In-Situ Measurement of Fission Product Plateout in In-Pile Gas Loop Using Portable Ge(Li) Gamma-Ray Spectrometer

概要

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A nondestructive and quantitative method of measuring fission products deposited on inside surface of the primary duct has been developed. A portable Ge (Li) detector with a lead collimator was used for the external scanning of γ-rays emitted from the fission product plateout in the duct. Upon termination of the first irradiation cycle for the coated particle fuels in the high temperature in-pile gas loop OGL-1 installed in JMTR (Japan Material Testing Reactor), in-situ measurements of the plateout were carried out by the above method at different points in the primary system. Identified nuclides in the measured r-ray spectra were 131I, 133I, 95Zr, 95Nb, 137Cs, 110mAg, 99Mo, 140La, 60Co, 58Co, 54Mn, 51Cr, 65Zn, 59Fe, 122Sb, 124Sb, 182Ta, 181Hf, 22Na and 46Sc. The plateout densities of these nuclides were obtained using conversion coefficients determined by detector calibration and calculation, which were from 10-5 to 10-2 μCi/cm2. It was shown clearly by the experiment that the present measuring method using an in-situ r-ray spectrometer is useful in the studies of fission product plateout in the primary cooling system of a high temperature gas cooled reactor.