Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[turi]

From the article: http://search.japantimes.co.jp/cgi-bin/nn20110529x1.html
[...]
"The temperature of the core and the fuel pool had reached 93.6 degrees and 46 degrees, respectively, by noon Sunday compared with 68 degrees and 41 degrees at 9 p.m. Saturday.
[...]
The temperature must stay below 100 degrees to maintain cold shutdown status.
[...]
And is it really okay to let the temperature rise that high without using the alternative water-injection system?

As the normal operational temperature is much higher than 100° Celcius (somewhere between 215°C and almost 295°C) that's no problem. "Cold shutdown" is just an easily remembered state you reach after some time of cooling and a state where you don't mind pressure loss that much anymore.

 

[zapperzero]

so they are injecting salt water to 5 ??

No. The salt water is from the sea, it cools the water that's used to cool the reactor.

 

[zapperzero]

I don't actually know why they want to switch away from fire line, I asked about this recently on this thread but nobody responded.

A fire line is not meant for extended periods. What fire takes two months to extinguish?

 

[Bandit127]

They should change pump without waitning, also there was information that pump could be damaged by salt water, so they are injecting salt water to 5 ??

The pump was one that pumped seawater to a heat exchanger from the sea - standard architecture for this reactor. This side is open loop. Seawater in, seawater plus some extra heat out.

The other side of the heat exchanger is closed loop and contains (as far as I know) processed (DI) water. This is the water that cools the reactor and SFP.

That they had emergency cooling systems as a backup may not make it all OK, but it does seem to be less of a problem than it first appeared.

 

[mscharisma]

As the normal operational temperature is much higher than 100° Celcius (somewhere between 215°C and almost 295°C) that's no problem. "Cold shutdown" is just an easily remembered state you reach after some time of cooling and a state where you don't mind pressure loss that much anymore.

I apologize for my completely non-scientific mind, but I thought the whole point was to keep the water temperature below 100 degrees, i.e., below boiling point, to avoid steam generation and loss of water level, etc.? What am I misunderstanding?

 

[turi]

I apologize for my completely non-scientific mind, but I thought the whole point was to keep the water temperature below 100 degrees, i.e., below boiling point, to avoid steam generation and loss of water level, etc.? What am I misunderstanding?

As in a pressure cooker the water boils at a higher temperature than 100 °C. During operation you have something like 7 MPa in the pressure vessel.

 

[Bandit127]

I apologize for my completely non-scientific mind, but I thought the whole point was to keep the water temperature below 100 degrees, i.e., below boiling point, to avoid steam generation and loss of water level, etc.? What am I misunderstanding?

You are missing pressure. Water boils at 100°C only at atomspheric pressure.

It boils at about 75°C on top of Everest and 0°C in a vacuum.

The opposite is also true, as pressure increases so the boiling point increases. To understand the relationship between boiling point and pressure, have a look at a steam table.
http://www.simetric.co.uk/si_steam.htm

This means that (for instance) water at 2 bar (i.e. atmospheric pressure x 2) boils at 120.42°C.

So, if the pressure vessel is (for instance) at 2 bar, 94°C is still quite a way from boiling.

 

[biffvernon]

But this particular pressure vessel is no longer a pressure vessel. It's more like a sieve.

mscharisma's point is valid. Going over 100 produces a lot of steam.

 

[Bandit127]

But this particular pressure vessel is no longer a pressure vessel. It's more like a sieve.

mscharisma's point is valid. Going over 100 produces a lot of steam.

This is Unit 5 - I have not seen anything yet to suggest that the RPV is leaking pressure.

To be fair, I cannot find any data that states what the pressure is in the Unit 5 RPV either.

If it is still a "pressure vessel", then if steam starts to be formed then the pressure will rise and the system will self limit and not boil up.

 

[biffvernon]

Ah, right,#5. my bad. Apologies.

 

[mscharisma]

You are missing pressure. Water boils at 100°C only at atomspheric pressure.

It boils at about 75°C on top of Everest and 0°C in a vacuum.

