

Another Explosion at Fukushima Nuclear Plant - olivercameron
http://bbc.co.uk/news/world-asia-pacific-12729138

======
radicaldreamer
Insightful reporting on the scale of the problem from NYT:
[http://www.nytimes.com/2011/03/14/world/asia/japan-
fukushima...](http://www.nytimes.com/2011/03/14/world/asia/japan-fukushima-
nuclear-reactor.html?hp)

The major issue seems to be that the power equipment is in a room that is
flooded, so regular cooling is impossible. They're pumping in seawater, but
they have to release pressure as it builds up and this released steam is
irradiated. Until some kind of regular cooling system is rebuilt, this process
to prevent meltdown will continue for the forseeable future.

~~~
waterlesscloud
How long does this post-shutdown cooling process take?

I thought I'd read something like 48 hours in the immediate aftermath of the
quake, but that's obviously not correct.

~~~
redthrowaway
I'd read that the problem was residual heat, as the control rods should have
dropped as soon as coolant flow halted. This means that no new heat is being
added to the system, but that the reactor will experience a gradual decline
from its 3000 MW operating capacity. All of that energy is stored as
irradiated steam, which can be forced into pools of seawater beneath the plant
to cool it, but only so much.

~~~
jeza
I don't think it's true to say no new heat is being added. The uranium fission
process has stopped, but there are secondary radioactive elements created by
the decay of uranium. These elements will continue to decay, as such the core
is still producing the heat. Though eventually this heat will decline to a
safe level, provided there isn't a meltdown beforehand.

The design oversight seems to be that they depend on external AC power or
diesel generators for backup. Surely there should be an emergency generator
that can run off the heat that the core still produces in order to at least
partially operate the cooling system. Much like aeroplanes have a small dynamo
that runs off a tiny wind emergency wind turbine so they can still operate the
hydraulics with no engines running. A saving grace in the case of Gimli Glider
(<http://en.wikipedia.org/wiki/Gimli_Glider>).

~~~
redthrowaway
Ah, thanks for the explanation. As I said, that was just what I had read. I
appreciate the further info. What you said makes sense, and explains why steam
pressure is still building.

~~~
jeza
No problem. Further to my comments about the design, I read in another story
linked to on HN that generation III reactors now use convection based cooling.
I gather this means the water is taken elsewhere as steam to cool then returns
via gravity to the core. Therefore you wouldn't have this same kind of issue
with a modern reactor.

~~~
redthrowaway
Interesting. That seems like a smart way of doing it.

------
desigooner
Timeline from BBC Live Page: (Reverse Chronological Order)

0328: Seven people are missing and three people have been injured by the
explosion at the Fukushima 1 nuclear plant, the AFP news agency reports,
quoting an official from Tepco, the company which operates the plant.

0247: Mr Edano said major radiation leaks were unlikely from Reactor 3.

0243: Japanese government spokesman Yukio Edano has just spoken on TV. Says
that water injection at Reactor 3 seems to be continuing, and the containment
vessel is still safe.

0242: Reactor 3 withstood the explosion(s), its operator says - Japanese news
agency Jiji.

0240: The governor of Tokyo orders radioactivity levels in the city to be
measured - Kyodo.

0239: The 600 people still living within 20km of the plant where the
explosion(s) occurred are ordered to get inside buildings - Kyodo.

0236: The wall of a building collapsed as a result of the blast(s) at Reactor
3 - Japanese TV.

0232: Update on the explosion(s) at Reactor 3: "We believe it was a hydrogen
explosion. It is not immediately known if it affected the reactor" - nuclear
safety agency spokesman Ryo Miyake.

~~~
shod
Another update: Tepco has confirmed that 11 engineers were injured in the
blast. No word on their condition.

------
dmfdmf
To be clear this is Unit 3, not the same reactor that blew up previously (Unit
1). Though dramatic, these are NOT nuclear explosions but hydrogen explosions
that result from venting steam from the reactor. The primary containment and
the reactor pressure vessel remain intact. Tepco (the Japanese utility)
previously warned that this might occur to Unit 3.

------
chaffneue
Video Here: [http://my.firedoglake.com/scarecrow/2011/03/13/japan-
nuclear...](http://my.firedoglake.com/scarecrow/2011/03/13/japan-nuclear-
watch-possible-new-explosion-at-naiichi-3/)

