Use of mathematical simulation to extend the scope of applicability for the procedure to measure the mass of 235u in solid radioactive waste
Determination of the mass (activity) of 235U in solid radioactive waste by gamma-spectroscopic method requires the use of the known dependence of absolute efficiency on energy and space for particular conditions of measurement. The In Situ Object Counting System (ISOCS) eliminates the need for laborious and time-consuming graduation measurements using reference standards to obtain the absolute efficiency curve since the so-called characterized detector is used which has a file with a set of efficiencies for different measurement geometries.
In many cases, a set of reference standards with parameters exceeding the range of the 235U mass measurement in the variation ranges of influencing factors, including density, nonuniformity, isotopic composition, geometry, etc., is highly expensive and, most often, impossible to create. Proceeding from this, a computational and experimental approach was adopted using the results obtained by Monte Carlo method based on the MCNP code with variation of the key influencing parameters within broad intervals.
Calculations were performed for detector-recorded spectra of gamma-quanta from a cask that contained waste differing in the density of the cask content (the density was calculated with regard for the uranium contained in waste) – in a range of 0.016 to 1 g/cm3, in the mass of uranium in the waste – in a range of 0.64 g to 2 kg, and in the matrix material (graphite, cellulose, quartz, cellulose with 20% of iron powder).
Boundaries have been defined for the applicability of the developed procedure to measure uranium-containing waste in terms of the material matrix (~ 2.2%) and its density (~ 10%), and the contribution of the uncertainty of the cask-contained uranium mass to the obtained result has been estimated (5% for dense matrices, 10% for porous matrices).
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nondestructive analysis of nuclear materials solid radioactive waste uranium mass gamma-spectrometry ISOCS system absolute efficiency curve Monte Carlo method MCNP code measurement procedure measurement procedure range