Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[NUCENG]

Ok thanks. I think the list of these retrofits in US is like described in this document, right?

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html

I'm still trying to find an accurate description and drawing of what this hardened venting (enabling it seems direct venting from primary containment to environment) looks like. I read somewhere that some venting -like the illustration below- was placed in the Torus, but this is secondary containment.

http://www.netimago.com/image_201117.html


Does hardened venting means direct venting from primary (so with pressures much higher)?

That is a drawing of the hardened wetwell vent. The torus is part of primary containment.

 

[mscharisma]

...

These reactors have been through some retrofit to improve the flaws but it is unclear right now which ones are implemented at Daichi (the hardened venting seems part of this, also some deflectors in the torus?)

But still retrofit has its limits of course...

In another NYT article, it is claimed that hardened vents were installed at Fukushima:

"American officials had said early on that reactors in the United States would be safe from such disasters because they were equipped with new, stronger venting systems. But Tokyo Electric Power Company, which runs the plant, now says that Fukushima Daiichi had installed the same vents years ago. "

http://www.nytimes.com/2011/05/18/w...son8.nytimes.com/pages/world/asia/index.jsonp

 

[SteveElbows]

Disappointingly this dataset does not appear to include data for the pressure peak during the early hours of March 21st. (I inferred from your previous words that it did.)

Yes it does. That post links to multiple documents, one of which is this one:

http://k.min.us/ilnMjk.pdf

The pressure peak is right there, in the tables of data.

 

[MiceAndMen]

These are the major mods in the US.
http://resources.nei.org/documents/japan/major_mod_usbwr_4511.pdf

It's not clear if they were implemented in Japan.

This 17 May article in the New York Times says the hardened vents were implemented in Japan.

http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

In early April, Massachusetts Congressman Markey asked the NRC whether the Fukushima Daiichi Mark I reactors had the "hardened vents" installed. The NRC also says they were implemented in Japan.

http://markey.house.gov/docs/4-6-11markey_e-mail_2_-nrc_question_regarding_fukushima_unit_2.pdf

This could wind up being another black eye for the industry, GE in particular, and the NRC. A 10-year study and safetly modification program (apparently designed to address precisely some of the conditions encountered at the Fukushima Daiichi reactors) came up with critical modifications that failed when most needed. This assumes, of course, that the hardened vent system did fail there.

There are also potentially significant implications here for Mark I operators in the US.

 

[jlduh]

This 17 May article in the New York Times says they did.

http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

Massachusetts Congressman Markey asked the NRC whether the Fukushima Daiichi Mark I reactors had the "hardened vents" installed. The NRC says they did.

http://markey.house.gov/docs/4-6-11markey_e-mail_2_-nrc_question_regarding_fukushima_unit_2.pdf

This won't be good for General Electric if they spearheaded an industry working group for a decade and one of the outcomes of that group's work was the "hardened vent", and when most needed those vents did not work as planned.

So, hardened vent or not hardened vent, that is the question!

Let's assume that Fukushima has the hardened vent implemented since several years, then, my next question is: what kind of "non hardened" vent was in place before?

As you can see, on this 1975 picture of Daichi (N°6 is still under construction), the stacks are already there with the tubings coming from 1/2 and 3/4 reactors...

http://www.netimago.com/image_201119.html

So if hardened vent is a vent from the torus towards the stack (according to the little sketch i posted), what is a "not hardened" vent?

I don't know if I'm the only one to get lost with these vents, but really the infos are very contradictory!

And apart from the little sketch hand written, i couldn't find one clear official drawing explaining the difference between the "before and after" modification.

 

[MiceAndMen]

I'm still trying to find an accurate description and drawing of what this hardened venting (enabling it seems direct venting from primary containment to environment) looks like. I read somewhere that some venting -like the illustration below- was placed in the Torus, but this is secondary containment.

http://www.netimago.com/image_201117.html Does hardened venting means direct venting from primary (so with pressures much higher)?

The torus is part of the primary containment.

The hardened vent provides a manual way for an operator to vent from the torus directly to the stack, bypassing the normal gas treatment system. The diagram shows this "new pipe", connected to a manual valve, pretty clearly.

Venting from the RPV is normally done, as far as I understand it, through the torus so that radioactivity can be "scrubbed" to a degree by the water in the suppression chamber before being released to the outside atmosphere.

 

[rowmag]

Yes, largely speaking. However, in the case of unit 3, we do have videos showing firetrucks targeting the north end of the building, while the SFP is situated in the south end of it.

I'm not sure they were targeting the north end of the building. I only remember hearing that they were targeting the SFP. I think the area to the north side of Unit 3 was more approachable (lower radiation levels), so they may have tried to shoot over the top from there. I do recall that the first attempt was reported as a failure, with the water not going far enough. This may look like they were targeting something they weren't.

 

[MiceAndMen]

So, hardened vent or not hardened vent, that is the question!

Let's assume that Fukushima has the hardened vent implemented since several years, then, my next question is: what kind of "non hardened" vent was in place before?

As you can see, on this 1975 picture of Daichi (N°6 is still under construction), the stacks are already there with the tubings coming from 1/2 and 3/4 reactors...

http://www.netimago.com/image_201119.html

So if hardened vent is a vent from the torus towards the stack (according to the little sketch i posted), what is a "not hardened" vent?

I don't know if I'm the only one to get lost with these vents, but really the infos are very contradictory!

