tonight on "nightline," nuclear crisis. a last-ditch attempt to head off a full-scale nuclear disaster in japan. with radioactive fuel burning through reactor walls, is it too late to head off a meltdown that could be deadly for decades? plus, suicide mission? dozens of heroic workers go back into the japanese nuclear plant and fight the toxic flames to protect their countrymen. in a mission they know will likely fail. and, desperate hours. thousands stranded inside the evacuation zone without fuel, unable to leave. thousands more in a frantic exodus. the story of one american family's incredible journey. >> announcer: from the global

resources of abc news, with terry moran and cynthia mcfadden in new york city and bill weir in japan, this is "nightline," march 16th, 2011. >> good evening, i'm cynthia mcfadden. tonight, a special broadcast on what today became an acute nuclear emergency in japan. with three reactors melting down, a fuel fire in a fourth and spent fuel rods exposed to the air. one official told abc news, quote, it would be hard to describe how alarming this is right now. and, as a small group of remaining workers battle to cool the molten rods at the reactor's core, nuclear scientists voiced alarm, as well. there is grave concern that if the containment walls around the plants fail, a dense radioactive cloud might be spewed into the air and be carried by wind and weather to large population centers in japan. the news prompted expatriates and japanese alike to crowd

airports and roads looking for ways out. many left sendai, north of the damaged nuclear plant. abc news' clarissa ward reports from osaka japan, about 360 miles southwest of the plant. >> reporter: we've come down to the southern city of osaka, it's about 240 miles south of tokyo. the reason we've come here, of course, is because of that increasingly dicey situation at the nuclear plant in fukushima. the japanese military is now dumping water literally into a hole in the roof of reactor number three, caused by an explosion. and they were spraying water on reactor number four. they tried yesterday and had to abort due to high levels of radiation. all in an attempt to cool down the radioactive rods that are now fully exposed. all day long, the last line of defense against a full-on nuclear catastrophe has been a small group of employees, working deep inside the plant, armed with flashlights and hoses. it would be hard to describe how

alarming this is right now, an american official told abc news. he said, everyone recognizes this is a suicide mission. the only glimpse of what was going on inside the plant came from their family members. "my husband is working, knowing he could be radiated," said the wife of one. "he wrote me an e-mail. it was pretty desperate. please continue to live well. i cannot be home for awhile." another wrote in an e-mail to the japanese television network nhk, "my father is still working at the plant. they're running out of food. he said he has accepted his fate, much like a death sentence." so, we brought a copy of the newspapers here, and, of course, the nuclear fallout is dominating coverage and everywhere you go, people are talking about it, but what's not the focus here is the men who are going inside and risking their lives in order to try to put out the crisis.

it's kind of interesting. when you talk to people here, they don't see these men as heroes in the same way as maybe you or i would do. they see them more as fulfilling their duty or taking care of their responsibilities. "when you build nuclear power plants, you have to think this sort of thing could happen," this taxi driver tells me. "even so, i really appreciate what they're doing." "well, it's a hard job, i know, but they have to do it," this man says. "if they don't we'll be in serious danger." it was a day filled with ominous developments. radioactive rods entirely exposed. a surge in radiation levels. and smoke billowing from reactors. at one, an explosion blew out the roof and outer walls, possibly cracking the critical cement containment vessel that holds the radioactive material inside. the japanese government ordered residents within a 12-mile radius of the plant to evacuate. those who could did. those who could not received a terrifying directive.

stay inside, close your windows and doors. essentially, shut yourselves off from exposure to the outside elements. a local japanese television crew defied that directive and found patients stranded inside a hospital. and doctors who had stayed behind to care for them. "we aren't really supposed to stay here, but it's our job," one of them says. the staff is too scared to open their locked doors to outsiders. and only do so after scanning for radiation. at a home for the elderly, a staff member said, "my family has already evacuated and i want to run to join them. but i'm hanging on and continuing my work here. i want to move the elderlies to a safer location." and at this school where people are taking shelter, the situation is just as grim. "my blood pressure has shot up and i've forgotten my medicine." the doctor here told the tv crew, "we can't last another three days. they are distributing drugs but so far, i haven't gotten any."

