Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[tsutsuji]

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110817/0525_taisaku.html Tepco is planning a new strategy to further reduce radiations in addition to building cover structures above the reactors : pumping contaminated gases directly out of the containment vessels. At present the radiations released outside through the interstices created by the explosions are 1,000,000,000 Bq/hour. This will be implemented after technical issues are solved.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110817/index.html Based on measurements made over the past two weeks, the radiations released outside the plant premises are estimated to be less than 2,000,000,000 Bq/hour (I am not sure how this figure is related to the above one). This is 5 times less than one month ago and 10,000,000 times less than in mid-March. Tepco says that this is an estimate, with the exact value remaining unknown as no direct measurement method has been found.

http://www3.nhk.or.jp/news/genpatsu-fukushima/20110817/1850_teishi.htmlIt was found by the Government's investigation committee that managers such as the plant manager took some countermeasure-related decisions on the day of the accident at unit 1 while ignoring that some emergency cooling equipments had been shut down by the plant operators relying on their own judgment(*). According to specialists, the failure to pass safety-related information could have made the situation worsen. It is known that from about 6:30 PM on 11 March an emergency condenser was shut down for three hours. Because they could not observe any steam, the plant operators believed that the condenser was subject to a "boil-dry" as it is called when water has run out, and they shut it down in order to preserve it from being broken(*). This event was not reported to the managers in the seismic-isolated building such as plant manager Yoshida. Mr Yoshida admitted that this failure in the information flow was "a big mistake". An Institute of Applied Energy expert says "If the emergency condenser had been running, a certain level of water should have been secured, but what was actually happenning was that the water level was quickly declining and a different water injection method should have been immediately implemented. As they were persuaded that they had some latitude until a meltdown would occur, it is possible that the situation was made more serious".

The suspicion that the earthquake caused severe damage to the reactors is strengthened by reports that radiation leaked from the plant minutes later. The Bloomberg news agency has reported that a radiation alarm went off about a mile from the plant at 3.29pm, before the tsunami hit.
http://www.independent.co.uk/news/w...truth-behind-fukushimas-meltdown-2338819.html

Kurion Vice President and Chief Technology Officer, Dr. Mark Denton, summarized the Kurion strategy as “delivering (...): i) isotope extraction – using special inorganic media with very high isotope removal capacity (even in seawater conditions), high radiation resistance, and ability to be vitrified with little or no off-gassing and ii) isotope stabilization – by vitrification of the depleted media to volume reduce and immobilize the radionuclides in a leach resistance glass matrix waste form normally reserved for high level waste.”
http://www.timescolonist.com/business/CORRECTING+REPLACING+Kurion+Specific+Media+System+Achieving+Water/5258292/story.html?cid=megadrop_story#ixzz1VJ0XLNdU

* Note : I edited two sentences after rmattila quoted me below. I was a bit confused about who said what, but the main information remains unchanged.

 

[rmattila]

Tepco plans to install desalination systems and decontamination systems with zeolite at units 2,3,4 spent fuel pools [How about unit 1?].

IIRC, they never needed to pump seawater into unit 1:s SFP, since its decay heat was sufficiently low to allow waiting for fresh water to be available for cooling. Thus, there should be no need for desalination at unit 1:s SFP.

 

[rmattila]

As a result of the testimonies of Tepco-related people it was found by the Government's investigation committee that managers such as the plant manager took some countermeasure-related decisions on the day of the accident at unit 1 while ignoring that some emergency cooling equipments had been shut down by the plant operators relying on their own judgment. According to specialists, the failure to pass safety-related information could have made the situation worsen. It is known that from about 6:30 PM on 11 March an emergency condenser was shut down for three hours. Those Tepco-related people said that because they could not observe any steam, the plant operators believed that the condenser was subject to a "boil-dry" as it is called when water has run out, and they shut it down in order to preserve it from being broken. This event was not reported to the managers in the seismic-isolated building such as plant manager Yoshida. Mr Yoshida admitted that this failure in the information flow was "a big mistake". An Institute of Applied Energy expert says "If the emergency condenser had been running, a certain level of water should have been secured, but what was actually happenning was that the water level was quickly declining and a different water injection method should have been immediately implemented. As they were persuaded that they had some latitude until a meltdown would occur, it is possible that the situation was made more serious".

This still doesn't fit to the figure given in GE:s documentation for the water reserves at the secondary side of the IC.

If I have gotten the pieces right, TEPCO now tells us that

• The IC valve was closed at some time around 3 pm, after the quake but before the tsunami (is the accurate time given somewhere?)
• It is "uncertain" whether the valve remained closed between 3 pm and 6:10 pm, but at 6:10 pm it was "confirmed" open.
• The valve was closed again "around 6:30" (6:25 in some documentation) since no steam was observed, and it remained closed until 9:30 pm,
• If they had known the IC valve was closed between around 6:30 and 9:30, that could have helped the situation.
• No mentioning is made whether water was being fed for the IC at any time.

The way I see it, if the figure (found in GE:s generic BWR documentation) of 90 minutes is valid for 1F1, it could well be that the IC had really boiled dry between 3 pm and 6:25, and the notion of no steam was correct. Then it would not have made any difference at all if the valve was open or closed if they at no time fed any water to the IC. The crucial question is: did they? If they did at some time between 6:30 and the core damage time, then the closing of the valve apparently was the crucial error that led to the core uncovery and damage. But if they at no time fed any fresh water to the system, and its capacity really only is 90 min, then it was the failure to replenish the IC rather than the closure of the valve that was obviously the more crucial error.

EDIT: And thank you, tsutsuji. You are really doing a great job to keep many people up-to-date of the data that sometimes is quite difficult to obtain from other sources here at the other side of the world.

