No abstract

A range of performance assessments have indicated that the long-lived activation product (36)Cl will be among the more significant contributors to dose following release to the biosphere from deep or near-surface repositories for radioactive wastes. Described here are results of a BIOPROTA model intercomparison study, investigating dose assessment uncertainties and variability on the basis of six (36)Cl models from three countries. The models share a compartmental approach with transfers between compartments handled on the basis of empirical transfer factors (IMARC, ERB2A, Aquabios), on the basis of defined specific activities (AquaCl36, SA_36Cl), or on a combination of these methods (MTA_Cl36). The dose estimates that these models produce for a consensus well-water irrigation scenario, as well as the effect of altering certain critical assumptions, are reported, and the causes of variation examined. For the scenario considered, the calculated doses are within a factor of 15 of each other. Major differences were attributable to the data used for stable Cl concentrations and (36)Cl transfer parameter values, both typically site-specific parameters. Additional critical assumptions were studied such as the impact of stable chloride in the diet on dose coefficients, the effect of irrigating pasture with contaminated water on (36)Cl concentrations in animal products, and the explicit consideration of foliar uptake.

Abstract. Scaling factors, used to predict radionuclide uptake as a function of mass, have tremendous potential to provide a more transparent approach to risk assessment. Although the historical literature might seem to offer a wealth of data for the purposes of testing these scaling relationships, a more defensible alternative may be to conduct new site-specific data collection efforts. Trace element analysis was conducted on 16 plant species from a single location in Oregon. Results for ten elements and six species exhibit mass dependence on trace-element uptake. Transfer factors calculated for several elements spanned only an order of magnitude across all plant species. Conversely, radionuclide data taken from the open literature was inconclusive in the analysis for mass effects.

Abstract. There has been recent interest in the transport and fate of 36Cl in the environment. The IUR task force on Radioecology and Waste has identified the need for further uptake data. Reported here are the results of a 6-month study of the uptake in ryegrass of 36Cl in five lysimeters. Lysimeters were deployed in a greenhouse from November 2007 to May 2008. Except for an initial watering, exterior reservoirs connected to the base of the lysimeters maintained the water tables at a constant level with a solution containing 36Cl in a chloride form. A destructive analysis of the lysimeters showed that between 75 and 80% of 36Cl added to the system during the course of the experiments was taken up into the plant tissue. The quantities of 36Cl found in weekly soil tests and a simple mass balance provide supporting evidence for the significant bioavailability of 36Cl in a chloride form.

Abstract. NCRP report No.160 states medical exposures constituted nearly half of the total radiation exposure of the US population from all sources in 2006 [1]. Part of this increase in exposure is due to the rise in nuclear medicine procedures. With this observed growth in medical radionuclide usage there is an increase in the activity being released into wastewater after medical procedures. Often medical radionuclides are not 100% radionuclide pure, but meet a certain standard of purity. Of particular interest are the longer lived impurities associated with these medical radionuclides. The longer lived impurities have a higher chance of reaching the environment. The goal of this study is to identify radionuclide impurities associated with some of the more common radiopharmaceuticals Tc-99m and I-131, locate and quantify the levels of these impurities in municipal wastewater, and make a determination as to the potential long-term impact.