Structural investigation of thorium in molten lithium–calcium fluoride mixtures for salt treatment process in molten salt reactor

• Published in: Progress in nuclear energy (New series) Vol. 53; no. 7; pp. 994 - 998
• Main Authors: Numakura, Masahiko, Sato, Nobuaki, Bessada, Catherine, Okamoto, Yoshihiro, Akatsuka, Hiroshi, Nezu, Atsushi, Shimohara, Yasuaki, Tajima, Keisuke, Kawano, Hirokazu, Nakahagi, Takeshi, Matsuura, Haruaki
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Kidlington Elsevier Ltd 01-09-2011; Elsevier
• Subjects: Applied sciences; Calcium fluoride; Cations; Density; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Fluorides; Fuels; Fused salts; Installations for energy generation and conversion: thermal and electrical energy; Lithium fluoride; Molecular dynamics simulation; Molten salt reactor; Nuclear fuels; Nuclear power generation; Nuclear reactor components; Nuclear reactors; Thorium; Thorium fluoride; X-ray absorption fine structure; Molten salt reactor; X-ray absorption fine structure; Molecular dynamics simulation; Thorium fluoride; Lithium fluoride; Calcium fluoride; Measurement; Fluctuations; Stability; Molecular dynamics; Nuclear reactor; Molten salt; Case study; Fine structure; Anions; Zirconium; Simulation; Cations; Yttrium; X ray absorption; Thorium
• ISSN: 0149-1970
• DOI: 10.1016/j.pnucene.2011.04.026

X-ray absorption fine structure (XAFS) measurements on thorium fluoride in molten lithium–calcium fluoride mixtures and molecular dynamics (MD) simulation of zirconium and yttrium fluoride in molten lithium–calcium fluoride mixtures have been carried out. In the molten state, coordination number of thorium (
N
i
) and inter ionic distances between thorium and fluorine in the first neighbor (
r
i
) are nearly constant in all mixtures. However the fluctuation factors (Debye–Waller factor (
σ
2) and C
3 cumulant) increase until
xCaF
2
=
0.17 and decrease by addition of excess CaF
2. It means that the local structure around Th
4+ is disordered until
xCaF
2
=
0.17 and stabilized over
xCaF
2
=
0.17. The variation of fluctuation factors is related to the number density of F
− in ThF
4 mixtures and the stability of local structure around Th
4+ increases with decreasing the number density of F
− in ThF
4 mixtures. This tendency is common to those in the ZrF
4 and YF
3 mixtures. However, in the case of YF
3 mixtures, the local structure around Y
3+ becomes disordered until
xCaF
2
=
0.40 and it becomes stabilized by addition of excess CaF
2. The difference between ThF
4 mixtures and YF
3 mixtures is related to the difference of Coulumbic interaction between Th
4+–F
− and Y
3+–F
−. Therefore, the variation of local structure around cation is related to not only number density of F
− in molten salts but also the Coulumbic interaction between cation and anion.
► Coordination number of ThF
4 mixtures decreased from c.a 9 to 7 and inter ionic distances between thorium and fluorine in the first neighbor also decreased from c.a. 2.34 to 2.30 Å by melting. ► The local structure around Th
4+ is disordered until xCaF
2 = 0.17 and stabilized over xCaF
2.= 0.17. However, in the case of YF
3 mixtures, the local structure around Y
3+ becomes disordered until xCaF
2 = 0.40 and it becomes stabilized by addition of excess CaF
2. ► The variation of local structure around cation is related number density of F in molten salts and the Coulumbic interaction between cation and anion.