Just a reminder - Three Mile Island Unit 2 was not defueled and decontaminated until 1993

14 years after the accident - and it cost nearly a billion dollars.

<snip>

edit] Cleanup

Three Mile Island Unit 2 was too badly damaged and contaminated to resume operations; the reactor was gradually deactivated and mothballed. TMI-2 had been online only three months but now had a ruined reactor vessel and a containment building that was unsafe to walk in — it has since been permanently closed. Cleanup started in August 1979 and officially ended in December 1993, having cost around US$975 million. Initially, efforts focused on the cleanup and decontamination of the site, especially the defueling of the damaged reactor. Starting in 1985, almost 100 short tons (91 t) of radioactive fuel were removed from the site, the defueling process was completed in 1990, and the damaged fuel was removed and disposed of in 1993. However, the contaminated cooling water that leaked into the containment building had seeped into the building's concrete, leaving the radioactive residue impractical to remove. In 1988, the Nuclear Regulatory Commission announced that, although it was possible to further decontaminate the Unit 2 site, the remaining radioactivity had been sufficiently contained as to pose no threat to public health and safety. Accordingly, further cleanup efforts were deferred to allow for decay of the radiation levels and to take advantage of the potential economic benefits of retiring both Unit 1 and Unit 2 together.

<snip>

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

very, very difficult - next to impossible even. This is why such plants should not have been built in the first place. All should be systematically closed down before tragedies occur. Obviously, this has to be done in an orderly way, but the experiment has failed. Time to dismantle the experimental apparatus.

If your engine throws a rod, kiss it goodbye. If your bicycle frame get bent, chuck it. If you have structural weakness after some disaster, kiss your home goodbye.

Should we have not made any of those things because of that? There are a lot of reasons, but that's not a very good one.

environment for longer than civilization has existed. I consider that, too. Perspective is helpful when assessing things, I think.

That carbon 14 has a half life of 5000 years. It's in our bodies and the earth creates it all the time. So if something is going to "poison" the ground for 7000 years, it's not very radioactive at all.

Try 50-100 years.

Of course, you might try to make it out that I don't think it matters. It does. It's just not as bad, in the long term, for the environment, as you think it is.

the planet, and the almost infinitesimal amount of radiation it creates is actually harmless. Even Uranium occurs widely over the planet. Again, the concentration is small enough that it poses little hazard to anyone. However, when you collect enough of it to support a chain reaction, as is done in these power plants, the balance is very important. In a meltdown, radiation at levels that are extremely dangerous to humans and other living things are released and spread over wide areas.

It's not that radiation doesn't exist everywhere. It does. But not in levels that are harmful. In fact, that background radiation may be responsible for the genetic changes that power evolution.

To attempt to equate the radiation from the few atoms of C-14 in your body to a melted down nuclear power plant core is specious. Your point is poorly made, because it is not relevant to the situation. But thanks for participating.

If something is highly radioactive it will only be so for a short while. You can't say something is both highly radioactive and will be so for thousands of years.

It is either: Harmlessly (as in the fact that our bodies can heal the damage) radioactive, and it will be so for thousands of years, or, Highly radioactive (as in the fact that the damage is so severe that it can't be healed) and will be so for around a hundred years.

It's not that radiation doesn't exist everywhere. It does. But not in levels that are harmful. In fact, that background radiation may be responsible for the genetic changes that power evolution.
==================================

As you point out, radiation exists everywhere. In fact, the amount of radioactivity in the
Carbon-14 of the world dwarfs the radioactivity of these reactors by orders of magnitude.

If the worst happened, and the radioactivity in the reactors were dispersed through out the
world, then the result would be orders of magnitude LESS than the concentration of
radioactivity due to natural Carbon-14.

The anti-nukes seem to want to have it both ways. If these Japanese reactors were to
disgorge their radioactive inventory and it spread across the world ( diluted in the process ),
the anti-nukes would decry that it was a horrible catastrophe to have that much radioactive
material in the environment.

When one points out that Mother Nature has put more radioactivity in the environment, the
anti-nukes say that it is diffuse and low level and harmless.

