Why Fukushima Isn’t Like Chernobyl
Image Credit: Flickr / Daveeza

Why Fukushima Isn’t Like Chernobyl


Is the kind of massive radiation release that occurred with Chernobyl possible at the Fukushima plant?

No, it can’t have that kind of massive release. It simply can’t do that. The question is to what extent the zirconium alloy, which clads the fuel pellets, is damaged in the core, and how much of the fuel has failed. And I don’t necessarily mean melted, I mean failed. There’s been an ambiguous use of the word ‘melting’ applied to the core. But when people talk about meltdown, they should be very specific about what they mean by the word.

At Fukushima, there are four primary barriers to releases: the fuel zircalloy cladding, a pressure vessel, an inner containment structure, and a confinement building. To a large extent, the core material seems to be contained. Apart from, of course—and this is where the speculation runs wild—there’s the question of the source of the radiation they’re detecting in certain areas where water has accumulated. Indications today are that it isn’t the cores. They’ve been dumping or spraying tremendous amounts of water onto and into the damaged buildings, so surely someone is considering this water as a possible source.

But until they go in and see, we have little more than speculation to go on, because they don’t know to what extent—if any—the cores are damaged, and they don’t know to what extent the pressure vessels are damaged, although that’s unlikely. They also don’t know to what extent the pipes are damaged, and they don’t know to what extent the lower portion of the containment building is damaged. So, on the one hand, I can’t speculate on what is going on inside. But even so, and given what nuclear engineers know in terms of the plant layout, it’s just not true that it’s a Chernobyl situation.

So, you’d say it was unfair to draw parallels between Fukushima and Chernobyl?

They are very, very different and it’s very unfair to draw that parallel. There are two parts to this. One is the myths that currently surround Chernobyl. The other is the sheer difference between the incidents—the causes of the accidents and the structural, engineering and physics differences.

For a start, there are three or four primary and important differences between the two reactor designs. The first is the difference between the Western Light Water Reactors—pressurized water reactors and (like those at Fukushima) boiling water reactors—and the plant at Chernobyl.

Western Light Water Reactors are water cooled and water moderated. The first one is simple—water is used to cool the fuel, to take away the heat, to eventually create steam and then after that make electricity. It’s the water moderation that’s the very important difference. What moderation means is that the water is used to slow down neutrons in the core and make them accessible for the reaction to take place. In the Chernobyl type reactor, water is a coolant, but it’s not a moderator—the moderator is graphite, and that points to one important design and structural difference.

In the Light Water Reactor core, apart from the fuel itself, it’s virtually all metal. You have the fuel contained in a special kind of zirconium alloy, there’s the stainless steel vessel, and the super structure is metal. In the Boiling Water Reactor (BWR) that you find at Fukushima, you have a reactor pressure vessel that’s approximately six inches thick steel—it’s basically a big kettle that contains the core. In the Chernobyl reactor, there was no pressure vessel. So right there, there are two very big differences—the BWR is contained in a very robust pressure vessel, the Chernobyl reactor was not. The BWR reactor is a singular metallic vessel, while the Chernobyl reactor is approximately 1700 individual pressure tubes piercing about 2,000 tonnes of graphite. Western LWRs contain essentially no graphite. Those are very big differences.


[...] Despite the Fukushima disaster, nuclear energy output is expected to grow by 2.6 percent a year, compared to an average growth rate of 1.6 percent over the last two decades. 88 percent of growth in nuclear energy will come from China, India and Russia. By 2026, China is seen overtaking the United States as the largest producer of nuclear power. Four years later Beijing will account for 30 percent of nuclear energy production, according to BP. [...]

April 3, 2011 at 04:21

I say is too soon to draw rational conclusions. Let the japanese and other nuclear engineers do the work that urgently need to be done. Once things are under control let us conduct world hearings and an independente investigation about what happened. Then we will be able to make ourinds up. In the mean time take much of what the media healines as tragedy-based infotainment, not information. Let us not forget that US style media have succeeded into paralizing the US as an industrial country where they do not wanto to do any industrial innivation for fear of lawsuits, this is why even Apple will be unable to manufacture the Iphone in the US; the technology is simply not available in the US.

