Japan Earthquake: nuclear plants

Bodge

Nobody has tackled this question. Reasoned speculation would be fine!

Quote by Bodge

So, is it currently feasable for there to be a large steam explosion in (under) any of reactors 1-3?

Could there be corium in an unbreached RPV, suspended above a saturated area?

0131413

Quote by Soafcom

Another IAEA reading of Cs-137 in Iitate was reported to be 163 kBq/kg on Wed:
http://soafcom.com/m/Fukushima_I_Nuc...#24_March_2011

Since Bq/m² isn't easily convertible to Bq/kg, it's tough to tell how these readings might be related. Can anyone shed some light on a way to estimate one unit from the other and the pitfalls of doing so? I tried and fell into the "How do I know how much depth of soil the area measurement represents?" trap.

Unfortunately, the linked Reuters article doesn't specify if the reading was taken in the same place (or what was measured.) Does anyone have the original IAEA information? It's not on their news page: http://www.iaea.org/newscenter/news/

http://hps.org/publicinformation/ate/q7878.html

Apparently you need the penetration of the coring device...convenient.

*Joe Neubarth*

Quote by Bodge

Nobody has tackled this question. Reasoned speculation would be fine!

We need to know what you think would be suspending it.

Astronuc

Quote by Bodge

Nobody has tackled this question. Reasoned speculation would be fine!

I don't believe there is evidence of a 'large' (not quantified) steam explosion in any of the units. I would expect a big plume of steam if that were the case.

IF (and for now that's a BIG IF) there was a sufficient melting - I think it would dribble down into the water, so it would drop in, get quenched with steam blanketing the melt, which would prevent rapid heat transfer to the surrounding water.

If anyone has seen lava from Kilauea in the ocean - it's doesn't explode. It just oozes and bubbles.

If the water activity rises, it probably means more fuel is exposed. That does not necessarily require melting, but rather could be accomplished by simply oxidation and/or fracturing of the Zircaloy-2 cladding. This is a rather slow process.

Whatever is happening has been happening over two weeks - going on three weeks now. So far - It has been a slow process!

Pheesh

what other scenarios could explain 18sv/hr in the secondary containment besides the core melting through the floor of the primary? Does this imply the core has gone critical, or not necessarily so?

*Joe Neubarth*

Quote by Pheesh

what other scenarios could explain 18sv/hr in the secondary containment besides the core melting through the floor of the primary? Does this imply the core has gone critical, or not necessarily so?

Well, the one machine that they are using to measure the 18 Sieverts could be faulty.

Astronuc

Quote by Pheesh

what other scenarios could explain 18sv/hr in the secondary containment besides the core melting through the floor of the primary? Does this imply the core has gone critical, or not necessarily so?

S/C = Suppression Chamber. If there is water there and it came from the RPV, then I would expect dissolution of exposed fuel - IF the activity is due to fission products.

If one only measures activity, that doesn't necessarily tell one what isotopes are causing the activity. One needs to perform radioassays, e.g., gamma spectroscopy, and key on certain elements.

If one detects very short-lived radionuclides, with half-lives of seconds, then that would indicate a recent criticality event based on the fact that they haven't yet decayed away. I don't think we're seeing that.

If there is water in the base of the RPV - there is no melting. That's straightforward physics. If there has been water in the base of the RPV since March 12, there has been no melting through the RPV.

Quote by Joe Neubarth

Well, the one machine that they are using to measure the 18 Sieverts could be faulty.

That's a possibility. There is also the possibility of accumulation of radioactive source near the detector.

BTW - （English version） Readings at Monitoring Post out of 20 Km Zone of Fukushima Dai-ichi NPP
http://www.mext.go.jp/english/radioa...il/1304082.htm

AtomicWombat

Quote by ivars

High radiation outside Japan exclusion zone: IAEA

(Reuters) - Radiation measured at a village 40 km from Japan's crippled nuclear plant exceeded a criterion for evacuation, the U.N. nuclear watchdog said on Wednesday, the latest sign of widening consequences from the crisis.

The finding could increase pressure on Japan's government to extend the exclusion zone beyond 20 km (12 miles) around the Fukushima power plant, which has leaked radioactive particles since it was hit by a huge earthquake and tsunami on March 11.

Criticized for weak leadership during Japan's worst crisis since World War Two, Prime Minister Naoto Kan has said he is considering enlarging the evacuation area to force 130,000 people to move, in addition to 70,000 already displaced.