And apart from the little sketch hand written, i couldn't find one clear official drawing explaining the difference between the "before and after" modification.

I've read several documents regarding the Mark I Owners Group modifications, and the little drawing you posted is the only sketch I've seen depicting the hardened vent. The tall stacks do indeed pre-date any discussion of hardened vents.

Each reactor building also has a vent pipe attached directly to it (looks to be approximately 1 meter in diameter). I haven't seen anything that indicates what they are for. Perhaps they're for regular non-power-plant-related building services, e.g. plumbing, HVAC, etc.

 

[jlduh]

This 17 May article in the New York Times says the hardened vents were implemented in Japan.

http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

In early April, Massachusetts Congressman Markey asked the NRC whether the Fukushima Daiichi Mark I reactors had the "hardened vents" installed. The NRC also says they were implemented in Japan.

http://markey.house.gov/docs/4-6-11markey_e-mail_2_-nrc_question_regarding_fukushima_unit_2.pdf

This could wind up being another black eye for the industry, GE in particular, and the NRC. A 10-year study and safetly modification program (apparently designed to address precisely some of the conditions encountered at the Fukushima Daiichi reactors) came up with critical modifications that failed when most needed. This assumes, of course, that the hardened vent system did fail there.

There are also potentially significant implications here for Mark I operators in the US.

From http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

One reason the venting system at the plant, which was built by General Electric, did not work is that it relied on the same sources of electricity as the rest of the plant: backup generators that were in basements at the plant and vulnerable to tsunamis. But the earthquake may also have damaged the valves that are part of the venting system, preventing them from working even when operators tried to manually open them, Tokyo Electric officials said.

In either case, regulators in the United States and Japan will now need to determine if such systems at similar plants designed by G.E. need to undergo expensive and time-consuming retrofitting or redesign to allow them to function even in severe accidents.

Hummm, if confirmed, this will be called retro-retrofitting, right?

As workers scrambled to comply with their new directive, they faced a cascading series of complications.

The venting system is designed to be operated from the control room, but operators’ attempts to turn it on failed, most likely because the power to open a critical valve was out. The valves are designed so they can also be opened manually, but by that time, workers found radiation levels near the venting system at Reactor No. 1 were already too high to approach, according to Tokyo Electric’s records.

At Reactor No. 2, workers tried to manually open the safety valves, but pressure did not fall inside the reactor, making it unclear whether venting was successful, the records show. At Reactor No. 3, workers tried seven times to manually open the valve, but it kept closing, the records say.

The results of the failed venting were disastrous.

Reactor No. 1 exploded first, on Saturday, the day after the earthquake. Reactor No. 3 came next, on Monday. And No. 2 exploded early Tuesday morning.

With each explosion, radioactive materials surged into the air, forcing the evacuation of tens of thousands of earthquake survivors living near the plant, contaminating crops and sending a faint plume of radioactive isotopes as far as the United States within days

Humm, that's a nice serie of failures.

Something is strange though as we saw several times on Tepco webcam some steam plume exiting the stacks, right?

 

[MiceAndMen]

From http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

Hummm, if confirmed, this will be retro-retrofitting, right?

Yes, until the next unforseen accident scenario unfolds that exceeds the ability of the retro-retrofit to cope, at which time they'll need to develop a retro-retro-retrofit.

In all seriousness, however, the program that resulted in the "hardened vent" modification was a long drawn-out affair that lasted well over 10 years. The hard vent was only 1 of the "critical modifications" that came out of that process. I don't know for sure, but I suspect that the reason the hard vent system was not designed to operate during a station blackout, was based on economics. Existing Mark I operators now face the prospect of having the entire rationale behind their calculated safety margins called into question, and that will happen regardless of whether or not it's justified.

If you notice in those recent NYT articles, General Electric would not comment. GE was the technical leader of the working group that came up with the retrofit plan that started in 1974 and lasted well into the 1990s.

A good summary of the process can be found in this report:

http://www.nei.org/filefolder/Report_-_BWR_Mark_I_Containment_03192011_2.pdf

The last 2 pages list the important modifications that have been made to the Mark I design over the years, including the hardened vent.

Ok thanks. I think the list of these retrofits in US is like described in this document, right?

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/gen-letters/1989/gl89016.html

Also it's interesting that GL 89-06 from the NRC says the hardened vent modification is an optional requirement. If an operator thought it was too expensive to implement, they didn't have to do it. They were required only to submit a cost estimate.

 

[razzz]

While reading the electronic reams of papers trying to satisfy my curiosity with this event, the latest and greatest idea was to vent any hydrogen directly to the outside atmosphere plus flare it (burn it off, radioactive or not) hence the term 'hardened' for the plumbing involved. If I ever find the article again, I'll post it.

 

[razzz]

I wonder what prompted a late Level 7 call after Units 1,2 and 3 had already spewed their poisons?

 

[mscharisma]

Don't know if this document is of any use in the discussions about what Japan may or may not have implemented in terms of retrofitting, but I thought I'd share.

 

[mscharisma]

... I don't know for sure, but I suspect that the reason the hard vent system was not designed to operate during a station blackout, was based on economics. Existing Mark I operators now face the prospect of having the entire rationale behind their calculated safety margins called into question, and that will happen regardless of whether or not it's justified.
...

