Japan Earthquake: nuclear plants Fukushima part 2

[Azby]

Hi all. I mentioned some time ago that I was working on an update to the Safecast Report. I finished it a couple of weeks ago, actually, and it's available for download here:
http://blog.safecast.org/the-safecast-report/
Section 2.1 deals with issues at Daiichi. I cited some of Sotan's summaries on this forum of Japanese-language documents and provided links to them.
Any comments or criticisms will be welcome.

 

[turi]

The control room for the water treatment facilities has been relocated and is quite a bit more spacious than before:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160517_01-e.pdf

While the big picture of all the work going on at Fukushima is what I am mainly interested in, I am always amazed at all the small details that have to be taken care of as well.

 

[Sotan]

http://photo.tepco.co.jp/library/160526_01/160526_06.pdf
Brief report (in Japanese) on the progress of the muon imaging experiment at Reactor 2

Page numbered as 1: The measurement has been going on since 22 March. This is an intermediary report.
Pages 2-3: Explanation of the measurement method and what kind of images can be obtained
Page 4: after an explanatory sketch and two "simulation" images of possible results (with/without nuclear fuel in the RPV), the image on the right side lower part is the actual result of muon observation measurements taken until 20 May.
Page 5: analysis of the obtained image. Darker spots mean more matter present. Structures such as thick concrete walls surrounding the RPV, and the spent fuel pool, are confirmed/observed. Not much else to be said from the data gathered until now, but data accumulates nicely.
Page 6: seems we are in the middle of the measurement, it is going to continue until mid-July.
Page 7: again enumerating the good points: structures identified, a shadow where the spent fuel pool is located, the core region is well within the frame of the measurement range. They appreciate that the method is useful and will consider using it on other units too.
Page 8: same image, with contrast increased. (I see strong shadows in the area of concrete walls and spent fuel pool, less strong in the core region, and much less color in the lower portion of the RPV.)
Page 9: the image even allows the identification of a "whiter" portion on it that corresponds to the expected effect of the geometry of an Earth embankment located to the West of the reactor.
Page 10: again, simulations and actual image and a discussion on the need to correct the image due to a tendency of the measurement method to make the center brighter and the margins darker.
Page 11: A reminder of the results obtained on Reactor 1.

 

[turi]

The ice wall is coming along:
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160606_01-e.pdf

 

[SteveElbows]

http://photo.tepco.co.jp/library/160526_01/160526_06.pdf
Brief report (in Japanese) on the progress of the muon imaging experiment at Reactor 2

Here is the version in english:

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160526_01-e.pdf

And here is the much older 2015 document that drew conclusions about unit 1 using that technique:

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2015/images/handouts_150319_01-e.pdf

Personally I think its an interesting technique but it seems hard to get the quality good enough to draw firm conclusions. I am interested as to why they felt able to draw unit 1 conclusions after not that long a period of testing, and they don't feel able to do the same with reactor 2. I suppose there is too much noise in vital regions of the image of unit 2 for them to tell much.

 

[VCortex]

Tepco to inject cement into ice wall to slow outward water flow rate & promote freezing.

http://www.tepco.co.jp/nu/fukushima-np/handouts/2016/images1/handouts_160602_06-j.pdf

 

[turi]

Personally I think its an interesting technique but it seems hard to get the quality good enough to draw firm conclusions. I am interested as to why they felt able to draw unit 1 conclusions after not that long a period of testing, and they don't feel able to do the same with reactor 2. I suppose there is too much noise in vital regions of the image of unit 2 for them to tell much.

I suppose there are many reasons that it could take longer to get good results. Possibly only a smaller detector could be fitted, the detection angle might be less favorable, a longer distance to the reactor's center etc. Possibly even less muons. Does anybody know whether muon influx varies greatly? The good thing is, a longer sampling time will give more results. And the interim results at least verify, that the system as such works.

 

[turi]

Possibly even less muons. Does anybody know whether muon influx varies greatly?

