JPS59116593A - Method of solidifying 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 [Field of Application of the Invention] The present invention relates to a method for treating radioactive waste generated from a nuclear power plant, and particularly to a solidification method suitable for pelletized radioactive waste.

[Prior art]

Various types of radioactive waste are generated as a result of the operation of nuclear power plants, etc., but reducing the volume of these radioactive wastes and stably solidifying them in solidification containers such as drums is an effective way to secure storage space within the facility. This is not only a renovation in terms of safety, but also safety issues and land storage, which is one of the future final disposal methods.
This is an essential technology for land disposal.

For example, one way to reduce the volume of radioactive waste is to
The recycled waste liquid (mainly composed of sodium sulfate) and waste ion exchange resin slurry, which are the main wastes generated from one WR nuclear power plant, are turned into dry powder using a dryer such as a centrifugal thin film dryer, and then subjected to briquerating. Attempts have been made to significantly reduce the volume of waste material by pelletizing it using a granulation machine, etc., and solidifying this pelleted radioactive waste in a Metrum can with an appropriate solidifying agent. . As a solidifying agent for the above pelleted waste, asphalt, plastic,
It is possible to use alkali silicate, etc., but a solidification method using alkali silicate (so-called water glass) is being developed as it is an easy-to-use and inexpensive material. The mechanical properties are almost the same as those of hardened cement, and it is well known that it has superior durability and weather resistance compared to plastics, etc. However, it is found in buildings using cement mortar or concrete. Thus, it is thought that even water vitrified material gradually undergoes weathering action and deteriorates after several decades or more. Therefore, in order to solidify radioactive waste using water glass, it is desirable to create a solidified material that has greater weather resistance or durability than currently available.

[Purpose of the invention]

An object of the present invention is to provide a method for assimilating water glass that is excellent in durability and individuality per surface.

[Summary of the revelation]

In order to improve the durability of water vitrified products, we first fundamentally investigated the causes of deterioration of assimilated products.

Equation (1) is a chemical formula showing the hardening reaction of water glass.

Na, o-5iO□-nr (204-P, 0. ・5
in2→Na, PO3-4-8i 02+nH7O(
1) Sunawachi, water glass (Na, 0-8i02・nH2
o) and a curing agent (P2O, 5102), S10. A matrix is formed and a solidified body is obtained. However, free water (n
H2O) is produced, which moves through the solidified body and is dissipated from the solidified body surface into the atmosphere. Similar to cement, water glass also has many connected voids (Qpe) in the solidified material.
n pore), and the specific surface area of the solidified material is an order of magnitude larger than the apparent surface area. It can be easily inferred from the research results in the field of 7-ment engineering that this increase in specific surface area is the cause of the decrease in solidified product durability. First, we confirmed that this assumption was correct through a durability test whose results are shown in Figure 1.

The specific surface area S shown on the horizontal axis in FIG. 1 can be changed by using water glasses having different values of n (the amount of water in the water glass) in equation (1). , (This corresponds to the change in the water/cement ratio in 6 cement.) The viscosity n shown on the horizontal axis together with the specific surface area S of the broken water glass indicates the viscosity of the water glass before hardening, and is used to facilitate the hardening operation. requires a viscosity of 103CP or less.

The conditions for the solidification experiment shown in Figure 1 were: 2.
It is 0°C.

From FIG. 1, it can be seen that as the specific surface area of the solidified material decreases, its durability also improves, and with a viscosity of 103CP, it has a service life of about 100 years. However, in order to extend the service life beyond this, it is necessary to further reduce the specific surface by using water glass with a viscosity of 103 CP or more, but in this case, the problem arises that solidification becomes difficult. A similar problem occurs in the field of cement engineering, and a similar method is attempted by adding a small amount of F+ (0.1 to 2 t) of additives such as water reducing agents (ASTN C494-71).
Although this is possible when water glass is used as the solidifying agent, there remains the problem that a small amount of the water reducing agent must be coupled to the solidifying agent at the proboscis, making the system somewhat sloppy.

