Korea Hydro & Nuclear Power (KHNP) was picked over rival French bidder EDF, despite lobbying for EDF from French President Emmanuel Macron.
Prague earlier this year widened the tender, which is run by 70%-state-owned energy company CEZ (CEZP.PR), opens new tab, to have the option to build multiple units, up from an originally planned one.
Under the plans, KHNP will build two new units at CEZ's Dukovany nuclear plant, and they will discuss an option for two more units at the Temelin power station.
The price for one new unit when building two at the same site was estimated at 200 billion crowns ($8.65 billion) at current prices, the government said, adding it suggested the price of electricity generated would be less than 90 euros per megawatt hour (MWh).
Contract details will be worked out by the first quarter next year before being signed, officials said.
"The Korean offer was better practically in all assessed criteria," Czech Prime Minister Petr Fiala told a news conference.
"We will build two blocks at Dukovany, and in this direction there will be negotiations. And we will discuss about options for another two blocks at Temelin about which we will be able to decide in the future."
KHNP has helped put several new reactors online in recent years, including the Arab world's first nuclear power plant in the United Arab Emirates. The Czech deal will offer another foothold in Europe.
In 2022, KHNP agreed with a Polish consortium to develop new nuclear reactors but that project is still uncertain.
KHNP CEO Whang Joo-ho said in a statement the company would enter final negotiations to "ensure that the APR1000 reactor is actually built in the Czech Republic", referring to its reactor model.
EDF, Europe's only builder of nuclear reactors. has not completed construction of a new unit since 2019 amid project delays.
The decision represented another setback for the French nuclear sector after Poland, in a separate deal, chose Westinghouse over EDF for a plant on the Baltic Sea in 2022.
NUCLEAR POWER EXPANSION
The Czech government had the final decision on the tender due to national security considerations and cost, which is too high for CEZ - even with a market capitalisation of $20.1 billion - to shoulder alone.
The central European country will lean more on nuclear power as it phases out coal in the coming decade. Nuclear is seen composing half the country's generation mix in the future, up from around a third now.
CEZ aims to start construction of the first new unit at Dukovany later this decade, with expected completion in 2036.
The government and CEZ widened the tender's scope to help lower the price of each block in what is expected to be the country's largest energy investment to date.
CEZ has agreed a financing model with the government for the first new unit at Dukovany, including low-interest loans and a scheme for pricing of produced electricity - called a contract for difference - to guarantee CEZ a return.
The European Commission has given approval to the state aid for the first unit and will still have to sign off on aid plans for further units. The Czech Finance Ministry aims to have a financing model for further units agreed by the end of the year.
