Japan:All N-fuel may have fallen to outer vessel/TEPCO: Up to 68 tons likely melted...

Yomiuri Shimbun ^ | 12/02/11

[TigerLikesRooster]

12/02/11

All N-fuel may have fallen to outer vessel / TEPCO: Up to 68 tons likely melted in No. 1 reactor, eroding concrete of containment unit

The Yomiuri Shimbun

Almost all the nuclear fuel inside the No. 1 reactor of the crippled Fukushima No. 1 nuclear power plant has melted, damaging the pressure vessel and eroding the concrete bottom of the containment vessel by up to 65 centimeters, the plant's operator has found.

Tokyo Electric Power Co. released its latest analysis Wednesday on the cores of the plant's Nos. 1 to 3 reactors, based on temperature, water levels and other data. TEPCO said the fuel inside the reactors has melted to various degrees following the March 11 earthquake and tsunami.

The No. 2 reactor's fuel is up to 57 percent melted, while that of the No. 3 reactor is up to 63 percent melted, TEPCO's analysis has shown.

TEPCO has made the latest analysis to judge to what degree the fuel has cooled, as well as to ascertain if it can achieve its year-end target of a cold shutdown of the reactors, as stipulated in the timetable the utility company and the government have compiled to bring the nuclear crisis under control.

[TigerLikesRooster]

P!

[bgill]

Is it too late to catch a ride on the Mars Rover?

[justa-hairyape]

There has been some reporting, on a non-profit site, that a rather large flame was seen all night long at the plant. Speculation is that is was burning of hydrogen gas. The wind speed at Fukushima has slowed, and it is very difficult to see any flame during the daylight. Might be interesting to check out once the sun sets. Tepco has been giving out information that might lead one to think they have new hydrogen gas buildup problems.

Possible Fire Or Controlled Hydrogen Venting At Fukushima Daiichi

UPDATE: Fire At Fukushima Likely Hydrogen Purge

[lefty-lie-spy]

Pretty wild stuff. The pressure vessel is typically 250mm thick 12 meters tall and 5 meters wide and is manufactured to withstand temperatures of at least 350c. Fast neutrons are pretty freaking amazing, eh? I love studying this stuff.

[razorback-bert]

thanks

[perks]

63 TONS of hot fuel burrowing into concrete is NOT cooled by 43 CM of water.

IE, reactor 2 is only 58% melted, yet it is releasing Xenon gas in significant quantities( as reported many places in early Nov. This would require temperatures of 1450K or about 2,200F.
http://en.wikipedia.org/wiki/Behavior_of_nuclear_fuel_during_a_reactor_accident )

So obviously the cooling in reactor 2 is not fully cooling the melted fuel and it is still eroding the containment vessel.

[justa-hairyape]

Well, apparently the Japanese Government says there is no problem. So therefore there is no problem.

Japan may announce Fukushima cold shutdown on Dec. 16: Yomiuri

(Reuters) - Japan may announce on December 16 that tsunami-damaged nuclear reactors in Fukushima are in a cold shutdown, the Yomiuri newspaper reported on Friday, an important milestone in its plan to bring under control the worst nuclear accident in 25 years.

[justa-hairyape]

See story above. Apparently the “Dont worry be Happy” story plan was going to be that the RPV’s lower temperatures have achieved cold shutdown. So therefore the problem is gone. Never mind that almost all of #1 reactor core and at least half of #2 and #3 reactor cores are now located no where near the bottom of the RPV’s. My guess is that nature and physics has other plans for the never mind crowd.

[djf]

Well, 2012 is just around the corner...

[E. Pluribus Unum]

It’s headed for Brazil.

[justa-hairyape]

It cannot be any worse then my Thanksgiving weekend. Don’t ask. Might have an interesting story to tell later :>

[sefarkas]

What’s been reported is a very conservative mathematical analysis that has yet to be physically confirmed. In other words, this is a worst case scenario. And as we’ve seen in our industry, even in the worst case scenario, there is still a very significant safety margin.

