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Japan Earthquake: nuclear plants

by gmax137
Tags: earthquake, japan, nuclear
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AtomicWombat
#3673
Apr13-11, 10:36 PM
P: 150
Radiation surges above 4's fuel pool

"The radiation level 6 meters above the spent-fuel storage pool at the crippled Fukushima No. 1 nuclear plant was measured at 84 millisieverts per hour Tuesday. Normally, it's 0.1 microsievert.

Tepco used a robot to take a water sample from the pool Tuesday to analyze the radioactive materials in it, which can tell them in greater detail what is happening to the spent fuel rods."


If they can measure radiation 6 metres above SFP 4 and sample it with robots, why can't they take a decent high resolution photo!

I feel more like a mushroom every day.
hbjon
#3674
Apr13-11, 11:17 PM
P: 38
I bet you didn't know that the garbageake mushroom has elevated levels of vitamin D when exposed to brief amounts of UV radiation. Much like the workers on site in Fukushima. They will probably see their vitamin D levels increase as well. Vitamin D is a beneficial nutrient the human body cannot store for long periods of time. Go easy Borek, go easy.
densha_otoko
#3675
Apr13-11, 11:18 PM
P: 3
Thanks for the updates. BTW, according to some Japanese documents I read a few days ago (cannot find now) the 4/08 R1 Drywell radiation reading was actually 187 Sv/h, not EXACTLY 100 as reported in some places. A Japanese source said 100 was the max limit reportable for some reason, but a conversion of the raw readings data released by Tepco translated to 187 Sv/h.

It bugs me that they delayed reporting #1 data right after the nitrogen injections started and then stopped reporting Drywell radiation after it started to go wild this week. And in your chart today we see a Torus radiation spike in #1. #1 is not looking stable indeed.

Also trying to find #4 fuel pool data trends. I think #4 pool has MOX fuel rods as well. Kyodo news says #4 has 204 unused/new fuel rods in addition to the 1,331 rods stored there. (http://english.kyodonews.jp/news/2011/04/85295.html)

Does the presence of unspent fuel rods make the situation more volatile or dangerous?



Quote Quote by Jorge Stolfi View Post
Updated my plots of #Fukushima reactor variables to NISA release 91 (13/apr 13:00) : http://bit.ly/gAuxse

(Note that release 89 merely repeated the data of release 88 for units #1 and #2, which were measured at 06:00 on apr/12.)
Reno Deano
#3676
Apr13-11, 11:34 PM
P: 128
Quote Quote by Cire View Post
You run the effluent out of the reactors into the water processing facility/ship then pump it back to the plant. Depending on temperatures you run it through appropriate radiator/coolers before it gets to the ship.
Have experience with one of those systems (cobalt 60 removal) they would soon be such a high radiation hazard (due to fuel particle buildup on the filtration system) that it would need to be towed out to sea to reduced area radiation levels. Also, the inplant radwaste system is not designed (shielded) for fuel particle removal.

Dean
Reno Deano
#3677
Apr13-11, 11:42 PM
P: 128
I notice from the NEI reports that Unit 1 is having water continously injected! Why not recirculated? Where is the water going? Seems to indicate that the RPV and primary containment are breached, and they cannot keep the core covered. If hydrogen is being generated in such a large scale to need a Nitrogen blanket, then the core must be uncovered or cycling through covered and uncovered. Your thoughts folks.

Dean
PietKuip
#3678
Apr14-11, 12:53 AM
P: 184
Quote Quote by densha_otoko View Post
Does the presence of unspent fuel rods make the situation more volatile or dangerous?
Unspent fuel produces less decay heat, but it is more likely to go critical.
Dmytry
#3679
Apr14-11, 01:08 AM
P: 505
Quote Quote by PietKuip View Post
Unspent fuel produces less decay heat, but it is more likely to go critical.
what the hell is unspent fuel doing in the pool? It doesn't need to be cooled, and in fact theres garbageton of precautions in transportation to prevent it from going critical if truck falls off bridge into a river.
Samy24
#3680
Apr14-11, 02:37 AM
P: 56
Quote Quote by Jorge Stolfi View Post
Updated my plots of #Fukushima reactor variables to NISA release 91 (13/apr 13:00) : http://bit.ly/gAuxse

(Note that release 89 merely repeated the data of release 88 for units #1 and #2, which were measured at 06:00 on apr/12.)
There is a jump in the Csupc readings (1930) of unint 1 in your plot regardng release 91. Where did you get this data?
razzz
#3681
Apr14-11, 02:41 AM
P: 205
Quote Quote by Reno Deano View Post
I notice from the NEI reports that Unit 1 is having water continously injected! Why not recirculated? Where is the water going? Seems to indicate that the RPV and primary containment are breached, and they cannot keep the core covered. If hydrogen is being generated in such a large scale to need a Nitrogen blanket, then the core must be uncovered or cycling through covered and uncovered. Your thoughts folks.

