An analytical method for strontium-89 in water

Abstract

The present invention belongs to the field of radiochemistry technology, and particularly relates to a method for analyzing strontium-89 in water. It includes the following steps: Step 1: Enrichment of strontium; Step 2: Separation and purification of strontium; Step 3: Separation of yttrium-90; Step 4: Measurement and calculation. The beneficial effects of the present invention are as follows: In the sample treatment process, a method combining precipitation enrichment and strontium-specific resin ion exchange is adopted, which can process a large number of water sample samples and remove all impurity components at one time, avoiding repeated cleaning to remove various interfering ions. The radioactive contents of strontium-89 and strontium-90 are measured with a liquid scintillation counter, which is more sensitive than the low-background beta measuring instrument in the existing method GB14883.3-2016, and the detection limit is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of radiochemistry, and particularly relates to a method for analyzing strontium-89 in water. Background Art

[0002] Strontium-89 is a radionuclide required to be measured in the newly compiled "Technical Specification for Radioactive Monitoring of Nuclear Power Plant Effluents" by the Radiation Environment Monitoring Technology Center of the Ministry of Environmental Protection. At present, a standard analysis method for strontium-89 in nuclear power plant effluents has not been established in China. Only the "Determination Methods for Radioactive Substances Strontium-89 and Strontium-90 in Foods" in GB14883.3-2016 contains the determination method for strontium-89.

[0003] There are three separation techniques in the GB14883.3-2016 method:

[0004] (1) Di-(2-ethylhexyl) phosphoric acid extraction method: Di-(2-ethylhexyl) phosphoric acid (abbreviated as HDEHP) is used to extract and separate yttrium and other rare earth impurities. After 14 days, the yttrium-90 generated in the aqueous phase is re-extracted with HDEHP, and the yttrium is back-extracted with 6 mol / L nitric acid and then precipitated as yttrium oxalate.

[0005] (2) Ion exchange method: Utilizing the difference in the complexing ability of ethylenediaminetetraacetic acid and calcium citrate with calcium, strontium, and barium, they are separated from each other on a cation exchange resin column. In the ethylenediaminetetraacetic acid effluent containing strontium, strontium is precipitated in the form of carbonate by the copper replacement method, and then decontaminated with iron hydroxide and left for 14 days.

[0006] (3) Fuming nitric acid method: The strontium is purified and separated by washing with nitric acid, oxalic acid, and barium chromate, and then decontaminated with iron hydroxide and left for 14 days.

[0007] GB14883.3-2016 measures the radioactivity of yttrium-90 using a proportional beta counter, and thus calculates the radioactive concentration of strontium-90.

[0008] Due to the differences in sample medium and radioactive content, the method of GB14883.3-2016 is used for the treatment of food ash samples, with a detection limit of 0.016 Bq / g ash. The sample treatment process is not applicable to the treatment of water samples, and it cannot meet the requirement of the detection lower limit of 0.1 Bq / L in the "Technical Specification for Radioactive Monitoring of Nuclear Power Plant Effluents" when used for the measurement of nuclear power plant effluents.

[0009] The main disadvantages of the GB14883.3-2016 method are: it is used for the treatment of ash samples and is not applicable to the treatment of water samples; the method has a relatively high detection limit. Summary of the Invention

[0010] The purpose of the present invention is to provide a method for analyzing strontium-89 in water, which can meet the requirement of the detection lower limit in the "Technical Specification for Radioactive Monitoring of Nuclear Power Plant Effluents".

[0011] The technical solution of the present invention is as follows: A method for analyzing strontium-89 in water, comprising the following steps:

[0012] Step 1: Enrichment of strontium;

[0013] Step 2: Separation and purification of strontium;

[0014] Step 3: Separation of yttrium-90;

[0015] Step 4: Measurement and calculation.

[0016] In the said Step 1, the sample is adjusted to a pH value less than 2 with a nitric acid solution, a strontium carrier and a barium carrier are added, the sample is heated to the boiling point, a phenolphthalein indicator is added, the sample is adjusted to turn pink with a sodium hydroxide solution, a sodium carbonate solution is added, stirred and reacted for 15 minutes, cooled to allow the precipitate to settle, the precipitate is collected by centrifugation and the strontium precipitate is dissolved with an 8M nitric acid solution to obtain a strontium enrichment solution.

