Japanese reactor crisis
 

Okay, before I begin I want to make something clear. I'm NOT a nuclear engineer. I have never worked in a nuclear power plant. I considered being a nuclear power plant technician when I was contemplating joining the Navy and during that time I read everything I could get my hands on regarding nuke plants, how they work and various post-mortems on Three Mile Island. I have the understanding that, say, a decent science reporter might have. I understand the underlying physics pretty well and I'm following this unfolding event very closely.

My purpose in starting this thread and posting is NOT to show off. Rather, I know that *I* am concerned and I imagine other people are as well. To that end, I'm going to try to share what information and understanding I have. If you have a question, I will do my best to answer them.

It might be helpful to explain how nuclear power plants work and why TMI is the better model for what is happening than Chernobyl.

So...

Nuclear reactors are just very fancy and highly efficient ways of boiling water. As Einstein demonstrated a hundred years ago, E=MC^2 or energy is equivalent to the mass multiplied by the square of the speed of light (~186,000 mps in vacuum). The practical upshot of this equation is that very small objects contain a HUGE potential for energy. When certain substances are split, they release energy and certain kinds of metals--like uranium--actually have their atoms split rather easily. When an atom is split what happens is that a neutron hits the nucleus of an atom, causing it to be broken into smaller, sub-atomic components. As the protons and electrons are stripped from the atom that process releases energy. One by-product of this is yet *more* neutrons which hit yet *more* nuclei of U-235 (uranium with an atomic weight of 235) which causes a chain reaction. Another by-product of this is heat. The mass of the uranium-235 is being turned into energy in the form of heat and radiation. Radiation is simply high-energy parts of the electromagnetic spectrum.

So, the way this process works is that you have fuel rods that are filled with refined uranium-235 in pellets. Those rods are lowered into the core of the reactor where the nuclear reaction begins. To keep the temperature manageable most Western reactors (the Japanese use designs closer to Western designs than the old Soviet design--more on that below) cool the core by immersing the whole thing in water. As long as the water is kept at a sufficient level, the reactor will do its job of heating water, turning it into steam, the steam turns a turbine which has an electromagnet in which creates electricity. There are also control rods made of a material that will absorb neutrons without fissioning themselves. These control rods are lowered into the 'pile' (the fissionable material) to absorb neutrons thus slowing the reaction or removed to allow more reactions.

The problem facing the Japanese right now is that with the pumps down, they can't keep circulating water through the reactor. That means that any water covering the core will evaporate. This will turn into steam and with the plant shut down that steam has no place to go. It will build up in the containment building until the pressure is too great. KNOWING that this kind of thing could happen, designers of reactors build the containment buildings so that any explosion caused by a build up of hydrogen gas (this is NOT a hydrogen explosion as you would see in a nuclear bomb) will push *outward* away from the reactor itself so even if the building is damaged the reactor should maintain its structural integrity.

If the core is uncovered the rods will start to melt and can actually burst into flame. This should give you an idea of how hot (in the heat sense not the radioactive sense) the core of the reactor can get to that metal doesn't just melt it actually *burns*. This is the most immediate concern is that they will lose all control of the reactor, the reactor will become uncovered, the rods and the reactor housing itself will all melt into slag and then the we have to hope that the concrete floor of the containment building will stop it. That is, of course, the worst case scenario.

Whenever a problem happens at a reactor, it will either automatically shutdown or be shutdown by the human operators. This is called a 'SCRAM'.

(I'm going to close this post out and do another one on TMI and Chernobyl)

Thanks for doing this! As a person living on the west coast, I am a bit concerned because the prevailing winds will blow whatever radiation is leaked to the west coast.

My understanding of the news this am is that the rods were left exposed twice yesterday/today. The second time has left the rods still exposed as I type.

There is also a second and maybe a third reactor in danger.

Here is an excerpt from the yahoo news article this am.

Water levels were restored after the first decrease but the rods remained exposed late Monday night after the second episode, increasing the risk of the spread of radiation and the potential for an eventual meltdown.

The cascading troubles in the Fukushima Dai-ichi plant compounded the immense challenges faced by the Tokyo government, already struggling to send relief to hundreds of thousands of people along the country's quake- and tsunami-ravaged coast where at least 10,000 people are believed to have died.

Later, a top Japanese official said the fuel rods in all three of the most troubled nuclear reactors appeared to be melting.

Of all these troubles, the drop in water levels at Unit 2 had officials the most worried.

"Units 1 and 3 are at least somewhat stabilized for the time being," said Nuclear and Industrial Agency official Ryohei Shiomi "Unit 2 now requires all our effort and attention."

In some ways, the explosion at Unit 3 was not as dire as it might seem.

The blast actually lessened pressure building inside the troubled reactor, and officials said the all-important containment shell — thick concrete armor around the reactor — had not been damaged. In addition, officials said radiation levels remained within legal limits, though anyone left within 12 miles (20 kilometers) of the scene was ordered to remain indoors.

