دانلود رایگان مقاله روشی برای تجزیه و تحلیل تریتیوم ارگانیک بدون رسوب با بمب احتراق

1. Introduction

Tritium and radiocarbon are currently the two main radionuclides that might be discharged in water bodies by the industry and particularly by heavy-water reactors, such as CANDU reactors. Tritium widely integrates into the water cycle and follows the water mass dynamics but it may also be integrated for long term into the organic pool, persisting in aquatic environment according to the recycling rates of organic matter (Eyrolle-Boyer et al., 2015). The experimental data indicated a time lag between concentrations of tritium in water and sediments, reflecting non-equilibrium attributed to the specific dynamics of tissue free water tritium (TFWT as HTO) and organically bound tritium (OBT) forms: TFWT follows the transfer of water while OBT depends on process linked to organic matter (biomass production, degradation and recycling). Tritium persistence through its OBT forms in biomass and aquatic systems may have a major impact on environmental compartments submitted to chronic releases (Eyrolle-Boyer et al., 2014), due to its significant radiotoxicity and contribution to the total dose (Galeriu et. al., 2010; UNSCEAR, 2000). Current measurement of organically bound tritium (OBT) from sediment using liquid scintillation counting (LSC) implies first of all conversion of organic matter in liquid water. In order to convert sediment organic matter to water it is necessary to perform a total oxidation process, which most commonly can be made through wet oxidation (Ware and Allot, 1999; Environment Agency, 2005) or combustion using different type of catalytic furnaces (Cossonnet et. al., 2009; Daillant et. al., 2004; Eyrolle-Boyer et al., 2014; Fournier et. al. 2002; Morris, 2006; Vichot et. al. 2005,) or the devices called oxidizers (Kim et. al., 2013).

4. Conclusions

The new developed method, less expensive (capital equipment cost and operational cost), can be used to OBT measurement in sediment with few precautions. The combustion water of the promoter must be checked to be tritium free water, the coal sample used in preliminary experiments having around 1 Bq L−1 tritium activity concentration in its combustion water and not being suitable for this type of experiments. The proper ratio sediment: heavy fuel oil in our experiments was between 1:3 and 1:2, higher ratio conducting to unreliable results, due to incomplete combustion of the sample. This method was used to determine the OBT activity from sediment received within the 2nd International OBT Intercomparison Exercise, using as promoter heavy fuel oil and sample to promoter ratio of 1:2 (wt.). The limitations of this method are the low levels of OBT and also low hydrogen content in sediment, due to the fact that mixing the sediment samples with a tritium free promoter conducts to dilutions of the OBT. The dilution factors varied between 37 and 25 for Sediment 1 with a hydrogen content of 0.79% and between 66 and 44 for Sediment 2 with a hydrogen content 0.44%. Due to tritium dilution during combustion, minimum measurable activity of the OBT was around 13 Bq L−1 (0.9 Bq kg−1 dry) for Sediment 1 (which for sample to promoter ratio of 1:2 has a tritium activity in sediment combustion water of 30.90 ± 5.45 Bq L−1 ) and around 18 Bq L−1 (0.7 Bq kg−1 dry) for Sediment 2 (which for sample to promoter ratio of 1:2 has a tritium activity in sediment combustion water of 41.90 ± 11.26 Bq L−1 ). Also minimum measurable activity of the OBT for the sediment received from the organizers of the OBT exercise was around 6 Bq L−1 (0.5 Bq kg−1 dry) for a hydrogen content of 1.03%. More investigations can be made to find another suitable tritium free combustion promoters, especially the ones which have lower hydrogen content and thus a lower dilution factor can be achieved.