[0017] In the said Step 2, the resin is washed through a column with demineralized water, and then pre-equilibrated by passing 6-8M nitric acid through the column. The strontium enrichment solution is passed through the column, the resin column is washed with 6-8M nitric acid, and then a mixed solution of 2-3M nitric acid - 0.03-0.05M oxalic acid is passed through the column to remove tetravalent radionuclides such as Pu, Zr, Ce, etc. Then 6-8M nitric acid is passed through the column to elute the residual oxalic acid, and 0.03-0.05M nitric acid is used to elute the strontium adsorbed on the strontium column. The strontium purification solution is collected, the strontium purification solution is made up to a constant volume for measuring the total strontium and the in-growth of yttrium-90.

[0018] In the said Step 3, the resin is washed through a column with demineralized water, and then pre-equilibrated by passing 6-8M nitric acid through the column. The strontium purification solution after 7 days of in-growth is added with a yttrium carrier and then passed through the column. 6-8M nitric acid is passed through the column to elute the yttrium-90 generated by the in-growth of strontium-90. The in-growth yttrium-90 eluate is collected, the yttrium-90 eluate is made up to a constant volume for measuring yttrium-90.

[0019] In the said Step 4, the detection efficiency and quenching correction curve of strontium-90 and yttrium-90 for the liquid scintillation spectrometer are obtained by calibrating with strontium-90 and yttrium-90 standard substances. The strontium purification solution and the yttrium-90 eluate after being made up to a constant volume are respectively measured for the total strontium and the yttrium-90 radioactivity with a liquid scintillation spectrometer, and the radioactivity of strontium-89 is calculated. The calculation formula is as follows:

[0020] Calculation of the total radioactive strontium activity concentration:

[0021]

[0022] Wherein, R a is the total β counting rate (cpm) of the sample, R b is the β counting rate (cpm) of the background, ESr-90 is the detection efficiency of the final strontium-90, E Y-90 is the detection efficiency of the final yttrium-90, λ Y-90 is the decay constant of yttrium-90, 3.008×10 -6 s -1 ; t1 is the date and time of strontium / yttrium separation, t2 is the date and time of the counting midpoint, Y is the chemical recovery rate of strontium, V is the sample volume (L), and DF is the correction factor for the decay of the sample from its reference date to the midpoint of the total strontium count;

[0023]

[0024] wherein, λ Sr-90 is the decay constant of strontium-90, 7.642×10 -10 s -1 ; t0 is the sample reference date and time, and t1 is the date and time of strontium / yttrium separation;

[0025] Calculate the activity concentration of strontium-90 based on the ingrowth of yttrium-90:

[0026]

[0027] wherein, S y is the counting rate of yttrium, cpm; B y is the background counting rate of yttrium, cpm; E y is the counting efficiency of yttrium-90, V is the sample volume, L; Y y is the recovery rate of yttrium, I y is the ingrowth factor of yttrium 1-exp((-ln2 / 2.6708)*(T 2 -T 1 )); D y is the decay correction of yttrium-90 = exp((-ln2 / 2.6708)*(T 4 -T 2 )); T 1 is the start time of yttrium ingrowth, T 2 is the end time of yttrium ingrowth, T 4 is the midpoint of yttrium sample measurement;

[0028] Calculate the activity concentration of strontium-89 based on the activity concentration formula (1) of total strontium and the activity concentration formula (2) of strontium-90:

[0029] AC Sr-89 = AC Tatal Sr - AC Sr-90

[0030] The strontium purification solution and the yttrium-90 eluate are respectively mixed with HisafeⅢ scintillation fluid in a ratio of 8:12 in a low-potassium glass bottle. The total strontium and yttrium-90 radioactivities are measured using a liquid scintillation spectrometer. The purification solution is mixed with HisafeⅢ scintillation fluid in a ratio of 8:12 in a low-potassium glass bottle and measured using a liquid scintillation counter. The net counting rates of the regions of interest of strontium-90 and yttrium-90 in the sample are calculated by setting different regions of interest.

