Japan may have lost race to save nuclear reactor

[Turborama]

Source: The Guardian

http://www.guardian.co.uk/world/gallery/2011/mar/29/japan-disaster-week-three-in-pictures">• In pictures: Fukushima nuclear emergency - week three

http://www.guardian.co.uk/world/interactive/2011/mar/16/japan-earthquake-and-tsunami-nuclear-sample?intcmp=239">• Interactive: Japan earthquake: Ian Sample on efforts to contain the nuclear accident

Ian Sample , science correspondent | Tuesday March 29 2011 16.53 BST

The radioactive core in a reactor at the crippled Fukushima nuclear power plant appears to have melted through the bottom of its containment vessel and on to a concrete floor below, experts say, raising fears of a major release of radiation at the site.

Richard Lahey, who has worked on the plant at Fukushima, told the Guardian officials seemed to have "lost the race" to save the reactor, but added that there was no danger of a Chernobyl-style catastrophe.

=snip=

At Fukushima, workers have been pumping water into three reactors in a desperate bid to keep the fuel rods from melting down. But Lahey, who was head of safety research for boiling-water reactors at General Electric when the company installed the units at the plant, said his analysis of radiation levels suggested these attempts had failed at reactor two.

He said at least part of the molten core, which includes melted fuel rods and zirconium alloy cladding, seemed to have sunk through the steel "lower head" of the pressure vessel and on to the concrete floor below. "The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell," Lahey said. "I hope I am wrong, but that is certainly what the evidence is pointing towards."

Read more: http://www.guardian.co.uk/world/2011/mar/29/japan-lost-race-save-nuclear-reactor

[thereismore]

1. It is now time to pump water OUT of the reactor building. Damn. They need to put a concrete

slab underneath that reactor, or it will be much worse than Chernobyl. nt

[MineralMan]

2. For reference, here's an image of the reactor as a diagram.

They're talking about a possible melt-through of the steel reactor vessel. It's surrounded on all sides by the steel containment vessel, which is surrounded by the concrete primary containment vessel. So there is concrete under the steel parts. Very thick concrete.

It's good to have an image to reference when reading these stories.

[bananas]

3. No, it says "melted through the bottom of its containment vessel and on to a concrete floor below"

They are saying it melted through both the reactor vessel and steel containment vessel onto the concrete floor below:

"He said at least part of the molten core, which includes melted fuel rods and zirconium alloy cladding, seemed to have sunk through the steel "lower head" of the pressure vessel and on to the concrete floor below. "The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell," Lahey said. "I hope I am wrong, but that is certainly what the evidence is pointing towards."

[MineralMan]

6. I think the concrete floor being referred to is the one of the

Concrete containment vessel shown in the diagram (the yellow part). The pressure vessel would be the steel containment vessel or the reactor vessel. That's how I interpret it, anyhow. I could be wrong, but I see no concrete in the diagram below the concrete containment vessel.

Under that steel "lower head" is the base of the concrete primary containment vessel. That part of the containment isn't pressurized, I think.

[bananas]

9. Ok, I think you're right - more diagrams in another thread.

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=439&topic_id=766258&mesg_id=766754

[MineralMan]

12. Well, I know for certain that the yellow part of the Primary containment

is concrete. That's standard. There's no metal, other than reinforcing steel, and a lot of it in that concrete. The reactor vessel and the steel vessel around that are both steel. The concrete is a last resort containment, since the heat reached by a molten core isn't high enough to melt concrete. That requires a very, very high temperature. Still, there are other problems that can develop, so I don't know what might happen under the worst possible conditions. I just know that the concrete part is designed to contain even a meltdown. Designed to. Whether it actually will is another issue.

[MineralMan]

13. Thanks. I'll check it out.

[stockholmer]

4. lets hope this steel & concrete fares better against nuclear pile than the WTC did against jet fuel

[bahrbearian]

5. So what keeps it from going up?

"They're talking about a possible melt-through of the steel reactor vessel. It's surrounded on all sides by the steel containment vessel, which is surrounded by the concrete primary containment vessel. So there is concrete under the steel parts. Very thick concrete."

[MineralMan]

7. What do you mean "going up?"

Exploding?

[4saken]

22. High-pressure melt injection?

"Allen said the situation was likely to play out for a long period of time: "These things could go on for months. You could lose all six of the reactors." If workers are unable to get cooling water into the reactor vessel, as they're trying to do with helicopters and water cannons, heat from the decaying fuel would boil away any water. If that happens, Allen says, "It'll melt through it like butter."

