Tag Archives: containment

Day thirteen after the tsunami

Update 22:30(UTC)/23:30(CET)/07:30/(JST)

I end todays updates with some heartbreaking pictures from the tsunami disaster. Its very hard to even just watch these pictures, I hope the resilience of the great japanese people will astonish the world when they rebuild after this disaster.

http://blogs.denverpost.com/captured/2011/03/18/captured-japan-earthquake-and-tsunami-one-week-later/2838/

Update 21:20(UTC)/22:20(CET)/06:20(JST)

Some Austrian researchers have analysed data from detectors used to verify the comprehensive test ban treaty and their analysis show that the emissions of iodine and cesium from Fukushima is approaching the same level as from the Chernobyl accident. Fukushima emitted around 1,3*10^17 Bq iodine per day the first days and the total emission from Chernobyl was 1,7*10^18 Bq. By now the iodine emissions must be much lower due to the short half life of iodine and they haven't reported any containment venting for about a week if my memory serves me right. The core inventory of I-131 is now reduced by more than half due to decay(half life 8.02 days) and the other iodine isotopes have even shorter half life. It will be interesting to see more data on this.

It's good that the evacuation from the area around the reactor was brisk and that iodine pills have been supplied. So far the ground fallout data from MEXI doesn't look very bad but it might be due to the  direction of the wind as stated in the article.

 

Update 19:15(UTC)/20:15(CET)/04:15(JST)

It is in the middle of night in Japan right now and the news flow is always a bit slower then for obvious reasons. But NISA has still released a new update (values from 18:05 which makes it older than the JAIF updated I wrote about in the last blog update. They have released a PDF with pictures from the control rooms and plant area, here is a direct link to it. They are ne day old and that is why the control room for reactor 1 is dark(they restored power to it today).

17 workers in total has exceeded a total dose of 100 mSv.

Uppdate 16:00(UTC) / 17:00(CET) / 01:00(JST)

New JAIF and NISA(link 1, link 2, link 3) updates. NISa has added a new file to its update that gives more data, among them the dose rates within the containments. The NISA uppdate is from 11:00 and the JAIF update from 22:00 JST. JAIF numbers first followed by NISA within ().

Reactor 1:
Water level in the core: 1.7 meters(1.7m) below the top of fuel assemblies
Core pressure: 523 kPa (532 kPa)
Containment pressure: 390 kPa (400 kPa)
Core temperature(feedwater nozzle): 175 Celsius
Dose rate within containment:  43.5 Sv/hour

Reactor 2:
Water level in the core: 1.15 meters(1.15m) below the top of fuel assemblies
Core pressure: unknown
Containment pressure: 110 kPa (110 kPa)
Core temperature(feedwater nozzle): 100 Celsius
Dose rate within containment: 48.4 Sv/hour

Reactor 3.
Water level in the core: 2.3 m (2.3 m) below the top of fuel assemblies.
Core pressure: 137 kPa  (137 kPa)
Containment pressure:  unknown
Core temperature(bottom head): 185.,5 Celsius
Dose rate within containment: 55.9 Sv/hour

The pressure in number 1 went up a bit and then started going down. Temperature has been lowered about 70 degrees Celsius. Dose rate by main gate seems to be on a slow decline. Iodine levels in Tokyo water has gone down below the infant limit of 100 Bq/liter. Testing of pumps are ongoing in reactor number 3. More and more vegetables with levels far exceeding the limits for cesium and iodine is found.

 

Uppdate 9:00(UTC) / 10:00(CET) / 18:00(JST)

During night(swedish) JAIF(link 1, link 2) and NISA(link 1, link 2) has released new updates. The NISA updates(the schematics of the reactors attached at the end of the post) is by the time of writing 13 hours old and the JAIF update 2 hours old. I will write the JAIF numbers below first and the NISA numbers within parenthesis so one can se the change over the last 11 hours.

Reactor 1.
Water level in the core: 1,7 meters(1,7m) below the top of fuel assemblies
Core pressure: 510 kPa (511 kPa)
Containment pressure: 385 kPa (385 kPa)
Core temperature(feedwater nozzle): 243 Celsius

The situation has been stable for the last 11 hours. Containment pressure and core pressure is up about 20 kPa since yesterdays update. The containment pressure is a bit to high for comfort I would say. All though the highest it has reached during the entire accident was about 800 kPa in one of the reactors so it can plausibly handle even a doubling in an emergency, but if it doesn't go down soon I am afraid TEPCO are going to have to vent the containment. Venting now could be problematic since the steam will contain quite a lot of activity and it could hamper work for hours due to radiation levels. On a positive note, the lights are now on in the number 1 control room showing that there is some progress in restoring electricity. Lets hope the pace will accelerate soon and that the coolant pumps are functional or at least easy to replace!

