Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[elektrownik]

That's a good question.
I guess the level of groundwater doesn't have to be the same although they are near each other.
Also the size of leak (through damaged waterproof systems or through concrete only) can differ - it can be "small", "big" or something in between.
Also the tsunami might have left more water in one place than other. Remember that two dead guys were found in the unit #4 turbine building and they were probably killed by tsunami waters. So the tsunami was probably able to hit directly at least turbine buildings.
Tsujitsu proposed this direct hit might also have happened in the reactor buildings. About that I don't know.

100% agree in case of turbine buildings, but how water flooded 2 basement floors of reactor 6 building...

 

[~kujala~]

100% agree in case of turbine buildings, but how water flooded 2 basement floors of reactor 6 building...

Your answer is as good as mine.

 

[MiceAndMen]

If core would hit groundwater we would see KABOOM, but anyway it is hard to say where cores are, sensor data are different for A and B, and also there is not much sensors at all in drywell. If someone would trust current data then it could say that unit 1 core is in drywell, unit 2 part of core in torus, and unit 3 is unknown, temperatures are increasing there but radiation isnt, so we can assume that it is cooling problem. Also parts of cores can be in concrede under drywell or around torus in the basement...

There is much uncertainty about how much has melted/relocated and where it is, true, but there is no obvious way for molten corium to get into the torus. Dropping straight down out of the RPV does not intersect any part of the torus, even if you pass through all the steel and concrete below.

The torus water can be highly radioactive depending on how many fission products have passed through it, but it seems highly unlikely that anything liquid or solid from inside the RPV could make its way there.

 

[jmelson]

Since the corium is producing heat at a nearly costant rate, its temperature will be nearly constant too; so this process could go on indefinitely, until the wall is breached.. If this is happening at all, the rate of progress may be very slow, and it may perhaps take several months for the RPV to be breached.

Thus, IMHO, the current situation of apparent stability --- with low pressures and temperatures near 100 C --- does not guarantee that things are under control.

YES! This is the doomsday scenario, and it is VERY hard to tell if such a process is happening or not!
You can think everything is heading toward a stable outcome, and then suddenly, BOOM! a huge radioactive steam blast.

 

[jmelson]

Good explanation, thanks!

One thing I don't understand about theormocouples is why the bimetal wires are usually extended all the way to the voltmeter. Why couldn't they be extended only to some cooler place nearby (such as just outside the concrete enclosure), and then have the signal be carried by copper wires to the meter? That would result in lower resistance for the signal and reduced risk of electrochemical effects along the way.

Connection to other metals causes an additional thermoelectric potential to develop. If you measure the temperature of that "cold junction" and compensate for it in the instrument, then you can do this. If the temperature of the cold junction is not known, then the error is also not known, and that could be a bad thing.

To maintain best accuracy, you should have no terminals, connections, or other hardware in the thermocouple loop other than the exact thermocouple alloys. So, terminal blocks, splices, etc. all are made from the same alloys.

In cases like this, the error might be pretty small, just a degree C or so worst case, but with uncontrolled mixing of various alloys (bare copper, tinned copper, brass terminal strips with nickel coating, and on and on) the error could be cumulative and totally unknowable.

So, that's why they typically run thermocouple wire all the way back to the indicator.

Jon

Jon

 

[swl]

[URL]http://www.tepco.co.jp/en/news/110311/images/110601_01.jpg[/URL]

I presume this is the heat exchanger for the Unit 2 SFP.

No, yes, no yes, Maybe?

http://nuclearstreet.com/nuclear_power_industry_news/b/nuclear_power_news/archive/2011/06/01/tepco-starts-spent_2d00_fuel-cooling-system-at-fukushima-unit_2c00_-reports-oil-leak-060102.aspx"

 

[jim hardy]

nice document on those thermocouples. Copper-constantan is a nice choice because neither alloy rusts.

""So, that's why they typically run thermocouple wire all the way back to the indicator.""

or at least to a place where the transition to copper is at a known temperature.

or to an electronic device in the field that takes the microvolt temperature signal, applies correction for local temperature and translates into a convenient higher level for transmission to control room.
Lots of industrial measurement is done with a linear signal of 4 to 20 milliamps as bottom and top of scale . That way if the system loses power the meter pegs low, because 0 milliamps is 25% below bottom of scale and there's no question the instrument is dead.

in my day they were simple analog devices, nowadays they're smart.

