Fukushima Daiichi; photo | 39 comments (39 topical, editorial, 0 hidden)

Re: Fukushima Daiichi; photo (4.00 / 2)

One possibility is that whatever meltdown was going to happen has already happened and that the water level is one metre below where the bottom of the rods would have been had there been any rods left and the rods are now in the form of molten (and refrozen on contact with water) corium at the bottom of the reactor.

Another possibility is that, two months after the reactor shut down, the fuel is no longer as "hot" as it would have been otherwise. Hot fission products will have decayed and unspent fuel might not heat up enough to melt or burn the Zircon fuel rods.

If the fuel rods are indeed fully exposed, presumably they have been for long enough that whatever disaster was going to happen has already happened.

Economics is politics by other means

by Carrie (migeru at eurotrib dot com) on Thu May 12th, 2011 at 11:06:35 AM EST
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Re: Fukushima Daiichi; photo (none / 0)

Thanks Migeru.

Even fully-spent fuel-rods need a lot of cooling, don't they, for quite some time after being withdrawn from the reactor?

by LondonAnalytics (Andrew Smith) on Thu May 12th, 2011 at 11:11:37 AM EST
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Re: Fukushima Daiichi; photo (none / 0)

Don't thank me as if I really knew what I'm talking about - I'm just a former physicist and am speculating from the best information I think I have so far.

The protocol for dealing with spent fuel appears to be to cool it in water for a year in the reactor's own spent-fuel pool, after which it is cool enough to move to on-site storate by human operators.

But this does not necessarily mean that a year is needed for the fuel to cool down enough for the rods not to melt or burn. It means a year is sufficient time (or comfortbly more than sufficient time, given the "defence in depth" philosophy at play here) for the fuel rods to not emit enough gamma radiation to be unsafe to handle by human operators wearing standard protective clothing. Keeping them in water for a whole year may also use the water as a radiation shield (for beta radiation mostly), not necessarily for cooling.

Economics is politics by other means

by Carrie (migeru at eurotrib dot com) on Thu May 12th, 2011 at 11:19:39 AM EST
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Re: Fukushima Daiichi; photo (none / 1)

Japan Earthquake: nuclear plants - Page 429

Lets just get the facts straight, using this data that 200GJ of energy is required for a melt through we can then calculate using the formulas provided that the time for melt through is using Po=1380MW
0 minutes after shut down - 4hours
01 hours after shut down - 5 hours
02 days after shut down - 11 hours
30 days after shut down - 26 hours
60 days after shut down - 36 hours

It's pointed out that that is time for fuel melt rather than melt of core through the bottom

Any idiot can face a crisis - it's day to day living that wears you out.

by ceebs (ceebs (at) eurotrib (dot) com) on Thu May 12th, 2011 at 11:18:32 AM EST
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Re: Fukushima Daiichi; photo (4.00 / 3)

I would go with water level is one metre below where the bottom of the rods would have been had there been any rods left, then.

Economics is politics by other means

by Carrie (migeru at eurotrib dot com) on Thu May 12th, 2011 at 11:22:09 AM EST
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Re: Fukushima Daiichi; photo (none / 1)

Nuclear fuel at Fukushima No. 1 unit melted after full exposure | Kyodo News

Tokyo Electric Power Co., the operator of the crippled Fukushima Daiichi nuclear power plant, revealed Thursday that holes had been created by melted nuclear fuel at the bottom of the No. 1 reactor's pressure vessel.
The company said it has found multiple holes adding up to several centimeters in welded piping. Earlier in the day, it said the amount of water inside the troubled reactor was unexpectedly low -- not enough to cover the nuclear fuel -- hinting that a large part of the fuel melted after being fully exposed.

Any idiot can face a crisis - it's day to day living that wears you out.

by ceebs (ceebs (at) eurotrib (dot) com) on Thu May 12th, 2011 at 02:55:41 PM EST
[ Parent ]

Re: Fukushima Daiichi; photo (none / 1)

So it was, after all, the meltdown that pierced the pressure vessel?

_{*Lunatic*, n.

One whose delusions are out of fashion.}

by DoDo on Thu May 12th, 2011 at 04:02:49 PM EST
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Re: Fukushima Daiichi; photo (none / 0)

The first of what you wrote.

Tokyo Electric says temperatures at the bottom of the reactor are between 100 and 120 degrees Celsius, suggesting that the fuel has fallen and is being cooled in the water below.

The utility says it does not believe the fuel has completely melted and spilled through the bottom of the reactor. It adds that instead, the fuel appears to be being cooled inside the reactor.

But maybe these are premature conclusions: the new makeshift water level gages might have been unfit for the purpose, too.

_{*Lunatic*, n.

One whose delusions are out of fashion.}

by DoDo on Thu May 12th, 2011 at 12:31:16 PM EST
[ Parent ]

Re: Fukushima Daiichi; photo (none / 1)

well no doubt TEPCO will withdraw these readings and apologise for the terrible mistake they have made in reporting this sometime tomorrow

Any idiot can face a crisis - it's day to day living that wears you out.

by ceebs (ceebs (at) eurotrib (dot) com) on Thu May 12th, 2011 at 12:52:40 PM EST
[ Parent ]

Re: Fukushima Daiichi; photo (none / 1)

Probably an hour or so after Kan declares that nuclear power has been a disaster for the country, and that Japan is firmly committed to a nuclear future.

by ThatBritGuy (thatbritguy (at) googlemail.com) on Thu May 12th, 2011 at 01:07:53 PM EST
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Re: Fukushima Daiichi; photo (none / 1)

I know from practice that an awful lot of factors can give you a false reading when you attempt measurements with non-standard equipment under non-standard circumstances. Only the uncertainty here can have grave consequences...

_{*Lunatic*, n.

One whose delusions are out of fashion.}

by DoDo on Thu May 12th, 2011 at 01:53:48 PM EST
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Re: Fukushima Daiichi; photo (none / 0)

Had a visitor today who used to work for a large Steel company, pre-retirement he was a specialist in ultrasonic examination of produced steel. he was talking about stress cracks in rail tracks, cracks in reactor pressure vessels and the time they were given unloaded reactor fuel tube material to test to see if it was possible for them to find a hole 15 thousandths of an inch across that had been made in the material. They explained that it would not be possible at steel production speeds of 20 feet per minute. The Nuke people said that wouldn't be a problem as their tube speeds were measured in inches per hour.

Any idiot can face a crisis - it's day to day living that wears you out.

by ceebs (ceebs (at) eurotrib (dot) com) on Thu May 12th, 2011 at 02:48:47 PM EST
[ Parent ]

Re: Fukushima Daiichi; photo (none / 1)

Reactor 1 fuel rods melted, sank to bottom | The Japan Times Online