For those who missed my previous diaries on this topic, I have a background in physics and worked at Oyster Creek Nuclear Generating Station providing computer support for the reactor core engineering group. For the entire qualifications spiel and/or some background on Boiling Water Reactor (BWR) containment structures, see
Everything You Never Wanted to Know about Nuclear Containments
That diary also contained a review of the then current status of each of the reactors at Fukushima. In a diary yesterday, I updated that status information and discussed the various possibilities moving forward from here and their relative likelihood. In continuing diaries on this topic I will update this information based on information from a number of sources including the UN's International Atomic Energy Agency, IAEA, The Japanese Atomic Industrial Forum, and media reports which quote directly from organizations such as Japan's Nuclear and Industrial Safety Agency. My intention here is to tie together the various strands of information to provide an overall picture of things and explain it in a way that is accessible to those without scientific training.
The main body of the diary is a copy of yesterday's with updated information noted in bold. In some cases this may include commentary on why yesterday's information remains unchanged.
This diary and others like it are not intended as a substitute for the ongoing liveblog diaries, but rather, to pull all of the info together in summary form.
I have also written previously on the topic of meltdowns in the diary
What, exactly, IS a nuclear meltdown?
Current Status of Reactors and Containment Systems at units 1 - 6
Unit 1
The fuel pellets and fuel rods in the reactor have almost certainly experienced melting due to high temperatures resulting from the fuel being uncovered. (I only say almost certainly because we cannot look into the reactor at this point to verify. The same is true for units 2 and 3.)
The reactor vessel and associated piping appear to be fully intact. Were this not so the reactor would not be able to retain the water being added and there would be unexplained pressure drops. This was a major point of contention in the comments in the previous diary. The chart at the JAIF site lists for each reactor that the reactor pressure vessel integrity was unknown. Based on this, I was criticized, (to put it mildly), for claiming that the reactor vessel was, in fact, intact. Further research into the criteria being used to evaluate the reactor pressure vessel integrity revealed that it was based purely on two data points, reactor water level and reactor pressure. The pressure measurements have not been working, unless one wishes to assume that there is a slight vacuum in units 2 and 3, and therefore they list the reactor pressure vessel integrity as unknown. This does not mean that they don't know whether the reactor vessel is intact. It means that they don't have a valid pressure reading.
The primary containment also appears to be intact. It was well shielded from the hydrogen blast and has not had any other reported troubles. There have also been no clouds of steam coming from unit 1
The secondary containment also appears to be intact. There also have been no reported problems with the fuel pool at unit 1 despite the explosion. It is, however, getting near the time frame when this fuel pool will start uncovering fuel if water is not added. I have read no reports on this. I suspect the utility was informed of the temperature there by the thermal imaging done the other day. The only saving grace I see here is the possibility that in the cold weather the collapsed roof is acting as a condensing surface for water that is evaporating from the pool and that at least some of that condensed water is making its way back into the pool. According to the JAIF site, they are now considering adding water to this pool. There was no mention of how they intended to reach the pool under the collapsed roof of the reactor building.
Unit 2
The fuel containment has been compromised as is made clear by the hydrogen explosion in the torus. It is also almost certain that there has been fuel melting due to the time that the upper parts of the fuel rods were uncovered.
The reactor vessel and associated piping seem to be intact here as well. There was a brief time when they had trouble maintaining water level increases but that was apparently resolved as a valving issue. There was also a steam release on Monday. It is not clear whether this was a planned release or what the mechanism for release might have been.
The primary containment has damage. Initial reports from TEPCO stated that the damage did not breach the primary containment boundary and instead is in an internal section of the torus chamber. This report turned out to be inaccurate. They are now reporting that the torus has damage in its lower portion. It is not clear if this was intentional withholding of information by TEPCO or whether it represented their evolution in understanding the situation. I suspect the former. This is a serious issue because it means that when they need to release steam from the reactor to reduce pressure, they no longer can use the large volume of water in the suppression pool to cool the steam. It is hopeful that they have isolated the torus from the drywell as a result of this. I do not have information to either confirm or deny this however.
As of today various reports have dialed back the claims of damage to the primary containment. This is both from JAIF and the NRC. They now say that it may be damaged or that damage is suspected. Given their apparent priority to get unit 2 power back it seems likely that there is still a problem there with the torus. And again, if they can isolate the torus from the drywell then they have a sealed containment. They just lack the cooling ability of the suppression pool, an ability that may have lost most of its efficiency already.
They also were able to restore power to unit 2 on Sunday and discovered that a pair of key pumps were not working. Replacements have been ordered but may be a week or more. (I wonder whether there are identical pumps at unit 4 that could be used ... The plants are the same design and power rating.)
