An improved equation of state for inert gases at high pressures

A hard sphere equation of state is developed in order to describe inert gas behaviour at high temperatures and/or pressures. In the low density limit it is shown to simplify to the reduced van der Waals equation of state. At high pressure the reduced van der Waals EOS is shown to be seriously in error with the limited experimental data whilst the hard sphere is in good agreement with this data. Further the use of the reduced van der Waals EOS to estimate the number of atoms in a bubble is shown to lead to an under estimate of that number, especially for small bubbles. This represents an important correction in fuel swelling and gas release calculations. Finally, the use of the hard sphere EOS in modelling fission gas behaviour during a thermal transient is shown to be a more robust estimator of the fission gas pressure in bubbles than the reduced van der Waals EOS.