Fukushima Japan Earthquake: nuclear plants Fukushima part 2

[mheslep]

@etudiant
salt water in switchgear renders it unuseable ...

Marine high power electrical gear is somewhat robust to salt spray, and is not permanently unuseable even if flooded for a time after a clean up. Dropping the standard marine power cable in the water for instance, the kind found around every marina, to follow your example, won't cause it to burn up. For a coastal plant to not have electrical backup equipment without some resilience to salt water, if that is actually the case, is curious.

 

[Hiddencamper]

Marine high power electrical gear is somewhat robust to salt spray, and is not permanently unuseable even if flooded for a time after a clean up. Dropping the standard marine power cable in the water for instance, the kind found around every marina, to follow your example, won't cause it to burn up. For a coastal plant to not have electrical backup equipment with some resilience to salt water, if that is actually the case, is curious.

The plant was considered a "dry" site, which is why the switchgear and diesels were allowed to be at lower elevations and not in watertight cubicles.

 

[gmax137]

... The plant was considered a "dry" site ...

Criterion 2—Design bases for protection against natural phenomena. Structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions. The design bases for these structures, systems, and components shall reflect:
(1) Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated,
(2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena and
(3) the importance of the safety functions to be performed.

There are about 60 of these General Design Criteria. This one is Number 2 for a reason.

 

[Hiddencamper]

There are about 60 of these General Design Criteria. This one is Number 2 for a reason.

In order to meet that GDC, you need to demonstrate that you are protected from hazards. At the time the plant was build, it WAS in compliance with it's tsunami analysis. In 2009 when TEPCO identified that a tsunami much larger than anticipated could have struck the site, they were no longer in compliance with their tsunami analysis. The regulator allowed continued operation under the pretext that a loss of all seawater pumps could be coped with using compensatory actions and other installed equipment (like the air cooled diesel generators - similar to station blackout generators in the US), as well as TEPCO getting an independent analysis performed by another organization.

This is where the real flaw is, because the comp actions were not sufficient for the type and level of damage which could have occurred. It's clear that TEPCO did not properly evaluate the effect a massive tsunami could have on the site, and the regulator did not challenge them.

But from a pure design standpoint, the site was designed over 40+ years ago, to standards and analysis from 40+ years ago, which is WHY the original design is the way it is.

 

[mheslep]

The plant was considered a "dry" site, which is why the switchgear and diesels were allowed to be at lower elevations and not in watertight cubicles.

Was considered? Clearly. But by whom and via what rationale?

 

[Hiddencamper]

Was considered? Clearly. But by whom and via what rationale?

Some excerpts from the following:

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111202e14.pdf

The major buildings of the Fukushima Daiichi NPS are located at an elevation of O.P. +10 m for Units 1 to 4, which suffered major damage, and at an elevation of O.P.+13 m for Unit 5 and 6. When obtaining the establishing permit, the Chilean tsunami had been envisioned as the greatest tsunami in history, and the tsunami height at that time was O.P. +3.1 m. At present, the tsunami height of O.P.+6.1 m, that was evaluated based on the “Tsunami Assessment Method” of the JSCE, is used for the design purpose. It was recognized that there would not be any tsunami that could run up to the level of the buildings.

Investigation on the plants revealed that EDGs are not located inside the reactor buildings that require air-tightness. U.S. plants that were under construction when Fukushima Daiichi Unit 1 was designed were designed to plant-specific seismic criteria as early as 1969, - 16 - using the existing subsurface conditions for the individual plants. U.S. designs are unique to the site soil conditions, supported by rock or a unique subsurface formation, or on spread-footer foundations. Hence, most of the buildings in which EDGs are installed did not require foundations built on base rock. In comparison, many buildings in Japanese NPSs have basement floors due to the necessity of being built on the base rock layer for seismic reasons. Due to such differences, EDGs were installed on the foundation (the lowest floor) in Japan in consideration of the large components’ seismic adequacy and vibrations.

Since Dr. Satake’s paper proposed wave source models, although they were not verified, TEPCO conducted a trial calculation using the two models proposed in the paper in December 2008. The result of the trial calculation showed a tsunami height of O.P. +7.8 m to 8.9 m (O.P. +7.8 m to 9.2 m, if a different accounting method for high tide is used) in front of the Fukushima Daiichi and Fukushima Daini NPS intake points.

 

[nikkkom]

NHK reports that a sarcophagus structure is under consideration, to seal off the buildings with the fuel inside.
Given the groundwater issues, is this a plausible option for even the relatively short term?

http://www3.nhk.or.jp/nhkworld/en/news/20160713_25/

I like this idea a lot.

 

[etudiant]

As for depressurization. From a practical perspective, depressurization would have helped minimize the potential for containment damage when the core melted through the vessel, however there are a lot of limits/issues with this. For one, you need DC power to operate the Safety-Relief valve solenoids to perform the blowdown, so you couldn't do this easily at units 1/2 without battery packs. The other issue is that you cannot intentionally violate cooldown rate. The 100 degF/55degC per hour cooldown rate is a strict cooldown limit. EOPs do not allow exceeding this limit unless you hit an Emergency Depressurization Required contingency, and you are not allowed to anticipate the requirement to blow down early unless the steam dumps to condenser are available (they weren't). So you cannot do an "early" blowdown, only a normal cooldown.

