The reactor at Khmelnitsky power station had to be shut down on Sunday, less than two hours after it went into operation, Interfax news agency reported on Wednesday. Further technical failures prevented it operating on Monday and Tuesday.

"These incidents do not represent any threat to the public or to the environment," state nuclear energy company Energoatom said in a statement.

Ukraine was the scene of the world's worst civilian nuclear disaster in 1986, when a reactor at Chernobyl nuclear power station exploded, contaminating large areas in Ukraine and neighbouring Belarus and Russia.

Energoatom confirmed incidents had occurred at Khmelnitsky but said it "saw no cause for concern".

"Certain media inflated the affair," it said.

The K2 Russian-designed VVER pressurised water reactor at Khmelnitsky, which has a capacity of 1,000 megawatts, was brought on stream on Sunday at a ceremony attended by Ukrainian President Leonid Kuchma.

But it ground to a halt almost immediately.

An official at Ukraine's governmental commission for atomic energy said that automatic security systems at the power plant had cut off the reactor from the electricity grid.

The reactor was reconnected to the grid three hours later but had to be totally shut down later because of a failure in the cooling system caused by a power breakdown, the official added.

The reactor was restarted on Monday, only to be stopped again on Tuesday, officially to test its shut-down system and cooling units.

Energoatom said the incidents had been linked to tests conducted after the start up of the reactor. These tests were expected to continue until December.

Four nuclear power stations provide nearly 50 percent of Ukraine's electrical power.

Chenrobyl finally closed down in 2000, a move imposed by the international community before it would provide further aid to Ukraine's power programme.

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