, respectively.

As is clear from FIG. 2, if 40 wt % or more of evaporated solidified powder (sodium sulfate) is mixed into incineration ash and molded into pellets, perfect pellets without cracking or peeling can be obtained. In FIG. 2, the areas ■, ■, and ■ indicate the same areas as explained in FIG. 1.

It can be seen from FIG. 6 that the compressive strength decreases as the amount of evaporated solidified powder (sodium sulfate) increases, that is, as the proportion of incinerated ash decreases. .

In FIG. 3, α indicates the case of 4.5 tons of tableting pressure, and β indicates the case of 2 tons of tableting pressure.

In this way, pellets formed by mixing evaporated solidified powder (sodium sulfate) and incinerated ash exhibit better properties by mutually exhibiting their features and compensating for each other's defects. In addition, from the perspective of the amount of waste generated at nuclear power plants, there is no addition of binders that would increase the amount.
This results in a net volume reduction of the solidified powder into pellets.1 Incidentally, the apparent density of the evaporated solidified powder and incinerated ash is 0.4 to 0.897 m3.

From FIG. 4, it can be seen that the density of the pellet increases as the amount of the evaporated solidified powder increases. In the figure, the α band is 4.
The tableting pressure is 5 tons, and the β band is the case with the tableting pressure of 2 tons.

For these reasons, in order to obtain good incineration ash pellets, the evaporated solidified powder must be heated to a concentration of 40% or more, preferably 40%
Pellets with sufficient compressive strength if mixed at a ratio of 70% by weight, i.e. 15oz according to the provisional ocean dumping guidelines.
It is clear that it is possible to mold pellets with a compressive strength of , and a density of 1,2'/cm3 or higher.

[Brief explanation of the drawing]

Figure 1 is a graph showing the state when a binder is added at various ratios of incinerated ash VCtm of combustible miscellaneous solids as a function of tableting pressure, and Figure 2 is a graph showing the state when a binder is added at various ratios of incinerated ash VCtm of combustible miscellaneous solids. The tableting pressure (tons) is the state when the evaporated solidified powder of the concentrated waste liquid is added.
The graph shown in Figure 3 as a function of is based on the amount of evaporated solidified powder in the mixture of the same incinerated ash and evaporated solidified powder,
A graph showing the compressive strength (kg/cm2) of the compressed product when the tableting pressure is 4.5 tons and 2 tons, and FIG. 'Am3
) This is a graph showing. Kochoba pressure [tons] Deep research mouth (proportion of U powder [weight %) 1] Kochoba pressure [tons] Proportion of Uomitsu solid powder (weight 2)

Claims (1)

[Claims] The incineration ash of combustible miscellaneous solids generated at a boiling water reactor power plant is mixed with evaporated solidified powder of concentrated waste liquid generated at one site of the same power plant at a concentration of 40 kg or more to solidify into pellets. A method for disposing of radioactive waste characterized by the following.