I've been following this as much as possible too. More in terms of the human element and suffering but also about the nuclear reactor, core meltdown and attempt to lower the temperature. There is a lot of info on the web and the news has been doing a good job of explaining how it all works, why the pumps stopped working, the failure of the backup generators, and how/why the meltdown happens. Can you post links to the articles you are reading?

Melissa

Nuclear reactors--when things go wrong
 

So, the two nuclear events that occurred that most people remember are TMI and Chernobyl. These were VERY different kinds of events caused by VERY different causes and by the design of both plants.

TMI was a less severe event than Chernobyl for two reasons:

1) TMI-2 (the reactor that had the problem) was in a containment building.
2) TMI-2 was a pressurized water reactor which are safer.

So what happened at TMI-2 was that a pump failed, then the main pumps feeding water into the system failed. This caused the reactor to SCRAM, as it was designed to. However, just as a pot stays hot for a little while after you remove it from flame, a reactor core stays hot for a while after the control rods are inserted into the pile. This is called decay heat. So the reactor still needed to be covered. TMI-2's operators violated an operating rule and had all three auxiliary pumps shut down for maintenance (the NRC requires that if you're doing this, you shut down the core). Because the pumps couldn't get water into the reactor, steam began to build up in the containment vessel. A valve got stuck open and this allowed coolant (water) to escape which caused the core to be partially uncovered.

To make matters worse, the human operators misinterpreted an indicator light on the stuck valve. The design of the light only recorded if power was going to the solenoid for the valve, NOT the actual valve position. So the operators interpreted the light being out as meaning that the valve was closed.

At this point, pressure in the reactor was dropping. The higher the pressure, the higher the boiling point of water. With the pressure reducing the coolant started to boil off, causing a buildup of steam. A hydrogen bubble formed but fortunately there was no oxygen in the containment vessel which meant that the hydrogen couldn't ignite or explode. To bring the reactor under control, the operators released steam (which was controversial at the time) and used other mechanisms which I won't belabor to shrink the hydrogen bubble.

As it turns out, even though people treat TMI as a truly horrific event, more things went right than went wrong. Even with a cascade of mechanical failures, exacerbated by human errors, there was no significant release of radiation to the atmosphere. Several epidemiological studies have been done in the last nearly 40 years and found no higher incidence of cancers in the area surrounding the TMI facility than would be otherwise expected.

Chernobyl was a very different kind of event:

During a test, one of the reactors experienced a power spike. This caused lots of bubbles to form and steam pressure to build up in the reactor core. This prevented water from getting into the system to cool it down. There were then two explosions which damaged the fissile pile, preventing the control rods from being fully inserted, which led to a second explosion. This explosion tore the roof off the building, set fire to an adjacent reactor building and ruptured the containment vessel. At this point the whole core was aflame.

Part of why Chernobyl went SO bad is that the containment vessel (which is metal) was not in a containment building. It was in a normal, industrial building, built to Soviet building standards at the time.

GAH! Thank you for this - I have many questions.

So, I deduced that this shit is hot by the fact that they were saying it would take sevreral days to cool down and was wondering how hot we are talking about? I mean, are we talking several hundred degrees or are we talking nitro molten lava?

The other thing Im wondering is that we noticed it was snowing as all of this was happening. If they are venting steam from the stacks and there have been explosions, could the snow be carrying radioactivity down to the ground and into the water table?

And what makes radioactivity dissipate? Does it actually go away or does it just get broken up into particles so small that they are no longer dangerous?

Japanese reactors--part 3. Some preemptive questions
 

1) Will the reactors explode like a nuclear bomb?

No. That can't happen. The physics of a nuclear bomb being detonated are different than the physics of a nuclear power plant. There are no conditions that could ever occur in the core of a reactor that would be sufficient for the large, immediate, release of ALL of the energy. A nuclear bomb is releasing all of the energy in the fissile material in a matter of a second. A nuclear power plant does not have the conditions necessary for that kind of fast reaction.

2) Will radiation kill me?

High enough doses of radiation will kill you. That said, you are exposed to radiation every day. The Sun is bombarding you with radiation, the ground is bombarding you with radiation. The thing is we evolved on this planet so our bodies are capable of, more or less, are capable of dealing with the daily exposures. The problem is when you get high doses of radiation. The kind of radiation that concerns us is ionizing radiation. The danger of this form of radiation is that it is high energy and thus enough to break chemical bonds. This includes the chemical bonds in our DNA which can cause replication errors leading to cancer.

3) Will the reactors experience a full meltdown?

No one knows. This is terra incognito however, the thing that is helping me sleep at night is that it is clear the the plant operators are trying to 'kill' the reactor instead of bring it down gracefully so it can be started up later. By 'kill' I mean that they are pumping sea water into it and, of course, salt is a corrosive. They are also injecting boric acid into the reactor. The key here is not the acid but the boron. That element absorbs neutrons without fissioning so it will slow down the reaction rate in the core. I would be FAR more concerned if they were trying to save the reactors.