The operability of hardened vents during station blackout was certainly a known problem (bolding added by me):

... "A hard pipe vent and vent valves capable of withstanding the anticipated severe accident pressure loadings would eliminate the problems with operating the vent system during a severe accident. The vent isolation valves should be remotely operable from the control room and should be provided with a power supply independent of normal or emergency AC power. Other changes, such as raising the RCIC turbine back-pressure setpoint, may also be desirable and could be considered. Venting capability, in conjunction with proper operating procedures and other improvements discussed in this item, would greatly reduce the probability of core-melt due to TW and station blackout sequences." ...

http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0933/sec3/157r1.html

Edit: oops, looks like this is a very recent document ...

 

[MiceAndMen]

The operability of hardened vents during station blackout was certainly a known problem (bolding added by me):

... "A hard pipe vent and vent valves capable of withstanding the anticipated severe accident pressure loadings would eliminate the problems with operating the vent system during a severe accident. The vent isolation valves should be remotely operable from the control room and should be provided with a power supply independent of normal or emergency AC power. Other changes, such as raising the RCIC turbine back-pressure setpoint, may also be desirable and could be considered. Venting capability, in conjunction with proper operating procedures and other improvements discussed in this item, would greatly reduce the probability of core-melt due to TW and station blackout sequences." ...

http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0933/sec3/157r1.html

Edit: oops, looks like this is a very recent document ...

That's true, but it still calls for a power supply, which they didn't have once the batteries gave out. From reading the news accounts it sounds like TEPCO wasn't sure whether they should vent or not at first. When the government ordered them to vent, they still did not do so for some hours. When they finally decided to vent - and this is not 100% clear to me yet - they were unable to do so because either the valves had no power or had malfunctioned.

Edit: ... or the reactors had already self-vented making the whole exercise moot.

Did any of the venting go completely according to plan? The explosions suggest not.

 

[mscharisma]

That's true, but it still calls for a power supply, which they didn't have once the batteries gave out. From reading the news accounts it sounds like TEPCO wasn't sure whether they should vent or not at first. When the government ordered them to vent, they still did not do so for some hours. When they finally decided to vent - and this is not 100% clear to me yet - they were unable to do so because either the valves had no power or malfunctioned.

http://www.nytimes.com/2011/05/18/w...son8.nytimes.com/pages/world/asia/index.jsonp

I think/hope this link is to page 2 of the article, which describes what happened regarding venting.

 

[razzz]

LOC makes venting a mute point. The reactors resorted to self venting or uncontrolled venting in this case. If there is no water available, do you just leave the vents open, waiting for water to return to the system? Maybe counter intuitive but the alternative is to allow the reactors to overpressurize with vents closed. Unit 2 overpressurized and blew around the torus area with the containment building still standing albeit is the source of a lot of the contaminated runoff to the ocean. Of course Unit 2 self vented somehow and sent a pop out panel flying out on its own according to workers who were sent to remove a pop out panel, finding that one gone already. A direct venting to the outside atmosphere, so to speak, with better results? (Not much)

 

[mikefj40]

Something is strange though as we saw several times on Tepco webcam some steam plume exiting the stacks, right?

You'll see stack venting here: http://www.youtube.com/watch?v=JAYGclBAym8&feature=related

3.12.11 15:00h @0:24
3.13.11 13:00h @0:30
3.13.11 14:00h @0:31

The video runs until April 6th, but no venting from the stacks seen after 3.13.11

 

[MiceAndMen]

http://www.nytimes.com/2011/05/18/w...son8.nytimes.com/pages/world/asia/index.jsonp

I think/hope this link is to page 2 of the article, which describes what happened regarding venting.

Link is good It leaves out the part where the Prime Minister went ballistic on Saturday morning when he discovered they did not vent as ordered.

http://www.houseofjapan.com/local/tepco-tardy-on-plant-emergency

 

[NUCENG]

This 17 May article in the New York Times says the hardened vents were implemented in Japan.

http://www.nytimes.com/2011/05/18/world/asia/18japan.html?_r=1&pagewanted=all

In early April, Massachusetts Congressman Markey asked the NRC whether the Fukushima Daiichi Mark I reactors had the "hardened vents" installed. The NRC also says they were implemented in Japan.

http://markey.house.gov/docs/4-6-11markey_e-mail_2_-nrc_question_regarding_fukushima_unit_2.pdf

This could wind up being another black eye for the industry, GE in particular, and the NRC. A 10-year study and safetly modification program (apparently designed to address precisely some of the conditions encountered at the Fukushima Daiichi reactors) came up with critical modifications that failed when most needed. This assumes, of course, that the hardened vent system did fail there.


There are also potentially significant implications here for Mark I operators in the US.

You may be right that there are still weaknesses in the design of the hardened vent. For instance, perhaps the valve operation needs to be power independent. Just remember that the system is designed to be used BEFORE containment pressure exceeds its design limnit. At Fukushima they delayed until containment pressure was more than double the limit.

If the piping for the hardened vent failed during venting due to overpressure it could explain how hydrogen gas was released into the reactor building.

 

[MiceAndMen]

You may be right that there are still weaknesses in the design of the hardened vent. For instance, perhaps the valve operation needs to be power independent. Just remember that the system is designed to be used BEFORE containment pressure exceeds its design limnit. At Fukushima they delayed until containment pressure was more than double the limit.

If the piping for the hardened vent failed during venting due to overpressure it could explain how hydrogen gas was released into the reactor building.

