Simultaneous Isotopic Analysis of U, Pu, and Am in Spent Nuclear Fuel by Resonance Ionization Mass Spectrometry

Abstract

Solid samples of spent nuclear fuel were analyzed for actinide isotopic composition by resonance ionization mass spectrometry. Isotopes of U, Pu, and Am were simultaneously quantified using a new method that removes and/or resolves the isobaric interferences at 238U/238Pu and 241Pu/241Am without sample preparation other than cutting and mounting small (∼10 μm) samples. Trends in burnup and neutron capture product distributions were correlated with the sampling positions inside the reactor. The results show the skin effect, in which the core and near-edge regions of a fuel pellet exhibit strong differences in actinide concentrations and isotope distributions due to differences in the neutron energy spectra between the pellet rim and the core. While no elemental concentration measurements were made, the ability to measure the 238Pu/239Pu ratio in the presence of a 7400× excess of 238U enabled an estimate of the enhancement in Pu concentration due to the skin effect at the rim of the pellet.

Simultaneous isotopic analysis of fission product Sr, Mo, and Ru in spent nuclear fuel particles by resonance ionization mass spectrometry

“…The laser parameters are shown in Table 1. To resolve the Mo and Ru isobars at m/z 100, the ionization of Ru was delayed with respect to Sr and Mo, in a manner previously described to separate Pu isobars from U and Am 6 .…”

“…were the same 10 μm UO 2 cubes we previously analyzed for U, Pu, and Am isotopic composition in an earlier study 6 , of which the vast majority of material still remained. The samples came from the Belgian Reactor No.…”

“…This results in greater production of fission products, and also in greater transmutation of those species due to neutron capture. In addition, elemental and isotopic compositions can change significantly within a few hundred micrometers of the edge of an individual fuel pellet due to the skin effect, in which epithermal neutrons are strongly captured by 238 U, resulting in copious production of Pu [5][6][7][8] . This in turn results in changes in the fission product distribution at the pellet edge because fission products of 239 Pu have a different elemental and isotopic distribution than those of 235 U.…”

“…Sample cutting and mounting is described in detail elsewhere 6,8 . Two sets of three 10 μm cubes from two different fuel pellets (originally 8 cm in diameter) within the same fuel rod were cut using a focused ion beam…”

Rapid and Precise Uranium Isotopic Screening in Natural Water Using Bis(2-ethylhexyl)phosphoric Acid-Modified Membranes

“…Most of the natural water samples contain detectable amounts of uranium: the average concentration in seawater is around 3 ppb, whereas groundwater may contain varying concentrations of uranium, ranging from less than 0.1 ppt to several ppm. , Because of the associated toxicity, uranium assay in natural water samples is of prime importance, and highly sensitive methods are required for monitoring trace or ultra-trace levels of uranium in water samples which are collected for prospective purposes. Although various instrumental techniques including spectrophotometry, fluorimetry, radiometry, atomic absorption/emission spectrometry, and XRF analyses are available for the determination of uranium, − mass spectrometric techniques, especially thermal ionization mass spectrometry (TIMS), inductively coupled plasma mass spectrometry (ICP-MS), and accelerator mass spectrometry (AMS) are known to provide the most accurate and precise data for uranium measurement. − …”