 

[Bandit127]

Tepco have released a new video, "Reporting from the grounds of Fukushima Daiichi Nuclear Power Station".
http://www.tepco.co.jp/en/news/110311/images/110817e.wmv" (It's nearly 45 MB).

If you can see beyond the reassuring spin, it is a good insight into what it is like for the various people working there.

Two scenes provide a perspective. The first is the fitting of the facemask and switching the noisy blower on. I wonder how many of them have such facemasks - I struggle to believe it is all of them.

The second was the guy proudly showing off his cooling vest with 4 freezer packs in it. That would be worth simply 4 kgs of extra weight 30 minutes after starting an 8 hour shift.

The people on the ground there have my utmost respect for what they go through to earn a day's pay.

 

[MadderDoc]

<..>
If I have gotten the pieces right, TEPCO now tells us that
The IC valve was closed at some time around 3 pm, after the quake but before the tsunami (is the accurate time given somewhere?)

Yes, in the Tepco document "Response after the Earthquake.." it says:

"At 15:03, reactor pressure of Unit 1 dropped so fast and the reactor coolant
temperature decreased 55 C per hour, exceeding a criteria in the Tech.Spec. Then
operators closed MO-3A and 3B, return isolation valves of IC. IC was in stand-by
condition with other valves in the IC remained open. Operators judged that only one
train of IC was sufficient to control the reactor pressure in 6 – 7 MPa. They decided
to use Train A and started to control the pressure by operating MO-3A."

[*]It is "uncertain" whether the valve remained closed between 3 pm and 6:10 pm, but at 6:10 pm it was "confirmed" open.
[*]The valve was closed again "around 6:30" (6:25 in some documentation) since no steam was observed, and it remained closed until 9:30 pm,
[*]If they had known the IC valve was closed between around 6:30 and 9:30, that could have helped the situation.
[*]No mentioning is made whether water was being fed for the IC at any time.
[/list]

According to the same Tepco document as above, the valve was opened at 6:18 pm, and closed again at 6:25 pm, and the system was observed to be functional. (I.e. this is in direct inconsistence with your information that steam was not observed) I've interpreted this to mean that once DC had been restored to indicate the status of the valves, the functionality of the IC system was briefly checked, found to be OK, and the system was then left on stand by (perhaps because the water level in the RPV had been unknown since 3:50 pm , so no data was available to guide the operation of the valves).

"In MCR, operators found indication light of MO-3A and MO-2A after temporary
restoration of DC power. The indicators showed the valves were closed. Then an
operator opened the valves at 18:18 and confirmed the light indicated the valve
status from close to open. Also steam generation was confirmed after the valve
operation. At 18:25, the operator closed the return line isolation valve (MO-3A)."

Then later,

"Reactor water levels were become clear for Unit 1 at 21:19"

The water level indicated was 200 mm above TAF. Shortly following that, apparently the IC system was then activated (and according to data water level in the RPV was indeed on the increase for a while thereafter ) :

"At 21:30, the operator opened the MO-3A and confirmed that steam was generated."

The way I see it, if the figure (found in GE:s generic BWR documentation) of 90 minutes is valid for 1F1, it could well be that the IC had really boiled dry between 3 pm and 6:25, and the notion of no steam was correct. Then it would not have made any difference at all if the valve was open or closed if they at no time fed any water to the IC. The crucial question is: did they? If they did at some time between 6:30 and the core damage time, then the closing of the valve apparently was the crucial error that led to the core uncovery and damage. But if they at no time fed any fresh water to the system, and its capacity really only is 90 min, then it was the failure to replenish the IC rather than the closure of the valve that was obviously the more crucial error.<..>

Maybe the notion that no steam was observed at 6:18 - 6:25 pm is incorrect, seeing we are told the opposite thing in the above-mentioned document. The increase in water level after 21:30 might indicate that the IC was functioning and supplied water to the pressure vessel, no alternative ways of injection had been implemented at that stage, so apart from IC there was only HPCI that could theoretically have fed the water.

 

[tsutsuji]

http://mainichi.jp/select/weathernews/20110311/news/20110817k0000m040142000c.html Sources close to the Government investigation committee say that Tepco said that nobody had foreseen the possibility of an hydrogen explosion before it occurred. It was also said that because they had no instruction manual for venting, they had to study the procedure using the plant blueprints. As a consequence of the blackout, necessary equipments such as batteries were ordered. As precise information concerning the needed types were not provided, several different types were delivered, and it became difficult to sort them afterwards. Some equipments were delivered to Fukushima Daini or to J-Village and they had to go to take them there. It was said that the support from Tepco's main headquarters was not sufficient. Concerning unit 4, although the possibility of hydrogen flowing backwards from unit 3 to unit 4 is being considered, it remains unknown if there was enough pressure for such a backward flow. Concerning seawater injection, it was apprehended that the quantity of freshwater in the fire suppression tank was limited and that it would become necessary at some stage to use seawater. When Tepco's main headquarters ordered to stop seawater injection, as that would have provoked terrible consequences, they pretended they had done so, while continuing seawater injection. The helicopter water drops forced to suspend blackout recovery work. A number of times the helicopter seemed to miss its target. Tepco said that no damage due to the earthquake was observed at units 2,3,5 where the East-West standard earthquake intensity was exceeded.

After reaching the bottom of the page, I discovered a link to an English translation (translating the top part of the Japanese article only) : http://mdn.mainichi.jp/mdnnews/news/20110817p2a00m0na016000c.html

The "no steam" event is reported in the English language NHK news too :

The worker told the investigators that the system appeared to be operating at boiling temperature but was not producing steam.
http://www3.nhk.or.jp/daily/english/17_28.html

http://mainichi.jp/select/weathernews/news/20110817dde001040067000c.html A NISA official, Mr Yamagarbagea had the following reactions : the NISA was putting much value on countermeasures against hydrogen explosions inside containment vessels, but was not sufficiently evaluating the risk of a hydrogen explosion inside the reactor building. Concerning the absence of a manual for venting during a blackout he said "venting was supposed to be operated from the (electric power supplied) control room. The lesson will be learned and implemented in safety measures in the future".

