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 ;)