Victor ben Abraham

The Rad Rider
April 2, 2011 at 05:28

Dear Nasu :

My best wishes are with you and your people but my wishes don’t change things.
If they did, this would never have occurred. The best that I can hope for at this time is that we don’t let something like this happen again.

Take Care

The Rad Rider
April 2, 2011 at 05:19

You are correct to point out that this is not over. Perhaps he used a crystal ball or a pan of water to look into the future. If so, I’d like to know the final outcome and I suspect, a great many others would as well.

The Rad Rider
April 2, 2011 at 05:07

Hi Informant :

No, posting a reply to this article is not the best I can do. I’ve also been in contact with the U.S. Senate and Greenaction-Japan. If you have found factual errors in any of my posts, please detail them and allow me to make corrections.

Thank you for you concern.

April 1, 2011 at 21:16

Wow, 3 decades and that is the best you can do? I guess maybe you need a couple more decades before you will begin to sound educated. @ Rad Rider

April 1, 2011 at 20:37

I live in Fukushima. Regardless of what all the experts say, the earthquake and tsunami have caused massive damage to people’s lives, homes, schools, roads, etc. With all the information from the Japanese media (TV and radio), and the news from sources outside Japan, it’s very difficult to paint an accurate picture of what’s going on. I live within 60km to 70km of the reactors, food and water is questionable, but said to be safe. Hearing the figures about radiation in food and water here is mentally exhausting. What information is accurate? Some of my Japanese friends question whether the government is not telling the whole truth, while others are trust the government completely. What can be said to be 100% accurate is, the Japanese governement is doing there best to get the situation under control. This earthquake and tsunami has changed Fukushima prefecture forever. It will never be the same again.

The Rad Rider
April 1, 2011 at 09:58

Hi Again :

Not wishing to take up another post for a spelling correction, I’ve provided a link to the Rasmussen Report in case some of you would like to read it for yourselves. You will find the quote I posted on page 28 of the report, in the right column, near the top of the page.


Happy Trails

The Rad Rider
April 1, 2011 at 08:00

Hi Another Guy :

Instead of trying to point out problems with your post, I’ll concentrate on using it to point out a couple of critical issues that substantiate mine.

“It happened two weeks ago, after all.”

Indeed it did. That being the case, I can not explain why the I-131 levels being reported are dramatically increasing instead of decreasing. The half live of this isotope is 8 days and it is only generated during active fission.

If, and only if, TEPCO is correct and fission is not occurring at any of their damaged reactors, the only logical explanation for the new reports to be much higher than the previous readings, would be that some of the reports are inaccurate.

“… I’d wager that if – if! – the vessel itself actually blew up, the weakest points would be its piping and connection to the supression pool below; not the top.”

The section of the Rasmussian Report to the NRC that supports my conjecture follows :

“If a steam explosion were to occur within the reactor vessel, it is considered possible that both large and small containments could be penetrated by a large missile. Such occurrences might release substantial amounts of radioactivity to the environment.”

They were attempting to inject water into the reactor vessel after they had noted that the water level was not sufficient to cover the fuel rods.

Best wishes

Another Guy
March 31, 2011 at 19:26

@The Rad Rider: You say you find no factual errors in your post, but since your post is a collection of suspicions, conjecture and guesswork, that’s not surprising. Sorry, but I had to say it.

If the MOX core had indeed been ejected wholesale into the atmosphere, I’m pretty sure quite a few monitoring stations around the world, not to mention inside Japan, would have spotted some serious fallout by now. It happened two weeks ago, after all.

You’re somewhat right about one thing, though: The blast at building 3 looks directional. That’s because the upper part of the reactor buildings at Fukushima are significantly thinner than the rest of the building. That’s plainly obvious looking just at pictures of building 1 after its (smaller) explosion.
My point is, that the entire building is a well-like structure with a thin lid, and explosions – whatever their cause – take the path of least resistance. As you say, much like a cannon fired straight up. But the cannon is not the reactor vessel. In fact, I’d wager that if – if! – the vessel itself actually blew up, the weakest points would be its piping and connection to the supression pool below; not the top.