information is scarce for those living in what has essentially become ground zero. said one man, "we weren't told when the first reactor exploded. we were only told on tv. we're isolated. we're being left here to die." after a week in which the situation in the nuclear plants here seems to be going from bad to worse, some experts are saying this crisis could rival the 1986 chernobyl disaster. the biggest concern now is keeping the reactors cool so that they don't melt and release radioactive particles into the air. outside the plant, radiation levels are in flux. at their worst, they are tantamount to getting 10,000 x-rays in an hour, some reaching distances as far as 70 miles away. emergency scenarios suggest that retirees would likely be asked to volunteer next. not because they are more skilled or because they're more expendable, but because even if they are exposed to massive

amounts of radiation, those radiation-induced cancers would likely take years to develop. cynthia? >> our thanks for that remarkable report. when we come back, we have the incredible story of an american family's journey through the epicenter of disaster. ooh, a brainteaser. how can expedia now save me even more on my hotel? well, hotels know they can't fill every room every day. like this one. and this one. and oops, my bad. so, they give expedia ginormous discounts with these: unpublished rates. which means i get an even more rockin' hotel, for less. my brain didn't even break a sweat.

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and crowding airports in an effort to get as far from the danger as possible. among them was an american family. tonight, from japan, my co-anchor bill weir has their story and one of his own. >> should i stay or should i go now? that lyric is the very serious question of the moment here in tokyo, where every flight out of town is booked and millions more are considering their exit options. when we arrived at haneda airport in tokyo in the wee hours, we found the floors covered with people anxious to take the first flight out. i met some americans who work for honda who said their company encouraged them to come back to the states until the situation and their nerves calm down. yesterday, we boarded a different kind of flight, hoping to visit the "uss ronald reagan," the aircraft carrier staging search and rescue missions. but moments after liftoff, we were turned back due to weather, and then later in the day the commander said they're too nervous about drifting radiation to allow us on board that ship.

and as for official advice on what to do, it really depends on what country you're from. the u.s. position is that all americans, including the 80,000-plus troops that are stationed here should stay at least 50 miles away from the damaged reactor. but that's more than twice as far as the official japanese no-go zone. now, while many of our colleagues are basing more than 150 miles away to cover this story, i'm going to catch a scheduled flight back to the states. and i've got to say i'm conflicted about leaving this major story. but also, relieved to be getting out of the danger zone. fears of radiation exposure sparked runs on food and other supplies in the affected areas. this woman says she has no gas, no heat and no matter how long the line, all she can do is wait. with over 4,300 officially dead, more than 10,000 missing, rescuers continue searching through debris, pulling bodies from the wreckage. makeshift morgues like this one have been set up. family members like this woman,

searching for her nephew, continue looking, hopeful for any signs of survival. but with the landscape so shattered, she wasn't exactly sure where the family's house once stood. six days into the crisis, the emperor of japan finally told his country not to give up hope, adding, i'm deeply concerned about the nuclear situation, because it is unpredictable. with the help of those involved, i hope things will not get worse. with simple facts so hard to come by, frustration is beginning to brew. this man from an evacuated area says, "there's hardly anything i can use to make any decisions by myself. i'm really confused." yumi is also worried. radiation cannot be seen, she says.52ñ we don't know how to find out whether it's been carried into the air or not. maybe our food is contaminated. >> i'm an executive with the professional baseball team in sendai, japan and also vice president of sendai university.

