The method of control of radioactive iodine in water cooled nuclear power plants

 

The invention relates to the field of radiochemical analysis. The inventive method of control of radioactive iodine in water cooled nuclear power plants is carried out by selection on the adsorbent, impregnowana silver. The sample fluid is passed through the organic membrane adsorbent with a pore size of 0.45-0.55 m and before passing the pre-adjusting reagent pH of the sample to a pH of 2.0 to 11.0. Advantages of the invention are to increase the radiochemical purity of emitted radionuclides of iodine, agility control, the lower limit of detection of radionuclides and improve safety. 4 C.p. f-crystals, 6 PL.

The invention relates to the field of radiochemical analysis and can be applied for monitoring of radionuclides of iodine in the coolant of nuclear power plants (NPP).

In the process of nuclear reactor coolant observed increase in specific activity of radionuclides. The reason for the growth of radioactivity is the first occurrence of gas leaks fuel elements (FE), and then and microcracks. The biggest on is in the coolant NPP is determined by the degree of tightness of fuel elements, technological equipment, as well as the level of safety of operation of nuclear power plants.

The known method (equivalent) definition of isotopes of iodine, based on its extraction allocation [1]. Determination of iodine carried out by extraction from samples of carbon tetrachloride, followed by the deposition of iodine vesatile and measuring the radioactivity of the precipitate. The disadvantages of the method are the duration of the analysis, the necessity of using a large number of reagents, glassware, toxicity of carbon tetrachloride.

The known method (prototype) of radionuclide iodine from the gas environment iodide adsorption reagent, containing silver or silver salt in a porous inorganic carrier having an average pore diameter of 50 nm [2]. Sorption reagent is injected into the filter cartridges and is used to remove radioactive iodine present in the form of gaseous iodine compounds, as in the case of industrial nuclear accident, and for the purposes of monitoring. The selection of radionuclides of iodine is carried out by passing the gas stream through the filter cartridges.

The disadvantages of this method are the inability of its use and several orders of magnitude lower than in water. In addition, there may be a probability of failure of iodine sorption reagent from friction and the likelihood of reducing the efficiency of selection due to radioiodine ablation of part of the radioactive iodine flow environment. The use of sorption agents with a pore diameter of from 6 to 200 nm does not allow the selection of radionuclides of iodine from aqueous samples without the use of high pressure (more than 10 kg/cm2). The conduct of radionuclide iodine without taking all of him in uniform chemical form does not provide high selectivity of the process.

The objective of the invention is to provide a method of radionuclide iodine directly from the aqueous phase of the fluid. The technical result, which is achieved by the use of the invention is to improve the radiochemical purity of emitted radionuclides of iodine, agility control, the lower limit of detection of radioactive iodine and improve safety.

To achieve the mentioned technical result in the method for determining radionuclides of iodine emitting porous adsorbent, containing silver, for the determination of radionuclides of iodine from aqueous environment with a pH-Outram then, from 0.45 to 0.55 μm.

The unit of sample preparation device of the definition of radioactive iodine (Fig.1) consists of a membrane separator 1, the capacity for sample 2, the drain tank 3 and the compressor 4. Membrane separator (Fig.2) consists of the upper 10 and lower flanges 6, connected by bolts 11. The drainage grid 7 rests on the lower flange 6. Drain the mesh is impregnated membrane 8, over which is mounted a membrane - mechanical filter 9. Membrane 8 and 9 is pressed to drain the grid 7 of the upper flange 10.

The method is as follows.

Unscrew the bolts 11 of the membrane separator (Fig.2) and the drainage grid 7 stack impregnated membrane 8 and the diaphragm 9. Moisten the membranes of two or three drops of distilled water for fixing them on the drainage grid 7, close the upper flange 10 and tighten the flanges 6 and 10 by bolts 11. Then connect the tank 2 for the sample and the drain tank 3 to the membrane separator 1 by line 12. The sample is poured into the container 2 through the neck 13, line 14 connecting the compressed air of the compressor 4. In the container 2 being organic reagent to adjust the pH in the range from 2.0 to 11.0 at a temperature of from 1 to 50oC. Open the valve 5. Under the action and the s 8 and 9 in the membrane separator 1, falls into the drain tank 3. The volume of a water sample is passed through the membrane adsorbent with a linear speed of not more than 5.0 cm/min, is not more than 200 cm3on 1 cm2of the membrane.

After filtration of the sample Unscrew the ring bolts 11 membrane separator, remove the upper flange 10 and take out the membrane 8 and 9. Dried membrane 8 in 1 minute on filter paper or in the air stream passing through the membrane when creating a rarefaction. Then the membrane is inserted into the unit of measurement of gamma-spectrometer or beta radiation.

The operation of impregnating the membrane consists of two stages: processing (impregnation) 2% aqueous solution of silver nitrate (40 mg of metallic silver on one membrane with a diameter of 7.0 cm) and restore it to metallic silver 20% solution of hydrazine hydrate is added. Restored membrane was washed with distilled water. For analysis it is possible to use membranes with a retention time less than one month. Prepared membranes stored in distilled water.

