Interlaboratory comparison exercises for organically-bound tritium in the development of reference materials of environmental samples.

The complex behavior of tritium and the probability of increasing tritium concentrations released in the environment were the promotors for the research and development of laboratory methods that enable to accurately determine the various forms of tritium including organically-bound tritium (OBT) for public and regulatory assurance. The measurement of tritium is a key step for dose and risk assessment. The Cernavoda Nuclear Power Plant (NPP) in Romania improved preparation methods and tested environmental matrices for OBT analysis through intercomparison exercises. This paper describes the international Organically-Bound Tritium (OBT) intercomparison exercise, organized by the Cernavoda Nuclear Power Plant (NPP) in 2019-2020, using fruit sample (quince) from Cernavoda town. Evaluation of the results from the participating laboratories was performed using both robust analysis (Algorithm A) method described in the ISO 13528:2015 standard and ANOVA method. The results obtained are encouraging as an increased number of participating laboratories did not change the observed dispersion of the results for activity concentration level around 50 Bq/L of combustion water. The stability of the remaining sample will be checked in time to investigate its use as a reference material for OBT analysis at the environmental levels.

Method for organically bound tritium analysis from sediment using a combustion bomb.

The method consisted in combustion, using a Parr bomb type 1121, of a sediment - tritium free promoter mixture. The proper ratio sediment to promoter in our experiments was between 1:3 and 1:2, higher ratio resulting in unreliable results, due to incomplete combustion of the sample. The described method was used to measure the estuarine sediment sample from the 2nd International OBT Intercomparison Exercise, the average reported value being 163±12Bqkg-1 dry matter (k=2).

Slovenian-Romanian bilateral intercomparison on tritium samples.

A Slovenian laboratory from the Jozef Stefan Institute (JSI) and a Romanian laboratory from the National Research and Development Institute for Cryogenics and Isotopic Technologies (ICIT) performed bilateral intercomparisons of tritium determination in environmental samples. On the basis of the results, the measurement and analysis methods were compared. Comparability and traceability were confirmed with the results from international radioactivity proficiency test exercises organized by IAEA and NPL where both laboratories participated. New knowledge gained leads to harmonized, precise and traceable results of low level tritium environmental samples measurements.

Applying direct liquid scintillation counting to low level tritium measurement.

Different types of procedures could be applied to measure environmental tritium level, but usually all are based on measuring tritium concentration in extracted samples water by liquid scintillation counting techniques. There are two standard methods published for tritium measurement in aqueous samples. The recommended tritium activities for tritium standard solutions can be found in these reference procedures. This paper reports the results from a comparative study carried out for different tritium standard solutions, in order to measure the counting efficiency using liquid scintillation method.