(359c) Tritium Distribution and Cycling on Savannah River Site

There are no standard doses for organically-bound tritium (OBT) therefore, this research aims to develop and enhance procedures for evaluating OBT levels for various plants and animal receptors. Samples were gathered and historical data were used for this investigation. Assays were performed using the freeze drying process and reverse transpiration respiration methods were used for assessing OBT concentrations. Thus, the research findings provide a basis for establishing OBT safe levels.

In recent years, there has been increased interest in the radiological hazards associated with ³H that has accompanied plans for expansion of nuclear power generation and public concerns associated with non-routine ³H releases at nuclear power facilities. For instance, non-routine spills of ³H that exceeded current the U.S. drinking water standard (DWS) have occurred at 46 of the 65 locations where commercial power plants have been operating.

Hence, the dose associated with ³H, a low energy beta emitter (0.0186 MeV), arises almost entirely from the ingestion pathway. Factors such as biological half-life and isotope discrimination can have a significant impact on ³H dose calculations in risk assessment scenarios. Therefore, research in the last decade has focused on improving our understanding of ³H assimilation in organic tissues, and the development of standardized procedures to measure the level of ³H associated with biological tissues, known as organically bound tritium (OBT).

Moreover, tritium (³H) is second only to radioactive carbon (¹⁴C) in terms of the collective radioactivity dose released from nuclear facilities. Tritium accounts for greater than 65% of the atmospheric and greater than 99% of the stream water environmental releases of radioactivity from the Savannah River Site (SRS). For example, multiple ³H sources exist on the SRS, including tritium-containing groundwater plumes that outcrop at various locations along the Fourmile Branch stream, a tributary to the Savannah River. Additionally, the SRS released 24,300 Ci of ³H to the atmosphere in 2014, most of which (>95%) were stack releases of water vapor from the tritium processing facility. Annual release levels from the processing facility depend on several factors, including annual production schedules, with an average annual release level of 31,460 Ci for the last ten years.

Consequently, the SRS provides an excellent setting for evaluating low-level tritium cycling dynamics in the environment, including the transformation of tritiated hydrogen (HT) and tritiated water (HTO) to OBT because there are multiple sites with documented histories of ³H exposure that provide excellent test cases. Thus, the current study will utilize SRS resources to develop and refine monitoring protocols for evaluating organically-bound tritium (OBT) levels in various plant and animal receptor species.