JPH06180393A - Solidifying method of radioactive waste - Google Patents

Abstract

PURPOSE:To increase the elution rate of cation while reducing treatment cost using normal cement by performing solidification on condition that bivalent cations of Ca are increased for the cement at the time of hardening reaction. CONSTITUTION:A water hardening inorganic solidification material is subjected to main hardening process where water reacts on the surface of the hardening material to produce a hydrate from which bivalent cations of Ca are then eluted. The reaction progresses gradually into the solidifying material and sustains until the bivalent cation of Ca exceeds a saturable solubility. When the saturable solubility is exceeded, Ca(OH)2 is deposited on the surface of the solidifying material. At that time, concentration of bivalent cation of Ca in the liquid increases and a part of cations of Ca stays in the solidifying material thus creating a gel phase of CaO-SiO2-H2O. Consequently, hardening is ended within a normal interval by adding a Ca compound having high solubility or increasing elution rate of bivalent cation of Ca from the solidifying material through high temperature curing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for solidifying radioactive waste generated from a nuclear power plant, which contains a substance that delays hardening of cement by using cement.

[0002]

2. Description of the Related Art A radioactive waste such as a used ion exchange resin is solidified by using cement. However, it has been known that when fluoride, boric acid, phosphoric acid, or the like is adsorbed on the ion exchange resin, it causes a curing retarding action at the time of solidification and inhibits a normal curing process. Therefore, conventionally, as shown in R & D on radioactive waste treatment and disposal (Industrial Technology Publication, 1983, Amana and Sakata), a special solidifying material such as vermiculite has been used, but the cost is high. There were drawbacks such as.

[0003]

When radioactive waste such as used ion exchange resin contains a fluoride which can be a hardening retarder for cement, or boric acid or phosphoric acid, the normal hardening process is temporary. It is known that the curing reaction is delayed due to the inhibition of

An object of the present invention is to provide a method for solidifying radioactive waste, which reduces the cost of solidification treatment by using ordinary cement, and completes a delayed hardening reaction within a normal period by changing solidification conditions. To do.

[0005]

[Means for Solving the Problems] Conditions for increasing the divalent cation of Ca during hardening reaction, that is, addition of a compound having a high saturated solubility of the divalent cation of Ca, or high temperature to cement. The curing is achieved by increasing the elution rate of Ca divalent cations from the solidified material.

[0006]

The main hardening process that acts on the hydraulic inorganic solidifying material is that the surface of the solidifying material reacts with water to form a hydration product, and then the divalent cation of Ca is produced from this hydration product. Elute. This reaction gradually progresses inside the solidified material, and Ca
Continues until the divalent cation of s exceeds the saturation solubility. When it exceeds the saturation solubility, Ca (OH) ₂ is deposited on the surface of the solidified material. At this time, since the divalent cation of Ca in the liquid becomes extremely high, a part of the divalent cation of Ca remains inside the solidifying material, and a gel phase composed of CaO—SiO ₂ —H ₂ O is formed. Is generated. The solidified body develops strength as these gradually crystallize and grow.

The inventors measured the concentration of a divalent cation of Ca in the hydraulic inorganic solidifying material with respect to a substance such as boric acid which causes retardation of curing, and
Since boric acid forms a complex salt with the divalent cation of Ca during the process of elution of the divalent cation of Ca, the concentration of the divalent cation of Ca in the liquid slowly increases as shown in FIG. However, it was found that the timing of precipitation of Ca (OH) ₂ crystals and formation of the gel phase was delayed, which was the cause of retardation of hardening.

Therefore, on the other hand, the divalent cation of Ca from the solidified material obtained by increasing the concentration of divalent cation of Ca, that is, by adding a highly soluble calcium compound or curing at high temperature. Curing is completed within a normal period by increasing the elution rate of.

[0009]

【Example】

 Example 1 Next, an example of the present invention will be described.

In this example, using ordinary Portland cement, only ordinary Portland cement, 1% boric acid added, 1% boric acid and calcium chloride
(CaCl ₂ ) was added by 1%, boric acid was added by 1%, and the inventors measured the period until the compressive strength reached 100 kg / cm ² in four cases when cured at 100 ° C. is there. The results are shown in Table 1. As described above, when the cement containing the set retarder was used, the Ca
It can be seen that an additive such as CaCl ₂ for increasing the concentration of divalent cations, or an increase in the elution rate of divalent cations of Ca due to curing at high temperature has an effect of promoting hardening.

[0011]

[Table 1]

<Embodiment 2> An embodiment of the present invention will be described with reference to FIG. This example is an example of solidifying an ion exchange resin containing 5 wt% of boric acid generated from a nuclear power plant using ordinary Portland cement.

