Author: Johan

Tepco has released more information about their plan to stabilize the Fukushima reactors(link 1, link 2). Their table of measures to be taken is hard to read, but the schematic of the plan is quite enlightening and i have attached it below.

They are basically facing 4 problems, ensuring long term cooling of the cores,  ensure cooling of the spent fuel pools, prevent release of radioactive material and mitigate the consequences of the releases that will continue for a while. I want to speak a bit more about cooling in this blog post since it is the most crucial problem.

As I have written before (and I will repeat it again, bear with me), the most important thing is to get circulation cooling going again. The current way of cooling the reactor, by pumping in water, letting it boil and then venting the steam out into the containment, is not a long term solution since one is continuously adding water to the system. The volume of the containments are large, but not infinite.  One can’t put more and more water in there without it sooner or later coming out out somewhere, somehow. We are seeing that in the large leakage from the number 2 reactor. Cooling by circulation simply means one pushes water into the core somewhere and take it out somewhere else. The water taken out is then run through a heat exchanger that cools the water by dumping the heat into a heat sink (the ocean). There are a bunch of different cooling systems in a reactor.

During normal operation of a BWR(boiling water reactor), heat is carried by steam from the core, the steam passes through a turbine that generates electricity and then the seam goes through a condenser that cools it into a liquid state again, before its pumped back into the core. The condenser in turn is connected to water flow from the sea, a river or some other big body of water that keeps the condenser cool so it is able to condense the steam.

When the reactor is shut down there is still decay heat that needs to be removed. One does not want to produce steam during shutdown so the normal cooling by letting steam go through the main steam line out to the condenser is not an option. All BWR’s has recirculation pumps that takes some of the core water and recirculates it within the vessel, during normal operation this is done to control the steam level in the core. Connected to this recirculation loop is pumps and pipes that can lead water to a heat exchanger that dumps heat to some heat sink before it is circulated back. This system is used to provide cooling during shutdown and is called the Residual Heat Removal (RHR) system. It’s capable of getting rid of the decay heat (heat that continues to be produced from decay of fission products, long after the fission chain reaction is shut down) and keeping the water in the reactor at below 100 degrees Celsius.

The above two options both require electricity do drive pumps, both for the internal circulation but also to get seawater to the heat exchangers that cool the water in the internal circuit. If for some reason pumping power is lost there is a system that kicks in and can run for a short time period (hours). The system is called the Reactor Core Isolation Cooling (RCIC) system. It works by using a temporary heat sink. All BWR has something called a “wetwell”, the wetwell is a water filled volume within the primary containment below the reactor pressure vessel (that contains the core). In an emergency one can shut the main steam outlet and the main feedwater inlet to isolate the containment from the sounding environment. The steam generated in the core is instead diverted into a small turbine that drives a pump that pumps water into the core from the wetwell or from a water storage tank. After passing through the turbine the steam is dumped down into the water in the wetwell. When mixing with the water the steam will condensed and can be pumped back into the core, at the cost of heating up the wetwell water. When the wetwell water gets close to boiling point it can no longer absorb any heat and it  stops acting as a heat sink. When that happens no more water gets returned to the reactor and water level starts to drop in the core. Usually it can absorb a couple of hours worth of decay heat. This system was the system that was cooling all the Fukushima reactors for the first hours after the accident. It is almost a passive system, it doesn’t require any large amounts of electricity but it do require some small power from batteries for control.

The trouble in Fukushima started after the RCIC shut down. There was no power to start up the RHR and water level started to drop causing the fuel in the core to be damaged and release radioactive material into the water in the core. As a emergency move TEPCO then started to inject water into the core to cover the fuel again, without having anywhere to dump the steam getting produced. They have been doing that during all the time so far. The hope was that they would be able to restart the RHR system after recovering power to the reactor. But the tsunami drenched all the switchboards for the control room and also flooded the turbine hall basement where apparently a lot of the equipment related to the RHR is located. Leaks from the core afterwards contaminated this water so much that workers can not get to the equipment to restore the RHR.