Emergency depressurization would not "scrap" the reactors, GE reactors are designed for an emergency blowdown and reflood, and require a vessel analysis after that is complete to verify the integrity of the vessel. Some plants have blown down rapidly before, at Laguna Verde in Mexico, an SRV stuck open and depressurized the core in under an hour from NOP/NOT, and they are still operating the unit today.

QUOTE]

Again, thank you hiddencamper for another very informative post.
It suggests that there needs to be a more effective emergency stop provision for current reactors. The Fukushima operators did their best to execute the shutdown procedures, yet their reactors would still have poisoned the Japanese heartland for centuries if the winds had not swept the debris out to sea.
Clearly reactors need a switch to allow them to fail in a manageable way if continued operator control is lost. Is that even possible?

 

[Astronuc]

Was considered? Clearly. But by whom and via what rationale?

TEPCO submitted an analysis and the regulatory authority accepted/approved it.

In the report cited by Hiddencamper, see section
3.4 Tsunami evaluation
(1) Evaluation of tsunami height
The establishing permits for the units of the Fukushima Daiichi NPS were obtained
between 1966 and 1972. At that time, there was no guideline for tsunami and the units were
designed based on the known tsunami traces. Specifically, the maximum tide level that was
observed at the Onahama Port (O.P. +3.122m), which was caused by the Chilean earthquake
and tsunami of 1960, was established as a design basis.

In 1970, the “Regulatory Guide for Reviewing Safety Design of Light Water Nuclear
Power Reactor Facilities” (hereinafter referred to as the “safety design review guidelines”)
was established. In the guideline, tsunamis were referred to as one of the natural conditions
that should be considered and the facility was required to be able to withstand the harshest
natural force that was foreseen based on past records. . . . .

Somehow, the utility and government regulator convinced themselves that the tsunami level was not going to be more than 5.4 to 5.7 m. Much of the eastern coastline in the Tohoku region was not adequately protected as is evidenced by the substantial flooding in areas like Sendai.

However, there were historical records of such tsunamis. One simply had to go looking for them.

 

[etudiant]

Fukushima can clearly be classified as a regulatory failure, as Astronuc's above post again makes clear.
Unfortunately, regulatory failure is not uncommon, as illustrated by experience elsewhere, in the financial industry for example.
That puts a heavier burden on the nuclear engineers, they have to allow for inadequate regulation in the design and operation of the plant.
The Fukushima disaster proves that that is beyond the capability of the current reactor installations. That threatens the industry's survival imho.
At this point, there are about 500 power reactors world wide, so maybe 15,000 reactor years of operation cumulatively. With at least 3 loss of reactor accidents in that time there is about one per 5000 reactor years. That suggests a going forward rate of one disaster per decade. It does not seem a sustainable path, so what are the possible remedies?

 

[mheslep]

That suggests a going forward rate of one disaster per decade. It does not seem a sustainable path, so what are the possible remedies?

Only if the reactor designs and method of operation continued as they did with the accidents. It may be that Fukushima style threat of accidents remain from tsunamis. But otherwise they are not the same designs, do not operate in the same manner.

 

[Rive]

he Fukushima disaster proves that that is beyond the capability of the current reactor installations. That threatens the industry's survival imho.

Not really, IMHO. Not through real dangers. This accident proves that except the oldest designs the reactors are quite well built. (Without the soon-be-closed U1 the disaster might had gone a different way.) Two of the three made it out of a beyond design basis accident with limited environmental damage, without actual loss of life. Compared to other industrial accidents that's quite something.

 

[etudiant]

The expectation, at least in the US, is that reactors will have their initial 40 year service life extended in 20 year chunks, with no fixed sunset limit,. Hence the existing inventory of reactors will not be replaced anytime soon by new designs. So the risk factors will only move very slowly.
It is a mistake, imho, to think of Fukushima as an accident with limited damage. If the winds had been different, Japan would have lost its heartland. The Reagan was getting unacceptable contamination although never closer than 100 miles from the site. Merkel's decision reflects her recognition that the small risk of a national catastrophe is too high a price to pay for cheap power. The very disparate circumstances of Chernobyl, Three Mile Island and Fukushima indicate that there are multiple avenues to failure, so there is not a silver bullet fix.
Ideally, reactors need an off switch that works unconditionally. The PIUS design from the 90s seemed one such option and there may be others, but none have gained market acceptance. That leaves the world with many aging nuclear plants that can fail very messily. A huge challenge for the industry and its regulators.

 

[mheslep]

The expectation, at least in the US, is that reactors will have their initial 40 year service life extended in 20 year chunks, with no fixed sunset limit,.