FIG. 1 shows a block diagram of a system for solidifying an ion exchange resin. In the solidifying material tank 1, cement and additives are sufficiently mixed and dispersed in advance with an appropriate composition and stored. A fixed amount of the solidifying material powder is supplied to the kneading machine 9 by the fixed amount transfer device 2. The waste resin tank 3 stores a used ion-exchange resin containing 5 wt% of boric acid, which is a curing retarder, and is also supplied to the kneading machine 9 by a fixed amount by the quantitative transfer device 4. Kneading water is also supplied from the kneading water tank 5 for a certain period of time through the electromagnetic valve 6. Also, in order to eliminate the delay of the hardening reaction due to boric acid, calcium chloride (C
aCl ₂ ) is also stored in the additive tank 7, and is supplied to the kneading machine 9 in a fixed amount by the constant quantity transfer device 8. The ratio of the supplied solidifying material, waste resin, CaCl ₂ , and kneading water is 100: 30: 1: 30 by weight. Kneader 9
Knead thoroughly to form a paste. A certain amount of the prepared paste is gradually solidified via the electromagnetic valve 10
Inject 1. After the injection, the solidified container 11 with the lid becomes a solidified body that can be carried out after standing for about 1 week. At this time, the compression strength of the solidified body is about 100 kg / cm ² . Although CaCl ₂ was put in the additive tank 7 in this embodiment, if an appropriate amount is dissolved in the kneading water in advance and supplied to the kneader, the additive can be easily dispersed.

When conventional CaCl ₂ is not added,
The period until the compressive strength of the solidified body reaches 100 kg / cm ² with the above-mentioned apparatus is about one month. This is due to the delayed curing due to boric acid. On the other hand, when CaCl ₂ is added, it reacts with the solidifying material and has high solubility xCaCl 2.
₂ · yCa (OH) ₂ · 2H ₂ O (x and y are constants) is generated. Therefore, the dissolution rate of the divalent cation of Ca is increased, and the decrease of the divalent cation concentration of Ca due to boric acid is blocked.

As described above, according to the present embodiment, the waste resin containing 5 wt% of boric acid placed in the solidification container of 200 liters has a compressive strength which can be carried out in about 1/4 period by adding calcium chloride. It has the advantage of becoming a solidified body.

<Embodiment 3> This embodiment is an example of solidifying cellulose using ordinary Portland cement. In the cases shown in Table 2, the inventors measured the period until the compressive strength reached 100 kg / cm ² when 3 wt% of cellulose was added to ordinary Portland cement.

[0017]

[Table 2]

The case of adding Ca (NO ₃ ) ₂ and 100
The fact that the number of days of strength development when aged at ℃ is shorter than that of ordinary Portland cement alone is due to the effect of retarding the hardening of cellulose.

Polysaccharides such as cellulose are hydrolyzed to a small amount of sugars by the alkaline component of the hydraulic inorganic solidifying material, which usually causes retardation of hardening of Portland cement. Even in such a case, it was confirmed that the addition of a highly soluble calcium compound or the curing at high temperature is effective.

[0020]

EFFECTS OF THE INVENTION According to the present invention, even when a substance that serves as a hardening retarder is contained in cement, it is possible to reduce Ca content during the hardening reaction.
By carrying out the solidification under the condition that the cation concentration of valence is increased, the reaction can be safely completed in the usual curing time.

[Brief description of drawings]

FIG. 1 is a block diagram of a radioactive waste solidification device.

FIG. 2 is a characteristic diagram of changes with time of divalent cations of Ca when a curing retarder is added.

[Explanation of symbols]

1 ... Solidifying agent tank, 2, 4, 8 ... Quantitative transfer device, 3 ... Waste resin tank, 5 ... Kneading water tank, 6, 10 ... Electromagnetic valve, 7 ... Additive tank, 9 ... Kneading machine, 11 ... Solidifying container .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Komori 7-2-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Energy Research Laboratory

Claims (5)

[Claims] 1. When solidifying radioactive waste containing a substance that delays the hardening of cement generated from a nuclear power plant using cement, the hardening is performed under the condition of increasing the calcium concentration during hardening reaction. Method of solidifying radioactive waste. 2. The method for solidifying radioactive waste according to claim 1, wherein a calcium compound having a high saturated solubility is added to the cement. 3. The method for solidifying radioactive waste according to claim 2, wherein the calcium compound having high saturated solubility is calcium chloride or calcium nitrate. 4. The method for solidifying radioactive waste according to claim 1, wherein the cement is cured at a high temperature. 5. The method for solidifying radioactive waste according to claim 4, wherein the high temperature is 100 ° C. or higher.