Why the double standard?

PamW

Why... just yesterday I saw a chart of expected exposure levels from a meltdown.

The West Coast of the U.S. had dosed in the 750 rad range in just ten days.

< /sarcasm>

I looked up some numbers.

Wikipedia:
"All radioisotopes contained in the waste have a half-life—the time it takes for any radionuclide to lose half of its radioactivity—and eventually all radioactive waste decays into non-radioactive elements.

Certain radioactive elements (such as plutonium-239) in “spent” fuel will remain hazardous to humans and other creatures for hundreds of thousands of years.

Other radioisotopes remain hazardous for millions of years. Thus, these wastes must be shielded for centuries and isolated from the living environment for millennia.<2>

Some elements, such as iodine-131, have a short half-life (around 8 days in this case) and thus they will cease to be a problem much more quickly than other, longer-lived, decay products, but their activity is much greater initially."
http://en.wikipedia.org/wiki/Radioactive_waste

the threat comes from the fact that our bodies don't see a difference and will use it in place of what it is suppose to use.

http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/plutonium.html

Plutonium Isotope Half-Lives

"There are 15 isotopes (another form) of plutonium. Some isotopes of plutonium are fissionable meaning that the atomic nucleus is unstable and will split apart, resulting in the release of large amounts of energy. Pu-239 and Pu-241 are the most abundant of the fissionable isotopes of plutonium.

A half-life is the time in which one half of the atoms of a radioactive substance disintegrates into another nuclear form, hence, the time to halve its radioactive strength. Pu-239 has a half-life of 24,000 years and Pu-241's half-life is 14.4 years. The plutonium isotope with the shortest half-life of 20 minutes is Pu-233. Plutonium-244, which occurs naturally, has the longest half-life of 80,000,000 years."


Pathways in the Body

"The most common form of plutonium is plutonium oxide which is virtually insoluble. The behavior of plutonium oxide in the body varies with the way in which it is taken. If one drinks or eats it, a very large percentage of it will be eliminated from the body quite rapidly in body wastes. If plutonium oxide is inhaled, part of it, usually between 20 and 60 percent depending upon such things as the size of the particles, is retained in the lung. The rest is eliminated from the body within several days. Of that which remains in the lungs, about half will be removed each year, some to be excreted, some to lodge in the lymph nodes, and a very small amount will be deposited in other organs, mainly bone. If plutonium enters the body through an open wound, depending on its form, it may move directly into body organs, mainly bone and liver. The next most common form of plutonium is plutonium nitrate-a chemical that is somewhat more soluble than the oxide. Plutonium nitrate's behavior in the body is similar to plutonium oxide, however, it moves out of the lung more rapidly."

Toxicity

"Recent research with one of the least radioactive isotopes of plutonium (plutonium-242, which has a half-life of 376,000 years) indicates that plutonium in the body may contribute to the development of tumors. In general, however, plutonium isotopic mixtures that are commonly encountered in the nuclear fuel cycle, nuclear weapons programs, or thermoelectric generator applications exhibit much higher radiological toxicity than chemical toxicity."

Certain radioactive elements (such as plutonium-239) in “spent” fuel will remain hazardous to humans and other creatures for hundreds of thousands of years.
===========================================================

Whether Pu-239 is hazardous to humans depends on what form it is in.

Solid Pu-239, that is found in spent nuclear fuel is not hazardous to humans.
Pu-239 is an "alpha-emitter". The type of radiation it emits in radioactive
decay is an "alpha particle". Alpha particles are very easily shielded - a
piece of paper will do. Alphas particles can't even get through the dead layer
of skin.

Just before the Soviet Union exploded their first atomic bomb, a copy of the
Trinity device that the USA exploded in New Mexico on July 16, 1945, the scientists
brought the Plutonium-239 core of the device to Joseph Stalin. Stalin even held
the Pu-239 core in his hands. It wasn't dangerous.

So where does Pu-239 get its bad reputation?

