Fuel isotope measurement

While quantifying the sources and sinks of CH4 has been difficult, isotopic measurements of l3CH4 and CH,D4, x are promising. Various sources have characteristic isotopic signatures e.g., as mentioned previously, fossil fuel derived CH4 is depleted in l4C (Lowe et al., 1988, 1994 Wahlen et al., 1989). The sinks of CH4, e.g., reaction with OH, reaction with Cl, and uptake by soil bacteria, also exhibit kinetic isotope effects and these have been used to probe the causes of the observed recent changes in CH4 growth rates (e.g., see Gupta et al., 1996, 1997). Measurements of isotopic... 

Worldwide acceptance of analytical results requires reliable, traceable, and comparable measurements. A key property of a reliable result is its traceability to a stated reference. Traceability basically means that a laboratory knows what is being measured and how accurately it is measured. It is also an important parameter where comparability of results is concerned and is usually achieved by linking the individual result of chemical measurements to a commonly accepted reference or standard. The result can therefore be compared through its relation to that reference or standard. Every link in the traceability chain must be based on the comparison of an unknown value with a known value. The stated reference might be an International System of unit (SI) or a conventional reference scale such as the pH scale, the delta scale for isotopic measurements, or the octane number scale for petroleum fuel. In order to be able to state the uncertainty of the measurement result, the uncertainty of the value assigned to that standard must be known. Therefore a traceability chain should be designed and then demonstrated using the value of the respective standard with its uncertainty.11... 

Sampling, Extraction and Isotope Measurement of Fuel Oxygenates. 104... 

Betti (1996) and co-workers used GD-MS for sample screening in isotopic measurements of zirconium, silicon, lithium, boron, uranium, and plutonium in nuclear samples. The results obtained from the GD-MS were compared with results from thermal ionization mass spectrometry (TIMS). For boron and lithium concentrations from //g/g to ng/g levels, isotopic ratios determined by GD-MS were comparable to TIMS in terms of accuracy and precision. Uranium isotopic ratios determined by GD-MS were also in good agreement with values measured by TIMS with regards to accuracy. Chartier et al. (1999) used GD-MS to analyze erbium and uranium in molybdenum-uranium fuel samples. The ratio of 166Er to 238U was then compared to numbers determined by thermal ionization mass spectrometry. The ratio of erbium to uranium was accurate to within 3% of the number determined by TIMS. 

Based on the data presented here and in the subsequent volumes of this report, the methodology employed in the generation of spent fuel isotopics and the criticality calculations using those isotopes is valid for bumup credit analyses. Further validation of the SCALE S AS2H sequence for generating spent fuel isotopics has been performed by comparison of calculated results with measured spent fuel chemical assay data. The criticality methods of CSAS/KENO V.a are validated against LWR-type fresh fuel critical experiments (both UO2 and MOX) in ref 19. 

The existence of some of these databases is acknowledged publicly. For example, as mentioned earlier, LLNL has a database that includes 1800 samples of yellow cake (Kristo and Dirnet 2013), and the Nuclear Forensics Analysis Center (NFAC) in Savannah River National Laboratory (SRNL) provides support for the FBFs Radiological Evidence Examination Facility (REEF) (Nichols 2011). The latter contains a database of spent nuclear fuel from several reactors in the United States and other countries. An example of the processing of interdicted nuclear material at REEF uses traditional forensics combined with nuclear forensics to determine the origin and make attribution. The results of the isotopic measurements are compared to known compositions in the database based on reactor physics models (see flowchart in Figure 5.19). 

The concentrations of the radionuclides originating from both the uranium concentration of the core and defective fuels are measured regularly. Iodine and cesium nuclides are measured by gamma spectroscopy. Occasionally, alpha and beta spec-trometric analyses are performed to determine transuranium and strontium isotopes, respectively. 

A PWR can operate steadily for periods of a year or two without refueling. Uranium-235 is consumed through neutron irradiation uranium-238 is converted into plutonium-239 and higher mass isotopes. The usual measure of fuel bumup is the specific thermal energy release. A typical figure for PWR fuel is 33,000 MWd/t. Spent fuel contains a variety of radionucHdes (50) ... 

Light-silver-colored element generated from a plutonium isotope (241Pu) by beta decay. Never detected in nature. Chemically similar to Europium. A few tons have been produced throughout the world through regeneration of fuel rods. Americium is a good source of alpha rays. Hence it is suitable to measure thicknesses, as a detector in smoke alarms, and for the activation analysis of the tiniest amounts of substances. 

The basic assumption of constant atmospheric X4C activity in radiocarbon dating is not strictly valid. We now have a record of the fluctuation of atmospheric 14C variations for the last 8,400 years B.P. obtained by measurement of the isotopes of carbon in dendrochron-ologically dated wood. Prior to contamination of atmospheric 14C activity by fossil fuel combustion and nuclear technology in the 20th century, the first-order secular variation can be closely approximated by a sine curve with a period of 10,600 years and an amplitude of ... 

After administration of C-labeUed hydrogencarbonate, the CO2 rapidly equilibrates with the CO2 in the whole body. Since the urea produced in the hver is in isotopic equihbrium with the CO2 produced from the oxidation of fuels, changes in the radioactivity in urea in the urine can be used to measure the rate of CO2 production and hence the rate of fuel oxidation. An advantage of the technique is that it is accurate over relatively short periods (e.g. 24 hours). 

Quantitative studies of energy metabolism and fuel utilisation in very prolonged physical activity were performed by Mike Stroud during his Antarctic expedition with Ranulph Fiennes in 1992. One part of the study was measurement of energy expenditure by the dual isotope techniques (Chapter 2). Calculated over the whole expedition, the average daily energy expenditure of Stroud and Fiennes was 29 MJ but on particularly arduous days it increased to... 

The isotope dilution results in Table II are on fuel source samples obtained from NBS which were considered homogeneous. The results in Table III are from the sampling points indicated in Figure 4. These summarized results are mostly by the SSMS general scan technique which has an estimated accuracy of better than 50%. The isotope dilution measurements are limited by the emulsion detector to 3-5%. The results are in grams of metal flow per minute. The mass balance for the various elements was computed by the following equations ... 

An alternative to the above described approaches is the radiocarbon method that allows a distinction of contemporary carbon (from biogenic emissions and combustion of biomass) and carbon from combustion of fossil fuels in particulate carbonaceous matter [15, 41,42]. In contrast to fossil fuels where the 14C isotope is completely depleted, CM emitted from WB shows a contemporary radiocarbon level. Radiocarbon measurements are often combined with measurements of complementary source specific tracers (macro-tracer) for additional information of source impacts [14, 43, 44]. 

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