Sunday, August 21, 2011

More on Fukushima II (Daini): Loss of Function to Remove Residual Heat for Up to 2 Days and 23 Hours, March 11 to 14

I hardly paid any attention to Fukushima II (Daini) Nuclear Power Plant in the early days of the crisis, but I got curious reading the comment from the reader "Joe Neubarth" to the post on the eyewitness account of Fukushima II on the day of the earthquake:

"Core Damage comes from a loss of cooling. I know of no report of loss of cooling at that facility. Did they go dark when the one electrical transmission tower fell north of Fukushima during the earthquake? Did they then have a delay if the startup of Emergency Diesel Generators? If there was a delay or if they lost the EDG's totally THEN there might be a melt down, BUT I have not heard of this happening."

I didn't know either (or I totally forgot). Did they or didn't they? So I went to TEPCO's site and see what they say.

Fukushima II Nuke Plant has 4 reactors. When the earthquake hit on March 11, control rods were successfully inserted in all 4 reactors at 2:48PM. Then the tsunami hit, and at 6:33PM on March 11:

Occurrence of a Specific Incident Stipulated in Article 10 of the Act on Special Measures Concerning Nuclear Emergency Preparedness (loss of function to remove residual heat)

This happened on Reactors 1, 2, and 4, at the same time.

Then, the Residual Heat Removal System re-started one by one, on March 14:

Reactor 1: 1:24AM, March 14
Reactor 2: 7:13AM, March 14
Reactor 4: 3:42PM, March 14

So, the reactors weren't cooled for as long as 69 hours in case of Reactor 4, and 55 hours in case of Reactor 1. Is 55 hours long enough for the coolant (water) inside the Reactor Pressure Vessel to evaporate and for at least part of the fuel rods to be exposed and get damaged?

For all 4 reactors, the Reactor Coolant Filtering System came online between June 4 and July 17.

TEPCO also says the Suppression Chambers of Reactors 1, 2 and 4 suffered some event that caused the "loss of function to suppress pressure" in the morning of March 12. The function was restored on March 14 morning.

The above information is from TEPCO's status report on Fukushima II (Daini) Nuclear Power Plant as of August 21 (click to enlarge, or go to the link):


Anonymous said...

everyone forgets Daini was used as one of the initial shelters for the nuclear tsunami refugees

Jeff Barkley said...

This is interesting information. Perhaps because, as we now know, Fukushima 1 was damaged by the initial earthquake enough that pipes broke and pressure was lost from the containment. Once pressure was lost, the water would boil at a lower temperature and evaporate much more quickly, thus causing the meltdowns to occur sooner than would be the case if the pipes had not been broken.

The Fukushima II plant may not have suffered as much damage during the initial quake. Since they were able to restore cooling on the 14th whereas they were not able to restore cooling to Fukushima I. Just speculating that Fukushima II may have been spared the meltdowns of Fukushima I because they did not lose as much pressure from containment by having cooling system pipes break.

Thank-you for all you do. The world is watching and you are one of the few that can be trusted.

Ono said...


I alreadly summarize situation of Fukushima II.
See My blog. but In Japanese sorry.

I worked at Fukushima II for 5years. So I paid an attention to this plants since the very begining. ( AS if my father...)

The key ... they did not loss external power supply from the beginig.

THE Plant still have very serious porblem---SALT DAMAGE from the sea water from TSUNAMI in the building.

Sorry in JAPANESE only

you can get more information from
(ALSO Japanese)

Anonymous said...

There is no reliable evidence that Fukushima I suffered broken cooling pipes nor is it necessary to invoke pipe breaks to explain what happened. The core melts/relocations that happened there can be sufficiently explained by lack of cooling water as these are boiling water reactors. The water turns to steam inside the reactor vessel. To protect the core, the level of liquid water has to remain above the core. When the cooling water supply fails, the level of liquid water drops because it turns to steam, thus uncovering the core. There is no need to invoke breakages in cooling pipes to explain what happened as the cooling water supply failed due to the electricity blackout which stopped the cooling water pumps.

A pressurized water reactor, on the other hand, does not have a water/steam interface inside the reactor vessel. Instead water is kept from boiling in the primary loop (which includes the reactor vessel) by virtue of high pressure and steam is produced at a heat exchanger between the primary loop and the secondary loop, which operates at lower pressure.