 

[drussell]

Hello, all! I finally had to un-lurk...

The suspicion that the earthquake caused severe damage to the reactors is strengthened by reports that radiation leaked from the plant minutes later. The Bloomberg news agency has reported that a radiation alarm went off about a mile from the plant at 3.29pm, before the tsunami hit.
http://www.independent.co.uk/news/wo...n-2338819.html

While there is certainly evidence that there were likely severe problems with the plants after the earthquake but prior to the tsunami, does anyone have a reference to any radiation alarm actually showing a radiation increase before the tsunami? I believe I have only seen reports of the monitoring post alarm which went off due to a monitoring station that was off-line and not reporting any data (ie. was probably damaged or disconnected by the earthquake) rather than an alarm due to an increase in radiation.

A special thank-you also, to Tsutsuji, for all your effort helping to keep us informed!

 

[MadderDoc]

<..>
The "no steam" event is reported in the English language NHK news too :
http://mainichi.jp/select/weathernews/news/20110817dde001040067000c.html <..>

The 'no steam observed' in that article seems to me to have reference to the period shortly after the quake, and before the tsunami, i.e. not to the period shortly after 6 pm, when the Tepco document clearly states that steam was observed. Also it seems to me (as a layman), that an recently switched on operating IC might not necessarily initially produce steam, but would do that only once a certain heat up on the shell side had occurred.

 

[rmattila]

According to the same Tepco document as above, the valve was opened at 6:18 pm, and closed again at 6:25 pm, and the system was observed to be functional. (I.e. this is in direct inconsistence with your information that steam was not observed) I've interpreted this to mean that once DC had been restored to indicate the status of the valves, the functionality of the IC system was briefly checked, found to be OK, and the system was then left on stand by (perhaps because the water level in the RPV had been unknown since 3:50 pm , so no data was available to guide the operation of the valves).

This would be a consistent explanation, however I have very difficult time grasping how the system could be left standing by instead of activating it, if the reactor was completely without feedwater. After an hour or so, the decay heat would boil off some 10 kg/s of coolant from the reactor, which means the core level dropping by some 3 cm per minute, or almost two meters per hour, if the IC is not removing the decay heat by boiling off water from the secondary side. Even though you are uncertain of your level measurements, it should be obvious that your level is dropping fast if you don't run the IC. A rule of thumb is that the core will be uncovered within half to one hour, if the decay heat removal is lost right after the scram. It appears they were able to remove the heat for a short while until they disengaged the IC for the first time at 15:03, but then it becomes very confusing to follow what was being done and why.

The way I see it, disconnecting the IC to stay within the TechSpecs RPV cooling rate for normal operation was probably quite appropriate as long as there was AC power at the plant, but when they entered the station blackout situation, the situation changed and the appropriate EOP:s should have instructed to prioritize the cooling of the reactor to optimizing the RPV transient budget. It's absolutely necessary to have the core covered at all times, while a one-time violation of the RPV cooldown rate most probably is no big deal, and this difference in consequences should somehow be reflected in the EOPs to make sure that the operators err in the correct direction, if they are unsure of the core status.

It can be that the deterioration of the situation from an AOO to a beyond-design basis accident did not affect the operations in the way it should have done, but this is probably something that will take a long time and proper examination to find out. For me, i think the biggest question regarding the whole series of accidents at Fukushima is this: why did they lose unit 1 even though it had the IC that appears to have been more or less functional? If the operators indeed disengaged the IC not realizing they were at risk of exposing the core, the situation ironically reminds that at TMI, where the core was left to get exposed by shutting down cooling systems as the operators thought there was sufficient cooling in the core. Preventing the reactor safety systems from fulfilling their task by intervening according to false understanding of the situation is something that should not happen.

 

[MJRacer]

TEPCO has considerable stake in claiming that the meltdowns were entirely the result of an unforeseeable, rare event (huge tsunami) rather than being initiated by earthquake damage from shaking that was within or just barely exceeded the plant design basis.

I assume that the judgement that the shaking was within or just barely exceeded the design basis was based on a publication by TEPCO of the Seismic Data measured at Fukushima (http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e27.pdf). From the table, 18 maximum response accelerations were reported for Dai-Ichi, one each for each direction (i.e. north-south, east-west and up-down) for each of the 6 reactors. 3 of the 18 exceeded design parameters by 25% (unit 2, E-W), 15% (unit 3, E-W) and 21% (unit 5, E-W), respectively. However, 17 of the 18 observations are marked with an asterisk showing that only about 2-3 minutes of the earthquake was recorded, due to a glitch in the software but TEPCO said that the error probably wasn't that significant.

Notwithstanding this report, it is clear that this was a huge earthquake and that strong shaking lasted between 3 and 5 minutes (http://www.scientificamerican.com/article.cfm?id=fast-facts-japan). When earthquakes are that long, simply measuring peak acceleration may be an incomplete statistic. What impact does earthquake duration have on structural damage? First, I looked at Effect of Earthquake Duration on Structural Reliability, Lindt & Goh, 2004, but they only looked at durations of 30 to 90 seconds (page 1591). Earthquakes of 3 to 5 minutes are apparently quite outside the norm.

