Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[MadderDoc]

<..>

"Also the levels of Cs-134 and Cs-137 measured at reactor 2 building are not exactly plummeting since they <..> did some filtering & ventilation:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110616_01-e.pdf

http://www3.nhk.or.jp/daily/english/16_23.html

Any ideas how they are able to give such positive numbers in that press article? Am I reading the graph wrong or are they using out of date info?

My best idea is that the numbers in the press article might be a -- perhaps somewhat positively skewed -- representation of data as it looked a few days ago, maybe when a Tepco application was made to authorities -- I imagine opening the reactor building to the environment would be one of those things that the utility would need official permission to do.

It seems clear from the Tepco press releases, that the full data set you reference includes the time for initiation of the air purification, quote Tepco,
"-We installed local exhausters and started to operate them at 12:42 pm on
June 11 in order to improve the working environment inside Reactor
Building of Unit 2."
and the full dataset then does not seem to support that there has been a reduction of the Cs isotopes over the period of operation so far, nor that the reduction of I-131 has had the magnitude expressed in the press article.

 

[joewein]

Looks like the new plan to provide unit 4 fuel pool cooling involves a pretty basic solution, attaching the end of a hose to some railings on the refuelling bridge.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110616_03-e.pdf

One of the ripped up pipes in this image at unit 4 was originally planned to be used for the closed loop cooling:

[PLAIN]http://img824.imageshack.us/img824/6213/11061104.jpg

Since the hot water is taken from the skimmer tank, the damaged pipe was probably the other end, i.e. the one feeding back into the pool. That's what the above railings attachment is about.

Also the levels of Cs-134 and Cs-137 measured at reactor 2 building are not exactly plummeting since they opened the doors and did some filtering & ventilation:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110616_01-e.pdf

This is speculation on my behalf, but perhaps the cesium in the air is steadily being replenished from evaporation of contaminated water.

For example, if steam was bubbling through hot water, or there was water leaking from a pipe above the ground so that evaporation was not happening from a quiet surface of standing water then dissolved solids would always end up as dust in the air.

 

[Jorge Stolfi]

If you are still looking for thermocouple locations try this:
http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/measuring_positions-e.pdf

Thanks!

 

[MadderDoc]

Looks like the new plan to provide unit 4 fuel pool cooling involves a pretty basic solution, attaching the end of a hose to some railings on the refuelling bridge.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110616_03-e.pdf
<..>

One could say the concrete pump method used so far is also pretty basic. and then there is the KISS principle. The alternative sfp injection there presented is of course not in principle different than using the concrete pump and it should work just as well. As a practical matter it would mean less obstruction for the ongoing work at the south face of the building to null the need to have the concrete pump around.

As an aside (see attachment) -- there is a square structure indicated in the drawing at what would be the east side of the unit 4 pool. I wondered if there is any significance to that depictured detail, as regards how the unit 4 pool set up is or is to be actually configurated. (The sketch could of course be of a generic pool and not refer in such specifics to the unit 4 pool.)

 

[joewein]

As an aside (see attachment) -- there is a square structure indicated in the drawing at what would be the east side of the unit 4 pool. I wondered if there is any significance to that depictured detail, as regards how the unit 4 pool set up is or is to be actually configurated.

I believe that's the skimmer tank. Every SFP has one.

To prevent any possibility of the pool draining from a ruptured pipe or from siphoning, there is no pipe connected to the bottom of the pool. Instead the water circulation system uses the skimmer tank such that when cold water gets added to the main pool it raises the level until it overflows into the skimmer tank, from where it is pumped into the heat exchanger (and from there back into the main pool).

 

[robinson]

A diagram of what the Fukushima reactor buildings/design actually look like would be really helpful. Or rather, what they used to look like. I know for a fact none of the one published yet are totally accurate.

