In the days after Japan’s Fukushima nuclear accident began, GlobalPost turned to Arnold Gundersen for an independent view of whether the reactors might melt down. A 39-year veteran of the nuclear industry, Gundersen has worked as a nuclear plant operator and served as an expert witness on the Three Mile Island accident. He is now chief engineer at Fairwinds Associates.

Back then, Gundersen said that the evidence suggested the accident was worse than authorities were revealing. This week, his assessment was shown to be accurate when Japan upgraded Fukushima to a 7, the worst possible rating for a nuclear accident.

So we contacted Gundersen again to get an update on Fukushima. In the following edited and condensed interview, Gundersen gives his expert view of what might happen, how authorities are handling the accident, and how Fukushima will affect health and the environment.

GlobalPost: Last month, officials said that the possibility of a large scale radiation release from Fukushima was “small.” You disagreed. You told GlobalPost that there was a “50-50 chance of a catastrophic release.” Now, nearly every day we hear about new releases. Has this added up to a catastrophic release?

Arnold Gundersen: Yes, Fukushima has released catastrophic levels of radiation. There hasn’t been a single Chernobyl size blast, but there have been three explosions, as well as radioactive venting that will continue into the future. And there are still potential bumps in the road. It’s not over yet.

This week the Japanese authorities elevated the crisis from 5 to 7. That suggests it’s on a par with Chernobyl. Is this accident as bad as Chernobyl?

It’s worse than Chernobyl. That accident involved a single reactor. Fukushima involves three reactors. Additionally, there are several years worth of fuel in the spent fuel pools of units 1 through 4. Added together, that’s roughly the equivalent of eight reactor cores.

Right now, I don’t think any single reactor is as bad as Chernobyl, but they have essentially eight different problems.

The Japanese government has said that Fukushima has released about 10 percent as much radiation as Chernobyl. Do you think that’s accurate?

I’d say that’s the minimum that’s been released. It’s possible that the accident has released as much as Chernobyl already. If not, we’re heading in that direction. I think the Japanese have wanted to avoid instilling fear. So as a result they are more likely to downplay than exaggerate the releases.

Estimating radiation releases is never easy. I’ve studied both Chernobyl and Three Mile Island. The statistics on how much radiation was released were made after the accidents were over, by scientists who have skin in the game. During a nuclear accident, all of the radiation detectors are blown to smithereens, so you’re not actually measuring the contamination, you’re calculating them based on sampling. When you do that you can introduce bias.

So if it’s worse than Chernobyl, is this the worst industrial accident ever?

I think this and the Bhopal accident in India [where hundreds of thousands of people were exposed to the toxic gas methyl isocyanate, killing thousands] are going to be neck and neck for that category. So it’s worse than Chernobyl but in the same category as Bhopal. But certainly from a cost standpoint, this is the most expensive one ever.

I absolutely disagree with the scientists who say that Fukushima’s not going to hurt anyone. The numbers I’ve seen, from reputable scientists, are that Fukushima is going to kill 200,000 from increased cancers over the next 50 years.

Is the evacuation zone big enough?

It’s not a question of size, but of timing. I was saying that it should be 19 miles (30 kilometers) a month ago. They’re now extending it to 19 miles, but they’re giving people a month to leave.

If there’s any good news from Fukushima it’s that the wind was blowing offshore most of the time. If the wind was blowing onshore, Japan would be cut in half. There would be an uninhabitable zone going right across the island if the wind was blowing the other way.

Are international organizations effectively keeping an eye on this?

The International Atomic Energy Agency has been behind in its analysis since the very first week. They were saying that 5 percent of the fuel was damaged when I was saying 70 percent. I don’t have any faith that the IAEA data is accurate.

How does an independent expert such as yourself get data?

I’m working with an informal network of independent university professors around the world. I’m actually hoping to get more people providing information through this network.

My experience with Chernobyl and Three Mile Island is that the government and industry will circle the wagons and try to prevent information from accumulating in private hands. The same happened with France, which gets much of its electricity from nuclear. The government there downplayed Chernobyl releases.

The difference now is that we have the internet. Independent scientists can more readily share information quickly, and bureaucracies don’t know how to respond to that. So I’m hoping that this will prevent governments from distorting information. Yet I do believe that they are getting away with downplaying the crisis right now.