Absolutely. I wish here in the US we could license some of the newer designs, such as the ABWR, just to see how they work out (if nothing else). Then maybe we could get around to decommissioning some of the older Mark I reactors. In an ideal world, these problems in Japan would help to move that process along, but I don't know. Economic and political factors are going to conspire against that for quite a while now. Saying the new designs "can't be any worse" isn't going to convince enough people, I'm afraid.

 

[NUCENG]

So, hardened vent or not hardened vent, that is the question!

Let's assume that Fukushima has the hardened vent implemented since several years, then, my next question is: what kind of "non hardened" vent was in place before?

As you can see, on this 1975 picture of Daichi (N°6 is still under construction), the stacks are already there with the tubings coming from 1/2 and 3/4 reactors...

http://www.netimago.com/image_201119.html

So if hardened vent is a vent from the torus towards the stack (according to the little sketch i posted), what is a "not hardened" vent?

I don't know if I'm the only one to get lost with these vents, but really the infos are very contradictory!

And apart from the little sketch hand written, i couldn't find one clear official drawing explaining the difference between the "before and after" modification.

The non-hardened vent system is the Standby Gas Treatment System. In an emergency it takes a suction on the secondary containment and discharges to the stack through particulate HEPA filters and activated charcoal filters to remove radiation from the vented air. The system maintains secondary containment at a small negative pressure so any leakage of the building is from the atmosphere to the building. Later in an accident the system can be used to take a suction on containment to clean up radiation inside a depressurized containment. Again it would discharge through the filters to minimize the release.

The whole purpose of the hardened vent is to allow a high pressure vent path from the torus air space to save containment integrity. The only motive force is containment pressure. The drywell will releve through the downcomers to the torus water pool which will also hold up soluble contaminants. As torus pressure drops whole containment is being vented.

 

[razzz]

http://www.asahi.com/english/TKY201105170428.html"


http://ex-skf.blogspot.com/2011/05/fukushima-i-nuke-plant-workers-enter.html"

The workers wear a "tungsten vest" to prevent external radiation exposure. They also carry oxygen tanks on them.

http://www.entergy.com/News_Room/newsrelease.aspx?NR_ID=2145"

In fact, tungsten shielding was recently sent to Japan for use in their current incident at Fukushima.

Jim Bacquet, radiation protection supervisor and project team leader, said, “Now that it has gone to Japan, it continues to be a real team success story. Because of the flexibility of the material and embedded magnets, we call it the ‘snap-on-snap-off shield because it attaches easily in the field. It is lightweight and so versatile – we even have tungsten duct tape for small spaces. The effectiveness overall is unmatched as we can maximize weight at a source, cut it in the field, lay a tungsten sheet for flooring if needed and, of course, there is the tungsten vest. Our team wears tungsten vests and gains protection we never had prior.”

Tons of tungsten shielding blankets and sheets along with 160 tungsten vests have been sent to Fukushima to date.

 

[MadderDoc]

I'm not sure they were targeting the north end of the building.

In the video from which this frame is from, the waterspray hit the north end
and the spray was also directed towards that end of the building. It does not look at all like a failed attempt to reach the sfp.

 

[MadderDoc]

Yes it does. That post links to multiple documents, one of which is this one:

http://k.min.us/ilnMjk.pdf

The pressure peak is right there, in the tables of data.

Yes, you are absolutely right, it is there, thank you. I really should have looked more carefully.

Knowing the data for the pressure peak in the more recently available data-series is in the column for the RPV A sensor, I went to look for it for that sensor in the older version of the data set. However in that dataset the high pressure data has been assigned to the RPV B sensor.

 

[artax]

That's a perfect non-argument. The a priori chances of its landing in _any_ particular configuration is near zero.



Why do you think so?

TBH I am having second thoughts based on some images posted earlier of it not being there before the explosion but I still think it very unlikely.
If you look at the pipe coming out of the end of the cream/yellow cylinder, it is bent vertically downwards. The bend is a manufactured bend and I think it even more unlikely that any ballistic object would land like that.
however I don't think it was 'installed' after the explosion by the fuku50 because it's there on the First Helicopter flyby vids.
So I am open minded but unconvinced!

 

[tsutsuji]

The sentence where this appears could also mean something like "... TEPCO performed water leak countermeasures at a different building" - which, from what is written before that, could mean that the current facility is overburdened and they need to prepare another place.
In any case, whether it means fixing leaks, in my opinion "more watertight" is not a good translation. It is also logically wrong (someone already said that).

Even if you think the translations are good English (something I can probably not judge), I think we should look at the original text when there is some strange sounding information.

Thank you also for correcting my impression.

In slightly more detail, I interpreted the original to mean they were fixing another building (than the one used to receive Unit 2's water) within the Centralized Waste Treatment Facility. Which, yes, I guess I can agree is another inaccuracy in the translation that might have contributed to the original poster's complaint.

(For that matter, I suspect it was not a "building" (建物) that they were concerned about, but rather some holding tank or piping within a building. But that may have been an issue with the original terminology -- or my own mis- or over-interpretation. And I issue the caveat that I am not a professional translator.)

Yes, I definitely agree.

