A system and method for sealing a multilateral junction in an oil well is described. Molten material, such as a eutectic or non-eutectic alloy, flows into the junction area and forms a durable seal upon cooling. An expanding alloy may be utilized, which expands upon solidification and which has a melting temperature that is higher than the maximum anticipated well temperature. The alloy is placed within a cavity in the well and held at a temperature above the melting point of the alloy, after which the alloy is cooled down to the ambient well temperature and solidifies and expands within the cavity.