TY - JOUR
T1 - Effect of carbonate on the migration behavior of neptunium in compacted bentonite
AU - Idemitsu, Kazuya
AU - Arimitsu, Hajime
AU - Hirakawa, Masayuki
AU - Yoshida, Keisuke
AU - Inagaki, Yaohiro
AU - Arima, Tatsumi
N1 - Funding Information:
ICP-MS/MS measurements of Np were performed at the International Research Center for Nuclear Materials Science, Institute of Materials Research, Tohoku University.
Publisher Copyright:
© 2022, The Author(s), under exclusive licence to The Materials Research Society.
PY - 2022/3
Y1 - 2022/3
N2 - The diffusion behavior of neptunium (Np) in compacted bentonite with bicarbonate was investigated at various NaHCO3 concentrations. Typical Japanese purified Na-bentonite, Kunipia-F, which contains approximately 95 wt % montmorillonite, was used. The Na-bentonite was compacted with a jig into cylindrical pellets 10 mm in diameter and 10 mm high with dry densities of 0.7 to 1.4 Mg/m3. Each pellet was inserted into an acrylic resin column and saturated with carbonated water containing 0.25 to 1.0 M NaHCO3 for more than 1 month. The bottom interface of the compacted bentonite saturated with carbonated water was spiked with 5 µL of tracer solution containing 10 ppb of Np in 0.1 M HNO3, and the diffusion periods were in the range of 2.7 years. After the diffusion period, the bentonite specimen was pushed out of the column and cut into 0.3- to 1.0-mm-thick slices. Each slice was submerged in 1 N HNO3 to extract the tracer ion and the liquid phase was separated by centrifugation. The supernatant was analyzed for Np by inductively coupled plasma-tandem mass spectrometry. The Np concentration profile increased over time and reached the final profile in 2 years. The final profile showed logarithmic decay with a decay or filtration coefficient of 3.2 ± 0.1 mm−1. This final profile indicated that Np could diffuse but would be filtered by the bentonite medium. Np may exist as carbonate complexes, which could be larger than the pores constituting the diffusion path.
AB - The diffusion behavior of neptunium (Np) in compacted bentonite with bicarbonate was investigated at various NaHCO3 concentrations. Typical Japanese purified Na-bentonite, Kunipia-F, which contains approximately 95 wt % montmorillonite, was used. The Na-bentonite was compacted with a jig into cylindrical pellets 10 mm in diameter and 10 mm high with dry densities of 0.7 to 1.4 Mg/m3. Each pellet was inserted into an acrylic resin column and saturated with carbonated water containing 0.25 to 1.0 M NaHCO3 for more than 1 month. The bottom interface of the compacted bentonite saturated with carbonated water was spiked with 5 µL of tracer solution containing 10 ppb of Np in 0.1 M HNO3, and the diffusion periods were in the range of 2.7 years. After the diffusion period, the bentonite specimen was pushed out of the column and cut into 0.3- to 1.0-mm-thick slices. Each slice was submerged in 1 N HNO3 to extract the tracer ion and the liquid phase was separated by centrifugation. The supernatant was analyzed for Np by inductively coupled plasma-tandem mass spectrometry. The Np concentration profile increased over time and reached the final profile in 2 years. The final profile showed logarithmic decay with a decay or filtration coefficient of 3.2 ± 0.1 mm−1. This final profile indicated that Np could diffuse but would be filtered by the bentonite medium. Np may exist as carbonate complexes, which could be larger than the pores constituting the diffusion path.
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U2 - 10.1557/s43580-022-00210-9
DO - 10.1557/s43580-022-00210-9
M3 - Article
AN - SCOPUS:85123908331
SN - 2059-8521
VL - 7
SP - 140
EP - 143
JO - MRS Advances
JF - MRS Advances
IS - 7-8
ER -