The present invention uses water glass with a viscosity of 1.0'CP or more, and reduces the specific surface area of the assimilate without adding additives such as water reducing agents to increase durability. One to improve!゛Akoto's voice is a gift.

As a result of various basic research, it was found that it is good to apply pressure exceeding atmospheric pressure during the hardening process of water glass.

Figure 2 shows an example of the results of a basic experiment.The viscosity of water glass is 2
It is CP. From this, it can be seen that as curing is carried out at high pressure, the specific surface area of the solidified material decreases, and at the same time, the durability of the solidified material increases.In other words, the durability when hardened at atmospheric pressure (1 atm) is While it is estimated to last about 40 years, 5 ATM is estimated to have a durability of 70 years, and LQ ATM is estimated to have a durability of over 100 years. Furthermore, it has been found that when the above-mentioned water reducing agent and other additives are added at the same time as curing at high pressure, a solidified product with even better durability can be obtained due to the synergistic effect of the two.

(1) The main feature of Mokishokumei is that in the method of solidifying radioactive waste pellets using a mixture of an alkaline silicate solution and a hardening agent acting on it as a hardening agent, a large amount of It involves applying pressure greater than atmospheric pressure.

(2) An existing feature of the present invention is that a water reducing agent capable of improving the fluidity of the solidifying agent is added to the assimilating agent.

Example Based on the above results, a third example of solidifying radioactive waste in a 200-ton drum can, which is normally used for solidifying radioactive waste, was developed.
This will be explained using figures.

'There are 1 piece of paper in 1 f200t drum and 2 pieces.
Approximately 250 kg of radioactive waste pellets 3 containing Na and So as main components are filled into the container. Next, the alkali silicate solution 4 and the hardening agent 5 were uniformly mixed in a mixer 6, and the viscosity was 2 x 102 CP.After mixing in this way, the hardening agent 8 was flowed into the 200t drum 1. After filling the voids between the radioactive pellets 3, the 200t drum 1 is transferred to the pressure chamber 7, where the drying atmosphere is heated to a pressure F of 10 atm.
The hardening was completed in a few hours, and a solidified material as shown in Figure 4 was obtained. It is estimated to have a durable life of 20 years.

In the above example, a mixture of an alkaline silicate solution and a hardening agent was used as the solidifying agent, but a single weight percent of naphthalene sulfonic acid formaldehyde was added as a water reducing agent to the solidifying agent to prepare a 2X102CP solidifying agent. When the radioactive pellet 3 was solidified at 1 Oatm, the solidified product had a durability index of 92, and is estimated to have a lifespan of 200 years or more.

This indicates that the synergistic effect of high-pressure curing and water-reducing agent resulted in a more durable assimilate.

As a water reducing agent, use ligninsulfonic acid or oxygen.
It was found that similar effects can be obtained by using carboxylic acids or their salts.Furthermore, in the above examples, a pressure chamber with a dry atmosphere was used, but even if a high-pressure water tank is used for underwater curing, the same effect can be obtained. The effect of this can be obtained.

〔Effect of the invention〕

According to the present invention, the following effects can be achieved. In other words, l'lli of water glass that is easy to solidify
A solidified product with excellent durability can be obtained within the range of properties.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the results of an experiment according to the conventional method, Fig. 2 is a diagram explaining the present invention in detail, and Fig. 3 is a diagram showing the solidification method according to one embodiment of the present invention. Groove diagram of the device, 4th
FIG. 12 is a diagonal diagram showing a row of solidified bodies produced according to the present invention. 1... Drum, 3... Pellet, "&
- Disposal' proboscis, 7...pressure chamber, 8...solidifying agent. Representative Patent attorney High-class Akira 1 Mebo Prefecture q (c-P) θ fρl171θρθf
D 5 (2nd / 2nd 0.5″/θ 50,000 4
ni Kasuri - Pressure (d Yuzujimo 3 Memu 4)

Claims (1)

[Claims] 1. In a method of solidifying radioactive waste pellets using a mixture of a silicic acid-r alkali solution and a hardening agent acting on it as a hardening agent, adding a force of pressure equal to or higher than atmospheric pressure during hardening of the assimilating agent is Characteristic radioactive waste assimilation method.