Fukushima Technical Discussion

[Pup]

Since the other thread fell victim to our seemingly bipolar moderating, let's see if we can't start anew - this time with neither nuclear promotion nor fear-mongering, and hopefully with no mention at all of shark fins, iPods, or Gaia.

Looking at the aerial of both the Fukushima Daiichi and Fukushina Daini sites, I might have spotted a now-obvious design fault. 20/20 hindsight and all that.

Here's the aerial view of Fukushima Daiichi...



I tried to locate the diesel generators that were taken out by the tsunami. Looking for a group of six generator-sized things for each reactor and assuming they aren't located inside a building, it looks like the best, perhaps only candidates are here, marked in red...



You can see a similar setup at it's sister reactor, Fukushima Daini. Here, reactor 1 has six units, marked in red, and each of the other reactors have 3 larger units each, marked in yellow - these look more like turbines to me, but they're placed in a similar location relative to the other reactors...



The first thing of note at both of these plants is that the generators are located on the seaward side, with some, but little protection from a tsunami event. Given the plants' location to the earthquake epicenter, the tsunami would have come from the NNE or NE, almost tangent to the shore. A smaller scale map shows how the tsunami would have hit Daiichi...



And Daini...



So it looks like a wave large enough to top the barriers would have had a fairly unobstructed path heading south along the road between the buildings, which of course is right where I think the generators are located.

A closer inspection reveals something even more interesting - take a look at the shadows of generators and the surrounding buildings at Daiichi...



And Daini...



As you can see, the pattern of shadows around the generators make them appear to be located within a pit. Of course if they are, there would be drainage but if those drains are insufficient then the pits could have easily filled with water - perhaps almost instantly, depending on the amount of water sent over the barriers. This would surely choke the generators with salt water and put them out of commission for good, which would explain why they couldn't be repaired.

I'll remind you that I'm making wild guesses here based on blurry photos. But it seems logical to me.

[autogyro]

Trying to protect generators in the face of a level 9 earthquake and then a large tsunami will be next to impossible.
The question is a simple one. Why were nuclear reactors built close to the Pacific ring of fire earthquake faults?

I keep being told that they built one of the spent fuel rod storage tanks on the roof of a reactor. Perhaps you can deny or confirm this?

I think the biggest question most people will have, is why all the pro nuclear people and nuclear so called experts are on record as saying that certain things cannot happen 'ever' and then they do happen.

I am afraid they have all lost their credibility and it is pointless arguing otherwise.

[Pup]

Yes, the spent fuel is tossed into a plastic kiddie pool on the roof. The pellets are used to start the BBQ and to fire the hot tub.

No, no - I kid. When the fuel rods are replaced, they are removed via the top of the reactor. They then place the pellets in an adjacent cooling pool. The fuel, while no longer usable in the reactor, is still too hot for safe transport, so they keep it on site for a period. Since they work from the top, the pool has to be accessible from the top. So it isn't on the roof as you say, but on the upper level. It's part of the reinforced concrete structure. You can read more about it here...

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

And you can see the location of the pool in this (mislabeled) diagram...

[Richard]

Pup - Generators are normally surrounded by a bund to catch fuel spillages.

Autogyro - that's not a technical posting

[Pup]

Richard, those wouldn't be that deep though, would they? Judging by the size of the shadows within the wells, they appear to be quite deep. I wish we had a better photo to judge.

Sticking to the cooling pools, I'm wondering if the quake caused some of the spent fuel in the tanks of the offline reactors to move and get close enough together to start reacting. That would explain the increased temperatures that have been reported.

[WhiteBlue]

I agree that the general design of the Fukushima plant is showing a bad design compromise compared to Californian reactors. With good planning the reactors are build at 30 m above sea level to avoid flooding of ancillaries by tsunamis. There is also a big water reserve basin missing with a location above the actual plant which would make it possible to bring water by gravity feed to all parts of the plant.