 

[MadderDoc]

I wonder if anyone here has been able to identify where this photo was taken?

http://www.tepco.co.jp/en/news/110311/images/110611_05.jpg

In the Tepco handout page the photo has this mysterious caption which does not really make any sense:
"Side Part of Skid of Water Treatment Facility of Fukushima Daiichi Nuclear Power Station
(pictured on June 9, 2011)
Pictured at South Side on 4th floor of Unit 4 Reactor Building"

 

[MadderDoc]

I believe that's the skimmer tank. Every SFP has one.

To prevent any possibility of the pool draining from a ruptured pipe or from siphoning, there is no pipe connected to the bottom of the pool. Instead the water circulation system uses the skimmer tank such that when cold water gets added to the main pool it raises the level until it overflows into the skimmer tank, from where it is pumped into the heat exchanger (and from there back into the main pool).

Thank you joewein. If that is the skimmer tank, the indicated position confuses me. As I had made for myself a mental map of the set up, excess water would leave through openings at top edge of the pool, to be collected in surge tank(s) placed under deck on one or on either side of the fuel transfer chute.

 

[biggerten]

Looks like the new plan to provide unit 4 fuel pool cooling involves a pretty basic solution, attaching the end of a hose to some railings on the refuelling bridge.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110616_03-e.pdf

I'm sure they will, but just so it's said, I hope they have check valves installed so that the 'solution' does not become a siphon and drain the pool should a failure occur....

 

[etudiant]

I'm sure they will, but just so it's said, I hope they have check valves installed so that the 'solution' does not become a siphon and drain the pool should a failure occur....

Is this just the first step?
Was not the plan to restore the cooling of the pool by recirculating its water through a heat exchanger?
Thus far, nothing is indicated beyond a simple replacement of the pumper vehicle. Has there been any detail on the rest of the installation, including the heat exchanger and the tap from the skimmer pool?

 

[Quim]

were designed for ultra-pure water.

Were designed to operate safely for 40 years?

The likeliest scenario is that the molten corium is now covered in a solid crust, due to having been cooled constantly and being a rather poor conductor of heat in the first place...

zapperzero, I think you have provided some of the best descriptions of the condition of the corium - this was also yours:

he corium does not exist in beautiful isolation anyway Lots of things could be sending neutrons back into the corium. The steel. The water. The miscellaneous stuff that's IN the water. The crust around the corium, which is of uncertain composition and density.

I imagine that "crust" to be fairly thick already.
We just need to give it some help.

But maybe we don't even need to do that.

 

[biggerten]

Is this just the first step?
Was not the plan to restore the cooling of the pool by recirculating its water through a heat exchanger?
Thus far, nothing is indicated beyond a simple replacement of the pumper vehicle. Has there been any detail on the rest of the installation, including the heat exchanger and the tap from the skimmer pool?

I seem to recall that that plan fell through due to damaged plumbing. Maybe this is just to buy some time, I'm sure these pumper trucks were never rated for nuclear plant cooling!

 

[zapperzero]

Were designed to operate safely for 40 years?

And those 40 years are up (a few months left, if that, iirc).

It's not very well understood why the corium stopped flowing, at Chernobyl. Maybe Dimitry was right and it self-distilled, releasing all/most of the fission products and so decreasing its heat production. I don't know, no one knows, but I don't see how not cooling the corium is better than cooling the corium.

What's the worst that can happen? The exclusion zone gets a bit more radioactive. Big whoop. It's already radioactive enough that you don't want to live there. Barring another explosion or something, things can't get MUCH worse, even if there's steam coming out 24/7.

And no, I don't care about the whales glowing in the dark. They can use a break from Japanese "marine biology research" anyway.

 

[Jorge Stolfi]

I imagine that "crust" to be fairly thick already.

It is not obvious that the crust will get thicker with time. The corium is not just hot, it is generating heat continuously. To a first approximation the crust thickness should be constant, defined by an equlibrium between the power generated by the radioactivity inside it and the power absorbed by the boiling of water outside it.

