In the event of energetic core disruptive accident in Sodium Fast Reactor, a high temperature high pressure volume of molten fuel, termed as fuel vapor bubble is formed. The fuel vapor bubble expands in to sodium pool and transports radioactive fragmented fuel particles from the disrupted core to liquid sodium pool, contributing to the radiological source term. In this regard, a parametric analysis has been carried out to evaluate the unrestrained fuel vapor bubble expansion in the disrupted core by ignoring the presence of reactor internal structures. The fuel vapor bubble evolution inside the liquid sodium pool was analyzed for initial pressures 2, 3 and 4 MPa with initial volumes 1, 0.8 and 0.6 m³ to understand the influence of initial conditions on fuel vapor bubble evolution. Results show that the bubble oscillation time period is in the order of few hundred milliseconds for initial conditions envisaged during the fuel vapor bubble expansion. Also, the fuel vapor bubble expansion and oscillation is less sensitive to initial volume than initial pressure for the range considered in the parametric analysis. The results would serve as a datum for further detailed analysis to evaluate the radiological source term and their consequences due to severe accidents in SFR.