The secondary containment has been compromised by flying debris from the explosion at unit 3. It was reported that there was a hole in the wall of the reactor building. Whether any equipment was affected by this is not clear from reports. This, combined with the damage to the torus creates a situation where, when they need to vent, the steam is not cooled by the torus meaning that the pressure and temperature rise considerably in the drywell leading to a greater need for venting which now goes directly to the environment.I saw a photo today that showed steam coming out from the open section of the building. And while the JAIF site lists this as slightly damaged as opposed to severely damaged for units 1 and 3, I believe the damage to the building at unit 2 has greater consequences because it is the secondary containment that is open. That does not appear to be the case with units 1 and 3.
There have been no reports of fuel pool issues at unit 2. They began using the new power line on Sunday and pumped thousands of gallons of water into the fuel pool at unit 2.
Unit 3
Clearly the fuel integrity has been compromised at unit 3 and there has almost certainly been fuel melting there as well.
The reactor vessel and associated systems appear to be intact and reactor water level is able to be maintained.
The primary containment at unit 3 was reported to be intact by TEPCO in the aftermath of the hydrogen explosion. Over the weekend they have admitted that there appears to be damage. (They should know better than to do this kind of stonewalling. Very frustrating.) Based on the events at unit 3 and observations of steam coming from the roof of the secondary containment, it is likely that the damage was to the drywell dome plug. If you look at the BWR diagram below you'll see the cross section of the three layers to this seal directly above the dome of the reactor vessel. The sealing surface is a compressed o-ring which may have been disrupted by the explosion in the space above. This would mean that when they vent steam, any that is not recondensed by the torus - which is a larger amount now because the torus water has become hot over time and less effective at suppression - becomes free steam in the drywell and can escape through this breach in the primary containment.
This assessment has also been dialed back. This may have something to do with the fact that the containment has been holding pressure again, as there were reports of rising pressure yesterday. There were reports of dark smoke coming form the refuel level (current "roof") yesterday. It is unclear whether this was coming from the reactor containment or from the area around the fuel pool
The secondary containment at unit 3 took a hell of a hit from the hydrogen explosion, much more energetic than the others. (Units 2 & 3 are roughly 1-1/2 times as powerful as unit 1) From the various photos I've seen it still appears that the damage was largely confined to the refuel level - this would include the plug for the primary containment mentioned above. I do not discount the possibility of further damage within the reactor building as a result of this blast but have not seen any evidence that would confirm this.
The fuel pool at unit 3 is a major concern. It appears that there is a leak in the pool causing it to lose water faster than the heat load should cause. Many have raised concerns about plutonium due to the use of MOX fuel at unit 3. However, that only began recently and from what I have read, there are just 30 fuel rods in the pool that contain MOX fuel. There would be plutonium in the pool anyway as a result of it being a fission product - this means that it is created in the reactor as a result of the nuclear fission process. Efforts have been ongoing to dump tons of water onto the refuel floor in an effort to refill this pool. Because the pool is recessed into the floor, just getting the water close is what counts, gravity can do the rest. Current reports claim that the efforts appear to be succeeding. This is based on the levels of radiation dropping - what would be expected as more fuel is covered by water, and covered more deeply.
Unit 4
The condition of the reactor and containment at unit 4 is relatively unimportant given that all of the fuel was offloaded to the fuel pool to do maintenance on the reactor shroud, (the wall immediately surrounding the reactor cylinder).
The fuel pool at unit 4 may be the biggest concern at the moment. There have been reports that it had run completely dry but they appear now to have been inaccurate. There was also a rumor the other night about the pool starting to go critical - meaning that a nuclear reaction had started there. Again this was not borne out by later reports. But regardless, it is losing water faster than it should and refill operations are crucial. Again, one of the saving graces here is the fact that they don't need to get the water directly into the pools. And as with unit 3, current reports indicate dropping radiation levels which indicate that efforts are having an effect.
Units 5 and 6
These reactors were both in cold shutdown at the time of the earthquake and did not have near the cooling needs as units 1-3. They have remained stable and there have been no reports of fuel breakdown or melting. They have recently connected portable generators and been able to run their fuel pool cooling pumps. The temperatures in the pool have dropped considerably in the past day due to this operation. As a precautionary measure the other day TEPCO cut holes in the roof of the building at both 5 and 6. It now appears that while being a prudent measure, the holes will not be needed, either to vent hydrogen or to refill the pools from the air.
Prognosis - The Good, the Bad, and the Ugly
The Good - Each of the reactors at Fukushima appear to be on a path to cold shutdown. Thermal imaging reports suggest that the vessels at units 1-3 are each close to 100 C. Cold shutdown would bring them down to around 95 C. There also appears to be measurable headway in getting water into the fuel pools at units 3 and 4, though these efforts will need to continue for the foreseeable future to keep the fuel covered until a more permanent solution can be devised.
