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. This diary is intended as an update reflecting what is known through this evening. Instead of copying and adding as I did in the last update, this one will have the information consolidated to simply reflect the current state of things. Anyone wishing to trace the evolution can look back through the previous update diaries here and here.
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, JAIF, 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.
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?
New Developments
Late reports from Monday have confirmed that the new off-site power line has been successfully connected to all of the 6 reactors at the site. And in what must be a morale boost for workers there, the lights were finally back on in the control room of unit 3. The task now is confirm the physical status of various pieces of equipment at each plant. To the extent possible they will be doing visual inspections prior to attempting to operate any pump, valve, etc. This has already begun and some pumps have been operated for fuel pool filling operations. Many more systems will be tested over the next few days and needed repairs planned.
The other big thing that happened today was that nothing significant happened. There were no crises or evacuations, just ongoing work to get needed systems back online. There were some significant aftershocks in Northeast Japan but they had no apparent affects on the plants.
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 no significant pressure buildups requiring venting. You may note that the status chart kept by JAIF shows the reactor vessel Integrity to be unknown. Looking into their methodology it becomes clear that they evaluate this parameter based on reactor water level and reactor pressure. Accurate pressure measurements have not been available for either reactor for several days. Hence they list the reactor pressure vessel integrity as unknown, this does not mean that the pressure vessel itself is not intact. update - Temperatures rose Wednesday morning in unit 1 to near 400C. Water pumping was increased to combat this. This is likely a case of not keeping the heat removal up at unit 1 while they were focused on the bigger issues at units 2 and 3 plus the fuel pools at units 3 and 4.
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. (For those who question this evaluation in the aftermath of the hydrogen explosion there I refer you to my diary on containment structures linked in the intro. It has a discussion of my analysis of the explosion and why I don't believe either unit 1 or unit 3's secondary containment to be badly damaged.)
There also have been no reported problems with the fuel pool at unit 1 despite the explosion. 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. There were reports the other day of plans to use army tanks to help remove debris from the tops of units 1, 3, and 4 to make the fuel pools more accessible.
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 may have damage. If so, 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. As of yesterday 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 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 due to heating of the water.
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. 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. They were reportedly able to get the temperature there down to 50 C. I believe their normal operating temperature is 45 C / 81 F.
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 status of the primary containment has been reported as compromised, and as not compromised. It apparently began holding pressure again in the past two days after failing to do so in the immediate aftermath of the hydrogen explosion. I believe I may have an explanation for what has happened. If you refer to the BWR diagram below you will see the drywell dome plug in the center of the top floor of the secondary containment, under the roof on the refuel level. The seal for this plug is an O-ring which gets compressed between the slabs of this plug. When the explosion happened, I believe the blast forced the top slabs to smash the O-ring momentarily before rebounding into place. I also doubt that this pressure would have been evenly spread over the surface of the plug. This would result in a deformed O-ring, leaving a gap where it had been most severely squashed and allowing reactor gases to escape at will.
But after a few days of steam venting through that gap, the rubber has had a chance to recover and re-expand to fill the gap. Thus the containment is holding pressure once again and caused them to dial back the damage assessment. This would also mean that the containment cannot be counted on to perform up to its design specifications as the condition of that O-ring seal and its capacity to withstand higher pressures would still be marginal. Again, this is a theory. I base this on the structure of the building, the location of the explosion, and the changing reports regarding containment status. This is a serious enough issue that TEPCO would not have released the information that the containment had been compromised unless it were absolutely so.
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 remains a large concern but appears to be stabilizing. And as with unit 3, current reports indicate dropping radiation levels which indicate that efforts are having an effect. I also read a report claiming that the temperature there had been measured at 84 C. This is far from where they want it but much better than boiling.
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 now been able to use grid power to run their fuel pool cooling pumps. The temperatures in the pool have dropped considerably since they got the cooling pumps in operation and appear to be stabilizing. 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 from a few days ago suggest that the vessels at units 2 and 3 are each close to 100 C. Cold shutdown would bring them down to around 95 C. The temperature increase at unit 1 has turned around and is decreasing again as more water is being added. This does not appear to be a major setback. 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. Getting power back was huge because they can now use things like lights and power tools without being tethered to a generator.
