Development of an Analytical Method for Estimating Three-Dimensional Distribution of Sediment-Associated Radiocesium at a Reservoir Bottom

Abstract

After the Fukushima Daiichi Nuclear Power Station accident, the distributions of sediment-associated radiocesium were investigated to evaluate the dispersion and accumulation of radiocesium in the reservoir field. To develop an analytical method for measuring the horizontal and vertical distributions of radiocesium on a wide scale, we obtained 253 gamma-ray spectra at the bottoms of 64 ponds in Fukushima during 2014-2016 by using a NaI(Tl) scintillation detector. For visualizing horizontal distribution, the correlation between detector counting rate and radiocesium concentration of the bottom sediment was confirmed. In estimating vertical distribution, the depth profile of sediment-associated radiocesium was found to be correlated to the intensities of scattered and photo peaks. Good agreement was observed between the results of in situ spectrometry and core sampling. These results indicate that the developed method is suitable for understanding the behavior of radiocesium and determining whether decontamination of reservoirs is required.

The ecological half-life of radiocesium in surficial bottom sediments of five ponds in Fukushima based on in situ measurements with plastic scintillation fibers

“…This study employed comparison with laboratorymeasured sediment activity concentration. Examples of studies that also employed this kind of calibration are 25,[36][37][38] and earlier PSF studies. 32,33 A total of 81 sediment cores were collected from the ponds at points coinciding with PSF measurement lines.…”