The dilemma for TEPCO is that they can’t repair the equipment for the RHR as long as the cores are leaking radioactive water, but the cores will continue to leak as long as TEPCO continues to inject water into the cores without having restored the RHR circulation. So what can they do in a situation like this? They have desperately been trying to find some way to pump out enough water to be able to start repairs, but to no good. Even if they could it is doubtful the repairs can be made quickly, likely the entire system is completely trashed after having been drenched with salt water for weeks. That leaves TEPCO with only one option, create a new RHR loop.

What they are planning to do as far as I can tell is to install a bunch of heat exchangers somewhere with access to seawater. Then they will pump water out of the reactors, through the heat exchangers and then back in. Just like the RHR would do. The difference is that they are going to have to pump the water in pipes straight out of the containment and reactor building. One would normally never do such a thing since the risk of a leakage is not trivial and due to the radioactivity of the water, once they start pumping, no one will be able to be close to the pumps or pipes. It would not be very pleasant for instance if a new earthquake where to rip the pipes apart while they are pumping, but the option of not doing anything isn’t really an option at all and if they can get that cooling working then they could more briskly get to work on restoring the real RHR system.

What confuses me at this point is where they will connect the new temporary system. First they where talking about connecting it to the feedwater line and some kind of fire extinguishing system, both connecting to the reactor vessel. That would be ideal since it would prevent crap from getting out of the core and into the containment, which is the main problem, since the containment on the number 2 reactor is leaking and causing the big problem in the turbine hall basement. But now, from the plan I posted above, they indicate will instead flood the containment and connect one end of the temporary RHR to it while the other end goes into the core. They will in other words circulate water:

From core -> into containment -> out of the containment through a heat exchanger -> then back into the core.

I don’t see how this solves anything since it is the amount of water present in the containment that seems to be causing the leakage problem in the first place! But I guess their plane will become more clear in the future.

As for other news. There is nothing new about the status of the reactors as can be seen from the pictures below, temperatures in all three reactors continue to go down. Pressure in number one reactor seems to have stabilized a bit and the declining trend in radiation levels around Fukushima continues.

 

 

 

 

Links(English)
World Nuclear News Roadmap for Fukushima Daiichi restoration
World Nuclear News Plans for Fukushima basement pumping
Kyodo News Japan bans residents from remaining within 20-km of Fukushima plant

Blogs(English)
Brave New Climate Energy debates in Wonderland
Depleted Cranium Assessing the Long Term Danger to Fukushima Workers
NEI Nuclear Notes TEPCO’s Plans to Stabilize Fukushima-Daiichi
NEI Nuclear Notes Analysis of Replacing Japan’s Nuclear Plants With Other Technologies
Atomic Power Review AREVA awarded water treatment plant contract…
Damian Carrington Unsure about nuclear power? Here’s the five questions you must answer to decide
NEI Nuclear Notes ANS Nuclear Cafe – “Why is there irrational fear of radiation?”
NEI Nuclear Notes Italy, Poland (and Its Neighbor Germany), Exxon
All Things Nuclear Cleanup Lessons from TMI for Fukushima?

Links(Swedish)
Uppsala Tidning ”Ompröva kärn­kraftsbeslutet”

Blogs(Swedish)
Jinge Vad har vi lärt oss?
Svensson Fukushima lika allvarligt som Tjernobyl
Supermiljöbloggen Kina gör svängom efter Fukushima
Förbannad Pacifist Marianne Stieger: En strålande framtid
Kunskapssamhället Säkerhetszon runt Fukushima

/Johan

13 Comments

It seems like TEPCO has realized it will take some time for them to restore the internal circulation pumps in reactor 1-3. The equipment has been drenched in salt water for some time now and the highly radioactive water in the turbine halls makes it very hard to do any kind of work. The normal cooling works by having water circulating through the core, then going through a heat exchanger that transfers heat from the water to an outer circulation loop that transports the heat to some kind of heat sink (in this case the ocean). The form of cooling that TEPCO has been doing since this accident started is to simply pump water into the cores, where it boils and creates steam that they then blow down into the wetwell. This means water is going into the building, but not leaving it. As anyone can realize that can’t go on forever until water comes out somewhere because the wetwell and containment doesn’t have infinite volume to store water. All the crap water that has been leaking into the sea is a result of this cooling method.

