Radiation probes indicate no melt through at Fukushima Unit 1

[wtmusic]

"Tepco has recently released measurements that provide convincing evidence that virtually all of the corium in Fukushima Daiichi unit #1 remains safely stored inside an intact reactor pressure vessel. Despite all claims to the contrary, no substantial quantities of that material have melted through the pressure vessel to fall onto the concrete floor of the surrounding containment structure.

It has always seemed far fetched to me to think that material from a nuclear reactor that melted several hours after fission has stopped contains the power density necessary to melt through carbon steel pressure vessels that are 6-12 inches thick. My basis for making that statement comes from having spent several sleepless nights in a drydock watching people with specially designed torches cutting into submarine hulls to provide maintenance access. I also had the opportunity during at least one repair period to be the guy responsible for signing the requisition chits for the pallets full of gases used to power those torches.

Melting thick steel is not a job for a mass of metal that is only being heated by radioactive decay whose heat production is falling rapidly."

http://theenergycollective.com/rodadams/124446/radiation-probes-indicate-no-melt-through-fukushima-unit-1?utm_source=feedburner&utm_medium=feed&utm_campaign=The+Energy+Collective+%28all+posts%29

No comment from Arnie Gundersen yet.

[OKIsItJustMe]

1. TEPCO succeeds in taking water sample from crippled No. 1 reactor

It seems odd to me that TEPCO wouldn’t announce such good news with trumpets. …
http://english.kyodonews.jp/news/2012/10/187744.html

[font face=Serif][font size=5]TEPCO succeeds in taking water sample from crippled No. 1 reactor[/font]

TOKYO, Oct. 12, Kyodo

[font size=3]The operator of the crippled Fukushima Daiichi nuclear power plant succeeded Friday in taking a sample of water from the No. 1 reactor's primary containment vessel, the first such attempt since the accident at the plant occurred last year.

Considering the water's radiation level and other data, Tokyo Electric Power Co. said the fuel, which is believed to have melted through the pressure vessel and accumulated in the outer primary container, does not appear to be releasing large amounts of radioactive substances because it is kept cool.

The water contained 19,000 becquerels of cesium 134 per cubic centimeter and 35,000 becquerels of cesium 137, lower than the density levels of the water accumulating at the building housing the reactor.

…[/font][/font]

http://www.tepco.co.jp/en/press/corp-com/release/2012/1221982_1870.html

[font face=Serif][font size=3]…[p]Below is the status of TEPCO's nuclear power stations (Fukushima Daiichi and Fukushima Daini).
[p]* The updates are underlined.
[p][strong]|Fukushima Daiichi Nuclear Power Station|[br][/strong]･ Unit 1 to 4: Abolishment (April 19, 2012)[br]･ Unit 5 to 6: Outage due to regular inspections before the earthquake
[p]-On October 12, we sampled the accumulated water of PCV from one of the penetration holes of Unit 1 PCV (X-100B penetration), and analyzed the water. The results of the analysis were as follows.
[p]  Iodine: Below the detection limit[br]  Cesium 134: 1.9 x 10⁴ Bq/cm³[br]  Cesium 137: 3.5 x 10⁴ Bq/cm³
[p]-From 9:30 AM to 11:30 AM on October 13, we installed a permanent monitoring meter (thermometer, water gauge) from one of the penetration holes of Unit 1 PCV (X-100B penetration) to the inside of PCV. We checked its functionality and the output data, and confirmed that there was no problem. The measured data by the permanent monitoring meter were as follows (as of 1:00 PM).
[p]  Water level of PCV: Approx. 2.4m - 3.2m from the floor of the dry well (provisional)[br]  Atmosphere temperature: Approx. 34.1°C - 35.1°C[br]  Accumulated water temperature: Approx. 37.0°C - 37.4°C
[p]The measured data of the existing temperature at the same time was Approx. 34.4°C - 41.5°C, there is little difference between the existing temperature and the thermometer installed this time. We will continuously monitor the data of the permanent thermometer.…[/font][/font]

Perhaps your source knows something TEPCO doesn’t?