However, the boiling water may be slowly eroding the oxides in the crust, so it may even be getting thinner with time. And if it were to get dry, it would probably melt completely, perhaps in a matter of minutes.

 

[Quim]

It is not obvious that the crust will get thicker with time.

I think it is if you consider particles which land on top of the corium pile(s) to be part of that crust. (Could it be that the salt from the early saltwater injections is now providing a beneficial contribution to the "crust" surrounding the corium?)

The corium is not just hot, it is generating heat continuously. To a first approximation the crust thickness should be constant, defined by an equlibrium between the power generated by the radioactivity inside it and the power absorbed by the boiling of water outside it.

However, the boiling water may be slowly eroding the oxides in the crust, so it may even be getting thinner with time. And if it were to get dry, it would probably melt completely, perhaps in a matter of minutes.

It appears to me that our only practical experience with corium has been at TMI and Chernobyl. In both cases, the corium failed to deliver the catastrophic behavior predicted of it.

I think we should accept those experiences into our body of knowledge about the behavior of corium packages.

 

[clancy688]

Did anyone notice the abnormal behavior of the Unit 1 Drywell Radiation sensor?

http://atmc.jp/plant/rad/?n=1

Radiation going up and down, but every time it's going higher. According to TEPCO it's defect, but the data looks funny for a grilled sensor.

 

[robinson]

Can someone remind me why radioactivity inside a reactor is displayed in human dose units? And how can they know, without a detailed analysis of the different sources, what the Sieverts would even be? You have to multiply by different units to get Sieverts.

Wouldn't they want to know the actual level of radioactivity in there?

 

[Ms Music]

Is the presence of corium a fact?

Thanks in advance.

 

[clancy688]

Is the presence of corium a fact?

Yes. According to TEPCO and NISA, the fuel rods in Units 1-3 melted down, probably totally. Corium is a mixture out of control rods, fuel cladding, fuel elements, and, in case the reactor was breached, steel and concrete. Basically everything which mixed with the molten fuel.

But since there's molten fuel present, there's also corium.

 

[Jorge Stolfi]

Can someone remind me why radioactivity inside a reactor is displayed in human dose units?

Those readings are not from inside the reactor pressure vessel (RPV) but from the primary containment (the bulb-shaped "drywell" and the donut-shaped "surge suppression chamber") . In normal conditions, those spaces may not be "clean" but (AFAIK) may have to be entered occasionally by people for repairs. Moreover the air/steam/whatever in them may have to be vented to the atmosphere. Thus it makes sense to use sieverts to measure the contamination of the gas in the primary containment.

And how can they know, without a detailed analysis of the different sources, what the Sieverts would even be? You have to multiply by different units to get Sieverts. Wouldn't they want to know the actual level of radioactivity in there?

Since the power failed, only a handful of analog instruments have been working, sort of. The CAMS meters are pipes that take a sample of the air in the containment and bring it to some location further out in the building, where its radiactivity is evaluated by some automatic equipment. The CAMS meters were obviously not meant to diagnose meltdowns, but they are the only info we have about the radioactivity inside the primary containment.

 

[Jorge Stolfi]

Did anyone notice the abnormal behavior of the Unit 1 Drywell Radiation sensor?

My guess is that it is some fluid instability. Like, say, gobs of corium dripping from the RPV and splattering on the floor below. Or a part of the corium that is sometimes covered by water, sometimes exposed to the drywell atmosphere.

 

[jim hardy]

""You have to multiply by different units to get Sieverts. ""

indeed.
Last couple decades manufacturers have come up with detectors that approximate flesh so give better estimate of "equivalent dose" . But if you read the fine print they are most accurate for specific range of incident energy. The instruments do a reasonable job for what they are intended - protecting life forms. Like all machines they're a compromise.

But it's a fact for different types of radiation you use different meters.
Gamma rays are most common so that's what most measure via an ion chamber of some sort.
Neutron meters require a little different sensor , the ones i know of have a teeny bit of boron in them to change the neutrons into alpha particles and measure the resulting ionization.

