KHNP won the 260 billion-won (US$188 million) project last year at the Cernavoda Nuclear Power Plant, some 170 kilometers east of Bucharest, intended to extract tritium from heavy water and store it safely.
The state-run firm said it received regulatory approvals in May, and the construction is scheduled to be completed by September 2027.
"We aim to work closely with the Romanian government, the client and other partners for successful construction," KHNP CEO Whang Joo-ho said in a statement.
The project marks the company's first engineering, procurement and construction project in Europe.