The Bad - Having lost the integrity of the primary containment at both unit 2 and unit 3 is quite significant. It means that more radioactive material has been released than would otherwise have been necessary. At least with the containments intact it was possible for them to let some materials settle out before releasing to the environment. Now this buffer space/time is lost. It also means that if something were to happen to take the reactors back into unstable conditions, the design level of protection is no longer available. These containments can no longer hold their pressure or gaseous contents. They may be able to survive an internal steam blast simply because they now have escape routes for the expanding gases.
And despite waffling claims today, the condition of each of these primary containments is compromised in some way. There is also still no explanation given for the steam or smoke that emerged from units 2 and 3 yesterday, an action which caused a temporary evacuation of workers to nearby buildings.
The condition of the spent fuel pools is also an ongoing concern. While they appear to have made progress, this will be a long fight and there may be more hurdles ahead. And with the structural integrity of the pools at 3 and 4 being highly in question, having significant aftershocks in the region cannot be helpful as they only add stress to these fractures and potentially make them worse.
Also bad is the fact that food and water are now being affected in the area around the plants. This is adding to the already enormous humanitarian crisis in Japan.
The Ugly - The releases from unit 2 will need to continue until they can get the cooling pumps installed and working. This is the only means they have for removing heat from the reactor, and the reactor is going to continue to generate heat. It is bad enough that these need to be done. The least TEPCO could be doing would be to plan them for early morning hours and do them on a regular basis rather than allowing the pressure to build until the releases are unavoidable.
Personal note: Please remember the bigger picture here. There are millions of people still suffering in Japan at this hour. The aftermath of the earthquake and tsunami have created enormous problems and left many thousands dead, injured, or isolated and left unattended. This event is a natural disaster of unfathomable scope. The nuclear emergency, while certainly an important part of what is happening there, has not had near the effect on the population that the other events have to this date. If you can find it in your heart to contribute in some way to the humanitarian efforts for Japan you will truly make a difference in someone's life.
The Red Cross and Shelter Box USA
Also, my purpose with these diaries is to provide technical understanding of what is happening at Fukushima and discuss the likely ramifications of these events. It is not to engage in pie fights over the future or appropriateness of nuclear power. There are plenty of diaries for those discussions for people who choose to so engage.
Unfortunately there are some who just want to fight. I have been vilified, repeatedly called a shill, a liar, a propagandist, and more simply because one or two commenters disagreed with my analysis. This is simply wrong. If you wish to engage in namecalling and personal attacks, please take it elsewhere. I really cannot continue responding to people whose only intention is to be rude and insulting.
Also, the report on DKos earlier this evening about workers evacuated was actually the story from yesterday that I mentioned above. The time delay makes things confusing as does the date difference. For clarity, Japan is 16 hours ahead of Pacific Coast time. It has been Tuesday there for a while already. Also, I will stick around for comments for a while but really need to catch up on some sleep. I'm also not sure exactly when the diary will be published from the group queue so I'm not sure how much time that will give me. I promise to get back to questions tomorrow.
BWR Mark I Containment
Updated by kbman at Mon Mar 21, 2011 at 10:59 PM PDT
As per a suggestion from Jim P in the comments,
This diary represents my take on the situation as of 3:00AM on 3/22/11 UTC.
Updated by kbman at Tue Mar 22, 2011 at 11:57 AM PDT
From Plubius in the comments, The new off-site power line has now been connected to all six reactor sites, and the lights are on in the control room at unit3 -
http://www.nikkei.com/...
I've also been thinking about that leaking primary containment at unit 3 that they now say is holding pressure. That would be completely consistent with my theory about the drywell dome plug being disrupted. If the rubber O-ring had been compressed by the force of the blast pushing on the seal that would be enough to cause it to leak. And given that the pressure wasn't likely symmetrical across the seal there may have been uneven compression causing a fairly large gap in a portion of the ring. Even a fraction of an inch is significant in this case as that is plenty to allow unimpeded flow of air. The seal itself would have rebounded into its threads to leave this gap.
Now that they have blown steam through that gap for a few days, the heat may have been enough to re-expand the rubber O-ring to fill the gap. This would probably not mean that the primary containment is able to withstand design pressure anymore as they have just passed the threshold where it can hold positive pressure.
Updated by kbman at Tue Mar 22, 2011 at 12:20 PM PDT
From kalmoth in the comments, here is a photo of the smoke coming from Unit 3 on Monday
Uploaded with ImageShack.us
Updated by kbman at Tue Mar 22, 2011 at 12:22 PM PDT