If you make an aerosol of Pu-239, that is you vaporize the Pu-239, and then inhale
it, the Pu-239 can lodge in your lungs and it and its daughter isotopes can irradiate
you. You are no longer protected by the dead layer of skin. The radioactive atoms
are right up against living tissue.

But solid plutonium external to the body is not a health risk.

PamW

leave it sitting in you front yard. You can make it a lawn sculpture, if you are so inclined. It will have no effect on anything other than itself. It doesn't make the ground it is sitting on unusable for the next 3000 years.

Carbon 14 has a half life of 5000 years. It's in our bodies and the earth creates it all the time. So if something is going to "poison" the ground for 3000 years, it's not very radioactive at all.

Try 50-100 years.

Of course, you might try to make it out that I don't think it matters. It does. It's just not as bad, in the long term, for the environment, as you think it is.

:rofl:

Hmmm... I could have sworn I read that's what would happen.

atomic BOMBS are designed to FORCE a runaway reaction, and one of the hardest engineering challenges in creating the atomic bomb was figuring out how to prevent the fuel from naturally moving too far apart to keep the reaction going.

elevators are designed in such a way that brakes naturally stop the car from falling when there's a power failure -- it takes active intervention to prevent the brakes from doing their job so that the car can operate normally, precisely so that the default action is the safest one.

so, why aren't nuclear reactors designed in such a way that if there's a problem, the fuel naturally moves apart so as to slow down the reaction?



actually, they probably ARE designed like this to handle many problems, but obviously, there are still some problems that aren't handled like this.

...but the pebble bed reactor design wasn't invented until after the TMI incident had pretty much shut down new nuclear construction in the US, and all of the fuel and handling infrastructure is geared toward older designs which require certain active systems to be working to keep them safe.

There haven't been ANY "runaway reactions" reported in Japan. The reactors were shut down almost immediately. (Chernobyl DID "run away", but was of a different design).

It's just that decay heat can still be substantial and, if left uncooled, can still melt parts of the core (all without a runaway reaction... or really any fission at all).

On edit - of course that's "fission".

These are fission reactions, not fusion. It's sort of hard to take your point seriously when you make such a basic error.

Typing on an iPhone leaves me with many such issues. :)

Wouldn't it be nice if the Japanese had figured out fusion, eh?

so, why aren't nuclear reactors designed in such a way that if there's a problem, the fuel naturally moves apart so as to slow down the reaction?
=================================================

You don't understand the problem...

Actually nuclear reactor are designed to shutdown when there is a problem, and
the ones in Japan did. You don't even have to have the material move, just the decrease
in density of the material when it gets hot is enough to shutdown the reactor. Additionally,
there's Doppler broadening and the control rods that did their jobs. Here's a link to some
course notes from a course at MIT in reactor control:

http://ocw.mit.edu/courses/nuclear-engineering/22-05-neutron-science-and-reactor-physics-fall-2006/lecture-notes/lecture30.pdf

You don't understand the problem. There's no neutron-induced nuclear chain reactions
going on. There's no "new" nuclear energy being created.

What you have here is a reactor that is both thermally and radioactively "hot".
That's what needs to be cooled.

I attempted to get this point across yesterday here, but it's like "pulling teeth" - people
are so "locked in" to what they "think" is happening, they can't understand the reality when
it is presented to them.

There are no nuclear chain reactions that need to be stopped - the nuclear chain reaction was
stopped by the reactor when it first sensed the earthquake last Friday.

Perhaps an analogy might help. How many here have slide projectors, or perhaps you have a
digital projector for home theater at home or for presentations at work. When you turn the
projector off, the fan continues to run to cool the projector.

That's what we have here. When you turn the projector off, there's no "new" heat being
generated. The bulb has gone off. The bulb is no longer heating the projector. However,
the projector still needs to have active cooling by the fans in order to be protected.
When the projector is turned off, the heat energy in the projector redistributes since it
can no longer support the temperature gradients and hence heat flow that one had when the
bulb was on.

Scale that up a billion-fold. Even though the reactor is shutdown, it is still thermally
hot, and also radioactively "hot". That energy doesn't magically "disappear" just because
no more energy is being generated.

