Patent Description:
As conventional techniques for solidifying radioactive waste, a solidifying-agent composition comprising ordinary Portland cement and admixtures such as a polymer, paraffin, and the like, which are mixed together, is disclosed, but is not actually used.

The cost of storing and managing solidified radioactive waste products amounts to at least <NUM> million won for <NUM> of radioactive waste.

In the case where radioactive waste is solidified using a conventional ordinary-Portland-cement-based solidifying-agent composition, it is recommended that the solidifying agent be used <NUM>% (<NUM>:<NUM> ratio) relative to the mass of radioactive waste to be solidified in order to satisfy physical and chemical safety requirements. As such, the increase in the volume of the radioactive waste is considered to be <NUM>% or more.

Currently, many attempts to treat radioactive waste using a solidifying agent are merely made to satisfy only physical and chemical safety, and are limited in that an increase in the volume during the solidification process is not considered. In particular, the amount of domestic radioactive waste that has not been solidified to date is considerable, and taking into account the treatment costs for radioactive waste that will continue to be generated in the future, the development of technology for reducing the volume of the solidified radioactive waste product is urgently required.

Accordingly, the present invention is intended to provide a method for solidifying radioactive waste, as defined in claim <NUM>. The added solidifying-agent composition includes alumina cement and a gypsum powder, thereby solidifying radioactive waste in a physically and chemically safe manner.

Therefore, the present invention provides a method for solidifying radioactive waste, as defined in claim <NUM>.

The solidifying-agent composition may include, of the total of <NUM> parts by weight of the composition, <NUM> to <NUM> parts by weight of alumina cement and <NUM> to <NUM> parts by weight of a gypsum powder, and may further include, of the total of <NUM> parts by weight of the composition, <NUM> to <NUM> parts by weight of a resin powder, <NUM> to <NUM> parts by weight of a reaction accelerator, <NUM> to <NUM> parts by weight of a retention agent, <NUM> to <NUM> parts by weight of a defoaming agent, and <NUM> to <NUM> parts by weight of a fluidizing agent.

The method according to the invention comprises the steps of (<NUM>) adding a fluidizing agent and water to radioactive waste and performing stirring, (<NUM>) adding a solidifying-agent composition to the radioactive waste containing the fluidizing agent and the water added in the step (<NUM>) and performing stirring, and (<NUM>) curing the radioactive waste containing the solidifying-agent composition added in the step (<NUM>).

In the step (<NUM>), the solidifying-agent composition is added <NUM> to <NUM> parts by weight of <NUM> parts by weight of the radioactive waste, and includes alumina cement and a gypsum powder. The solidifying-agent composition may include, of <NUM> parts by weight thereof, <NUM> to <NUM> parts by weight of alumina cement and <NUM> to <NUM> parts by weight of a gypsum powder, and may further include, of the total of <NUM> parts by weight of the composition, <NUM> to <NUM> parts by weight of a resin powder, <NUM> to <NUM> parts by weight of a reaction accelerator, <NUM> to <NUM> parts by weight of a retention agent, <NUM> to <NUM> parts by weight of a defoaming agent, and <NUM> to <NUM> parts by weight of a fluidizing agent.

In the step (<NUM>), the curing may be performed for <NUM> days.

According to the present invention, a solidifying-agent composition includes alumina cement and a gypsum powder, and thus, during the solidification of radioactive waste, an increase in volume of the solidified radioactive waste product can be effectively minimized to a level satisfying physical and chemical safety regulations.

Also, the use of the solidifying agent, which is necessary for manufacturing a solidified radioactive waste product satisfying the radioactive waste treatment standard proposed by the Nuclear Environment Authority, can be effectively reduced by a maximum of <NUM>%.

Hereinafter, a detailed description will be given of the present invention.

