Development of analytical equations for void fraction in biphasic systems using gamma radiation and MCNP6 code.

This study presents the development of mathematical equations for calculating void fractions in pipes using gamma densitometry. A traditional measurement setup, consisting of aCs point source and a NaI(Tl) scintillator detector, was simulated using the Monte Carlo method via the MCNP6 code. To validate the proposed equations, water-gas biphasic models were simulated in tubes with square and cylindrical cross-sections, varying diameters, and radiation sources (Am, Cs, Co) through gamma-ray transmission. A comparative analysis with existing equations from the literature was conducted. The void fractions, determined from the transmission photopeak, were in close agreement with the actual values. The proposed equations demonstrated a maximum mean relative error of 0.21% for cylindrical tubes in stratified and annular flow regimes.