[0031] The beneficial effects of the present invention are as follows: In the sample treatment process, a method combining precipitation enrichment and strontium-specific resin ion exchange is adopted, which can process a large number of water sample samples and remove all impurity components at one time, avoiding repeated washing to remove various interfering ions. Measuring the radioactive content of strontium-89 and strontium-90 with a liquid scintillation counter is more sensitive than the low-background β measuring instrument in the existing method GB14883.3-2016, and the detection limit is greatly reduced. Brief Description of the Drawings

[0032] Figure 1 It is a flow chart of an analysis method for strontium-89 in water provided by the present invention. Detailed Embodiments

[0033] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0034] In the nuclear power plant reactor, uranium-235 fission generates strontium-90, strontium-89 and some short-lived strontium isotopes. In particular, strontium-90 and strontium-89 have a great impact on the environment, and the fission yield of strontium-90 can reach 5.8%. The half-life of strontium-90 is 28.6 years. After strontium-90 decays, it generates yttrium-90, and the maximum β energy is 0.546 MeV. The half-life of yttrium-90 is 64.1 hours, and it can continue to β decay to generate stable zirconium-90. In a sample placed for a long time, strontium-90 generally reaches an equilibrium state with yttrium-90. At this time, the activities of strontium-90 and yttrium-90 are also equivalent. This equilibrium state results from the fact that the half-life of the parent nuclide is much longer than that of the daughter nuclide. The half-life of strontium-89 is 50.5 days. Strontium-89 is also a pure β radioactive nuclide, and its maximum energy is about 1.492 MeV. Finally, it decays into the stable nuclide yttrium-90.

[0035] An analytical method for strontium-89 in water provided by the present invention adds a strontium carrier to a nuclear power plant effluent sample, and after equilibration, the sample is concentrated by the coprecipitation method of strontium carbonate / barium carbonate. Heating and centrifugation are used to rapidly enrich strontium from the water body. The enriched precipitate is dissolved in nitric acid, and a strontium-specific resin selective for strontium is used for ion exchange separation to obtain a purified solution of strontium isotopes. A liquid scintillation counter is used to measure the total strontium radioactivity in the purified solution. Seven days later, the remaining purified solution is subjected to ion exchange separation with a strontium-specific resin to separate yttrium-90 generated by the in-growth of strontium-90, and then the radioactivity of yttrium-90 is measured with a liquid scintillation counter. The radioactive content of strontium-89 is obtained by calculation.

[0036] An analytical method for strontium-89 in water, comprising the following steps:

[0037] Step 1: Enrichment of strontium

[0038] Prepare a strontium carrier by mixing strontium nitrate (Sr(NO 3 ) 2 ) with a nitric acid solution, which contains a certain amount of strontium element. The added non-radioactive nuclide strontium will not affect the final measurement result. Prepare a barium carrier by mixing barium nitrate with a nitric acid solution. Prepare a yttrium carrier by mixing yttrium nitrate with a nitric acid solution.

[0039] Adjust the pH value of the sample to less than 2 with a nitric acid solution, and add the strontium carrier and barium carrier. Heat the sample to near boiling point, add a phenolphthalein indicator, adjust the sample to turn pink with a sodium hydroxide solution, add a sufficient amount of sodium carbonate solution, stir and react for 15 minutes, cool to allow the precipitate to settle, centrifuge to collect the precipitate, and dissolve the strontium precipitate with an 8M nitric acid solution to obtain an enriched solution of strontium.

[0040] Step 2: Separation and purification of strontium

[0041] Wash the resin with deionized water through the column, and then pre-equilibrate with 6-8M nitric acid through the column. Pass the strontium enriched solution through the column, wash the resin column with 6-8M nitric acid, and then pass a mixed solution of 2-3M nitric acid - 0.03-0.05M oxalic acid through the column to remove tetravalent radioactive nuclides such as Pu, Zr, and Ce. Then pass 6-8M nitric acid through the column to elute the residual oxalic acid (record the end time and date of elution as t1, i.e., the "strontium separation time" and the "yttrium growth start time"). Elute the strontium adsorbed on the strontium column with 0.03-0.05M nitric acid, collect the obtained strontium purified solution, and make up the volume of the strontium purified solution for measuring the total strontium and the in-growth of yttrium-90.