Thus liquid water completely fills the reactor vessel and all of the primary loop piping in a pressurized water reactor. As long as sufficient pressure is maintained, the core would remain under water and would thus be unlikely to suffer the kind of damage that happened at Fukushima I. Three Mile Island (also a pressurized water reactor) suffered a partial core melt/relocation because the level of liquid water inside the reactor vessel dropped, thus uncovering its core.

Has TEPCO reported any drop in liquid water levels inside the reactors at Fukushima II? If there were no such drops, I would say that there is a high probability that the cores there were either not damaged or not damaged very much.

Morbid said...

I can't believe they lost cooling for 3 days. If they did the cores would have melted down within about 10 hours.

These plants come with failure simulation software. Like this it is immediately known what the damage will be. Just like the inner circle knew Plant I had melt-through within the first day but only dribbled out the news months later.

Anonymous said...

I think that there may be a problem with nomenclature/translation. The reference from our good host clearly references the "loss of function to remove residual heat." However, the reports for Daini for March are listed at Looking through these reports for Daini, they report instead loss of the "Reactor Core Isolation Cooling System" (RCIC), which had been injecting water, due to the loss of the reactor suppression function because the temperature of the suppression chamber exceeded 100°C. So they switched and started injecting water using the Make-up Water Condensate System and reduced the pressure of the reactor containment vessel through a partial discharge of air containing radioactive materials (but apparently not to the environment).

Water levels remained stable in all reactors until the reactor core cooling function could be completely restored and the temperature of the suppression chamber could be lowered below 100°C, at which point, presumably, the RCIC was restarted. There was no blackout as grid power was never lost.

Bottom line: An emergency that apparently was handled as designed. No station blackout. No drop in water levels and, therefore, no uncovering of the cores. Finally, supposedly, no discharge of radioactivity to the environment.

(This is my interpretation of the reports from TEPCO at the link, which were presumed to be accurate.)

Anonymous said...

??? Anonymous? wonder if you in this case are a paid blogger??
"I think that there may be a problem with nomenclature/translation. The reference from our good host clearly references the "loss of function to remove residual heat."--". A TEPCO or government worker? Is there a conflict of interest in your statements?

from a REAL person not paid or working for any Japanese company or government.

Capt said...

Starting about 4 pages ago (10:26 AM) be sure to read all the " Click Here To See them All" for the full discussion.

Here is my take:Despite what TEPCO's Log states, I believe that at least one reactor was in the first stages of melting (through or down) and that the Tsunami just was the icing on the cake!

I don't believe TEPCO logbooks or "Black Box" because they have a history of falsifying records, link are on this thread of the last one...

I think that the Corium (one or more) have already gone downward enough to have made contact with the landfill/E­arth below the complex, and that it is moving downward toward the water table/ Ocean water interface much faster than TEPCO expected!

If what I envision is indeed the case, then it (Elvis) will cause a steam event that will put the entire complex in N☢T water (No pun intended) and or vapor that will follow the winds for s long as they remain suspended!

Anonymous said...

(This is my interpretation of the reports from TEPCO at the link, which were presumed to be accurate.) i do believe the las5 persons on earth will still believe TEPCO & that there is really no hope.

evendine said...

I agree with Morbid that if indeed there was a ...'loss of function to remove residual heat...' for more than two days (which the TEPCO reports make clear), then it is inevitable that all of the cores would have melted down and worse...

During the NRC initiated NUREG-1150 'Severe Accident Risks Assessment' study in 1991, Peach Bottom boiling water reactor failure modes were reviewed and the conclusion was that in the event of loss of core cooling capability, +melt through+ would occur within 8 hours!


Peach Bottom has the same basic design as the GE BWR reactors at Daiichi and Daini sites:

The wiki page on Daini indicates that the plant was inundated with sea water and that the cooling systems did indeed fail for far longer than 8 hours:

Perhaps somehow they avoided the hydrogen explosions and have therefore been able to cover-up?

Anonymous said...

@ Anon 11:42,
"There is no reliable evidence that Fukushima I suffered broken cooling pipes nor is it necessary to invoke pipe breaks to explain what happened."

see Fukushima II (Not I) Nuke Plant Wants to Dump 3,000 Tons of Water into the Ocean
"No pipe breaks" must explain how cobalt ended up in Daiini's basement water?
"JP said...
we also know that an exclusion zone was declared around FUK 2."

