Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[biffvernon]

It was pretty much get out any way you could, and run away.

That's the rational human response to what appears at the time to be a life-threatening event.
Nuclear power stations ought to be designed to be safe whenever all the staff unexpectedly rush for the exit and the electricity supply fails. How many of the world's power plants fit that?

 

[tsutsuji]

US BWRs I am familiar with have pump houses to protect the cooling water pumps for General Service Water, Emergency Service Water and Circulating Water systems. These buildings are safety-related, sesmically qualified and water tight where to protect the pump motors. Impeller shafts drive the impellers through a water sealed fitting on the motor floor. Power cables can be elevatedor routed in water tight conduits. So it is possible to protect pumps from flooding damage even if they are located near the water edge.

An electric motor does not need to have contact with the atmosphere, so it is possible to create very watertight designs. For example a conventional submarine basically consists of a very watertight electric motor. Mechanical shocks caused by boats or cars or oil tanks brought by the tsunami wave could also be averted with some sort of concrete bunker.

Do the seawater pumps have a safety for loss of NPSH?

Surely they sucked air when the sea retreated in the moments before the tusnami!

You may want to have a look at my reply to a similar question at https://www.physicsforums.com/showthread.php?p=3306874#post3306874

 

[NUCENG]

That's the rational human response to what appears at the time to be a life-threatening event.
Nuclear power stations ought to be designed to be safe whenever all the staff unexpectedly rush for the exit and the electricity supply fails. How many of the world's power plants fit that?

One of the lessons learned from TMI2 was the need to control the access amd distractions in the control room. Employees and others crowded into the control room to help. They didn't run away. It was necessary to order people to leave the site. Technical Support Centers and Emergency Operating Facilities have been put in place outside the control room on site and off site respectively. These facilities have dedicated communications and monitoring systems. The EOF has specific provisions for the media, Links to regulators, police, emergency response providers and local and state government are provided. These groups feed recommendations and support to the control room with less noise, congestion, and distraction.

 

[seeyouaunty]

This report is a verbatim quote from other news reports. My first criticism is the description of a 3 cm or 7 cm fault. A linear crack is not a significant leak. Leakage requires a differential pressure AND a break AREA. If this is a newsperson misquote and the answer is 3 cm² or 7 cm² that is way less than the area that would be classified as containment failure.

Tepco said if it hypothesizes that a breach of about 3 cm wide occurred at the reactor 1 containment vessel 18 hours after the quake and widened to about 7 cm 50 hours later

http://search.japantimes.co.jp/cgi-bin/nn20110526a1.html

Seems to me that if there is a crack that is 7cm wide (not long, but wide) that would make the opening at least ~40cm². Its worth noting that this is a hypothesis by Tepco to explain the various instrument readings from the reactor, so they probably have a particular flow-rate in mind for the theoretical leak.

"If we do our analysis on the premise that there was a leak in the piping, it matches (data) in reality," a Tepco official said at a news conference.

 

[elektrownik]

What is with unit 2 sfp ? They can't fill it with water, size is the same like in unit 4, but in unit 4 after injection water level is ~6400mm, in unit 2 (after injestion) only ~3500mm, also the temperature jumps are strange, maybe sensor damage ? Temperature is bigger after water injection...
for example
5/22 11:00 2000mm 46C
5/23 05:00 4000mm 70C
5/26 05:00 3000mm 45C

 

[zapperzero]

That's the rational human response to what appears at the time to be a life-threatening event.
Nuclear power stations ought to be designed to be safe whenever all the staff unexpectedly rush for the exit and the electricity supply fails. How many of the world's power plants fit that?

Many. Most, in fact. Nuclear plants are the exception, really. Anyway, even these reactors can scram all by themselves and keep cool automatically for as long as power and water is available. The operators are there to finesse things like fuel consumption and respond to emergencies... just like in an airliner.

One stupid difference from an airliner is they can't generate electricity for themselves. It would be trivial to retrofit. You could patch a derivation and a small steam turbine in anyone of the existing circuits. You could put three of them in just to be sure, make one run off steam coming out from that emergency pressure valve that vents to the outside air. It could do double duty as a nice, apocaliptically loud evacuation siren if you dimension it properly.

