Compositions – Radioactive compositions
Reexamination Certificate
1998-07-28
2001-10-02
Warden, Jill (Department: 1743)
Compositions
Radioactive compositions
C405S128350, C405S129200, C588S014000, C588S015000
Reexamination Certificate
active
06296786
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a treated waste disposed of in ultra-deep underground, a method for making it and, an apparatus for making the treated waste.
2. Description of the Related Art
Recently, a method for treating waste such as a high level radioactive waste which adversely affects the environment or a human body for a long period is performed by burying or storing the wastes in the ultra-deep underground. It is important that the waste remains in the originally treated condition for a long period in order to avoid leakage and diffusion of substances to be disposed within the waste to the surroundings after disposal in the ultra-deep underground.
Therefore, a variety of procedures have been proposed and developed for stabilizing the wastes. For example, it is known from Japanese Examined Patent Publication No. 57-960 that the waste is treated by a process having the steps of filling a space portion in a container with incombustible powder, sealing the container with deaeration, and performing a hot isostatic pressing process to transform the treated waste being a block state. According to this processing method, oxidization or nitriding of the treated waste is inhibited by means of the incombustible powder so that it is possible to maintain a strong binding strength of the treated waste obtained by solidifying into theoretical density state having reduced volume for a long period of time.
Further, in Japanese Unexamined Patent Publication No. 8-20557, there is disclosed a method for producing treated waste by solidifying waste using water glasses added by a hydroxide or an oxide of an alkaline metal. In this procedure, it is possible to maintain the solidified state for a long period by maintaining an alkaline condition by means of the alkaline metal and by inhibiting the production of water of crystallization of an inorganic salt.
However, even though the treated waste stays in the originally treated condition by inhibiting oxidization or nitriding of the treated waste, or by inhibiting the production of water of crystallization, there is a problem that a substance to be disposed in the waste is ionized and transformed into an easily dissolving configuration in ground water, because the environment in the ultra-deep underground has reducing conditions due to low oxygen concentration. As a result there is a problem that the substance to be disposed in the waste leaks into the surroundings at an early stage.
As shown in
FIG. 4
, the environment on the ground has oxidizing conditions because of high oxygen concentration high Eh), on the other hand the enviroment in the ultra-deep underground has reducing conditions (low Eh), because its oxygen concentration is significantly lower than that on the ground.
Thus, when the waste contains the substance “I”(radioactiveiodine) to be disposed of the form of a metal compound “AgI” and exists on the ground having the oxidizing conditions, ionization of “Ag” and “I” in accordance with a reaction AgI→Ag
+
+I
−
and consequent dissolution in water will be substantially avoided because of the low solubility ([Ag
+
][I
−
]=10
−16
), even if water is brought into contact with “AgI”.
On the other hand, when “AgI” exists in the ultra-deep underground where there are reducing conditions, a reducing agent causes the following reaction:
AgI+e
−
→Ag
0
+I
−
and stimulates the ionization of “I”.
Although the treated waste maintains the originally treated configuration, a large amount of ionized “I” is dissolved in the ground water in the case the treated waste is penetrated by the ground water according to the following reaction:
6AgI+3H
2
O→6Ag
0
+IO
3
−
+6H
+
so that “I” leaks and diffuses in the surroundings through the ground water at an early stage.
SUMMARY OF THE INVENTION
Accordingly, with attention to reducing conditions in the ultra-deep underground, it is an object of the present invention to provide treated waste, wherein the treated waste inhibits ionization of the substance to be disposed of caused by reduction of a metal compound, even when the treated waste is disposed of in an environment having reducing conditions. The invention also provides a method and an apparatus for making such a treated waste.
To this end, according to one aspect of the present invention, there is provided a treated waste treated so as to suppress release of a substance to be disposed of when the waste is disposed of in the ultra-deep underground where there are reducing conditions, comprising: a compound containing the substance to be disposed; and a high oxygen potential agent having a higher oxygen potential than the compound.
In accordance with these features of the invention, the compound in the waste immediately after the treatment, containing the substance to be disposed of, is not affected by any reducing condition, even when the waste is exposed to the reducing conditions at ultra-deep underground. This owes to the fact that the high oxygen potential agent serves to provide an oxidizing condition for the waste. This effectively suppresses reducing tendency of the compound, thus preventing ionization and release of the substance to be disposed of from the compound immediately after the disposal. When the reducing effect on the treated waste caused by a reducing agent derived from the reducing condition has become substantial with times the high oxygen potential agent is preferentially bonded to electrons, so as to prevent reduction of the compound containing the substance to be disposed of, whereby ionization of the substance to be disposed of is retarded. Therefore, the treated waste can retain the substance to be disposed of in the form of the compound for a long time. As a consequence, dissolution of the substance in ground water is substantially eliminated, even when the waste is penetrated by the ground water. It is thus possible to suppress release of the substance to be disposed of for a long period.
The compound and the high oxygen potential agent may have been treated to form solidificates.
According to another aspect of the present invention, there is provided a method for making a treated waste of the type set forth above, the method comprising effecting a solidification treatment for solidifying the treated waste. The solidification treatment serves to reduce the area of contact with the reducing atmosphere, thus further suppressing reduction of the treated waste.
The solidification treatment may be performed by filling the solidifying material. In this case, the treated waste can be obtained by a simple process of filling the solidifying material.
Alternatively, the solidification treatment may be performed using a hot isostatic pressing process.
In this case, the waste is solidified while reducing its volume, thus realizing a further decrease in the area of contact with the reducing atmosphere, thereby greatly suppressing the reduction of the compound under the reducing environment. The hot isostatic pressing process, when conducted at an appropriate temperature, forms a layer on the surface of the solidified waste. The substance to be disposed, even when ionized and freed from the compound, is retained in the waste by the layer which serves as a retainer layer.
According to still another aspect of the present invention, there is provided an apparatus for making a treated waste treated so as to suppress release of a substance to be disposed of when the waste is disposed of in the ultra-deep underground, where there are reducing conditions, comprising: means for mixing a compound containing the substance to be disposed of and a high oxygen potential agent having a higher oxygen potential than the compound to form a mixture; and means for applying a pressure by means of a hot isostatic pressing process to the mixture.
It is thus possible to prepare the treated waste by using a simple system which has the mixing process and the pressing process.
REFERENCE
Imakita Tsuyoshi
Kurimoto Yoshitaka
Nishimura Tsutomu
Sugimura Yasushi
Wada Ryutaro
Cole Monique T.
Kabushiki Kaisha Kobe Seiko Sho.
Reed Smith Hazel & Thomas LLP
Warden Jill
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