Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[gmax137]

Does anyone have any reliable info on the nuclear plants - the reports on the news seem garbled to me.


Edit by Borek:

To All:

Please stick to technical aspects and to things happening at the Fukushima Daiichi NPP.

There are several other threads discussing different aspects of the disaster:

Why is Fukushima nuclear crisis so threatening?

Fukushima radiation detection and measurement

The "more political thread" besides "Japan Earthquake: nuclear plants" scientific one

Japan earthquake - contamination & consequences outside Fukushima NPP

 

[Astronuc]

Unless one has direct contact from someone in the plant, the best one can do is the releases by TEPCO or METI, but METI is probably getting it second hand. I haven't seen any official releases from METI though.

TEPCO press releases

http://www.tepco.co.jp/en/index-e.html

http://www.tepco.co.jp/en/press/corp-com/release/11031103-e.html
http://www.tepco.co.jp/en/press/corp-com/release/11031104-e.html


WNN - http://www.world-nuclear-news.org/RS_Massive_earthquake_hits_Japan_1103111.html

IAEA - http://www.iaea.org/newscenter/news/2011/tsunamiupdate.html

WANO is behind the curve.


I have not found any direct press release from METI, but
Fukushima reactor pressure may have hit 2.1 times capacity: METI
http://www.reuters.com/article/2011/03/11/us-japan-quake-tepco-pressure-idUSTRE72A7DB20110311

Woah - not good. That's a big NO-NO.

Problems at a second unit

TEPCO: loses control of pressure at 2nd nuclear plant
http://www.reuters.com/article/2011/03/11/us-japan-quake-tepco-daini-idUSTRE72A8GM20110311

If this is true, I can see a lot of managers getting sacked.

And there is this AP article on Yahoo - http://finance.yahoo.com/news/Japan-quake-causes-apf-1121920057.html?x=0

 

[DR13]

Is there any real chance at a meltdown or is that just the typical media hype?

 

[Astronuc]

At the moment, I don't see a 'real' chance of a meltdown. It is a worst case scenario, which is what licensing space is all about.

Some of the worst case scenarios involve extraordinary, and not necessarily physical real situations. It's a bit like crash testing a car by dropping it out of an airplane at several thousand feet, knowing full well that such a car would never be able to achieve such a velocity on level ground since the engine could not achieve the speed or the tires would blow out well before the speed could be achieved.

Some in the media will sensationalize the situation in order to grab the audience in order to sell commercials for useless stuff. But I digress.

I'd like to keep the discussion here on the technical aspects - as soon as we learn from reliable sources.

We have the earthquake thread in P&WA.

 

[DR13]

I'd like to keep the discussion here on the technical aspects - as soon as we learn from reliable sources.

Ok. This question is pretty 'elementary' but I do not know much about how a NPP works. I read an http://news.yahoo.com/s/nm/20110311/pl_nm/us_japan_quake_nuclear_clinton" that said that the US delivered coolant to Japan. Why does Japan need the coolant? I don't understand how an earthquake and a tsunami can make a NPP lose its coolant? Also, what specific purpose does the coolant serve in the plant (what exactly does it cool) and what would happen if Japan could not get more coolant?

 

[Astronuc]

Ok. This question is pretty 'elementary' but I do not know much about how a NPP works. I read an http://news.yahoo.com/s/nm/20110311/pl_nm/us_japan_quake_nuclear_clinton" that said that the US delivered coolant to Japan. Why does Japan need the coolant? I don't understand how an earthquake and a tsunami can make a NPP lose its coolant? Also, what specific purpose does the coolant serve in the plant (what exactly does it cool) and what would happen if Japan could not get more coolant?

There was some miscommunication. I'm not sure who said what to whom, but apparently Sec of State Clinton mentioned coolant was being flown to Japan. That is incorrect.

They might airlift some generators, but I have not heard any details.