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 may no longer be able to hold their gaseous contents at higher pressures.
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 an expanding area around the plants. This is adding to the already enormous humanitarian crisis in Japan.
The Ugly - There is still a large amount of seawater inside these reactors. Seawater is corrosive and provides a very complex chemistry inside the reactor given the number of elements present. Where this will have an effect sooner rather than later is on the metal surfaces that meet to form seals in valves, (the valve seat), and also on the internal moving surfaces/seals that maintain pumping pressure. This will not necessarily be a safety concern as the reactors are now closing in on being under boiling temperature and should never again expose these surfaces to the kinds of operating pressures for which they were originally designed. It may add costs and delays however if pumps fail and need replacement due to this cause.
It also means that the plant needs to be cleaned up and decommissioned as soon as possible. The longer it sits with its seawater nuclear stew, the more opportunities it has to cause new problems due to systems degradation and failures.
Appeal for the people of Japan
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. I also request that people refrain from personal attacks and other forms of ad-hominem argument. This is an emotional topic for some folks but that does not excuse rudeness and personal insults.
BWR Mark I Containment
As per a suggestion from Jim P, This diary represents my take on the situation as of 2:00AM on 3/23/11 UTC.
Updated by kbman at Tue Mar 22, 2011 at 09:48 PM PDT
the headline on the current mothership diary claims that the temperature of reactor 1 has risen. The Reuters link does not make clear where this temperature was measured ...
The temperature within part of Japan's tsunami-damaged nuclear reactor has risen above design limits, but there is no immediate danger, the nation's nuclear safety watchdog said on Wednesday.
The agency said the temperature had climbed to near 400 degrees Celsius within a pressure container at reactor No.1 at the Fukushima Daiichi plant, compared with a design limit of 302 degrees.
I'll update this as more information becomes available. Remember, when the fuel was melting the temperatures in that part of the core had to be on the order of 2800 C.
Updated by kbman at Tue Mar 22, 2011 at 11:14 PM PDT
More on the Unit 1 temperature rise ... from Kyodo news
As of 10 a.m. Wednesday, the temperature of the No. 1 reactor vessel dropped to 390 C degrees, but it was still above the maximum temperature of 302 C degrees set by its designer. To deal with the situation, the utility known as TEPCO had increased the amount of water injected into the reactor by 9 times.
Nishiyama said the reactor vessel is not expected to start melting at these temperatures, and that TEPCO will carefully continue to inject massive amounts of water into the No. 1 reactor so as not to raise the pressure in the reactor.
High pressure in the reactor increases the risk of damage to the facility, and workers would be required to release radioactive steam from the reactor to lower the pressure.
As part of routine monitoring activities, helicopters of the Self-Defense Forces examined temperatures at the Fukushima nuclear power station Wednesday morning.
Updated by kbman at Tue Mar 22, 2011 at 11:52 PM PDT
Forgot to mention, I just read in the Kyodo update that the 2 missing workers were found ...
"The plant operator Tokyo Electric Power Co. also said two workers who had been installing a makeshift power source from Tuesday night were injured and taken to hospital, but they were not exposed to radiation."
MAJOR UPDATE, New Smoke at 4:20 PM JPN
More black smoke ...
Black smoke has been seen rising from the No. 3 reactor at Japan's stricken nuclear power station, its operator Tokyo Electric Power Co. said Wednesday.
TEPCO said workers evacuated from the Fukushima Daiichi plant's No. 3 and No. 4 reactors after the smoke that was first reported around 4:20 p.m.
It said no blaze was seen and that no other details are available yet.
Hmmm ...
Within an hour the smoke was decreasing. No word yet on radioactivity. More likely an electrical related issue trying to power something up, could also be bad bearing overheating, any number of things on large equipment can smoke for an hour.