Japan Earthquake: nuclear plants

gmax137

Does anyone have any reliable info on the nuclear plants - the reports on the news seem garbled to me.


Edit by Borek:

To All:

Please stick to technical aspects and to things happening at the Fukushima Daiichi NPP.

There are several other threads discussing different aspects of the disaster:

Why is Fukushima nuclear crisis so threatening?

Fukushima radiation detection and measurement

The "more political thread" besides "Japan Earthquake: nuclear plants" scientific one

Japan earthquake - contamination & consequences outside Fukushima NPP

Astronuc

Unless one has direct contact from someone in the plant, the best one can do is the releases by TEPCO or METI, but METI is probably getting it second hand. I haven't seen any official releases from METI though.

TEPCO press releases

http://www.tepco.co.jp/en/index-e.html

http://www.tepco.co.jp/en/press/corp...1031103-e.html
http://www.tepco.co.jp/en/press/corp...1031104-e.html


WNN - http://www.world-nuclear-news.org/RS...n_1103111.html

IAEA - http://www.iaea.org/newscenter/news/...amiupdate.html

WANO is behind the curve.


I have not found any direct press release from METI, but
Fukushima reactor pressure may have hit 2.1 times capacity: METI
http://www.reuters.com/article/2011/...72A7DB20110311

Woah - not good. That's a big NO-NO.

Problems at a second unit

TEPCO: loses control of pressure at 2nd nuclear plant
http://www.reuters.com/article/2011/...72A8GM20110311

If this is true, I can see a lot of managers getting sacked.

And there is this AP article on Yahoo - http://finance.yahoo.com/news/Japan-...20057.html?x=0

DR13

Is there any real chance at a meltdown or is that just the typical media hype?

Astronuc

At the moment, I don't see a 'real' chance of a meltdown. It is a worst case scenario, which is what licensing space is all about.

Some of the worst case scenarios involve extraordinary, and not necessarily physical real situations. It's a bit like crash testing a car by dropping it out of an airplane at several thousand feet, knowing full well that such a car would never be able to achieve such a velocity on level ground since the engine could not achieve the speed or the tires would blow out well before the speed could be achieved.

Some in the media will sensationalize the situation in order to grab the audience in order to sell commercials for useless stuff. But I digress.

I'd like to keep the discussion here on the technical aspects - as soon as we learn from reliable sources.

We have the earthquake thread in P&WA.

DR13

Ok. This question is pretty 'elementary' but I do not know much about how a NPP works. I read an article that said that the US delivered coolant to Japan. Why does Japan need the coolant? I don't understand how an earthquake and a tsunami can make a NPP lose its coolant? Also, what specific purpose does the coolant serve in the plant (what exactly does it cool) and what would happen if Japan could not get more coolant?

Astronuc

There was some miscommunication. I'm not sure who said what to whom, but apparently Sec of State Clinton mentioned coolant was being flown to Japan. That is incorrect.

They might airlift some generators, but I have not heard any details.

A light water reactor (LWR) uses water coolant under pressure to both moderate the neutrons and cool the nuclear fuel. The Fukushima units are boiling water reactors (BWRs), in which the water is boiled in the core at a pressure of ~1055 psia at Tsat ~ 286 C. The steam is sent directly to a high pressure turbine, and then the exhaust of the high pressure turbine feeds a set of low pressure turbines. The units are about 33% efficient, so about 67% of the heat is rejected through condensers to the environment, which at Fukushima is the sea.

When the reactor shutdowns, there is still some heat being generated from the decaying fission products. "At the moment of reactor shutdown, decay heat will be about 7% of the previous core power if the reactor has had a long and steady power history. About 1 hour after shutdown, the decay heat will be about 1.5% of the previous core power. After a day, the decay heat falls to 0.4%, and after a week it will be only 0.2%." Ref: http://en.wikipedia.org/wiki/Decay_h...rs_in_shutdown

So it is important to cool the reactor for several days following shutdown.

The RCIC requires power from off-site or emergency diesel generators. Well the plant lost off-site power. The EDGs worked for about 1 hour then stopped. Now plant personnel are trying to get power from some other source. It's not clear why the EDGs quit, but they are supposed to work for days.

5.4.6 REACTOR CORE ISOLATION COOLING SYSTEM (BWR)

DR13

Ok. Thank you for all of the information. Hopefully they can get the problems resolved soon.

aquitaine

So the coolant system was knocked out, can't they scram the reactor?

Hologram0110

The reactor is off but keeps producing heat has radioactive isotopes decay. Basically when it is on it produces a heat and radioactive isotopes which decay to more stable isotopes and give off more heat in the process. You can't turn this second process off, it just keeps going. The amount of heat the second process gives off goes down over time. However that means you have to keep cooling it for a number of days otherwise it would melt into a pile of radioactive goo (and take your expensive reactor with it).

aquitaine

So it's already off and wont explode? Cool, thanks.

QuantumPion

It looks like the containment building has exploded. My educated guess is, what they feared might happen at TMI has happened here. The core melted down, releasing lots of hydrogen gas in the chemical reaction with the cladding, which then ignited.

Pengwuino

Is it safe to assume the winds go towards the Pacific Ocean at the site? In case of an exposed meltdown?

Astronuc

At the time of the explosion, the wind was apparently moving toward the northeast, so any vapor would be carried out to sea.

However, I understand that the building where the explosion has occurred is not associated with containment, but I have not been able to verify this.

From World Nuclear News -
http://www.world-nuclear-news.org/RS...s_1203111.html So pressure in containment is about 8.4 atm rather the 4 atm, the nominal design pressure.

and and meanwhile at the plant next door, Fukushima Daiini (plant 2)The situation is serious. What has happened, shouldn't have happened.

caffenta

A TEPCO spokesperson made a statement on Japanese TV about 20 minutes ago. The explosion was supposedly from a buildup of hydrogen around the containment vessel. Apparently, they will flood the containment vessel with seawater (and boric acid?) Does that make sense? They also increased the evacuation zone to 20km. The reporters present didn't seem to like the contradiction of TEPCO's claim that everything was still safe and the expansion of the evacuation zone.

Caveat: my Japanese is not so great, so I may have misunderstood some of it.

EDIT: after checking online, looks like I got most of it right, but it was a government official, not a TEPCO spokesperson

vanesch

I have to say I don't understand how you can have a hydrogen explosion blowing apart the confinement building, and not the reactor vessel.

I also don't understand how you can let any pressure build up in the confinement building at the risk of rupture if it is slowly. One should prefer steam releases (even contaminated) in order to ensure the integrity of the confinement building if ever the reactor vessel breaks, no ? Now we are not very far from a full release of the core in the environment.

DrDu

I tried to consult the japanese dose rate surveillance site, but it appears they don't have information for the northern prefectures:
http://www.bousai.ne.jp/eng/

I don't know how they transmit their measurements, supposedly via internet. Did the internet break down completely in the northern part of japan?

Astronuc

I have read much the same in English. So far, I have heard conflicting claims - that the explosion was / was not the containment building. I'd have to find a map of the site to figure out if the explosion was near unit 1 or 4. Unit 1 has the most severe problem, while unit 4 was shutdown cold already. From the picture, it looked like the explosion was near unit 4.

See this article - http://mdn.mainichi.jp/mdnnews/news/...dm073000c.html

If the containment is breached with an uncooled reactor, that is very serious.

I have heard that Chief Cabinet Secretary Yukio Edano mentioned cooling unit 1 with seawater, but I don't know where he is getting the information.

Cooling directly with seawater would be a drastic step.

The news from the area is rather sketchy.