"The first assessment indicates that one of the IAEA operational criteria for evacuation is exceeded in Iitate village," Denis Flory, a deputy director general of the International Atomic Energy Agency (IAEA), said.

"We have advised (Japan) to carefully assess the situation and they have indicated that it is already under assessment," he told a news conference.

Greenpeace this week said it had confirmed radiation levels in this village northwest of the plant high enough to evacuate. But Japan's nuclear safety agency on Monday rebuffed a call by the environmental group to widen the evacuation zone.

There are nearly 2 million people with 80 km of Fukushima Daiichi. I can understand the reluctance to evacuate. On the other hand that is a lot of people potentially at risk.

Bodge

Cs-137 - 3.7 megabecquerels / m^2 @ 25km NW of plant.

http://blogs.nature.com/news/thegrea...t_the_o_1.html

http://www.iaea.org/newscenter/news/...iupdate01.html

It is a disgrace to not evacuate from these areas.

I can understand not evacuating in the 1st week of the crisis, but not evacuating now is nothing short of criminal.

edit, also 25 Mbec/m^2 of I-131 - has everyone been issued KI tablets at these distances?

AtomicWombat

Quote by Bodge

Nobody has tackled this question. Reasoned speculation would be fine!

I strongly suspect that the explosion of the R3 building originated within the primary containment, given its highly directional nature (upwards). (I can't see evidence for this in R1 or R2.)

I originally believed this was due to fuel melting through to a flooded drywell creating a steam explosion plus a violent reaction of super-hot zirconium with water. I've posted my thoughts previously including estimates of the "impulse pressure" required to lift the reactor plug segments to a height of about 500 metres - seen in the video of the explosion. This pressure estimate was ~ 3 times the design pressure for the reactor. But these are still speculative calculations.

The radiation contamination figures do not seem to bear this out. The most contaminated water leakage is from reactor 2.

So I concede it is possible that a steam explosion in the wet or dry well may be the origin of the explosion in R3, without a catastrophic rupture of the reactor vessel (RV). I still have not worked out a mechanism.

Also, Arnie Gundersen's suggestion that the main leakage in reactor 2 is from leaking seals on the control rod drive mechanism may give a direct route to the outside, assuming the pipe breakages are in the secondary containment. So it's possible that the situation in reactor 3 is more dire, but that transfer of radioactive material is better contained. This is just hand-waving so I'll stop now.

Astronuc

Quote by Bodge

Cs-137 - 3.7 megabecquerels / m^2 @ 25km NW of plant.

http://blogs.nature.com/news/thegrea...t_the_o_1.html

http://www.iaea.org/newscenter/news/...iupdate01.html

It is a disgrace to not evacuate from these areas.

I can understand not evacuating in the 1st week of the crisis, but not evacuating now is nothing short of criminal.

edit, also 25 Mbec/m^2 of I-131 - has everyone been issued KI tablets at these distances?

I believe they started moving people out two weeks ago.

From the IEAE site

The second team made additional measurements at distances of 32 to 62 km, at directions North to Northwest from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.5 to 6.8 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.05 to 0.45 Megabecquerel per square metre.

Based on measurements of I-131 and Cs-137 in soil, sampled from 18 to 26 March in 9 municipalities at distances of 25 to 58 km from the Fukushima Nuclear Power Plant, the total deposition of iodine-131 and cesium-137 has been calculated. The results indicate a pronounced spatial variability of the total deposition of iodine-131 and cesium-137. The average total deposition determined at these locations for iodine-131 range from 0.2 to 25 Megabecquerel per square metre and for cesium-137 from 0.02-3.7 Megabecquerel per square metre. The highest values were found in a relatively small area in the Northwest from the Fukushima Nuclear Power Plant. First assessment indicates that one of the IAEA operational criteria for evacuation is exceeded in Iitate village. We advised the counterpart to carefully access the situation. They indicated that they are already assessing.

As far as food contamination is concerned, 35 samples taken from 25-29 March, and reported on 29 March, for various vegetables, fruit (strawberry), seafood, pork and unprocessed raw milk in nine prefectures (Chiba, Gunma, Ibaraki, Kanagawa, Nagano, Niigata, Saitama, Tochigi and Yamagata), stated that results for iodine-131, caesium-134 and caesium-137 were either not detected or were below the regulation values set by the Japanese authorities.