"The company said smoke was detected in the turbine building of reactor No. 1 at the Fukushima Daini nuclear power plant around 6 p.m.
.. Japanese authorities also detected cooling-system problems at the Fukushima Daini plant, and those living within a 10-kilometer radius (6 miles) of Fukushima Daini were ordered to evacuate as a precaution."

"At Fukushima Daiini unit 3 one worker received a radiation dose of 106 mSv."

"So, in a normal operation, radioactive cesium will fly from a nearby nuke plant and somehow land on [in] the basement of the enclosed reactor building. Right." the blog's host

"Water levels remained stable in all reactors until the reactor core cooling function could be completely restored .." [something broke]
.. "and the temperature of the suppression chamber could be lowered below 100°C" [something boiled]
.. "at which point, presumably, the RCIC was restarted." [something broke was fixed 55-69 hrs. later]

"Bottom line: An emergency that apparently was handled as designed."
[reactor cooling was lost when something broke, radiation was released and we're to believe it was "as designed"?] [at least they fixed it?]

At Daiichi damage from the quake was sufficient to cause onsite inspectors to flee, pipes buckling and breaking.
Daiini is how far south of Daiichi? Why would an M9 quake be any less severe so close to Daiichi?

pat said...

I suspect at Daini, they were able to keep the EDG's running, so, the scale of the problem never got out of hand. I suspect that allowed the operators to start pumping water through the fire fighting system, and reduce the total amount of core damage.

I wouldn't doubt Daini is trashed, that this far from the quake, and the TEPCO people are not even talking about a restart of Daini, tells me the units are smoked. Fortunately i think because they weren't blacked out, the seawater trick reduced daini from a INES 7+ incident to a INES 5 incident.

They have a problem on scale with TMI, with released gases, thousands of tons of seawater and 4 trashed units. Compared to Daichi, small potatoes.

To Recap, i don't doubt the tops of the racs are melted, but, because they never lost power they were able to run the hydrogen venting system, and dumped several hundred billion BQ of radioactive gas and several thousand tons of radioactive water, but maybe 1% of Daichi.

Anonymous said...

"the TEPCO people are not even talking about a restart of Daini, tells me the units are smoked."
Very good.

"because they never lost power they were able to run the hydrogen venting system"

Also very good, in that if core cooling is lost, and core cooling is still required during 'cold shutdown', even then fuel rods will melt and hydrogen gas is produced, they must have vented.

Three Mile Island-type partial melting. Not even TEPCO would house evacuees near full-meltdown reactors?

evendine said...

Hmm... Not convinced that the Daini emergency diesels actually survived the tsunami Pat. Here's an excerpt from a report at the time (11/3/11:

...'JAIF has reported that TEPCO sent the emergency report because emergency diesel generators at the two sites (i.e. Daini and Daiichi) are out of order. (Nuclear power plants need power to operate pumps and other emergency equipment, including equipment to remove decay heat from the reactor.)...'


Projected time from loss of power to failure of the reactor vessel is actually less than four hours (rather than eight as I suggested earlier, which relates to failure of the bottom head wall).

In the wiki entry (which seems biased towards the TEPCO story) it is suggested that from 6:10 JST on the 12/3/11 all emergency cooling systems became ineffective, however:

'...After this point, operators used a non-emergency system known as the Makeup Water Condensate System MWCS to maintain water level. While this system was not designed for an accident scenario, it was successful in maintain a stable water level until the primary coolant systems could be repaired...'

Looking at the NRC saftey spec of the MWC system, it becomes clear that only 570 tons of water are available for cooling and that at maximum, this will cool a reactor in station blackout for 8 hours.

(See: - section

Therefore it seems highly likely that all options for cooling failed by approximately 14:10 JST on the 12/3/11 around 35 hours before the first of the reactors regained residual heat cooling (#1 at 1:24 JST 14/3/11).

It seems certain that 35 hours is more than enough for a complete melt-through...

Where did the 3000 tons of water come from? Leakage of the primary circuit?

Does anyone know something about the radioactive landscape at Daini now?

Anonymous said...