The opposite is also true, as pressure increases so the boiling point increases. To understand the relationship between boiling point and pressure, have a look at a steam table.
http://www.simetric.co.uk/si_steam.htm

This means that (for instance) water at 2 bar (i.e. atmospheric pressure x 2) boils at 120.42°C.

So, if the pressure vessel is (for instance) at 2 bar, 94°C is still quite a way from boiling.

Thank you (and others) for helping me understand this better. I suppose, it struck me as odd that TEPCO decided not to use the emergency water injection system and to rather not "work in the dark." Given that they have about a million things going wrong everywhere else, it seemed overly nonchalant to me to not proceed with the utmost caution.

 

[MadderDoc]

<..>
I don't actually know why they want to switch away from fire line, I asked about this recently on this thread but nobody responded.

Perhaps everybody here also do not know, certainly I do not :-) Could it be -- I speculate -- that using the normal feed water line (to which they appear to be switching) can be expected to become a more practical/convenient way to inject water to the rpv in the long term, considering there is, afaik, a plan to recycle some of the leaked water through pumping into the condensers of the turbine buildings?

 

[mscharisma]

This is Unit 5 - I have not seen anything yet to suggest that the RPV is leaking pressure.

To be fair, I cannot find any data that states what the pressure is in the Unit 5 RPV either.

If it is still a "pressure vessel", then if steam starts to be formed then the pressure will rise and the system will self limit and not boil up.

Here is pressure data for unit 5 on page 8: http://www.nisa.meti.go.jp/english/files/en20110529-2-2.pdf
Unless I'm still not getting this right, 0.108MPa is around atmospheric pressure, no?

 

[~kujala~]

I don't actually know why they want to switch away from fire line, I asked about this recently on this thread but nobody responded.

I think they can pump more water into the reactor using the feedwater line than the fire line. It might be something to do with the technical differencies between the two lines.
Although they are not using max capacity now they probably want to have some reserve if the temperatures starts suddenly raising.
Another option is that they are testing the feedwater lines now because at some point they have to switch to a closed circuit. Was it the feedwater line they are going to use or some other line?

Something to note also: For units #1 and #2 in the latest IAEA report stands:
"The need for boric acid injection is investigated be TEPCO"
http://www.slideshare.net/iaea/tabl...shima-daiichi-nuclear-power-plant-18-may-2011
http://www.slideshare.net/iaea/tabl...shima-daiichi-nuclear-power-plant-18-may-2011

Unit #3 and #4 summaries:
http://www.slideshare.net/iaea/tabl...shima-daiichi-nuclear-power-plant-18-may-2011
http://www.slideshare.net/iaea/tabl...shima-daiichi-nuclear-power-plant-18-may-2011

When was it last time they injected boric acid to #1 and #2?

 

[turi]

Here is pressure data for unit 5 on page 8: http://www.nisa.meti.go.jp/english/files/en20110529-2-2.pdf
Unless I'm still not getting this right, 0.108MPa is around atmospheric pressure, no?

Yes, that's about atmospheric pressure. Before cold shutdown pressure was above atmospheric pressure, e.g. at March 20th pressure was 1296 MPa. http://www.nisa.meti.go.jp/english/files/en20110320-3.pdf

 

[elektrownik]

Yes, that's about atmospheric pressure. Before cold shutdown pressure was above atmospheric pressure, e.g. at March 20th pressure was 1296 MPa. http://www.nisa.meti.go.jp/english/files/en20110320-3.pdf

so it was boiling after pump failed ? it was 94C...

 

[turi]

so it was boiling when pump failed ? it was 94C...

Um, no. Sorry, I don't know what exactly you mean. At 94 °C there would have to be underpressure to make water boiling.

 

[mscharisma]

Um, no. Sorry, I don't know what exactly you mean. At 94 °C there would have to be underpressure to make water boiling.

Whether boiling or near boiling, I just don't understand why they would let it get that close, given that they had an emergency system in place they could have used?

"The temperature of the core and the fuel pool had reached 93.6 degrees and 46 degrees, respectively, by noon Sunday compared with 68 degrees and 41 degrees at 9 p.m. Saturday.

