14 research outputs found
Rapid analysis method for the determination of 14C specific activity in irradiated graphite.
14C is one of the limiting radionuclides used in the categorization of radioactive graphite waste; this categorization is crucial in selecting the appropriate graphite treatment/disposal method. We propose a rapid analysis method for 14C specific activity determination in small graphite samples in the 1-100 μg range. The method applies an oxidation procedure to the sample, which extracts 14C from the different carbonaceous matrices in a controlled manner. Because this method enables fast online measurement and 14C specific activity evaluation, it can be especially useful for characterizing 14C in irradiated graphite when dismantling graphite moderator and reflector parts, or when sorting radioactive graphite waste from decommissioned nuclear power plants. The proposed rapid method is based on graphite combustion and the subsequent measurement of both CO2 and 14C, using a commercial elemental analyser and the semiconductor detector, respectively. The method was verified using the liquid scintillation counting (LSC) technique. The uncertainty of this rapid method is within the acceptable range for radioactive waste characterization purposes. The 14C specific activity determination procedure proposed in this study takes approximately ten minutes, comparing favorably to the more complicated and time consuming LSC method. This method can be potentially used to radiologically characterize radioactive waste or used in biomedical applications when dealing with the specific activity determination of 14C in the sample
CO<sub>2</sub> flow intensity signal measured by TCD (black line) and cps spectra of samples No. 3 (green), No. 6 (blue) and background (red) as determined with the semiconductor detector.
<p>In total, three combustion cycles (400 s each) were used to completely combust the non-ground graphite sample.</p
An example spectrum of <sup>14</sup>C measured using semiconductor detectors.
<p>The green color denotes the spectrum of sample No. 3 and the black color denotes a typical background spectrum. Both spectra were collected over 100 s time intervals.</p
Correlation between LSC and semiconductor detector data.
<p>The horizontal axis represents LSC measurement data of <sup>14</sup>C activity and the vertical axis represents semiconductor β detector pulse counts obtained per 100 s. The parameters of linear approximation (y = a + bx) are a = 8.83, b = 0.63, R = 0.94.</p
Rapid system for <sup>14</sup>C specific activity determination in the sample.
<p>System contains elemental analyzer (autosampler, oxidation and reduction columns, water trap, gas chromatography column, thermal conductivity detector (TCD)) and β particle detection system. In the present study, gas catchers (3 M NaOH) and LSC were used to evaluate the accuracy of the measurements of samples with low <sup>14</sup>C activity.</p
Correlation between <sup>14</sup>C activity and the mass of graphite samples.
<p>The parameters of linear approximation (y = a + bx) are: a = -34 ± 45, b = 0.8 ± 0.2; R = 0.62. Sample mass was determined by the elemental analyzer.</p
Experimentally determined activity of <sup>137</sup>Cs, <sup>60</sup>Co and <sup>14</sup>C in the graphite sample.
<p>The mass of the same sample was determined by two methods: weighing with balances, and later by combustion in an elemental analyzer.</p
CO<sub>2</sub> gas flow in the TCD and the β counter chamber during the first cycle of combustion of sample No. 6.
<p>CO<sub>2</sub> gas flow in the TCD and the β counter chamber during the first cycle of combustion of sample No. 6.</p
The correlation of the graphite sample mass as determined by two independent methods: Weighing and combustion in the elemental analyzer.
<p>Graphite sample mass in the same sample was determined by weighing with balances (horizontal axis) and by combustion in the elemental analyzer, measured from the resulting CO<sub>2</sub> (vertical axis). The parameters of linear approximation (y = a + bx) are: a = 3 ± 10, b = 0.96 ± 0.06, R = 0.97.</p
Radiocarbon spectra of a graphite sample.
<p>(<b>a</b>) from the first catcher, (<b>b</b>) from the second catcher.</p