Restoration at nuke plant disrupted, radiation fears spread to Tokyo

Kyodo News Japan ^ | 24 March 2011

[OA5599]

First off, don’t use the word “critical” when speaking of reactors unless you know what it means. The definition of critical is “the same number of neutrons were born in this generation as were born in the previous generation.”

Translation: reactor power is stable

FYI subcritical means reactor power is decreasing and supercritical means reactor power is increasing.

All of the reactors at Fukushima are subcritical. The heat created in a shutdown reactor is not from fission of the fuel, but decay of the fission products.

Second, the breakdown of the cladding at high temperatures is not a nuclear reaction; it’s a chemical reaction between the zirconium and water. It produces zirconium dioxide and hydrogen gas.

I forget what temperature that happens since I’ve never melted a core much less created a water-metal reaction in a reactor.

The danger of this reaction is not the heat, but the pressure and explosive gas created.

Third, water moderated reactors such as these GE BWRs have a negative temperature coefficient of reactivity. Cooling the reactor with water will *help* the reactor go critical, not prevent it.

Cooler water —> denser water —> more effective at “slowing down” neutrons from “fast” to “thermal” —> more likely U-235 and Pu-239 to absorb neutron and fission

You are correct about boron. It’s one of the best neutron sponges out there. (Hafnium and xenon are other notables)

[GOPJ]

LOL-Loved the graphic - up until the end:

"I'm sure I've added in lots of mistakes; it's for general education only. If you're basing radiation safety procedures on an internet PRG image and things go wrong, you have no one to blame but yourself."

[Errant]

Here are some real ones ...

There are many others ...

[GOPJ]

They had to use land that was already approved for use, and in use, for power generation. Some of that is along coastlines, where the older units, that use once-through cooling, were sited to have access to a large thermal reservoir. If they had not been stopped by intervenors, the companies would have built more plants inland, using cooling towers or reservoirs, as a heat sink. So the anti-nuclear groups bear a large portion of the blame for these plants beings sited where they are. Because the power companies were still required to build capacity to meet the growing electrical demand of an increasingly industrialized and technological society.

The MSM will NEVER be interested in this type of information...

[palmer]

There will be no flash burns. Nuclear weapons cause them, not meltdowns and not even Chernobyl (exposed fission reaction). Plus the image he posted is an artist rendering, not real.

[palmer]

So why did you imply the one you posted was real?

[Balding_Eagle]

She’s posting her emotions, not facts.

[Errant]

How far out could flash burns occur?

That, I don't know. Just guessing that it would depend upon size of the bomb and and other factors (e.g. humidity, smoke, clouds, detonation height and etc). Danger from burns should dissipate rapidly with distance however danger to eyesight, probably extends to a great distance.

[palmer]

Your comment will be gone soon, thanks for not posting any more like that in the future.

[Errant]

So why did you imply the one you posted was real?

Sorry, I didn't mean to imply that. I just like the way it looked; kind of artistic and surreal.

My apologies if I insulted your sensibilities ...

[Clay Moore]

“Well, then, wonderful!!! I’ll inform the folks in Chernobyl that they can come home whenever they want to”

I realize that was supposed to be sarcastic, but you are comparing apples to oranges.

Chernobyl was a graphite bodied reactor that burned. There was no containment building.

[chimera]

Certainly if heat energy is absorbed by the cladding to the point of cracking or melting, that will carry off a significant amount of thermal energy. Whenever you have a phase change you get a “bonus” in heat removal. That's why wet cooling towers are very nice for cooling of the condenser recirc water in a power plant.

But in the event of fuel overheating, it is better if the cladding takes the heat than just the fuel pellets alone.

[palmer]

Apology accepted. The picture didn’t (doesn’t since it is still there) insult my sensibilities, but it insulted my intelligence because I though it was real until someone pointed out otherwise. The truth is sufficient as in the later pictures you posted for me. Please do not stretch the truth, or do better research next time.

[blackdog]

Lycoming 320 in a Cherokee.

[chimera]

I'm just not sure that the "we had to do it because they made us" argument is the best argument for this situation.......that's just my opinion.

Well, they are in a no-win situation. The anti-nuke kooks won't let them build on new sites. The national government says the utilities have to meet the power demands. So which will it be? Tell the kooks to take a hike (my choice), or reneg on your duties as a citizen of the Japanese Nation (something shameful which makes you "lose face", a very unpleasant fate).

So they made the best choice they could. They met their obligations to supply energy. They sited the plants where they were allowed, on existing sites, and built them to the specifications required. The design basis earthquake for the Fukushima units was 8.3. This was a 9.0 event. That is 0.7 points higher than the design basis. On a log10 scale, that is about a factor of five. They survived an event five times more powerful than the design was based on. I don't think there are many other industrial facilities that could have done likewise. But for seawater entering the fuel lines of the emergency diesels, this would have been pretty much a non-event.

Regardless of who is right or wrong about this, after what has happened, I doubt very seriously that they will repeat the same "mistakes" in future construction.

Many times, good things follow bad things..........Maybe in the future, the Japanese people will come to understand that better plants in a more safe location will be to their advantage........

If they can get the kooks off their backs, then yes, they can build units in other locales.

[meyer]

Thanks - as you can tell, I’m not a nuke (but I play on on the internet). :-)

This whole episode has been a learning experience for me, and for some reason, I find it somewhat fascinating. Not because of the danger (percieved and real), but because of the series of problems and the way they are slowly being dealt with.

I’ve never melted a core either. Closest thing was a little copper a couple of times, but that wasn’t necessarily intentional either.

[blackdog]

A food grade weld has no undercut or cold bead edge which can collect and harbor bacteria or contaminants. The USDA requires such welds on all direct food contact equipment. Such welds are done on stainless steel which is to be used on all food contact surfaces until packaging takes place. Then mild steel and other things like plastics can be used to convey finished goods.

Stainless steel is tricky to weld. It is done with a TIG welder (Tungsten Inert Gas)which forms a plasma arc at the end of a sharp tip. The arc is as hot as the sun, or so I am told. The inert gas is argon, which shields the arc area from oxidation. The heat is focused to a pinpoint spot and filler rod is fed by hand or automated at a rate which fills the void or joint. The extremely intense heat makes for twisting of the metal. You can't just start a bead and work along the joint because the result would twist and buckle. You have to manage the heat patterns and work a little here, a little there, and so on. The end result has to be a continuous food grade surface which you polish but should not have to grind.

[Domestic Church]

10 hours at # 2 and your a dead duck, 5 hours and you start to shed the mucosa.