[en] Reactivity effects of fuel pin melting under flow blockage conditions and the consequences of resulting power excursion are analysed for the Indian Prototype Fast Breeder Reactor fuelled with oxide, carbide and metal cores. Reactivity addition under melting of different segments of pins and slumping downward is calculated. It is observed that up to the melting of 6-sub-assemblies in the case of oxide core and a melting of 7-sub-assemblies for carbide and metal cores, the fuel pin melting and fuel slumping does not lead to a severe power excursion and the reactivity feedback of the systems can nullify the positive reactivity from fuel melting and slumping. (author)