Because the tsunami took out the back-up generators, the "cooldown" cycle on the reactor,
like the cooldown cycle on your projector could not be performed, and that's why there
is the current problem.

The nuclear reactions have been shutdown. The question is what to do with the
energy that had already been released - in thermal or radioactive form - prior to the
earthquake / tsunami.

PamW

i now understand that the nuclear reaction itself stops quickly, and i would expect that in many, if not all cases, safety systems are built so that this is the case whenever anything unexpected or problematic occurs.

however, understanding that at any moment, the heat and radioactivity already generated is substantial and problematic if left uncooled. why are systems designed such imperfect power sources are needed in order to prevent signficant problems arising from inadequate post-shutdown cooling?

back to one of my analogies, the elevator has a mechanical failsafe in case of complete loss of power -- the brakes are normally held back by an electrical system; when power goes out, there's nothing to hold back the brakes, so they automatically go "on" and prevent the car from plummetting down and crashing.

similarly, why are nuclear reactors not designed to handle the cooling needed at any point without relying on electricity or or other unreliable power sources? is there no way so that there is a mechanical way to cool things down, or at least to drain and/or disperse things into containers that are able to sustain the heat and radioactivity, at least long enough so that active cooling systems can be brough back online?

can't it be like a giant commode, where the hot, radioactive water is flushed out of the important/dangerous part of the reactor and into a separate containment area, which does nothing but keep it separate and provide several means for cooling?

back to one of my analogies, the elevator has a mechanical failsafe in case of complete loss of power -- the brakes are normally held back by an electrical system; when power goes out, there's nothing to hold back the brakes, so they automatically go "on" and prevent the car from plummetting down and crashing.
=======================

Fair enough, let me try again with your own analogy.

Suppose we have a skyscraper in Tokyo. It has the fail-safe braking system
that you postulate above. Suppose Tokyo and the skyscraper are hit with a
massive earthquake like last Friday.

The building loses electrical power, so the elevators need those fail-safe brakes.
Unfortunately, the acceleration of the earthquake produced high forces on those
fail-safe brakes and those brakes broke. The elevator car goes plummeting down
tens of stories and kills the occupants.

Someone could say, why aren't elevators designed so that you don't have to rely
on electricity that can fail, or brakes that can fail. Perhaps we should give up
on elevator technology and everyone uses the stairs.

The answer is it is hard to design something that stands up to everything, especially
when you are talking about something as powerful as an earthquake. This recent
earthquake was a monster.

If you know how to reliably do what you specified in your last paragraph, then do the
world a favor and tell someone. You need a way to force water through the core. Just
letting it sit there, or use natural circulation doesn't give you enough cooling.

You need a forced water flow. That usually means a pump, and pumps usually get their
power from electricity. The Japanese reactors had electric pumps, but not a reliable
source of electricity. Those reactors were BWRs. BWRs (boiling water reactors) have
another source of pumping power. They have pumps that are hooked to small steam turbines.
As long as there is residual steam and steam pressure in the system, those turbines can
drive pumps to cool the reactor. Why didn't that work? Right now I don't know. Perhaps
the turbines were broken by the forces of the earthquake.

Your commode idea is on point in a way. Why does your home commode work without power.
It's because the level in the tank is higher than the level in the bowl, and gravity
can do the job. Why don't they do something like that with nuclear power plants?

They do!! Use Google Satellite to look at an aerial view of the Diablo Canyon nuclear
power plant in California. Near the plant, just inshore of the reactor buildings, you
will see a big pond. The pond actually sits on a bluff that overlooks the power plant.
In case Diablo Canyon loses power for the pumps, they have a way to provide water that
is being forced by gravity.

Nuclear power plants are like airliners, but even more so. They have backup systems for
the backup systems for the backup systems..... Unfortunately, the Japanese reactors got
hit with a natural disaster, a truly monster quake, that took out all those back ups.

It's really, really hard to design something that never ever fails, especially when there
are things like this monster quake out there to get you.

PamW