I then looked at a FEMA publication called Structural Dynamics of Linear Elastic Single-Degree-of-Freedom (SDOF) Systems (http://www.nibs.org/client/assets/files/bssc/Topic03-StructuralDynamicsofSDOFSystemsNotes.pdf ). Among other things, it covers the important issue of resonances induced by earthquakes in structures. It is well worth reading to understand the next point, unless you are familiar with the subject. On page 88, there is a "Four-way Log Plot of (the) Response Spectrum (Plotted vs. Period)." It would seem that this is the same type of plot in TEPCO's publication on page 5. TEPCO's pdf is of very good quality and one can zoom in on the two 4-way log plots to see them better. Figure 2-2 is of ground motion at the GN4 Observation Point. If you look carefully at the zoomed-in 4-way plot, it looks like the plot of the South Point exceeds 500 gals (peak ground acceleration) for wavelengths (TEPCO calls it a period) between about 0.06 seconds to about 0.22 seconds. The plot appears to approach 1000 gals at a wavelength of just over 0.1 seconds in the E-W direction. If you call it 950 gals, that would be more than twice the approximately 450 gals design basis. The N-S plot (Fig. 2-4) also appears to significantly exceed 500 gals for a wavelength of 0.1 seconds. (I am looking at the lines on the plot that are in the SW to NE direction and that are labeled "50," "100," "200," "500," "1000," and "2000." Outside the top right of the plot there is a label shown diagonally in the same direction as "cm/s2," which would be gals.)

On page 6 of TEPCO's report, Fig. 4-1 seems to show the acceleration response spectra for the base mat of unit 1 exceeding 1000 gals for a wavelength of just over 0.5 seconds. Likewise, Fig. 4-2 shows the response spectra for unit 2 as substantially exceeding 1000 gals for a wavelength peaking at about 0.3 seconds. Similarly, Fig. 4-3 shows a peak for unit 3 of about 1500 gals for a wavelength peaking also at 0.3 seconds. Fig. 4-4 for unit 4 is lower but still has peaks that clearly appear to be above 500 gals. Fig. 4-5 is for unit 5 and shows a peak exceeding 1000 gals also at a wavelength of about 0.3 seconds. Fig 4-6 is for unit 6 and shows a peak approaching 1000 gals at a wavelength of about 1.25 seconds. These are all in the E-W direction.

In the N-S direction, Fig. 4-9 for unit 3 shows a peak almost at 1000 gals for a wavelength of about 0.45 seconds. Figures 4.7 (unit 1) and 4.8 (unit 2), show peaks clearly above 500 gals and maybe closer to 800 - 900 gals at a wavelength also of about 0.45 seconds. Figures 3-1 through the top plot of 3-6 clearly show the data recording stopping abruptly.

Unless I am completely misunderstanding these plots, it would seem that the peak accelerations at Fukushima Dai-Ichi greatly exceeded the design basis of about 450 gals at least at specific wavelengths.

So, I looked further to see if there were other measurements of earthquake intensity. I looked at Analysis of Cumulative Absolute Velocity (CAV) and JMA Instrumental Seismic Intensity (I_JMA) Using the PEER-NGA, Strong Motion Database, Campbell and Bozorgnia, 2010 (http://peer.berkeley.edu/publicatio...s_2010/webR_PEER10_102_Campbell_Bozorgnia.pdf).

On pdf pg. 14,

Cumulative absolute velocity (CAV) is defined as the integral of the absolute value of an acceleration time series... (and) ...includes the cumulative effects of ground motion duration. This is a key advantage of CAV over other peak ground motion and response-spectral parameters and is one of the reasons that EPRI (1988) found it to be the ground motion parameter that best correlated with structural damage out of the many ground motion parameters that it investigated.

The authors then defined a slightly different measure that they termed standardized CAV in which accelerations below a threshold value are not counted (pdf pg. 16) on the basis that small magnitude earthquakes of long duration (which may cause no damage whatsoever) could have a large CAV. On that same page, they note that

(t)he USNRC (U.S. Nuclear Regulatory Commission 1997) uses standardized CAV as one of the ground motion measures to determine whether a nuclear power plant must be shut down after an earthquake when the operating basis earthquake (OBE) ground motion is exceeded.

On page 22:

The CAV check is exceeded if anyone of the three components of the standardized CAV from the free-field ground motion is greater than 0.16 g-sec. If both the response spectrum check (see pdf pp. 21 & 22 for details) and the CAV check are exceeded, the OBE is considered exceeded and plant shutdown is required.

The paper then goes into detail regarding the JMA seismic intensity scale (I_JMA) (JMA = Japan Meteorological Agency). The rest of the paper is interesting but can be skipped for the purposes of this discussion.

I then looked at Damage Indicating Parameters and Damage Modes of Mechanical Components by K. Ochiai (Japan Nuclear Technology Institute), K. Kobayashi (TEPCO) and A. Chigama (IAEA) (http://www.jnes.go.jp/seismic-symposium10/presentationdata/4_sessionC/C-24.pdf ). On pdf page 3, there is a table that compares I_JMA and standardized CAV. Damage measured by I_JMA is due to a "Large Effective Inertia Force" and is related to "First Excursion Damage." In other words, I-JMA best measures the damage caused by a transient large amplitude deflection. Damage measured by standardized CAV is due to "Much Energy Accumulation" and is related to "Cumulative Damage (Fatigue/Ductility Exhaustion)." In short, standardized CAV is a measure of fatigue due to repeated cycling of structural elements and is related to the total energy absorbed by the structure.

Page 5 has a chart for several earthquakes plotting standard CAV on the y-axis and I_JMA on the x-axis. The S-CAV scale is from 0 to 4.5. Page 6 shows peak accelerations at Kashiwazaki-Kariwa NPS No. 7 unit of 673 gals N-S and 1007 gals E-W at the turbine pedestal top. Page 7 shows several data points for K-K, but none exceeding a S-CAV of 3 (on the right hand side where the units for S-CAV are in (g-sec)). Now, please skip to page 11. On the lower right is a chart again plotting S-CAV against 2 JMA scales. on that chart is a shaded box labeled "Design Base" which has a maximum S-CAV of about 2.25. Let's focus on that number.

