He jishu (Sep 2022)
Analysis of the accuracy of 14C in gaseous effluent of nuclear power plant by direct measurement method
Abstract
BackgroundThere is no national standard specifically for the analysis of gaseous effluents 14C from nuclear power plants in China, only one group standard available for reference. The group standard is technical specification for 14C analysis of gaseous effluents for nuclear power plants (TBSRS 005―2019). Most nuclear power plants in China refer to this group standard and use direct measurement method to analyze 14C in gaseous effluent.PurposeThis study aims to investigate the accuracy of 14C in gaseous effluent of nuclear power plant by the direct measurement method.MethodsA series of experiments were carried out, including optimal ratio of sample and scintillation cocktail, quenching effect, entrainment of tritium and influent factors of tritium on the analysis of 14C. The optimal ratio of sample and scintillation cocktail was selected after measuring different volume ratios of sample and scintillation liquid. The experiment of quenching effect was to measure the samples with different quenching degrees and to observe the influence of different quenching degrees on the measurement efficiency. Entrainment of tritium and the influence level experiment of tritium was to determine the existence of entrainment of tritium through the comparison of samples spectrogram, and to determine the influence level of tritium on the counting of 14C by added different proportions of tritium to 14C sample. Finally, direct measurement results of sixty-seven 14C samples of gaseous effluent from a nuclear power plant were statistically analyzed.ResultsThe experimental results show that tritium is entrained in the gaseous effluent 14C sample when the HAGUE 7000 14C sampler is used, and 1%~2% of the entrainment of tritium is contributed to the count of 14C. The optimal ratio of sample and scintillation cocktail is 6 mL vs. 14 mL. The difference of sample quenching causes the deviation of detection efficiency. The direct measurement results of sixty-seven 14C samples show that the maximum efficiency difference of 4.6% is introduced for different quenching degrees of samples.ConclusionThe main factors affecting the accuracy of the direct measurement method are the ratio of sample and scintillation cocktail, entrainment of tritium and accuracy of detection efficiency. The influence of entrainment of tritium can be reduced by resolving spectral channel, using suspension analysis method or changing sampling method.
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