In the event of an energetic core disruptive accident in sodium fast reactor, the expansion and oscillation of fuel vapor bubble into the liquid sodium pool takes place. The expanding fuel vapor bubble is capable of doing mechanical work on the primary containment. This mechanical work on the primary containment could challenge its integrity. During the expansion, the sodium entrainment at the bubble-coolant interface can either increase or decrease the total work done by the bubble. In this regards, a numerical model to understand the influence of the expanding fuel vapor bubble's interface acceleration on the sodium entrainment process and the associated sodium vapor generation is developed. The model considers Rayleigh Taylor instability at the accelerating interface for the evaluation of entrained sodium mass. It also evaluates the entrained sodium droplet size distribution, and the sodium vapor mass generated from the droplets due to heat transfer from the fuel vapor. The hydrodynamics of bubble expansion is described with a representative function that can accommodate the non-sphericity effect. A parametric analysis is carried out with the model for bubble oscillation time periods 0.2, 0.25 and 0.3 s, which are typical in a medium sized pool type sodium fast reactor geometry. Results show that the minimum entrained sodium droplet diameter range from 2.1 to 3.2 mm and the generated sodium vapor mass varies from 43.1 to 14.7 kg. The developed model's predictions are comparable with the published data available in the literature.