. . . .

1 MBq = 27 uCi.

I'm not minimizing this very serious situation.

http://www.new.ans.org/pi/resources/dosechart/msv.php

0.3 mSv = typical background in US, vs 61 mSv based on 1 year at 7 uSv/hr. It is certainly higher (200x) than background, but I don't believe someone would stay at the same exposure for all of 1 year.

I expect people in that area have been evacuated. Certain places do have higher activity than one should be exposed to on an ongoing basis.

AtomicWombat

Quote by Bodge

Cs-137 - 3.7 megabecquerels / m^2 @ 25km NW of plant.

http://blogs.nature.com/news/thegrea...t_the_o_1.html

http://www.iaea.org/newscenter/news/...iupdate01.html

It is a disgrace to not evacuate from these areas.

I can understand not evacuating in the 1st week of the crisis, but not evacuating now is nothing short of criminal.

edit, also 25 Mbec/m^2 of I-131 - has everyone been issued KI tablets at these distances?

From the UCS site:

IAEA Confirms Very High Levels of Contamination Far From Reactors

The full text:

"Today the IAEA has finally confirmed what some analysts have suspected for days: that the concentration per area of long-lived cesium-137 (Cs-137) is extremely high as far as tens of kilometers from the release site at Fukushima Dai-Ichi, and in fact would trigger compulsory evacuation under IAEA guidelines.

The IAEA is reporting that measured soil concentrations of Cs-137 as far away as Iitate Village, 40 kilometers northwest of Fukushima-Dai-Ichi, correspond to deposition levels of up to 3.7 megabecquerels per square meter (MBq/sq. m). This is far higher than previous IAEA reports of values of Cs-137 deposition, and comparable to the total beta-gamma measurements reported previously by IAEA and mentioned on this blog.

This should be compared with the deposition level that triggered compulsory relocation in the aftermath of the Chernobyl accident: the level set in 1990 by the Soviet Union was 1.48 MBq/sq. m.

Thus, it is now abundantly clear that Japanese authorities were negligent in restricting the emergency evacuation zone to only 20 kilometers from the release site."

Bodge

Thanks for all your replies Astronuc, much appreciated.

re. soil contamination in the areas where the hourly dose rate is shown to be highest, we have no way of knowing how much dust could be ingested by people and their pets.

I certainly wouldn't want to keep a dog that was digging in that dirt!

"Japan has ordered those within a 20 km radius from the plant to leave and is encouraging those living in a 20-30 km ring to do the same, and if they don't, to stay inside."

The NRC weren't kidding on the 17th when they recommended a 50km ring.

Reno Deano

Quote by AntonL

Wrong!

With water being boiled by a 4.3MW heater at a rate of 6m3/hour, and the fuel rods being about 4metres tall and the upper 1.7 to 2 metres being above water, steam is escaping at some fantastic rate at any outlets above the water level.

If the top was intact and the leak at the bottom then no water would be in the vessel

You must always consider all facts before making a decision.

The dry well will hold water and leak it, as was being proven by flooding it. More than likely there is almost equal water in the dry well as in the RPV. You just have to keep adding more water due to size of the Dry Well and Primary containment area. If there was only a exit avenue above the Guide Plate then they would have succeeded in flooding the RPV long ago.

M. Bachmeier

Has the subject of Sodium Pentaborate been brought up?

http://www.ceradyneboron.com/product...m-pentaborate/

Was Fukushima Daiichi equipped with such systems and if not why?

*AntonL*

KYODO 11:16 31 March
NEWS ADVISORY: Radioactive iodine 4,385 times legal limit found in seawater near plant

M. Bachmeier

NHK (world live) just reported radioactive iodine 4485 times normal in sea water by plant. (EDIT not 44185, sorry... AntonL got there before me)

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Pheesh	what other scenarios could explain 18sv/hr in the secondary containment besides the core melting through the floor of the primary? Does this imply the core has gone critical, or not necessarily so?

M. Bachmeier	Has the subject of Sodium Pentaborate been brought up? http://www.ceradyneboron.com/product...m-pentaborate/ Was Fukushima Daiichi equipped with such systems and if not why?

AntonL	KYODO 11:16 31 March NEWS ADVISORY: Radioactive iodine 4,385 times legal limit found in seawater near plant