Article

3He mass spectrometry for very low-level measurement of organic tritium in environmental samples

LSCE, CEA-CNRS-UVSQ, CEA/Saclay, 91191, Gif-sur-Yvette, France.
Journal of Environmental Radioactivity (Impact Factor: 2.48). 11/2009; 101(2):185-90. DOI: 10.1016/j.jenvrad.2009.10.005
Source: PubMed

ABSTRACT

The design, setup and performance of a mass spectrometric system for the analysis of low to very low-level tritium in environmental samples are described. The tritium concentration is measured indirectly by the (3)He ingrowth from radioactive decay after complete initial degassing of the sample. The analytical system is fully computer-controlled and consists in a commercial helium isotope mass spectrometer coupled with a high vacuum inlet system. A detection limit of 0.15 Bq/kg is routinely obtainable for sample sizes of 20g of water equivalent and an accumulation time of three months. Larger samples (and/or longer accumulation time) can be used to obtain lower detection limits. In addition to the benefit of a lower detection limit, another advantage of this non-destructive method lies in the simplicity of the analytical procedure which strongly limits the risk of contamination. An inter-comparison was successfully performed with the conventional beta counting technique on lyophilized grass samples, in a range of tritium concentrations of environmental interest. It shows that the (3)He mass spectrometry method yields results that are fully consistent with the conventional liquid scintillation technique over a wide range of tritium concentrations.

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    • "OBT duplicates were well-correlated with a r 2 fit of 0.90, and a slope of 1.12 (Figure S2). Lastly, combustion results for OBT were cross-checked by mass spectrometry (MS) (Jean-Baptiste et al., 2010) at the University of Ottawa for six soil and three vegetation samples (encapsulated for helium ingrowth, range of 3e220 Bq/L). Results from the two methods were well correlated (r 2 fit of 0.73 with a slope of 0.88, Figure S3). "
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    ABSTRACT: The dynamics of tritium released from nuclear facilities as tritiated water (HTO) have been studied extensively with results incorporated into regulatory assessment models. These models typically estimate organically bound tritium (OBT) for calculating public dose as OBT itself is rarely measured. Higher than expected OBT/HTO ratios in plants and soils are an emerging issue that is not well understood. To support the improvement of models, an experimental garden was set up in 2012 at a tritium processing facility in Pembroke, Ontario to characterize the circumstances under which high OBT/HTO ratios may arise. Soils and plants were sampled weekly to coincide with detailed air and stack monitoring. The design included a plot of native grass/soil, contrasted with sod and vegetables grown in barrels with commercial topsoil under natural rain and either low or high tritium irrigation water. Air monitoring indicated that the plume was present infrequently at concentrations of up to about 100 Bq/m3 (the garden was not in a major wind sector). Mean air concentrations during the day on workdays (HTO 10.3 Bq/m3, HT 5.8 Bq/m3) were higher than at other times (0.7–2.6 Bq/m3). Mean Tissue Free Water Tritium (TFWT) in plants and soils and OBT/HTO ratios were only very weakly or not at all correlated with releases on a weekly basis. TFWT was equal in soils and plants and in above and below ground parts of vegetables. OBT/HTO ratios in above ground parts of vegetables were above one when the main source of tritium was from high tritium irrigation water (1.5–1.8). Ratios were below one in below ground parts of vegetables when irrigated with high tritium water (0.4–0.6) and above one in vegetables rain-fed or irrigated with low tritium water (1.3–2.8). In contrast, OBT/HTO ratios were very high (9.0–13.5) when the source of tritium was mainly from the atmosphere. TFWT varied considerably through time as a result of SRBT's operations; OBT/HTO ratios showed no clear temporal pattern in above or below ground plant parts. Native soil after ∼20 years of operations at SRBT had high initial OBT that persisted through the growing season; little OBT formed in garden plot soil during experiments. High OBT in native soil appeared to be a signature of higher past releases at SRBT. This phenomenon was confirmed in soils obtained at another processing facility in Canada with a similar history. The insights into variation in OBT/HTO ratios found here are of regulatory interest and should be incorporated in assessment models to aid in the design of relevant environmental monitoring programs for OBT.
    Full-text · Article · Mar 2016 · Journal of Environmental Radioactivity
    • "In order to compare the tritium concentration of the river water and TFWT with the tritium concentration bound in the biota tissues , the specific hydrogen concentration of each sample was needed. To determine the specific hydrogen concentration, a CHN analyser is usually used (Jean-Baptiste et al., 2010). For OBT measurements with the LSC technique, organic samples are combusted in dry oxygen current and the activity of water generated is measured (Bogen et al., 1973; Takashima et al., 1987; Lockyer and Lally, 1993; Pointurier et al., 2003). "
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    ABSTRACT: Danube water, sediment and various aquatic organisms (snail, mussel, predatory and omnivorous fish) were collected upstream (at a background site) and downstream of the outlet of the warm water channel of Paks Nuclear Power Plant. Gamma emitters, tissue free-water tritium (TFWT) and total organically-bound tritium (T-OBT) measurements were performed. A slight contribution of the power plant to the natural tritium background concentration was measured in water samples from the Danube section downstream of the warm water channel. Sediment samples also contained elevated tritium concentrations, along with a detectable amount of (60)Co. In the case of biota samples, TFWT exhibited only a very slight difference compared to the tritium concentration of the Danube water, however, the OBT was higher than the tritium concentration in the Danube, independent of the origin of the samples. The elevated OBT concentration in the mollusc samples downstream of the warm water channel may be attributed to the excess emission from the nuclear power plant. The whole data set obtained was used for dose rate calculations and will be contributed to the development of the ERICA database.
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