I see two possibilities. The first possibility is that the Centralized Waste Treatment Facility was designed some years ago for a given capacity of liquid waste. Storing larger quantities of highly contaminated water there straight away would have somehow meant breaking the rules. So they had to enhance their water leaking countermeasures, like having some more pumps and empty tanks ready in case a leak would occur, and ask NISA for approval. An other possibility is that the building was not designed at all to store liquids, but they made it watertight so that they can flood it with the contaminated water.

According to http://www.yomiuri.co.jp/science/news/20110517-OYT1T01016.htm , the Centralized Waste Treatment Facility enjoys a high level of shielding against radiations.

The video at http://www.tv-asahi.co.jp/ann/news/web/html/210516022.html shows that the pipes are running through the "high temperature incinerator building" before reaching the "Main process building".

I guess the "Centralized Waste Treatment Facility" is a set of several buildings including both the "main process building" where the contaminated water is being sent, and the incinerator building.

The worker who died on May 14th "had been working on the drainage system of the centralised radioactive waste store" : http://www.world-nuclear-news.org/RS-Fukushima_fuel_melt_confirmed-1605115.html

 

[MadderDoc]

TBH I am having second thoughts based on some images posted earlier of it not being there before the explosion but I still think it very unlikely.
If you look at the pipe coming out of the end of the cream/yellow cylinder, it is bent vertically downwards. The bend is a manufactured bend and I think it even more unlikely that any ballistic object would land like that.
however I don't think it was 'installed' after the explosion by the fuku50 because it's there on the First Helicopter flyby vids.
So I am open minded but unconvinced!

Yes, the bend certainly looks like a manufactured bend, the question is if the cylinder is actually attached to it. Since I have been unable to find any signs of the presence of a cylindrical object there before the explosion, in photos that should have shown it if it was there, it seems impossible that it is actually attached. So, by an improbable stroke of chance it must have come to rest on the crushed remains of the original piping, such that it deceptively _looks_ as if it is attached to the bend.

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth" (said Sherlock Holmes in "The sign of four")

 

[swl]

Does anyone here now what the pressure relief or steam relief valves are set for on one of these BWRs? Maybe running them above double design pressure is risky.

Also, did they actually ever successfully vent any of the 3 reactors or did they all blow a gasket, or rupture disk?

 

[westfield]

LOC makes venting a mute point. The reactors resorted to self venting or uncontrolled venting in this case. If there is no water available, do you just leave the vents open, waiting for water to return to the system? Maybe counter intuitive but the alternative is to allow the reactors to overpressurize with vents closed. Unit 2 overpressurized and blew around the torus area with the containment building still standing albeit is the source of a lot of the contaminated runoff to the ocean. Of course Unit 2 self vented somehow and sent a pop out panel flying out on its own according to workers who were sent to remove a pop out panel, finding that one gone already. A direct venting to the outside atmosphere, so to speak, with better results? (Not much)

Yes much better idea to permanently sacrifice your primary containment in order to prevent what might only be a minor atmospheric release. /sarcasm off ;)

 

[artax]

some interesting stuff here

http://online.wsj.com/article/SB10001424052748704281504576329011846064194.html

I'd hope they release these documents and I'd like to see the whiteboard scribblings from the time prior to the explosions!

The continuing conflicting reports about the situation are a nightmare,... I was talking to a colleague last week who said everything's OK there now. Just depends which paper you read!

 

[clancy688]

Also, of interest, i put this article on "passive cooling" (no external power required to cool the reactor).

http://motherjones.com/blue-marble/...chnology-safer-not-always-japans-crisis-shows

BWR3 reactors are of this type, and number 1 unit is a BWR3 (that's why it has a different cooling principle than the others, that we just learned Tepco workers have possibly volountarily turned off after Tsunami and shutdown, in a procedure to "protect" the reactor).

The article is a joke, IMHO. If I understand it correctly, it's telling that the passive safety systems of the BWR/3 is better than later, energy driven safety systems. That's ridiculous.
First, we can perfectly see what happens if an Isolation Condenser is used to cool a nuclear reactor - total meltdown within 16 hours. It was switched off, but switched on again three hours after the earthquake.

And second, the Isolation Condenser is not even designated to provide emergency cooling for extended time periods. In a pdf regarding safety issues of the BWR/Mark-I design it's stated that the IC pool will be boiled dry within 1,5 hours! (Which would allegedly leave enough time to secure other means of cooling - ha, my ***...)

Moreover, the emergency cooling systems of Unit 2 und 3 (RCIC) worked much longer than the IC - for up to three days in case of Unit 2.

 

[~kujala~]

http://www.tepco.co.jp/en/challenge/energy/nuclear/plants-e.html

the plants are built on solid bedrock

I think I found out why they are using this term.

Here is how Merriam-Webster defines "bedrock":
http://www.merriam-webster.com/dictionary/bedrock

the solid rock underlying unconsolidated surface materials

Here is how Wikipedia defines it:

In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil.

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

The main thing is "unconsolidated". Mudstone happens to be a special form of shale/clay/mud that has accumulated during million years in the sediment layer of the ground and is considered to be "consolidated":

When consolidated and relatively massive it is known as mudstone (or claystone)...

http://www3.hf.uio.no/sarc/iakh/lithic/mudstone.html

Below "mudstone" is a harder/older layer of consolidated rock but still "mudstone" is thought to be part of "bedrock" when we use the word "bedrock" in its general meaning. If we want to divide between these two some special words has to be used. Like they use words "Mesozoic bedrock" and "Franciscan bedrock" in this page:
http://earthquake.usgs.gov/regional/nca/soiltype/
(I am using the word "harder bedrock" here.)

