Sealing method and apparatus

According to the present invention there is provided an apparatus for forming a plug in a passsageway, the apparatus comprising a carrier which in use is lowered into the passageway, the carrier comprising an elongate body of a material resistant to creep which supports first and second spaced apart portions and a body of material supported on the carrier, said material having a melting point which is higher than the temperature within the passageway and which expands as it solidifies. The carrier may comprise a skirt that extends axially from a lower end of the carrier, the skirt being dimensioned to define a clearance between the skirt and the passageway; and means for melting the body of material such that melted material fills a space defined between the first and second portions, and flows into the clearance defined between the skirt and the passageway. The apparatus may comprise.a removable heater operative to melt the body of material such that melted material fills a space defined between the first and second portions.