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Merged nuclear power safe?

Japanese nuclear plant’s safety analysts brushed off risk of tsunami

TOYKO — A Japanese government agency that spent several years evaluating the Fukushima Daiichi nuclear plant declared the facility safe after dismissing concerns from a member of its own expert panel that a tsunami could jeopardize its reactors.

Yukinobu Okamura, a prominent seismologist, warned of a debilitating tsunami in June 2009 at one of a series of meetings held by the Nuclear and Industrial Safety Agency to evaluate the readiness of Daiichi, as well as Japan’s 16 other nuclear power plants, to withstand a massive natural disaster. But in the discussion about Daiichi, Okamura was rebuffed by an executive from the Tokyo Electric Power Co., which operates the plant, because the utility and the government believed that earthquakes posed a greater threat.

That conclusion left Daiichi vulnerable to what unfolded on March 11, when a 9.0-magnitude earthquake struck off Japan’s northeast coast. Experts now say that Daiichi, as designed, withstood the quake. It was the ensuing tsunami, with waves more than 20 feet high, that knocked out the facility’s critical backup power supply and triggered a nuclear emergency, resulting in widespread releases of radiation.
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Japan Extended Reactor’s Life, Despite Warning

TOKYO — Just a month before a powerful earthquake and tsunami crippled the Fukushima Daiichi plant at the center of Japan’s nuclear crisis, government regulators approved a 10-year extension for the oldest of the six reactors at the power station despite warnings about its safety.

The regulatory committee reviewing extensions pointed to stress cracks in the backup diesel-powered generators at Reactor No. 1 at the Daiichi plant, according to a summary of its deliberations that was posted on the Web site of Japan’s nuclear regulatory agency after each meeting. The cracks made the engines vulnerable to corrosion from seawater and rainwater. The generators are thought to have been knocked out by the tsunami, shutting down the reactor’s vital cooling system.

The Tokyo Electric Power Company, which runs the plant, has since struggled to keep the reactor and spent fuel pool from overheating and emitting radioactive materials.

Several weeks after the extension was granted, the company admitted that it had failed to inspect 33 pieces of equipment related to the cooling systems, including water pumps and diesel generators, at the power station’s six reactors, according to findings published on the agency’s Web site shortly before the earthquake.

Regulators said that “maintenance management was inadequate” and that the “quality of inspection was insufficient.”

Less than two weeks later, the earthquake and tsunami set off the crisis at the power station.
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New Problems at Japanese Plant Subdue Optimism

Nuclear engineers have become increasingly concerned about a separate problem that may be putting pressure on the Japanese technicians to work faster: salt buildup inside the reactors, which could cause them to heat up more and, in the worst case, cause the uranium to melt, releasing a range of radioactive material.

Richard T. Lahey Jr., who was General Electric’s chief of safety research for boiling-water reactors when the company installed them at the Fukushima Daiichi plant, said that as seawater was pumped into the reactors and boiled away, it left more and more salt behind.

He estimates that 57,000 pounds of salt have accumulated in Reactor No. 1 and 99,000 pounds apiece in Reactors No. 2 and 3, which are larger.

The big question is how much of that salt is still mixed with water and how much now forms a crust on the uranium fuel rods.

Crusts insulate the rods from the water and allow them to heat up. If the crusts are thick enough, they can block water from circulating between the fuel rods. As the rods heat up, their zirconium cladding can rupture, which releases gaseous radioactive iodine inside and may even cause the uranium to melt and release much more radioactive material.
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Can't they truck in fresh water?
 
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57,000 pound of salt, is 26,000 Kg about and thus about 26 tons of salts. Assuming sodium chloride mainly, at 2 g per cubic centimeter in solid phase that is 13 cubic meter... That would mean they pumped (at 35 g salts per liter) at least 750 tons of sea water, which subsequently 100% evaporated.

I have no idea if it is a lot or not.
 
Hindmost said:
For info: All commercial light water reactors will have some plutonium. As the fuel cycle progresses, the reactor will breed Pu from U238. It just doesn't breed as much as a fast breeder reactor. Typically, there is a breeding ration of about 0.7. So, at the end of a fuel cycle about 30 to 50% of the power from the reactor will be from Pu depending on the length of the fuel cycle. There will always be Pu in the spent fuel. With MOX, Pu is just a "substitute" for the uranium 235, but the fuel will still breed some Pu as the cycle progresses. The plant has too be modified a bit because Pu is a bit more reactive. In the US, we are buring Pu from Russian weapons to get rid of the stuff.
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Thanks for the additional info, Hindmost.
 
Aepervius said:
The first link is not saying anything, as it does not say with which probability the seismologic predicted such an event could happen. If he said the plant & japanese government it was a very rare event (which it is to that intensity) then they rightfully dismissed him.

The second link is pretty damning OTOH.
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How rare is rare though? There have been 5 earthquakes of magnitude 9.0 or greater since 1950, and all caused tsunamis. The 2004 one was the most destructive.

http://en.wikipedia.org/wiki/Lists_of_earthquakes#Largest_earthquakes_by_magnitude
 
Aepervius said:
If you count all earth you are right, but the japanese governement probably ignored the risk of magnitude 9.5 earthquake in chile...

Reduce it to Japan and the picture is different.
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Well, hindsight is 20/20, but Japan is one of the most tsunami-prone places on the globe. They even invented the word for it.

Oh well, no excuse after this now.
 
Puppycow said:
Well, hindsight is 20/20, but Japan is one of the most tsunami-prone places on the globe. They even invented the word for it.

Oh well, no excuse after this now.
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This one was bigger than anything they had been hit with previously though. They had sea walls to protect from tsumani and safe points located so that people would know how far to run of one was coming, both failed.
 
MarkCorrigan said:
There is a major problem, but "There's a major problem" =/= "It's emitting dangerous levels of radiation".
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The moment they lost control, emitting dangerous levels of radiation became a real possibility. For those working in the plant, it is a real danger, that is why their exposure time is being carefully managed.
 
Aepervius said:
being on an active fault is not enough. KNOWING the frequency of such strong tsunami is what is needed. That has been told over and over.
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You aren't going to get that, since we can't predict such events. We do know that you are more likely to get events such as a strong tsunami when you are on a fault line. Put it this way, Japan has very strict building codes, but they don't know the frequence of major quakes, either. Not "KNOWING" is not a reason for complacency, it's a cause of concern in a major fault area, such as the 'ring of fire'.
 
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