So when TEPCO says they have built Fukushima plants on solid bedrock they are not lying. Still I feel little bit cheated as the qualities of mudstone and harder bedrock probably differ a lot as seen from the earthquake stand of point. Again referring to previous page:
Vs > 1500 m/sec Includes unweathered intrusive igneous rock.
1500 m/sec > Vs > 750 m/sec Includes volcanics, most Mesozoic bedrock, and some Franciscan bedrock.
750 m/sec > Vs > 350 m/sec Includes different kind of sand, sandstones, mudstones and limestones.

Note 1: I am quite sure TEPCO has made some research concerning the qualities of harder bedrock (-46 meters from the current ground level) and mudstone and it would be very interesting to get the results from this research.
Note 2: They removed a 25 meter layer level of soft sand to get to the mudstone layer. Would it have been possible to remove a 46 meter layer of mudstone to get to the harder bedrock layer? But if they had done that the whole plant would have been below sea level which I guess would have been impossible.

 

[zapperzero]

I was talking to a colleague last week who said everything's OK there now.

Your colleague has an interesting idea of what OK is.

 

[MadderDoc]

<..>
5) On one of the T-Hawk videos it can be seen that the service floor is broken only under the north crane boom.

Rive, sorry to be so late in catching up with this. I think quite on the contrary of what you say, in one of the T-Hawk videos the drone hovers close to the west end of the south crane boom, and it is readily apparent that the service floor in this position is also not intact (seeing that the floor has sunk under the boom.)
This is from the THawk video no3 from April 15th.

 

[~kujala~]

I see two possibilities. The first possibility is that the Centralized Waste Treatment Facility was designed some years ago for a given capacity of liquid waste. Storing larger quantities of highly contaminated water there straight away would have somehow meant breaking the rules. So they had to enhance their water leaking countermeasures, like having some more pumps and empty tanks ready in case a leak would occur, and ask NISA for approval. An other possibility is that the building was not designed at all to store liquids, but they made it watertight so that they can flood it with the contaminated water.

Whether A or B I still see problems here. The thing is building watertight systems is not easy and if you do it "fast" you might fail. These things need time and good design to succeed and if you have to improvise it you never know what's the end result going to be.

On the other hand, I assume they simply don't have enough space so they have no other choice as to do it on the fly.

 

[tsutsuji]

some interesting stuff here

http://online.wsj.com/article/SB10001424052748704281504576329011846064194.html

I'd hope they release these documents and I'd like to see the whiteboard scribblings from the time prior to the explosions!

The continuing conflicting reports about the situation are a nightmare,... I was talking to a colleague last week who said everything's OK there now. Just depends which paper you read!

The documents are here : http://www.tepco.co.jp/nu/fukushima-np/index10-j.html (in Japanese). For example you can see some of the snapshots of whiteboards mentioned by the Wall Street Journal from page 17/55 of http://www.tepco.co.jp/nu/fukushima-np/plant-data/f1_4_Nisshi1_2.pdf

 

[jlduh]

The non-hardened vent system is the Standby Gas Treatment System. In an emergency it takes a suction on the secondary containment and discharges to the stack through particulate HEPA filters and activated charcoal filters to remove radiation from the vented air. The system maintains secondary containment at a small negative pressure so any leakage of the building is from the atmosphere to the building. Later in an accident the system can be used to take a suction on containment to clean up radiation inside a depressurized containment. Again it would discharge through the filters to minimize the release.

The whole purpose of the hardened vent is to allow a high pressure vent path from the torus air space to save containment integrity. The only motive force is containment pressure. The drywell will releve through the downcomers to the torus water pool which will also hold up soluble contaminants. As torus pressure drops whole containment is being vented.

Ok thanks NUCENG this is much clearer now.

So in fact hardened vent is not so hardened as it has to be operated in a reliable manner (which is the main problem!) very early in a severe accident case, otherwise it's not enough hardened to bear the high pressures.

Do we have data (in the US) about the values of max pressures allowable we are talking about for an" hardened vent" system?

Lookin at the speed at which H2 fills the much too small Mark I containment, yes this has to be VERY quick...

Now, the point that are unclear concerning the venting at Unit 1 during the 3 additional hours after Kan visit are:

- was it because the workers couldn't open the valves?
- was it because Tepco management had some fears of opening them (would be very interesting to know the content of the discussions during the 3 hours)?
- did it finally explode because they finally vented but the pressure was already too high and the tightness of Mark I containment already failed, with H2 entering the top floors (probably first at containment cover seal which was considered to be a weak point, based on data discussed here on the forum)?
- did it finally explode because they vented but the venting (supposedly hardened) failed because of too high pressure and the leak path of H2 entered the building and the top floors before exploding?

These question are currently unresolved IMHO.

 

[jlduh]

The article is a joke, IMHO. If I understand it correctly, it's telling that the passive safety systems of the BWR/3 is better than later, energy driven safety systems. That's ridiculous.
First, we can perfectly see what happens if an Isolation Condenser is used to cool a nuclear reactor - total meltdown within 16 hours. It was switched off, but switched on again three hours after the earthquake.

And second, the Isolation Condenser is not even designated to provide emergency cooling for extended time periods. In a pdf regarding safety issues of the BWR/Mark-I design it's stated that the IC pool will be boiled dry within 1,5 hours! (Which would allegedly leave enough time to secure other means of cooling - ha, my ***...)