A light water reactor (LWR) uses water coolant under pressure to both moderate the neutrons and cool the nuclear fuel. The Fukushima units are boiling water reactors (BWRs), in which the water is boiled in the core at a pressure of ~1055 psia at Tsat ~ 286 C. The steam is sent directly to a high pressure turbine, and then the exhaust of the high pressure turbine feeds a set of low pressure turbines. The units are about 33% efficient, so about 67% of the heat is rejected through condensers to the environment, which at Fukushima is the sea.

When the reactor shutdowns, there is still some heat being generated from the decaying fission products. "At the moment of reactor shutdown, decay heat will be about 7% of the previous core power if the reactor has had a long and steady power history. About 1 hour after shutdown, the decay heat will be about 1.5% of the previous core power. After a day, the decay heat falls to 0.4%, and after a week it will be only 0.2%." Ref: http://en.wikipedia.org/wiki/Decay_heat#Power_reactors_in_shutdown

So it is important to cool the reactor for several days following shutdown.

The reactor core isolation cooling (RCIC) system in a boiling water reactor (BWR) is a safety system which serves as a standby source of cooling water to provide a limited decay heat removal capability whenever the main feedwater system is isolated from the reactor vessel.

The RCIC requires power from off-site or emergency diesel generators. Well the plant lost off-site power. The EDGs worked for about 1 hour then stopped. Now plant personnel are trying to get power from some other source. It's not clear why the EDGs quit, but they are supposed to work for days.

5.4.6 REACTOR CORE ISOLATION COOLING SYSTEM (BWR)

 

[DR13]

Ok. Thank you for all of the information. Hopefully they can get the problems resolved soon.

 

[aquitaine]

So the coolant system was knocked out, can't they scram the reactor?

 

[Hologram0110]

So the coolant system was knocked out, can't they scram the reactor?

The reactor is off but keeps producing heat has radioactive isotopes decay. Basically when it is on it produces a heat and radioactive isotopes which decay to more stable isotopes and give off more heat in the process. You can't turn this second process off, it just keeps going. The amount of heat the second process gives off goes down over time. However that means you have to keep cooling it for a number of days otherwise it would melt into a pile of radioactive goo (and take your expensive reactor with it).

 

[aquitaine]

So it's already off and won't explode? Cool, thanks.

 

[QuantumPion]

It looks like the containment building has exploded. My educated guess is, what they feared might happen at TMI has happened here. The core melted down, releasing lots of hydrogen gas in the chemical reaction with the cladding, which then ignited.

[PLAIN]http://img855.imageshack.us/img855/1472/20mai00383969.gif

 

[Pengwuino]

Is it safe to assume the winds go towards the Pacific Ocean at the site? In case of an exposed meltdown?

 

[Astronuc]

At the time of the explosion, the wind was apparently moving toward the northeast, so any vapor would be carried out to sea.

However, I understand that the building where the explosion has occurred is not associated with containment, but I have not been able to verify this.

From World Nuclear News -
http://www.world-nuclear-news.org/RS_Battle_to_stabilise_earthquake_reactors_1203111.html

Tepco has said that the pressure within the containment of Fukushima Daiichi 1 has reached around 840 kPa, compared to reference levels of 400 kPa.

So pressure in containment is about 8.4 atm rather the 4 atm, the nominal design pressure.

and

Television cameras trained on the plant caputured a dramatic explosion surrounding unit 1 at around 6pm. Amid a visible pressure release and a cloud of dust it was not possible to know the extent of the damage. The external building structure does not act as the containment, which is an airtight engineered boundary within. The status of the containment is not yet known.

and meanwhile at the plant next door, Fukushima Daiini (plant 2)

Unit 1's reactor core isolation cooling system had been operating normally, and this was later supplemented by a separate make-up water condensate system. However, the latter was lost at 5.32am local time when its suppression chamber reached 100ºC. This led Tepco to notify government of another technical emergency situation.

The situation is serious. What has happened, shouldn't have happened.