The backup pump kicked in at 12:31 p.m. Sunday, and the temperature of the core had been brought down to 83 degrees by 1 p.m., a Tepco spokeswoman said by phone later Sunday."

Edit: Kyodo is reporting on this unit 5 incident also, sounding more alarming than the Japan Times did.
http://english.kyodonews.jp/news/2011/05/94090.html

 

[PietKuip]

This ought to keep us busy for a few hours:

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

Something I noticed about the earthquale accelerations on page 13: those at unit 4 are smaller than the other units. As a seismological layperson, I find such large difference very surprising, and I do not know what this means. Is unit 4 more loosely connected to the ground? Are lower values good, or does it indicate possible trouble?

(Assuming this is not caused by instrument error, transcription error, or all the other problems with Tepco data.)

 

[DSamsom]

Radioactive release into the ocean increases again. Probably due to the difficulties of dealing with the amount of radioactive water. And this was before the heavy rain:

http://www3.nhk.or.jp/daily/english/30_01.html

 

[frangin]

Seawater Levels of Iodine at unit 2 Iodine-131: 24,000 becquerels/liter on may 28 (was only 5,200 becquerels/liter at the same place the day before) : is this rising significant and can be related to RVP/corium state ?

 

[jim hardy]

Mr Charisma

maybe i can put it in real basic terms here for a non engineer.

in the spent fuel pool , as you know normal heat removal is via a pump and heat exchanger.

If that path is lost the pool will heat up until evaporation is carrying away all the heat that's being added. That heatup is somewhat slow because the pool is so big that it can absorb a lot of heat.

I'm an old guy , still use English units . One BTU heats a pound of water one degreeF, and one BTU per second is within 5% of a kilowatt which is convenient for in-your-head calculating... So a ton of water can absorb one kilowatt for an hour and only get heated 3600 btu/2000lb = about 1.8 degreeF. well that's a ~5% approximation. But it gives you a feel.

Now the heat carried away by evaporation goes up with temperature of course, for as you know warm water evaporates quicker.

If it takes 212 degrees to carry away the heat that's where the pool will settle. It can't get hotter than that at sea level. But at 212 we stop calling it evaporation and start calling it boiling. It could be a benign quiet 212 or a vigorous roiling boil, whatever is required to carry away the heat.

Boiling would be no big deal for the fuel , remember it is accustomed to making steam at around around 547 degreesF.. but it makes the area uncomfortable for people and wets all the equipment that's nearby. And the rapid evaporation carries contamination into the air in the room. So they try to keep the pool at a comfortable temperature not so much to protect the fuel but for convenience and safety of the workers. Somebody could fall in... It's just good sense to keep it comfortable.

An excursion up to boiling is not a big deal but it temperature cycles the stainless steel pool liner plate which will tend to expand and maybe buckle a little bit, so should be avoided.

just an aside - water is a really neat substance for moving heat. To change a pound of it from 212F water to 212F steam takes about 900 BTU's . Compare that to the measly 180BTU's to go from icewater to boiling it's 5X as much...
So as evaporation speeds up due to temperature climbing so does heat removal and by a lot. and that's why the old watched pot never boils...

i hope this helps you form a good mental picture in your head..

 

[mscharisma]

Mr Charisma

maybe i can put it in real basic terms here for a non engineer.

in the spent fuel pool , as you know normal heat removal is via a pump and heat exchanger.

If that path is lost the pool will heat up until evaporation is carrying away all the heat that's being added. That heatup is somewhat slow because the pool is so big that it can absorb a lot of heat.

I'm an old guy , still use English units . One BTU heats a pound of water one degreeF, and one BTU per second is within 5% of a kilowatt which is convenient for in-your-head calculating... So a ton of water can absorb one kilowatt for an hour and only get heated 3600 btu/2000lb = about 1.8 degreeF. well that's a ~5% approximation. But it gives you a feel.

Now the heat carried away by evaporation goes up with temperature of course, for as you know warm water evaporates quicker.