[0042] Step 3: Separation of yttrium-90

[0043] Wash the resin by passing deionized water through the column, and then perform pre-equilibration by passing 6 - 8M nitric acid through the column. Add yttrium carrier to the strontium purification solution after 7 days of in-growth, pass it through the column, and elute the yttrium-90 generated by the in-growth of strontium-90 with 6 - 8M nitric acid through the column (record the end time and date of elution as t2, i.e., "the stop time of yttrium growth"), collect the in-growth yttrium-90 eluate, make up the volume of the yttrium-90 eluate, and use it to measure yttrium-90.

[0044] Step 4: Measurement and calculation

[0045] Obtain the detection efficiency and quenching correction curve of the liquid scintillation spectrometer for strontium-90 and yttrium-90 by calibrating with strontium-90 and yttrium-90 standard substances. Take the made-up strontium purification solution and the yttrium-90 eluate and measure the total strontium and yttrium-90 radioactivities with a liquid scintillation spectrometer respectively, and calculate the radioactivity of strontium-89. The calculation formula is as follows:

[0046] Calculation of total radioactive strontium activity concentration:

[0047]

[0048] where R a is the total β count rate (cpm) of the sample, R b is the β count rate (cpm) of the background, E Sr-90 is the detection efficiency of the final strontium-90, E Y-90 is the detection efficiency of the final yttrium-90, λ Y-90 is the decay constant of yttrium-90, 3.008×10 -6 s -1 ; t1 is the date and time of strontium / yttrium separation, t2 is the date and time of the counting midpoint, Y is the chemical recovery rate of strontium, V is the sample volume (L), and DF is the correction factor for the decay of the sample from its reference date to the midpoint of the total strontium count;

[0049]

[0050] where λ Sr-90 is the decay constant of strontium-90, 7.642×10 -10 s -1 ; t0 is the sample reference date and time, and t1 is the date and time of strontium / yttrium separation.

[0051] Calculate the activity concentration of strontium-90 according to the in-growth of yttrium-90:

[0052]

[0053] where S y is the count rate of yttrium, cpm; B y is the background count rate of yttrium, cpm; E yis the counting efficiency of yttrium-90, V is the sample volume, in L; Y y is the recovery rate of yttrium, I y is the ingrowth factor of yttrium

[0054] = 1 - exp((-ln2 / 2.6708) * (T 2 - T 1 )); D y is the decay correction of yttrium-90 = exp((-ln2 / 2.6708) * (T 4 - T 2 )); T 1 is the starting time of yttrium ingrowth, T 2 is the ending time of yttrium ingrowth, T 4 is the midpoint of the yttrium sample measurement.

[0055] Calculate the activity concentration of strontium-89 according to the activity concentration formula (1) of total strontium and the activity concentration formula (2) of strontium-90:

[0056] AC Sr-89 = AC Tatal Sr - AC Sr-90

[0057] Take the strontium purification solution and the yttrium-90 eluate and mix them with HisafeⅢ scintillation liquid at a ratio of 8:12 in a low-potassium glass bottle. Use a liquid scintillation spectrometer to measure the total strontium and yttrium-90 radioactivity. The purification solution and HisafeⅢ scintillation liquid are mixed at a ratio of 8:12 in a low-potassium glass bottle and measured using a liquid scintillation counter. Calculate the net count rate of the regions of interest of strontium-90 and yttrium-90 in the sample by setting different regions of interest.