 

[LabratSR]

No, yes, no yes, Maybe?

http://nuclearstreet.com/nuclear_power_industry_news/b/nuclear_power_news/archive/2011/06/01/tepco-starts-spent_2d00_fuel-cooling-system-at-fukushima-unit_2c00_-reports-oil-leak-060102.aspx"

From the press photo archives:2011.5.14
http://www.tepco.co.jp/en/news/110311/index-e.html

"Carrying Work for New Cooling System (Air-cooled) for Residual Heat Removal System in Fukushima Daiichi Nuclear Power Station
(pictured on May 13th,2011)"

Heat Exchanger and drain http://www.tepco.co.jp/en/news/110311/images/110514_f1_1.jpg

Fan http://www.tepco.co.jp/en/news/110311/images/110514_f1_2.jpg


NHK Article http://www3.nhk.or.jp/daily/english/31_42.html

 

[jlduh]

Also in TMI if I understand correct only upper part of core melted and corium doesn't hit RPV

Yes, Only around 50% of the core melted, and only a part of the debris finished at the very bottom.


http://www.osti.gov/bridge/servlets/purl/6161525-9eIBpx/6161525.pdf

 

[Derpin]

I have a couple questions:
• What is the current status of reactors 1-4?
• What techniques/work have nuclear engineers done to achieve this status?
• Are reactors 5 and 6 really worth mentioning relative to 1-4?

You ask some questions with potentially some very long answers ;) You might start here:
http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1306898792P.pdf
or here
http://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster

Thanks, I tried the wikipedia article before but it was just way too information-intensive, that is to say I couldn't digest everything they were saying. I'll try to take what I need out of this pdf.

 

[LabratSR]

Thanks, I tried the wikipedia article before but it was just way too information-intensive, that is to say I couldn't digest everything they were saying. I'll try to take what I need out of this pdf.

You may be interested in this.

http://dels.nas.edu/resources/static-assets/nrsb/miscellaneous/SekimuraPresentation.pdf

 

[Bodge]

If fuel is indeed molten, what are the chances of heavier elements collecting together?

Can the Uranium and Plutonium separate from the boron and steel?

 

[LabratSR]

If fuel is indeed molten, what are the chances of heavier elements collecting together?

Can the Uranium and Plutonium separate from the boron and steel?

This may be helpful.

http://www.osti.gov/bridge/servlets/purl/5408170-9LI8uV/5408170.pdf

 

[etudiant]

YES! This is the doomsday scenario, and it is VERY hard to tell if such a process is happening or not!
You can think everything is heading toward a stable outcome, and then suddenly, BOOM! a huge radioactive steam blast.

The scale of such a blast could be estimated. The cores are currently producing between 4-8 megawatts of thermal decay heat each. That amount of heat will generate 5-10 tons of steam per hour, roughly speaking.
TEPCO is currently cooling the reactors with about double that amount of cooling water each hour. This is not quenching all of the steam, but we do not currently have volcanic steam eruptions, but rather a steady strong boil.
So afaik the risk from a core melt into a flooded drywell is that the steam that continues to be produced cannot be released effectively and consequently ruptures the containment more seriously. Or am I missing something?

 

[razzz]

It's a waiting game. Chernobyl timeline is another 125 years (give or take) before the remnants of the melted core (corium) can be approached for removal because to this day it is so radioactive.

Here you have 3 cores melted down awaiting enough time to elapse for cooling down just to begin containment, let alone worry about where all the contaminated cooling water ends up.

If the design works for the corium then its path is meant to flow to the bottom of the secondary containment (drywell), spread out, sit there and cool down. Bottom of the drywell is concrete with part of the steel containment shell embedded in the concrete which the corium would have to dissolve/melt through both and then encounter a mass of thick concrete below the shell before it could find natural earth. Cracks in the concrete would not have been envisioned neither would the corium traveling somewhere it's not suppose to like the torus (wetwell). Still it would have a thick concrete foundation to dissolve and melt through but should cool down before that happens.

So, you need time, cooling and keep the corium in place until it cools down. Further contamination is a given, hopefully it can be just localized.