Google 'homebuilt radiation detector' and you'll find several you-tubes showing simple hobbyist ion chambers.

 

[robinson]

In normal conditions, those spaces may not be "clean" but (AFAIK) may have to be entered occasionally by people for repairs.

Thanks. I should have figured that out myself.

 

[SteveElbows]

Since the power failed, only a handful of analog instruments have been working, sort of. The CAMS meters are pipes that take a sample of the air in the containment and bring it to some location further out in the building, where its radiactivity is evaluated by some automatic equipment. The CAMS meters were obviously not meant to diagnose meltdowns, but they are the only info we have about the radioactivity inside the primary containment.

They used CAMS to try to estimate percentage core damage early on, and I don't think the numbers generated were well regarded by people at the time.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e19.pdf

If these percentages referred to amount of fuel that's ended up in containment, rather than the percentage of fuel that was damaged, then maybe I could buy into the numbers a bit. But yes, I think its better to presume that CAMS is more useful for detecting much smaller amounts of damage that could occur under a situation much less dire than what happened at Fukushima.

 

[robinson]

Reminder to any new eyeballs, the documentary on the construction of the plant.

http://youtu.be/sspp6D8giHc

http://youtu.be/cTshYXmN1AY

 

[MikeIt]

But yes, I think its better to presume that CAMS is more useful for detecting much smaller amounts of damage that could occur under a situation much less dire than what happened at Fukushima.

Typically, BWRs use their high range drywell or torus area radiation monitors to estimate % core damage. Often they are called Containment High Range Area Radiation Monitors or CHARMS. These are seven or eight decade, logarithmic meters that have a bug source to keep a reading onscale since normal drywell/torus radiation levels are too low to register on these meters. Apparently, these monitors have been functioning at Fukushima.

 

[CaptD]

New question for PF Newbie
On this thread;
http://www.huffingtonpost.com/2011/...ment-radiaton-estimate-doubles-_n_871887.html (which now has over 6100 comments)

See comment today at 7:27, 3:47 and 9:39

☆ A number of us have been discussing what is causing the chart to look like this:
...We have two different ideas: http://atmc.jp/plant/rad/?n=1

...BTW: A level up, it contains a huge number of other chart links...

From labmonkey1313
1. What do you think of this theory? Bubble cavitation where the uranium or plutonium gets pushed to the "skin " of a bubble of steam, then some bubbles collapse, creating a critcal condition. Heats up solution and makes more bubbles on rods and sides, some collapse again, cycle continues. ...

"When the cavitation bubbles collapse, they force energetic liquid into very small volumes, thereby creating spots of high temperature and emitting shock waves,"

http://en.wikipedia.org/wiki/Cavitation

Then from CaptD
2. The cycle are getting shorter not longer and the temp. is trending higher; so things are becoming more not less reactive!

To me this it then most important chart to keep watching,
... as #1 is turning itself on and off, which is some form of
... as yet another Un-named criticality;
... which I am naming, "The Fuky Effect"...

Note that the numbers are trending higher,
... as is the slopes of the graph,
... with about a two day "reversal" recently,
... If it continues to climb to 300 before reversing,
... then "The Fuky Effect" will become news Worldwide!

Links

http://en.wikipedia.org/wiki/Behavior_of_nuclear_fuel_during_a_reactor_accident
Any thoughts?
Thanks

 

[razzz]

One could say the concrete pump method used so far is also pretty basic. and then there is the KISS principle. The alternative sfp injection there presented is of course not in principle different than using the concrete pump and it should work just as well. As a practical matter it would mean less obstruction for the ongoing work at the south face of the building to null the need to have the concrete pump around.

As an aside (see attachment) -- there is a square structure indicated in the drawing at what would be the east side of the unit 4 pool. I wondered if there is any significance to that depictured detail, as regards how the unit 4 pool set up is or is to be actually configurated. (The sketch could of course be of a generic pool and not refer in such specifics to the unit 4 pool.)

