Anya wasn't even born when Chernobyl exploded nearly 30 years ago, but even today its radioactive fallout stalks her and other Ukrainian youngsters growing up near the disused plant.

The world's worst nuclear disaster saddled the sparkly-eyed 16-year-old with chronic cardiovascular and respiratory problems, thanks to contamination that lingers in the air, water and ground soil around her village.

A brief break comes each summer when Anya and a few dozen other children and teens trade their homes for a "clean" holiday on Portugal's west coast.

"A month's vacation in Portugal can extend their life expectancy by one or two years," said Fernando Pinho, citing a study by doctors at Ivankiv hospital, 45 kilometres (28 miles) from Chernobyl.

Pinho, 59, heads "Blue Summer", a project started in 2008 by employees of the Liberty Seguros insurance company to give Ukrainian children a chance to reduce the levels of radioactive caesium that creep into their systems at home.

Similar programs are also held in Belgium, France, Germany, Ireland, Italy and Spain, offering a "cure" of sun, sea, clean air and good food to several hundred young Ukrainians each summer.

Thirty-four of them came to Portugal this year. "Blue Summer" finances their transport and health insurance and they stay with volunteer host families, who cover their everyday needs.

- 'Invisible evil' -

"I discovered the ocean here, its wonderful smell. I never tire of looking at it," said Anya in near perfect Portuguese.

It is her seventh summer in the seaside town of Peniche, north of Lisbon, in the bright, white villa of Maria Joao and Hernani Leitao, her "second family", near sand dunes as far as the eye can see.

On April 26, 1986 when one of the four reactors exploded at Chernobyl in then-Soviet Ukraine, it spewed out huge quantities of radioactive particles -- some estimates say 200 times that of the nuclear bomb at Hiroshima.

Thirty-one deaths have been directly attributed to the catastrophe, though the UN Chernobyl Forum says the radiation could eventually cause up to 4,000 deaths. The environmental watchdog Greenpeace, meanwhile, says the death toll from radiation could eventually hit 100,000 to 400,000 in Ukraine, Belarus and Russia.

Aside from environmental damage, long-range effects in Chernobyl region include thyroid and other cancers, leukaemia, heart and liver problems, deformations, cataracts, immune system troubles and mental health issues.

The UN Chernobyl Forum, in fact, calls the mental health impact "the largest public health problem created by the accident", according to the World Health Organization website.

Today it may be the parents who have the most health problems but "tomorrow it will be the children's turn", said Pinho.

Bogdan, nine, from the town of Ivankiv, has so far shown no signs of health problems. It is his first trip to Portugal and though he doesn't speak the language, he quickly found ways to communicate with Jonas, the 11-year-son of his host family in Santa Iria de Azoia near Lisbon.

"He was a little shy at first but our cats helped break the ice," said Jonas' mother Anabela Pereira, 43, whose own bout with thyroid cancer, diagnosed in 2007, has made her sensitive to the risks in Chernobyl.

"Radioactivity is an invisible evil that wreaks havoc," she said.

In the Chernobyl area alone, more than 6,000 children have been diagnosed with thyroid cancer and the numbers are expected to rise, according to UNSCEAR, the UN Scientific Committee on the Effects of Atomic Radiation.

- 'Deathly silence' -

Anya, from Mussiki, about 40 kilometres (25 miles) from Chernobyl, grew up eating fruits and vegetables grown in the fields near the modest home she shared with her mother and little sister Anastasiya, before starting studies in the capital Kiev.

Not far away from her village, hundreds of thousands of people were evacuated from a 30-kilometre zone around the nuclear plant -- an area that still has restricted access today.

Anya's host "father", Leitao, 63, an active member of "Blue Summer", actually travelled to this exclusion zone in 2010.

"I saw deserted villages where there was deathly silence, abandoned classrooms still stocked with books and dolls left by children," he said.

He showed photos of Pripyat, a ghost town three kilometres from the Chernobyl plant where time stopped after the 50,000 residents were evacuated.

Anya's own uncle, Anatoli, still works at Chernobyl where he is in charge of maintenance of the plant's equipment as work continues to seal off the damaged reactor with a massive steel and concrete cover to limit radioactive contamination. The target date for completion of this "sarcophagus", as it is called, was initially set for 2015 but has been extended to 2017.

As for Anya, she has no plans to stay in Ukraine.

"When I finish my studies in four years, I'll return to Portugal to work in the tourism industry," she said smiling.