The positive feedback RBMKs are gone already. So no Chernobyl style accident applies to the statistical case you are trying to make.

" If the winds had been different, Japan would have lost its heartland."

That's a bold claim. Do you have some evidence to show how that's even plausible, given the exclusion/evacuation zone was 30 km, and the outskirts of Tokyo are 160 km.

2011:

 

[Hiddencamper]

The expectation, at least in the US, is that reactors will have their initial 40 year service life extended in 20 year chunks, with no fixed sunset limit,. Hence the existing inventory of reactors will not be replaced anytime soon by new designs. So the risk factors will only move very slowly.
It is a mistake, imho, to think of Fukushima as an accident with limited damage. If the winds had been different, Japan would have lost its heartland. The Reagan was getting unacceptable contamination although never closer than 100 miles from the site. Merkel's decision reflects her recognition that the small risk of a national catastrophe is too high a price to pay for cheap power. The very disparate circumstances of Chernobyl, Three Mile Island and Fukushima indicate that there are multiple avenues to failure, so there is not a silver bullet fix.
Ideally, reactors need an off switch that works unconditionally. The PIUS design from the 90s seemed one such option and there may be others, but none have gained market acceptance. That leaves the world with many aging nuclear plants that can fail very messily. A huge challenge for the industry and its regulators.

The reactors were "off". The scram system is fail safe and uses pre stored energy; and we know all reactors at Fukushima were off when the earthquake occurred. BWR control rods each have a pressurized accumulator which can insert the rod. On a loss of power, the scram pilot valves fail open causing this accumulator to inject underneath the control rod drive piston. In the event the accumulator fails, the control rod drive hydraulic pumps or the reactor's own water pressure can cause the rod to insert.

Please take some time to learn about decay heat. It will explain to you why Fukushima and three mile island accidents occurred, even though at both places, the reactors were shut down hours before core melting began.

 

[Astronuc]

Ideally, reactors need an off switch that works unconditionally. The PIUS design from the 90s seemed one such option and there may be others, but none have gained market acceptance.

As Hiddencamper indicated the reactors were scrammed, i.e., shutdown, and appropriate cooling was actuated. All went well until the tsunami hit and took out the power. Decay heat cannot be turned off, since it comes from alpha (from actinides, particularly transuranics) and beta decay (from fission products), and that is inherent in the process. That's why we have residual heat removal (RHR) systems, which performs shutdown cooling among other tasks.

http://nrcoe.inel.gov/resultsdb/SysStudy/RHR.aspx
See also Decay Heat Removal (page 3-7) of http://www.nrc.gov/reading-rm/basic-ref/students/for-educators/03.pdf

As I recall PIUS used natural circulation, so as long as the coolant inventory is maintained in the primary system, the natural circulation removes the heat. That is the principal behind GEH's ESBWR.

The expectation, at least in the US, is that reactors will have their initial 40 year service life extended in 20 year chunks, with no fixed sunset limit,. Hence the existing inventory of reactors will not be replaced anytime soon by new designs. So the risk factors will only move very slowly.

There is a lot of research going looking at aging effects in plants. There is no certainty that plants will automatically get another 20 years beyond 60 years. That will only happen if it can be demonstrated that the RPV and other major systems do not degrade at 60 years and beyond. If a plant experiences a component failure due to aging, any life extension will likely come to a halt. There is a lot of monitoring going on at the moment.

 

[Sotan]

I am sure that by "Ideally, reactors need an off switch that works unconditionally" etudiant meant some kind of design that includes the safe and efficient management of decay heat after SCRAM - including in terrible circumstances such as the prolonged loss of power that happened at Fukushima.

 

[Hiddencamper]

I am sure that by "Ideally, reactors need an off switch that works unconditionally" etudiant meant some kind of design that includes the safe and efficient management of decay heat after SCRAM - including in terrible circumstances such as the prolonged loss of power that happened at Fukushima.

And that is ultimately going to require gen 3+ or newer designs.

ECCS was really designed around the idea that a rupture of the primary coolant system can lead to an unrecoverable core melt which ultimately causes containment failure. If you prevent core melting from even starting, you protect the containment boundary. It wasn't really designed under the idea that you have these multi-day long loss of power events.

Decay heat removal can be accomplished in a number of ways. Active DHR is one method. Venting of containment is a less preferred method that can be employed. With newer reactors there is the possibility for passive decay heat removal as well.

 

[etudiant]

As Sotan notes, the issue is graceful failure despite decay heat.
If that takes gen3+ or newer designs, as hiddencamper indicates, none of the current reactors are adequate. Merkel's decision to shut them down seems logical in that light.