After a bit of googling: There seems to be intraday and intra year variation in muon flux. It seems to be atmosphere temperature dependent: https://arxiv.org/pdf/1202.6403.pdf. Atmosphere temperature dependency does sound like atmosphere density dependency to me, which my non-physicist-brain accepts as reasonable.
Edit: Just found this: http://www.nature.com/articles/srep23054

 

[turi]

I'm a bit slow today: https://lanl.gov/org/padste/adeps/physics/_assets/docs/muon-tomography.pdf says unit 1 detectors were 7 m by 7 m, while http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2016/images/handouts_160526_01-e.pdf says that the "downsized to approx. 1m × 1m × 1.3m(height)" device was used at reactor 2. So the slower data acquisition might simply be due to the fact that the new detector had to be much smaller to fit in the available useful place.

 

[Sotan]

http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20160526_e.pdf
This is the English translation of the "Progress Status and Future Challenges of the Mid-and-Long-Term Roadmap toward the Decommissioning of TEPCO’s Fukushima Daiichi Nuclear Power Station Units 1-4 (Outline)" dated May 26 and posted on Tepco's site on June 22.

 

[Red_Blue]

Going back to March 11th 2011 about 15:50 and the SBO of unit 1, is it a correct conclusion from current understanding that the four AC operated internal containment isolation valves of the isolation condenser (MO-1A, MO-1B, MO-4A and MO-4B) inside the PCV were partially closed (April 1, 2011 TEPCO survey) due to the fail safe function of the IC pipe rupture detection system?

Is it also correct, that their exact position has not been yet confirmed, but is thought to be tending more towards closed than open, as the rupture detection system was able to fully close the DC operated valve MO-2B of train B that started fully open and was never operated by the personnel?

It appears these valves could have been manually opened from inside the PCV, but this was never attempted. Also it appears opening of any other train B valves was never attempted either after automatic actuation of train B after the earthquake and subsequent remote manual closing of MO-3B to shut down train B with train A.

Considering this, what were the prospects of activating Unit 1 HPCI by opening its valves MO-3 and MO-8 locally and manually?

Has anyone done a scenario exercise to evaluate what would have been the fastest response with available resources to restore core cooling for unit 1?

Is it still the current prevailing view that unit 2 venting failed because the rupture disc opening pressure was not reached in containment?

Would it have been possible to vent through the SGTS instead, accepting potential damage to it in exchange of achieving a less than totally blocked venting path to the stack?

It appears there is some evidence to the theory that unit 3 venting directed hydrogen through unit 4 SGTS inside unit 4 RB and that the system maintained integrity in that flow direction.

If it is further assumed that also units 1 and 3 had leaks in the containment before achieving rupture disk opening pressure and successful venting, could earlier venting through their SGTS, or otherwise bypassing the high operating pressure rupture disk, have decreased hydrogen leakage from primary containment enough to potentially avoid the hydrogen explosions in units 1, 3 and 4?

Is it a correct characterisation of the extremely high pressure venting strategy, that it did not take into account severe accident conditions where failure to vent earlier would certainly result in radiologically hot leakage from the containment anyway?

 

[Rive]

...stuff...

Well, I don't think that you will find many people who still keep in mind all the fine stuff what would be needed to answer your questions in detail, but think it's a safe guess that your real question is not about a wall of 'what if' scenarios?

 

[Red_Blue]

The what-if questions are very interesting from the human performance standpoint. In transportation safety investigations it's standard practise to try to evaluate what would have been the optimal human response and most of the time to also try to validate that performance model with human operator tests of surviving or similar equipment, high fidelity simulators or at least with computer simulations.

I have read a bit on the human performance of this event, including the short study by Man Cheol Kim. However, none of the studies or reports have really touched on alternative scenarios of how plant safety could have been restored and ensured. Considering that core damage at unit 1 started the domino effect which adversely affected the working conditions of the entire site, destroyed or set back many ongoing efforts for the other units as well as pulled available resources away from them, I think that is the most interesting unit to deal with.

 

[Rive]

When a game is already lost not even a master can save it... That's why you won't really find any scenarios about saving the situation in Unit 1.

