Distribution and Retention of ¹³⁷Cs in Sediments at the Hanford Site, Washington

Abstract

137Cesium and other contaminants have leaked from single-shell storage tanks (SSTs) into coarse-textured, relatively unweathered unconsolidated sediments. Contaminated sediments were retrieved from beneath a leaky SST to investigate the distribution of adsorbed 137Cs+ across different sediment size fractions. All fractions contained mica (biotite, muscovite, vermiculatized biotite), quartz, and plagioclase along with smectite and kaolinite in the clay-size fraction. A phosphor-plate autoradiograph method was used to identify particular sediment particles responsible for retaining 137Cs+. The Cs-bearing particles were found to be individual mica flakes or agglomerated smectite, mica, quartz, and plagioclase. Of these, only the micaceous component was capable of sorbing Cs+ strongly. Sorbed 137Cs+ could not be significantly removed from sediments by leaching with dithionite citrate buffer or KOH, but a fraction of the sorbed 137Cs+ (5-22%) was desorbable with solutions containing an excess of Rb+. The small amount of 137Cs+ that might be mobilized by migrating fluids in the future would likely sorb to nearby micaceous clasts in downgradient sediments.

Cs–sorption in weathered biotite from Fukushima granitic soil

“…The major radioactive isotope is 137 Cs, which has a longer half-life of~30 years than other anthropogenic radioactive isotopes such as 131 I (~8 days) and 134 Cs (~2 years). Numerous previous studies have proposed that clay minerals, especially weathered micaceous minerals constitute favorable sorption and fixation sites for Cs (e.g., Wahlberg and Fishman, 1962;Sawhney, 1972;Francis and Brinkley, 1976;Komarneni and Roy, 1988;Cornell, 1993;McKinley et al, 2001). Because the contaminated areas in Fukushima are mainly covered with weathered granite soil (called 'masa' in Japanese), weathered biotite is abundant.…”

A Discussion of Reversible and Irreversible Sorption for Sr, Cs, Np, and Pu

“…The exchange reactions can then be used to write a mass action equation for binary Cs-M exchange: Assessing the reversibility of Cs exchange is crucial for predicting its mobility. Measurements of Cs desorption from contaminated S-SX sediments at Hanford (41-09-39 and SX-108) suggest partial fixation of the sorbed Cs pool (McKinley et al, 2001). The reversibility of Cs exchange was examined by following the sorption stage with a desorption stage using an identical injection solution but without Cs ( Figure 5).…”

Geological Disposal of Nuclear Waste: Fate and Transport of Radioactive Materials

“…A huge amount of radioactive wastes have been stored in liquid and solid form from nuclear electricity/bomb production plants from several decades at different locations in the world. For example, the Hanford Site is a most decommissioned nuclear production complex on the Columbia River in the U.S. state of Washington, operated by the United States federal government as shown in fig 1 [21,28,50]. Hanford was the first large-scale plutonium production reactor in the world.…”

“…Recently, several countries in Europe, America and Asia are investigating sites that would be technically and publicly acceptable for deep geological storage of nuclear wastes. For example, a well designed geological storage of nuclear waste from hospital and research station is in operation at relatively shallow level in Sweden and a permanent nuclear repository site is planning to be built at deep subsurface system for nuclear spent fuel in Sweden in order to accommodate the stored and running nuclear waste from ten operating nuclear reactors which produce about 40 percent of Sweden's electricity (In Sweden, the responsibility for nuclear waste management has been [50]. transferred in 1977 from the government to the nuclear industry, requiring reactor operators to present an acceptable plan for waste management with a so called absolute safety to obtain an operating license.…”

“…It has led to re-thinking of researcher and responsible organizations for protecting their underground stored radioactive wastes and implementing multi-protection mechanisms for deep geological storage of the hazardous radioactive wastes. In the event of accidental release/leakage of radioactive materials into the subsurface system, there is a possibility of its migration with the soil-pore water flow and to be transported to the surface and groundwater bodies as shown in fig 1 [21,50,76]. Furthermore, some radioactive contaminants do not move through soil pores in dissolved form but rather attach strongly to fine soil particles (1 nm to 1 µm size, commonly called "colloid").…”