Dean
One would have to conclude at the least that the plumbing is broken, crack or missing to all three cores whether or not the cores remain inside some kind of containment due to the fact all the cooling liquid going in comes out contaminated. So, like unit 4, the fuel rods are all exposed to the environment without watering. A description like 'containment' would be a misnomer as far as I'm concerned.
bidou
#3682
Apr14-11, 02:44 AM
P: 2
Hello everyone.
First I want to thank you all. I follow this discussion since 10 days and its really interesting.
Big Kudos!

I have some questions about the Corium.
We know that the Fuel is in pretty bad shape.
Some says Corium may be present.
Others are more confident and says that Corium IS present.
(I've read that after 10 hours without cooling everything is potentialy melting).
So what do you think? Are Corium ponds present in Fukushima?

Second question.
IF Corium is present. Can it go critical?
Corium is an indistinct molten mass of a little bit everything.
Is it possible that it goes critical? Or hardly?
IF Corium is present and it can go critical.
What are the risks? Does this "only" throw radiation everywhere or can it heat so rapidly to explode?

Yes I know there is many IF and many questions :/
Thank you in advance.
georgiworld
#3683
Apr14-11, 02:51 AM
P: 22
Quote Quote by razzz View Post
Nice work georgiworld, that took some time and effort. Can't add much. Looks like entombment looks impossible due to debris having to be removed first. Everything contaminated and not approachable doesn't help.
I must clarify that these images are not my work. I noticed new images and a different interpretation of old ones and wanted feedback from the experts on this forum. The website is quite comprehensive and deserves attention. There are probably errors in the analysis, which I hope the members here can point out.

I have thanked the author for her work and in no way want to take credit for the fine job done.
georgiworld
#3684
Apr14-11, 03:17 AM
P: 22
I wonder if someone can clear something up for me. From the beginning I thought Reactor 4 posed the most danger since the fuel in it, both spent and unspent, were outside of containment. Since then most attention has focused on the three other reactors and the possible breaching of the RPV with a concomitant oozing of corium .

There have now been reports of fires at number 4, which has refocused attention on it and which concerns me greatly.

As I understand it, the decay heat that is emanating from the spent fuel has created the need for a great deal of water to be added in order to remain cool. While this effort appears to have worked since there remains water in the pool, the amount of heat generated maybe too much to deal with and the excess heat has found another outlet.

Now what I'd like to know is could this heat be melting the unspent fuel rods? Is that what is on fire?

Are we looking at an open-air reactor with widespread dissemination of radiation?

Can anyone reassure me that this is not the case.
Arm_Chair_QB
#3685
Apr14-11, 03:25 AM
P: 4
Quote Quote by bidou View Post
Hello everyone.
First I want to thank you all. I follow this discussion since 10 days and its really interesting.
Big Kudos!

I have some questions about the Corium.
We know that the Fuel is in pretty bad shape.
Some says Corium may be present.
Others are more confident and says that Corium IS present.
(I've read that after 10 hours without cooling everything is potentialy melting).
So what do you think? Are Corium ponds present in Fukushima?

Second question.
IF Corium is present. Can it go critical?
Corium is an indistinct molten mass of a little bit everything.
Is it possible that it goes critical? Or hardly?
IF Corium is present and it can go critical.
What are the risks? Does this "only" throw radiation everywhere or can it heat so rapidly to explode?

Yes I know there is many IF and many questions :/
Thank you in advance.
There is the saying: never say never. Certainly this recent tragedy is once again a testament to this philosophy and a stark reminder to all engineers and scientists.

Given that disclaimer, these civilian nuclear reactors are designed with contingency in place to ensure they (for the most parts) do not go critical when they aggregate into a lumped mass corium at the bottom of a reactor containment and beyond. This is because firstly the nuclear fuel is of low purity in terms of fissile elements. Secondly, neutrons generated directly from fission of say uranium have too high energy - this results in a low probability of causing other fission events of other uranium atoms thereby eventually freezing out a chain reaction.