Since they have to try to prevent more leakage into the sea and they can’t get the internal cooling working TEPCO was left with the choice to build a new closed loop with new heat exchangers. All one really need is a pipe where one can put water into the reactor and another pipe where one can take the water out. Connect that to a heat exchanged and voila you have new circulation cooling without any need to fill the wetwell with steam. That is exactly what TEPCO is going to do.

That isn’t a solution without problems though. The reactor circulating through the core will become very radioactive due to the partially melted fuel, so any pumps and pipes used will be dangerous to approach. Everything has to be set up in such a way that once started it will run quite reliably, because repairing things won’t be easy. It would also be quite dirty if the pipes or pumps starts leaking so they better make them tight.  Still it seems like a better and more long term solution than what they doing right now and it seems to be necessary in order to get rid of the radioactive water in the turbine halls, in order to get access to the real pumps and restore/replace them. Right now water is leaking out as quickly as they can pump it away.

The above strategy is a part of a bigger plan to stabilize all the reactors, stop all leakage of radioactive material and put all 3 reactors into cold shutdown. TEPCO estimates it will take 6-9 months before its all finished. Among other things TEPCO will build up storage and processing facilities for the radioactive water, build covers over the damaged reactor buildings , somehow repair the breach in the number 2 wetwell (one article mentioned “sticky concrete”) and inject nitrogen into all the containments.  Atomic Power Review has a nice short list.

It is positive that TEPCO seems to have a long term plan, lets hope they will be able to proceed with all the steps without to many unexpected problems.

TEPCO has driven around inside the reactor buildings with a robot equipped with radiation detectors and the dose rates within the buildings are around 50 mSv/hour. A worker could only work there for 5 hours before they exceed the maximum allowed dose limit. I wonder how they plan to deal with that and I also wonder how they have measured it.

The status of the reactors are fairly unchanged. Temperature going down in the number one reactor.

Dose rates are going down, the gamma dose rates are according to IAEA

Gamma dose rates are measured daily in all 47 prefectures. The values tend to decrease over time. For Fukushima, on 18th April a dose rate of 1.9 µSv/h was reported. In the Ibaraki prefecture, a gamma dose rate of 0.13 µSv/h was reported; in all other prefectures, reported gamma dose rates were below 0.1 µSv/h.

Dose rates are also reported specifically for the Eastern part of the Fukushima prefecture, for distances beyond 30 km from Fukushima-Daiichi. On 16th April, the values in this area ranged from 0.1 to 25 µSv/h.

Only in a few prefectures, I-131 or Cs-137 is detectable in drinking water at very low levels. As of 16^th April, one restriction for infants related to I-131 (100 Bq/l) is in place in a small scale water supply in a village of the Fukushima prefecture.

 

The areas with a ground contamination of more than 1 MBq/m^2 of Cs-137 sounds quite limited, seems like there are some hot spots west of Fukushima. From IAEA:

 

Only in a few prefectures, I-131 or Cs-137 is detectable in drinking water at very low levels. As of 16^th April, one restriction for infants related to I-131 (100 Bq/l) is in place in a small scale water supply in a village of the Fukushima prefecture.

On 15^th and 16^th April, the IAEA Team made measurements at 44 different locations in the Fukushima area at distances ranging from 20 to 58 km, West from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.6 to 37 µSv/h. At the same locations, results of beta-gamma contamination measurements ranged from 0.03 to 2.8 Megabecquerel/m2. The highest values were observed at distances of less than 30 km from the power plant.

On 17^th April, the IAEA Team made measurements at 17 different locations in the Fukushima area at distances ranging from 20 to 62 km, North and Northwest from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.4 to 3.3 µSv/h. At the same locations, results of beta-gamma contamination measurements ranged from 0.03 to 0.27 Megabecquerel/m2.

