Rare gas especially 41Ar released from research nuclear reactor and its in-situ measurement, (2)

The rare gas, especially 41Ar, which is released from the research nuclear reactor KUR, was measured and evaluated. The KUR is the light water-moderated reactor fueled with 90% enriched uranium, and has the thermal output of 5000 kW. The core is set in the aluminum tank with 2 m diameter and 8 m height. The experimental apparatuses consist of eight irradiation holes, one penetrating hole and two thermal neutron experimental facilities. The rare gas 41Ar is produced due to the irradiation of leaking neutrons to 40Ar in the air and 40Ar resolved in the core tank water. The calculated results of the 41Ar production are presented for each experimental apparatus. As for the diffusion of 41Ar released from the KUR in the atmosphere and the evaluation of exposure dose, the ventilation system of the KUR is shown with the flow diagram, and the actual measured rate of released 41Ar at the outlet of the stack is also presented with wind speed and direction data. The exposure dose at the point 400 m apart from the outlet was estimated, using the measured release data and meteorological data, by the superposing method. It is recognized that the values are larger than those by the meteorological guide line on safety analysis. The in-situ γ-spectrometry of the KUR was carried out, utilizing a NaI (Tl) detector, an ionization chamber and a Ge (Li) detector. The measured data and the evaluation of 41Ar utilizing a NaI (Tl) detector are presented here, including the temperature effect of the detector on the spectra, the count rate fluctuation in long time range and the continuously measured released irradiation dose of 41Ar. (Nakai, Y.)