 

[caffenta]

However, I understand that the building where the explosion has occurred is not associated with containment, but I have not been able to verify this.

A TEPCO spokesperson made a statement on Japanese TV about 20 minutes ago. The explosion was supposedly from a buildup of hydrogen around the containment vessel. Apparently, they will flood the containment vessel with seawater (and boric acid?) Does that make sense? They also increased the evacuation zone to 20km. The reporters present didn't seem to like the contradiction of TEPCO's claim that everything was still safe and the expansion of the evacuation zone.

Caveat: my Japanese is not so great, so I may have misunderstood some of it.

EDIT: after checking online, looks like I got most of it right, but it was a government official, not a TEPCO spokesperson

 

[vanesch]

I have to say I don't understand how you can have a hydrogen explosion blowing apart the confinement building, and not the reactor vessel.

I also don't understand how you can let any pressure build up in the confinement building at the risk of rupture if it is slowly. One should prefer steam releases (even contaminated) in order to ensure the integrity of the confinement building if ever the reactor vessel breaks, no ? Now we are not very far from a full release of the core in the environment.

 

[DrDu]

I tried to consult the japanese dose rate surveillance site, but it appears they don't have information for the northern prefectures:
http://www.bousai.ne.jp/eng/

I don't know how they transmit their measurements, supposedly via internet. Did the internet break down completely in the northern part of japan?

 

[Astronuc]

A TEPCO spokesperson made a statement on Japanese TV about 20 minutes ago. The explosion was supposedly from a buildup of hydrogen around the containment vessel. Apparently, they will flood the containment vessel with seawater (and boric acid?) Does that make sense? They also increased the evacuation zone to 20km. The reporters present didn't seem to like the contradiction of TEPCO's claim that everything was still safe and the expansion of the evacuation zone.

Caveat: my Japanese is not so great, so I may have misunderstood some of it.

I have read much the same in English. So far, I have heard conflicting claims - that the explosion was / was not the containment building. I'd have to find a map of the site to figure out if the explosion was near unit 1 or 4. Unit 1 has the most severe problem, while unit 4 was shutdown cold already. From the picture, it looked like the explosion was near unit 4.

See this article - http://mdn.mainichi.jp/mdnnews/news/20110312p2g00m0dm073000c.html

If the containment is breached with an uncooled reactor, that is very serious.

I have heard that Chief Cabinet Secretary Yukio Edano mentioned cooling unit 1 with seawater, but I don't know where he is getting the information.

Cooling directly with seawater would be a drastic step.

The news from the area is rather sketchy.

 

[caffenta]

The articles are just popping up on Japanese pages. The latest may not be translated to English yet. Every Japanese channel has been showing explanations about the containment vessel and the seawater insertion, so I guess they are going to do it.

 

[Reno Deano]

More than like the explosion was within the Off-gas system external to the reactor building and below the off-gas vent towers you see. Primarily due to radiolytic hydrogen build-up. Radiation level increases would be due to premature release of radioactive noble gases (Ze, K, I whcih are normal held up for decay).

 

[Reno Deano]

The suppression chamber at 100 C appears to be within or at the limit of DBA parimeters. It is doing what it is supposed to do cool the water and provide cooling water to the LPCIS. The steam driven HPISs are probably out due to lack of vaible carry over steam in the system. If the diesel generators went south then the LPCIS will be failling.

 

[Reno Deano]

BTW, 1,000 times increase in radiation levels is not that serious, in that the baseline measurement point is background levels in the control rooms and environment. This results in about 50-100 mrem in control room and 30 mrem immediately external to the plant out to the licensee controlled perimeter. Airborne doses to K, Ze, I would be measurable, but a very small portion of allowed emergency doses.

 

[Reno Deano]

The reactor in question is I believe a BWR 4 GE designed unit. This model is over 40 years old and use less robust safety system that more modern BWRs use.

