Stand Up of Uranium Capability for Swipe Analysis

Abstract

The INL has established the capability to process and analyze swipe samples to determine if the amount of U and Pu present on equipment and facilities are at the level typical for natural background, to quantify their isotopic composition and to determine if any off-normal isotopic ratio present in the sample is statistically relevant. A previous report detailed this capability for Pu and preliminarily for U; this report describes the measurements and analysis that were performed to demonstrate the INL capability for U. To establish that a piece of equipment is not contaminated with the element to be sampled, a fabric swipe is used to collect a sample of the materials present on the surface. The swipes are then processed and analyzed to determine if Pu and U are present on the sample at levels above what is accepted as natural background and, for the case of U, whether the isotope ratios deviate from the accepted natural background levels. Both the method applied for chemical processing of the swipes to remove and isolate the U and Pu and the method used to analyze the extracts influences the sensitivity and specificity. Over the years various methods have been developed for processingmore » and analyzing these types of samples; the gold standard for these measurements involves a lengthy and complex separation process followed by analysis using thermal ionization mass spectrometry (TIMS). However, this method is expensive and time consuming, thus driving a need for a less complicated and more efficient method that provides the necessary level of sensitivity and specificity. Advances in Inductively Coupled Plasma Mass Spectrometry (ICPMS) over the last decade have enabled analyses of U and Pu that rival that of TIMS. This, coupled with the potential for simplifying the extraction and separation process required for an ICPMS analysis, prompted the INL’s development of methods that provide the analysis of swipes in a timely and efficient manner. U is present in the blank swipe material at nanogram (~2 x 10-9 g) levels for a typical sample, a level easily detected with ICPMS. The abundance of the isotopes ranges over 4 orders of magnitude for the naturally occurring 234U, 235U and 238U and a goal was set to be able to detect the presence of 236U at 6 orders of magnitude lower than the 238U. The 236U measurement is particularly important because the presence of 236U is a strong indicator that the uranium as been in a nuclear reactor. To demonstrate these capabilities the following sample types were used: blank swipe material, blank process reagents, swipe material spiked with a natural abundance U isotope standard, swipe material spiked with an environmental standard (Columbia River sediment), and swipes taken at various locations within the processing laboratories and the INL environment. This report summarizes the method used to extract the U from the swipe material, the ICPMS analyses that demonstrate the limit of detection (LOD) and the limit of quantification (LOQ) for the U isotopes of interest, the precision of the measured isotope ratios and the dependence of precision on the quantity of U present, and the method proposed to determine if an off-normal ratio is statistically relevant.« less