  We have used electron and neutron powder diffraction to elucidate the
structural properties of superconducting \NaD. Our measurements show that our
superconducting sample exhbits a number of supercells ranging from ${1/3}a^{*}$
to ${1/15}a^{*}$, but the most predominant one, observed also in the neutron
data, is a double hexagonal cell with dimensions \dhx. Rietveld analysis
reveals that \deut\space is inserted between CoO$_{2}$ sheets as to form a
layered network of NaO$_{6}$ triangular prisms. Our model removes the need to
invoke a 5K superconducting point compound and suggests that a solid solution
of Na is possible within a constant amount of water $y$.