This crisis is now labeled a 7, the most severe possible nuclear accident. Does this accurately represent how bad the accident is, or if there were an 8 or 9, would you rate it worse?

It’s a 7 now. If you’re asking, does it have the potential to get worse? The answer is yes. Let me explain the biggest risks for the future.

In unit 1, there’s so much mud in the reactor that they can’t get water into the core, which they would normally need to do to prevent it from overheating and melting down. Instead, it appears that they are flooding it from the outside, and cooling it that way.

That’s working, except that the containment structure on unit 1 was not designed to handle all the excess weight from the water. If there’s an earthquake — not a magnitude 9 on the Richter scale, like the one that kicked off the accident, but one just over 7 — the containment could fail.

If that happens, unit 1 could become a Chernobyl on its own.

But my biggest fear right now is the unit 4 spent fuel pool — the area outside the containment where they store the degraded but still-radioactive fuel that they’re no longer using to power the reactor. That worries me a lot.

There was a report this week that they found iodine-131 in that fuel pool. Iodine-131 can only come from nuclear fission, and because it has a short life, it disappears after about 80 days.

In other words, the presence of iodine-131 suggests that the spent fuel has started its own chain reaction without any human intervention.

That tells me that the racks that have been distorted — by the earthquake, or by the crane that fell in, or by the heat that caused the first explosion.

You’re talking about the racks in the fuel pool that keep the spent fuel apart, preventing the chain reaction that normally goes on in the reactor. And you’re saying that these racks were apparently damaged, enabling the fuel to reach critical mass and re-start the chain reaction on their own, without controls?

Yes. As workers pour water into unit 4 — which they need to do to keep it cool — they might essentially be creating a nuclear reactor, without control rods used to shut down the reaction, and without a containment building to keep the radiation in.

So unit 4 is still a significant risk. The fuel could get hot enough from the chain reaction that it will boil the water out again. So we could still get a fuel pool fire. That would volatilize some really heavy elements, sending some highly carcinogenic materials into the atmosphere. This should be a very big concern.

And that’s not the only problem. Another concern is that as a result of the accident, the building housing unit 4 is very weak structurally. They’re going to have to shore it up somehow from below so it can handle all the extra weight. Right now there’s little or no water in the fuel pool. They need to add water to keep the fuel cool. The pool has a crack in it, so it’s not clear that they can fill it with water. If they do, they will add so much weight that if there’s another seismic event it could cause the building to break, which would not be good.

How likely is it that the accident will get worse?

My read is that the accident could get worse if an earthquake impacts unit 1, or if unit 4’s spent fuel starts a nuclear reaction without any human intervention. Both of those are maybe a 10 or 20 percent probability.

So there’s about a 70 percent chance that the worst is behind us, and a 30 percent chance that things could still get worse.

There are a lot of balls in the air. As Dave Lochbaum from the Union of Concerned Scientists says, "Even the best juggler in the world can have too many balls in the air. They have a lot of critical things in the air, and one wrong move could make the situation much, much worse."

What about the risks to units 2 and 3?

In unit 2, they’re pouring water in the top to cool the fuel. Nuclear reactors are usually cooled using a closed system, in which cooling water circulates through the fuel rods. When the water gets hot, it is cooled via a heat exchanger and re-used in the reactor. Because it never leaves the reactor the radiation stays inside.

But the water they’re pouring into the top of unit 2 is flowing out the bottom because the containment is leaking. So unit 2 is the biggest polluter of the Pacific. It’s going to constantly pour out water at a terrible level but it’s stable. I don’t think it’s going to get worse.

What about unit 3?

Unit 3 is the one that looks the worst, with the most rubble. But the reactor is actually the closest to being cool. It’s almost at boiling, 200 degrees Fahrenheit cooler than any of the other units.

That said, the spent fuel pool on unit 3 looks from all the pictures to be partially obliterated. And it’s the most highly contaminated because of the explosion. The damage to this facility tells me that the fuel has been scattered, and will be hard to reconstitute.

Do you think TEPCO and the Japanese authorities are doing a good job handling the crisis, and communicating the risks?