 

[Rive]

About 7,000(?) posts ago I also pondered the possibility of a mechanical backup. It seems reasonable something could operate off the excess heat - like a giant thermostat - to open and let sea/fresh water in - then close when the temperature drops?

All this is about the design basis. Of course it's possible to design more systems, pools, heat exchangers, cooling towers but first you have to set up your design basis. Then if something bad happens you can check if it was an error in build, in design or in design basis.

 

[tsutsuji]

Each of the plants has three circulating water pumps (Unit 1 may only have 2). Those are the largest pumps in your pictures. Each plant probably also has two general service water pumps and two emergency service water pumps. If you look at Unit 4 you see the four small pumps and three circular areas at the inlet that are where the motors for the circulating water pumps should be. Since the plant was in an outage the motors may have been removed for maintenance. Or they may have been destroyed in the tsunami.

Yesterday I found a Tepco report confirming that unit 4's 3 main seawater pumps were removed for maintenance : https://www.physicsforums.com/showthread.php?p=3321704#post3321704

What is the purpose of "service water pumps" ?

I add a picture showing how they look like -these are from N°5 reactor and got hit by this big blue structure, but they look similar to the others:

http://www.netimago.com/image_202944.html

The trajectory of the big blue structure, a gantry crane, is shown on page 40 of http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110525_01-j.pdf. I guess this is the crane that is used, among other purposes, when the pumps are removed for maintenance.

English version is now available at http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf

 

[NUCENG]

Yesterday I found a Tepco report confirming that unit 4's 3 main seawater pumps were removed for maintenance : https://www.physicsforums.com/showthread.php?p=3321704#post3321704

What is the purpose of "service water pumps" ?



The trajectory of the big blue structure, a gantry crane, is shown on page 40 of http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110525_01-j.pdf. I guess this is the crane that is used, among other purposes, when the pumps are removed for maintenance.

General service water pumps feed non-safety coolers/ Emergency service water feeds the safety related coolers such as the diesels.

 

[tsutsuji]

General service water pumps feed non-safety coolers/ Emergency service water feeds the safety related coolers such as the diesels.

Thanks. The two safety-related ones are probably those belonging to the 12 (=6 units x 2) failed "RHR sea water systems" mentioned on page 50 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf

 

[NUCENG]

http://search.japantimes.co.jp/cgi-bin/nn20110526a1.html

Seems to me that if there is a crack that is 7cm wide (not long, but wide) that would make the opening at least ~40cm². Its worth noting that this is a hypothesis by Tepco to explain the various instrument readings from the reactor, so they probably have a particular flow-rate in mind for the theoretical leak.

That is about 1/4 the size of leakage expected in: http://www.osti.gov/bridge/servlets/purl/5630475-EX87x5/5630475.pdf.

That would be considered leakage, not containment failure. Are they fitting the data to their theories or developing their theories to fit the data? I think the containment pressure and temperature conditions reached in unit 1 almost guarantee more leakage than that.

 

[tsutsuji]

Do we know more on this for the various reactors/plants? Which pumps did fail?

These pumps should at least be put in a bunker if they have to stay close to the sea...

At Daini, from the picture i posted, i don't see the main pumps being inside a building. This picture is from the 12th of March, one day after the tsunami.

[PLAIN]http://www2.jnes.go.jp/atom-db/en/trouble/individ/power/g/g20051102/051102.gif
Diagram for Fukushima Daini unit 2, taken from http://www2.jnes.go.jp/atom-db/en/trouble/individ/power/g/g20051102/news.html

On page 46 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf the building by the sea is called "heat exchanger building". This raises the possibility that the building was not built in order to provide tsunami protection, but in order to provide housing for the heat exchanger(s) of the RHR and Diesel generator systems.

 

[rmattila]

It's been years since I've done a calculation on the turbine side, but I remember a vacuum drawn on the condenser since the water temperature is cold (relative to the turbine) and the vapor pressure is very low - less the 1 atm. That water would be passed to the reheaters coming off the LP stages.

Typical pressure in a BWR condenser is a few tens of millibars (abs), i.e. rather good vacuum. Loss of vacuum (absolute pressure 0.2 - 0.3 bar) results in a turbine trip. In order to maintain vacuum, a constant suction is needed due to accumulating hydrolysis gases, which are transferred through recombiners to the off-gas system and eventually to the exhaust stack.