The US arrangement means that you have to pump up all the sea water for the cooling circuits to a higher location above sea level which is costly. But the US design is inherently much safer. As Pup pointed out the Fukushima emergency generators could have been positioned behind the reactors on the land side. Or they could have been positioned on a sturdy concrete platform 25-30 m above sea level with a catch pool underneath for diesel fuel. Unfortunately all those options were not used.

[marekk]

They'll designed the site to whitstand 8 degree earthquake and resulting wave hight of 6,0 m. Added some 5% safety margin. But it was 9 degree and 7-8 m.
It's a sort of thinking i know from my hometown: there was never flooding in this area as far as we know, so let us build nice settlement near this beatifull river.
And one year you look at hundreds of buildings flodded up to third floor. For weeks, because there is a flood levee preventing water from going back.

[WhiteBlue]

My view is that you have to look at true worst case scenarios when you deal with nuclear risks. It means you look at the biggest known earth quakes and tsunamis and not at the biggest known on your particular fault line if you are building in seismic active areas. It also means you have to build domes over the reactors and the fuel ponds that withstand the impact of a fully loaded biggest wide body aircraft known at that time. Everything else is not good enough.

[marekk]

Found both sites on google earth and this placement of diesels just makes no sens to me.
If we can trust google's elevation, diesels/generators are at 10-11m, reactor buildings at 19-20. There is even big water reserve basin at 48m on daini site.
But there is no real anti-tsunami wall on either site.
A few km south of daini there's a big gas/oil instalation, at first look tepco's one - just on the shore, maybe 3-4 m above sea level.
Doesn't look as they'll thinked about tsunamis at all.

[WhiteBlue]

http://www.pbs.org/newshour/bb/weather/ ... 03-15.html Some expert thoughts.

Some thoughts about the assumptions and the risk management you ought to make for nuke plants in the future

http://www.bbc.co.uk/news/science-environment-12740649

About 10 years ago, a team led by Professor Koji Minoura, from Japan's Tohoku University, analysed sediments from the Sendai and Soma coastal plains that preserved traces of the tsunami in 869. Their results indicated that the medieval tsunami was probably triggered by a Magnitude 8.3 offshore quake and that waters spread more than 4km from the shore.
Start Quote: "It can also be dangerous to plan on past events only - even in Japan where the record is long, it might still not be long enough” End Quote (Hermann Fritz Georgia Tech University)
They also found evidence of two earlier tsunamis on the scale of the Jogan disaster, leading them to conclude that there had been three massive events in the last 3,000 years.

The scientific community in Japan had positive knowledge for at least 10 years that the tsunami assumptions and nuclear plant requirements in the 70's had been faulty. One has to ask the question why this intelligence hasn't lead to a review of the guide lines and positive risk management of the Japanese nuclear industry. There is a simple principle to all risk management. You have to close the loop and run through it consistently:

• periodically research and update risk intelligence
• conduct FMEA with the experts for design and operation
• identify action items
• assign responsibility for action
• check in much shorter loop that items are properly actioned

I reckon that sometime soon people will ask questions why there was no risk management or why it did not lead to actions that would have prevented the Fukushima accidents.

The report, which I linked clearly points out that the paleoseismologists from Professor Minoura's team traced the tsunamis for more than 4 km inland by taking drilling probes and analysing sediments. That way you can exactly confirm how high the tsunami waves were. They even predicted that the last big one had been triggered by a quake of a magnitude of at least 8.4 on the Richter scale. The discovery that the big tsunamis could even be predicted with a period of every 1000 years puts a clear and computable probability to the event. Such risk probability cannot be ignored. You cannot ignore existing data and claim that you are doing responsible risk management at the same time.