Moreover, the emergency cooling systems of Unit 2 und 3 (RCIC) worked much longer than the IC - for up to three days in case of Unit 2.

You are right of course, but the main idea of this article is to say that passive cooling is maybe a more reliable system than active ones (meaning the necessity of AC or DC power). Personally i have no idea of the problems associated with that principle which seems on the paper interesting. But what the paper says is that the newst generations of reactors seem to re-include that kind of systems. Again I have no idea if it is "marketing oriented stuff" (passive cooling seems great!) or if there is real improvement, and the article qustions this also by the way.

That's how I understand the spirit of this article.

 

[artax]

a bit of an update on allthingsnuclear from yesterady.

http://allthingsnuclear.org/

 

[jlduh]

http://www.tepco.co.jp/en/challenge/energy/nuclear/plants-e.htmlI think I found out why they are using this term.

Here is how Merriam-Webster defines "bedrock":
http://www.merriam-webster.com/dictionary/bedrockHere is how Wikipedia defines it:

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

The main thing is "unconsolidated". Mudstone happens to be a special form of shale/clay/mud that has accumulated during million years in the sediment layer of the ground and is considered to be "consolidated":

http://www3.hf.uio.no/sarc/iakh/lithic/mudstone.html

Below "mudstone" is a harder/older layer of consolidated rock but still "mudstone" is thought to be part of "bedrock" when we use the word "bedrock" in its general meaning. If we want to divide between these two some special words has to be used. Like they use words "Mesozoic bedrock" and "Franciscan bedrock" in this page:
http://earthquake.usgs.gov/regional/nca/soiltype/
(I am using the word "harder bedrock" here.)

So when TEPCO says they have built Fukushima plants on solid bedrock they are not lying. Still I feel little bit cheated as the qualities of mudstone and harder bedrock probably differ a lot as seen from the earthquake stand of point. Again referring to previous page:
Vs > 1500 m/sec Includes unweathered intrusive igneous rock.
1500 m/sec > Vs > 750 m/sec Includes volcanics, most Mesozoic bedrock, and some Franciscan bedrock.
750 m/sec > Vs > 350 m/sec Includes different kind of sand, sandstones, mudstones and limestones.

Note 1: I am quite sure TEPCO has made some research concerning the qualities of harder bedrock (-46 meters from the current ground level) and mudstone and it would be very interesting to get the results for this research.
Note 2: They removed a 25 meter layer level of soft sand to get to the mudstone layer. Would it have been possible to remove a 46 meter layer of mudstone to get to the harder bedrock layer? But if they had done that the whole plant would have been below sea level which I guess would have been impossible.

Ok i admit the definition of bedrock can be discussed and your infos are very interesting.

But as you, "I feel little bit cheated as the qualities of mudstone and harder bedrock probably differ a lot as seen from the earthquake stand of point". I feel also a little bit cheated with their illustrations i posted yesterday in their safety section.

By the way they also did some tests of liquefaction of soil during this survey, this could also be interesting. Anyway this is i think a secondary problem based on the current accidents.

 

[SteveElbows]

Have we noted that drywell CAMS data for reactor 1 started to be published again? I noticed it on japanese version of data today, but if I look at yesterdays data in English it seems to have appeared one data release earlier there...

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/table_summary-e.pdf

One of the sensors is reading 218 Sv/h in that data!

 

[NUCENG]

Does anyone here now what the pressure relief or steam relief valves are set for on one of these BWRs? Maybe running them above double design pressure is risky.

Also, did they actually ever successfully vent any of the 3 reactors or did they all blow a gasket, or rupture disk?

Are you confusing the fardened wetwell vent with the SRVs? The Safety Relief Valves vent the RPV to the torus. The pressure that was double its limit was containment pressure.

SRVs have automatic setpoints, mechanical setpoints, depressurization timers and are operated manually in accordance with Emergency Operating procedures. The mechanical setpoints are designed with sufficient capacity that the vessel should never exceed its design limit.

 

[jlduh]

Have we noted that drywell CAMS data for reactor 1 started to be published again? I noticed it on japanese version of data today, but if I look at yesterdays data in English it seems to have appeared one data release earlier there...

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/table_summary-e.pdf

One of the sensors is reading 218 Sv/h in that data!

As I keep seeing very variable and it seems inconsistent CAMS numbers from the very beginning, do some specialists here have an idea of what could be considered as the maximum thinkable radiation reading in mSv/h? Let say close to a corium mass, which number could we imagine? I guess there must be some data from testing and or historical recordings?

This would enable us to clarify is it is useful data or just jaggies from unreliable equipement.

 

[gbettanini]

I found a presentation that describes the accident’s phases and the venting processes.
http://www.scribd.com/doc/52131245/fukushima-areva

This scaring phrase in the NYT article:
“the pressure inside Reactor No.1 had reached roughly twice the maximum pressure the unit had been designed to withstand, raising fears that the vessels that house fuel rods would rupture, setting a possible meltdown in motion.”
… seems to be not true, the RPV can withstand a pressure of over 8 MPa, the primary containment can withstand a pressure of around 0.8 MPa, so the wet-well could have ruptured well before the RPV (as in reactor n.2… maybe).
So the question is if TEPCO could have been able to vent hydrogen and radionuclides through the stack before the explosions… but is seems to me a question of secondary importance, the amount radionuclides released would have been quite the same, maybe monitoring the wind direction the releases could have been diluted and directed to the sea but the total amount of PBq released must have been quite the same.
So this second sentence of the NYT article seems to be not true:
“venting would have allowed some radioactive materials to escape, analysts say that those releases would have been far smaller than those that followed the explosions at three of the plant’s reactors”

 

[SteveElbows]

As I keep seeing very variable and it seems inconsistent CAMS numbers from the very beginning, do some specialists here have an idea of what could be considered as the maximum thinkable radiation reading in mSv/h? Let say close to a corium mass, which number could we imagine? I guess there must be some data from testing and or historical recordings?