 

[NUCENG]

Thanks. The two safety-related ones are probably those belonging to the 12 (=6 units x 2) failed "RHR sea water systems" mentioned on page 50 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf

I agree. A rose by another name. One of the safety loads for each pump is likely the RHR (A or B) heat exchanger which is an ECCS component.

 

[NUCENG]

http://www.japantoday.com/category/national/view/japan-ends-projections-of-radioactive-substance-spread-from-nuclear-plant

1 Bq per 72 hours of I131? We wish! Obviously the reporter dropped a few orders of magnitude.

 

[Rive]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110526_01-e.pdf"

 

[clancy688]

1 Bq per 72 hours of I131? We wish! Obviously the reporter dropped a few orders of magnitude.

Isn't that probably well below the radioactivity release of an normally operating NPP? Just wondering...

 

[NUCENG]

Isn't that probably well below the radioactivity release of an normally operating NPP? Just wondering...

TThat is about 2% of the decay rate of potassium in a banana. ;-}

 

[AntonL]

That would be considered leakage, not containment failure.

Were is the border between leakage and containment failure?
To my understanding something that leaks does not contain.

 

[clancy688]

TThat is about 2% of the decay rate of potassium in a banana. ;-}

Oh boy, I'll never eat bananas again. Only using them for irradiating food. =D

---------------------------------------------------------------------------

And new infos from EX-SKF again.

http://ex-skf.blogspot.com/2011/05/fukushima-i-nuke-plant-reactor-1-rpv.html

Today, TEPCO admits the Reactor 1's Reactor Pressure Vessel (RPV) may have broken right after the earthquake and the pipe connected to the High Pressure Coolant Injection system (HPCI) for the Reactor 3 probably also broke during the earthquake. (The article linked below doesn't say the piping is for the HPCI, but the earlier Mainichi Japanese article on May 25 says so.)

A diagram showing temperature changes at the reactor's containment vessel indicates that temperatures and pressure momentarily shot up immediately after the quake.

Mitsuhiko Tanaka, a former nuclear reactor design engineer, says high-temperature steam apparently leaked out to the containment vessel after either the reactor's pressure vessel or its accessory piping was partially damaged.

The operator, Tokyo Electric Power Co., admitted Wednesday that critical cooling piping at the same plant's No. 3 reactor may also have been damaged in the quake.

 

[swl]

US BWRs I am familiar with have pump houses to protect the cooling water pumps for General Service Water, Emergency Service Water and Circulating Water systems. These buildings are safety-related, sesmically qualified and water tight where to protect the pump motors. Impeller shafts drive the impellers through a water sealed fitting on the motor floor. Power cables can be elevatedor routed in water tight conduits. So it is possible to protect pumps from flooding damage even if they are located near the water edge.

Fascinating information. Thanks for sharing.

Which US BWRs would it be that you're familiar with?

Are there any references for us to better understand the details of the characteristics you described? It would be great to have a source we could quote, but of course I understand that you may have been simply describing from memories of personal experience.

Do you know how they handle cooling with these huge (1,000~kW?) motors running in these hardened buildings?

 

[fluutekies]

Dave Lochbaum's analyses:

Fukushima Dai-Ichi Unit 1: The First 30 Minutes:
http://allthingsnuclear.org/post/5835907657/fukushima-dai-ichi-unit-1-the-first-30-minutes

Fukushima Dai-Ichi Unit 2: The First 60 Minutes
http://allthingsnuclear.org/post/5835961953/fukushima-dai-ichi-unit-2-the-first-60-minutes

Fukushima Dai-Ichi Unit 3: The First 80 Minutes
http://allthingsnuclear.org/post/5836043245/fukushima-dai-ichi-unit-3-the-first-80-minutes

 

[jpquantin]

What is with unit 2 sfp ? They can't fill it with water, size is the same like in unit 4, but in unit 4 after injection water level is ~6400mm, in unit 2 (after injestion) only ~3500mm, also the temperature jumps are strange, maybe sensor damage ? Temperature is bigger after water injection...
for example
5/22 11:00 2000mm 46C
5/23 05:00 4000mm 70C
5/26 05:00 3000mm 45C

This is not water level in the SFP, but in the FPC skimmer tank. If this level increases, it simply tells that SFP is full. Otherwise, no conclusion can be drawn.

