Uncertainty of current understanding regarding OBT formation in plants

Abstract

Radiological impact models are important tools that support nuclear safety. For tritium, a special radionuclide that readily enters the life cycle, the processes involved in its transport into the environment are complex and inadequately understood. For example, tritiated water (HTO) enters plants by leaf and root uptake and is converted to organically bound tritium (OBT) in exchangeable and non-exchangeable forms; however, the observed OBT/HTO ratios in crops exhibit large variability and contradict the current models for routine releases.Non-routine or spike releases of tritium further complicate the prediction of OBT formation.The experimental data for a short and intense atmospheric contamination of wheat are presented together with various models' predictions. The experimental data on wheat demonstrate that the OBT formation is a long process, it is dependent on receptor location and stack dynamics, there are differences between night and day releases, and the HTO dynamics in leaf and ear is a very important contributor to OBT formation.

Assimilation and transport of organic bound tritium in an irrigated pine forest

“…These authors collectively classify tritiated water in tissues as "tissue free water tritium" (TFWT). In this report due to the complexity of terminology, TFWT in environmental material will be referred to as HTO (as in Melintescu and Galeriu, 2017); OBT will be defined as NE-OBT or E-OBT when the analytical results support the assignment of NE-OBT and/or E-OBT; otherwise, "OBT" will collectively signify all types of OBT. 16 Tree rings have occupied considerable research interest due to their potential to be a metric of historic tritium releases.…”

“…In this report due to the complexity of terminology, TFWT in environmental material will be referred to as HTO (as in Melintescu and Galeriu, 2017); OBT will be defined as NE-OBT or E-OBT when the analytical results support the assignment of NE-OBT and/or E-OBT; otherwise, "OBT" will collectively signify all types of OBT. 16 Tree rings have occupied considerable research interest due to their potential to be a metric of historic tritium releases. 17,18,19,20,21 Cellulose-based tritium is thought to be a highly stable form of OBT within the tree and comparisons between cellulose tritium and wood tritium have produced similar results.…”

A Mini Review of Organically Bound Tritium in the Environment

“…It has been investigated that atmospheric tritium can be transferred to plants and subsequently converted into OBT making it available in the soil [5]. However, OBT concentration in soil is not well understood due to the limited data, limited methods of soil analysis for OBT and varying tritium values which are difficult to explain [6].…”

“…Also, a minute percent of natural inventory is due to neutron capture by 6 Li in the earth's crust similar to Li neutron capture processes in fission/fusion reactors. Tritium from past weapons testing persists in the atmosphere.…”

“…Its behavior in the atmosphere is like other radionuclides in terms of transport and dispersion, however, HTO is re-emitted by plants and soil into the air [4]. Geleriu et al [6], found out HT is not incorporated by plants due to its low dry deposition velocity. Further, it has a low dose per unit intake during inhalation therefore do not pose significant risk.…”