I then looked at a Preliminary Report done by ITER consult on the accident at Fukushima Dai-Ichi (http://www.iter-consult.it/ITER_Report_Fukushima_Accident.pdf) dated May 2011. On page 13, it states that

Daiichi units 2, 3 and 5 exceeded their maximum response acceleration design basis in E-W direction by about 20%. Recording was over 130-150 seconds,

which is in agreement with TEPCO's report referenced above.

However, the ITER report goes on to say:

Various parameters have been proposed in the literature for estimation of the destructive power of an earthquake. Among these parameters, the CAV (cumulative absolute velocity) has been recently proposed. Using the data recorded in the Tohoku event, the CAV can be evaluated in 10, whereas in Kashiwazaki-Kariva earthquake of 2007 the CAV was equal to 2 with a recorded Peak Ground Acceleration (PGA) much higher tha(n) in Fukushima. This is apparently due to the exceptional duration of the Tohoku event.

Recalling the report on Damage Indicating Parameters, the charts showed standardized CAV with a maximum of 4.5 and the "Design Base" at about 2.25, yet here they are mentioning a CAV of 10 for the Tohoku (March 11, 2001) earthquake. It is not clear whether the 10 is a CAV or a standardized CAV. See Fig. 2.1 of the Campbell and Bozorgnia paper on pdf page 15 for a chart showing the difference between CAV and S-CAV. Even if the 10 is CAV, that would still give a very large value for recomputed standardized CAV for the Tohoku earthquake.

Now referring back to page 9 of the Damage Indicating Parameters presentation, they report a piping vibration test with a maximum acceleration of 1,877 gals that resulted in a crack during the "5th excitation" (repetition of the test). The S-CAV was reported as 23.2 g-sec or about double the CAV of the Tohoku earthquake. On page 10, they show the "Damaging Excitation Motion" test run (looks like a seismogram) and compare it to an actual seismogram from Unit 1 (presumably at K-K) at the same scale with a peak acceleration of 884 gals and an S-CAV of 2.4 g-sec. They did not have a crack in a pipe until the 5th repetition. In other words, a pipe break (which would cause a LOCA) did not take place in the test until the piping had been subjected to 5 simulated earthquakes of more than twice the intensity (measured by CAV) each of the Tohoku earthquake.

If the CAV for the Tohoku earthquake reported by ITER was calculated at Fukushima Dai-Ichi (it isn't clear), then it means that the earthquake that hit that power plant was truly huge, but yet maybe unlikely to have caused a break in piping, if the test at K-K is comparable to Fukushima.

One caveat on the ITER report as on page 2 they report:

In fact 12 out of 13 back-up D/Gs on site, located in the basements of the turbine buildings, were disabled. Only one air-cooled D/G (all others were seawater-cooled) was able to supply electrical power to units 5 and 6, which remained under full control after some initial troubles.

I had made that statement in a prior post and we all now know that is wrong, but I knew I had read it somewhere and I hadn't made it up. So the possibility exists that the ITER report has other errors in it.

In conclusion, it isn't altogether clear that "the shaking (at Fukushima) was within or just barely exceeded the design basis." The intensity as measured by CAV or S-CAV may have greatly exceeded the design basis.

 

[tsutsuji]

http://mainichi.jp/select/weathernews/news/20110729ddm008040075000c.html This is a 29 July article, but I don't remember if this information was already reported in this thread : Tepco had mentioned in May the possibility of an earthquake damage to a HPCI pipe as the possible cause of the sudden pressure decline on 12 March at unit 3. But as a result of new investigations, this is now ruled out. It became clear that a worker had entered a location close to the HPCI pipe for a flow adjustment shortly after the HPCI stopped. If there had been a steam leak, the high temperature would have prevented this worker to work so closely.

http://www.tohoku-epco.co.jp/news/atom/1183461_1065.html Tohoku Electric reports to NISA that they have checked their seismometers and are able to confirm that their seismometers are safe from the record gap troubles which happened at Fukushima Daiichi and Daini during the 11 March earthquake.

http://mainichi.jp/select/wadai/news/20110811k0000m040125000c.html It has been found that Kansai Electric failed to report to NISA some test results in 2009 and 2010 about a steam-turbine related equipment at Ohi nuclear plant unit 3. Units 1 and 2 have 4 extraction steam pipes, but unit 3 has 5. As the Kansai Electric employee copy-pasted the unit 1 and unit 2 form, he forgot the 5th one.

 

[westfield]

snip >

It's absolutely necessary to have the core covered at all times, while a one-time violation of the RPV cooldown rate most probably is no big deal, and this difference in consequences should somehow be reflected in the EOPs to make sure that the operators err in the correct direction, if they are unsure of the core status.
<snip.

While it is absolutely necessary to have the core covered at all times at this moment we don't even know if the large overshot of the predetermined cooldown rate was perhaps itself a complicating factor at Unit #1. Exceeding the cooldown rate even once is not a small deal, particularly in a plant that has already been stressed by a major earthquake and could well be a contributing factor to the units later problems. While probably not high on the list it cannot be discounted.

The thermal stress of fast cooldown cycling with fast heatup (when IC was turned off) is really pushing things in a plant so old, so brittle and so shaken by the quake.

I'm agreeing that of course the core should be covered but pointing out that nothing is at all black and white. Cycling the IC system while they were chasing the cooldown\heatup may not turn out to have been a good thing to do but should they have just let it exceed the cooldown rate instead? Well no, they didn't want to risk breaking the plant any further so they would not want to do that. It would have been a massive gamble to let the temperature drop uncontrolled.

