GWEN IFILL: The nuclear crisis in Japan immediately brought back memories of the meltdown at Chernobyl, which still ranks as the world's worst nuclear accident.
Nearly 25 years later, NewsHour science correspondent Miles O'Brien returned last week to see what life is like there now.
MILES O'BRIEN: For an infamous ghost town of epic proportions, Chernobyl sure is a busy place. Past the guards, through the gates, and into this time capsule of the life Soviet, you must first find your way to the exclusion zone office, where the phone does not stop ringing these days.
Marina Polyakova tells me it's mostly reporters calling, wanting to visit since the meltdown at Fukushima.
What am I paying for here? What am I getting for 1,064?
WOMAN: That's for the entrance.
MILES O'BRIEN: Paying the entrance fee, I remember many Ukrainians who would like to open the place to tourists, a macabre theme park, to be sure.
Do you think tourists would come here?
People can come to the area to see everything themselves and then make their own opinion, she told me, not on the basis of what journalists say about this place.
No offense taken, I guess. But what a difference 25 years can make.
ROBERT MACNEIL, former PBS anchor: Good evening.
In the news today, there was an accident at a Soviet nuclear plant, causing some casualties.
MILES O'BRIEN: Two days before the Soviet government announced the problem, reactor number four at the Chernobyl nuclear power plant, 80 miles north of Kiev, blew up, spewing out more radioactivity than 100 Hiroshima bombs. With a cloud of fallout rapidly spreading north and west over Europe, there could be no state secrets. The Kremlin could not keep a lid on Chernobyl in every respect.
MAN: The results were alarming. Significantly higher than normal levels were recorded.
MILES O'BRIEN: About 30 workers and firefighters died in the first week, untold numbers in the 25 years since.
GENNADI MILINEVSKY, University of Kiev: Very important to have these devices.
MILES O'BRIEN: My guide inside the Chernobyl exclusion zone was physicist Gennadi Milinevsky of the University of Kiev.
GENNADI MILINEVSKY: It should be 12 microrems per hour.
MILES O'BRIEN: So, this is a little bit...
GENNADI MILINEVSKY: It's a little -- it's twice more.
MILES O'BRIEN: This is two, almost three times more background radiation just right here.
GENNADI MILINEVSKY: Two more times right here more than the ground. But...
MILES O'BRIEN: So, should we be worried about that?
GENNADI MILINEVSKY: No, not really.
MILES O'BRIEN: Not that big a deal?
It's not enough to cause harm within a short period of time.
GENNADI MILINEVSKY: For those who saved the world.
MILES O'BRIEN: We stopped by a monument to the firefighters who fought valiantly for 10 days to douse the nuclear inferno.
Are they heroes?
GENNADI MILINEVSKY: Yes, heroes. It's -- many of them received a dose not connected with -- with life.
MILES O'BRIEN: Yes.
GENNADI MILINEVSKY: They died in one month.
MILES O'BRIEN: Really?
GENNADI MILINEVSKY: Yes. They were sent to Moscow to special clinic for treatment. But they were -- died.
MILES O'BRIEN: Helicopters finally smothered the fire with sand, clay, boron, lead, and liquid nitrogen. Eventually, 600,000 Soviet army conscripts were dispatched to Chernobyl to shovel the lethal mess back into the remnants of the reactor, so that it could be encased in steel and concrete.
VASYL KAVATSIUK, Chernobyl liquidator: Our job was to put the radioactive material back...
MILES O'BRIEN: I see.
VASYL KAVATSIUK: ... to the reactor, yes.
MILES O'BRIEN: I see. So, then -- so they could cover it over?
VASYL KAVATSIUK: That's exactly right.
MILES O'BRIEN: So you -- you were in very close proximity to this stuff?
VASYL KAVATSIUK: Cannot be closer.
MILES O'BRIEN: They called them liquidators. And Vasyl Kavatsiuk was one of them. A demolition expert, he spent 37 days working at the wrecked reactor.
VASYL KAVATSIUK: If you think about that, you are getting more sick more than you're supposed to be. You are just thinking I have to do this. This is my job. I have to finish this. I have to do this. Anybody -- anyhow, somebody must do that.
MILES O'BRIEN: Until he collapsed and had to be medevaced to Moscow. His wife, Maria, gave birth to a girl, Marta, in 1987. Just shy of her second birthday, she died suddenly of leukemia. In 1989, they had another daughter, Maria. She too contracted leukemia, but survived.
Is there a lot of cancer in your family?
VASYL KAVATSIUK: Never had one.
MILES O'BRIEN: Never?
VASYL KAVATSIUK: Never.
MILES O'BRIEN: Is there any doubt in your mind that the leukemia your two daughters had, had something to do with Chernobyl?
VASYL KAVATSIUK: I have no doubt about that.
MILES O'BRIEN: There's no doubt radiation causes cancer and genetic defects. The fast-moving subatomic particles plow into molecules with enough energy to knock lose electrons. The dinged molecules, called ions, can kill or damage cells. Enough of this will kill you quickly. Less damage can cause cancer or, if DNA is the target, create genetic mutations.
This is the town of Pripyat.
MILES O'BRIEN: Pripyat was just one of 150 towns and settlements evacuated after the accident. More than 300,000 people were displaced, while a few hundred stubborn holdouts remain on their land, people like Maria, who, at 75, says she is more worried about her cottage falling down than radiation.
