Shock Compression, Adiabatic Expansion and Equation of State of Uranium Dioxide*

Equation of state for matter over wide range of pressures and densities is interesting for modeling of physical phenomena in shock-compressed media. In the present study we have obtained data on the shock compressibility of porous uranium dioxide UO$_2$ samples with initial densities 4.25 and 2~g/cc up to pressures $P \approx 82$~GPa. We have also measured states of UO$_2$ samples in adiabatic release waves using barrier technique down to $P \sim 0.05$~GPa. We propose a semiempirical equation of state $E(P,V)$ for UO$_2$ optimally generalized the newly acquired and available at high energy densities experimental data. The equation of state obtained has a simple analytical form $P=P(E,V)$ and it can be used efficiently in numerical simulations of shock-wave processes.