Dynamic X-ray diffraction (DXRD) has been used to identify and quantif
y the solid-state reactions that take place between sodium nickel ferr
ocyanide, Na2NiFe(CN)6, and equimolar concentrations of sodium nitrate
/nitrite, reactions of interest to the continued environmental safety
of certain waste storage tanks at the Hanford site in eastern Washingt
on. The results are supportive of previous work that indicated that en
dothermic dehydration and melting of the nitrates take place prior to
the occurrence of exothermic reactions, which begin about 300-degrees-
C. The DXRD results show that a major reaction set at these temperatur
es is the occurrence of a series reaction which produces sodium cyanat
e, NaCNO, as an intermediate in a mildly exothermic first step. In the
presence of gaseous oxygen, NaCNO subsequently reacts exothermally an
d at a faster rate to form metal oxides. Measurements of the rate of t
his reaction are used to estimate the heat release, and comparisons of
this with heat-transfer rates from a hypothetical ''hot spot'' show t
hat, even in a worse case scenario, the heat-transfer rates are approx
imately eight times higher than the rate of energy release from the ex
othermic reactions.