Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[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.

 

[Angry Citizen]

And I would further ask, "What exactly is the significance of those numbers?" Is that even a significant quantity of radiation?

 

[eXorikos]

Last time I checked with a proportional counter (friday) background (indoors) was 5-10cps...

The significance of those number also depends on the type of radiation and the place where the contamination is on/in the body. Just cps or cps says nothing really.

 

[alxm]

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.

Well, it does seem to be where the explosion occurred though. I just found http://www.nei.org/filefolder/BoilingWaterReactorDesign.jpg" which at least seems to say as much. Although there seems to be a lot of conflicting information out there; one report claimed it occurred between the outside wall and a steel containment wall, which I'd interpreted as a Mark-III kind of containment, which isn't correct for the Fukushima reactor.

In theory though, it's life could have been extended another 20 years.

Yup, it'd require heavy investments though. A friend of mine was until recently involved in the upgrades in-progress at http://en.wikipedia.org/wiki/Oskarshamn_Nuclear_Power_Plant" , which is a BWR contemporary to Fukushima (although it's a different, ASEA design)

 

[promecheng]

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

The structure that was destroyed does contain the crane to lift the containment cover and is used during fueling operations. I'm not sure if it is considered secondary containment, but I do believe that it is a bit more secure than a simple metal enclosure. During refueling operations there is a small amount of radioactivity present and I believe the environment within the top portion of the building is controlled and not freely vented to the outside.

Another concern with the loss of the top part of the building is the spent fuel pool. I believe that the SPF is within the structure that was destroyed. If the water in the SPF was lost during the blast, the spent fuel can overheat and potentially melt. With no structure to contain the environment above the SPF any release of radiation would be freely vented to the outside.

Also, I believe that the unit-1 reactor is a BWR/4 design by GE with a MK-1 containment design. I believe this is typical with the wet-well torus design used to suppress a Loss of Coolant Accident (LOCA) within the primary containment. Any steam would be directed to the wet well where it would exit the venting system submerged, and thus condense and relieve any pressure buildup.

 

[Astronuc]

It does appear that the spent fuel pool is in the upper level of the contaiment, unless they have it in another building adjacent to containment.

I hope they are maintaining cooling there too.

It would appear from pictures that the overhead crane is probably damaged, and possibly the fuel handling machine(s).

 

[edgepflow]

Are the pumps they are using to pump seawater for reactor cooling motor driven or steam turbine driven? Are these the pumps designed for this emergency cooling or an alternate configuration?

 

[promecheng]

Are the pumps they are using to pump seawater for reactor cooling motor driven or steam turbine driven? Are these the pumps designed for this emergency cooling or an alternate configuration?

I think I read on TEPCO's, (Tokyo Electric Power Co.), website http://www.tepco.co.jp/en/press/corp-com/release/index-e.html that they were using Fire Pumps to inject seawater into the reactor. These are probably portable diesel-powered pumps that they have somehow hooked up to the Emergency Core Cooling System (ECCS), either the Core Sprayer system or the Low-Pressure Core Injection (LPCI) system. I think they still do not have AC power at the site to power their permanently installed pumping systems.

Basically these Fire Pumps are only used as a last resort, when all else fails. I know plants here in the U.S. also have Fire Pumps available in case of worst-case scenarios, like loss of site power and loss of all Emergency Diesel Generators.

 

[promecheng]

Here are some pictures and sketches of a BWR. I got them from a good site if your interested in learning more on nuclear power plants, http://www.nucleartourist.com/

Another cutaway of a BWR/3 or BWR/4 with MK-1 containment:
http://www.nucleartourist.com/imagemaps/rx-bldg1.jpg

Pictures of reactor building floor during refueling outage. I believe this is looking inside the part of the building that was destroyed:
http://www.nucleartourist.com/images/rflg-fl2.jpg
http://www.nucleartourist.com/images/rflg-fl1.jpg

Reactor head being lifted during refueling. They have already lifted the top of the primary containment, which is a very thick steel-reinforced concrete cover and weighs many tons. (notice people near reactor are wearing protective suits):
http://www.nucleartourist.com/images/headlift.jpg

Pictures of inside of torus:
http://www.nucleartourist.com/images/torus1.jpg
http://www.nucleartourist.com/images/torus2.jpg

Sketch of emergency cooling systems: (Note, this appears to be from a later design BWR, probably BWR/5 or BWR/6. The systems will be similar however for the BWR/3 or /4:
http://www.nucleartourist.com/images/nmp-g3.gif

 

[PietKuip]

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

I had used the http://www.nisa.meti.go.jp/english/files/en20110313-3.pdf" . The count rates are on page 13; "measured without shoes, though the first measurement exceeded 100,000 cpm" sounds like that was the highest reading the instrument could give.

The same pdf also says: "A radiation level exceeding 500 microSv/h was monitored at the site boundary (15:29, March 12)." Also this sounds as if the meters had maxed out.

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.