My comment about Fukushima taking out Japan's heartland reflects Kan's comment that he was considering evacuating Tokyo and the US government evacuating dependents from Yokosuka.
The contamination map is a helpful indication of how lucky Japan was, the finger of highest contamination was deposited during a brief westerly wind shift in overwhelmingly east winds. The Reagan at 100 miles out was finding ambient radiation sufficient to reach the public exposure limit in 10 hours, according to official sources quoted here: http://apjjf.org/2014/12/7/Kyle-Cleveland/4075/article.html

 

[Hiddencamper]

As Sotan notes, the issue is graceful failure despite decay heat.
If that takes gen3+ or newer designs, as hiddencamper indicates, none of the current reactors are adequate. Merkel's decision to shut them down seems logical in that light.

My comment about Fukushima taking out Japan's heartland reflects Kan's comment that he was considering evacuating Tokyo and the US government evacuating dependents from Yokosuka.
The contamination map is a helpful indication of how lucky Japan was, the finger of highest contamination was deposited during a brief westerly wind shift in overwhelmingly east winds. The Reagan at 100 miles out was finding ambient radiation sufficient to reach the public exposure limit in 10 hours, according to official sources quoted here: http://apjjf.org/2014/12/7/Kyle-Cleveland/4075/article.html

It's only a logical decision if one looks only at consequences at not risk. But that's really for a different discussion topic.

 

[etudiant]

It's only a logical decision if one looks only at consequences at not risk. But that's really for a different discussion topic.

Well, there are obvious downsides to her decision, including much increased coal consumption and higher costs.
However, the German nuclear industry had also blotted its copybook with several instances of extreme sloppiness, notably the Juelich pebble bed reactor and also the Asse nuclear waste salt mine depository (somewhat akin to the WIPP). So there was no basis to be confident that its performance in an emergency would be better than it was at Fukushima. Indeed, the Juelich performance suggests the operators are a major risk factor in an off design situation. That is hard to plan for, but cannot be ignored.

 

[mheslep]

...
My comment about Fukushima taking out Japan's heartland reflects Kan's comment that he was considering evacuating Tokyo and the US government evacuating dependents from Yokosuka.

The discussions about evacuating Tokyo are not the same thing as showing how the "heartland" could be destroyed.

The contamination map is a helpful indication of how lucky Japan was, the finger of highest contamination was deposited during a brief westerly wind shift in overwhelmingly east winds.

You're repeating your earlier assertion. If the wind blew in another direction during the accident, shifting the higher sv/hr radiation in another direction, how would that have made things materially worse? Any easterly wind during the accident would have blown most of the radiation out to sea.

 

[etudiant]

The discussions about evacuating Tokyo are not the same thing as showing how the "heartland" could be destroyed.
You're repeating your earlier assertion. If the wind blew in another direction during the accident, shifting the higher sv/hr radiation in another direction, how would that have made things materially worse? Any easterly wind during the accident would have blown most of the radiation out to sea.

Iirc, the winds were persistently blowing out to sea from the plant, during the first two weeks of the accident. I mistakenly said they were blowing from the east, I should have said west. My error and I apologize for causing confusion..
There was only a relatively brief swing to a more inland orientation that laid down the more contaminated corridor. It seems reasonable to me that if the winds had not been so favorable, the level of contamination the Reagan experienced while 100 miles from the plant would instead have been inland, rather than offshore. A 100 mile radius around Fukushima would reach Tokyo and cover much of the Honshu plain, which is considered the Japanese heartland.

 

[jim hardy]

Is this old news ? First i'd heard of it, stumbled across it tonight.
excerpts:

http://www.nytimes.com/2016/03/01/w...ecutives-over-fukushima-nuclear-disaster.html
Japan Indicts 3 Former Executives Over Fukushima Nuclear Disaster
TOKYO — Japanese prosecutors indicted three former executives of the Tokyo Electric Power Company, the owner of the ruined Fukushima Daiichi Nuclear Power Station, on Monday, charging them with criminal negligence for their role in reactor meltdowns after an earthquake and tsunami five years ago.
.....
The three executives — Tsunehisa Katsumata, 75; Sakae Muto, 65 (no relation to Ruiko Muto); and Ichiro Takekuro, 69 — are accused of failing to take measures that would have protected the nuclear plant from the damage the tsunami wrought.Studies by seismologists before the tsunami had suggested that waves higher than the Fukushima plant’s roughly 30-foot sea wall could strike the Pacific Coast, the site of the plant.

“They know that measures were necessary, but for economic reasons they did nothing,” said Yuichi Kaido, a lawyer and politician who supports the Fukushima plaintiffs’ group.A rarely used feature of Japanese law allows committees of private citizens to examine prosecutors’ decisions on whether to indict suspects. In certain circumstances, they can order those decisions reversed. Two such committees revived the Fukushima case, and both determined that the Tepco executives should be criminally charged.Prosecutors initially declined to bring charges in the case. They said there was not enough evidence that failings by Tepco or its leaders had amounted to criminal wrongdoing. But their decision angered Fukushima residents and antinuclear campaigners, who formed the organization led by Ms. Muto, the Fukushima Nuclear Disaster Plaintiffs Group, to demand a review.

i still think had somebody apprised executives of the danger they'd have done something.

 

[nikkkom]

i still think had somebody apprised executives of the danger they'd have done something.