A solidifying-agent composition for solidifying radioactive waste, which may be used with the present invention, includes alumina cement and a gypsum powder. The solidifying-agent composition may include, of the total of <NUM> parts by weight thereof, <NUM> to <NUM> parts by weight of alumina cement and <NUM> to <NUM> parts by weight of a gypsum powder, and may further include, of the total of <NUM> parts by weight thereof, <NUM> to <NUM> parts by weight of a resin powder, <NUM> to <NUM> parts by weight of a reaction accelerator, <NUM> to <NUM> parts by weight of a retention agent, <NUM> to <NUM> parts by weight of a defoaming agent, and <NUM> to <NUM> parts by weight of a fluidizing agent. If the amount of alumina cement is less than <NUM> parts by weight, the curing reaction (solidification reaction) of the solidifying agent is delayed and the compressive strength of the solidified product is not exhibited to a certain level. On the other hand, if the amount of alumina cement exceeds <NUM> parts by weight, the curing reaction of the solidifying agent occurs too rapidly, making it difficult to ensure pot life, and problems such as hydration heat generation, surface cracking, and low strength occur. The gypsum powder functions to realize strong bonding of alumina cement and waste, and the amount of gypsum powder is preferably <NUM>% of the amount of alumina cement (<NUM> parts by weight relative to <NUM> parts by weight of alumina cement) in order to exhibit desired strength. The resin powder improves the overall quality by increasing the chemical resistance and water resistance of the solidifying-agent composition. The retention agent regulates the curing time and is excellent in controlling the curing rate of alumina cement in the present invention. The defoaming agent removes foam from inside the solidifying-agent composition, and the fluidizing agent imparts fluidity to facilitate the mixing process, thus ensuring fluidity and attaining the homogeneity of radiative waste to be solidified.

The present invention provides a method of solidifying radioactive waste, comprising the steps of: (<NUM>) adding a fluidizing agent and water to radioactive waste and performing stirring; (<NUM>) adding a solidifying-agent composition to the radioactive waste containing the fluidizing agent and the water added in the step (<NUM>) and performing stirring; and (<NUM>) curing the radioactive waste containing the solidifying-agent composition added in the step (<NUM>).

The step (<NUM>) is performed to ensure the fluidity of the radioactive waste and to attain homogeneity of the radioactive waste to be solidified. When homogeneity is attained, the total radioactivity of the radioactive waste may be determined through a sampling process. If the radioactive waste has high viscosity or high hardness, it may be difficult to mix with a solidifying agent, and in the case where the solidifying agent and the radioactive waste are mixed poorly, the quality of the solidified product may deteriorate. Hence, the radioactive waste is added with water and a fluidizing agent to obtain a certain fluidity, after which the solidifying agent may be mixed, thereby yielding a homogeneous solidified product.

In the step (<NUM>), the solidifying-agent composition is added <NUM> to <NUM> parts by weight of <NUM> parts by weight of the radioactive waste. If the amount of the solidifying-agent composition is less than <NUM> parts by weight, the compressive strength of the solidified product is not exhibited to a certain level. On the other hand, if the amount thereof exceeds <NUM> parts by weight, the amount of solidifying agent used for the waste is increased and the volume of the solidified waste product is increased to thus raise the costs of radioactive waste treatment. According to the invention, the solidifying-agent composition includes alumina cement and a gypsum powder, and the solidifying-agent composition may include, of <NUM> parts by weight thereof, <NUM> to <NUM> parts by weight of alumina cement and <NUM> to <NUM> parts by weight of a gypsum powder, and may further include, of the total of <NUM> parts by weight thereof, <NUM> to <NUM> parts by weight of a resin powder, <NUM> to <NUM> parts by weight of a reaction accelerator, <NUM> to <NUM> parts by weight of a retention agent, <NUM> to <NUM> parts by weight of a defoaming agent, and <NUM> to <NUM> parts by weight of a fluidizing agent.

In the step (<NUM>), the curing is preferably performed for <NUM> days in a sealed state. When the top of the waste is sealed and curing is performed, water evaporation is prevented, thereby reducing cracking of the solidified product and enhancing the compressive strength thereof, thereby making it possible to manufacture a solidified product that is more stable, both physically and chemically.

A better understanding of the present invention will be given of the following examples, which are merely set forth to illustrate but are not to be construed as limiting the scope of the present invention, as will be apparent to those skilled in the art.

A solidifying-agent composition was prepared by mixing <NUM> of alumina cement, <NUM> of a gypsum powder, <NUM> of a resin powder, <NUM> of a reaction accelerator, <NUM> of a retention agent, <NUM> of a defoaming agent, and <NUM> of a fluidizing agent.

