Water is the most fundamental hydrogen-bonded compound on Earth and its physical properties are essential for research areas ranging from live sciences to planetology. In this beamtime request we want to address the issue of the volume isotope effect (VIE) in ice VIII. In ordinary ice (Ih), the VIE is known to be anomalous: The replacement of H2O by D2O leads to an expansion of its volume, in contrast to ‘normal’ solids where deuteration leads to a contraction of the unit cell volume. First principles calculations predict that ice VIII exhibits a normal VIE at 0 GPa, i.e. the behavior of ice Ih may be singular for solid water. We will investigate this fundamental question by determining the structure and thermal expansion of H2O VIII and D2O VIII to high resolution in the range 1.5-120 K. Cm3-size samples of quenched H2O VIII and D2O VIII have already been prepared in our laboratory