The lack (or inadequate amount?) of hydrogen recombiners, the wrong placement of reserve diesels, the lack of filtering on the vent stacks, the old design (IC instead of HPCI), the out of date design basis - that unit were lost in the moment the tsunami arrived.

To save the situation that unit should have been upgraded seriously - or just closed down long ago.

The performance of U2 and U3, that's a different matter. They might have been saved (to some extent).

 

[jim hardy]

There's an ORNL analysis for "Loss of all AC power" to a BWR that proved pretty accurate.

Basically ,
if they'd known they were about to lose all power,
getting the reactor to cold shut down beforehand would have been helpful
so that containment temperatures don't rise so quickly and melt the containment penetration seals
but, one does not flippantly violate his cooldown rate .

if there's a people-performance issue
i'd say it lies with the culture of 'responsible design organization' that handles "what if" analyses.
that exercise can degrade into a bureaucratic potato toss where the object becomes just to get the ball into the other guy's court .

When those records of old tidal waves going way up the hill
where people of the time had placed rocks to mark the events
came to light

somebody should have made TEPCO executives aware they had flock of a sitting ducks .
and put a submarine hull around the electrical rooms

my two cents

 

[Red_Blue]

The lack (or inadequate amount?) of hydrogen recombiners, the wrong placement of reserve diesels, the lack of filtering on the vent stacks, the old design (IC instead of HPCI), the out of date design basis - that unit were lost in the moment the tsunami arrived.

Unit 1 did have HPCI, it was lacking RCIC. However, there is no evidence of any attempt to start HPCI in unit 1 during the accident.

I'm not at all convinced IC was inherently a worse design than RCIC+HPCI for high pressure cooling. In fact, it is making a comeback in ESBWR. It appears more like there was over reliance on it working due to being a gravity flow system without the need of pumps. The efforts to confirm RCIC operation in unit 2 appear to have been much more aggressive and persistent than the equivalent efforts for unit 1 to confirm proper IC operation. Yet IC was the Plan A for unit 1, with ongoing attempts to replenish water to it from the DDFP.

I think the unanswered key questions are what kind of a flow rate and cooling efficiency the IC did achieve with the partially closed inner isolation valves. The outer valves were not opened for long enough to evaporate more than 20% of the train A shell side inventory.

Also, what would have happened, if
a) after the initial DC power loss to all instrumentation, crews had been sent to manually verify the outer valve positions and finding them closed, directed to open the train A outer valves,
b) another crew was sent outside the reactor building to verify with close and direct observation the steam venting rate from the RB west side steam vents,
c) considering that no operator present had experience operating the IC and that steam observations were difficult to quantify even if done directly (instead of from the other side of the building, looking from the emergency exit of the MCR to observe steam above the building with the vents not visible at all, as was actually done), more aggressive attempt to approach the IC room was done to read local flow rate and temperature gauges,
and
d) upon earlier realisation (as opposed to the actual 18:20 time frame) from the insufficient performance of the IC system, that the inner valves could have closed by the automatic isolation function, crews then sent to verify and manually open all of the internal and external isolation valves of both trains of IC?

TEPCO and NISA had spent quite a lot of effort to investigate whether IC was actually functioning without significant leakage after the earthquake and before the tsunami and their findings indicate that it was not only operable but operating, at the earliest point with both trains. So I fail to see any reason why it could not have been brought back to operation after the tsunami, had its failure been recognised and acted upon. It would not have required any power or compressed air sources. It appears the only resource required would have been people with the correct instructions and perhaps some PPE and tools.

 

[Rive]

I'm not at all convinced IC was inherently a worse design than

IC is not inherently worse, but that IC had inadequate water budget due an old design basis and miss of revision/upgrade. Even in best case (cooling at full throttle after the emergency trip, till power lasts) it would not last long enough.

But as you can see it's old stuff for me anyway (for example the miss of RCIC/HPCI).

 

[Red_Blue]

IC is not inherently worse, but that IC had inadequate water budget due an old design basis and miss of revision/upgrade. Even in best case (cooling at full throttle after the emergency trip, till power lasts) it would not last long enough.

