Plug and abandon with fusible alloy seal

A method of zonal isolation in a wellbore, the method comprising:

• forming a seal at a location in a tubular by:
• heating at least one material comprising a hypo-eutectic or a hyper-eutectic to provide a melted material, wherein heating comprises reacting a metal via an exothermic reaction and transferring heat produced by the exothermic reaction to the at least one material;
• and
• solidifying the melted material at the location in the tubular to form the seal, wherein the melted material expands upon solidifying, and wherein the seal plugs the wellbore for plug and abandon;
• and
• prior to the heating, placing into the tubular a wellbore tool comprising:
• a pressure vessel containing the at least one material, the metal, and a concentrated acid or base, a first barrier between the concentrated acid or base and the exterior of the pressure vessel, and a second barrier between the metal and the concentrated acid or base, and comprising a first activation component configured to, when activated, cause failure of the first barrier, whereby water enters the pressure vessel and combines with the concentrated acid or base to provide a diluted aqueous acid or base, and a second activation component configured to, when activated, cause failure of the second barrier, whereby the diluted aqueous acid or base contacts the metal to initiate an exothermic reaction and heat from the exothermic reaction melts the at least one material to provide the melted material.