 

[sono]

I have been lurking for a while (this is about the only place on the net where a meaningful discussion takes place) and i figured you guys might be interested in this:

---
A meltdown occurred at one of the reactors at the Fukushima No. 1 Nuclear Power Plant three and a half hours after its cooling system started malfunctioning, according to the result of a simulation using "severe accident" analyzing software developed by the Idaho National Laboratory.

Chris Allison, who had actually developed the analysis and simulation software, ...
---
http://mdn.mainichi.jp/mdnnews/news/20110523p2a00m0na019000c.html

 

[swl]

During BWR plant operation there are areas that get to 1 Sv per hour primarily near steam piping due to N-16 gamma radiation. These areas are locked high radiation errors where personnel access is not allowed during operation. Examples include the steam jet air ejector area, the reactor water cleanup area, and the steam tunnel between the reactor building and turbine building.

With a 16 second half life, I'm guessing the radiation is not coming from the N-16. After all the time that's passed, I'd guess the least bad scenario would be one of the Cs isotopes.
(thread regarding the radioactive pile of rubble, in case anyone is wondering)

 

[jlduh]

US BWRs I am familiar with have pump houses to protect the cooling water pumps for General Service Water, Emergency Service Water and Circulating Water systems. These buildings are safety-related, sesmically qualified and water tight where to protect the pump motors. Impeller shafts drive the impellers through a water sealed fitting on the motor floor. Power cables can be elevatedor routed in water tight conduits. So it is possible to protect pumps from flooding damage even if they are located near the water edge.

Thanks for the details. The question is:

it's possible to protect them (resistant to tsunami may be tougher though?), but was it the case, and is it the case everywhere on a so critical part of the nuke plants?

Also, what about the risks of damaging the impellers/shafts loads during water hammering? The longer an axis is, the weaker it is in case of tsunami hit.

 

[tsutsuji]

Isn't there something strange with the diagrams page 53 of http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110525_01-e.pdf ?

First I am surprised to learn about a new difference between Fukushima Daiichi and Fukushima Daini, with the presence of an additional cooling loop and heat-exchanger between the diesel engine and the sea at Daini.

What about the air-cooled diesel generators at Fukushima Daiichi units 2,4,6 ? Why should they need a heat-exchanger (between two liquids coolants? oil and water ?) in addition to the radiator ?

 

[jlduh]

In case it was not already known , one of the three diesel generators at Tokai NPP failed after tsunami hit. IAEA is going to investigate.

http://mdn.mainichi.jp/mdnnews/news/20110526p2a00m0na010000c.html

 

[swl]

This also imply the possibility of direct release from an RPV (or less likely from an SFP): otherwise it would be trapped in the torus.

TEPCO admits to having performed dry venting of the No 2 pressure vessel on 15Mar.

I assume "dry venting" indicates that the RPV was vented to atmosphere without traveling through the wet filtration of the torus.

http://search.japantimes.co.jp/cgi-bin/nn20110330a3.html"

 

[jlduh]

Again, I am not saying there wasn't seismic damage. there were reports of water leakage inside reactor buildings, but apparently it was not radioactive as some workers feared. Unit 3 had a fairly significant delay before starting RCIC or HPCI and there is no clear explanation why. But both systems were used later. There was speculation that the Unit 1 Isolation Condenser failed due to sesmic damage, but now it appears that was operator action that secured the system after only a few minutes. I just haven't seen any conclusive evidence of safety system failures prior to the tsunami.

There is this statement that Tepco workers entered the building N°1 during the night and the building was full of steam with measurement around 300 mSv/h. I agree that this was during the night of the 11-12 th of March (so after tsunami ), that Tepco press releases on their site does not mention this AFAIK, and that it is very possible that at this time, there was already significant damage on the core from the loss of coolant event (this new american study talking about a few hours for meltdown, which was by the way i think the order of magnitude of the severe accident study on BWR done I think in 1979 (?)).

So this doesn't prove clearly that it was from earthquake, i agree. But it may be an element to take into account.

