In Vitro Dissolution Tests of Plutonium and Americium Containing Contamination Originating From ZPPR Fuel Plates

Abstract

Assessing the extent of internal dose is of concern whenever workers are exposed to airborne radionuclides or other contaminants. Internal dose determinations depend upon a reasonable estimate of the expected biological half-life of the contaminants in the respiratory tract. One issue with refractory elements is determining the dissolution rate of the element. Actinides such as plutonium (Pu) and Americium (Am) tend to be very refractory and can have biological half-lives of tens of years. In the event of an exposure, the dissolution rates of the radionuclides of interest needs to be assessed in order to assign the proper internal dose estimates. During the November 2011 incident at the Idaho National Laboratory (INL) involving a ZPPR fuel plate, air filters in a constant air monitor (CAM) and a giraffe filter apparatus captured airborne particulate matter. These filters were used in dissolution rate experiments to determine the apparent dissolution half-life of Pu and Am in simulated biological fluids. This report describes these experiments and the results. The dissolution rates were found to follow a three term exponential decay equation. Differences were noted depending upon the nature of the biological fluid simulant. Overall, greater than 95% of the Pu and 93% of the Am were in a very slow dissolving component with dissolution half-lives of over 10 years.

Take a Swipe at Actinide Bioavailability: Application of a New In Vitro Method

“…5a, Am is transferred more rapidly than Pu. This is in agreement with other data from accident or experimental scenarios using material collected on aerosol filters (Rateau-Matton 2004;Bauer et al 2012;Miller et al 2016). For comparison, and to underline the usefulness of the assay for actinide transportability, only the data for transferred Pu activity from the swipe are shown in Fig.…”

“…The present experiments with DTPA were carried out specifically to investigate whether addition of this chelator would stimulate transfer in the simple NaCl/KCl solution. The use of DTPA in dissolution tests using material obtained from aerosols collected from nuclear industrial or accident settings has almost exclusively been confined to the addition of this chelator to the SUF (serum ultrafiltrate simulant) dissolution media to (1) prevent adherence of actinides to glassware/plastic containers or (2) to prevent precipitation by phosphate ions so keeping the actinide in solution (Eidson and Mewhinney 1983;Cheng et al 2004;Rateau-Matton et al 2004;Bauer et al 2012). One interesting comment about the presence of DTPA in the dissolution media (serum ultrafiltrate SUF medium) is that this "could simulate individuals treated with DTPA" (Bauer et al 2012).…”

“…To date very few dissolution or transportability data are available for radionuclides obtained from swipe test filters (Bauer et al 2012;Miller et al 2016). This has been attributed to a more even distribution of activity on aerosol filters as compared to that picked up by a swipe test (Bauer et al 2012).…”

“…This approach allows the classification of actinide behavior by the so-called transportable fractions (Stather et al 1975;Khokhryakov et al 1998;Aladova et al 2007). To date very few dissolution or transportability data are available for radionuclides obtained from swipe test filters (Bauer et al 2012;Miller et al 2016). This has been attributed to a more even distribution of activity on aerosol filters as compared to that picked up by a swipe test (Bauer et al 2012).…”

“…The purpose of the present study was to dissolve the filter or the filter coating in order to maximize activity recovered on the swipe filter to reduce the problem of uneven activity distribution (Bauer et al 2012). This approach is coherent with proposed treatment for air monitoring filters whereby the entire air particulate filter would be converted to a homogeneous form, such as a digestate using various aggressive chemical means (US EPA 2009).…”