Claims

1. An analytical method for strontium-89 in water, characterized in that, it comprises the following steps: Step 1: Enrichment of strontium; The said Step 1 is to adjust the sample to a pH value less than 2 with a nitric acid solution, add a strontium carrier and a barium carrier, heat the sample to the boiling point, add a phenolphthalein indicator, adjust the sample to turn pink with a sodium hydroxide solution, add a sodium carbonate solution, stir and react for 15 minutes, cool to allow the precipitate to settle, centrifuge to collect the precipitate and dissolve the strontium precipitate with an 8M nitric acid solution to obtain a strontium enrichment solution; Step 2: Separation and purification of strontium; The said Step 2 is to wash the resin by passing demineralized water through the column, then pre-equilibrate with 6 - 8M nitric acid by passing it through the column, pass the strontium enrichment solution through the column, wash the resin column with 6 - 8M nitric acid, then pass a mixed solution of 2 - 3M nitric acid - 0.03 - 0.05M oxalic acid through the column to remove the tetravalent radionuclides of Pu, Zr, and Ce, then pass 6 - 8M nitric acid through the column to elute the residual oxalic acid, elute the strontium adsorbed on the strontium column with 0.03 - 0.05M nitric acid, collect to obtain a strontium purification solution, make up the volume of the strontium purification solution for measuring the total strontium and the in-growth of yttrium-90; Step 3: Separation of yttrium-90; The said Step 3 is to wash the resin by passing demineralized water through the column, then pre-equilibrate with 6 - 8M nitric acid by passing it through the column, add a yttrium carrier to the strontium purification solution after 7 days of in-growth and then pass it through the column, elute the yttrium-90 generated by the in-growth of strontium-90 with 6 - 8M nitric acid by passing it through the column, collect to obtain an in-growth yttrium-90 eluate, make up the volume of the yttrium-90 eluate for measuring yttrium-90; Step 4: Measurement and calculation; The said Step 4 is to obtain the detection efficiency and quenching correction curve of the liquid scintillation spectrometer for strontium-90 and yttrium-90 by calibrating with strontium-90 and yttrium-90 standard substances, take the made-up volume of the strontium purification solution and the yttrium-90 eluate and measure the total strontium and yttrium-90 radioactivity with a liquid scintillation spectrometer respectively, calculate the radioactivity of strontium-89, and the calculation formula is as follows: Calculation of the total radioactive strontium activity concentration: where, R a is the total beta counting rate (cpm) of the sample, R b is the beta counting rate (cpm) of the background, E Sr-90 is the detection efficiency of the final strontium-90, E Y-90 is the detection efficiency of the final yttrium-90, λ Y-90 is the decay constant of yttrium-90, 3.008×10 -6 s -1 ; t1 is the date and time of strontium / yttrium separation, t2 is the date and time of the counting midpoint, Y is the chemical recovery rate of strontium, V is the sample volume, and DF is the correction factor for the decay of the sample from its reference date to the midpoint of the total strontium count; Among them, λ Sr-90 is the decay constant of strontium-90, 7.642×10 -10 s -1 ; t0 is the reference date and time of the sample, and t1 is the date and time of strontium / yttrium separation.

2. The analytical method for strontium-89 in water according to claim 1, characterized in that, the said Step 4 includes the following: Calculate the activity concentration of strontium-90 according to the in-growth of yttrium-90: Among them, S y is the counting rate of yttrium, cpm; B y is the background counting rate of yttrium, cpm; E y is the counting efficiency of yttrium-90, V is the sample volume, L; Y y is the recovery rate of yttrium, I y is the ingrowth factor of yttrium 1-exp((-ln2 / 2.6708)*(T 2 -T 1 )); D y is the decay correction of yttrium-90 = exp((-ln2 / 2.6708)*(T 4 -T 2 )); T 1 is the starting time of yttrium ingrowth, T 2 is the ending time of yttrium ingrowth, T 4 is the midpoint of yttrium sample measurement; Calculate the activity concentration of strontium-89 according to the activity concentration formula (1) of the total strontium and the activity concentration formula (2) of strontium-90: AC Sr-89 = AC Tatal Sr -AC Sr-90 。 3. The analytical method for strontium-89 in water according to claim 2, characterized in that, the said Step 4 includes the following: Take the strontium purification solution and the yttrium-90 eluate and mix them with HisafeⅢ scintillation liquid in a ratio of 8:12 in a low-potassium glass bottle, measure the total strontium and yttrium-90 radioactivity with a liquid scintillation spectrometer, mix the purification solution with HisafeⅢ scintillation liquid in a ratio of 8:12 in a low-potassium glass bottle, measure with a liquid scintillation counter, and calculate the net counting rate of the regions of interest of strontium-90 and yttrium-90 in the sample by setting different regions of interest.

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