Cold trapping of fission products in a stainless steel sodium loop.

概要

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The behavior of fission products in sodium system was studied using a cold trap installed in the Toshiba Fission Product Loop, which is a stainless steel inpile sodium loop. The fission products were generated within the liquid sodium by irradiating UO2 fuel under sodium convection. The cold trapping behavior of 95Zr, 95Nb, 132Te, 131I, 137Cs and 140La (140Ba) was examined by measuring the γ-rays in the cold trap and in the sodium dump tank by means of Ge(Li) detectors. Such fission product nuclides as 131I, 132Te and 137Cs were found to be reversively removed by the cold trap at lower temper-atures, with negligible hysteresis. The distribution coefficient K(cm) for the cold trap surface was found to be expressible by log K=(3.08±0.17)-(0.0112±0.0006)×T(°C) for 131I, and by log K=-(4.55±0.29)+(1830±140)×1/T(K) for 137Cs. The behavior of 131I and 137Cs during cold trapping can be explained clearly by adsorption model using these K values. While 95Zr, 95Nb, 103Ru and 140La(140Ba) also were detected in the cold trap, the efficacy of cold trapping is far lower for these nuclides than for 131I and 137Cs, and changing the cold trap temperature did not appear to have any appreciable effect on the cold trapping. Presence of 141Ce and 144Ce was not detectable in the cold trap, although small amounts of these nuclides were detected in the sodium dump tank.
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