I can't respond to all the comments without making this a little too long, so with apologies I will try to cover as much as possible. On further reflection, I think that what happened at Daini is probably most comparable to what happened at Unit 5 at Daiichi. Unlike Units 1, 2 and 3 at Daiichi, at Daini there was reportedly no station blackout or loss of coolant (LOCA), so the studies that predict core damage within hours don't appear to apply. On this basis, I would guess that no pipes broke and that the primary or secondary cooling circuits did not fail. Instead, my guess (and it is just a guess) is that there was a LUHI or loss of ultimate heat sink because the tsunami (not earthquake) damaged the seawater pumps. As a result, heat could not be removed from the cooling circuits as these were water cooled by seawater. So, I am guessing that what they were doing was what somebody was calling "Bleed and Feed," where water is added to the primary cooling circuit or to the reactor vessel itself and water vapor (not air) is vented. They tried the same thing with Units 1, 2 and 3 at Daiichi, but they could not feed enough water to the reactors and the level of liquid water dropped uncovering the cores. If, as TEPCO reported, the water levels did not drop and the cores did not get uncovered at Daini, then the likelihood is that there would have been little to no damage to the Daini cores.

As with Daiichi Unit 5, I guess that they were able to rig some sort of replacement seawater pumps at Daini to restore cooling and then were able to bring all of the reactors to a cold shutdown. The water vapor that was bled (not air as probably mistranslated in the TEPCO press releases) would have been contaminated with radioactivity and may have condensed inside the buildings and ended up as the contaminated water that Anon 9:45 AM makes reference to. So, there may have been loss of cooling, but not loss of coolant and therefore probably little to no damage to the cores. The radioactivity release to the environment would thus be limited to what was in the water vapor that was vented and, hopefully, almost all of the fission products would have remained safely contained in the core. At least, I would hope that is the case.

I added the caveat that TEPCO's reports were presumed accurate, because I was uncomfortable with the way they worded the press releases. I wanted readers to understand that my comment was based on that assumption of accuracy, so that they could independently make their own judgement of the credibility of the TEPCO press releases (as many commenters have indeed done) and not simply assume that I am or was the source.

P.S. @ evendine 6:15 PM

TEPCO (not me) reported in their press releases that there was no loss of offsite power at Daini, so no blackout. It is unclear from your link how much water would have been available when there was no blackout. All it says is 570 tons when there is a blackout. Loss of the seawater pumps would have also meant loss of the generators that were water-cooled, but if, as TEPCO reports, grid power was not lost, there would have been no blackout with loss of the generators.

Anonymous said...


TEPCO estimated that the tsunami that followed the earthquake and inundated the plant was 14 meters high which is more than twice the designed height.[6] This flooded the pump rooms used for the essential service water system transferring heat to the sea, the ultimate heat sink of the reactors.[12] While the cooling system for unit 3 was undamaged, the other reactors were affected. The cooling systems remained operational, but heated up due to the lack of a heat sink. The high pressure coolant injection (HPCI) system (powered by reactor steam) was used as additional cooling.[12] On March 12, the cooling system for three reactors (numbers 1, 2 and 4) at the torus had topped 100 °C between 05:30 and 06:10 JST,[13][14][15] rendering all cooling systems (which depend on a temperature difference between the torus and the reactor) ineffective.[12] After this point, operators used a non-emergency system known as the Makeup Water Condensate System to maintain water level. While this system was not designed for an accident scenario, it was successful in maintain a stable water level until the primary coolant systems could be repaired. However without the Torus, pressure in the reactor and containment vessel was unable to be controlled, and operators prepared to vent the containment however this operation did not end up being executed.
Fukushima I and II Nuclear Accidents Overview Map showing evacuation and other zone progression and selected radiation levels.

The coolant systems in the pump room were repaired and activated in Units 1, 2 and 4 in the days following the emergency shutdown after cooling could recommence.[13] Coolant temperatures below 100 °C (cold shutdown) were reached in reactor 2 about 34 hours after the emergency shut down (SCRAM).[13] Reactors 1 and 3 followed at 1:24 and 3:52 on March 14 and Reactor 4 at 7:00 on March 15.[16] The loss of cooling water at reactors 1, 2 and 4 was classified a level 3 on the International Nuclear Event Scale (serious incident) by Japanese authorities as of March 18.[17][18][19]

Officials made preparations for release of pressure from the plant on March 12.[20][21] As of March 20, however, no pressure release had been reported.[13][22]

Please see the Wikipedia article for links to the references. So, according to Wikipedia, no meltdowns, safe shutdowns and no venting. So where did the reported contaminated water come from?

evendine said...

