Ji, Y.-Y.; Joung, S.; Min, B.I., and Suh, K.-S., 2021. Development and performance of underwater gamma-ray spectrometry for riverbed monitoring. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 330–334. Coconut Creek (Florida), ISSN 0749-0208.

The atmospheric release and fallouts of radionuclides have produced the radioactive contamination over wide area in the accident at the Fukushima Daiichi nuclear power plant (FDNPP). They still affect the environment around the Fukushima Prefecture, such as resident area, fields, mountainous area, river and stream, and reservoir. In JAEA (Japan Atomic Energy Agency), diverse monitoring platforms have been developing and successfully applying to the assessment of environmental radiation and deposited nuclides. Especially, there are about 3,700 irrigation reservoirs around the Fukushima Prefecture, which can be effected from direct fallouts in reservoirs as well as dispersions of the contamination in the other sites, depending on weather conditions. Underwater survey system is an important tool to assess the radioactive contamination in the river, stream and reservoir, including the bottom sediments. In this study, underwater gamma-ray spectrometry, named as MARK-U1, was developed to rapidly estimate the underwater radioactivity for the emergency preparedness, according to the lesson learned from the nuclear accident of FDNPP. A 3”ϕx3” NaI(Tl) detector is equipped in this underwater system and the lateral shielding around a detector was also designed using lead with a thickness of 1 cm to confine the field of view. Finally, its performance test was conducted by evaluating the natural radioactivity of 214Bi, 208Tl, and 40K in the riverbed of reservoir.

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