Innovative alpha-radioactivity monitor for clearance level inspection based on ionized air transportation technology (1). Comparison with mass spectral analysis using uranium-attached samples

We have been developing an alpha-radioactivity monitor based on ionized air transportation technology (alpha clearance monitor) for efficiently performing clearance level inspection of massive amounts of uranium-contaminated waste. This paper is one of a series related to a method for quantitatively evaluating alpha radioactivity from a measured ion current value. Using a prototype alpha clearance monitor, we measured alpha radioactivities of uranium-attached components used in back-end facilities of the nuclear fuel cycle (uranium-attached samples). We compared the measured radioactivities with reference radioactivities by assaying the samples with an inductively coupled plasma mass spectrometer and the radioactivities measured with a scintillation survey meter. The radioactivities of curved plate samples measured with the prototype monitor were highly linear with respect to the reference radioactivities (a residual standard deviation of 8%). Absolute values of the radioactivities obtained with the prototype monitor and with the survey meter were about 40% and 50% smaller than the reference radioactivities, respectively. Measurements of complex-shaped samples indicated that, to measure diverse-shaped waste, it was necessary to classify the waste by shape and determine conversion coefficients corresponding to each group in advance, experimentally and theoretically. (author)