I think you're missing the central point - that the primary core cooling system failed at Daini. The Tsunami took out the primary cooling system heat-sink, i.e. the way heat is dissipated into the environment from the reactor.

'...The essential service water system (ESWS) circulates the water that cools the plant’s heat exchangers and other components before dissipating the heat into the environment. Because this includes cooling the systems that remove decay heat from both the primary system and the spent fuel rod cooling ponds, the ESWS is a safety-critical system...'


There were 35 hours between the Makeup Water Condensate System becoming inoperable and the Residual Heat Removal System being re-started - easily enough time for a melt through (less than 4 hours without cooling are required)...


Anonymous said...

"So, according to Wikipedia" .. and Wiki's band of editors ..

"Preparations for opening the vents of nuclear reactors to prevent hydrogen explosions were made at the Fukushima No. 2 nuclear power plant shortly after the March 11 earthquake and tsunami damaged the plant's cooling systems, according to data released Wednesday by Tokyo Electric Power Co.

TEPCO did not have to open the vents because it repaired the cooling systems in time."

"On the day of the disaster, the Nos. 1, 2 and 4 reactors suffered damage to cooling pumps, the data showed."

So if they restored the Residual Heat Removal System, they had to replace the pumps. They may have dumped the system's water.

As others more knowledgeable have said, introducing sea water for cooling is the reactor's death knell.

Their most recent tension is why replace the pumps if the sea water kills the reactors?

evendine said...


I think as our host mentioned in the original article above, much of what happened at Daini has been overlooked, probably because of the terrible events at Daiichi, but from my research, it seems likely that a melt-through occurred at Daini too.

The Yomiuri link you posted has an interesting section:

'...Preparations for opening the vents of nuclear reactors to prevent hydrogen explosions were made at the Fukushima No. 2 nuclear power plant shortly after the March 11 earthquake...'

By implication, if TEPCO was preparing to vent the containment due hydrogen build up, a melt-down must have been in progress, as hydrogen is only produced when the core reaches (c)2,240 °F leading to a zircalloy reaction producing hydrogen. At slightly above this temperature, the core will inevitably melt without cooling...


Does anyone have a recent picture of the Daini site? Couldn't find anything useful on google...

evendine said...

Interesting that Fukushima doesn't even get a mention here, don't you think?:

Anonymous said...

Seawater is not normally pumped into the reactor vessels. Instead it is pumped through heat exchangers to cool other circuits. shows schematics of the various systems at the different reactors at both Daiichi and Daini. Page 5 shows the schematics for Daini.

In the schematics for Daini, the Make-Up Water Condensate System (MUWC) shows it drawing water from the Condensate Storage Tank. The size of the tank is not shown. However, if you look at the schematic for Daini and follow the arrows from the MUWC, there is a branch that goes to the FPC (which is identified on page 8 of the schematic link as the Fuel Pool Cooling and Filtering System). Then if you look at the line coming out of the Skimmer Surge Tank of the Spent Fuel Pool, there is an arrow that goes to the RHR (identified on page 12 as the Residual Heat Removal System). On that same page it says that the RCIC and RHR can work together. So, if the suppression pool had been heated to 100°C, thus shutting down the RCIC as TEPCO IIRC said, then it may be possible to use water from the spent fuel pools (which is normally kept at closer to 20°C). The spent fuel pool for each reactor is much larger than the Condensate Storage Tank. Obviously, you would be heating the spent fuel pool faster as the spent fuel pool becomes the heat sink for the reactor vessel, but it would buy you precious time, I would think.

I don't know if that is what they did. Their press releases are short on detail. states: "Units 1, 2 and 4 were prepared for potential pressure release, but this was never required."

Anonymous said...

I like that analysis 7:50.

Fuel rod damage is not uncommon.

Tsunamis really shuffle the deck of options and they scramble to keep it under control.

Anonymous said...

When the plant shutdown they started cooling with the RCIC. After reduction from high pressure the RCIC shuts down due to lack of steam, so after this they injected water directly from the Condensate storage tank using the MUWC pumps to maintain the water level throughout the duration period. At one point in unit 4 the high pressure core spray was repaired so in that unit they switched to that. Eventually once RHR was available they used the LPCI mode of the RHR to maintain water level until the suppression pool was cooled down then they switched to shutdown cooling mode where you directly cool the reactor water.

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