 

[ferrelhadley]

More than like the explosion was within the Off-gas system external to the reactor building and below the off-gas vent towers you see. Primarily due to radiolytic hydrogen build-up. Radiation level increases would be due to premature release of radioactive noble gases (Ze, K, I whcih are normal held up for decay).

Others I have heard a suggesting the hydrogen many have been used in the generator as a lubricant which is housed near the reactor. Any coment on that?

 

[Astronuc]

Others I have heard a suggesting the hydrogen many have been used in the generator as a lubricant which is housed near the reactor. Any coment on that?

Hydrogen is used to cool generators. Hydrogen gas has good thermal conductivity and low viscosity. The generator is housed in the auxilliary building or turbine hall, which is adjacent to the containment. The generator is not housed near the reactor.

Steam from the reactor is passed in steam lines (massive pipes) to the turbines, and the turbines drive the generator.

 

[DR13]

Here is a link to some expert testimony:

http://news.yahoo.com/s/nm/20110312/ts_nm/us_japan_quake_experts

They seem to think that everything is under control.

 

[Astronuc]

The best statement:

"We don't have any information from inside the plant. That is the problem in this case.

Otherwise, everyone outside is simply speculating.

 

[Waxbear]

They certainly are cautious with public announcements.

http://www.tepco.co.jp/en/press/corp-com/release/11031225-e.html

"Today at approximately 3:36PM, a big quake occurred and there was a big
sound around the Unit 1 and white smoke."

otherwise known as an explosion...

and here:

http://www.tepco.co.jp/en/press/corp-com/release/11031224-e.html

this update is called "occurence of a specific incident stipulated in article 15, clause 1 of the act on special measures concerning nuclear emergency preaparedness"

if you look up article 15, clause 1 in said document you can see that the title of the update basically translates to "occurence of abnormally elevated radiation levels".

 

[oldsloguy]

BTW, 1,000 times increase in radiation levels is not that serious, in that the baseline measurement point is background levels in the control rooms and environment. This results in about 50-100 mrem in control room and 30 mrem immediately external to the plant out to the licensee controlled perimeter. Airborne doses to K, Ze, I would be measurable, but a very small portion of allowed emergency doses.

Something I don't understand. How would you get K, Ze & I out of the core without melting part of the fuel?

 

[QuantumPion]

From what I understand, this type of BWR has instead of a strong outer concrete containment like PWR's have, it has a smaller steel containment dome around the reactor pressure vessel, and a weaker outer containment building. So it is possible that the hydrogen was released from the inner containment, and then blew up the outer containment, but leaving the reactor more or less in tact. However, reports I read indicate they are detecting cesium and iodine in the vicinity, indicative of core damage and release.

The story also said dose rates were 1500 micro Sv/hour 5km away from the plant around the time of the explosion (150 mrem/hr). Far above background levels, but not a health hazard. The situation may have changed since last night though.

 

[QuantumPion]

Hydrogen is used to cool generators. Hydrogen gas has good thermal conductivity and low viscosity. The generator is housed in the auxilliary building or turbine hall, which is adjacent to the containment. The generator is not housed near the reactor.

Steam from the reactor is passed in steam lines (massive pipes) to the turbines, and the turbines drive the generator.

I doubt there is enough hydrogen in the generator to create an explosion that big, especially since it is not contained in a pressurized container. The pictures clearly show the containment building exploding, and there is a visible fireball with the shockwave.

 

[jumpjack]

Are satellites able to detect if the core is melting/melted?
i.e., are they capable of detecting a 2000°C temperature difference in an 2x2 meters area?
What kind of satellite should they be? Standard meteo satellites, or secret military atomic-detonation-detector satellites?

 

[jumpjack]

Could these image be used to monitor the meltdown?!?
http://webpanda.iis.u-tokyo.ac.jp/IIS/L1B/
http://www.nodc.noaa.gov/dsdt/cw/

 

[Astronuc]

Something I don't understand. How would you get Kr, Xe & I out of the core without melting part of the fuel?