 

[rmattila]

I'm agreeing that of course the core should be covered but pointing out that nothing is at all black and white. Cycling the IC system while they were chasing the cooldown\heatup may not turn out to have been a good thing to do but should they have just let it exceed the cooldown rate instead? Well no, they didn't want to risk breaking the plant any further so they would not want to do that. It would have been a massive gamble to let the temperature drop uncontrolled.

Since the pressure vessel must have enough transient budget to withstand a large break LOCA in a steam line, which leads to a very rapid cooldown, I don't see a significantly slower cooldown attainable by IC a massive gamble from point of view of safety. It might have been a gamble from point of view of continued plant operation afterwards, but I doubt it. After all, after they had lost all AC power, they were at a beyond design basis situation, and saving the further operability of the plant should not be a factor affecting operations at that stage.

 

[Borek]

In appreciation of Tsutsuji-san efforts to keep us informed about the events, his account was upgraded to a gold one

 

[tsutsuji]

In appreciation of Tsutsuji-san efforts to keep us informed about the events, his account was upgraded to a gold one

Thank you Borek. I hope I will be able to keep being worthy of this honour.

http://www.jiji.com/jc/zc?k=201108/2011081100397 (11 August) The NISA found two modelling mistakes in the earthquake safety calculations of Fukushima Daini unit 2. The influence of earthquakes had been underestimated for two reactor-related equipments. Other plants using the same Hitachi-GE Nuclear Energy technology must check if they made the same mistake.

http://www.jiji.com/jc/c?g=soc_30&k=2011081700310 SARRY had a filter clogged, probably due to the presence of rust in the pipes, and it took two hours to change the filter, Tepco reported on 17 August.

http://www.nikkei.com/tech/news/article/g=96958A9C93819595E3E5E2E0E38DE3EAE2EAE0E2E3E39790E0E2E2E2;da=96958A88889DE2E0E2E5EAE5E5E2E3E7E3E0E0E2E2EBE2E2E2E2E2E2 The launch of SARRY using highly contaminated water is planned for 18 August in the middle of the day. If any of the three systems (Kurion, Areva, SARRY) breaks down, the remaining two can go on with the water purification, which should contribute to the stabilisation of the facility. The utilisation rate for the 10-16 August week is 88%. The rate from the 17 June start till now is 69%. After the water levels in the buildings have declined enough, Tepco will be able to raise the injection rates into the reactors and cool them more effectively.

http://www.nikkei.com/news/category...E5E2E6858DE3E5E2EAE0E2E3E39180EAE2E2E2;at=ALL The NISA reports that 24 seismometers have been found all over Japan with the same data recording software bug that occurred at Fukushima Daiichi and Daini during the 11 March earthquake. The Hokkaido, Chubu, and Kyushu electric power companies, with Japco and Jaea made the necessary repairs.

Kazuro Hirahara, president of the Seismological Society of Japan:

We expect aftershocks for more than five years in areas surrounding the hypocentral region. There is the possibility that an earthquake measuring close to magnitude 8.0 could strike.
(...)
we had missed the fact that a huge amount of energy had been stored under the sea near the Japan Trench. We have set up a panel at the Seismological Society of Japan to identify problems and look into what went wrong with our forecast.
http://www.asahi.com/english/TKY201108170256.html

http://www.yomiuri.co.jp/dy/national/T110815004956.htm Cracks found in seabed off Sanriku coast

 

[tsutsuji]

The 'no steam observed' in that article seems to me to have reference to the period shortly after the quake, and before the tsunami, i.e. not to the period shortly after 6 pm, when the Tepco document clearly states that steam was observed. Also it seems to me (as a layman), that an recently switched on operating IC might not necessarily initially produce steam, but would do that only once a certain heat up on the shell side had occurred.

Mainichi's source for the "manager Yoshida did not know IC is shut down" story is a memorandum on the hearings at the fact-finding panel which is summarized in the lower part of http://mainichi.jp/select/weathernews/20110311/news/20110817k0000m040142000c.html : 担当作業員がＩＣを１１日午後６時半から約３時間、停止させたが、吉田所長らは把握せず、動いていることを前提に対策を講じた - The employee in charge shut down the IC on the 11th from half past 6 PM for 3 hours. Yoshida and other plant managers did not know about it and were deciding countermeasures on the premise that it was still running.

Both Mainichi and NHK seem to understand their source(s) nearly the same way, except that the "no steam observed" part is being reported only by NHK. If what you say is right, it could mean that the memorandum writer made a mistake.　Other news sources don't report this story.

 

[tsutsuji]

Pages 8 and 9 of http://www.tepco.co.jp/cc/press/betu11_j/images/110524d.pdf explain why the breakers tripped :

Okuma 1L : breaker O-1 trips because of the damage of breaker O-81
Okuma 2L : breaker O-32 trips because of the damages of breaker O-82 and disconnector O-82
Okuma 3L : breaker O-33 trips because of the arc at tower No. 7 (arc traces were observed, showing a conductor touched or came close to the tower)
Okuma 4L : breaker O-34 trips because of the arc at tower No. 11 (arc traces were observed, showing a conductor touched or came close to the tower)
Yonomori 1L : breaker O-93 trips because conductors touched or came close to each other. Also, Yonomori tower No. 27 collapsed.
Yonomori 2L : breaker O-94 trips because conductors touched or came close to each other. Also, Yonomori tower No. 27 collapsed.

For people who are curious about this Tepco 24 May press release "Submission of a report on investigation of causes of damage situation of power facilities inside and outside of Fukushima Daiichi Nuclear Power Station to NISA" which was never translated into English, I found that the NISA's evaluation, which contains much of what Tepco said on that topic is available in English on the NISA website :

TEPCO believes that the damage of electric facilities such as major transformers was caused by the earthquake since the tsunami did not reach the Shin-Fukushima Substation.
In addition, these electric facilities were designed with some margin against the seismic design guideline (JEAG5003) issued by the private sector, but since they were damaged nevertheless, a detailed analysis is required to investigate the cause of these damages.
http://www.nisa.meti.go.jp/english/files/en20110528-4.pdf page 22/33

 

[Bodge]

Please can somebody explain where the Xe-131m in Reactor 2's containment is coming from?