Selection of optimal conditions for quantitative selection was based on the study of the chemical forms of radionuclides in the aqueous phase coolant NPP at different chemistries.

crystals, traditionally used for such purposes, given the overall characteristics differ or high fragility (ceramics, coal), or the complexity of a given porous structures (metals).

In comparison with the known methods of determination of radionuclides of iodine in the coolant NPP this method using organic membranes impregnated with silver, and organic reagent to generate analyzed in the aqueous phase of the working fluid pH and oxidation-healing capacity provides increased selectivity of iodine excretion, lowering the detection limit in 10 times, reduces the number of operations increases the efficiency of the control and safety of the process.

Examples of specific performance.

Example 1. The choice of the material composition of the membrane (cellulose acetate, hydrocellulose, polytetrafluoroethylene) and material (Hell, Bi, tri-n-octylamine (TOA) for impregnation.

Model solution of iodine-131 is filtered in parallel through different membranes impregnated with metallic silver with various filtration rate.

Model solution of iodine-131 was prepared by diluting 1 ml of Na131I distilled water to 100 ml, the Activity of the membranes was measured on the efficiency of the sample, Bq/l 1104The diameter of the tablets with TOA, mm 25,0 Height pills with TOA, mm - 18.0 Diameter membranes, mm 70,0 filtration Rate, cm/min - 5.0 Effectiveness of the allocation of radioiodine on the membranes (, %) was determined by the formula (1)

where A0- volume activity of the original solution, Bq/l;
Andf- volume activity of the filtrate, Bq/L.

The specific activity of iodine-131 in solution was (1-5)106Bq/L. the Results are presented in table.1.

From the above table.1 the results show that for separation of radioiodine from solution most applicable membranes based on cellulose acetate MFAS-M-2, with high sorption efficiency (98%) with good filtration characteristics, however, can be applied membranes of other materials, while the use of reimpregnation membranes for separation of radionuclides of iodine is impossible, because the sorption does not occur (see examples 11 and 12).

When selecting131I on the granular inorganic sorbent Hell (sample 1) completeness of the allocation does not exceed 70% (prototype), on tablets with TOA (sample 2) weight allocation is 90%, and the scatter of results 10%.drop131I on membranes made of different materials (cellulose acetate, cellulose acetate on polyamide, hydrocellulose on the polyamide and polypropylene, polytetrafluoroethylene on the propylene, a copolymer of cellulose acetate with polyethyleneimine), impregnated with silver (samples 3-9), iodine is excreted in efficiency from 82% (sample 9) to 98% (sample 4). When selecting131I ultrafine cellulose acetate membranes MFAS-M-2, impregnated with silver (sample 4), the efficiency of the allocation of the highest and compared with the prototype (sample 1) efficiency increases from 70% to 98%. The scatter of results (the error) is reduced from 10% to 3%.

Example 2. The radiochemical purity of the drug obtained silver-containing membrane and inorganic granular silicon sorbent (NGX).

The sample fluid NPP passed through ultrafine cellulose acetate membrane MFAS-M-2, impregnated with metallic silver. For separation of radionuclides adsorbed on the particles used in the particle lter from acetate.

Conditions of selection:
The temperature of the solution,oC - 20
pH - 3,5
Volume of sample, ml - 100
The diameter of the membranes, mm 70,0
The diameter of pores of the membrane, micron - 0,45-0,55
The thickness of the membrane, mm <0,1
The diameter of the Thoth preparations of iodine for silver-containing membrane is characterized by selectivity and is determined by the formula (2) percentage of impurities99Mo,187W and239N. From table.2 shows that nearly 100% of the radioactive iodine are highlighted in silver-containing membranes, and the content of impurities in the Hell is <0,04%,

where AIAgthe activity of the iodine in hell is the membrane, Bq;
AMoAgthe activity of molybdenum on Ad-membrane, Bq;
AIp- activity iodine in solution, Bq;
AMorthe activity of the molybdenum in solution, Bq.

From the calculation of the selectivity coefficients of radionuclide iodine on silver compared to tungsten (see formula 3) shows that

where AIAgthe activity of the iodine in hell is the membrane, Bq;
AWAgthe activity of tungsten on Ad-membrane, Bq;
AIp-activity iodine in solution, Bq;
AWpthe activity of tungsten in solution, Bq.

From table. 2 shows that the inorganic granular silicon sorbent with silver stands out about 50% of the initial activity of radionuclides of iodine, and the content of impurities it is more than 98% of the total activity of the membrane.

Example 3. Model solution of iodine - 131 is filtered through ultrafine cellulose acetate membrane impregnated with metallic silver with different filtration rate.

Conditions of selection:
The temperature of the solution,o the membranes, mm - 70
The diameter of pores of the membrane, micron - 0,45-0,55
From table. 3 shows that the use of ultrafine cellulose acetate membranes impregnated with metallic silver, allows quantitatively (96,2%) to remove the radionuclides of iodine in filtering the samples with a linear speed of from 0.03 to 5.0 cm/min.

