Method for burying liquid radioactive wastes

FIELD: burying liquid radioactive wastes; waste recovery at radiochemical plants.

SUBSTANCE: proposed method for burying liquid radioactive wastes incorporating hydrolyzing admixtures into deep-seated container bed includes correction of waste pH by nitric acid solutions and pre-treatment of container bed by forcing nitric acid solutions therein. Nitric acid solution is introduced into container bed in amount sufficient for neutralizing carbonates contained in soil which enters in reaction with waste and for attaining void liquid pH of 1.5, as well as into wastes until their pH is brought to 1 - 1.5. Under such conditions wastes are passed into deep-seated formations without precipitating over long distances.

EFFECT: elongated working time of well, enhanced safety of burying wastes into deep-seated beds.

1 cl, 3 ex, 3 tbl

 

The invention relates to methods for disposal of liquid radioactive waste and can be used for radiochemical enterprises for recycling.

When radiochemical reprocessing irradiated standard uranium blocks generate waste containing radionuclides. To prevent the harmful effects of radioactive waste on human health and the environment used method of disposal of liquid waste in an underground repository.

Known process of radioactive isotopes (U.S. patent No. 3959172, 1976, MKI G21F 9/24). This method of fixation of radioactive isotopes found in virtually insoluble form, involves drilling a main wellbore in a subterranean zone vyvetrivayuschiesya basalt. According to the method in the main borehole is pumped concentrated hydrochloric acid. As a result of basalt washed aluminum, iron and calcium and forms a large cavity at the bottom of the main well. The main well is washed with water and caustic is introduced for the dissolution of silicon that has accumulated on the bottom of the cavity, resulting in the formed silica gel. Then in the main borehole is pumped solution of radioactive isotopes. Radioactive isotopes interact with the free ions of aluminum and silicon, and the product of this reaction vegetali ulybaetsa in the form of insoluble complex metallasiloxanes.

The disadvantage of this method is the high cost of disposal of radioactive waste. Due to the significant cost and high complexity method is applicable for the disposal of small quantities of waste.

Know the use for the disposal of liquid radioactive waste deep reservoirs geological formations. Allocated for the deep disposal of process wastes contain nitric acid, sodium nitrate and heavy metals - corrosion products of iron, chromium, manganese and other Layers of the storage are aluminosilicate rocks with carbonate inclusions. Produced water have a pH of 7-8. When removing waste in the reservoir as a result of their interaction with the soil reservoir and dilution of produced water may occur a sharp decrease in the acidity of the waste and the precipitation of slightly soluble hydroxide, exciting, and sasagawa nuclides. It can be precipitation of metal cations of waste (especially iron and chromium) and cations of metals leached waste of rocks. Precipitation in prefiltrov the well area impedes the passage of waste from wells in the volume of reservoir designated for burial. The accumulation of precipitation in prefiltrov the well area can lead to clogging, clogging of wells is, overheating of the reservoir, outgassing, the prerequisites of emergency situations. To prevent this you can ensure phase stability of liquid radioactive waste (homogeneous resistance) in their preparation for injection and in contact prepared waste ground, especially in prefiltrov zone.

There is a method of disposal of liquid radioactive waste by removing them in the deep reservoir, including pre-preparation waste. (Rybalchenko A.I., Pimenov, M.K., Kostin P.P., and other Deep disposal of liquid radioactive waste - M.: Publishing house of Al, 1994, page 91).

Preparation of waste includes adjusting the pH of the waste and the use of complexes of reagents to obtain sustainable waste solutions. Practical application found the option of using as reagent complexes and to adjust the pH of acetic acid (Us). Gidrolizuacy the heavy metal cations are stabilized liquid waste through the formation of acetate complexes.

However, the acetate complexes have limited stability and collapse in the reservoir under the influence of temperature, radiation exposure, by reducing the acidity of the waste at a dilution of their produced water. Due to these phenomena evolving processes of hydrolysis, precipitation is formed hydroxides, based on the which is iron. There is the possibility that precipitation in prefiltrov zone.

The known method consists in the following. Pre-preparation of the reservoir by injection of acid solutions to reduce the accumulation of nuclides in prefiltrov zone injection wells. Before injection of pre-preparation waste, including translation of slightly soluble compounds in the composition of the soluble complexes with acetic acid.

The objective of the invention is to develop a method of disposal of liquid radioactive waste, to prevent precipitation in prefiltrov zone injection well and cheaper than the method using acetic acid.

The set task is solved by the fact that in the method of disposal of liquid radioactive waste containing gidrolizuacy impurities in the deep reservoir, comprising adjusting the pH of the waste and the preliminary preparation of the reservoir by injection of nitric acid solution, a nitric acid solution is injected into the reservoir in an amount sufficient to neutralize the carbonates contained in the soil interacting with the waste and achieve pH interporous liquid 1-1,5, and waste to pH 1-1,5.

Example 1. Serves 4 soil sample, differing in the degree neutralizes and carbonates soil nitric acid. The soil is treated with a solution of nitric acid to a pH value of the solution and incubated for 2 weeks until equilibrium is reached. Then the solutions otfugovyvajut, decanted and the wet soil in contact with the solution-simulator. All soil samples in contact with the solution-a simulator containing NaNO3- 250 g/l, Fe - 0.4 g/l HAc - 12 g/l, HNO30.6 g/l, pH of 1.5. Solution-simulator incubated with the substrate in a capped test tubes (tubes are fixed clamps) for 2 hours at t=100°C. Then the sample is cooled, and incubated for 3 days, otfugovyvajut, decanted solutions and analyze their Fe. The results are shown in table 1.

