Three-dimensional flow and temperature fields within a 19-pin wire-wrapped fuel bundle of fast reactor with internal blockage have been predicted by Computational fluid dynamic (CFD) studies. Simulations are carried out for a stream-wise length of seven helical pitches. Blockage geometry (shape and size), its radial position and blockage porosity which influence the clad temperature and hence increase the risk of sodium boiling, are systematically varied in a parametric study. Clad temperature, cross-stream sodium velocity and cross-stream temperature distributions are investigated in detail. Axial variation of clad temperature is seen to exhibit strong fluctuations due to the interaction of helical spacer wire and coolant flow through a subassembly with porous blockage. The maximum difference in the circumferential temperature of clad, which is a critical parameter for fuel pin mechanical design, is large in pins that are partially exposed to blockage. Effect of porous blockage is found to be limited to the porous zone and the peak clad temperature is proportional to the volume of the porous zone. Peak temperature in the blockage is strongly influenced by the radial extent of blockage and it is higher if the radial extent is larger. Maximum difference in the circumferential clad temperature is relatively low for a corner blockage compared to that of a central blockage. Sodium boiling is imminent in fuel pin bundle with six blocked sub-channels located at the centre when porosity value reduces below 45%. © 2014 Elsevier Ltd. All rights reserved.