"Today, November 23, 2006 at 16:37 pm (1437 GMT), energy block No. 6 was switched back on to the country's electric energy grid," a statement from the plant said Thursday.

"The block's 1,000-megawatt reactor was supplied with fresh nuclear fuel," it added.

Reactor No. 6 was switched off for refuelling on September 3, but routine checks in October detected a minor leak of radioactive solution into a pipeline in the turbine hall, although there was no contamination.

Bulgaria's Nuclear Regulatory Agency ranked the incident as level zero or "no safety significance" on the seven-level International Nuclear Event Scale (INES) but this was the second incident at the plant this year.

In March, another incident at the 1,000-megawatt reactor No. 5 highlighted defects in part of the control rods of the reactor's protection system. The bloc was safely switched off but the nuclear regulator ranked the accident as level two on the INES scale.

Reactors No. 5 and No. 6 are the newest of Kozloduy's four operational reactors and the only two considered safe enough to remain in use after Bulgaria joins the European Union in 2007.

The country already mothballed two older reactors in 2002 and agreed to shut down two other older but revamped 440-megawatt reactors.

To compensate for the lost capacity, Bulgaria last month signed a four-billion-euro (5.2-billion-dollar) contract with Russia's Atomstroyexport to construct two pressurised-water reactors of 1,000 megawatts each at another plant at Belene, in the north of the country.

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