Studies on Movement of ⁹⁰Sr, ¹⁰⁶Ru, ¹³⁷Cs, ¹⁴⁴Ce in Environment, connected with the City Water Supply

Abstract

In order to examine radioecologically behavior of radionuclides in environment of water supply, levels of radionuclides in the soil, raw water from river and its suspension, river bottom sediment, and water supplied for drinking were quantitatively investigated, and then various aspects on transfer of radionuclides in the land, river, and water works were hydrometeorologically analyzed. On three basins, Agano, Edo, and Yodo River, movements of ¹⁰⁶Ru, ¹³⁷Cs and ¹⁴⁴Ce were derived from data of ⁹⁰Sr. ⁹⁰Sr was removable compared with other radionuclides in various samples. The following equations were established by the regression analysis between "ratio on each of the radionuclides to ⁹⁰Sr" in soil (Rd) and that of river bottom sediment (RBS), between Rd and that in river water with suspension (R[W+S]), and between radionuclides concentration in the river water (C ; pCi/100 liter) and weight of the river suspension (S ; gr. of ash/100 liter). [numerical formula] Coefficients a₁ and b₁ were 8.46-1.35 and 2.35-0.62 for ¹⁰⁶Ru, 4.14-0.989 and 2.58-0.31 for ¹⁴⁴Ce, and 2.80-0.836 and 3.49-0.879 for ¹³⁷Cs, respectively. The a₂ and b₂ for ¹³⁷Cs were 0.085-0.055 and 0.26-0.19. The a₃ and b₃ in the Agano River were 0.00229 and 1.49 for ⁹⁰Sr, and 0.0229 and 0.64 for ¹³⁷Cs. These data indicated that the degree of deposition to the soil, adsorption, and absorption to the river bottom of ¹⁰⁶Ru, ¹³⁷Cs and ¹⁴⁴Ce are higher than those of ⁹⁰Sr, in the following order : ¹⁰⁶Ru>¹⁴⁴Ce>¹³⁷Cs>⁹⁰Sr. As for the pathway of contamination, part of ⁹⁰Sr is soluble and most of ¹⁰⁶Ru, ¹³⁷Cs and ¹⁴⁴Ce is insoluble in the river, and a part of these radionuclides exists in the river suspension and considerable amounts of ¹⁰⁶Ru, ¹³⁷Cs and ¹⁴⁴Ce are precipitated on the river bottom. It was observed on the decontamination rates (DR%) of radionuclides in the water works that the greater the content of the suspension increases, the higher DR become. The correlation of DR and S was shown by the following equation. [numerical formula] The coefficient a₄ was 0.0462 for ¹³⁷Cs in the Niitsu City water works, Agano River basin. During 1962 to 1969, DR in the three water works were observed as 50% for ¹⁰⁶Ru, 48% for ¹⁴⁴Ce, 31% for ¹³⁷Cs, and 15% for ⁹⁰Sr in average value.