They were lining up make up water to the IC pool from the fire protection system tank through the DDFP that was already running in idle. I believe there were 3 valves outside primary containment that would have needed manual opening for this to work. This plan was only changed to core injection after about 90 minutes when it was considered that the IC had probably failed. That plan B didn't actually go anywhere until several hours later, because there was no serious attempt to depressurise the RPV first and they essentially waited for the RPV to self depressurise. It appears it's still unclear how that RPV depressurisation happened, except that it wasn't through the IC. Most probably by core damage induced RPV breach of some sort.

I've read estimates of 4 to 8 hours of cooling capacity from the IC without any water replenishment. Also the fact that the core damage appears to have been delayed by a couple hours while the total IC water inventory only dropped about 13% seems to indicate that using all of it would probably have given several hours more time to deal with water replenishment.

 

[nikkkom]

d) upon earlier realisation (as opposed to the actual 18:20 time frame) from the insufficient performance of the IC system, that the inner valves could have closed by the automatic isolation function, crews then sent to verify and manually open all of the internal and external isolation valves of both trains of IC?

How in those circumstances would people enter a PCV to open any valves inside it? (1) Is there a door which can be opened without electricity? (2) IIRC PCV is inerted, people who would try to enter it and work there for tens of minutes need to have something like oxygen tanks?

Not likely, considering that these people had difficulty simply going to the other side of the building exterior and assess IC steam generation...

 

[Red_Blue]

How in those circumstances would people enter a PCV to open any valves inside it? (1) Is there a door which can be opened without electricity? (2) IIRC PCV is inerted, people who would try to enter it and work there for tens of minutes need to have something like oxygen tanks?

They were using SCBA gear with 20 minute tanks and full body suits to enter other parts of the reactor buildings due to radiological conditions already after midnight of March 12th. That equipment must have been present onsite and not brought in, as such external supplies started to only arrive on the morning of 12th.

I would expect the PCV airlock to be manually operable as an option, suggesting otherwise doesn't make much sense. There were several missions during the accident to high radiation fields inside the reactor buildings to manually open valves. I don't see how the PCV would have been any different, especially considering that the dose rate there was under 10 mSv/h by CAMS before core uncovery and damage. I was also under the assumption that some of the missions actually went inside containment during the middle phases of the accident, but I would have to check to confirm that. At least the crews went to the torus rooms and several ground and 2nd floor rooms of the RBs.

 

[nikkkom]

I'm not saying it is impossible, I'm saying it's hard to imagine workers to succeed in such a difficult task when they were confused, unprepared and untrained and as a result, failed many simpler tasks.

"They were using SCBA gear with 20 minute tanks and full body suits to enter other parts of the reactor buildings due to radiological conditions", yes. That work wasn't done in the conditions anywhere close to the conditions inside the PCV, which was at the moment a pitch-black hot cavern filled with N2, with unknown radiation levels.

 

[jim hardy]

I don't see how the PCV would have been any different,

What was temperature inside PCV after even an hour with no coolers running ? And "Heat Index" ?(i hate that term)
You can't cool by perspiration in whole body PC's.
I don't think they had dewpoint meters, don't recall seeing any such readings
but i can say from personal experience
when you enter a containment that's 115°F and dewpoint is greater than your body temperature because the seawater coming into your plant is 95°F
you won't stay long.

Dewpoint is more important than temperature .
When you come into a containment from 95°F outside and your glasses fog up and hot dew forms on your face, you have to concentrate your way out of shock , "What is it i came in here to do ?" .
Within minutes you are nauseous, dizzy, and headed back for the hatch. Radiation is the least of your worries.
They never had to carry me out but i came close.
Probably some sailors have tales they could share.

Before ascribing fault to humans for not going into PCV
do homework on what was likely the physiological conditions in there after loss of heat removal.

old jim

oops that attachment was an accident ,

 

[Rive]

They were using SCBA gear with 20 minute tanks and full body suits...

Erm. To fetch one Bruce Willis to save the world could had been even faster?

