Continuous measurement of radionuclide distribution off Fukushima using a towed sea-bed gamma ray spectrometer

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• 作者：Blair Thornton ; Seiki Ohnishi ; Tamaki Ura ; Naoteru Odano ; Tsuneo Fujita
• 关键词：Fukushima Dai-ichi Nuclear Power Plant ; Radiation ; Marine sediments ; Towed gamma ray spectrometer
• 刊名：Deep Sea Research Part I: Oceanographic Research Papers
• 出版年：2013
• 出版时间：September, 2013
• 年：2013
• 卷：79
• 期：Complete
• 页码：10-19
• 全文大小：3550 K

文摘

Instrumentation and data processing methods to continuously map the distribution of radionuclides on the seafloor have been developed and applied to survey radioactive discharge from the Fukushima Dai-ichi Nuclear Power Plant following the M9.0 earthquake and tsunami that struck the east coast of Japan on March 11 2011. The instrument consists of a flexible rubber hose with an integrated gamma ray spectrometer that measures the full gamma spectrum between 0.1 and 1.8 MeV while being towed along the seafloor by a ship. The data processing methods described allow for quantification of ¹³⁷Cs and ¹³⁴Cs concentration in marine sediments, and a technique has been developed to optimize the spatial resolution of the measurements for each radioactive species for a given level of statistical uncertainty. The system was deployed during August and November 2012 to measure the distribution of radionuclides along three transects within an 80 km radius of the plant. Increased levels of ¹³⁷Cs and ¹³⁴Cs were recorded and their distributions mapped continuously over distances of 1.6, 12.5 and 22 km respectively. The levels of ¹³⁷Cs and ¹³⁴Cs were found to vary significantly with location. The in situ measurements show good agreement with laboratory analyzed samples obtained during the surveys. The results demonstrate that the instrument and data processing techniques described enable high resolution, quantitative measurements of ¹³⁷Cs and ¹³⁴Cs in marine sediments, and provide an effective solution for rapid, low cost monitoring of radioactive material on the seafloor.