The responsible people like IAEA Director of Nuclear Power, professor Akira Omoto of the Tokyo University were tasked with such risk assessment and analysed for instance the lessons learned from the 2004 tsunami catastrophe in the Indian ocean. Secondary source because IAEA blocks original URL Prof. Omoto is a doctor of engineering and is the scientific advisor of Tepco, the owner of the Fukushima plant. He was also involved in the design of the Fukushima plant. Source He positively knew about the Indian NPP that had been inundated in 2004 by a 10 m high tsunami wave because he visited the site.

"There are scores of nuclear power plants operating in coastal areas and some of these may need to take a renewed look at this external hazard," IAEA Director of Nuclear Power, Mr. Akira Omoto said. "It is also true for plants presently under construction." It is common for nuclear power plants to be built in coastal areas, drawing the seawater to cool the reactor.

Specialists from around the world will scrutinize the potential impact of natural disasters on nuclear reactors, at the IAEA organized International Workshop on External Flooding Hazards at Nuclear Power Plant Sites. From 29 August - 2 September 2005 the world´s nuclear community will gather at the Kalpakkam nuclear complex to share latest knowledge and research developments and take home lessons learned, from this tsunami, and past flood events.

The IAEA has stringent safety standards designed to guard nuclear power plants against natural calamities like earthquakes, volcanoes, flooding, tsunamis and cyclones. The non-legally binding guidelines cover site and design requirements for nuclear reactors, as well as appropriate monitoring and warning systems.

In 2005 Professor Koji Minoura's findings had been published for four years. You can download it here since 2001. The results should have been considered by the IAEA and Tepco in a necessary re evaluation of the Fukushima safety and risk analysis. In the six years since 2005 the generators could have been re located at moderate cost. This has not happened and the Japanese public should ask their scientific, political and corporate leaders why they have failed them so miserably.

The actions taken in the USA are a good example of how the authorities reacted to the scientific advances in tsunami research. In May 2007 a comprehensive paper (Gutierrez report) Scientific and technical issues in tsunami hazard assessment of nuclear power plant sites. was published by the US NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA) that allowed prediction of tsunami consequences with scientific models. It led to the subsequent assessment of all American sites in just a few years. The complete work was finished in 2008.



In 2009 the U.S. Nuclear Regulatory Commission issued the paper Tsunami Hazard Assessment at Nuclear Power Plant Sites in the United States of America which is largely based on the Gutierrez report and makes the the scientific approach mandatory for the USA. Why did the Japanese experts at TEPCO and the Japanese regulatory bodies disregard the mountain of evidence that the 70's tsunami protection standards of Fukushima were totally inadequate?

[manchild]

Japan warned in 2008 over nuclear plant safety, says report

Mar 16, 2011, 11:02 GMT

London - Japan was warned in 2008 by the international nuclear watchdog that its nuclear power plants were not capable of withstanding powerful earthquakes, US diplomatic cables obtained by WikiLeaks were reported to show Wednesday.

According to the cable, an official from the International Atomic Energy Agency (IAEA) said in December 2008 that safety rules were out of date and strong earthquakes would pose a 'serious problem' for nuclear power stations, the Daily Telegraph said.

The concerns were raised during a meeting of the Nuclear Safety and Security Group of the Group of Eight (G8) nations in Tokyo in 2008.

The cable states: 'He [the IAEA official] explained that safety guides for seismic safety have only been revised three times in the last 35 years and that the IAEA is now re-examining them.'

'Also, the presenter noted recent earthquakes in some cases have exceeded the design basis for some nuclear plants, and that this is a serious problem that is now driving seismic safety work.'

The cables also disclosed how the Japanese government opposed a court order to shut down another nuclear power plant in western Japan because of concerns it could not withstand powerful earthquakes, according to the Daily Telegraph.

© Deutsche Presse-Agentur

[WhiteBlue]

http://www3.nhk.or.jp/daily/english/16_41.html

SDF gives up on dousing No.3 reactor

Japan's Self-Defense Forces have postponed a mission to dump water by helicopter on the No.3 reactor at Fukushima Daiichi nuclear plant, because radiation above the facility has climbed too high for such work.