That humongous concrete boom pumper will be used to pump wet sand, slurry, concrete, more water or anything else needed that the pistons can push through when the time comes to encase the corium. Not that it will be complete confinement since groundwater flows at will to corium unless the entire site is de-watered like, forever more. The pumper is already a write-off as it will be to contaminated to be reused anywhere else but had undergone some 'hardening' for the occasion before being delivered onsite.

 

[jim hardy]

"Any thoughts?"

As bad as that #1 chart looks ,

remember it's a seven decade logarithmic scale on that instrument
so those readings are like your car speedometer bouncing between 1mph and 5mph, not a lot when compared to full scale.. 250Sv is 1/400th of the instrument's range and the linear graph shows the variation better than would a log graph..

i'd look at site boundary readings for similar pattern.

here's a link to a typical CAM instrument datasheet and this manufacturer even let's you download a partial manual:

http://www.flukebiomedical.com/Biomedical/usen/Nuclear-Power-Systems/Area-Monitors/875.htm?PID=55441

i do not know if this is the same instrument GE or TEPCO uses.
But they all are designed for the same function.

i see from their manual it's designed to survive 3 hours at 180degC which is probably typical. Was drywell temp much hotter than that? if so their 'broke' tag could be valid.

But it could be still tickin' like the proverbial Timex. Do any nearby monitoring points show that same four day cycle?

old jim

 

[Quim]

Not that it will be complete confinement since groundwater flows at will to corium unless the entire site is de-watered like, forever more.

I think the confinement will be complete once they stop pouring water on it. I believe that once the corium reaches temperature equilibrium with its surroundings, a dry region will be created around it after the last of the water evaporates off the region which remains above 100 C.

I believe it will make its own boundary zone.
The groundwater flow will be underneath it.

 

[NUCENG]

They used CAMS to try to estimate percentage core damage early on, and I don't think the numbers generated were well regarded by people at the time.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e19.pdf

If these percentages referred to amount of fuel that's ended up in containment, rather than the percentage of fuel that was damaged, then maybe I could buy into the numbers a bit. But yes, I think its better to presume that CAMS is more useful for detecting much smaller amounts of damage that could occur under a situation much less dire than what happened at Fukushima.

http://adamswebsearch2.nrc.gov/idmws/DocContent.dll?library=PU_ADAMS^pbntad01&LogonID=507a9449dcb934f4b821c20b93e649ed&id=003957314

CAMS has two functions as a post-accident monitoring instrument per RG 1.97:
Low Range (minimum from 1 to to 1e4 R/hr) is used for detection and verification of a breach in reactor coolant pressure boundary. High Range (up to 1e7 R/hr) is used for detection of significant releases, release assessments, long term surveilance and emergency plan actuations.

It is supposed to respond over an energy range from 60 keV to 3 MeV within an accuacy factor of 2.

I think the low required accuracy is because you can't predict the time varying energies of fission product decays. It is useful for trending and is not meant to read out in human dose. When you are talking about 1E7 R/hr does it really matter whether it kills you in 1 minute or 1 minute 17.5 seconds?

Edit: The detectors are outside containment. CAMS has pumps which draw samples from the drywell or wetwell to the detectors and returns to the source.

 

[westfield]

I wonder if anyone here has been able to identify where this photo was taken?

http://www.tepco.co.jp/en/news/110311/images/110611_05.jpg

In the Tepco handout page the photo has this mysterious caption which does not really make any sense:
"Side Part of Skid of Water Treatment Facility of Fukushima Daiichi Nuclear Power Station
(pictured on June 9, 2011)
Pictured at South Side on 4th floor of Unit 4 Reactor Building"

At first the pattern of the sun shining in there made me think the photo is facing west (ie the photographer has basically turned 90 degrees to his right after taking http://www.tepco.co.jp/en/news/110311/images/110611_04.jpg" shot ) but so far I havn't found a match from the outside.