[AtheistCrusader]

2. Sort of makes sense.

Since the water is being pumped into and back out of the RPV, if the radiation levels in the water are high, and there is no evidence of Corium on the floor of the containment, and the water on the floor of the containment has less contamination of the pump building, that suggests the RPV is intact.

[Yo_Mama]

5. They know the reactor vessel is not intact

Because they aren't pumping water in and out of the reactor vessel. They are pumping water into the reactor vessel and pumping it out of the basement, where it accumulates. In no sense is this a contained system. Water is flowing out of the reactor vessel at very high rates.

The TEPCO briefing portions listed by a helpful poster are discussing the containment vessel, which is outside the reactor vessel.

The flooded drywell clearly has some fuel at the bottom, but it may have spatters. If most of the melted fuel is still in the reactor vessel, it would make eventual cleanup much easier.

Don't forget that this is a very old reactor. The fuel rod assembly is inserted at the bottom of the reactor vessel in this type. Under normal circumstances, the aperture has very strong seals. Those are long eroded, and the water may be leaking through mostly the pre-existing apertures. The water may well be entering the basement through broken piping.

Containment for this type of reactor has multiple levels, with the first level of containment being the outer coating of the fuel rods themselves. Under "normal" operation, every once in a while you will have a failure of that containment, which would result in higher levels of radioactivity in the coolant (water). That would cause shutdown, a cooling cycle, decontamination of the water within the closed system, and eventual removal of the fuel rods, replacement and a restart.

The next level is the reactor vessel itself, which really includes all the apertures and piping which cycle the coolant, all of which is normally a closed system. In extreme circs, there may be a venting of steam to the outside environment, which is theoretically a violation of containment but not a very serious one, because the coolant itself is not very contaminated.

The reactor vessel containment is breached.

Overall the findings are encouraging, because it indicates that cooling is working and that probably you don't have huge blobs of the melted fuel down there. If you did, you would expect higher levels of radioactivity because cooling would be less effective.

[Yo_Mama]

7. A shorter answer

They absolutely know that the reactor vessel is not intact.

The reason that they know that is that they drilled into the containment structure to get these readings, and the highest reading (11 sieverts per hour), was taken at the point of entry, which was much closer to the bottom of the reactor vessel than the water surface.

If the reactor vessel were intact, there would be not only no water leakage, but there would be no radiation leakage of that magnitude.

However, the fact that radiation readings within the containment vessel dropped so sharply as they took readings further from the reactor vessel strongly suggests that the bulk of the fuel is "up there" rather than "down here".

Now it is true that the pool of water in the drywell (about 2.8 meters or nine feet from the original drywell surface) would serve to contain radiation from the corium concentrations in the drywell. But if there were a big blob of it down there, then cooling would be ineffective and that water near the corium should be very perturbed from heat transfer, which should make the surface radiation levels higher than the 0.5 sieverts per hour measured. So I don't see how their conclusions could be wrong.

I am sure that someone somewhere with a fertile imagination is forming the theory that the massive blob of corium bored right through the drywell and infrastructure and is halfway through the outer mantle on its way to Yellowstone. But yet there are technical problems with this theory, including, but not limited to the problem that the water is pooling on the bottom of the drywell.

It only supports the nutcases to make the contention that the RPV is intact. It is clearly not. Nor can one say that there is "no evidence" of corium on the floor of the drywell. There probably is some. It would be great if they could get temperature readings of the water at the surface and multiple points below the surface. That would go a long way toward resolving the question.

[AtheistCrusader]

8. I should have been more precise.

Maybe 'largely intact'. My point was that these new readings only make sense if the bulk of the fuel is still inside the RPV. I feel like I wasted your time a little bit by being imprecise. I apologize.

Earlier you mentioned the fuel rod assembly is inserted from below in this reactor (GE Mark 1 BWR). Did you mean Control rod assembly? I was under the impression all fuel loading, removal, is done from above in this reactor type.