These reactors are purposely designed to have neutron moderators placed between fuel rods to slow down and reduce the energy of these neutrons from fission, so that they can cause fission and sustain a chain reaction. In other words, when fuel rods are melted down into a corium, there is presumably no more neutron moderators between the fuel rods and fuel elements (that is, the water), thereby from that point on you are primarily concerned with high energy neutrons generated from fission which have low probability of sustaining a chain reaction while thermal neutrons (lower energy) that can sustain a chain reaction are reduced in a hypothetical corium configuration.

This is the best case scenario of course. If it so happens that the civil structure of the plant itself unknowingly had neutron reflecting material nearby, it may be able to sustain a reaction to a degree. Theres also the possibility that the corium achieves localized critical mass configurations within the corium that can sustain a reaction (though not likely as the fuel is purposly designed to have low purity and is assumed to be homogenous in composition). All of this is purely hypothetical of course as are any other plausible scenarios people can draw up.

That is also not the end of the story of course, as life is never that perfect: it is not just 100% fuel configuration with control rods in place or 100% corium lump mass. If it is partially melted with a corium and some spent fuel assembies, presumably with neutron moderating water inbetween, this can again lead to criticality, especially since control rods that would have otherwise prevented criticality may be ineffective to block neutrons between the corium and the fuel assemblies though they will be far away in distance and the reaction rate should not be very high.
elektrownik
#3686
Apr14-11, 03:37 AM
P: 296
New thermal images, very bad, so hot: http://www.mod.go.jp/j/approach/defe...ren/230414.pdf
bidou
#3687
Apr14-11, 03:56 AM
P: 2
Thank you for the answer.
Maxion
#3688
Apr14-11, 03:57 AM
P: 36
Quote Quote by elektrownik View Post
New thermal images, very bad, so hot: http://www.mod.go.jp/j/approach/defe...ren/230414.pdf
Please not the scale of the temperature. Nothing is very hot.
PietKuip
#3689
Apr14-11, 04:31 AM
P: 184
Quote Quote by Maxion View Post
Please not the scale of the temperature. Nothing is very hot.
Look at the right column: some temperatures are rising quite a bit.

Also, some hot spots are too small on the detector to resolve the real temperature.
The are measuring from 3000 ft high, and do not dare to take a closer look.
jpquantin
#3690
Apr14-11, 04:50 AM
P: 33
Quote Quote by tsutsuji View Post
A research team from Kyoto, Hiroshima, Kokugakuin, Nihon universities presents its "Interim Report on Radiation Survey in Iitate Village area conducted on March 28th and 29th" : http://www.rri.kyoto-u.ac.jp/NSRG/se...port110404.pdf. It includes a gamma ray radionuclide analysis of soil samples.
Thanks, tsutsuji ! This pointed to the level triggering actions in case of radiation exposure. I later found here the criteria for actions:
  • For an estimated exposure between 10 and 50 milliSieverts (per year I guess), people should shelter in door
  • Above estimated annual dose of 50 milliSieverts, people should shelter in concrete building or evacuate

Well with the provided report, I was able to do a calculation of the hour dose on today that would trigger either the first or second action.

WARNING : This calculation is based on readings on graphs in the report, so there could be some errors. It is also an extrapolation of measurements in Iitate.

Projected total dose after 84 days would be 96 miiliSieverts in Magata, 62 milliSieverts after 42 days (graph page 6). After 21 days, I considered the dose linear in time. That would lead to a total of 323.47 milliS in Magata in one full year (96 up to day 84, then prorata, approx 0.80 per day)

To reach 50 milliS per year, this is a factor of 6.47. Reading at Magata on March 31st was 24 microSieverts per hour. Assuming the rate fell by decay from a 10/13 factor (reading on graph page 5 - not very accurate) till now, reading at Magata today should be around 18.46 microSieverts per hour.

Therefore, applying the 6.47 factor, the hourly limits today should be :
  • Above 2.85 microSieverts per hour : shelter in concrete or evacuate
  • Above 0.57 microSieverts per hour : shelter indoor

Now if all this is accurate, look at the latest readings, and determine which area should have received action 1 or 2. Fukushima inhabitants would have been told to stay indoor.

Any comments ?


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