four days ago, my family and i survived the fourth largest earthquake in the history of the world. >> reporter: this family are among the growing number of people who believe getting out is the safest move. >> now we realize that fukush a fukushima, 60 miles south, is a huge nuclear problem which really concerns us. we've decided to get out of town. here's our bags. we've packed up, are leaving very shortly and getting out of sendai. >> reporter: they packed their bags yesterday morning and left sendai for kyoto to stay with family. and they know they're lucky to even have this option. >> my wife, daughter and i are leaving our apartment right now and unfortunately, for the people of sendai, especially where they were hurt really badly, it's snowing right now. and that's going to hurt the people who have no housing and are without shelter. >> reporter: in their hybrid mini van, marty, his wife and their 7-year-old daughter

documented the 16-hour-long journey. first stop, a gas station. >> they're not selling any gasoline but they are selling kerosene. and people are coming, lined up to get it for the kerosene stoves to heat their houses, in many cases don't have electricity right now. >> reporter: then more lines in the dreary day, people huddled under umbrellas, waiting for a chance to go into the supermarket. >> there's a great shortage of food. in every place there are long lines in the entire town to get food. and this line seems to go down the hill for quite a ways. >> reporter: the bare shelves of a local convenience store are what awaits. >> if they want any food, they're out of luck. there's practically nothing left in the store at all. >> reporter: as they drive along the slush-covered streets, another desperate sight. cars backed up. more than can be counted. waiting for precious gasoline. >> 90% of the gasoline stations are closed. and all the restaurants in the area, most all of them are all closed. >> reporter: but at restaurants close to ngata a dramatic change.

life looks almost normal. a rest stop shows people quietly eating. >> it's hard to believe that just six hours away, there's all that death and destruction. because here in this rest area, which has a little store you can see, right now, there's abundance. >> reporter: and a hot meal over halfway there. still no signs of the disaster gripping much of the country. >> we've been on the road about 10 1/2 hours now and we stopped here now and it's very calm here. >> reporter: and an hour shy of their destination -- >> 15 hours. not so bad. >> reporter: finally, an opportunity to fill up. >> there's no lines. not any cars in line and we're getting gas tonight. >> reporter: at the end of their journey, a sense of relief. >> we're in kyoto now, we made it after going through seven prefectures, over 16 hours and over 750 kilometers.

so, we're so happy to be here in the old peaceful capital of japan. and sorry to say that we're glad to be out of sendai, but you don't think it's very safe now because of the nuclear reactor problems in fukushima. and we're so sorry that everybody else in sendai area and the whole area can't get out. >> one happy story, we'll be happy to have you home safe and sound, bill weir. after six days, the crisis is still developing. as you heard in bill's report, rescuers were further slowed by biting cold and snowfall as they search for the thousands still unaccounted for. one more challenge for them and one more danger for those left homeless by the disasters. up next, can a nuclear disaster be averted? what comes next?

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we turn now to the specific nature of the danger facing people should that japanese reactor in fact melt down. joining me, abc news consultant, physics professor michio kaku. we've seen the helicopters dropping water on the site. if that doesn't work, what's next? >> that helicopter dropping water is like a squirt gun

trying to put out a forest fire. too little, too late. i think we're extremely close now to the point of no return. just a few more slight glitches and we're going to be in an uncontrolled breach of containment. that is a class seven accident that is a full-scare chernobyl. >> you think meltdown is inevitable at this point? >> almost inevitable. at a certain point, the workers going into that site will be on a suicide mission. they will have to abandon ship. and without anyone taking care of the reactor core, as we will have three simultaneous breach or containments. already, units two and three have cracks in their containment vessels. already, unit four has a raging fire, we think, involving spent fuel that is not contained by any containment vessel. so, we are very close now to something that is even bigger than chernobyl. >> so, professor what does the worst case scenario look like 12

miles around the reactor. are people going to die within that region? what about the radiation plume? >> worst case scenario, you have breach of containment. the containment structure springs a leak, you have an explosion, the thing cracks apart and releases large quantities of radiation into the atmosphere. that area will become a dead zone. it will be impossible to grow anything, people in that area will die. we're talking about lives at stake. and that's why i would say, if i had the ear of the prime minister, forget about using squirt guns. call in the jaap neepanese air . hit that reactor with concrete, sand and boric acid. seal it, entiomb it just like chernobyl in 1986. i think we're close to that option now. >> professor kaku, thank you. and thank you for watching abc news.