I hope someone will soon release maps of ground contamination so one can get a sense for how much land will be unusable.

Links(English)
World Nuclear News Robots investigate Fukushima reactors
World Nuclear News Roadmap for Fukushima Daiichi restoration
Reuters  Opposition to huge India nuclear plant hardens
Reuters Special Report: The nuclear industry’s trillion dollar question
Reuters Japan nuclear operator aims for cold shutdown in 6-9 months
Reuters Inside Fukushima

Blogs(English)
Atomic Power Review Tepco plans further details
NEI Nuclear Notes UCS Science: How Many Cancers Did Airlines Really Cause
Idaho Samizdat Fukushima’s future blueprints are incomplete, danger persists
Idaho Samizdat Impact of Fukushima on new U.S. reactor projects?
Depleted CraniumTerrified of Nuclear Energy, Germany Goes for Fossil Fuel

Links(Swedish)
DN debatt ”S uppdrag är att skrota kärnkraften”

Blogs(Swedish)
Mats Engström Granska Strålsäkerhetsmyndigheten
Begrundat och plitat Twitter om Fukushima och Tepcos plan (som just presenterades) radioaktiviteten ner om 3 månader
Flute Hänt i veckan 10-17 april, del 1
Sven Tycker Avveckla kärnkraften
Dr Angel Sanningen om Fukushima – vi klarar bara små doser åt gången
Motvallsbloggen Fukushima? Vadå, vi har ju inga jordbävningar här?

5 Comments

22:00(CET)/20:00(UTC)/05:00

Not much newsworthy to report today. JAIF report as usual on the status of the reactors. No new NISA update on the reactor status in English but in Japanese, some values are taken from IAEA rather than NISA. Links to graphs are links to the blog #FNPP1 and Irradiation. Pressure is continuing to rise in the number one reactor but still quite low. Seems like there is some kind of leakage out of the containment in number one, otherwise one would have expected higher pressure due to the nitrogen injection. Pumping of water from the number 2 turbin building basement is ongoing but slow, TEPCO say the work can take weeks.

 

	Reactor 1	Reactor 2	Reactor 3
Water level (meter)*	-1.65	-1.5	-2.2
Flow rate(liters/min)	100	116.67	116.67
Core pressure (kPa)	1034	100***	100***
Containment pressure (kPa)	190	100***	100***
Wetwell pressure (kPa)	165	–	168
Feedwater nozzle temp (Celsius)	204.5	166.9	92.2 **
Bottom head temp (Celsius)	119.0	208.0	116.0
Containment dose rate (Sv/hour)	–	27.9	16.9
Wetwell dose rate (Sv/hour)	10.3	0.653	0.653
*Distance from top of assembly
– broken gauges or missing data
** Probably faulty reading
*** IAEA states atmospheric pressure

Yesterday NISA released this info about how much activity has escaped from the Fukushima reactors and compare it to Chernobyl.

Like I said yesterday its roughly 10%. The move from 5 to 7 on the INES scale has gotten a lot of media attention, but what does it really mean? Nothing became worse yesterday than it has been, no dramatic event changed the rating etc. What happened is that NISA estimated that the release of I-131 and Cs-137 is beyond a treshold of what is considered “Major release of radioactive material” acording to the level 7 definition:

Level 7.

• Major release of radio active material with widespread health and environmental effects requiring implementation of planned and extended ­countermeasures

That is all, NISA hasn’t made any statement about health impacts. They certainly don’t claim the effects will be as severe as the effects where from Chernobyl. One can at this point exclude the possibility that Fukushima will be as severe. So what are the differences?

1. In Chernobyl 134 workers got exposed to high enough radiation(over 1 Sievert) to develop symptoms of acute radiation sickness, 28 of them died during the first year following the accident,  two others died from injuries not related to radiation. A lot of kids got exposed to I-131 due to no quick warnings not to drink milk and no supply of iodine pills. 4000 kids got thyroid cancer and 15 died due to it. 600 000 liquidators where exposed to doses around 100 mSv.

