[en] In this report, an attempt is made to model, in a mechanistic way, the events following pin failure which may lead to fuel freezing and hence plugging of coolant channels. It is argued that plugging of channels can occur if the fuel is in a molten state when it contacts the upper, cooler fuel pin walls, or if the newly formed thin solid crust of a molten fuel particle breaks open because of induced thermal stresses and/or impact stresses as the particle hits a solid surface. In this study, emphasis has been placed on determining the physical state of, and the axial location of, a fission heated fuel particle as it moves in the coolant channel. Based on the proposed physical mechanisms, it is concluded that some freezing and plugging of coolant channels of a proto-type fast reactor may occur during overpower transients. The probability of such an occurrence is higher for an irradiated pin than for a fresh pin. The conclusions of this study have been compared with and are in basic agreement with the non-proto-typical qualitative TREAT test results