[Yo_Mama]

12. Yes, thanks

The reactor vessel sits inside the containment vessel. There is a cap on the containment vessel that is removed when necessary, and a cap on the reactor vessel that is removed when necessary.

Occasionally in some of these older reactors they have removed the entire reactor vessel and replaced it.

This is the type of assembly we are looking at:


But that is misleading. There's a much better diagram for BWR-3 & 4 in this pdf:
http://www.oecd-nea.org/press/2011/BWR-basics_Fukushima.pdf

There you can see the flux monitor and control rods that go through the bottom of the reactor. Those go up through the bottom shroud to where the fuel rods normally will be. But the apertures at the bottom are a definite weakness in this type of an event.

Above the fuel rods you have the sprayer & steam assemblies. All of the piping, valves, and assemblies need maintenance and inspection, and that is normally done by going in from the top. But inspections and maintenance are also routinely done down in the drywell inside the containment vessel. And of course the seals for the control rods and the reaction monitor are also inspected and replaced. There are really two sets of seals, one in the bottom of the reactor vessel and then those going through that bottom plate.

In the diagram in the pdf you can see how the top and bottom plates and shroud normally are a contained unit within the reactor vessel. Those plates are very thick. The theory that a giant blob of fuel melted through that bottom plate and then through the bottom of the reactor vessel to land on the bottom of the drywell is what you were correctly disputing.

How could that have happened given what they found?

But the reactor vessel is breached to some extent.

You didn't waste my time, and I apologize for wasting some of yours. Given the remarkably bad press coverage and some obviously ill-founded putatively expert speculation, it's well to be as precise as possible (and I was more imprecise than you!).

Originally when they flooded the drywell it was with seawater. That water is now fresh, so there's some leakage from the drywell.

[FBaggins]

3. I think that it's Adams' assumptions...

rather than a TEPCO conclusion.

[wtmusic]

4. This isn't news.

There's never been any evidence of a massive leak of corium from the reactor vessel. Rod Adams & Leslie Corrice (both people who have hands-on experience running nuclear reactors) are merely announcing that new tests appear to confirm it.

Geared toward the Arnie Gundersen, hair-on-fire China Syndrome crowd.

[Yo_Mama]

6. Well, they normally ignore that crowd.

I think the focus here is on cleanup modalities. Obviously it would be easier if there were no large amount of fuel on the floor of the drywell.

Paradoxically, it may mean a longer cycle for the reactor vessel, because if the fuel is substantially blobbed on the fuel rod assembly, it would take longer to cool.

The people who thought (and apparently still do) that breach of the reactor meant a huge lump of corium boring its way through to the earth's core apparently get all their engineering info from movies and TV. Ever since I realized that 1 to the fourth power is a very large number in Hollywood (episode of the original Star Trek) I have avoided that trap.

[RobertEarl]

9. Idn't that great

You have this all figured out, eh?

TEPCO feeds you a bit of info and you extrapolate that into "I know where the corium is. Look at me, I'm so smart!!"

If you were smart you wouldn't let TEPCO lead you on. Instead, you get all nasty and start slamming people who think, that, by gawd, that shit could have burned through the whole fucking containment. And it sure as fuck may have.

TEPCO , the lying bastards who let this shit happen and now blame the "crazies'' for it, sure doesn't know where their shit is. But you do? Gawd that is some damn foolish shit. "

[Yo_Mama]

10. No

Not at all.

The article posted is written by people who do have extensive background, and it's just reporting the results of a test that TEPCO did. The interpretation is their own, but not well explained.

The other post is an excerpt of a standard TEPCO update, and was clearly meant to rebut the idea that the fuel was still all in the reactor vessel.

When has TEPCO ever blamed anyone outside the industry for the accident?

[RobertEarl]

11. TEPCO just a few days ago

Said that they would have done something to keep this from happening but TEPCO "feared the political, economic and legal consequences of implementing them."

Meaning if people hadn't been so mean and wanted them to tell the truth and spend the funds needed, they would have gone ahead and done the right thing.

DU thread link:
http://www.democraticunderground.com/112725726

TEPCO, all of us should know by now is NOT to be trusted.