That's it for now. I will answer questions as asked to the best of my ability. I'll update this thread as I get more information and process it.

Cheers
Aj

Melissa:

Part one, where I discussed the basics of how reactors work was mostly done off memory. Where I needed to look up some terms to make sure I was using them correctly and to just make sure I had not left out anything *critical* to understanding (obviously I oversimplified quite a bit) I checked against the 2008 Encyclopedia Britannica which I keep a copy of on my hard drive.

Part 2, where I discussed the TMI and Chernobyl I used Britannica again and Wikipedia's articles on the subject. My explanations are simplified distillations of:

http://en.wikipedia.org/wiki/Chernobyl_disaster

and

http://en.wikipedia.org/wiki/Three_Mile_Island_accident

Part 3:

Questions 1 and 3 are operating off internal information. Question two was from memory and reality-checked against http://www.hss.energy.gov/HealthSafe...intro_9_5.html.

My updates are coming from

http://www.talkingpointsmemo.com

and

http://www.bbc.co.uk/news/world-asia-pacific-12733393

Is that what you were asking for?

Cheers
Aj

At the danger zone we're talking temps in the 1500 - 3000 F (815 - 1648 C) range. Hot enough to melt most metals and cause some to burnst into flame! (molten lava is typically in the 1300 - 2400 F (~700 - 1300 C) range)

Yes, that absolutely could happen. That is one of the dangers of a meltdown is that the containment vessel will be ruptured and radioactivity will get out into the atmosphere. In fact, one of the reasons why Chernobyl was magnitudes worse than TMI was the *fire*. All of that smoke was radioactive as hell and that is why the entire city of Pripyat had to be abandoned.

Over time, the radioactive material will break down and get absorbed back into the atmosphere. Depending upon the nature and extent of contamination this can take varying amounts of time.

Cheers
Aj

Ohhh crap. Trying not to wring my hands but just heard on CNN that the second reactor had an explosion and that they think the containment vessle has been ruptured and that radioactive material may be leaking out.
On the surface I get what this means, but do we have a way of determining how much material will leak and how fast? An equation that says something like "Size of Vessel x temperature of exposed fuel rods x length of exposure = amount of radiation that will escape"? And further, what is the area that will be affected?

And would there be other factors that would affect how much and how long radiation will leak? Like, and pardon my ignorance here, if the temperature is cold outside vs hot and humid, does that make a difference? Does snow help drop that radiation to the ground? What if it rains?

(just call me chicken little)

You are not being chicken. We should be asking questions and researching about what all of this could mean. I was feeling much more reassured with info from top nuclear power scientists and engineers just yesterday about containment "vessels" and buildings. Unfortunately, the news thus far about this situation goes beyond the parameters some of these folks talked about and into much more serious scenarios- some unknown or un-chartered territory (just like the Gulf deep water oil spill).

Waiting for the current experts to weigh in instead of the news media per se. Also, when these plants were built and went online is significant in terms of the possible dangers. Some of the hype is not helping in terms of fear factors. Japan has some of the worlds leading people in their nuclear power plant development and research.

Yes, as in past, I think about the fact that these kinds of natural disasters can push the envelope past the theory behind construction and management of these plants into mother nature being the one with the final say- or human error pushing it (hope the containment cement was mixed properly and inspected properly, for example) . Yet, there are people dealing with this that have a lot at stake including millions of their country-people.

Also from Daily What (comparison photo between Sendei 2011 and Nagasaki bombing of WWII) :

http://chzdailywhat.files.wordpress....2dbb149c5e.jpg

http://www.latimes.com/news/nationwo...,2212206.story

Word, Atlast!
I have been trying to read multiple news sources over the last several days and have been looking at diagrams of nuclear facilities so that I can try to understand what is happening.

It also helps having someone with a scientific background (Thanks AJ!) draw a verbal diagram. Im fairly negative about depending on one news source to tell us everything we need to know and have pretty much accepted that we aren't getting the whole story.

From where I sit, it looks very much like there is a radioactive event of large proportions happening in Japan right now. I hope Im wrong but am fearful that Im not.

This is so frustrating! This article reads as there has been no meltdown and another site http://e.nikkei.com/e/fr/freetop.aspx is talking about how high the radiation shot up after the explosion.

I have been reading BBC news as well but this article from Reuters is fairly enlightening:

http://www.reuters.com/article/2011/...72D8LM20110314

It says the shell is 4 - 8 inches of steel. That's something I didnt know; I thought it was an inch or two (hoping it's closer to 8 than 4!!)

I think the disparity in news is the effect of the internet. We probably won't know for sure until a day or two later. The reality is that news agencies are tripping over each other for the latest and "accurate" (I question how accurate since I don't think they are actually verifying). At the same time, I don't know even if Japanese officials know since the people who would know are doing what they are supposed to: try and contain this as best as they can.

I wonder if there will be a point where they will say "We cannot do anything more.."

Good points! And I hope your last statement never happens! And lets face it, things like this get entangled with political motivations as well.