The effect of that would be a "high-pressure melt injection" into the water-filled concrete cavity below the reactor. The sudden injection of the ultrahot contents of the reactor into cold concrete would be "like somebody dropped a bomb, and there'll be a big cloud of very, very radioactive material above the ground," Allen said. "

Source:
http://nymag.com/daily/intel/2011/03/worst_case_scenarios_at_the_fu.html

I really hope that is not the future of this plant. :,(

[MineralMan]

26. Worst-case scenarios are just that - Worst cases.

That seems unlikely to me. It's remotely possible, but lots of resources are focused on this plant, and all the reactors were shut down due to the earthquake, so the worst-case scenario is very unlikely.

I prefer to be as optimistic as possible. The probabilities are strong that this will be resolved without the worst-case occurring. It's bad enough as it is. As my grandmother used to say, "Don't buy trouble."

[daleo]

8. If something can melt through steel (8 inches, I believe)

It may well melt through concrete, even thick concrete. Who knows what the intense heat, seawater, steam, corium, etc might so.

[MineralMan]

10. You could be right. Concrete is pretty hard to melt, though.

That's why they build that part of the containment vessel out of concrete. The melting point of concrete is very, very high, and depends on the aggregate used. However, excessive heat can cause cracking of concrete. It's not a good thing, but that's why the concrete is there on these reactors. It's tough to get through.

[daleo]

24. I was thinking more along the lines of a big crack

Water alone can do surprising things to concrete (e.g. via freeze-thaw cycles). And the concrete must have re-bar in it, which complicates the chemistry and physics, especially given the fact that salt water is now in the mix.

A concrete bridge collapsed not so long ago in Minnesota and another in Quebec. Time and salt takes a toll. The radioactive meltdown mass will have to be contained for years, decades.

[MineralMan]

27. There's more rebar in that concrete than you can imagine. I watched

them build the Diablo Canyon plant. The concrete containment structure blew my mind. I could not conceive of any way it could fail. It's not a driveway, with 6-6-10 mesh in it. It's almost bizarre how much reinforcement goes into that stuff. And the mix is super rich, with aggregate that is especially chosen for high melting point, etc. No salt has touched that concrete until this incident.

At this point, we don't even know how much melting has occurred. It's way to early to predict catastrophe. What has happened is bad enough.

[Taft_Bathtub]

15. That's why they're trying to keep it cool

By pumping in water with Boron to shut down the reactor. The reactor won't be able to produce electricity anymore but that's fine.

[DeSwiss]

16. Corium.....

...may also include molten concrete from the reactor room floor:

Corium (nuclear reactor)
From Wikipedia, the free encyclopedia

Corium, also called fuel containing material (FCM) or lava-like fuel containing material (LFCM), is a lava-like molten mixture of portions of nuclear reactor core, formed during a nuclear meltdown, the most severe class of a nuclear reactor accident. It consists of nuclear fuel, control rods, structural materials from the affected parts of the reactor, products of their chemical reaction with air, water and steam, and, in case the reactor vessel is breached, molten concrete from the floor of the reactor room.

MORE: http://en.wikipedia.org/wiki/Corium_%28nuclear_reactor%29

Corium-concrete interactions

Thermal decomposition of concrete yields water vapor and carbon dioxide, which may further react with the metals in the melt, oxidizing them and being reduced to hydrogen and carbon monoxide. Decomposition of the concrete and volatilization of its alkali components are endothermic processes. Aerosols released during this phase are primarily based on concrete-originating silicon compounds. Otherwise volatile elements, e.g. caesium, can be bound in nonvolatile insoluble silicates.<2>

