Radioactivity of fission product and heavy nuclides deposited on soil in Fukushima Dai-Ichi Nuclear Power Plant accident

Based on periodically performed radioactivity measurements on soil samples in the site of Fukushima Dai-Ichi Nuclear Power Station, activity ratios to Cs-137 of fission product and heavy nuclides were obtained for Sr, Nb, Mo, Tc, Ru, Ag, Te, I, Ba, La, Pu, Am, and Cm isotopes. By exponentially fitting or averaging, the activity ratios at the core shutdown were estimated. Using correlations of activity ratios of Cs-134 to Cs-137, and Pu-238 to the sum of Pu-239 and Pu-240 against fuel burnup, burnup of the fuel sourcing the deposited activity of the soil was estimated. The activity ratios to Cs-137 of each nuclide on the deposited activity were divided by those calculated on the fuel at the shutdown to obtain the deposited activity fraction of each nuclide as a relative value to Cs-137, which also corresponds to the deposited fraction of each element as a relative value to Cs. The obtained deposited fractions relative to Cs are the orders of 10(-4) to 10(-2) for Sr, 10(-5) to 10(-3) for Nb, 10(-2) to 10(-1) for Mo, 1 to 10 for I, 10(-3) to 10(-2) for Ba, 10(-2) for La, 10(-6) to 10(-3) for Pu, 10(-6) to 10(-4) for Am, and 10(-7) to 10(-5) for Cm. The deposited fractions for Tc, Ag, and Te were not estimated due to the lack of the calculated inventories in the fuel for the relevant measured radioactive nuclides.