But then there is an "I" beam rail up at the ceiling with a chain block at the end of it which appears as though it mayt extend outside the building, which made me think of the green scaffolding that was set up on the eastern side of Unit 4 before all this happened. However, I thought that was one level down. But if it is facing east that would mean the sunlight is shining in from a northerly angle which doesn't seem right does it?

I will try and find an outside image to match but I don't have high hopes.

edit: this photo like many other really brings home to me how old the equipment is in these plants.

Edit edit : But the concrete floor "joists" seem to tend to run E\W in #4 so that messes with that.

 

[joewein]

I hope they have check valves installed so that the 'solution' does not become a siphon and drain the pool should a failure occur....

The pipe hooked up to the handrail does not reach into the spent fuel pool. It pours the water into the pool from above. Therefore no check valve is necessary.

 

[thehammer2]

I'm sure they will, but just so it's said, I hope they have check valves installed so that the 'solution' does not become a siphon and drain the pool should a failure occur....

I suspect that they'll use an airgap. It's simple and it's how your water supply is unable to set up a siphon and drain your sink or bathtub. If they don't put an airgap, I hope they wouldn't extend the pipe to the bottom of the pool. If they must terminate in the pool, I'd only stick the pipe into the pool a few inches below the pool's level. Then it can only drain the pool until it lowers the pool enough to take in air and break suction.

Reason I bring this up is that checkvalves or siphon breakers fail and relying on them to prevent siphons isn't inherently safe, though it is safer than nothing if you have a closed system. With the pool, you can introduce the airgap and completely eliminate the possibility of draining the pool that way.

EDIT : I see someone else had the same thought right before me

 

[joewein]

At first the pattern of the sun shining in there made me think the photo is facing west (ie the photographer has basically turned 90 degrees to his right after taking http://www.tepco.co.jp/en/news/110311/images/110611_04.jpg" shot ) but so far I havn't found a match from the outside.

But then there is an "I" beam rail up at the ceiling with a chain block at the end of it which appears as though it mayt extend outside the building, which made me think of the green scaffolding that was set up on the eastern side of Unit 4 before all this happened. However, I thought that was one level down. But if it is facing east that would mean the sunlight is shining in from a northerly angle which doesn't seem right does it?

The sun light appears to come in from the left.

The EXIF data of the picture says it was taken at 16:36 (late afternoon), which would make the left West (towards sunset).

The wall on the right, behind the electrical box would be on the East (towards the turbine hall). We'd be looking north (towards unit 3). If this is the fourth floor as claimed then our back would be facing the hole in the http://www.tepco.co.jp/en/news/110311/images/110611_04.jpg" from the outside. The top of the pool would be a floor above, the pool itself behind the wall on the right.

The previous picture taken from inside through the 4F hole (seen from the outside with the red Putzmeister truck) was taken at 16:29, 7 minutes earlier. Both share the same GPS coordinates:

Latitude: 37, 25, 24.67 (North)
Longitude: 141, 1, 54.81 (East)

According to Google Earth this point is hundreds of meters from unit 4, so I am not sure what the deal is there.

 

[~kujala~]

NRC has now officially corrected the claim made by Gregory Jaczko that the unit #4 spent fuel pool would have dried up at some point:

Spent fuel pool never dried up at Fukushima plant: U.S. regulator
http://www.breitbart.com/article.php?id=D9NSMF980&show_article=1

 

[joewein]

New question for PF Newbie
On this thread;
http://www.huffingtonpost.com/2011/...ment-radiaton-estimate-doubles-_n_871887.html (which now has over 6100 comments)

See comment today at 7:27, 3:47 and 9:39

☆ A number of us have been discussing what is causing the chart to look like this:
...We have two different ideas: http://atmc.jp/plant/rad/?n=1

It's been discussed here before, e.g.
https://www.physicsforums.com/showpost.php?p=3323788&postcount=8312

See also my blog post at:
http://www.joewein.net/blog/2011/05/30/fukushima-1-unit-5-water-pump-fails/
"Unit 1 dry well radiation levels"

 

[Cire]

Yes. According to TEPCO and NISA, the fuel rods in Units 1-3 melted down, probably totally. Corium is a mixture out of control rods, fuel cladding, fuel elements, and, in case the reactor was breached, steel and concrete. Basically everything which mixed with the molten fuel.