   In Fukushima so far 22 workers have been exposed to over 100 mSv, the highest getting 198 mSv, thus there where 30 000 times as many people exposed to 100 mSv or more in Chernobyl compared to Fukushima so far! The only two deaths at the power plant was direct deaths due to the tsunami. No one has died due to the nuclear accident itself, not from any of the explosions, not from radiation etc. Dose estimates for the people outside of the evacuation zone, especially the people within 30km, has not been given so far.

2. In Chernobyl the radionuclide release was directly into the atmosphere and it was going on for several days driven by the graphite fire. Other radionuclides than I-131 and Cs-137 could easily escape and was spread (even though Cs-131 is the biggest issue). The areas around Chernobyl where not quickly evacuated. The core blew apart due to a runaway chain reaction(a inherent weakness to that design that was well know, but the Russians ignored it and built them anyway),

   In Fukushima it is still not entirely clear what caused the majority of release, it was either the venting of the containments or due to the breach in the number 2 wetwell. Regardless of the cause the atmospheric emissions was much smaller in magnitude, took place during a shorter time period, after the civilian population had already been evacuated! We are seeing pretty much only Iodine and Cesium(trace levels of other radionuclides have been detected, but no large release of them has been reported). The cores are largely intact, two of the containment vessels are likely breached but by far from cracked open like eggs. The cause of the emissions are partial meltdowns of the cores, a much slower process than the runaway explosion in Chernobyl. After the first few days of venting where over the majority of leakage goes into the sea, although that is not a “good” thing it is unlikely it will have any measurable impact on health. Anything going into the sea will get diluted fairly quickly. Even if the total release will increase to the same size as the ones from Chernobyl the different release path means it will have much less impact on public health or the environment.

Those two points alone mean that Fukushima is not another Chernobyl. The public health effects will not be as large and the environmental impact will be smaller. It remains to be seen how large surface areas have gotten high Cs-137 fallout, that will be the determining factor in how large areas will be unfit for farming or living on.

 

 

Links(English)
Reuters Japan struggles with nuke plan
World Nuclear News Fukushima workers start emptying trench water

Blogs(English)
Atomic Insights Rational Answer to Carl Pope’s Dismissal of Nuclear Technologies
Depleted Cranium Shameful Reporting From the New York Times
NEI Nuclear Notes Wednesday Update
Atomic Power Review Boiling Water Reactors Part 1 and Part 2
Atomic Power Review Fukushima Daiichi developments… Tuesday evening
Atomic Power Review A couple of afternoon updates….

Links(Swedish)
Aftonbladet Tyvärr har jag fått rätt
SvD Fukushima inte lika allvarligt som Tjernobyl

Blogs(Swedish)
Den blinde Argus Kortsiktighet, instabilitet och populism
Begrundat och plitat Fukushima, risken för nya olyckor, och sanningens ögonblick
Tänkvärt? Eller inte Fukushima likvärdig med Tjernobyl.
SNF’s blog Fukishima kan vara värre än Tjernobyl
Nolow Kärnkraftverk
Hovbergs blog Nukleära utrymningsområden<
Röda Berget Skräcken för strålning skapar nya offer
Harald i Uppsala Reflektioner 13 april

41 Comments

11:20(CET)/09:20(UTC)/18:20

NISA has increased the level of the Fukushima accident to 7 on the INES scale, 7 is the highest level on the scale. Before Fukushima only Chernobyl was on that level,  the descriptions of levels 5, 6 and 7 are these

Level 7.

• Major release of radio active material with widespread health and environmental effects requiring implementation of planned and extended ­countermeasures

Level 6.

• Significant release of radioactive material likely to require implementation of planned countermeasures.

Level 5.

• Limited release of radioactive material likely to require implementation of some planned countermeasures.
• Several deaths from radiation.
• Severe damage to reactor core.
• Release of large quantities of radioactive material within an installation with a high probability of significant public exposure. This could arise from a major criticality accident or fire.

