JPH0232600B2 - IONKOKANJUSHISUISEIEKIKONGOBUTSUOSEMENTOCHUNIFUNYUSURUHOHO - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for encapsulating ion exchange resins. PRIOR ART In pressurized water nuclear reactors, ion exchange resins are used to purify the water used in the primary loop of the reactor. After a certain period of time, the ion exchange resin becomes contaminated with radioactive or other contaminants and must be discarded. The primary loop of a nuclear reactor also contains a boric acid solution that absorbs neutrons and exchanges their kinetic energy into heat, and which must be disposed of from time to time for various reasons. The Nuclear Regulatory Commission (NRC) requires that low-concentration radioactive waste be converted into a separate unit for transportation and disposal. In the industry, the boric acid solution is mixed with ion exchange resin to avoid the need to add clean water to the ion exchange resin, and then the mixture of boric acid solution and ion exchange resin is mixed by adding cement. It is transformed into a solid single body. However, if the boric acid concentration is below about 30% by weight, a soft pasty composition initially forms which must be stored for several months before solidifying. This makes the disposal of the radioactive waste more costly. U.S. Pat. No. 4,249,949 describes the solidification of organic polyisocyanates, nonionic surfactants free of isocyanate functionality, alkaline fillers such as Portland cement, water, and aqueous solutions of radioactive wastes such as spent ion exchange resins or borax. Discloses the use of a composition comprising a plasticizer, optionally used for use. U.S. Pat. No. 4,122,028 discloses a method of solidifying radioactive boron-containing solutions and suspensions into transportable blocks by sequentially adding slaked stone and cement to the solutions and suspensions. SUMMARY OF THE INVENTION The present invention provides an aqueous mixture of ion-exchange resins containing 1-30% by weight of dissolved solids with 1-3% by weight, based on the weight of the ion-exchange resin, of a fouling agent; an ion exchange resin aqueous liquid mixture, characterized in that a sufficient amount of basic accelerator is added to increase the water:cement weight ratio to at least 7; It consists in a method of encapsulating in cement. Ion exchange resin mixed with boric acid or nitrates or nitrates can be converted into a solid unitary body in just 2-3 days by adding cement, if the sequestering agent and basic retarder are first added to this mixture. It has been found that it can be done. Because the method utilizes readily available materials such as waste products in nuclear reactor facilities, the present invention is an inexpensive method for accelerating cement setting time. Furthermore, the invention can be safely and easily implemented using already available equipment. The ion exchange resin slurry solidified in the method of the invention is preferably a solid ion exchange resin mixed in a solution of boric acid or a nitrate or sulfate such as sodium nitrate or sodium nitrate;
It may also contain other contaminants. This mixture is typically heated at a temperature at which the solution leaves the waste evaporator;
Generally processed at approximately 71°C (160°C). It is preferred to process the mixture at this temperature, since below this temperature the boric acid crystallizes out of solution and interferes with the hardening of the cement. The mixture typically contains 15 to 20% (by weight) ion exchange resin, 1 part dissolved solids.
30% to 30% water, 20% to 25% water, and less than 1% contaminants. Ion exchange resins are typically synthesized organic polymers such as styrene resins, epoxy amine resins, or acrylic resins. Particle size should be about 3 mm or less. Larger particle sizes result in unacceptable rewetting stability, excessive swelling of the ion exchange resin, and fracture of the cement body. Preferably the ion exchange resin particle size is less than 200 microns;
At this time, the rewetting stability is increased to the extent that the cement alone can be stored in water. Contaminants may include non-radioactive contaminants such as iron, corrosion products as well as radioactive contaminants such as cobalt, cesium, strontium, and radionuclides. A sequestering agent and basic promoter are added to the ion exchange resin-boric acid mixture. Sequestering agents are compounds that can effectively inhibit chemical ion exchange by ion exchange resins. Sequestering agents are well known in the art and include, for example, motor oil, hydraulic oil, water-soluble cutting fluids, oil-based soaps, iron hydroxides, and alum, as these are generally to be avoided during operations. Motor oil is the preferred sequestering agent;
This is because it is commonly available as a waste product in nuclear reactor plants. Adhesive is 0.1 to 0.3%
(weight of ion exchange resin weight standard) should be used. A base promoter is necessary to neutralize the mixture. The PH should be at least 7, preferably 10 or higher for best results. Basic promoters include alkali metal hydroxides, alkaline earth metal hydroxides, and other compounds that generate hydroxy groups in solution. A preferred basic promoter is sodium hydroxide since it is inexpensive and readily available. The amount of basic promoter required depends on the acidity of the mixture, but is generally only a few percent. After the sealant and basic accelerator are added to the mixture, the cement is added. Although almost any type of cement can be used, Portland cement is preferred because it hardens rapidly and produces a strong product. The cement should be mixed in an amount such that the water:cement weight ratio is between 0.4:1 and 0.6:1. The total mixture containing cement and water should consist of a proportion of 40-60% by volume of the ion exchange resin-boric acid-water mixture and 40-60% by volume of cement. The cement-containing mixture is thoroughly stirred and cured or poured into a curing mold. Curing typically takes 3 to 5 hours. The present invention will be explained below based on Examples. EXAMPLES OF THE INVENTION All additive parametric testing was conducted in 16 oz. glass bottles with small motor driven impellers for mixing. Previous high shear tests showed good correlation between the bottle test and the utility scale test on a relative basis. When the best mixture was obtained in the bottle test, the ratio was calculated for a utility scale test with the addition of a condensed pressurized water reactor (PWR) contaminant for leaching tests. The table below shows the weight or volume of the final mixture.

[Table] The utility scale tests were based on a 1/3 drum volume mix (68), but other volumes are also possible in direct proportion to the standard. In both tests, the ion exchange resin is first added to the mixing vessel, followed by approximately 12 W/O boric acid at 71.1°C (160°). The sequestering agent was then added, followed by a utility scale test condensed PWR contaminant (replicating a typical waste stream from a waste holding tank), followed by cement and sodium hydroxide. Mixing time after adding last ingredient is 5
It was set as 1 minute. Utility-scale mixing tests of similar compositions without sequestrants or accelerators have shown that after 60 days the permeation resistance is only approx.
It was 1.8Kg/cm ² (25psi). Penetration resistance in bottle tests using sealants and accelerators (ASTM403
-77) is 394Kg/cm ² (5600psi) after about 4 days,
In a practical scale test, it was 197Kg/cm ² after about 5 days.
(2800 psi), which was clearly improved by the mixture of the present invention.

Claims (1)

[Claims] 1 Adding 1 to 3% by weight, based on the weight of the ion exchange resin, of a chemical that can effectively inhibit chemical ion exchange by the ion exchange resin to an aqueous mixture of ion exchange resins containing 1 to 30% by weight of dissolved solids. a sequestering agent; a sufficient amount of basic accelerator to raise the pH to at least 7; and a water:cement weight ratio of
A method for encapsulating an aqueous ion exchange resin mixture in cement, characterized in that sufficient cement is added to give a ratio of 0.4:1 to 0.6:1.