But since there's molten fuel present, there's also corium.

Melting down doesn't automatically imply corium. A meltdown can be cladding splitting open and dumping pellets to the bottom of the RPV.

 

[SteveElbows]

My best idea is that the numbers in the press article might be a -- perhaps somewhat positively skewed -- representation of data as it looked a few days ago, maybe when a Tepco application was made to authorities -- I imagine opening the reactor building to the environment would be one of those things that the utility would need official permission to do.

It seems clear from the Tepco press releases, that the full data set you reference includes the time for initiation of the air purification, quote Tepco,
"-We installed local exhausters and started to operate them at 12:42 pm on
June 11 in order to improve the working environment inside Reactor
Building of Unit 2."
and the full dataset then does not seem to support that there has been a reduction of the Cs isotopes over the period of operation so far, nor that the reduction of I-131 has had the magnitude expressed in the press article.

Ah well, the latest data shows a major drop, not sure why it trended in this fashion.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110617_01-e.pdf

Also thanks to people for their thoughts on CAMS and use for measuring percentage of core damage.

 

[SteveElbows]

Sounds like we will soon have an updated roadmap, and a TEPCO account of the first 5 days to chew over:

http://www3.nhk.or.jp/daily/english/17_17.html

http://www3.nhk.or.jp/daily/english/17_09.html

Not sure if we will get the 5-day account in english straight away or not, nor whether there will be much new in it.

 

[clancy688]

Melting down doesn't automatically imply corium. A meltdown can be cladding splitting open and dumping pellets to the bottom of the RPV.

Of course, but that didn't happen at Fukushima. I think it's VERY unlikely that we're only dealing there with dumped pellets. It's a full scale meltdown in all three reactors.
Remember TMI. The coolant loss there was nothing compared to the loss at Fukushima. And still corium formed.

 

[Borek]

Of course, but that didn't happen at Fukushima. I think it's VERY unlikely that we're only dealing there with dumped pellets. It's a full scale meltdown in all three reactors.

Truth is we don't know what have happened. No doubt there is a mess inside, but stating anything as a known fact is premature.

 

[MadderDoc]

Ah well, the latest data shows a major drop, not sure why it trended in this fashion.
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110617_01-e.pdf
<..>

It is not plausible that the exhauster after having done relatively little to lower the air contamination over a 5 day operation period, then suddenly over a 12 hour period appears to have decimated it. It is also not plausible that it is due to a measurement or graphing error.

But Tepco could plausibly have opened the door, letting in fresh air. Yesterdays press article reported that taking this step had been authorized.

 

[clancy688]

Truth is we don't know what have happened. No doubt there is a mess inside, but stating anything as a known fact is premature.

That's why I said that dumped pellets are unlikely instead of impossible. We won't know for sure what's actually present in- or outside the RPV. We'll get facts when they open up the reactors, which won't happen during the next few years. So we should work with the most likely scenario. That is, in my opinion, and especially if we take TMI2, the time the cores were uncovered and the water height in the vessels during the melting (In Unit 1 possibly zero) into consideration, the presence of corium. Moreover most discussers here seem to have implemented the presence of corium into their reasoning. So I don't see much problems telling that corium is very likely present.

 

[biggerten]

The pipe hooked up to the handrail does not reach into the spent fuel pool. It pours the water into the pool from above. Therefore no check valve is necessary.

That will do the trick.

