  We explore the distribution, morphology and structure of zirconium hydrides
formed using different cooling rates through the solid state Zr+[H] --> Zr +
hydride transus, in fine and blocky alpha Zircaloy-4. We observe that cooling
rate and grain size control the phase and distribution of hydrides. The blocky
alpha (coarse grain, > 200 micrometer) Zircaloy-4, has a smaller grain boundary
area to grain volume ratio and this significantly affects nucleation and growth
of hydrides as compared to fine grain size (~11 micrometer) material.