Reactor 2.
Water level in the core:  1,2m (1,2m) below the top of the fuel assemblies
Core pressure: Unknown(the readings claim below atmospheric pressure so the gauge is most likely broken)
Containment pressure:  105 kPa (105 kPa)
Core temperature(feedwater nozzle):  102 Celsius

Compared to yesterday pretty much nothing has changed. The core temperature and both core pressure and containment pressure remains low. Nothing new about the radiation levels in the turbine building(reported to be around 500 mSv/hour yesterday) that prevents access for repairing equipment.

Reactor 3.
Water level in the core: 2,3 m (2,3 m) below the top of fuel assemblies.
Core pressure:  (142 kPa)
Containment pressure:  unknown(JAIF states "downscale")
Core temperature(feedwater nozzle): 80,7 Celsius

The JAIF update has changed the status of the containment from "might be not damaged" to "not damaged", that is very good news indeed! It means the only damaged containment is on reactor 2 that appears to be quite stable and cool. Sometime during yesterday they seem to have been able to hook up a pump to one of the pipes leading to the spent fuel pool and they can now provide seawater through the cooling and purification line. Hopefully that means there is no need anymore for blind spraying of the number 3 building. Yesterday they managed to restore lights to the control room, but no news about instrumentation or the filtration system to bring down radiation levels inside the control room.

Reactor 4.

The concreter pump truck continues to deliver water to the spent fuel pool at a rate of 50 000 liters per hour.

General remarks:

We have been hoping for the electricity to be restored to the pumps etc since Saturday now. There is no explanation on what problems they have encountered or the status of the pumps. In the Fukushima Daini plant they had to replace pumps after the quake and tsunami so perhaps pumps needs to be replaced at Daiichi as well. The situation appears stable at the moment, but seawater cooling can not continue forever. At some point the salt depositions in the core will start to cause real problems but I do not know what time span we are talking about. If one estimates the salt deposition from the amount of water that could have been evaporated by the decay heat so far one ends up with several tens of cubic meters of salt. It's hard to know where all of this salt has been deposited though since we don't know the flow path of the water. On the bright side it seems like the workers are able to access more of the reactor building now as indicated by the fact that they have switched the path of seawater injection for the number 3 spent fuel pool and the number 1 reactor.

Three workers have been exposed to close to 200 mSv. It's encouraging that they manage to keep the worker doses below 200 mSv so far. If TEPCO is being honest then its unlikely we will see any acute radiation sickness in workers.

Iodine levels in water and vegetables in prefectures close to Fukushima continues to be high.

We'll try to keep it in english from now on...

Update 07:30 (UTC) / 16:30 (JST)

JAIF just released their 16:00 update. One bit of happy news there is that they now write that the number 3 containment vessel is "Not damaged".

Screenshot of the update will follow soon when the guy that has access to saving PDF to JPG gets to his computer. 🙂

Radiation levels in the Tokyo water also seem to be dropping again... but it's too soon to speak of any general trends. Also no new word on Caesium-137 in farmlands or water.

The work to bring electricity to Fukushima I continues (slowly).

The Forsmark incident was not Chernobyl

This is the second blog response to a blog entry made by The King of the country Lagom. The previous entry dealt with his claims that opinions are sacred and how one must not speak up against them. This entry will deal with the purely factual errors of his claims about nuclear power.

The King of Lagom claims that an incident that took place in 2006 at the Forsmark nuclear power plant could have escalated into a Chernobyl-type accident.  Well... first he says that, and then he says it could have become something entirely different. If this sounds confusing it is because the King of Lagom probably doesn't quite know what he's talking about but rather builds this statement on misconceptions about what actually happened at Chernobyl and Forsmark respectively. So let's examine the incidents and compare.

The 1986 Chernobyl accident

April 26, 1986. The night shift at reactor 4 at the V.I Lenin Nuclear power plant, 20 km north west of the town of Chernobyl, Ukraine, has been ordered to do a test. Due to operator error, they accidentally poison the RBMK-type reactor which makes it almost grind to a halt. They don't know why the reactor is giving so little power though because they were mostly coal plant workers, inexperienced with nuclear power, and oblivious to things such as nuclear poisoning. The shift boss, determined to finish the test, gives orders to proceed, telling the operators to perform actions that go against several operating rules of the reactor. This puts the reactor in an unstable state.

When the test is finished and they shut down the reactor, a fatal flaw in the reactor's control system causes the reactivity to spiral out of control, making it output between ten to onehundred times normal thermal effect. The water in the reactor flash boils and the enormous steam pressure blows the building apart. A few seconds later a chemical explosion, when water that has been split into hydrogen and oxygen burns, rocks the complex again. The reactor is on fire for ten days, resulting in a large plume of radioactive fallout.

There are several factors that allowed this accident to happen.

First it was operated by poorly educated personnel, in a political system where safety came second. In the Soviet Union, you did not rise to attractive jobs like this one by being good at your craft but by kissing up to the communist party. Also you did not stay at jobs like this by speaking up against safety issues, because such things made the party look bad. For instance this particular test was supposed to have been run years ago when the plant was commissioned. But since it failed back then, it had to be done again, this time in secret from the Soviet nuclear regulatory authorities.

