The deadline for submitting offers is November 19, NPP Kozloduy said in a tender notice.
Bids will be ranked solely based on price.
According to previously published documents, two companies expressed interest in the contract during the market consultations - local Tita-Consult and the Bulgarian branch of Westinghouse Energy Systems.
Kozloduy NPP has two operational units - Units 5 and 6 - of 1,000 MW each. The plant's four other units, of 440 MW each, were closed down to address nuclear safety concerns of the European Union prior to Bulgaria's accession to the bloc in 2007.
(1 euro = 1.95583 levs)