If there was some corrosion of the cladding, or the fuel rods overheated, then the softer cladding balloon to the point of perforation. That is not core melting, and in general, core melting is something of a misnomer.

It's not clear what temperatures are reached in the core - whether the cladding got to 100 deg C or 1000 or more, or somewhere in between. While there is water boiling, then the cladding temperature is near the saturation temperature of the boiling water - at 4 atm or 8 atm or whatever the ambient pressure is.

In the steam region, the temperature would be higher because of the poor heat transfer in the steam, especially without forced convection.

One only needs a small breach in the cladding to release Xe, Kr and a little I. Iodine is water soluble, and it is more likely in the coolant.

An infrared thermometer could be used to gauge the temperature of the exposed drywell and inner containment.

 

[Reno Deano]

Something I don't understand. How would you get K, Ze & I out of the core without melting part of the fuel?

Excerpt: 3.1.3 Release of Fission Products from Fuel Contaminant
Even though the reactor core may contain no defective fuel, natural uranium contamination of core construction materials and Zircaloy cladding, as well as enriched uranium contamination of the external cladding surfaces, could be the source of fission products in the coolant during power operations. The recoil range of a fission product is approximately 10 microns; therefore, only the fissions that occur within ≈10 microns of the outer surface of the Zircaloy cladding can introduce fission products into the coolant. It is safe to assume that half of the recoils from the fissioning nuclei will escape to the coolant and the other half will be embedded in the host material.

More Info: http://www.nap.edu/openbook.php?record_id=9263&page=35 [/url

 

[alxm]

I have read much the same in English. So far, I have heard conflicting claims - that the explosion was / was not the containment building. I'd have to find a map of the site to figure out if the explosion was near unit 1 or 4.

NHK English is currently reporting that the hydrogen explosion didn't rupture the containment vessel. (Albeit the outer wall of the building) From what I know of these things, that's pretty much where it would be expected to happen - given that they try to vent the steam 'under the dome' rather than to the outside?

I have heard that Chief Cabinet Secretary Yukio Edano mentioned cooling unit 1 with seawater, but I don't know where he is getting the information.

Cooling directly with seawater would be a drastic step.

Drastic mostly in terms of radiation leakage, then? I mean, I doubt they have much concern for the reactor itself at this point.
They were due to be decommissioned soon even without this disaster, so I think it's safe to say these reactors will never go critical again.

 

[Astronuc]

NHK English is currently reporting that the hydrogen explosion didn't rupture the containment vessel. (Albeit the outer wall of the building) From what I know of these things, that's pretty much where it would be expected to happen - given that they try to vent the steam 'under the dome' rather than to the outside?

The upper level of containment, the metal walls and roof, was destroyed. That structure is over the inner containment, which is reinforced concrete. I believe the reinforced containment had the pressure increase, which was vented. The venting would be through those stacks (towers) that one sees behind (to the west of) the units. Venting into the upper containment would not be the case as far as I know.

Drastic mostly in terms of radiation leakage, then? I mean, I doubt they have much concern for the reactor itself at this point. They were due to be decommissioned soon even without this disaster, so I think it's safe to say these reactors will never go critical again.

Drastic in the sense that seawater would not normally be introduced directly into the core. Salt water would corrode the stainless steel in the core. It's probably safe to say that unit 1 will not be restarted, but decommissioned. In theory though, it's life could have been extended another 20 years.

 

[oldsloguy]

Excerpt: 3.1.3 Release of Fission Products from Fuel Contaminant
Even though the reactor core may contain no defective fuel, natural uranium contamination of core construction materials and Zircaloy cladding, as well as enriched uranium contamination of the external cladding surfaces, could be the source of fission products in the coolant during power operations. The recoil range of a fission product is approximately 10 microns; therefore, only the fissions that occur within ≈10 microns of the outer surface of the Zircaloy cladding can introduce fission products into the coolant. It is safe to assume that half of the recoils from the fissioning nuclei will escape to the coolant and the other half will be embedded in the host material.