The levels are as you can see quite loosely defined. We have been expecting it to be be increased from 5 but it has not been clear if it was gonna end as a 6 or a 7. Up until today Fukushima was a 5 on the scale due to the severe core damage(any one of the items on the list for INES 5 is enough by itself to classify it as a 5). Now NISA has upgraded it due to the large releases of radioactive material, even though there is yet no assumption that the release will lead to large scale health effect.

World Nuclear News has published a map from IAEA of the fallout from Fukushima (attached at the end) and writes this about how much radioactive materials has been released in total.

“As a result of re-evaluation, total amount of discharged iodine-131 is estimated at 1.3×10¹⁷ becquerels, and caesium-137 is estimated at 6.1×10¹⁵ becquerels. Hence the Nuclear and Industrial Safety Agency has concluded that the rating of the accident would be equivalent of Level 7.”

One can see from the map that the majority of fallout has landed in a limited area, it remains to be seen how large parts of that area wont be fit for agriculture anymore.

Chernobyl released 17.6*10¹⁷ Bq of I-131 and 85*10¹⁵ Bq of Cs-137, so compared to Chernobyl we are looking at around 10% of release of the volatile fission products.

However TEPCO also announced today that the total amount of radioactive material released might exceed that of Chernobyl if they can not stop the leakage of radioactive water. It is good to keep in mind though that this release is going into the sea where it will quite quickly dilute, in Chernobyl everything went into the air and then could be spread over farmland, cities etc. Anything going into the sea will have very limited, if any, health impact.

Chief cabinet secretary Edano made this statement about the INES level.

“The change in the level reminds us the accident is very big. What’s different here from the Chernobyl accident is that we have not yet seen a direct impact on the health of the people as a result of the nuclear accident. The accident itself is big, but we will make, as our first priority, our utmost effort to avoid any health impact on the people.”

This statement is very important and it highlights a fact that media now seems to neglect, the raising of the INES level is due to the total amount of radioactivity released (most if it was released during the first week), not due to expected or already occurring health consequences. So far the Fukushima accident has not killed a single person and it seems unlikely the radiation dosages to the public have been so large that they can cause any significant(i.e detectable) increase in cancer rates. The increase on the INES scale doesn’t mean the situation has turned dramatically worse, it is just a raising of the level due to the high releases that occurred initially.

The Neutron Economy has a very good blog post, Fukushima Daiichi to INES Level 7 – Some Numbers on Why, about the INES rating, Fukushima and eventual consequences if one applies the Linear No Threshold model of the risk of radiation exposure.

 

 

Links(English)
CNBC Nuclear Power Fears at New Heights Despite Safety, Viability
World Nuclear News Fukushima moved to Level 7
CNN Japan nuclear disaster tops scale
BBC Fukushima: What happened – and what needs to be done
Reuters Japan raises nuclear crisis to same level as Chernobyl

Blogs(English)
NEI Nuclear Notes “Years of Unchallenged Mythology”
Depleted Cranium On the Ground Pictures of Fukushima
Atomic Insights As Fukushima gets moved from 5 to 7 remember that 0 (deaths) is still an applicable number
Idaho Samizdat Fukushima accident rating from 5 to 7 on INES?
Atomic Power Review Fukushima Accident: Level 7.
Atomic Power Review Level change note…
Atomic Power Review APRA Special: Observations on Fukushima Daiichi

Links(Swedish)
SvD Fukushima inte lika allvarligt som Tjernobyl
Aftonbladet Lika allvarligt som Tjernobyl
Expressen Japan skakat av nya skalv idag
SvD Japan uppgraderar kärnkrafthaveriet
DN Fukushimaolyckan på Tjernobyl-nivå

Blogs(Swedish)
Röda Malmö Vidden av katastrofen växer
APSO sverige Spridningen av Cesium 137
Blott sverige svenska preppers har Fukushima på samma nivå som Tjernobyl
Den svenska argus Sjuan kom

22 Comments