Example 4. Sample liquid with an ammonia-water-chemical regime, the sample fluid with boric water-chemical regime and the sample fluid with miscorrection water-chemical regime is filtered in parallel through ultrafine cellulose acetate membrane, impregnated with metallic silver and the inorganic granular silicon sorbent with silver.

Conditions of selection:
The temperature of the solution,oC - 20
pH - 3,5
Volume NGX, cm3- 50
Volume of sample, ml - 100
The diameter of the membranes, mm - 70
The diameter of pores of the membrane, micron - 0,45-0,55
The sample fluid with miscorrection water-chemical regime was prepared by diluting 1 ml of Na131I distilled water to a 100 ml. Sample of the coolant with boron water-chemical regime was prepared by diluting 0.4 g of boric acid in 100 ml of brine with ammonia water regime, then brought the pH to 10 by adding caustic potash. The activity of membranes esmerald fully released from the samples of fluids with different water-chemical regimes (miscorrection, ammonia, boric), which are widely used in nuclear power plants.

Example 5. The sample liquid with an ammonia-water-chemical regime filtered through impregnated membrane with a pore diameter of from 0.45 to 0.55 μm at different pH of the coolant.

Conditions of selection:
The temperature of the solution,oC - 20
Volume of sample, ml - 100
Diaphragm diameter, mm - 70
The pore size, ám 0,45-0,55
The infiltration rate, cm/min to 5.0
pH of 2.0-11,0
The results are presented in table.5. This example shows that radioactive iodine can be extracted on impregnated with metallic silver membranes with a pore diameter of 0.45-0.55 m in the range of pH from 2.0 to 11.0.

From this example it follows that the radionuclides of iodine on silver-containing membranes can be distinguished with a high degree of efficiency (79,9% to 100%) of the sample fluid NPP in a wide range of pH (from 2.0 to 11.0). However, as can be seen from the table, the highest efficiency of radionuclide iodine and greatest purity of its allocation is achieved in the weakly acidic region of about pH 3.5.

Example 6.

Samples of aqueous fluid with ammonium water-chemical regime filtered through ultrafine cellulose acetate membrane, impregnated metallic silver is mm - 70
The pore size, ám 0,45-0,55
The infiltration rate, cm/min to 5.0
From table. 6 shows that the silver-containing membranes iodine quantitatively excreted 90% efficiency (slippage in the filtrate is 10%) of the sample volume to 4.0 l when the diameter of the membrane 70 mm, which is 200 cm3samples on 1 cm2the membrane surface. Growth is hampered by the increase in hydrodynamic resistance and increased leakage of iodine in the filtrate. The maximum volume of sample, in which the overshoot131I in the filtrate is less than 5%, equal to 2.5 liters

For control of radioactive iodine possible temperature samples of the aqueous phase coolant NPP is 1-80oC, but at temperatures over 50oThe membrane can be deformed continue to deteriorate. At 0oWith the sample freezes. For analysis was selected as the optimum temperature range of the analyzed samples from the +1oWith up to 50oC.

This method of control total activity of radionuclides of iodine in an aqueous carrier in comparison with known methods allows to increase the efficiency of control at least 2 times by reducing the measurement time of the radiation source - sorbent (in the prototype, the sorbent is granulirovaniem - the membrane displacement of 0.0001 DM3). Reducing the amount of source 250 times can improve the detection efficiency of the radiation as you would use to measure gamma-ray spectrometers, and beta-radiometers and, thus, to lower the detection limit of at least 250 times and also to reduce the measurement time, i.e., to increase the efficiency of the control.

The implementation of this control method allows to simplify the selection of reference radionuclides of iodine, which is responsible for the condition of the fuel elements. The materials used and the reagents are non-toxic and explosive fireproof, are produced on an industrial scale, so this method is industrially applicable. Use a reliable method of monitoring the integrity of the fuel element cladding also not only increases the safety of operation of NPP, but also environmental safety.

SOURCES of INFORMATION
1. Dubinin O. D.) R. I. Method for the determination of radioactive isotopes of iodine in the environment and the biomaterial. Hygiene and sanitation, 1981, 6, S. 53-54.

2. Patent US 5750461 And, publ. 12.05.1998,, IPC 01 J 23/50.


Claims

1. The control method of radionuclides them silver, characterized in that the sample fluid is passed through the organic membrane adsorbent with a pore size of 0.45-0.55 m, before passing the sample is pre-adjusted with an organic reagent to a pH of 2.0-11.0 in.

2. The method according to p. 1, characterized in that the volume of the sample fluid is not more than 200 cm3on 1 cm3membrane, and the sample temperature is from 1 to 50°C.

3. The method according to p. 1, wherein the sample fluid adjust ascorbic acid.

4. The method according to p. 1, wherein the sample fluid is passed through the adsorbent with a linear speed of not more than 5 cm/min.

5. The method according to p. 1, characterized in that the material of the membrane matrix using cellulose acetate.

 

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