I had similar discussions with forummates on a different forum and it was really hard to stop the 'they could have chop that line with even an axe' kind of arguments. It's better not to start that line.

For the first unit, it was a beyond-design-basis accident, what's already a failure alone and basis of every failure what's followed.

 

[mheslep]

getting the reactor to cold shut down beforehand would have been helpful

The tsunami hit 41 minutes after the quake. How could a cold shut down have been acquired under those circumstances?

 

[Red_Blue]

Erm. To fetch one Bruce Willis to save the world could had been even faster?

I had similar discussions with forummates on a different forum and it was really hard to stop the 'they could have chop that line with even an axe' kind of arguments. It's better not to start that line.

There's no need to bring in straw men in the form of fictional action heroes. We already know the plant operators did many unconventional, hazardous and even unprecedented things when they had adapted to the realisation that they were managing a very severe accident with life threatening consequences. Unfortunately that adaptation took about a day and night, even though the factors forcing that adaptation (almost total loss of remote control and monitoring) were present immediately after the tsunami.

For the first unit, it was a beyond-design-basis accident, what's already a failure alone and basis of every failure what's followed.

If you are willing to stifle discussions about the proper response to a beyond design basis accident, then you are really suggesting that you can always design for every accident scenario, which has proven time and time again unfeasible. It's interesting to compare the response in Fukushima 2 that suffered from the same earthquake and tsunami, but maintained effective reactor cooling during the same time period as Fukushima 1 had core melts and hydrogen explosions. The designs and plant systems were hardly different. The significant difference appeared to be that F-2 operators never lost control of their reactors, while F-1 operators never really regained it after the tsunami. It also appears that the most critical factor in losing control was not the loss of control systems, but the loss of incoming information about plant status and subsequent breakdown in effective decission making.

 

[Rive]

The tsunami hit 41 minutes after the quake. How could a cold shut down have been acquired under those circumstances?

As it was discussed in the old days, after the emergency trip they followed the standard procedures and kept a constant cooling speed which was slower than the maximal. They had even had to switch off the IC partially to keep the allowed maximal temperature change speed.
Would they know about the tsunami approaching, they could be able to switch to maximal cooling instead.
I don't know if they could be able to reach the 'cold shutdown' state, but it could mean a great deal of heat removed when it matters most - the early stage when the power output is still high.

But at that time nobody knew about the tsunami, and even if they had knewn about it, such violation of rules would require permissions (what means delay).

Ps.: posts around https://www.physicsforums.com/threads/japan-earthquake-nuclear-plants.480200/page-411#post-3322059

 

[mheslep]

I don't know if they could be able to reach the 'cold shutdown' state, but it could mean a great deal of heat removed when it matters most - the early stage when the power output is still high.

Yes, though with decay heat still at ~ 6MW at the time of cooling failure, I don't think anything is accomplished besides buying a couple more hours before that inevitable explosion.

Another alternative: I've never seen the possibility raised of restarting the reactor post quake and running cooling directly off a tap from the generator mains, i.e. self-powered, so I suppose there is some obvious reason why it should not be done that I'm missing. Clearly restarting the reactor after a strong quake carries some risk, but after cooling power failure the outcome was inevitable.

 

[jim hardy]

The tsunami hit 41 minutes after the quake. How could a cold shut down have been acquired under those circumstances?

try it on your simulator ?
They're more maneuverable than people think.
I've seen my plant back online and at full power fifty minutes after a scram .
New folks find that incredible.

...................

Your bootstrap is plausible except that their switchgear rooms were flooded with saltwater.

My vintage Westinghouse plant is in theory capable of rolling turbine on natural circulation and bootstrapping itself up
but it's not within bounds of permissible operation.
I assume BWR is similar.
try it on your simulator ?

old jim

 

[nikkkom]

It's interesting to compare the response in Fukushima 2 that suffered from the same earthquake and tsunami, but maintained effective reactor cooling during the same time period as Fukushima 1 had core melts and hydrogen explosions. The designs and plant systems were hardly different. The significant difference appeared to be that F-2 operators never lost control of their reactors, while F-1 operators never really regained it after the tsunami. It also appears that the most critical factor in losing control was not the loss of control systems, but the loss of incoming information about plant status and subsequent breakdown in effective decission making.