Historically, Japanese management was known to be quite bad when it comes to such matters as knowingly putting people in danger. For example, did you know about this outrageous story?

https://en.wikipedia.org/wiki/Minamata_disease

Yes, it was in 1960s, but I'm not sure this does not still linger in the culture.

 

[jim hardy]

For example, did you know about this outrageous story?

no, first i'd heard of it. I hope we no longer use mercury in pesticides here .

When i look back over my life i am amazed how environmentally insensitive we were sixty years ago. "Down the drain" used to be the end of it.
It's human nature to toss our troubles 'over the fence' . We're populous enough now that doesn't work any more.

Jailing those old guys wouldn't do society any direct good, they don't hold up gas stations or snatch purses
but the humiliation of indictment will send shock waves through executive circles.
I remember about 30 years ago a series of industrial accidents at a Ford foundry killed some workers.
US threatened oops initiated charges against Ford executives for the deaths and threatened them with prison time.
All of a sudden the safety culture down at my level took a major turn toward seriousness - safety meetings became more frequent and longer, management participation became active and serious, safety equipment like earplugs and eyewash stations and first aid kits became cornucopian and we got an onsite medical clinic. Despite its being a completely unrelated industry !

We can only seek perfection and settle for progress.

old jim

 

[etudiant]

Historically, Japanese management was known to be quite bad when it comes to such matters as knowingly putting people in danger. For example, did you know about this outrageous story?

https://en.wikipedia.org/wiki/Minamata_disease

Yes, it was in 1960s, but I'm not sure this does not still linger in the culture.

Minamata was a dirt poor area of Japan, way out in the sticks. Shellfish, fishing and agriculture were the major activities. So the community was thrilled to get a set of chemical operations that brought jobs and a measure of prosperity to the area. Because it is low lying and tidal land, with a sluggish stream running through it, the effluent of the plants was carried all over, but no one thought anything of it. Then the cats,which ate mostly fish scraps, began to act strange, It is only when people began to lose the ability to walk that a real investigation began and quickly pinned down the nature of the problem. Admitting this was not easy for the companies though. It was a bitter fight for the victims to get any compensation. The chimney of the plant still looms over the area, perhaps as a reminder.

It is relevant that Japan's last two operating reactors are in Kyushu, the home island where Minamata is located. The recently elected governor, a relative outsider, ran on a platform of shutting down these reactors, even though they are inland, by a lake and far from any ocean. Clearly the population in Kyushu is much less willing to trust corporate assertions than perhaps elsewhere in Japan.

 

[nikkkom]

Minamata was a dirt poor area of Japan, way out in the sticks. Shellfish, fishing and agriculture were the major activities. So the community was thrilled to get a set of chemical operations that brought jobs and a measure of prosperity to the area. Because it is low lying and tidal land, with a sluggish stream running through it, the effluent of the plants was carried all over, but no one thought anything of it. Then the cats,which ate mostly fish scraps, began to act strange, It is only when people began to lose the ability to walk that a real investigation began and quickly pinned down the nature of the problem. Admitting this was not easy for the companies though. It was a bitter fight for the victims to get any compensation.

You missed my point.

My point is that the company *actively fought against* attempts to figure out why people are falling ill. When in-house research clearly showed that it's their effluent was causing it, they ordered it to stop!

Chisso failed to co-operate with the investigation team from Kumamoto University. It withheld information on its industrial processes, leaving researchers to speculate what products the factory was producing and by what methods.[20] The Chisso factory's hospital director, Hajime Hosokawa, established a laboratory in the research division of the plant to carry out his own experiments into Minamata disease in July 1959. Food to which factory wastewater had been added was fed to healthy cats. Seventy-eight days into the experiment, cat 400 exhibited symptoms of Minamata disease and pathological examinations confirmed a diagnosis of organic mercury poisoning. The company did not reveal these significant results to the investigators and ordered Hosokawa to stop his research.

But this wasn't the end.

They installed a *BOGUS* effluent "treatment" system and were duping people for nine years, while people continued to be poisoned!

On October 21, 1959, Chisso was ordered by the Ministry of International Trade and Industry to switch back its wastewater drainage from the Minamata River to Hyakken Harbour and to speed up the installation of wastewater treatment systems at the factory. Chisso installed a Cyclator purification system on December 19, 1959, and opened it with a special ceremony. Chisso's president Kiichi Yoshioka drank a glass of water supposedly treated through the Cyclator to demonstrate that it was safe. In fact, the wastewater from the acetaldehyde plant, which the company knew still contained mercury and led to Minamata disease when fed to cats, was not treated through the Cyclator at the time. Testimony at a later Niigata Minamata disease trial proved that Chisso knew the Cyclator to be completely ineffective: "The purification tank was installed as a social solution and did nothing to remove organic mercury."