White plumes started rising from the reactor on Wednesday morning. Tokyo Electric Power Company says the vapor was steam caused by water evaporating from the reactor's storage pool for spent fuel rods, which is heating up.

In an effort to avert the fuel rods' exposure, a Self Defense Force CH47 helicopter took off from the Sendai base hauling a large container of water on Wednesday afternoon.



But the plan was aborted after radiation levels above the plant were found to have largely exceeded 50 millisieverts -- the maximum permissible for SDF personnel on a mission.

The Self-Defense Forces say it is ready to recommence work when radiation levels and other conditions allow.

Wednesday, March 16, 2011 19:06 +0900 (JST)

http://www3.nhk.or.jp/daily/english/16_35.html

TEPCO Nuclear Plant woes

Here's what has happened so far on Wednesday at the Fukushima Daiichi Nuclear Power Station.

At around 5:45 AM, a Tokyo Electric Power Company, or TEPCO, employee noticed flames coming out of the Number Four reactor building. The power company says the flames were not visible half an hour later.

The fire occurred at almost the same place where a blaze erupted Tuesday morning. TEPCO had said that fire died out by itself.

Wednesday's fire occurred where two 8-square-meter holes could be seen on the building's outer wall on Tuesday.

The cause of the fire has not been determined. The fire may be linked to the temperature rise in the pool for spent fuels.

Shortly before 10:00 AM, an NHK helicopter caught footage of what appeared to be white smoke rising from the nuclear power station. The footage showed the smoke rising intermittently. The helicopter was flying more than 30 kilometers away from the site.

TEPCO told reporters that the smoke appeared to be steam coming out of the Number Three reactor building. The steam could indicate that water in the pool is vaporizing. If that is the case it would mean that the cooling system for the pool, which contains 514 spent fuel rods, is not working.

At the Number Two reactor, where the suppression pool was found to be damaged on Tuesday, the likelihood of a radiation leak grew stronger on Wednesday.

The suppression pool is designed to work as a reactor's pressure control system.

The Nuclear and Industrial Safety Agency said the radiation level near the power station's main entrance spiked to 10 millisieverts per hour at around10:40 AM.

The safety agency cited reports from TEPCO that damage to the suppression pool at the Number Two reactor may responsible for the rise in the radiation level.

The company evacuated its workers to safety as soon as it detected a surge in the radiation level near the plant's main entrance.

The evacuation order was lifted less than an hour later, as the radiation level dropped.

Wednesday, March 16, 2011 17:19 +0900 (JST)

http://www3.nhk.or.jp/daily/english/16_36.html

High radiation levels detected 20 km. from plant

Japan's science ministry has observed radiation levels of up to 0.33 millisieverts per hour in areas about 20 kilometers northwest of the quake-damaged Fukushima Daiichi nuclear power plant.

Experts say exposure to such radiation for 3 hours would result in absorption of 1 millisievert, or the maximum considered safe for 1 year.

The ministry gauged radiation levels for 10 minutes from 8:40 PM local time on Tuesday at 3 places in Fukushima Prefecture, whose residents are being instructed to stay indoors. The measurements produced readings as low as 0.22 millisieverts per hour.

It is not known whether these levels have changed since the measurements.
A former chief of the Radiation Effects Research Foundation, Shigenobu Nagataki, said radiation at such levels does not immediately affect human health. But he said that if such levels continue to be observed, authorities must review ways to evacuate people.

The ministry said it also observed maximum radiation levels of 0.0253 millisieverts in areas 30 to 60 kilometers from the plant on Wednesday morning. The levels are slightly higher than normal.

Wednesday, March 16, 2011 17:58 +0900 (JST)

Today's situation is critical in my view. The last information yesterday about on site radiation levels was 30-400 mSv/h. Now we learn this morning that a 50 mSv/h limit of the Japanese Airforce is largely exceeded. That leads to the assumption that radiation levels on site are in excess of 100 mSv/h over the hottest spots.

