Depleted uranium isotope content

The nuclear fuel used in almost all commercial reactors is based on uranium in the form of UO, either enriched so that the content has been increased to a few percent, or — less commonly — with the natural 0.7 % abimdance of the fissile isotope Some power reactors also use fuel containing depleted uranium ( 0.3% " U) in which plutomum is bred and/or Pu mixed with as a replacement for ("mixed oxide fuel"). Th, in which fissile is bred, has also been used in a few cases. 

The experience of the analyst needs to be taken into account when interpreting the results. One may interpret a corrected isotope ratio that is within one standard deviation of the natural uranium isotopic signature as consistent with natural uranium. Two standard deviations may be the preference of others. In our experience, the majority of natural uranium-containing samples produced results that were within one standard deviation of the natural 23Su/238 j isotope j-gtio since the level of confidence in the results has often been a critical factor, we have typically repeated analysis of the small minority of samples that have had ratio results that have fallen below one deviation from natural uranium to eliminate doubt as to whether a small amount of depleted uranium may have contributed to the total uranium content. More often than not, results that were within two standard deviations of the natural uranium isotope ratio were very low-concentration samples. 

For further assurance, a separate 20 ng/L uranium spike was prepared in urine and analyzed in every run. This standard was prepared with depleted uranium content of less than 3% as described in the QC and Standard Preparation section, such that the isotope ratio was calculated to be 0.00710. The mean results of analysis of this standard in five separate analytical runs over a 16-month period were isotope ratios of 0.00711,0.00709,0.00715,0.00706, and 0.00713 (0.007108 + 0.00003). 

Natural (NU or Unat), depleted (DU), low-enriched (LEU), and high-enriched (HEU) uranium the content of the only natural fissile isotope, U—is an important feature of uranium applications and value. In natural uranium, the content of this isotope is 0.720 atom % or 0.711 wt% (Table 1.2). LEU is defined as U content between 0.720% and just below 20%, while HEU encompasses uranium with U content above 20%. The 20% borderline between LEU and HEU is artificial and was based on the assumption that nuclear weapons with 20% or less U would not be efficient. The waste, or tails, of the isotope enrichment process contains less U than in natural uranium and is defined as depleted uranium (DU). The U-235 content in DU is usually in the range of 0.2%-0.4%. DU is used mainly in armor piecing ammunition, in reactive armor of tanks, in radiation shielding, and is also used as ballast weights in aircraft. In addition, many of the commercially available fine chemicals of uranium compounds are based on the tails of uranium-enrichment facilities and usually labeled as not of natural isotope composition. 

U) that can be used for isotope dilution mass spectrometry (IDMS), dual standards (233U/236U) for correction of instrumental isotopic mass bias, uranium-plutonium double spike mixtures and U/ Pu), and a series standards with certified content ranging from depleted uranium to LEU at 4.52%. In addition, there... 

During the initial stages of development, it was assumed that the isotopic composition of plutonium in the fresh fuel would correspond to reactor-grade plutonium extracted from the cooled spent fuel of a typical light water reactor (e.g., from a 900 MW(e) PWR fuel irradiated up to a bum-up of 33 MW-d/kg U, reprocessed after 10 years of cooling) and loaded in the RBEC-M reactor in two years. The isotopic composition of uranium corresponds to depleted uranium with a content of 0.1 weight %... 

Because of the possibility of natural depletion of U and because of the availability of tails from isotope separation plants that might become mixed with natural uranium, it is important that natural uranium feed for an isotope separation plant be analyzed for its U content. 

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