Bulgaria's only nuclear power plant on Monday began using nuclear fuel produced by US company Westinghouse Electric Corporation, a key step in the country's move away from dependence on Russian energy.

The state-owned Kozloduy power plant on the Danube River supplies more than a third of the country's electricity and has until now relied on Russian fuel for its two operating 1,000-megawatt Soviet reactors.

The oldest reactor was connected to the national grid on Monday morning after "43 fuel assemblies manufactured by Westinghouse were loaded into the reactor," the plant said in a statement.

The process of gradual transition to a new type of fuel is expected to take four years, the company added.

Following Moscow's 2022 invasion of Ukraine, Kozloduy signed nuclear fuel supply agreements with Westinghouse and Framatome – a subsidiary of French energy giant EDF – to replace supplies from Russia.

Before the full-scale invasion, Bulgaria, which is a member of NATO and the EU, was almost entirely dependent on Russian energy supplies, but has since diversified.

The second reactor of the Kozloduy plant will be supplied with Framatome fuel. In addition, by the 2030s, it is planned to install two American-made nuclear reactors at Kozloduy.

The Czech Republic, Slovakia and Hungary have also signed nuclear fuel supply agreements with Westinghouse and Framatome.