If it takes 212 degrees to carry away the heat that's where the pool will settle. It can't get hotter than that at sea level. But at 212 we stop calling it evaporation and start calling it boiling. It could be a benign quiet 212 or a vigorous roiling boil, whatever is required to carry away the heat.

Boiling would be no big deal for the fuel , remember it is accustomed to making steam at around around 547 degreesF.. but it makes the area uncomfortable for people and wets all the equipment that's nearby. And the rapid evaporation carries contamination into the air in the room. So they try to keep the pool at a comfortable temperature not so much to protect the fuel but for convenience and safety of the workers. Somebody could fall in... It's just good sense to keep it comfortable.

An excursion up to boiling is not a big deal but it temperature cycles the stainless steel pool liner plate which will tend to expand and maybe buckle a little bit, so should be avoided.

just an aside - water is a really neat substance for moving heat. To change a pound of it from 212F water to 212F steam takes about 900 BTU's . Compare that to the measly 180BTU's to go from icewater to boiling it's 5X as much...
So as evaporation speeds up due to temperature climbing so does heat removal and by a lot. and that's why the old watched pot never boils...

i hope this helps you form a good mental picture in your head..

Thank you for your efforts. I really appreciate it. However, I was not talking about the SFP, but rather the water temperature in the pressure vessel. It was my understanding that it should be kept from boiling when in a cold-shutdown state. Apparently, TEPCO wasn't that concerned with it getting close to boiling temperature, even though they could have used the emergency water injection system. That's what I don't understand.

As Kyodo writes here: http://english.kyodonews.jp/news/2011/05/94090.html
"If the unit had been left unattended with the temperature surpassing 100 C, the water containing nuclear fuel inside the reactor could have boiled and evaporated, thereby exposing the fuel and damaging it."

Or, in other words: how close to boiling does it have to come before the emergency water injection system should be used? Shouldn't it have been used immediately, just to not take any chances?

 

[Gary7]

I think this is a question that none of us can answer; "Why didn't Tepco act sooner?" It is a question that only Tepco can answer, and we can only speculate on. Obviously the reactor core is made to handle boiling water and steam (it being a "boiling water reactor"), and so the temperature of 94c isn't particularly worrisome if the RPV is undamaged. Since the reactor has been in stable shutdown for some two months now, I think they can assume there is no critical structural damage to the RPV. Given the many erroneous readings in the past, perhaps it is an assumption that we should not easily make. Be that as it may, there certainly seems to be no catastrophic damage to #5. Was there a danger of the water level becoming so low as to expose the fuel? I suppose so - eventually - but before this would happen I believe there were other systems available to pump water into the RPV. Regarding whether or not Tepco should have taken measures sooner than they did, it is probably a question for the "more political thread".

 

[jim hardy]

Well the laugh is on me! Sorry for the misunderstanding, it was at my end..

Or, in other words: how close to boiling does it have to come before the emergency water injection system should be used? Shouldn't it have been used immediately, just to not take any chances?

Just as in the pool you have some time before enough water evaporates to lower the level very much.

i haven't followed status of unit five - is the vessel open and pool flooded up to refueling level? if so the vessel and pool are one body of water with deep end at vessel and there's lots of water.

if they are separated, same logic applies - get some pump cooling before it gets warm enough to make things uncomfortable. One assumes they made a decision to fix the failed pump rather than manipulate the valves to align another one, and that may have been actually faster. They know how much effort is involved in each operation, i don't. if it was heating slowly they knew how much time they had.

In that industry things are very proceduralized and "by the book".
Physics and common sense may say you're fine, but if cold shutdown is let's say defined as 95.0 degrees and you get to 95.06 degrees it's a violation of the rules. It gets treated administratively no different than a truly serious one.
I would bet they did what they felt was the safest...and they were probably right. conditions are bad there and if they had to send men into a dangerous area to manipulate the valves, well, it weighed in their decision.

but to your question of what conditions dictate start of emergency equipment - that'll be in their written procedures and probably involves a time factor too.. i simply don't know their operation.

sorry to dodge your question - that's best i can do. A BWR operations guy could answer it better.

i still have faith in the plant guys. They are doing the impossible over there and i pray for them.old jim

edit gary answered while i was typing... thanks G!