No. I think they’re doing a better job now than they were at first. But I don’t think they’re doing a good job. Part of the problem for at least the first three weeks was that the data was so poor. You can’t make good decisions based on bad data. I think that affected some decisions that were made poorly.

Things are better now as far as getting control, but I don’t think they’re really conveying the risks to the public.

Let's talk about the impact on people. What does this mean for Japan? When will people be able to go back to their homes?

Within six miles, I don’t think they’re going back within a generation. There will be so much contamination and it will take too long to clean. They’ve already found plutonium in the form of fuel rods off of the nuclear plant site.

There are also indications that some areas 25 miles away have cesium concentrations higher than Chernobyl. You’re going to be monitoring dairy and beef cattle for years.

How will this affect the ocean? And how will it affect fish?

Here’s how it works: The cesium settles on the seafloor. That gets absorbed by aquatic plants, seaweed and other life. The bottom feeders eat that, and other animals eat them, and it works its way up the food chain. Eventually, it will make it into the larger fish that we and the Japanese eat — the tuna and the salmon, for example.

You’ll be monitoring fish, I think, for decades.

Will that be limited to Japan?

I think most of the contamination will be localized to within 100 miles of the plant. The problem is that fish swim. The bigger fish swim longer distances, and now of course they’re flown around the world for eating. It’s too early for that contamination to show up in these predators. It has to work its way up the food chain. You’re probably safe to eat fish in Tokyo now. I’d worry about it more in three or four months than I do now. They’ll have to monitor fish markets by sampling the meat and putting it in a detector to see if it’s contaminated.

That said, they’ve already found contamination in small fish 35 miles south of the plant.

Is it likely that the levels of contamination will be harmful for human consumption?

Yes. Here’s an example: Chernobyl wafted cesium 137 into Germany. We’re talking about more than 300 miles. Even now, 25 years later, the wild boar that eat the mushrooms on the soil that’s absorbed the cesium 137, can’t be eaten.

When hunters capture a wild boar, they give it to a state lab to determine whether it’s clean. One-third of the wild boars are contaminated. So with that as an example on an airborne release, I can’t imagine that a waterborne release will be any different.

What about the many products that are manufactured in Japan and transported around the world? Are they safe?

Aside from food, I wouldn’t worry about Toyotas or silicon chips for computers or other industrial products. They’ll be fine.

Will there be health impacts in North America? What are you doing to protect yourself?

I bought Iodine pills, but I’m not using them. I don’t think the radioactive iodine releases in New England, where I live, are going to be significant enough to worry about. I haven’t looked at California or Alaska or other West Coast data.

After our last interview, you were criticized as an alarmist by people ranging from a Vermont state senator to Rush Limbaugh. Now that the crisis has been elevated to a 7, the maximum level, how would you respond to them?

I was really being objective. I think that rather than me being an alarmist, they were being apologists. The record has shown that the alarmists were right and the apologists were wrong.

Some commentators are saying that even with the Fukushima accident, nuclear power is far safer than coal, which kills thousands of people each year from mining accidents, pollution-related lung cancers and the like. Do you agree with this?

Coal kills a lot of people, there’s no doubt about it. But it’s a false alternative to say we need more nukes because coal kills more people.

I think we need to reconsider the central power station paradigm — where big power plants provide electricity to a large area. Whether it’s coal or nuclear, that was right for the 20th century. It’s wrong for the 21st century.

My thought is that we shouldn’t shut nuclear reactors down immediately because they’re killing people in Japan. You simply can’t do that. Instead, Fukushima forces us to look at this paradigm of putting enormous amounts of money into one plant. The Votgle plants in Georgia — two of them will be pushing $20 billion. I think our money would be better spent distributing the grid.

With the advent of smart grids and distributed transmission of electricity and power sources like a 2 megawatt windmill or a gas-powered “bloom box” fuel cell that generates electricity very efficiently, I think that by 2040 we’ll be a distributed energy network. New nukes are like the Maginot line of electricity. By building them, we’ll be trying to solve a problem that technology has already surpassed, the way the French built the Maginot line tried to prevent the Germans from invading. Instead, they just went around.

Follow David Case on Twitter: @DavidCaseReport

Editor's note: Here's GlobalPost's first interview with Gundersen, conducted immediately after the accident.