 

[rmattila]

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110526_01-e.pdf"

Those curves seems to be in rather good agreement with the quesstimate I presented earlier in post 5788 on page 362.

 

[tsutsuji]

Switchgear or fuel tanks could have been damaged with the same result as flooding the generator rooms themselves. If it turns out impossible to protect the whole site, protect the essential parts of the site from inundation.

On Mamoru's layout plan for Fukushima Daiichi unit 3 at http://3.bp.blogspot.com/-JaxFid8Qo...AAko/t5TVRl5sb-4/s1600/R3++completa+small.jpg there is a white rectangle a few steps south of Diesel engine 3A called (in Italian) "boccaporto cisterna carburante" (Fuel tank hatch). So, my understanding is that the fuel tanks used by the diesel generators are located there, underground. If they can withstand the pressure from the water during the flooding and if the air intakes are located high enough, these tanks are probably OK.

 

[biffvernon]

What's all this >200Sv/hr in the #1 dry-well about?

http://atmc.jp/plant/rad/?n=1

 

[zapperzero]

1 Bq per 72 hours of I131? We wish! Obviously the reporter dropped a few orders of magnitude.

That was the source used for the simulation.

 

[Rive]

TEPCO admits to having performed dry venting of the No 2 pressure vessel on 15Mar.

I assume "dry venting" indicates that the RPV was vented to atmosphere without traveling through the wet filtration of the torus.

http://search.japantimes.co.jp/cgi-bin/nn20110330a3.html"

As I recall the fuel was already damaged at that time, so...

 

[NUCENG]

Thanks for the details. The question is:

it's possible to protect them (resistant to tsunami may be tougher though?), but was it the case, and is it the case everywhere on a so critical part of the nuke plants?

Also, what about the risks of damaging the impellers/shafts loads during water hammering? The longer an axis is, the weaker it is in case of tsunami hit.

Never really thought about it since the plants I'm familiar with are inland. However looking at the overhead photographs and drawings in the TEPCO handouts it appears that each pump is in a separate well or bay in the intake structure and thus is partially shielded from the insurge and probably completely shielded from runback forces. The impeller, shaft, volute and riser pipes can be mounted and anchored to the walls of the bay or well. How well they are protected I don't know for sure, but the motors look like they were more exposed to the tsunami than the pumps may have been. How well mounted and protected they are from surge effects will determine whether shafts or impellers are subject to damage.

I can't answer the question on how well protected these pumps at all plants. I have been in US plants on the Great Lakes that have to protect against seiche effects which are similar to tsunamis but come from harmonic amplification of waves back and forth across the lake.
These plants have quite detailed analysis to support the design basis wave heights and to demonstrate how vital systems are protected. I think some of their protective walls may be bigger than the seawall at Fukushima Daichi. Other plants are evaluated for river flooding which usually gives some notice and allows for procedure driven preparation to add protection such as sandbagging or installing panels over louvers or other similar actions.

A couple years ago plants in the US Midwest were subjected to a "1000 year flood" and continued to operate with minimal impact other than making the trip to work a little longer to avoid water. At one plant operators had to take a boat to the intake structure for inspection tours and maintenance.
I'm not sure how water hammer is involved in these pumps. Water hammer is the high pressure impact on a system caused when flow is initiated into a voided portion of the system and the void collapses causing the hammer effect. Cavitation and vibration are bigger threats to these centrifugal pumps.

In addition, plants all over the world should be watching the Fukushima event closely for lessons learned.

 

[tsutsuji]

The Incinerator building basement, where the contaminated water from unit 3 had been moved, was suspected of leaking :

Engineers learned that the water level had dropped by 4.8 centimeters over a 20-hour period, meaning some 57 tons of water has been lost.
Thursday, May 26, 2011 19:57 +0900 (JST) http://www3.nhk.or.jp/daily/english/26_34.html

The missing water has finally been found in a tunnel joining two buildings. There has been no leak into the ground water, according to http://mainichi.jp/select/science/news/20110527k0000m040110000c.html

 

[NUCENG]

As I recall the fuel was already damaged at that time, so...

That may explain why the hydrogen explosion in unit 2 was in the torus. Venting from the drywell would have lowered H2 concentration there, but the amount of hydrogen from the tous through the vacuum brakers to the drywell would have been slower to reduce H2 concentration in the torus.