From the results of table 1 it is evident that the greatest effect is observed when the neutralization of the soil to pH interporous fluid 1,0-1,5 (about 75% of iron is in solution). Deeper soil acid impractical because it leads to the leaching of components. Thus, to reduce the amount of sediment falling from the waste in contact with the ground, it is necessary to pre-treat the soil nitrate solution until the pH interporous liquid of 1.0-1.5.

Table 1.
Conditions of soil treatmentThe content of Fe in solution-imitate the e after contact with the soil (% Fe from the initial content)
Neutralization to pH 4 interporous fluid37
Neutralization to pH 3 interporous fluid45
Neutralization to pH 2 interporous fluid65
Neutralization to a pH of 1.5 interporous fluid75
Neutralization to a pH of 1.0 interporous fluid75

Example 2. Prepare waste solutions with different pH value without acetic acid and the control solution with HAc: a solution of 1 NaNO3- 250 g/l, Fe - 0.4 g/l, pH of 1.5; solution 2 - NaNO3- 250 g/l, Fe - 0.4 g/l, pH 1; a solution of 3 - NaNO3- 250 g/l, Fe - 0.4 g/l, pH 0,62; a solution of 4 - NaNO3- 250 g/l, Fe - 0.4 g/l HAc - 12 g/l, pH of 1.5. The soil is treated with nitric acid to pH interporous liquid 1.5 and incubated for two weeks until equilibrium is reached. Then the solution otfugovyvajut, decanted, and the wet soil in contact with the solutions. The solution with the soil is kept in a capped test tubes (tubes are fixed clamps) for two hours at a temperature of 100°C. Then the sample is cooled, soak in for three days, otfugovyvajut, decanted solutions and analyze for iron. The results of the experiments are shown in table 2.

Table 2.
no source rest the RA, pHThe content of Fe in solution after contact with the soil, g/l (%)
Solution 1, pH of 1.5of 0.38 (95)
Solution 2, pH 10,40 (100)
Solution 3, the pH of 0.620,48 (120)
Rastvor, pH 1,5 (AU)of 0.38 (95)

From the results of table 2 shows that pre-treatment of soil nitric acid allows you to have sustainable solutions at pH 0.6 to 1.5 in the absence of acetic acid. However, when the pH of 0.62 dissolves the soil, and the content of iron in solution after contact with the ground increases. Therefore, you should bring the pH of the solution entering the landfill, up to 1-1,5.

Example 3. 2 g of soil in contact with 20 ml of 0.1 mol/l solution of HNO3(pH 1) for 10 days at t=30°C and atmospheric pressure (periodically mix). Then the acid is decanted and poured the soil test solution. It was prepared two solutions, one with the acetate ion, the other without it, the content of sodium nitrate - 95 g/l, pH of both solutions is 1.5. In the original solution is injected iron, chromium, Nickel, manganese. After cooling of the solution with the soil for 100 hours in an autoclave at a pressure of 30 atmospheres at a temperature of 70°the solution is decanted and analyzed by those impurities that are introduced into the solution (iron, chromium, Nickel, manganese). In addition, determine some the e components, which can vydeliajutsia from the soil (potassium, magnesium, calcium, silicon). Data on the content of components in solutions after contact with the ground, past the nitric acid treatment, are shown in table 3.

From the results of table 3 it can be seen that if the soil is treated with nitric acid, the introduction of the acetate ion in the original solution does not provide any additional effect on the stability of solutions in contact with the ground. BaselCement impurities from the soil occurs approximately at the same level. The content of chromium, Nickel, manganese in solution is practically unchanged by contact with the ground. The iron content was slightly reduced compared with its content in the initial solution (with Ac-ion, and without it), which is consistent with the results in table 2 (experiment 1 and experience 4).

Thus, realizing the mode of deep waste disposal in which the waste solutions have the same environment as a reservoir in which to conduct the injection of wastes, the conditions of passage of fluids in deep formations without precipitation at long distances from prefiltrov zone wells. The use of the proposed method eliminates costly reagent acetic acid, to increase the duration of the well and to improve security of deep waste disposal.

table width="90%" border="1" cellpadding="0" cellspacing="0" frams="all"> Table 3IndicatorsThe original solutionsSolutions after contact with the soilwithout ACACwithout ACACpH1.51.51.51.5Fe, mg/l300.3300.3281.1279.5Cr, mg/l320.0340.0320.0340.0Ni, mg/l250.0280.0250.0280.0Mn, mg/l655.0650.0655.0650.0Ca, mg/lNoNo2.73.8Mg, mg/l--55.055.0K, mg/l--34.435.4Si, mg/l--16.014.1

The method of disposal of liquid radioactive waste containing gidrolizuacy impurities in the deep reservoir, comprising adjusting the pH of the waste and the preliminary preparation of the layer-call the Torah by injection of nitric acid solutions, characterized in that the nitric acid solution is injected into the reservoir in an amount sufficient to neutralize the carbonates contained in the soil interacting with the waste and achieve pH interporous liquid 1-1,5, and waste to pH 1-1,5.



 

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