I suspect the buildings were pretty much designed to cope with explosions in that way: Explosions in the building, but outside the vessel, blow the roof off. And blow if off easily to release pressure quickly, rather than have the building be a bigger bomb. Also, they blow it upwards and away from neighboring reactor buildings. Meanwhile, if the vessel itself blew, it would likely blow downward or sideways inside the building, which is another reason why the reactor is partly below ground and the side walls of the building are so much thicker.

As for the cloud being dark, I’m pretty sure it’d look the same if you intentionally filled the building with hydrogen and ignited it. Or threw some dynamite in there. The explosion in building 1 looked “cleaner”, but was also much smaller, and only blew off the top panels of the building, leaving the struts beneath intact. The explosion in building 3 was bigger, so the idea that it’d hurl a lot more dust, soot and other debris around isn’t exactly far fetched, is it? Dark smoke does not a reactor core explosion make.

So that’s my conjecture and guesswork. I’m biased, of course, but it seems a lot more plausible than yours.

The Rad Rider
March 31, 2011 at 11:59

I need to make a correction on my time of service.
1977 through 2006 is a little less than three decades.

Otherwise, I can find no factual errors with my posts.

Stay in school,
Study hard,
Party little.

Live long and prosper.

The Rad Rider
March 31, 2011 at 11:46

Hi :

“Rad Rider you have no clue….. ”

Having retired after more than three decades of nuclear work, you may be correct. Perhaps I’m simply senile.

“Chernobyl was a power excursion that caused the core to exploded into bits. There is no way a hydrogen buildup explosion could cause the core to be launched that far into the sky.”

My assertion was that a steam explosion ejected the # 3 reactor core.

“On top of that there are government monitoring units and independent (teams from other countries in the field) teams monitoring the radiaiton levels, the radiation spike from that event would be unprecedented and would have been picked up already.”

I have no doubt that accurate readings are possible. Just as I was sure that the radiation reports, that were constantly reported as being from the main gate, were fluctuating wildly due to the wind. A valid assessment would have required that the ring of monitors that surround the plant were polled to account for the change in wind direction.

Were you to try and read my post again, slowly, you may see that I suspect that the truth is being not being shared with you.

Think what you will but think for yourself.
Thinking is not the same as guessing.

A guy
March 31, 2011 at 09:38

Rad Rider you have no clue….. Chernobyl was a power excursion that caused the core to exploded into bits. There is no way a hydrogen buildup explosion could cause the core to be launched that far into the sky. On top of that there are government monitoring units and independent (teams from other countries in the field) teams monitoring the radiaiton levels, the radiation spike from that event would be unprecedented and would have been picked up already.

Sorry, but you are an alarmist without cause…..

March 31, 2011 at 05:32

The need is for a new type of reactor design that is inherently incapable of “melting down”. Thorium powered reactors supposedly would meet that criteria (Russian and India are working on this technology), there are also other designs that supposedly would simply shut down and cool off in another Fukushima-type event. It is time to accelerate development of these improved designs, and realise that many of the oder designs are inherently flawed. Their closure and replacement with newer designs should be expedited. I would like to hear Mr. Sich’s thoughts on these new technologies.

March 30, 2011 at 16:35

@ the rad rider
replace Fukushima with twin towers and Hydrogen with aviation fuel and the same old ‘cant prove it but its true’ conspiracy theory comes alive.Hollywood explosions are not real world explosions as the Hollywood ones always have to be bigger, better and more firebally.
i suggest watching mythbusters when they blow things up using gas, not much fireball but certainly a lot of force!


oh and a directional blast where there a place in the structure was (intentionally made) weaker.

The reactor at the time wasnt operating and certainly wasnt molten(as in all melty and gooey). The amount of pressure needed to make the containment vessal fail is stupidly high and if it had failed the devastation to the surrounding area would be massive.
sorry to use these guys again but its my fave demonstration.

yep one small 1/4 inch steel tank. Fukushima reactor containment vessel is 6 inch’s thick.

The experts have been over cautious with their danger assessments in my opinion, that is the ones that know about nuclear engineering not nuclear science but you would know that if you had read the article.

I have learned to read up before I comment to avoid ‘foot in mouth’ syndrome. I live in hope that all other commentators learn that too. But I’m not holding my breath.