This shouldn't have been a problem. But the second reason the accident could take place was the deliberate violations of the operating rules of the reactor. The test was to have taken place when the reactor was outputting at least 700 MW; they started when it was at 200 MW. They were not allowed to withdraw more than a certain number of control rods; they withdrew almost all of them. They were not allowed to increase water flow in the reactor past a certain amount when operating at low power; they did. They were not allowed to disengage the safety systems that would have shut down the reactor when they did any of the aforementioned; but they did indeed disable them.

All of this made reactor come into an unstable state that let its most critical design flaw come into play: the positive void coefficient. The void coefficient is a quality in a nuclear reactor that tells us what happens when it gets too hot. When coolant boils in a reactor that has a positive void coefficient, the nuclear reaction increases. This makes the reactor hotter, which makes more water boil. This speeds up the reaction more, making it even hotter... and so forth. And not only was the void coefficient in the RBMK-reactors of the Chernobyl plant positive, it was also dangerously high.

Finally, because the reactor had no real core vessel, nor any concrete containment, the force of the explosion wrecked the building completely. A fire started in the hundreds of tons of graphite that was in the reactor. Also the building itself that was supposed to have been made from fireproof material, was not, and the debris caught fire as well.

This is what is known as a criticality accident, when the nuclear reaction goes out of control. In this case it produced so much heat that the entire reactor blew up from all the thermal energy. This accident was not a nuclear meltdown.

The 2006 Forsmark incident

July 27, 2006. At the switch-yard for Forsmark-1, an electrical arc causes a short circuit which leads to the unit being disconnected from the power grid. This is serious as the plant relies on power to keep all pumps going.

If a nuclear reactor does not have working pumps, eventually the cooling water in the reactor will boil away. If that starts to happen you must engage the emergency core cooling, reserves of water kept for this very purpose. If this too fails and the reactor boils dry, the heat can be such that the reactor core becomes damaged, popularly called a meltdown. This can happen even when the nuclear reaction has been stopped because decay heat continues to be produced a few hours after a reactor is shut down as very short-lived nuclear waste falls apart. This is what happened at Three Mile Island in 1979.

So when a nuclear plant becomes disconnected from the power grid, the reactor is shut down and on-site diesel generators start to provide power for the pumps to deal with the decay heat, and this was what happened at Forsmark 1. However in this case, two out of the four diesel generators did not start, disabling two safety trains out off four. But the two remaining diesel generators were more than enough to drive the pumps. Hence the reactor was cooled and emergency core cooling was not necessary. The reactor shutdown proceded normally.

Similarities?

No, there are no similarities between these two incidents. The Chernobyl disaster was the case of a criticality accident that caused an extremely violent explosion that completely wrecked the reactor core; the building it operated in; burned for days. The Forsmark incident was the case of  slight degradation of safety features while the reactor and its cooling operated normally. The cooling system was operational the whole time; the emergency cooling did not need to be engaged; the reactor core was not damaged; the reactor tank was in no way threatened; the over one meter thick reactor contaiment remained perfectly safe. And fire? Naw... there is no graphite in Forsmark-1. Water handles that job instead.

So when the King of Lagom says that the Forsmark incident could have become another Chernobyl, he is wrong. There is no way that Forsmark-1 or any of the other Swedish nuclear reactor could undergo the process that led to the explosion in Ukraine in 1986. And this is not just because we employ people that know what they are doing; care about safety first; follow procedure; don't do things behind the back of the nuclear regulatory authorities. No, the most important reason why a Chernobyl-type criticality accident cannot happen in Sweden is the reactors themselves. Because unlike the RBMK-reactors of the Soviet Union, our boiler- and pressurized water reactors do not have a positive void coefficient. We did it the opposite way, so that when water starts boiling in the reactor, the nuclear reaction slows down because of inescapable laws of physics. It's nature's own choke collar on nuclear reactions.

Conclusion

The RBMK-type of reactor was employed only in the Soviet Union. The international community is working hard to get the twelve RBMK's that are still in operation closed. Even though I'm a nuclear friend I'm not an idiot, and as such I am very glad that one of the remaining RBMK's. Ignalina-2, will be shut down in 2009, meaning that Lithuania no longer operates them. Now we just need to get Russia to shut down theirs and we'll finally be rid of this blight.

When discussing nuclear safety, anyone that uses Chernobyl as an example of what could go wrong in nuclear reactors is ignoring reality. The BWR/PWR reactors of the world hold about as much in common with the RBMK-design of the Soviet Union as does slavery to common work; as does forced child soldiers to commissioned adults. There just is no comparing them as they operate differently down to subatomic level.

The Forsmark incident was not, and could not have become, another Chernobyl. This is not an opinion, it is physical reality.

/Michael

ADDENDUM: As I posted a link to this entry in his blog,  and called him on his Ad hominem attacks, he first approved the entry, then he cencored it and claimed that I was violating his right to have "free opinions", i.e. he doesn't want anyone telling him he's wrong.