Aside:
Concrete consists mainly of small rocks (example 3/4" or 1") and sand with cement as the binder (glue) and its major usefulness in this case is a hardened thick mass but nothing magical even with embedded steel reinforcement or maybe some type of plating. As the cement itself hardens over its approximate 116 year lifetime (before becoming inert) it takes about 45 years for it (the cement) to become as hard as the natural rock it contains (now concrete is referred to as having a half life of 50 years or so depending on the mix design).

 

[dh87]

I have two questions/comments:

1. All the news stories about cooling the #2 SFP say that the point of this operation is to reduce the humidity inside the #2 building. Does anything establish that the humidity actually comes from the SFP? Presumably, there are holes in the containment vessel, and probably in the RPV, and steam is escaping. The steam can be seen in photos of the blow(n)-out panel in the east wall of unit #2. Can the high humidity result from the reactor steam instead of from the SFP steam?

2. A lot of Cs and Sr isotopes have already been washed out of the cores (and, for Cs, vaporized in the first couple of days). Over time, more will be washed out. If the core is molten and covered with a solid shell that is permeable is any way, and the core is immersed in flowing hot water, then almost all the soluble radioisotopes will eventually be washed out. I am pretty sure that the chemical forms of Cs and Sr that occur in corium are readily soluble in water (generally, these are oxides, which dissolve in water to make the corresponding hydroxides). This dissolution will have a very bad effect on the water collection and purification efforts. However, the loss of these materials from the corium should greatly reduce its heat-generating ability and its radioactivity. The fissionable materials should have already decayed (or mostly decayed?), and most of the heat produced now (and in the longer term) is from radioactive decay (unless I'm missing something). It seems to me that TEPCO could end up with very hot water (that Areva thinks they can cleanse and I think will mostly end up in the ocean) and not-that-hot cores that will actually solidify and not pose the type of explosion risk that some posts suggest.

 

[tsutsuji]

The water level in the basement of the incinerator building has stopped decreasing. As the water leaked into the corridor between buildings, the measured radiation increase in nearby ground water is believed to be mainly caused by the rain : http://www3.nhk.or.jp/news/html/20110601/t10013241691000.html .

The water level decrease in the basement of unit 1 reactor building is suspected to be caused by a leak on the unit 2 side : http://mainichi.jp/select/jiken/news/20110603k0000e040073000c.html

If nothing is done, the contaminated water from unit 2 and unit 3 will start leaking into the sea on June 20th, but the water purification system is supposed to start on June 15th. However it is possible that heavy rains may cause a leak before June 15th : http://mainichi.jp/select/jiken/news/20110603k0000e040073000c.html

In mid-August, [Tepco] will also install an underground storage tank that can hold 100,000 tons of highly radioactive water.
http://www3.nhk.or.jp/daily/english/03_19.html

 

[elektrownik]

I have two questions/comments:

1. All the news stories about cooling the #2 SFP say that the point of this operation is to reduce the humidity inside the #2 building. Does anything establish that the humidity actually comes from the SFP? Presumably, there are holes in the containment vessel, and probably in the RPV, and steam is escaping. The steam can be seen in photos of the blow(n)-out panel in the east wall of unit #2. Can the high humidity result from the reactor steam instead of from the SFP steam?

No, I don't think that it is from SFP, unit 2 SFP power is much smaller than in unit 4, and unit 4 wasnt generating steam always, also unit 2 SFP temperature was for example 45C but steam was still there, and unit 2 core and drywell are at atmospheric pressure, also on pne of movies when they zoom in into hole in wall we can see some debris and that steam is not only from left (sfp location) but also from center

 

[tsutsuji]

Maybe I am stupid but I can't understand how unit 5 have 300m3 from ground water and unit 6 13500m3 from ground water, they are so close and 45 times difference...

That's a good question.
I guess the level of groundwater doesn't have to be the same although they are near each other.
Also the size of leak (through damaged waterproof systems or through concrete only) can differ - it can be "small", "big" or something in between.
Also the tsunami might have left more water in one place than other. Remember that two dead guys were found in the unit #4 turbine building and they were probably killed by tsunami waters. So the tsunami was probably able to hit directly at least turbine buildings.

According to the following Tokyo Shinbun article, the earthquake caused cracks in the walls of unit 5 and unit 6, through which ground water has been leaking. From April 4th, about 10000 tons of that water were released into the sea in order to prevent the diesel generator(s) and pump(s) at those units from being flooded : http://www.tokyo-np.co.jp/article/feature/nucerror/list/CK2011052002100005.html

I see one more possibiliy explaining the larger amount of water remaining now in unit 6 : the sea discharge could have been mostly from unit 5.