 

[Astronuc]

Thank you for your efforts. I really appreciate it. However, I was not talking about the SFP, but rather the water temperature in the pressure vessel. It was my understanding that it should be kept from boiling when in a cold-shutdown state. Apparently, TEPCO wasn't that concerned with it getting close to boiling temperature, even though they could have used the emergency water injection system. That's what I don't understand.

As Kyodo writes here: http://english.kyodonews.jp/news/2011/05/94090.html
"If the unit had been left unattended with the temperature surpassing 100 C, the water containing nuclear fuel inside the reactor could have boiled and evaporated, thereby exposing the fuel and damaging it."

Or, in other words: how close to boiling does it have to come before the emergency water injection system should be used? Shouldn't it have been used immediately, just to not take any chances?

Ideally, the reactor is made as cold as possible, or below boiling so there is not increase in pressure that would allow fission products, particularly volative fission products to be more mobile.

Ideally, fission products are enclosed in the fuel rod cladding tubes. When there is a fuel breach, the gaseous and volatile fission products like I and Cs, can get into the coolant, and steam if there is any steam. In order to mitigate transport of fission products from breached fuel, one wants to get the reactor (and spent fuel) as cool as possible. It is also an issue for the workers. They cannot work around scalding steam unless they have heat resistant suits.

 

[SteveElbows]

Sounds like they are already starting to admit that the roadmap timescale is unrealistic:

http://english.kyodonews.jp/news/2011/05/94111.html

Bit cheeky blaming this on the analysis of meltdowns and containment damage though, considering they should have been able to form those conclusions long before they even wrote the roadmap.

 

[mscharisma]

I think this is a question that none of us can answer; "Why didn't Tepco act sooner?" It is a question that only Tepco can answer, and we can only speculate on. Obviously the reactor core is made to handle boiling water and steam (it being a "boiling water reactor"), and so the temperature of 94c isn't particularly worrisome if the RPV is undamaged. Since the reactor has been in stable shutdown for some two months now, I think they can assume there is no critical structural damage to the RPV. Given the many erroneous readings in the past, perhaps it is an assumption that we should not easily make. Be that as it may, there certainly seems to be no catastrophic damage to #5. Was there a danger of the water level becoming so low as to expose the fuel? I suppose so - eventually - but before this would happen I believe there were other systems available to pump water into the RPV. Regarding whether or not Tepco should have taken measures sooner than they did, it is probably a question for the "more political thread".

My question is not so much "why didn't TEPCO act sooner" or in any way political. I'm merely interested in whether or not it is safe from a technical standpoint to let the water come so close to boiling while installing a new pump instead of using already in place emergency systems. Of course, if it's not safe and/or not "by the book", then my question would certainly become "why didn't they act sooner."
Maybe in my lay(wo)man's mind, I just assumed (yes, I know the saying about "assume") that it's pretty much an automatic process: if one cooling system fails or part of it fails, no questions asked, the next one is put in operation. It takes me by surprise that it's apparently up to the ... hm, who? ... to decide when emergency cooling is activated and when not?

 

[MathMajor3_14]

New at this, first post. Thinking; so far weather patterns have saved the situation. Weather is changing, any comments for the next few months? Seasonal patterns?

See this link for excellent WX in the area:

> http://www.yr.no/place/Japan/Other/Fukushima_I_Nuclear_Power_Plant/ <

 

[MiceAndMen]

Sounds like they are already starting to admit that the roadmap timescale is unrealistic:

http://english.kyodonews.jp/news/2011/05/94111.html

Bit cheeky blaming this on the analysis of meltdowns and containment damage though, considering they should have been able to form those conclusions long before they even wrote the roadmap.

Without veering too much into the political realm, that assumes the roadmap plan was not merely a Public Relations device. For those of us who believe that, it's not surprising at all.

Wait and see what happens now with the rainy season approaching. I think their water pumping strategy will not work as soon as the runoff and leakage through cracks quickly overwhelms their ability to deal with it.