Have a look at Tepco's recent handout:
http://ex-skf.blogspot.com/2011/08/fukushima-i-nuke-plant-krypton-85-and.html

47 bec/cm3

Is the corium fissioning in a water saturated environment?

 

[Bodge]

http://fukushima.over-blog.fr/article-le-corium-de-fukushima-2-effets-et-dangers-81400782.html"

“The worst case would be a corium locking himself in the concrete or soil, which not only provides the best possible shape to maintain its integrity, increase the number of neutrons recovered, but in addition, the mass would de facto inaccessible, which would make it impossible to cool."

Would saturated concrete/soil/bedrock make a good neutron reflector?

Could there be another moderator affecting things?

Would it be harder for a fissioning corium to create voids if 'locked in'?

What about Uranium and Plutonium migrations in a 'locked' corium - will the concentrations of fissile material vary throughout the corium?

Still so many questions!

 

[MJRacer]

TEPCO believes that the damage of electric facilities such as major transformers was caused by the earthquake since the tsunami did not reach the Shin-Fukushima Substation.

http://www.tepco.co.jp/en/press/corp-com/release/11051613-e.html

This link is to a press release on May 16, 2011 regarding damage to electrical facilities at Fukushima Daiichi. There are links to ten attachments with further details, including schematics and photos. http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e17.pdf has an overall schematic of the Shin Fukushima substation. It appears to show 7 different feeds from the grid into Fukushima. 6 failed for different reasons and one(?) was down for maintenance (part of the legend is unreadable). It would seem as if there was plenty of redundancy here.

 

[zapperzero]

Would saturated concrete/soil/bedrock make a good neutron reflector?

It would be quite a bit worse than just water

Could there be another moderator affecting things?

No.

Would it be harder for a fissioning corium to create voids if 'locked in'?

I suppose you mean "would it make more, or less bubbles while it's eating into soil?" The answer is "probably, less". It may be that it would not go straight down, but instead spread out, like a root system or something. Dilution would probably happen, too, decreasing its specific temperature.

What about Uranium and Plutonium migrations in a 'locked' corium - will the concentrations of fissile material vary throughout the corium?

Probably, yes. At Chernobyl, a few kg of Pu ended up gathered all in one place. Went critical after rainwater infiltrated the basement, years after the accident. Some brave soul eventually went in there and sprayed gadolinium on it.

BUT! We have no indication that corium is critical right now.

 

[zapperzero]

It would seem as if there was plenty of redundancy here.

I laughed for real. All the lines went to a single substation. How is that "redundant"?

 

[rmattila]

Please can somebody explain where the Xe-131m in Reactor 2's containment is coming from?

In addition to being a fission product, Xe-131m is also produced by decay of I-131.

 

[MJRacer]

I laughed for real. All the lines went to a single substation. How is that "redundant"?

It is redundant because (a) "all the lines" did not go to a single substation and (b) the substation had its own internal redundancies.

If you look at (http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e25.pdf"), you can observe that the substation had two main busses: one at 275kV and one at 500kV. There were 6 separate lines connecting these busses to the switchyards at the plant itself: Okuma 1L, 2L, 3L and 4L and Yonomori 1L and 2L. The 2 Yonomori lines suffered 2 faults: a cave in at the substation and a tower collapse close to the plant. Okuma 3L suffered a broken cable and both 3L and 4L were affected by a tilting of a steel structure at the substation. Okuma 1L suffered damage to a transformer at the substation. However, Okuma 2L was undamaged but tripped at the substation (presumably the trip was due to the damage at the plant). All the lines except Okuma 1L (which tripped at the plant) tripped at the substation, presumably due to downstream damage, but trips are not considered damage.

So the internal redundancy at the substation worked as 1 of the 6 lines (Okuma 2L) there survived and the failures involved separate elements. Okuma 3L and 4L were not redundant with respect to each other, because they shared a steel structure that was tilted, but they were redundant with respect to the other 4 lines. Likewise, Yonomori 1L and 2L were not redundant with respect to each other as they shared Tower #27 which collapsed, but they were redundant with respect to the other 4 lines.

The surviving line, Okuma 2L, suffered a fault at the switchyard for units 1 and 2 (at the plant and not at the substation), where a circuit breaker and a line switch failed (see http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110516e23.pd"). Again, these were separate elements, so failure of these 6 lines was caused by separate failures in separate elements, with only 2 elements in common among only 2 lines at a time. It was not a failure of redundancy. It was a massive earthquake.

In fact, the redundancy of the substation (i.e. many separate elements) was used to restore power using parts of Yonomori 1L and Okuma 3L to a "Portable MC" supplying power to Units 1, 2, 3 and 4 on March 18. Part of Yonomori 2L was used to restore power to Unit 5 on March 20.

Finally, Appendix 1 shows a 66kV line identified as 1F. Appendix 9 identifies the same line as the Toden Genshiroku Line. From the way it is drawn, it appears to be completely independent of the Shin Fukushima substation. According to Appendix 1, it suffered a damaged cable (another independent element). Power was restored on March 15. So no, not "all the lines" appear to have gone through a single substation.

 

[~kujala~]

While there is certainly evidence that there were likely severe problems with the plants after the earthquake but prior to the tsunami, does anyone have a reference to any radiation alarm actually showing a radiation increase before the tsunami?

According to Bloomberg's original news the monitoring post was set to go off at high levels of radiation. But I guess if there would have been high levels of radiation 1.5 km from the no. 1 reactor also some other monitoring posts would have been triggered?

