Washington considers the participation of Korean companies all but essential to its nuclear expansion, a U.S. government official familiar with the matter said in Seoul Thursday, as the two countries look to build reactors at home and in third countries. “I think it's almost mandatory that we will have Korean companies involved,” the official said, after attending the International Ministerial Conference on Nuclear Power in Incheon. “We would like to have Korean companies participate in moving forward the renaissance in U.S. and around the world,” the official added. “We do need Korean companies, who have very good experience in this area already, to help in that process.” The official said the 123 Agreement, the bilateral pact governing civil nuclear cooperation between the two countries, does not prevent Korean firms from participating. Requirements attached to exported technology amount to standard export-control matters rather than a barrier under the agreement itself, the official noted. The Korean industry is already embedded in several U.S. projects. SK is among the la