Several reactions occur between the concrete and the corium melt. Free and chemically bound water is released from the concrete as steam. Calcium carbonate is decomposed, producing carbon dioxide and calcium oxide. Water and carbon dioxide penetrate the corium mass, exothermically oxidizing the nonoxidized metals present in it and yielding gaseous hydrogen and carbon monoxide; large amounts of hydrogen can be produced. The calcium oxide, silica, and silicates melt and are mixed into the corium. The oxide phase, in which the nonvolatile fission products are concentrated, can stabilize at temperatures of 1300–1500°C for a considerable time. An eventually present layer of more dense molten metal, containing fewer radioisotopes (Ru, Tc, Pd..., initially composed of molten zircaloy, iron, chromium, nickel, manganese, silver, and other construction materials and metallic fission products, and tellurium bound as zirconium telluride) than the oxide layer (which concentrates Sr, Ba, La, Sb, Sn, Nb, Mo, etc. and is initially composed primarily of zirconium dioxide and uranium dioxide, possibly with iron oxide and boron oxides), can form an interface between the oxides and the concrete below, slowing down the corium penetration and solidifying within a couple of hours. The oxide layer produces heat primarily by decay heat, while the principal heat source in the metal layer is exothermic reaction with water released from the concrete. Decomposition of concrete and volatilization of the alkali metal compounds consumes substantial amount of heat.<2> The fast erosion phase of the concrete basemat lasts for about an hour and progresses into about one meter depth, then slows to several centimeters per hour, and stops completely when the melt cools below the decomposition temperature of concrete (about 1100°C). Complete melt-through can occur in several days even through several meters of concrete; the corium then penetrates several meters into the underlying soil, spreads around, cools and solidifies.<3> During the interaction between corium and concrete, very high temperatures can be achieved. Less volatile aerosols of Ba, Ce, La, Sr, and other fission products are formed during this phase and introduced into the containment building at time when most of early aerosols is already deposited. Tellurium is released with progress of zirconium telluride decomposition. Bubbles of gas flowing through the melt promote aerosol formation.<2>

MORE:http://en.wikipedia.org/wiki/Corium_%28nuclear_reactor%29#Corium-concrete_interactions

[daleo]

25. It sounds like uncontrollable stuff, to say the least. n/t

[Taft_Bathtub]

14. No they don't

They already have something like that, it's called the secondary containment structure that surrounds the reactor. It's enough concrete to withstand a direct impact from a Boeing 747.

Basically what this person, who has not been to the site, is speculating is that the reactor is destroyed. That means no more power generating capability and TEPCO being out billions of dollars/the surrounding community unable to produce power from that reactor for probably a decade while they disassemble it and install a new reactor.

[intaglio]

17. You mean the person who helped design this reactor.

and is saying that he is fairly sure a melt through of the steel pressure vessel and that the damaged drywell containment is all that is stopping massive radiation release is talking rubbish.

Well, I'll be sure to give your idea my fullest consideration :sarcasm:

[Taft_Bathtub]

19. Yes, someone that has not been to the site and has read the same media reports

as you and me is speculating the reactor is destroyed. I appreciate your sarcastic reply it certainly adds to the discussion!

[intaglio]

23. Boy, I'm glad I'm not an idiot

and actually don't pay attention to people who know what they're talking about.

You're not Lewis Page are you?

[AtheistCrusader]

18. It was destroyed anyway

when they dumped seawater into it. Not 'damaged beyond use' but certainly out of tolerance. There's no way they would have used it again after that.

[Taft_Bathtub]

20. Exactly,

nt

[Kolesar]

11. "The New Jersey Syndrome"

If that Jane Fonda movie was based in Asia

[fascisthunter]

21. I'm Gonna buy Some Miso Soup

[Zorra]

28. That is truly awful news. Nukes, the gift that keeps on giving. nt

[w4rma]

29. I think he forgot that they recycled sea water through this reactor already so it cannot be saved no

matter what it's current state is.

[TacticalPeek]

30. Japan may have lost race to save nuclear reactor

Source: Guardian



The radioactive core in a reactor at the crippled Fukushima nuclear power plant appears to have melted through the bottom of its containment vessel and on to a concrete floor, experts say, raising fears of a major release of radiation at the site.

The warning follows an analysis by a leading US expert of radiation levels at the plant. Readings from reactor two at the site have been made public by the Japanese authorities and Tepco, the utility that operates it.

Richard Lahey, who was head of safety research for boiling-water reactors at General Electric when the company installed the units at Fukushima, told the Guardian workers at the site appeared to have "lost the race" to save the reactor, but said there was no danger of a Chernobyl-style catastrophe.
. . .

"The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell," Lahey said. "I hope I am wrong, but that is certainly what the evidence is pointing towards."



Read more: http://www.guardian.co.uk/world/2011/mar/29/japan-lost-race-save-nuclear-reactor

---

Lovely.

[aquart]

31. How long have we known about this inevitable outcome?

So what are they going to do about it NOW?

[Oak2004]

32. It's been core on the floor for days now

and it was probably destined to get there after the first 24 hours of this crisis. That's the only plausible thing that could have happened. We may have enough data now that outside observers feel secure in saying this has happened. But if you think through the accident step by step, core on the floor is where it all leads.