More Info: http://www.nap.edu/openbook.php?record_id=9263&page=35 [/url

If there was some corrosion of the cladding, or the fuel rods overheated, then the softer cladding balloon to the point of perforation. That is not core melting, and in general, core melting is something of a misnomer.

It's not clear what temperatures are reached in the core - whether the cladding got to 100 deg C or 1000 or more, or somewhere in between. While there is water boiling, then the cladding temperature is near the saturation temperature of the boiling water - at 4 atm or 8 atm or whatever the ambient pressure is.

In the steam region, the temperature would be higher because of the poor heat transfer in the steam, especially without forced convection.

One only needs a small breach in the cladding to release Xe, Kr and a little I. Iodine is water soluble, and it is more likely in the coolant.

An infrared thermometer could be used to gauge the temperature of the exposed drywell and inner containment.

Thanks, very interesting, that would explain why releases are observed but small.

When you say, “core melting is something of a misnomer“ are you meaning to imply that as a practical matter it would be difficult to actually achieve temperatures high enough to melt the fuel pellets? If so, does that mean that even in the worst case, release of fission products to the outside world would be pretty much limited to minor amounts due to the pellets remaining solid and thus sequestering the fission products? Can the noble gasses diffuse out of the pellets at rates what would be of any practical significance?

 

[DR13]

I'm too tired to summarize this but here is a link to the ANS updates:

http://ansnuclearcafe.org/

and a summary from ANS:

https://docs.google.com/viewer?a=v&...afe&zw&sig=AHIEtbTSEJaTJdTCiS0dp5Q2I04CnmM-aQ

 

[vanesch]

Drastic in the sense that seawater would not normally be introduced directly into the core. Salt water would corrode the stainless steel in the core. It's probably safe to say that unit 1 will not be restarted, but decommissioned. In theory though, it's life could have been extended another 20 years.

Maybe they will extend its life as the very first BSWR: Boiling Sea Water Reactor

 

[marwood]

update from WNN at
http://www.world-nuclear-news.org/RS_Venting_at_Fukushima_Daiichi_3_1303111.html

 

[FlyingEng]

How strong might be the impact to all the new builds? Does this influence OL3 and all the Chinese reactors? China planned to pour the concrete for the 1st commercial HTR end of this month... Maybe a delay?

Speculations only? What are your thoughts about it? Is there the next nuclear winter coming up soon?

FE

 

[FishmanGeertz]

I certainly hope it wasn't the reactor vessel itself that exploded...

 

[DrDu]

How strong might be the impact to all the new builds? Does this influence OL3 and all the Chinese reactors? China planned to pour the concrete for the 1st commercial HTR end of this month... Maybe a delay?

Speculations only? What are your thoughts about it? Is there the next nuclear winter coming up soon?

FE

Well, at least the German government announced to stop the use of nuclear technology after the events although they wanted before to prolong the time older reactors could still be used.

 

[Angry Citizen]

Well, at least the German government announced to stop the use of nuclear technology after the events although they wanted before to prolong the time older reactors could still be used.

A shame, because this is shaping up to be a textbook example of nuclear safety. Most of the backups and emergency procedures failed, yet it looks like little radiation has been or will be released. Considering this is a forty year plant that happened to be very near one of the largest earthquakes ever recorded, I'd say nuclear power is vindicating itself. Of course, I don't expect the ignorant masses to understand what's really going on. I swear, some people hate nuclear power just because it's got ATOMS.

 

[Reno Deano]

As I told a member of the public at a meeting concerning start-up of the Diablo Canyon plant, when ask, "what would be the consequences of the coastal area being hit by a 9.0 or larger earthquake". I replied that the nuclear plant would be the least of their worries, since they would be dead or swiming for their life in the sea anyway.