IIRC in Daini, they did not lose all external power. That is a huge difference.

 

[jim hardy]

@Red_Blue

This fellow rather specializes on Fukushima
https://www.researchgate.net/profile/Akira_Tokuhiro

i'd peruse his papers, maybe try to contact him ?

 

[Sotan]

Two presentations made relatively recently by IRID staff at an IAEA international conference:
First is
http://irid.or.jp/_pdf/20160523.pdf
Robot Challenges for Nuclear Decommissioning of Fukushima Daiichi Nuclear Power Station
Second is just one page:
http://irid.or.jp/_pdf/Overview of IRID R&D.pdf
Overview of IRID R&D Projects.

 

[Red_Blue]

But at that time nobody knew about the tsunami, and even if they had knewn about it, such violation of rules would require permissions (what means delay).

I think the correct phrasing is that nobody knew the incoming tsunami would be high enough to inundate the entire seaside of the site, until a few minutes before it was too late.

Situation and response from the time the earthquake hit until the arrival of the tsunami
(from approximately 14:46 to 15:35 on March 11, 2011)
Action taken by the NPS ERC
- -
The shift teams, the NPS ERC and the TEPCO ERC thought that they could put the
reactors into a state of cold shutdown before the loss of all AC power sources due to the
tsunami so long as they implement the prescribed procedures.

Obviously, at that point they didn't know they were going to have a SBO, just suspected it.
This is later clarified as:

Site Superintendent Yoshida first learned from the news on television that a three-meter
high tsunami would hit the Fukushima Dai-ichi NPS then he learned that the estimated
height had been changed to six meters. Site Superintendent Yoshida felt an apprehension
that the Residual Heat Removal System (RHR) might lose its cooling function if the
emergency seawater pump facilities would be damaged by the backrush of the tsunami.
At that moment, however, Site Superintendent Yoshida did not yet expect that more
than one units were to lose all AC power sources at once and station blackout would
continue for a long time. He thought that even if the emergency seawater pump facility
were damaged, the IC of Unit 1 and the RCICs of Units 2 and 3 could be used to cool
down the reactors or they could recover cooling capability by restoring the pump facility
while constructing power interchange facility between the units.

The timeline I've seen looks like this:
14:46 earthquake
14:49 first automatic tsunami forecast for F-1 region: 3 m
15:14 new forecast from JMA: 6m
15:27 5 meter runup from the first arriving tsunami (5.5m protection level)
15:31 new forecast: 10m
15:36 15m biggest tsunami arrives

So in other words, up until 15:31 it looked like they would be able to handle it. That left 5 minutes to do something about it, which would have been barely enough to consider a plan, let alone communicate or implement it.

In F-2 Superintendent Masuda ordered some staff from his ERC to go to the balcony of the 3rd floor of the seismic isolation building and look out to the sea and report back when they spotted the incoming tsunami. But in F-2 they also cooled the reactors at the limit rate by shutting down RCIC periodically.

It should be noted that the 55 C cooling limit was imposed in the emergency operation procedures, not a limit just for normal operations that could have been overruled easily.

 

[Hiddencamper]

BWR senior reactor operator here.

For cool down rate, 100degF per hour or 55C per hour is an ASME design limit for BWR vessels. BWRs are analyzed for a single emergency blowdown event, and require the vessel ASME code analysis to be updated after such an event. Momentarily exceeding the cool down rate typically isn't an issue. But the emergency operating procedures heavily protect this cool down limit. The only times that you are allowed to intentionally exceed the limit is if you lose adequate core cooling or if a primary or secondary containment parameter is going to exceed maximum safe limits, or if release rates are approaching general emergency levels. In almost all cases, the requirement is to perform an emergency blowdown using the automatic depressurization system, meaning you fully depressurize to under 50 psig.