 

[SteveElbows]

No, I don't think that it is from SFP, unit 2 SFP power is much smaller than in unit 4, and unit 4 wasnt generating steam always, also unit 2 SFP temperature was for example 45C but steam was still there, and unit 2 core and drywell are at atmospheric pressure, also on pne of movies when they zoom in into hole in wall we can see some debris and that steam is not only from left (sfp location) but also from center

As far as the documentation suggests, that temperature is for the skimmer surge tank, not the fuel pool itself. Thats why the temperature goes up when they inject water, because it causes some of the hot pool water to move into the skimmer tank.

I am very interested to learn how much of the steam in unit 2 is from the pool vs the reactor. I doubt that TEPCO or the regulators are very sure either, I have heard them say that steam may be coming from both, but that they believe a lot comes from the pool and cooling it will help a lot. This may be based more on wishful thinking than evidence, but it is possible that their explorations inside unit 2 building taught them something. We will all just have to see what happens when they get the pool cooling working for long enough to make a theoretical difference. I would not be shocked if the reactor was causing a lot of the problem, and they are just dealing with the fuel pool because its much easier to solve this than the reactor problems, but you never know, a lot of the steam really might be from the pool.

 

[SteveElbows]

A new pressure indicator for reactor 1 is being installed, tech details here:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110602_02-e.pdf

Same planned for reactors 2 & 3 if they can ever get working conditions inside the buildings improved.

 

[SteveElbows]

It seems the discussion here about unit 2 cooling was timely, we don't have long to wait to see if the pool cooling has helped humidity:

http://www3.nhk.or.jp/daily/english/03_03.html

TEPCO cools storage pool in No.2 reactor building
The operator of the Fukushima Daiichi nuclear power plant says it has succeeded in lowering the temperature in a storage pool for used nuclear fuel at the No.2 reactor after it started operating a cooling system there.

Tokyo Electric Power Company says the temperature in the pool dropped to 38 degrees Celsius on Thursday from about 70 degrees previously.

TEPCO had anticipated that it would take about one month to lower the temperature to about 40 degrees.

In the No. 2 reactor building, steam released by the storage pool has been pushing up the humidity level to 99.9 percent. Such excessive humidity has prevented recovery efforts so far.

The company installed a circulatory cooling system to lower the pool temperature in order to reduce humidity and began operating the system on Tuesday.

Since the temperature has sharply decreased TEPCO plans to inspect the interior of the building as it suspects humidity has also declined. If the situation has improved, it will install systems to remove radioactive substances.

The company plans to start operating similar cooling systems at the storage pools in the No.1 and 3 reactor buildings in June, and in the No.4 reactor building in July.
Friday, June 03, 2011 05:11 +0900 (JST)

I'll have to double check my time correlations but I think I was looking at TEPCOS live feed early Friday JST and the usual steam coming from reactor 2 building was apparent, so I do have my doubts as to whether TEPCO will discover a much better situation in reactor 2 when they enter, but I hope to be wrong.

 

[~kujala~]

According to the following Tokyo Shinbun article, the earthquake caused cracks in the walls of unit 5 and unit 6, through which ground water has been leaking. From April 4th, about 10000 tons of that water were released into the sea in order to prevent the diesel generator(s) and pump(s) at those units from being flooded : http://www.tokyo-np.co.jp/article/feature/nucerror/list/CK2011052002100005.html

Thanks, I translated it using Google translate. One paragraph says:

According to the Toukyoudenryoku and Nuclear Safety Agency, METI, diesel generator No. 6 reactor building basement, five or six pumps were in the basement of the turbine building of the Unit. The earthquake cracked walls, underground water had flowed.

Original:

経済産業省原子力安全・保安院や東京電力によると、ディーゼル発電機は６号機原子炉建屋の地下、ポンプは５、６号機のタービン建屋の地下にあった。地震で壁にひびが入り、地下水が流れ込んでいた。

It's really hard to tell if they mean unit 6 turbine building walls were cracked or unit 6 reactor building walls also. The latter would be more serious.