 

[Astronuc]

ANS has put out a brief which describes events at Unit 1:

• The plant was immediately shut down (scrammed) when the earthquake first hit. The automatic power system worked.
• All external power to the station was lost when the sea water swept away the power lines.
• Diesel generators started to provide backup electrical power to the plant’s backup cooling system. The backup worked.
• The diesel generators ceased functioning after approximately one hour due to tsunami induced damage, reportedly to their fuel supply.
• An Isolation condenser was used to remove the decay heat from the shutdown reactor.
• Apparently the plant then experienced a small loss of coolant from the reactor.
• Reactor Core Isolation Cooling (RCIC) pumps, which operate on steam from the reactor, were used to replace reactor core water inventory, however, the battery-supplied control valves lost DC power after the prolonged use.
• DC power from batteries was consumed after approximately 8 hours.
• At that point, the plant experienced a complete blackout (no electric power at all).
• Hours passed as primary water inventory was lost and core degradation occurred (through some combination of zirconium oxidation and clad failure).
• Portable diesel generators were delivered to the plant site.
• AC power was restored allowing for a different backup pumping system to replace inventory inreactor pressure vessel (RPV).
• Pressure in the containment drywell rose as wet well became hotter.
• The Drywell containment was vented to outside reactor building which surrounds the containment.
• Hydrogen produced from zirconium oxidation was vented from the containment into the reactor building.
• Hydrogen in reactor building exploded causing it to collapse around the containment.
• The containment around the reactor and RPV were reported to be intact.
• The decision was made to inject seawater into the RPV to continue to the cooling process, another backup system that was designed into the plant from inception.
• Radioactivity releases from operator initiated venting appear to be decreasing.

Since they can't see into the core, they cannot confirm the state of the core. The list is subject to revision/correction as more is learned. They could monitor the air and water for certain isotopes to get an idea if there is fuel release from the fuel.

It appears that the EDGs got knocked out by a tsunami, despite the fact that they should have ensured the EDGs would not be affected by a seiche or tsunami. The containment maybe intact, but it's not clear concerning the integrity of the pipes, primarily those of the recirculation system.

It now appears there is a similar problem at Unit 3.

 

[Reno Deano]

•Hydrogen in reactor building exploded causing it to collapse around the containment.

The reactor building for a BWR is nothing more than a thin weather protection building and all other components of major concern are within hardened structures within it.

 

[Astronuc]

•Hydrogen in reactor building exploded causing it to collapse around the containment.

The reactor building for a BWR is nothing more than a thin weather protection building and all other components of major concern are within hardened structures within it.

It also houses the crane(s) to lift the containment cover and vessel components. I haven't seen pictures of the crane.

 

[PietKuip]

A shame, because this is shaping up to be a textbook example of nuclear safety. Most of the backups and emergency procedures failed, yet it looks like little radiation has been or will be released.

Members of the public got contaminated, so there must have been a significant release of radioactive material. The incredibly horrible logs at http://www.nisa.meti.go.jp/english/ show that in Futaba-machi half of the people tested had counts between 18 000 and 40 000 counts per minute. Unclear whether a pancake detector was used for that, or a whole body counter. One person's shoes had over 100 000 cpm - maybe that made the detector max out. It seems that these people got contaminated why waiting in a school yard for buses to evacuate them.

Some radioactive material on your shoes is not dangerous at all, but these numbers show that an area well outside the power plant perimeter got severely contaminated.

 

[Astronuc]

Members of the public got contaminated, so there must have been a significant release of radioactive material. The incredibly horrible logs at http://www.nisa.meti.go.jp/english/ show that in Futaba-machi half of the people tested had counts between 18 000 and 40 000 counts per minute. Unclear whether a pancake detector was used for that, or a whole body counter. One person's shoes had over 100 000 cpm - maybe that made the detector max out. It seems that these people got contaminated why waiting in a school yard for buses to evacuate them.

What exactly is the source of those numbers? The link provides several pdfs.

Normal background btw is about 1-2 cps (60-120 cpm). Background comes from normal solar/cosmic radiation, and natural sources such as granite, and long-lived isotopes like K-40.