By the way, the water decontamination system is now online -

http://www3.nhk.or.jp/daily/english/17_34.html

 

[DSamsom]

By the way, the water decontamination system is now online -

http://www3.nhk.or.jp/daily/english/17_34.html

looking at the pictures of the decontamination system, i wonder how they are going to deal with the huge buildup of radioactivity in the filtersystems. Have they figured out a way to get rid of the radiating sludge fully automatically?

 

[etudiant]

looking at the pictures of the decontamination system, i wonder how they are going to deal with the huge buildup of radioactivity in the filtersystems. Have they figured out a way to get rid of the radiating sludge fully automatically?

In theory, the cesium, which represents the vast bulk of the activity afaik, is mostly adsorbed in the Kurion zeolite columns, which are sealed cartridges. So exchanging these would be fairly easy and quick, although looking at the pictures, there is no room for a robot handler, so people will have to take the radiation hit to make the exchange. These cartridges are apparently designed for direct vitrification, so provided Kurion can keep the cesium inside while the cartridge is getting glassified, rhat contamination can be safely locked away.

The rest of the process looks much more messy, as AREVA has indicated they expect several thousand cubic meters of toxic radioactive sludge to be produced. Japan has said the wastes will be stored in Japan, so we may look for an urgent search for a waste repository.
Maybe in Okinawa or some similar out of the way location :).

 

[SteveElbows]

Well this months roadmap update didnt contain anything surprising, or at least not that I've noticed. Perhaps a few small details of note, but none that I can think of off the top of my head.

http://www.tepco.co.jp/en/press/corp-com/release/11061702-e.html

However the following document does contain some pictures that I don't think I've seen before, outside reactor 3 building (demolished the damaged vehicle entrance tunnel by the looks of it). And also, joy of joys, a view of the site looking down from the top of the slope where the webcam is, so that we can actually see the ground around the reactors and further to the left of reactor 1 than normal. Its not very high res within this pdf, but it still gives me a much improved sense of the state of a good chunk of the site these days. (that photo, or rather 3 photos stitched together, is on page 13)

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110617e4.pdf

 

[Astronuc]

Is the presence of corium a fact?

Thanks in advance.

No. It is based on an analysis, apparently with conservative assumptions regarding heat transfer, or lack thereof. It is a fact that there is significant damage to the fuel. We won't establish the 'facts' until the vessel head is removed and the cores are visually inspected. Comments regarding fuel melting and corium are speculative for now.

There is certainly the question of whether or not the cores of units 1, 2 and 3 actually received the cooling water that was being pumped into the vessels. Some instruments indicated coolant levels in the core, but perhaps those instrument measurements are unreliable. If the vessel penetrations were breached early in the event, then it could be that the injected water simply flowed out. One the other hand, since the water found in the base of the reactor building was heavily contaminated with radioisotopes, it is likely the water contacted the fuel, so it seems there was water in the cores, or at least in the RPVs.

It also appears that TEPCO and NISA believe there was/is water in the lower plenums of the RPVs, and if that is so, then the fuel is less likely to have melted.

 

[MiceAndMen]

The rest of the process looks much more messy, as AREVA has indicated they expect several thousand cubic meters of toxic radioactive sludge to be produced. Japan has said the wastes will be stored in Japan, so we may look for an urgent search for a waste repository.
Maybe in Okinawa or some similar out of the way location :).

I don't remember reading about the average spent fuel load that was originally expected in your average BWR SFP, but I'm sure that those loads increased in large part due to the lack of off-site storage. High density racks for Spent Fuel Pools speak to the fact that the loads initially designed for have been exceeded. I guess that's pretty common knowledge nowadays, both in Japan and in the U.S. at least.

To now, the attitude seems to have been "we'll just continue to accumulate spent fuel on-site for the forseeable future and someone will eventually figure out how to deal with it." Hopefully the Fukushima Daiichi situation provides impetus going forward to deal with the off-site spent fuel repository "problem" in Japan. Too bad no such thing will happen in the U.S. and spent fuel will continue to accumulate at the plants indefinitely. One cannot continue to kick that can down the road forever.