Molten NaF-BeF2 salt is widely considered
a promising
candidate to replace FLiBe in molten salt reactor applications, which
is crucial to reducing the operating costs of the molten salt reactor.
Studies on beryllium compounds are rarely conducted due to their volatility
and high toxicity. Herein, the Be–F coordination structure
of NaF/BeF2 mixed salts was investigated in-depth through
various HT-NMR and solid-state NMR methods, which are optimized to
be appropriate for the detection of beryllium compounds. It was found
that Na2BeF4 and NaBeF3 crystals
were transformed into amorphous tetrahedral coordinated networks when
there was an increase in the BeF2 concentration in the
mixed salts. The main coordinate structure comparisons between FNaBe
and FLiBe were analyzed, which exhibit high similarity due to the
covalent effect of Be–F bonding, demonstrating the theoretical
feasibility of applying FNaBe salts as a substitute for FLiBe in MSR
systems. In addition, the transition from the crystal phase to the
amorphous phase occurred at a lower BeF2 concentration
for FNaBe than that for FLiBe. This was further verified by the results
of ab initio molecular dynamics (AIMD) simulation
that FNaBe melts had more disordered structures, thus causing slight
changes in their physical properties.