The deception was successful and almost all parties involved in Minamata disease were duped into believing that the factory's wastewater had been made safe from December 1959 onward. This widespread assumption meant that doctors were not expecting new patients to appear, resulting in numerous problems in the years to follow, as the pollution continued. In most people's minds, the issue of Minamata disease had been resolved.
...
Finally on 26 September 1968 — 12 years after the discovery of the disease (and four months after Chisso had stopped production of acetaldehyde using its mercury catalyst) — the government issued an official conclusion as to the cause of Minamata disease

 

[etudiant]

Thank you for adding the extra color.
I thought that just noting that it was not easy to get admission and much harder to get compensation would indicate the conflict.
The extra details you add about corporate duplicity is quite revealing, as it surely underpins the current reluctance of the people of Kyushu to believe the reassurances of the power company regarding reactor safety. The large Kunamoto quake this April, even though centered on a more northerly part of Kyushu, probably heightened voter concerns further.

 

[Gary7]

the US government evacuating dependents from Yokosuka

I hope this isn't seen as splitting hairs, but I think the above requires some qualification. The Navy authorized voluntary evacuations of dependents.

http://www.stripes.com/news/pacific/military-begins-voluntary-evacuation-of-families-in-japan-1.137999

 

[etudiant]

I hope this isn't seen as splitting hairs, but I think the above requires some qualification. The Navy authorized voluntary evacuations of dependents.

http://www.stripes.com/news/pacific/military-begins-voluntary-evacuation-of-families-in-japan-1.137999

Thank you, very helpful to give a sense of how the event translated into action for those not directly in US government service.

 

[Rive]

As it seems, in U2 it's still mostly within the RPV?
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160728_01-e.pdf

 

[Hiddencamper]

As it seems, in U2 it's still mostly within the RPV?
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160728_01-e.pdf

Unit 2 is the most likely of the three to have its fuel remain in the vessel. Between 70 hours of RCIC injection and the shorter delay between debris ejection and commencement of fire pump injection, it's definitely possible that it has a decent amount in the rpv.

 

[etudiant]

With the benefit of hindsight, what possible actions would have minimized the radiation release from Fukushima after the tsunami hit?
Assume the reactors are a writeoff, what would involve the least collateral damage.
Would venting to atmospheric pressure have been useful, was it even feasible? Or was unit 1 essentially autonomous after the impact?

 

[Hiddencamper]

With the benefit of hindsight, what possible actions would have minimized the radiation release from Fukushima after the tsunami hit?
Assume the reactors are a writeoff, what would involve the least collateral damage.
Would venting to atmospheric pressure have been useful, was it even feasible? Or was unit 1 essentially autonomous after the impact?

The Japanese containment vent design utilizes a rupture disc that's set at around twice containment maximum design pressure. So there was no way to vent early. Additionally for at least one of the units, the rupture disc did not rupture when it was supposed to.

Venting could have protected containment integrity and prevented the leaks that the containments have. Normal post accident response is to flood the containment to submerge the core to at least 2/3rds core height, and they have water leaking out to this day preventing that.

 

[etudiant]

The Japanese containment vent design utilizes a rupture disc that's set at around twice containment maximum design pressure. So there was no way to vent early. Additionally for at least one of the units, the rupture disc did not rupture when it was supposed to.

Venting could have protected containment integrity and prevented the leaks that the containments have. Normal post accident response is to flood the containment to submerge the core to at least 2/3rds core height, and they have water leaking out to this day preventing that.

I've no nuclear plant experience or background, so I may be using words such as 'venting' inappropriately.

Was there any action that the plant operators could have taken to limit the collateral damage? It is very clear that they had very limited information at the time and even less control, but with all we know now, is there a consensus that there was no action available to them that would possibly have limited the accident ? Or if there was, what would have been the better choice.

 

[Cire]

Looks like the Muon scan is done for Reactor #2.

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160728_01-e.pdf

 

[Astronuc]

Was there any action that the plant operators could have taken to limit the collateral damage? It is very clear that they had very limited information at the time and even less control, but with all we know now, is there a consensus that there was no action available to them that would possibly have limited the accident ?

Getting water into the core was the main priority. The reactors had scrammed, so they were shutdown, but the decay heat was still there.

The reactors were a write-off one they introduced seawater into the systems. The consequences of the boiling, oxygenated sea-water is not known, but it was probably corrosive.

Back when we were following the accident, we thought the water was getting into the core, but the level indicators were suspect. Clearly, there was water to react with the cladding to produce hydrogen. The question is, when did the cores melt, if they melted? I would also consider the possibility of a chemical reaction with the sea water, such that the cladding corroded and the fuel dissolved, which would have the consequences as melting, i.e., wide-spread breach of the cladding and release of volatile fission products. In other words, dissolution of the fuel would have the same effect as if the core had melted.

 

[etudiant]

Getting water into the core was the main priority. The reactors had scrammed, so they were shutdown, but the decay heat was still there.

The reactors were a write-off one they introduced seawater into the systems. The consequences of the boiling, oxygenated sea-water is not known, but it was probably corrosive.