The fuel storage pools of several reactors become the biggest concerns now because they all hold potentially hundreds of tons of highly radioactive nuclear waste from 4-6 years of operations. One must assume that the small group of 50 workers with water trucks and mobile pumps will not be able to keep the six ponds and unknown damaged reactors cool. The site is likely to contain 4,000 tons of high radioactive waste all together. If the radiation levels become too hight to allow active work on site the consequences are potentially very grave.

The good news at the moment is that the wind blows the substantial radiation out towards the sea where no immediate exposure for Japan is threatened. Of course that is not so good news for the fishery but that may be of secondary concern right now.

The report of 0.33 mSv/h maximum radiation at 20 km distance from the plant is very sobering. The evacuation zone seems to be too small if such radiation is measured on its edge.

One hopes that the wind stays constant in order for the radioactive cloud to stay away from the Japanese mainland and more than 30 million people in Tokyo. It is scary to think that the people's safety now depends of the wind direction. Japan is walking a very tight rope atm.

[Dragonfly]

I have a question to the more educated on this matter.
In case of a total melt-down of the core - nuclear fuel, rods, etc. will there be some kind of chain reaction or just a mess of highly radioactive melted mass, which will eventually cool down for a given period of time.

[Pup]

I have a question to the more educated on this matter.
In case of a total melt-down of the core - nuclear fuel, rods, etc. will there be some kind of chain reaction or just a mess of highly radioactive melted mass, which will eventually cool down for a given period of time.

Just a mess, and perhaps not even much of a mess. To remove the burned fuel, they just take out the whole pressure vessel intact after it has cooled - all the fuel is contained inside. At Three Mile Island, for example, the core melted, but was removed without any problems or exposure. Large-scale problems only occur if there is an explosion inside the pressure vessel which ruptures the vessel and sends the fuel flying. That's what happened at Chernobyl, and only happened because they didn't have the safety features that are in place at Fukushima, and didn't react properly to the incident. They also purposefully created a worst-case scenario to begin with, but that's a different discussion. I understand that at Fukushima, the reactor 1 core is about 70% melted, and #3 about 30%.

We have learned that the reason there are problems at reactors 4-6 is that they had just shut them down and were in the process of removing the fuel. That fuel was being placed in the pools as it was removed. They had completed the removal of the #4 fuel, which is why that pool is heating up the fastest.

We can assume that the pool of unit 4 is boiling, since there is steam. We can also assume that they are not too concerned about the problem since they called off the helicopter. In the US, at least, exposure limits for emergency work is 250mSv - 750mSv in life-saving work. So 50mSv isn't prohibitive and therefore they must be thinking they can handle the situation with a slower, but safer method. Keep in mind that the steam cloud where the helicopter would have to hover is the most radioactive area of the plant.

That said, the pools at this point are potentially far more dangerous than the reactors. The fuel in the pools aren't in a sealed containment like the reactors, so if the water did boil off and the fuel heated to the point of burning, it would release harmful, long-lasting radiation. Not as bad as a Chernobyl event, but let's just say that it's nothing you'd want to happen. But there's no indication yet that this is a real possibility. At the moment, though, that has become the worst-case scenario.

[marekk]

I have a question to the more educated on this matter.
In case of a total melt-down of the core - nuclear fuel, rods, etc. will there be some kind of chain reaction or just a mess of highly radioactive melted mass, which will eventually cool down for a given period of time.

AFAIK there will be no nuclear explosion involving bigger amounts of fissionable material. It's not that easy to make a nuclear bomb - to low density, to low concentration of "weapon grade" material, to many plutonium-240.
Rather "conventional" explosion (high pressure + hydrogen) - basically contained in this evacuated 20-30 km radius area.