Photon Factory Activity Report 2014 #32 (2015) B%/%/2012G150

Local structure of zirconium in molten lithium – calcium andlithium – magnesium fluoride

Haruaki MATSUURA*1, Atsushi NEZU1, Jun TAKEDA1, Masahiko NUMAKURA1,
Hiroshi AKATSUKA1
1Res. Lab. for Nucl. Reactors, Tokyo Tech., Ookayama, Meguro-ku, Tokyo, 152-8550, Japan

Results and discussion
By the stepwise-controlled temperature program, thespectra at molten phase were well identified in eachsample. The concentration dependence of EXAFS
structure functions at molten phase is shown in Fig. 1.
With increasing the ratio of xMgF2/xLiF, once interionicdistance between Zr4+ and F- increases, and thendecreases, as shown in Fig.1. On the other hand, withincreasing the ratio of xCaF2/xLiF, interionic distance
between Zr4+ and F- even decreases slightly. Further
lookng back to previous data of the thorium or terbium
mixture systems coexisting divalent cations, by additionof magnesium fluoride, the elongation effect of interionic

LiF-ZrF 4 (xZrF4 = 0.25)-MgF 2 (xMgF2 = 0 - 0.50)

LiF-ZrF 4 (xZrF4 = 0.25)-CaF2 (xCaF2 = 0 - 0.40)

xCaF2 = 0xMgF2 = 0
xCaF2 =0.1
xMgF2 =0.1

3Experimental
Zr K-edge EXAFS spectra have been collected withfixed time scan method by the X-ray from a double Si(111) crystals monochromator in transmission mode. To
avoid the contamination by oxygen, premixing treatment
was abandoned. Mixtures of ZrF4, LiF, CaF2, MgF2 wereweighed then, they were mixed with boron nitride powder,
and pressed into pellets in 13 mm diameter and 1 mmthickness. The mixing weight ratio of mixture salt to BN
was ca. 1: 2.5. To prevent chemical reaction of sample byatmosphere during performing high temperature EXAFS
measurements, these pellets were sanded by pyrolyticboron nitride plates. The electric furnace chamber was
filled with He gas under ca. 30 kPa. EXAFS data wereanalysed by using the WinXAS ver.3.1 and 3rd and 4th
cumulants were introduced for the curve fitting analysesof EXAFS data at molten phase due to existence of theirlarge anharmonic effect in some cases.

distances between Th4+ and F- or Tb3+ and F- wereidentified. These facts would be explained as follows: theeffect of interinoic disntance elongation by coordinatedfluorides removal around a cation with much larger
valence and the effect of interionic distance shorten byintroduction into network-like structure dominated bymagnesium fluoride is complexed depending upon
composition and species. Sometimes the only peak fitting
procesure of each spectrum tends to mislead theexplanation of local structure, thus, a molecular dynamics
simulation using well established inter-ionic potential
paramenters would be required to evalute proper
microscopic structure of these systems.

FT|(k)·k | [arb.unit]

Introduction
A molten salt reactor concept contains still fascinatingidea from the point of view of its self-sustainability with aclosed fuel cycle. In order to develop an on-line recycle
process of molten salt fuels, one of promisingtechnologies is an electrochemical separation of actinides(An) from lanthanides (Ln). To find the best electrolysis
condition to improve the efficiency of the pyrochemical
process, systematic investigations of the correlation
between structures of molten An (Ln)Fn and their
physico-chemical properties, such as electrochemical
behavior are useful. In this report, molten ZrF4-LiF-CaF2and ZrF4-LiF-MgF2 mixtures are focused as the structuralinvestigation by EXAFS.

xMgF2 =0.2

xCaF2 =0.2

xMgF2 =0.3
xCaF2 =0.3

xMgF2 =0.4
xMgF2 =0.5

xCaF2 =0.4

01

2
R [Å]

03

12
R [Å]

Fig.1 EXAFS structure functions of various
compositions of molten ternary systems at600 oC.
*hmatsuur@nr.titech.ac.jp

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