March 30, 2011 at 13:18

I largely agree with The Rad Rider, I’m sure we haven’t seen the end of this. Another thing I wonder are if they are continuing pumping water to the vessel and to the spent fuel pool, what happens to this water, you cannot continue pumping in, it also has to go out. I think what we see is contaminated water leaking out onto the ground and running on to the sea.
Also, the pumping in water would also just heighten the pressure in the vessels, there has been no reports of venting lately.

With Chernobyl there were never much contaminated material leaked directly into the sea, so I’m not sure if this have been studied before, but to mee it looks dangerous to live along that coast.

The causes of the accidents are largely different, as the author states. But the potential, if the containments are broken, is just as large as Chernobyl, if not larger. Here we have three reactors with troubles, in Chernobyl it was just one.

The key here is to restore power to the plant and make the most neccesary equipment (cooling) work, a project much larger than you think if you take into account that not only has there been a seawater tsunami overflowing most electrical switchboards on lower level, but also explosions in thebuildings that most likely has damaged electrical as well as piping installations.
Now, we do not hear much about this, and I fear this is because people cannot get into the buildings because of high radiation, and this makes the restoration of normal cooling very difficult.

Mary Mycio
March 30, 2011 at 12:22

Alex Sich does a great job of explaining many of the technicalities and the distinctions between Chernobyl and Fukushima, of which there are many. Nevertheless, I do not agree that the different reactor designs used in Chernobyl and Fukushima — and, hence, the different causes of each disaster — make much of a difference in terms of the ultimate effects of each. Judging by one source term estimate for I131 and Cs137 from Fukushima (that have not thus far been disputed), they are on Chernobyl orders of magnitude — and those are only from the first three days.

Chernobyl was one reactor. Fukushima is at least three and one spent fuel pond. The former exploded, the latter is smoking. The former seriously affected larger parts of the globe. The latter may be more localized. Chernobyl exploded chunks of core around the inner area, including a good deal of plutonium. Fukushima may release more total volatile radionuclides such as I131 and Cs137. Chernobyl had greater effects on human health. Fukushima will probably have less because of timely evacuations. All of that said, they are both severe accidents. To distinguish their cause from their effects can also be misleading.

After Fukushima, more nuclear accidents of this severity are likely. Each will be different. Being different isn’t the same as not being similarly bad.

March 30, 2011 at 04:57

Thank you – very helpful and very informative. Certainly nice to hear from someone who actually knows something as opposed to sensationalists with an agenda.

March 29, 2011 at 22:22

How can he know if it isn’t over yet?

The Rad Rider
March 29, 2011 at 19:54

No one likes an alarmist without cause, however, there appears to be ample cause for alarm.

All nuclear power plants that depend on electrical power are subject to meltdown and/or explosion if the electrical power is lost for an extended period. In the case of a massive solar storm that lasted for several days, power generation could be disrupted globally. Unless all of the vital equipment in nuclear power plants is absolutely shielded, the problems witnessed in Japan could be witnessed world wide.

Study the close up views of the #3 reactor explosion and you will see that the blast was not the type of explosion one would expect from the ignition of hydrogen. The fireball seen in the corner of the plant may have been due to hydrogen but it was much too small to cause the main blast. Not only that, inspection reveals that this was a directional blast. Much as if a cannon had been fired straight up from inside the reactor building.

This is what one would expect if the reactor dome exploded with enough force to take out the removable concrete pads covering it.

Injecting sea water into the molten core causes an immediate explosion of steam. If the temperature of the reactor vessel had reached critical temperature, it would not have had the integrity required to withstand this dramatic increase in pressure.

If my assessment is correct, the dark colored cloud we witnessed, that was shot approximately 1,000 feet into the air, contained the MOX core and made this accident worse than Chernobyl.

I also suspect that the #1 and #2 reactor vessels have lost their integrity due to the same process.

The so called experts that have been downplaying the seriousness of this accident, have an agenda other than disseminating the truth. It is long past time for the worlds leading scientists to speak up and show the discrepancies in the current story.

It is also long past time for news reporters to do the basic research required, before publishing erroneous and misleading details in their stories. This helps to ensure that when someone tells you something false, you will know that you are being intentionally mislead.

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