Back when we were following the accident, we thought the water was getting into the core, but the level indicators were suspect. Clearly, there was water to react with the cladding to produce hydrogen. The question is, when did the cores melt, if they melted? I would also consider the possibility of a chemical reaction with the sea water, such that the cladding corroded and the fuel dissolved, which would have the consequences as melting, i.e., wide-spread breach of the cladding and release of volatile fission products. In other words, dissolution of the fuel would have the same effect as if the core had melted.

Iirc, the sea water injections were a last resort when no other water sources were available and only took place a couple of days after the accident began. It was also recognized at the time that this was a reactor write off decision.
The possibility that the sea water accentuated or even catalyzed some of the fission product releases is new to me, I'd only seen speculation that salt deposits from evaporated sea water might be blocking coolant circulation.
I'd still love to hear whether the people operating the plant had any better outcomes available if they had known then all we know now about the situation.
Could they have altered the result in any way or not?

 

[jim hardy]

Could they have altered the result in any way or not?

here's one of the documents Tepco put out as things progressed
it conveys the direness of what faced those poor guys
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110618e15.pdf

I'd still love to hear whether the people operating the plant had any better outcomes available if they had known then all we know now about the situation.

The direction to go would have been to get the reactor cold and flooded
because a cold reactor vessel doesn't overheat the containment penetrations and make them leak
and the higher water inventory gives you more time

With only 41 minutes between the earthquake and the tidal wave wrecking the diesels,
http://www.scientificamerican.com/media/multimedia/0312-fukushima-timeline/

11 March 2011
A magnitude 9.0 earthquake hits 130 kilometers off Japan's northeastern coast at 2:46 P.M. local time. Several nuclear power plants automatically shut down; the Fukushima Daiichi nuclear power complex loses its connection to the electrical grid and diesel generators kick into continue delivering power to circulated cooling water around the hot nuclear core.

Diesel generators at Fukushima Daiichi shut down at 3:27 P.M. local time after getting slammed by a series of seven tsunamis, some as high as 15 meters.

there wasn't time to get very far with a cooldown even if they'd known what was coming.
I'm not a BWR guy so won't guess how far along a cooldown path they could have got
and I don't know whether the water tanks they'd have needed to floodup survived the tidal wave.I tried a search on " fukushia what should they have done different "
NPR article suggests earlier cooldown
http://www.npr.org/2011/07/05/137611026/what-went-wrong-in-fukushima-the-human-factor

most everybody seems to agree that failure to recognize possibility of bigger-than-designed-for tidal waves and harden the plant against them was the culprit.
http://carnegieendowment.org/files/fukushima.pdf

 

[Rive]

Could they have altered the result in any way or not?

By my understanding (and the posts from the last few weeks) to make a significant difference would have require so many violation of actual OpInst rules and so many knowledge about plant status and future events, that it's really a kind of 'what would have Bruce Willis done?' question.

everybody seems to agree that failure to recognize possibility of bigger-than-designed-for tidal waves and harden the plant against them is the culprit.

Agree. The underestimated height of possible tsunami and the presence of U1 with its far outdated design basis has already set up the situation, and any (realistic) course of decisions would have had only a very limited impact on the results.

 

[jim hardy]

Like Titanic- watertight doors weren't high enough.

 

[etudiant]

I recognize the plant was doomed by the tsunami, but was wondering whether there was a way to limit the resultant mess. Could doing absolutely nothing have been worse?

Astronuc has speculated that the sea water injections intended to cool the cores may in fact have damaged the fuel, which worsened the outcome.
There have been suggestions that most of the water injected flowed directly directly into the turbine building, with only very little actually reached the inside of the reactors, adding to the hydrogen build up rather than providing effective cooling.

 

[mheslep]

The Japanese containment vent design utilizes a rupture disc that's set at around twice containment maximum design pressure. So there was no way to vent early. Additionally for at least one of the units, the rupture disc did not rupture when it was supposed

No *automatic* rupture, yes, but could the disc have been manually blown?

 

[jim hardy]

Could doing absolutely nothing have been worse?

i can't opine, too interested ..

Does this say anything ?

http://www.nrc.gov/docs/ML1012/ML101270372.pdf

 

[mheslep]

By my understanding (and the posts from the last few weeks) to make a significant difference would have require so many violation of actual OpInst rules and so many knowledge about plant status and future events, that it's really a kind of 'what would have Bruce Willis done?' question. ...

I grant that discussion of alternative action is often ill informed (and is in my case). But I disagree that discussions of alternatives are necessarily indulgence in fantasy. The better comparison to a decisive personality, if there must be be one, is Captain Sullenberger and the landing in the Hudson. The Hudson River is not another numbered FAA runway. If Sullenberger had instead stubbornly headed back to the (out of glide range) runway with no engine power because of FAA regulations I'd have little time for those saying he was only following the rules, that nothing else could be done, or that pilot training and aviation operation are adequate, and that bird strikes and Tsunamis just happen.