~~~
olivercameron
Wow, I know nothing about nuclear plants and the fail safe's they have built
in, but that looks like a scarily powerful explosion.

~~~
chaffneue
NHK is saying it's another blast like Fukushima Daiichi #1 on Saturday/Sunday
- Hydrogen collecting in the reactor building because of the fuel cladding
burning and then being vented with the steam to reduce pressure.. according to
the authorities so far, the reactor containment was undamaged and workers in
the area are to remain indoors.

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chaffneue
A scaled up aerial photo of the blown out building #3 now the smoke has
cleared.

[http://gigazine.jp/img/2011/03/14/fukushima_daiichi_3rd/Capt...](http://gigazine.jp/img/2011/03/14/fukushima_daiichi_3rd/Capture20110314-113641.jpg)

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rbanffy
Why can't the hydrogen and oxygen be safely vented out and burned as soon as
they are produced?

~~~
A1kmm
Hydrogen and oxygen only react at significant rate at high temperatures. In a
hydrogen explosion, the rate initially starts off low, but as the reaction is
highly exothermic, heat from the reaction increases the temperature and causes
the reaction to accelerate until reactant concentrations are sufficiently
depleted.

This means that hydrogen and oxygen can only react quickly if the
concentration of hydrogen in a volume is high enough that the increase in
temperature from the exothermic reaction is faster than the dissipation of
heat, so the temperature will rapidly expand, causing an explosion. For this
reason, hydrogen tends to build up and then explode, rather than burning
continuously.

It might be possible to trap hydrogen in a small volume and burn it in a
series of small explosions; however, I don't think the reactors are designed
that way.

~~~
redthrowaway
Couldn't you stick a piece of platinum at the mouth of a vent and just vent it
steadily?

------
mrleinad
I read the article referenced here
(<http://news.ycombinator.com/item?id=2318980>), and since the author seems so
certain that the third containment shell would hold the meltdown safely: Can
someone answer me why won't they just allow it to happen, so they can clean up
the rest and get the whole nuclear plant back online? Is it just an economical
reason? Or is there any other risk?

~~~
mseebach
If you allow meltdown, you're looking at contaminating the entire reactor
building. Clean up costs would be astronomical. If the pressure vessel remains
intact, the whole thing can be lifted out with little effort, leaving an
uncontaminated building behind.

~~~
mrleinad
Why? Isn't the "last line of defense" prepared to avoid any contamination at
all?

~~~
mseebach
Yes, of the surrounding environment. This is a single building more or less
single-purpose-build to be contaminated as a last measure.

All these exercises are inherently economical -- they could just have walked
away on the first day and have the whole thing melt down, and the surrounding
area wouldn't have been any better or worse off, radiation-wise.

------
extension
The fact that these explosions aren't damaging the containment actually makes
me pretty confident that nothing else will either.

Something has been bothering me: if Japan is so well prepared for earthquakes,
how did they have a nuclear reactor right on the coast with no protection from
tsunami? Wouldn't a barrier of some sort have prevented this whole mess? Or
elevated backup generators?

~~~
SamReidHughes
They did have protection from tsunamis. This one was too big.

~~~
ChuckMcM
A couple of stories have covered this, their wave estimation was low. That
being said, its clear they can improve and had the imported generators been
able to connect to the plant's cooling power plugs this would have been moot.

My guess is that positioning backup generators are safe from tsunamis and that
can be moved into position quickly, and are pre-tested to be compatible with
the backup infrastructure will get added to the licensing regulations.

------
hop
Anyone know where all the engineers would be located in a plant like this - an
onsite shielded bunker? What if they were to get hit by an explosion like this
- remote redundant control far offsite?

~~~
dmfdmf
I think the main control room and nearby offices are not bunker like but
certainly reinforced to withstand damage from accidents. I have been onsite to
a couple of reactors and most of the engineers are housed in regular
administrative buildings with no special reinforcements but these are outside
of the reactor building where the control room is located. There is no remote
control room but there are (at least in the USA) dedicated communication
channels to industry experts (probably GE engineers that designed these
plants) available to assist and advise 24/7 during an accident. Unfortunately,
one report said that 11 workers were injured in the explosion at Unit 3.