A quick read of the article could give one the impression that the melted core was a little more than half a meter — about 2 feet — from reaching the external environment. I think it’s important to note that according to the TEPCO analysis only .7 meters (a little more than two feet) of concrete was actually eroded. In addition, as we’ve written before, plants have multiple redundant safety systems in place to protect the public, and that’s exactly the case with Fukushima Daiichi Unit 1.

In addition to the 2.6 meters (about 8.5 feet) of steel reinforced concrete inside the containment vessel, underneath the steel shell of the containment vessel lies another 7.6 meters (about 25 feet) of basemat reinforced concrete and steel. Altogether, that means there was 10.2 meters (about 33.5 feet) of reinforced concrete and steel standing between the reactor core and the outside of the plant before the accident.

Even if 2 meters (about 6.5 feet) of that structure has been eroded, another 8.2 meters (almost 27 feet) of reinforced steel and concrete lies between the melted fuel and the external environment.

It’s also important to note that according to tests of air samples from inside containment, it appears that the process of erosion – called corium interaction – has essentially ceased and no further damage is occurring at this time.

see more at http://neinuclearnotes.blogspot.com/

[justa-hairyape]

All that don't matter one bit if some of the corium flowed down the drywell sumps and out into the downcomers. And Tepco sure wont tell you if that actually occurred.

What you are actually reading is the best case scenario.

[little jeremiah]

Thank you for keeping at this.

I try to read and grasp the import but all I can come up with is “FUBAR”.

:-(

[sefarkas]

if some of the corium flowed down the drywell sumps and out into the downcomers

The point of the blog post provided for your reading pleasure and education was the consequence of corium outside the BWR reactor vessel. Look closely at how the reactor building is configured for a Mark I Containment. Do you see what they label "downcomer"? There is a second downcomer inside the reactor vessel between the core barrel and the reactor wall (where the jet pumps are). The drywell is immediately outside the reactor vessel (do you see that in the illustration provided?) -- the drywell sump is directly below the lower head of the reactor vessel. The bottom of the upside-down-light-bulb shaped drywell is filled with concrete. Then you reach the steel liner that is the upside-down-light-bulb itself. Then you start into the foundation of the reactor building supporting the 700 ton reactor vessel and all of the other equipment in the reactor building. The foundation is over twelve feet thick by itself. Now read the comment you posted. Does it make any sense??? I have to say that I have rarely read anything on FR as ignorant as the comment you wrote above. If you do work at an n-plant, then you need to think about a new line of work.

[mewzilla]

If they’re still having hydrogen gas problems, could they install some of those passive catalytic hydrogen recombiner thingies to take care of the gas buildup, anyone know?

[justa-hairyape]

The data I posted was extracted from the Reactor Safety Training Course (R-800) manual from the NRC. Perhaps you would like to complain to them ? And since you apparently work in the industry, perhaps you might want to read the manual. Sure could have helped those nuclear workers at TEPCO who apparently had trouble finding their own safety manuals the night the Tsunami hit.

The link below contains the following sections and chapters from the actual course manual, not pages on a blog

Special Considerations for BWR Facilities section 3.7
Accident Progression in the Containment chapter 4.0
Offsite Accident Impacts chapter 5.0

Reactor Safety Training Course (R-800) manual sections and chapters related to Fukushima accident

Give me a page number and show where I was wrong. Will be more then happy to correct myself with a cogent response.

[justa-hairyape]

Off the top of my head, there only has to be 4 % hydrogen gas present for there to be a possible explosion if oxygen is also present. They actually were surprised to find hydrogen at about 3 % when they looked for the first time into sections of reactor #2. Their main plan of attack, from what the news report state, is to insert nitrogen which is heavier then hydrogen. So they must be forcing the hydrogen up and out somewhere. Probably those two flame-offs that could be seen on a Fukushima web cam last night. Concerning passive catalytic hydrogen recombiner, do not personally know, but below is a link to an entire book on the subject.

Passive catalytic hydrogen recombiners for nuclear power stations

[justa-hairyape]

Actually that appears to be a Russian scientific paper converted to English. Those Russians are the experts on nuclear accidents, unfortunately for them.