This would enable us to clarify is it is useful data or just jaggies from unreliable equipement.

Yeah I try not to take the CAMS readings too seriously because of unknown quality of data, but still can't help observing them anyway.

Meanwhile I think I just saw the NHK world news ticker say that workers who entered reactor 2 building today had to leave after 14 minutes due to steam.

 

[swl]

Are you confusing the fardened wetwell vent with the SRVs? The Safety Relief Valves vent the RPV to the torus. The pressure that was double its limit was containment pressure.

Yes, I was confused. Thank you for that.

So now another question: Does the containment system have an automatic pressure relief valve to vent the system through piping rather than the first point of failure? If so, why did the pressure rise to double the design limit? If there is no automatic pressure relief valve for the containment, why not?

I imagine a controlled relief of contaminated steam would almost always be preferable to an uncontrolled and irreversible containment failure.

 

[tsutsuji]

You can see the data in table form, where it is easy to read the exact values around March 21st.

However there is a problem. Yesterday Tepcos links to modern graphs, tables of data, and csv files did not just contain very recent data like they normally do, they were much larger and contained data going all the way back to before the 20th march. But today the same links have returned to their normal state, just showing data from recent days in may. So I cannot give you links to this information, maybe someone can reupload the data or find different urls?

I have looked at http://www.tepco.co.jp/nu/fukushima-np/f1/images/syusei_level_pr_data_3u.pdf and found those 3 data (A系　原子炉圧力) (system A reactor pressure) :

2011/03/21 1:25 ... 8.968 MPa
2011/03/21 1:45 ...11.571 MPa
2011/03/21 2:30 ...10.774 MPa

Here is my post where I talked to someone about this new data yesterday, but as I said the links in it don't give the info I was talking about anymore :(

https://www.physicsforums.com/showpost.php?p=3305309&postcount=7502

In recent messages here I have been disagreeing with someone else about whether the smoke events of 21st march may be responsible for the increased radiation detected far away just a few hours later. I was blaming the weather. Well, I do not mean to sound so certain about this at all.

At first I was blaming the rain for most of the radioactivity in Kanto region after March 16th. But I had to revise my position after the discussion started at : https://www.physicsforums.com/showthread.php?p=3257862#post3257862

Its only that I do not want to rule the weather out completely, because I checked messages I posted at a different forum around 19th-20th march to remind myself what was being said then. Stories were already appearing in the press about food and water contamination by the 19th march.

Water or food problems are a complex result of a number of events that happened earlier at the plant. I agree that the later events, if responsible for anything, may be responsible for only one part of the problems.

I am also trying to check the wind direction to see if the peak at 6 AM on March 21st in Mito (1) is correlated with a sudden change of wind direction, but the data at http://www.data.jma.go.jp/obd/stats...CB&year=2011&month=3&day=21&elm=minutes&view= seem to say that the wind had been nearly steady with an East-North-East direction from 5 AM to 7 AM, without showing anything special at 6 AM in correlation with the peak. But we would need a thorough meteorological study to know exactly about atmospheric transport on that day.

(1) already mentioned attachment at https://www.physicsforums.com/showthread.php?p=3258585#post3258585

 

[ottomane]

Although it is off topic in relation to the current discussion I'd like to post another question:

The (control?) rods usually contain Boron to catch neutrons. Each Boron-nucleus can only catch one neutron once, so Boron is getting used up. So the rods have to be exchanged after some years.

If the fuel rods and control rods melt together into one mass, this changes the geometry and heat conditions in the reaction. Also water would be gone, so there is no moderator.

Does this setup affect the Boron consumption?

 

[ihatelies]

So I'm back from a mini vacation, and I see that TEPCO has finally admitted that the fuel has breached the RPV in unit 1 and probably the same in units 2 and 3.

I assume this has come as no surprise to anyone following the event, however it does negate much of the "data" that has been provided around RPV pressure, temperature and water level over the rods - which apparently no longer exist (as rods at least).

So I come back to my theory that some portion of the RPV#3 actually ejected during the explosion on March 14th. If you'll recall, many here said that I could not possibly be correct, because the temp and pressure data proves that the RPV is still intact.

However, now that we know the temp and pressure data is likely incorrect, that argument against my theory is dead.

I will remind everyone again, of the hole in the roof shown in this picture:

And I will provide Fred's excellent analysis of the roof structure and hole here. His conclusion as I recall was that it did appear that something went through the hole, but it must have fallen down rather than up. I'm not sure I agree with that view, but i will say I cannot refute it.
[PLAIN]http://k.min.us/jntf3c.jpg

My question is this. Can anyone factually rule out that all or part of the reactor did not eject in the explosion on March 13th, and if it did what are the consequences globally of the fallout?