The deposition behavior of solid fission products has been studied. Experiments were made in an in-pile helium loop for gas flow with Reynolds number ranging from 1,300 to 13,000 at a gas temperature of about 500°C. The distributions of the fission products deposited along stainless steel tubes which had been exposed to the flow were obtained from r-ray spectra measured with a Ge(Li) detector. The nuclides of the deposited fission products can be classified into three groups according to the distribution patterns: (a) 95Zr-Nb, 9 7 Zr, 9 9Mo, I0 3 Ru, 132 Te, (b) 91Sr, 1 40 Ba-La, 141 Ce and (c) 131 ! and 133 !. Cesium-137 shows features of both groups (b) and (c). The deposition coefficients were obtained for the nuclides of group (a), which gave exponentially decreasing distributions, The effect of the flow rate (Reynolds number) on the deposition coefficients is discussed. For a stream with Reynolds number below 13,000, the deposition rate of metallic fission products is largely determined by the mass transfer in the boundary layer of the stream rather than by the adsorption on the surface.
Passive neutron assay of irradiated nuclear fuel has been investigated by calculations and experiments as a simple, complementary technique to the gamma assay. Fr6m the calculations we have found that the neutron emission arises mainly from the curium isotopes, the neutrons exhibit very good penetrability of the assemblies, and the neutron multiplication is not affected by the burnup. From the experiments on BWR and PWR assemblies, we hav £ found that the neutron emission rate is proportional to burnup raised to 3.4 power. Our investigations indicate that the passive neutron assay is a simple and useful technique to determine the consistency of burnups between assemblies.
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