 

[tsutsuji]

Thanks, I translated it using Google translate. One paragraph says:Original:It's really hard to tell if they mean unit 6 turbine building walls were cracked or unit 6 reactor building walls also. The latter would be more serious.

I would translate the sentence quoted from http://www.tokyo-np.co.jp/article/feature/nucerror/list/CK2011052002100005.html as follows :

According to sources such as the NISA and Tepco, the diesel generator(s) were located in the basement of unit 6 reactor building and the pumps were located in the basements of unit 5 turbine building and unit 6 turbine building. Cracks were created in walls during the earthquake and the groundwater flowed inside.

In the following article published on May 8th, Tepco is reported as acknowledging the presence of cracks in the underground walls of turbine buildings, but the article does not say which units are concerned. An unnamed Tepco manager is quoted as saying "Because of the earthquake, cracks have expanded and new cracks have been created, so that there is a possibility that ground water is leaking inside. The earthquake resistance of turbine buildings is not as high as that of reactor buildings" : http://www.tokyo-np.co.jp/article/national/news/CK2011050802000039.html

A Chunichi article published on May 4th quotes an unnamed Tepco employee who was working at unit 6 when the earthquake struck : "cracks were formed on a part of the inside wall of the turbine building". Plant manager Masao Yoshida is quoted as saying that originally water was seeping in large amounts at units 5 and 6 before the earthquake : http://atmc-tokyo.com/radiation/1285/

So the tsunami was probably able to hit directly at least turbine buildings.
Tsujitsu proposed this direct hit might also have happened in the reactor buildings. About that I don't know.

1) Do you mean I (Tsutsuji, not Tsujitsu) ?

2) Could you provide a link to the post where I could have said this ? I don't remember.

 

[~kujala~]

2) Could you provide a link to the post where I could have said this ? I don't remember.

Sorry, I guess what you meant was the unit 6 turbine building was hit by the tsunami and then from there a flow of water could reach also the unit 6 reactor building:

What about #4 : Unit 6 hit and flooded by a tsunami ?

I thought you were referring to the unit 6 reactor building here as I was also talking about the reactor building:
https://www.physicsforums.com/showpost.php?p=3310809&postcount=7821
https://www.physicsforums.com/showpost.php?p=3310818&postcount=7822

 

[tsutsuji]

I thought you were referring to the unit 6 reactor building here as I was also talking about the reactor building:
https://www.physicsforums.com/showpost.php?p=3310809&postcount=7821
https://www.physicsforums.com/showpost.php?p=3310818&postcount=7822

Thanks for the links. I must have overlooked the fact that the preceding discussion dealt specifically with the reactor building. I confess that what I had in mind when I made that reply was unit 6 as a whole.

Anyway, the inundated area extends west of unit 6 reactor building, above the OP+13 m ground level as reported on http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110409e9.pdf and even west of units 5 and 6's high voltage transformer building as reported on page 29 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf

 

[elektrownik]

It is strange that tepco doesn't show us any pictures from unit 5 and 6, there is no much information about those units, they are working in control rooms there ?

 

[tsutsuji]

In the last part of the following video, dated May 8th, Arnie Gundersen argues that contaminated water is leaking from units 1,2,3,4 into the groundwater, which then moves northwards into unit 5 and 6's basements : http://wn.com/5-8-2011_Fukushima_Groundwater_Contamination_Nuclear_Disaster_Nightmare

 

[jim hardy]

Steve Elbows wrote:
"""Re: Japan Earthquake: nuclear plants
A new pressure indicator for reactor 1 is being installed, tech details here:

http://www.tepco.co.jp/en/nu/fukushi...10602_02-e.pdf

Same planned for reactors 2 & 3 if they can ever get working conditions inside the buildings improved."""

At Last! that will put to rest wondering about the sense point locations, elevation differences and health of existing instruments. i note their elevation head equates to 0.18Mpa not quite two atmospheres.

 

[tsutsuji]

The following article is reporting the detailed contamination data for the two nuclear power plant operators previously reported ( page 531 of this thread : https://www.physicsforums.com/showthread.php?p=3329327#post3329327 ) as "may exceed the 250 mSv limit" :

The 30 year old one has 210~580 mSv of internal contamination adding to the 74 mSv external contamination.

The 40 year old one has 200~570 mSv adding to 89 mSv.

http://www.yomiuri.co.jp/national/news/20110603-OYT1T00778.htm