Surely this cannot be the only monitoring post at the Fukushima plant, can it?

http://www.bloomberg.com/news/2011-05-19/fukushima-may-have-leaked-radiation-before-quake.html

A monitoring post on the perimeter of the plant about 1.5 kilometers (1 mile) from the No. 1 reactor went off at 3:29 p.m., minutes before the station was overwhelmed by the tsunami that knocked out backup power that kept reactor cooling systems running, according to documents supplied by the company. The monitor was set to go off at high levels of radiation, an official said.

“We are still investigating whether the monitoring post was working properly,” said Teruaki Kobayashi, the company’s head of nuclear facility management. “There is a possibility that radiation leaked before the tsunami arrived.” Kobayashi said he didn’t have the exact radiation reading that would trigger the sensor.

Why has TEPCO not given us any more information about this monitoring post? Or have they?

The next information about possible radiation comes from the workers who entered no. 1 reactor building but according to news this was in the night of 11th day - so way after tsunami:

Workers entered the No. 1 reactor building in the night to assess damage to the reactor but a few seconds later their dosimeter’s alarm was triggered, according to the sources at Tokyo Electric Power Co. The building was believed to be filled with steam with high radiation dose, prompting the workers to evacuate.

Based on dosimeter readings, radiation was estimated at around 300 millisieverts per hour, according to the sources, a result suggesting a large amount of radioactive materials from nuclear fuel in the reactor was already released.

http://www.nuclearevents.info/ines-scale/level-7/fukushima-daiichi-japan-level-7-update-may-16-2011/

Something TEPCO has confirmed is that at 18:30 pm (12th of March) they measured 0.07 micro-Sv/h neutrons - so this is also after tsunami:

3/12 18:30 0.07 micro-Sv/h neutrons confirmed between North Gate and West Gate (possibility of criticality accident)

http://www.geocities.jp/swingi70/_gl_images_/P1020249toudenn.jpg

Summary:
11th of March 3:29 pm - the monitoring post went off
in the night of 11th of March - dosimeters showing 300 mSv/h inside the no. 1 reactor
12th of March 18:30 pm - 0.07 micro-Sv/h neutrons confirmed

 

[elektrownik]

Why iodine is again detected after some time when it wasnt ?
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110818e6.pdf

 

[tsutsuji]

http://www.47news.jp/CN/201108/CN2011081901000911.html Yesterday SARRY was connected in series with the French and American systems. Today they are going to connect it independently from those systems, with the goal of increasing the water treatment facility's capacity from the present 45 tons per hour to 95 tons per hour.

http://www.jiji.com/jc/eqa?g=eqa&k=2011081900799 Tepco has announced that the independently connected SARRY has been started with a 25 ton per hour flow. They plan to increase the flow to 50 tons per hour.

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110819_02-j.pdf (not translated yet) Yesterday's decontamination factors using Kurion and SARRY in series. It seems the Areva system was not used.

http://www.47news.jp/47topics/e/218724.php Tepco is reducing little by little the water injection rate into unit 3 reactor, with the goal of reaching 6 tons per hour on August 20.

 

[joewein]

Why iodine is again detected after some time when it wasnt ?
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110818e6.pdf

In almost two months the concentration of I-131 should have dropped by about two orders of a magnitude below cesium revels, instead it popped up at half an order of a magnitude below the previous detection level.

 

[Bodge]

The obvious answer to the I-131/Xe-131m question is ongoing transient criticalities.

Is there enough pu-240 for significant spontaneous fission?

Can we trust the decay heat calculations, which are based on all fission stopping at SCRAM?

 

[elektrownik]

Also here (page 6&7): http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110819e9.pdf

 

[zapperzero]

The obvious answer to the I-131/Xe-131m question is ongoing transient criticalities.

Is there enough pu-240 for significant spontaneous fission?

Can we trust the decay heat calculations, which are based on all fission stopping at SCRAM?

Wikipedia gives 26% Pu-240 (from total Pu inventory) in spent fuel.

There are some temp spikes iirc in the graphs from the first few days and I don't really buy the "faulty sensors" explanation, because now the sensors seem to be doing just fine, tracking the water injection rates in a most satisfactory manner.

The question could be settled quite easily. But I have this sneaking feeling that TEPCO isn't checking for neutrons, 'cause they don't want to know.

 

[Bodge]

Also here (page 6&7): http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110819e9.pdf

So unit 2 has I-131 in water and Xe-131 in air (containment) as late as August.

 

[Bodge]

Can anyone debunk the obvious conclusion that fission is ongoing ?

 

[elektrownik]

Can we trust the decay heat calculations, which are based on all fission stopping at SCRAM?

I think that those calculation arent apply in this case, they are for normal reactor, not melted corium... We don't know where corium is now so we can't trust any sensors, for example temperature sensors will show correct values only when core is where it should be, but if corium is in basement then temp sensors will show lower readings... This is sad but we still don't know much about real situation inside reactors...

 

[rmattila]

It is very difficult to make any conclusions on the I-131 concentrations detected in different places, since the chemistry of iodine in the aqueous solutions found in different places of the Fukushima Dai-ichi complex is somewhat complicated. The pH of the containment water is affected by the materials from the instrumentation cables and the boric acid added to the injected water at at least some occasions, and then there's the salt etc.

It looks strange to see the levels of iodine with respect to Cs dropping slower than their decay ratio would suggest, but Cs tends to stick to surfaces, and there can well be chemical mechanisms that contribute to iodine migrating more rapidly. There's still plenty of I-131 left 5 months after the scram, even though it has halved every 8 days.

If you want to find signs of criticality, I think you would be better off finding anomalies in the ratios of short-to long lived nuclides of the same element (I, Cs) to be able to eliminate the effect of the chemical complications. However, it seems that the concentration of most radioactive isotopes is below the limit TEPCO is capable of detecting.