Children are the most vulnerable to the effects of radiation. After the explosion, there was a big spike in birth defects and thyroid cancer, extremely rare among children. And researchers say there is also a significant drop in the intellect in the region.
At the dilapidated regional hospital closest to Chernobyl, the medical staff is convinced there is a direct link between chronic exposure to radiation and a whole assortment of diseases and deformities.
I asked Dr. Constantine Cheres if he is convinced people are more sick here because of the Chernobyl accident. "Of course," he told me. "Of course they are more sick."
But the Chernobyl Forum, a group of U.N. agencies focused on the accident, estimates only 4,000 people died as a result of the explosion and its aftermath. One of the four members, the U.N. Scientific Committee on the Effects of Atomic Radiation, issued a report contending: "There is no clearly demonstrated increase in the incidence of cancers or leukemia due to radiation in the exposed populations. Neither is there any proof of any non-malignant disorders that are related to ionizing radiation. However, there were widespread psychological reactions to the accident, which were due to fear of the radiation, not the actual radiation doses."
But Ukrainian scientist Maryna Naboka begs to differ. She told me people here get sick more often and they become more seriously sick. They receive little doses of radiation, but they do it on a day-to-day basis, and the second generation continues getting the radiation.
Radiation contamination is very stubborn. Gennadi Milinevsky took me to a place inside the exclusion zone, 30 kilometers, or 18 miles, around the plant, that is still heavily irradiated.
They call it the red forest because why?
GENNADI MILINEVSKY: They call it red forest because this is strong radiation. The leaves of trees became red.
MILES O'BRIEN: Right.
It killed the trees.
The radiation killed pine trees in a 30-square kilometer, 11-square-mile swathe. As we hiked in, the Geiger counter got very excited.
All right, so now we're more than -- we're at 400 times. Are we OK?
GENNADI MILINEVSKY: Yes.
MILES O'BRIEN: Are we safe?
GENNADI MILINEVSKY: Safe.
MILES O'BRIEN: All right. All right. Just checking. We just don't want to stay here too long, do we?
GENNADI MILINEVSKY: Yes. If you put it on the ground...
MILES O'BRIEN: Yes.
GENNADI MILINEVSKY: ... it became much...
MILES O'BRIEN: Oh, look at that, look at that, 5.5 half right there. That's 500 times right there. This used to be pine trees as far as you can see.
GENNADI MILINEVSKY: Yes.
MILES O'BRIEN: And the cesium came through here after the explosion. And that's -- and to this day is...
GENNADI MILINEVSKY: Yes, still over there.
MILES O'BRIEN: Are there animals that can live here, or not?
GENNADI MILINEVSKY: No, no.
MILES O'BRIEN: Milinevsky's colleague, Tim Mousseau, believes animals are the key to settling the debate over the long-term health effects of Chernobyl. He and his team have spent more than a decade studying birds in the Chernobyl region and beyond.
TIMOTHY MOUSSEAU, University of South Carolina: But it's clear that this low-level contamination is -- is probably more dangerous in the long run than -- than having a single hot spot.
MILES O'BRIEN: In contaminated areas, there are half as many species and one-third number of birds you would expect. Their brains are smaller. Forty percent of male barn swallows have abnormal sperm. One in five have strange colored plumage that makes it hard to attract mates.
There are unusual beak deformities and large tumors that scientists have never seen before. What, if anything, can we extrapolate between that bird population, that population of barn swallows, and humans?
TIMOTHY MOUSSEAU: I would argue that, you know, we're all -- we're all animals, and birds are actually more similar to us than dissimilar to us.
MILES O'BRIEN: Mousseau's colleagues are also looking at Chernobyl's grasshoppers. They frequently have asymmetrical wings, and fruit flies, which are easily impacted by radiation. Those found around Chernobyl have gray eyes, instead of red, and deformed wings.
Biologist Irina Koretsky studies the little bugs, in part because they only live about a month, meaning she can track genetic changes through many generations in short order. She worries about the sporadic funding for research that could lead to some definitive answers about the Chernobyl riddle.
She told me: "This is the worst thing that can happen. If there are gaps in the research for two or three years, we cannot have this full picture."
At the remains of reactor number four, I saw the concrete and steel sarcophagus that was completed six months after the explosion.
Is it holding? Is it doing its job?
GENNADI MILINEVSKY: It's not -- not carefully doing this job, because there's many holes inside and, still, in windy weather, we have some dust coming outside.
MILES O'BRIEN: Ukraine is asking the west for $800 million to pay for a new shelter over the old sarcophagus that would last 100 years. Beneath it is all is a molten witch's brew of radioactive isotopes, including plutonium, with a half-life of 24,000 years, meaning, in 24,000 years, half of it will still be here, and 24,000 years later, half of that will still be here, and so on.
Do you think human beings are capable of keeping this thing safe for tens of thousands of years?
GENNADI MILINEVSKY: If he covers it, will try to keep it safe.
MILES O'BRIEN: Yes.
GENNADI MILINEVSKY: But this place, this area will be still not good for life.
MILES O'BRIEN: Forever.
GENNADI MILINEVSKY: Yes, forever, yes.
MILES O'BRIEN: And -- and...
GENNADI MILINEVSKY: That is problem for all nuclear power plants. When we build new nuclear power, power plants, always, you create some headache for future generations.
MILES O'BRIEN: And something for our generation to consider as we weigh the pros and cons of nuclear power.