A solidifying-agent composition was prepared in the same manner as in Example <NUM>, with the exception that <NUM> of a reaction accelerator, <NUM> of a retention agent, and <NUM> of a fluidizing agent were used.

<NUM> of radioactive waste (A) slurry containing <NUM>% water (volume: <NUM>, solid content: <NUM>) was subjected to solidification pretreatment through mixing with <NUM> of a liquid fluidizing agent and stirring for <NUM>. Thereafter, <NUM> of the solidifying-agent composition prepared in Example <NUM> was added thereto and stirred for <NUM>, after which a test specimen was manufactured using a mold for specimen production having a diameter of <NUM> and a height of <NUM>.

The same procedures as in Example <NUM> were performed, with the exception that <NUM> of the solidifying-agent composition prepared in Example <NUM> was used.

<NUM> of radioactive waste (B) containing no water (volume: <NUM>, solid content: <NUM>) was subjected to solidification pretreatment through mixing with <NUM> of a liquid fluidizing agent and <NUM> of mixing water and stirring for <NUM>. Thereafter, <NUM> of the solidifying-agent composition prepared in Example <NUM> was added thereto and stirred for <NUM>, after which a test specimen was manufactured using a mold for specimen production having a diameter of <NUM> and a height of <NUM>.

<NUM> of radioactive waste (A) slurry containing <NUM>% water (volume: <NUM>, solid content: <NUM>) was subjected to solidification pretreatment through mixing with <NUM> of a liquid fluidizing agent and <NUM> of mixing water and stirring. Thereafter, <NUM> of a typical solidifying agent was added thereto and stirred, after which a test specimen was manufactured using a mold for specimen production having a diameter of <NUM> and a height of <NUM>.

The same procedures as in Comparative Example <NUM> were performed, with the exception that <NUM> of a typical solidifying agent was used.

<NUM> of radioactive waste (B) containing no water (volume: <NUM>, solid content: <NUM>) was subjected to solidification pretreatment through mixing with <NUM> of a liquid fluidizing agent and <NUM> of mixing water and stirring. Thereafter, <NUM> of a typical solidifying agent was added thereto and stirred, after which a test specimen was manufactured using a mold for specimen production having a diameter of <NUM> and a height of <NUM>.

The same procedures as in Comparative Example <NUM> were performed, with the exception that <NUM> of mixing water and <NUM> of a typical solidifying agent were used.

The solidified radioactive waste products obtained through solidification in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were measured for volume and for compressive strength through sealing and wet curing for <NUM> days. Furthermore, compressive strength was measured after an immersion test for <NUM> days of air drying and immersion, and compressive strength was measured after a heat cycle test (<NUM> to -<NUM>, <NUM> cycles). The results are summarized in Table <NUM> below.

As is apparent from Tables <NUM> to <NUM>, upon the solidification of radioactive waste in order to satisfy the radioactive waste solidification standards (Table <NUM>), of <NUM> parts by weight of the radioactive waste, the typical solidifying agent was used <NUM> parts by weight, and the solidifying-agent composition of the present invention was used <NUM> to <NUM> parts by weight, and all of Examples <NUM> to <NUM> satisfied radioactive waste treatment standards. Thus, in the solidified radioactive waste product according to the present invention, the use of the solidifying agent is reduced by a maximum of <NUM>% compared to when using ordinary Portland cement (typical solidifying agent), whereby the volume of the resulting solidified product can be remarkably decreased.

Moreover, the volume change is <NUM> to <NUM>% upon the use of the typical solidifying agent, but is -<NUM> to <NUM>% upon the use of the solidifying-agent composition according to an embodiment of the present invention.

Claim 1:
A method of solidifying radioactive waste, comprising the steps of:
(<NUM>) adding a fluidizing agent and water to radioactive waste and performing stirring;
(<NUM>) adding a solidifying-agent composition to the radioactive waste containing the fluidizing agent and the water added in the step (<NUM>) and performing stirring; and
(<NUM>) curing the radioactive waste containing the solidifying-agent composition added in the step (<NUM>),
characterized by that
the solidifying-agent composition comprises alumina cement and gypsum powder, and
the solidifying-agent composition is added <NUM> to <NUM> parts by weight of <NUM> parts by weight of the radioactive waste.