The three-dimensional transient two-phase flow version of the computer programme BACCHUS-3D/TP (Two Phase) relies upon the basis supplied by the single phase flow version of the code. The bundle geometry typical of LMFBRs is modeled by means of the porous body approach based on the concepts of volume porosities, surface permeabilities, distributed resistances and heat sources. Two phase flow is described by means of two physical models available in two distinct versions of the code. One of these two-phase models is a three-equations Slip Model (SM) which provides as a subcase the Homogeneous Equilibrium Model (HEM) if no slip between the phases is assumed. The second is a six equation model referred to as Separated Phases Model (SPM) in which two coupled systems of governing equations are solved for the vapour and liquid phases. A fully implicit treatment of the conservation equations for the coolant flow is followed in the SM and a half-implicit approach in the SPM. The article outlines the present state of the code development and future activities aiming at unifying both variants in a comprehensive code version describing the transition between different two-phase flow regimes from bubbly flow to dispersed annular flow. An assessment of the present capabilities of the code has been made with the theoretical interpretation of out-of-pile sodium boiling experiments in a 7- and 37-pin bundle. Numerical results are discussed and compared with experimental data.