Venting directly from the drywell loses the scrubbing effect of the suppression pool when venting from the torus. So they increased the release to the environment and the public after being reluctant to vent unit 1 at all. I'd sure like to see their reasoning for that. The only thing I can think is that the dry venting may have been done after explosions in units 1 and 3, and they were trying not to repeat that experience again.

 

[~kujala~]

Those curves seems to be in rather good agreement with the quesstimate I presented earlier in post 5788 on page 362.

So it seems.
I took one check point, after 180 days for units 2 & 3, and for TEPCO it's about 1 MW and for your chart it's about 0,9 MW (or something like that):

http://varasto.kerrostalo.huone.net/decay_heat_mattila.png
http://varasto.kerrostalo.huone.net/decay_heat_tepco.png

Perhaps they copied your chart and put it in non-exponential scale to look like brand new?

This ~ 1 MW is also something we have for unit #4 SFP now, if I have understood correctly.

 

[tsutsuji]

TEPCO admits to having performed dry venting of the No 2 pressure vessel on 15Mar.

I assume "dry venting" indicates that the RPV was vented to atmosphere without traveling through the wet filtration of the torus.

http://search.japantimes.co.jp/cgi-bin/nn20110330a3.html"

My understanding of Japan Times' Tepco quoting sentence "Yesterday, we said the dry vent of the No. 2 reactor was done March 16 to 17, but it was the 15th" is that "done" means "attempted", not "performed".

According to the New York Times :

At Reactor No. 2, workers tried to manually open the safety valves, but pressure did not fall inside the reactor, making it unclear whether venting was successful, the records show.

17 May http://www.nytimes.com/2011/05/18/w...pagewanted=2&sq=fukushima valves&st=cse&scp=7

I am not sure if Tepco changed its position since May 17th about how successful these venting attempts have been.

 

[~kujala~]

We have some good news for a while:

it will increase the number of sampling spots for groundwater

http://mdn.mainichi.jp/mdnnews/news/20110526p2g00m0dm079000c.html

If they have sub-drains below waste facilities I am sure these are now included as sampling spots. We'll see.

If there are sub-drains below waste facilities it also means that even if some contaminated water leaks there the sub-drains should take care of it (or at least part of it) and collect it into the sub-drain pits - which later could be emptied.

 

[NUCENG]

With a 16 second half life, I'm guessing the radiation is not coming from the N-16. After all the time that's passed, I'd guess the least bad scenario would be one of the Cs isotopes.
(thread regarding the radioactive pile of rubble, in case anyone is wondering)

Sorry, I should have linked my post to Robinson's post instead of Zapperzero. I was replying to his thought that normal plants were not anywhere near 1 Sv/hr.

During a submarine refueling I witnessed a dribble of water fall onto the floor of the refueling shack while removing a spent fuel assembly into a transfer cask. A Health physicist took a swipe of the spill using a small paper swipe. When he checked the reading it overranged a frisker and so he checked it with another high range detector. It was 75 R/hr or about 0.75 Sv on contact. Apparently that dribble contained a bit of highly activated CRUD. That little piece of paper was a walking high radiation area. It doesn't take much volume to make a lot of radiation depending on the isotope and its half life.

 

[Astronuc]

I have been lurking for a while (this is about the only place on the net where a meaningful discussion takes place) and i figured you guys might be interested in this:

---
A meltdown occurred at one of the reactors at the Fukushima No. 1 Nuclear Power Plant three and a half hours after its cooling system started malfunctioning, according to the result of a simulation using "severe accident" analyzing software developed by the Idaho National Laboratory.

Chris Allison, who had actually developed the analysis and simulation software, ...
---
http://mdn.mainichi.jp/mdnnews/news/20110523p2a00m0na019000c.html

I suspect that the analysis might have been very conservative, and perhaps considered adiabatic conditions, i.e., no heat removal from the fuel. I would like to see Allison's report.

See also - http://www.world-nuclear-news.org/RS_Large_scale_melt_predicted_at_units_2_and_3_2605111.html


Meanwhile, Westinghouse is responding to the event by introducing a mobile emergency SFP cooling system.
http://www.world-nuclear-news.org/RS-New_system_to_keep_fuel_pools_cool-2605117.html

 

[Jorge Stolfi]

Is recriticality possible in corium too? It has no internal cavities for water

AFAIK it is not necessary for the moderator to penetrate the fuel; just surrounding the fuel with moderator should be enough.

