article

03.12.11

Japan Nuclear Fallout: How Bad Could It Get?

As Japan scrambles to cope with a nuclear reactor damaged in the quake, Josh Dzieza talks to a nuclear expert at MIT about how the plants work, worst-case scenarios, and more.

As Japan scrambles to cope with a nuclear reactor damaged in the quake, Josh Dzieza talks to Ron Ballinger, a nuclear expert at MIT about how the plants work, worst-case scenarios, and more. Plus, full coverage of Japan's catastrophe.

Shortly after Japan was hit with the double disaster of a magnitude 8.9 earthquake and subsequent tsunami, a possible third reared its head: nuclear meltdown. The quake caused 11 of Japan's nuclear reactors to shut down automatically, including three at the Fukushima Dai-ichi power plant, 170 miles northeast of Tokyo. But the quake also cut Fukushima off from the power grid, forcing plant operators to switch to emergency diesel generators in order to continue cooling the reactor core, generators that then failed shortly after the tsunami hit. By the end of the day Friday, Prime Minister Naoto Kan had declared a “nuclear emergency,” and 200,000 people near the plant had been told to evacuate.

Gallery: History's Worst Nuclear Disasters

Then, Saturday afternoon, a building at the plant erupted in a massive explosion, apparently the result of hydrogen from the superheated fuel rods interacting with oxygen as plant operators tried to vent increasing pressure inside the reactor. Officials say the reactor wasn't damaged in the blast, and that radiation levels have actually been declining since. Nevertheless, they took the extreme step of flooding the reactor with seawater in an attempt to cool it down, and news that the cooling system for a second reactor at the same plant has begun to fail did little to calm worries of a meltdown. As Japan copes with its worst nuclear mishap at least since the leak at Tokaimura, The Daily Beast spoke with MIT Professor of Nuclear Science and Engineering Ron Ballinger about worst-case scenarios, iodine tablets, and why he thinks everything is going to be fine. Plus, complete coverage of the quake.

What's the worst-case scenario?

Well, first off, we can't have a Chernobyl-like situation. The system is designed so that as long as we keep water in there to keep it cool, nothing will happen. There are three levels of protection here. One is the fuel cladding, and if that's damaged then it releases radioactive material into the pressure system, which is a steel container. Then there's a containment vessel around that. What likely happened is that you had fuel damage, damage to the first barrier, which produced hydrogen in the primary system, and then to keep the pressure down they vented the hydrogen into the building that was destroyed.

What happens if all the water boils off?

Hypothetically, if the water all boils and evaporates, then the fuel will stay molten and eventually melt through the steel vessel. But that's already beyond a hypothetical worst-case scenario for me. The steel vessel is four inches thick, and they could always put seawater around the vessel, and that would keep it cool, so it can't melt. If you put a frying pan in water, you could put a blowtorch on the other side and it won't make any difference. Then you have the other containment vessel, with a concrete faceplate underneath that's between four and 10 feet thick. But melting through that is hypothetical beyond normal reasoning.

Radiation spiked at 1,015 microsievert per hour before the explosion. Is that dangerous?

No, that's about 100 milirem. It's high, but you get about 35 milirems on a trans-Atlantic flight. And if you live in Denver, you get about 50 milirems per year.

What is the dangerous level, and what happens when that level is reached?

The LD50—that is to say, the point when 50 percent of the people exposed will meet Jesus—is in the order of 250 rem, or maybe 400. A big number. Keep in mind, what they've been exposed to is 0.1 rem, and about 50 percent fatality is on the order of 400 rem. What would happen with that kind of exposure is that they would get sick. Radiation damage destroys the immune system. Most people who die of radiation sickness die of pneumonia or a cold, they die of some disease which they have but their immune system can't fight off.

Why is Japan distributing iodine tablets?

One of the isotopes of fission products, when fuel melts, is an iodine isotope, and it goes in your body through your thyroid. So if you take iodine tablets, the non-radioactive iodine goes to your thyroid, you bulk up your thyroid with iodine and it prevents absorption of the radioactive iodine.

What failsafes are there to prevent a meltdown?

A lot. First there's the SCRAM system, it automatically ejects the control rods into the core and shuts the plant down. That happened right after the earthquake. Then there's a number of core spray systems, which inject water to keep things cool. Then, if the system needs to depressurize, there's something called a suppression pool that it vents steam into. Then, when the system is depressurized there are other systems that inject water at low pressure. And then, worst comes to worst, there are pumps that can take water from the local cooling water supply, in this case the ocean, and just pump water in there. As long as there's water in there, it might be expensive for the utility to get it cleaned up, but everything is going to be fine.

If they're pumping in seawater, does that mean all the other failsafes failed?

The earthquake plus the tsunami destroyed all the power sources to run pumps and things like that. There are diesel generators on the site that are supposed to run for that purpose, but for some reason they ran for a while and then stopped, maybe because of the tsunami. Then they hauled a bunch of portable generators to run the pumps.

How good a failsafe is pumping in seawater?

The ocean's pretty big. But it's salt water, so from an operational point of view you're pretty screwed. If you get saltwater into the primary system, it's very hard to get it cleaned up. Salt water's not good for the materials, it requires pure water. So if they have to put saltwater into the primary system, it would keep it cool, but it would damage a lot of things and there will have to be extensive cleanup.

How will we know when the crisis is over?

The fuel has to cool down to the point where the water that's cooling it is below the boiling point. Usually when they shut one of these plants down to refuel they have to open it up. It takes a couple days to get the plant shut down to the point where they can take the lid off and replace the fuel. It might be a financial disaster, but no member of the public has been hurt, and I doubt anybody will be.

Josh Dzieza is an editorial assistant at The Daily Beast.