 

[Hiddencamper]

I grant that discussion of alternative action is often ill informed (and is in my case). But I disagree that discussions of alternatives are necessarily indulgence in fantasy. The better comparison to a decisive personality, if there must be be one, is Captain Sullenberger and the landing in the Hudson. The Hudson River is not another numbered FAA runway. If Sullenberger had instead stubbornly headed back to the (out of glide range) runway with no engine power because of FAA regulations I'd have little time for those saying he was only following the rules, that nothing else could be done, or that pilot training and aviation operation are adequate, and that bird strikes and Tsunamis just happen.

Some things to think about:

When an accident happens, you are forced to respond to the conditions you are presented with.

To quote the BWR Emergency Operating Procedures:

"The EOPs impose various limits within which continued safe operation of the
plant is ensured and beyond which certain actions may be required. While conservative,
these limits have been derived using best-estimate engineering analyses rather than
licensing models. Consequently, these limits are generally not as conservative as the
limits specified in the Technical Specifications and conformance with these
guidelines does not necessarily ensure strict conformance with Technical Specifications
or other licensing bases. This does not imply, however, that operation beyond Technical
Specification limits is recommended. Rather, such operation may be required, and is now
permitted, to mitigate certain degraded conditions."

In other words, you should not just violate your license or regulations simply because you are in an emergency, but you may be forced to operate there. This is essentially what happened with the flight that landed in the Hudson.

Also remember that both the FAA and the US NRC allow violation of license/regulations as necessary to safeguard the plant and public. Japan had no such provision to the best of my knowledge.

http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0054.html

"(x) A licensee may take reasonable action that departs from a license condition or a technical specification (contained in a license issued under this part) in an emergency when this action is immediately needed to protect the public health and safety and no action consistent with license conditions and technical specifications that can provide adequate or equivalent protection is immediately apparent.

(y) Licensee action permitted by paragraph (x) of this section shall be approved, as a minimum, by a licensed senior operator, or, at a nuclear power reactor facility for which the certifications required under § 50.82(a)(1) have been submitted, by either a licensed senior operator or a certified fuel handler, prior to taking the action."

When transients happen at a nuclear plant, if anything didn't happen exactly per procedure or per plant design, the operators on shift will all go before a body consisting of regulatory personnel, senators/congressmen, company officials, to answer questions and be held accountable for actions they took. If you followed all the words on your EOPs as they were designed to be followed the likelihood of being prosecuted for an accident is slim to none, UNLESS you had some definitive knowledge that following the EOPs would result in a further accident.

In other words, trying to suggest the operators intentionally violate their license, government regulations, and the EOPs is insane and somewhat dangerous. The EOPs, tech specs, and other accident management documents were made with large amounts of engineering, to minimize the potential for fission product barrier loss, extend the coping time for events, and anytime you knowingly violate those you are making an on the spot decision with far less info about why those documents were made that way in the first place during a high stress situation. It carries a very high potential for a human performance failure. Something to think about

Also, to this day, I can't see any reasonable action that would have ensured safety unit 1.

Side note:

Do we need to have a talk about BWR EOPs??

 

[Hiddencamper]

No *automatic* rupture, yes, but could the disc have been manually blown?

There's no manual blow for these rupture discs. Japan's policy was to vent as late as physically possible and that is why these rupture disc point is set as high as it is. They used a Sandia national labs study that the containment should retain integrity at twice the design pressure as the basis for their decision.

 

[mheslep]

There's no manual blow for these rupture discs. Japan's policy was to vent as late as physically possible and that is why these rupture disc point is set as high as it is. They used a Sandia national labs study that the containment should retain integrity at twice the design pressure as the basis for their decision.

By manual blow I meant either demolition explosives, or hydraulics, or cutting torches, or whatever external device might be required to force open the disc. Yes the *policy* was undoubtedly double pressure. I'm exploring the applicability of the policy under these LOCA circumstances, and particularly would venting have lessened the possibility of the later H2 explosion.

 

[etudiant]

There's no manual blow for these rupture discs. Japan's policy was to vent as late as physically possible and that is why these rupture disc point is set as high as it is. They used a Sandia national labs study that the containment should retain integrity at twice the design pressure as the basis for their decision.

Very interesting detail and illuminating as to Japanese policy. Sort of an all or nothing approach.
Against that, Jim Hardy's reference ( http://www.nrc.gov/docs/ML1012/ML101270372.pdf ) concludes with this punch line:

'if the operators would be able to open both pressurizer relief valves after the core heatup
starts, this would have positive effect on further progression of the severe accident.'

To me, that suggests the Japanese policy may possibly have helped make matters worse than they could have been.Separately, I can only say 'Amen' to hiddencampers sharp reminder that manuals and procedures exist for good reason. They exist to guide operators in real life.

Fortunately we here at PF have the opportunity to speculate more freely. Also, in the case of Fukushima, the results were so poor that we must reexamine whether there was any possibility of some action that would have lesser consequences.

So the issue facing the operators, paraphrased, is how to set the reactors to melt down as gracefully as possible, knowing there is only a few hours of battery power to monitor the process.