To have fission one needs to have a significant fraction of the emitted neutrons slowed down and scattered back to the fissile material. If the fuel is immersed in a large amount of moderator, and there is no absorption, every neutron that leaves it will eventually be scattered back to it, by "drunkard's walk" statistics. (This is the same effect that makes sunlit clouds look white.)

The half-life of a free neutron's is 15 minutes, so decay should not be a significant factor.

I suppose that neutron absorption is the main factor preventing re-criticality. TEPCO has been using boron in the emergency cooling water; the effect should be like that of soot particles making smoke clouds black instead of white. Also the corium itself may (or may not) include neutron-absorbing material from the control rods.

Is this correct?

 

[havemercy]

Hello to all. I'am very sorry if this question has already been asked, but it is quite difficult to read all the posts to check.

Is it possible that the corium, we know TEPCO said has been in the bottom of the reactor vessel, has leaked out in a porous soil, and, with contact with the water in such soil, resulted in a low blast that everybody has interpreted as a replica of 5.6 on Richter scale ?

(Sorry for the english)

Many thanks in advance.

 

[SteveElbows]

resulted in a low blast that everybody has interpreted as a replica of 5.6 on Richter scale ?

When do you think this may have happened?

 

[SteveElbows]

What's all this >200Sv/hr in the #1 dry-well about?

http://atmc.jp/plant/rad/?n=1

This subject seems to keep coming up every day for several days in a row now. Is someone posting scare stories about this data elsewhere on the internet, or is it just that lots of people have been using that atmc website graphs all along and are now wondering why its showing scary stuff?

In any case, this subject has been addressed here multiple times in recent days. Main summary of points:

The atmc website makes some bad errors with what data it uses sometimes, so it is not a good idea to use it as main source. Use TEPCO data instead, which shows 2 x drywell CAMS and 2 x suppression chamber CAMS readings for all reactors.

Main data site index page: http://www.tepco.co.jp/en/nu/fukushima-np/index-e.html

The CAMS readings are part of the pressure & temperature data sheet, so for reactor 1 it is:

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11052606_level_pr_data_1u-e.pdf

So yes, one of the sensors is sometimes showing values of 200 or higher. But the other sensor shows much lower values, and TEPCO think the sensor(s) may be damaged because they don't agree with each other, and one of them fluctuates a lot.

Other thing to note is that this is not a new thing, only reason its suddenly being noticed is because TEPCO only started publishing the data for this sensor again recently (around may 17th), after not bothering for many weeks, probably because the readings seemed unreliable.

In conclusion, there are too many unknowns about this data to make any conclusions, and if there is a problem its not a new event, it happened quite a long time ago. I do not think the CAMS data is good enough to be able to use it to reach interesting and firm conclusions about how much of the core fell into the drywell, so there is no point getting excited about the big numbers. All it really tells us is that fuel got damaged, and we know that already.

 

[havemercy]

On April 22 :

According to RBC, the epicenter of the earthquake was located at a depth of 35.8 km at a distance of 74 km from the city of Fukushima, and only 22 km from the nuclear power plant "Fukushima-1. According to the US Geological Survey, tremors were recorded at 19:25 MSK.

http://mysouth.su/2011/04/in-fukushima-prefecture-earthquake-of-magnitude-5-6/

 

[elektrownik]

The problem is that second sensor which show low value can't be correct if any amount of corium is in drywell, this hight value can be corect if corium hit drywell cams sensor... Chernobyl was >300Sv around core, at this time we know on 99% that unit 1 core melted from rpv and damaged drywell

 

[mscharisma]

The Incinerator building basement, where the contaminated water from unit 3 had been moved, was suspected of leaking :

The missing water has finally been found in a tunnel joining two buildings. There has been no leak into the ground water, according to http://mainichi.jp/select/science/news/20110527k0000m040110000c.html

Does this fall into the good or the bad news category? No leak into groundwater is surely good, but there wasn't supposed to be any kind of leak, I assume? What, if anything, does it tell that also the wastewater facility leaks somehow?