Experimental Study Investigating the Effects of Concrete Conditions on the Penetration Behaviors of Cs and Sr at Low Concentration Ranges

Abstract

To decommission of the Fukushima-Daiichi nuclear power plant after the reactor accident, it is important to estimate the distribution of radionuclide contamination in the concrete for key elements such as Cs and Sr. A reaction transport model will be developed for these calculations. However, for a realistic model, the behaviors of Cs and Sr penetration in concrete must be experimentally investigated. A part of the results of a MEXT project called "The Analysis of Radionuclide Contamination Mechanisms of Concrete and the Estimation of Contamination Distribution at the Fukushima Daiichi Nuclear Power Station" are presented in this technical report. From our penetration analyses, the behaviors of neither Cs nor Sr were affected by each other. Additionally, the apparent diffusion coefficients of Cs and Sr were not significantly affected by the concentration or the presence of clay in the mortars. The penetration depth of Sr was smaller than that of Cs, and fly ash blended cement increased the resistance to penetration compared with ordinary Portland cement. Carbonation in the mortar samples increased the adsorption of Cs especially. Sr interacted with cement hydrates more than with clays. In oven-dried mortars, under the condition of water suction, the presence of clay retarded Cs penetration but had no effect on Sr. When the mortars were carbonated and oven-dried, the interactions between the solid phase and Cs or Sr took hours at least to complete.

Cement and Concrete for Nuclear Waste Management

“…The further experiments and discussions on the effect of elemental concentration on penetration depth are found in another publication (Yamada et al 2021a).…”

“…Of the radionuclides contained in the pollution source and the structures to be decommissioned, Cs-137 and Sr-90 are key nuclides owing to their significant radiation effects and long half-lives, and predicting their migration is particularly vital in F1NPS decommissioning. Moreover, as the concrete at F1NPS is thought to be exposed to various environmental actions (including carbonation before and after the accident, leaching (mainly Ca) to stagnant water, retention of contaminated water with varying ion concentrations, and drying before the accident and after the removal of stagnant water) that affect specific areas Yamada et al 2021;, prediction of the future migration of radionuclides using numerical or other methods must also consider the changes in the condition of the concrete contamination due to interactions with the external environment.…”