During the period of time between the earthquake and tsunami, the pressure control actions require you to STABILIZE pressure, that means to hold pressure as stable as possible. With only the IC in operation, this means you'll be maintaining a large pressure band, but well within the 100 degF per hour limit. If they chose to transition from STABILIZATION or COOLDOWN, the requirement is still to maintain that 100 degF per hour cooldown limit.

If the IC was in operation, they would have had hours of decay heat removal, plus they had IC gravity driven makeup tanks that could have extended that to close to a day I believe, and with fire pumps or portable pumps to refill the makeup tanks you could establish a relatively long term decay heat removal. But the issue I understand is the drywell inboard isolation went closed when DC power was lost. The valves auto closed on loss of control signal as designed. This made the IC non recoverable. If the drywell isolation valves didn't close, the operators could have opened and shut the outboard isolation valves manually (I believe the MO-3) to control cooldown rate. Unless the core was uncovered, the EOPs do not allow placing the IC in service and leaving it in service to violate the cooldown limit. If the core is uncovered, and alternate level control does not maintain level above the minimum steam cooling reactor water level (MSCRWL) (1500 degF temp limit), then the steam cooling contingency will mandate placing the ICs in service even if the cooldown limit will be violated, and allows level to drop to the minimum zero injection reactor water level (MZIRWL) (1800 degF temp limit). After that, or if any injection source becomes available, you need to open the automatic depressurization system valves to blowdown.

As for HPCI operation, I'll need to talk to someone at Dresden. I think HPCI should have been available, but if it isolated due to the loss of dc power it would be unavailable for black start. Given when they realized the IC wasn't functioning, and that the torus rooms and basement were pretty badly flooded, they may not have been able to access these areas to black start it. Without DC power, both automatic and remote startup methods would have been unavailable. HPCI auto starts on level 2 or high drywell.

Someone mentioned the daini site, my understanding was that they were in station blackout, and the reason they were able to survive was because they still had DC power, and because all units RCIC systems were in operation until they got ultimate heat sink capability back to cool the suppression pools.

RCIC and HPCI are pretty significant decay heat removal systems. HPCI can depressurize a BWR in 12 hours, and RCIC can remove a good chunk of decay heat (not all of it), but for low or moderate decay heat levels it can depressurize the core as well. Typically a BWR will run HPCI in pressure control mode (Recirculation) and RCIC in injection mode when the streamlines are shut to prevent relief valves from lifting. My plant doesn't have HPCI, but we have used RCIC when streamlines were shut and RCIC in combination with streamline drains was enough to get our decay heat out.

Someone mentioned black starting a BWR. I don't think any BWRs are analyzed for black start at this time. Typically BWR emergency generators are dedicated to class 1E ESF busses only. Not all BWRs have control Rod drive hydraulic pumps on their diesels either, which is required for Rod motion. BWRs are designed to perform an isolated startup and heat up, but it is hard to control and many plants have gotten rid of that section of procedures and require a heat up with main steam and condenser in service.

I'll post more as I get time.

 

[Hiddencamper]

They were using SCBA gear with 20 minute tanks and full body suits to enter other parts of the reactor buildings due to radiological conditions already after midnight of March 12th. That equipment must have been present onsite and not brought in, as such external supplies started to only arrive on the morning of 12th.

I would expect the PCV airlock to be manually operable as an option, suggesting otherwise doesn't make much sense. There were several missions during the accident to high radiation fields inside the reactor buildings to manually open valves. I don't see how the PCV would have been any different, especially considering that the dose rate there was under 10 mSv/h by CAMS before core uncovery and damage. I was also under the assumption that some of the missions actually went inside containment during the middle phases of the accident, but I would have to check to confirm that. At least the crews went to the torus rooms and several ground and 2nd floor rooms of the RBs.

The mark I is inerted. I believe the containment personnel air locks have shield walls that need to be moved. It depends on the design. I do not believe one could have easily or safely gotten into the drywell to open the inboards though. IIRC they are pretty high up and need some climbing.

 

[Hiddencamper]

The tsunami hit 41 minutes after the quake. How could a cold shut down have been acquired under those circumstances?

There's no allowable way in the emergency operating procedures to get there in this scenario.