Indeed, this is up to a 1000 times background levels. Maybe this was the origin of news reports mentioning that factor.

If a school yard gets contaminated like that, local agriculture is in big trouble.

 

[PietKuip]

And I would further ask, "What exactly is the significance of those numbers?" Is that even a significant quantity of radiation?

It is not dangerous to have shoes on which give 100 000 counts per minute. Just take them off, rinse them, and your problem is solved. If it is on your body, just take a shower (if showers are working in the afflicted area).

But it seems indicative of a large surface contamination over quite a large area, which means that the amount of radioactivity that was released is large.

The Japanese authorities should be able to give estimates on how many becquerel of activity were released into the environment. This cannot have been a negligible amount.

 

[lapsedgeo]

As a lapsed geographer of many years (and a Mum) trying to explain not only the earthquake and the tsunami but also what on Earth is going on with the reactors to her teenage son thank you for posting such helpful information - it's certainly keeping me up to date in a way that the media aren't.[

 

[PietKuip]

Another indication that there was a major release of radioactivity: Dutch radio just reported that the enhanced radiation levels at Onaga would be due to wind-driven activity from Fukushima.

This reminds me of how the Chernobyl accident first became public when radiation monitors at a Swedish reactor showed high levels of radiation.

 

[Astronuc]

Another indication that there was a major release of radioactivity: Dutch radio just reported that the enhanced radiation levels at Onaga would be due to wind-driven activity from Fukushima.

This reminds me of how the Chernobyl accident first became public when radiation monitors at a Swedish reactor showed high levels of radiation.

Is one referring to Onagawa plant? What is meant by enhanced?

There is some concern about the spent fuel pool at FK-I, Unit 1 and whether or not it went dry. I would hope they have checked that.


NEI has put together a pretty informative page/site:
http://www.nei.org/newsandevents/information-on-the-japanese-earthquake-and-reactors-in-that-region/

The have a general BWR Mk I diagram
http://i1107.photobucket.com/albums/h384/reactor1/BoilingWaterReactorDesign_3.jpg

 

[PietKuip]

Is one referring to Onagawa plant? What is meant by enhanced?

Yes, I meant the plant Onagawa plant. Levels were 21 microsievert or four times as much (depends on how one reads the information - maybe they have an alert level of 21 microSievert, levels were four times their alert threshold).

Anyway, if that indeed came from over 50 miles upwind, the release at Fukushima was gigantic. Which means that the authorities have been lying.

 

[Vanadium 50]

microsievert per what? 21 uSv is 2.1 mR. Typical backgrounds are 1 mR/day.

 

[PietKuip]

microsievert per what? 21 uSv is 2.1 mR. Typical backgrounds are 1 mR/day.

Sorry: microsievert per hour, according to http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=ja&tl=en&u=http%3A%2F%2Fmainichi.jp%2Fphoto%2Fnews%2F20110314k0000m040057000c.html".

My point is not that it would be terribly dangerous at Onagawa, but that the amount of activity released at Fukushima was massive.

 

[Astronuc]

Sorry: microsievert per hour, according to http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=ja&tl=en&u=http%3A%2F%2Fmainichi.jp%2Fphoto%2Fnews%2F20110314k0000m040057000c.html".

My point is not that it would be terribly dangerous at Onagawa, but that the amount of activity released at Fukushima was massive.

The cited report mentions 21 Sv, but not the time period, hr or day or otherwise.

1 μSv = 0.1 mrem
Nominal background = 2400 μSv/yr or about 0.27 μSv/hr
http://www.unscear.org/docs/reports/gareport.pdf

So the activity is not so clear.

Meanwhile - reports indicate that the activity at the Onagawa has returned to normal, so the increase in activity was transient rather than ongoing.

While the release of radioactive material from Fukushima is significant, it is premature to call it massive (and massive has not been quantified).

 

[turbo]

And where was it measured? When I was an environmental process chemist at a pulp mill, we measured emissions as far from the plant as legally allowable. Games that the EPA allows businesses to engage in.

 

[marwood]

21 microsievrts per hour according to the linked reference ''Tohoku Electric Power said, Onagawa (I long to) from a nuclear power plant (town Onagawa, Miyagi Prefecture Ishinomaki) on-site radiation monitoring system, the reference value of the reporting obligations prescribed by a Nuclear Disaster Special Measures Law about four times the radiation dose (21 microsievert per hour) is detected.''

The alleged source being the Fukushima Daiichi plant located approx 120 kilometers to the south. Given 120 kilometers of diffusion, assumedly by some sort of Brownian motion type process, the Fukushima release must have been very substantial.

 

[turbo]

The alleged source being the Fukushima Daiichi plant located approx 120 kilometers to the south. Given 120 kilometers of diffusion, assumedly by some sort of Brownian motion type process, the Fukushima release must have been very substantial.

We can't assume that, though. Particulate and aerosol releases can be very directional with well-concentrated plumes.