Japan Earthquake: nuclear plants

Rive

As I recall the fuel was already damaged at that time, so...

NUCENG

Never really thought about it since the plants I'm familiar with are inland. However looking at the overhead photographs and drawings in the TEPCO handouts it appears that each pump is in a separate well or bay in the intake structure and thus is partially shielded from the insurge and probably completely shielded from runback forces. The impeller, shaft, volute and riser pipes can be mounted and anchored to the walls of the bay or well. How well they are protected I don't know for sure, but the motors look like they were more exposed to the tsunami than the pumps may have been. How well mounted and protected they are from surge effects will determine whether shafts or impellers are subject to damage.

I can't answer the question on how well protected these pumps at all plants. I have been in US plants on the Great Lakes that have to protect against seiche effects which are similar to tsunamis but come from harmonic amplification of waves back and forth across the lake.
These plants have quite detailed analysis to support the design basis wave heights and to demonstrate how vital systems are protected. I think some of their protective walls may be bigger than the seawall at Fukushima Daichi. Other plants are evaluated for river flooding which usually gives some notice and allows for procedure driven preparation to add protection such as sandbagging or installing panels over louvers or other similar actions.

A couple years ago plants in the US Midwest were subjected to a "1000 year flood" and continued to operate with minimal impact other than making the trip to work a little longer to avoid water. At one plant operators had to take a boat to the intake structure for inspection tours and maintenance.
I'm not sure how water hammer is involved in these pumps. Water hammer is the high pressure impact on a system caused when flow is initiated into a voided portion of the system and the void collapses causing the hammer effect. Cavitation and vibration are bigger threats to these centrifugal pumps.

In addition, plants all over the world should be watching the Fukushima event closely for lessons learned.

tsutsuji

The Incinerator building basement, where the contaminated water from unit 3 had been moved, was suspected of leaking :

The missing water has finally been found in a tunnel joining two buildings. There has been no leak into the ground water, according to http://mainichi.jp/select/science/ne...40110000c.html

NUCENG

That may explain why the hydrogen explosion in unit 2 was in the torus. Venting from the drywell would have lowered H2 concentration there, but the amount of hydrogen from the tous through the vacuum brakers to the drywell would have been slower to reduce H2 concentration in the torus.

Venting directly from the drywell loses the scrubbing effect of the suppression pool when venting from the torus. So they increased the release to the environment and the public after being reluctant to vent unit 1 at all. I'd sure like to see their reasoning for that. The only thing I can think is that the dry venting may have been done after explosions in units 1 and 3, and they were trying not to repeat that experience again.

~kujala~

So it seems.
I took one check point, after 180 days for units 2 & 3, and for TEPCO it's about 1 MW and for your chart it's about 0,9 MW (or something like that):

http://varasto.kerrostalo.huone.net/...at_mattila.png
http://varasto.kerrostalo.huone.net/...heat_tepco.png

Perhaps they copied your chart and put it in non-exponential scale to look like brand new?

This ~ 1 MW is also something we have for unit #4 SFP now, if I have understood correctly.

tsutsuji

My understanding of Japan Times' Tepco quoting sentence "Yesterday, we said the dry vent of the No. 2 reactor was done March 16 to 17, but it was the 15th" is that "done" means "attempted", not "performed".

According to the New York Times :

I am not sure if Tepco changed its position since May 17th about how successful these venting attempts have been.

~kujala~

We have some good news for a while:

http://mdn.mainichi.jp/mdnnews/news/...dm079000c.html

If they have sub-drains below waste facilities I am sure these are now included as sampling spots. We'll see.

If there are sub-drains below waste facilities it also means that even if some contaminated water leaks there the sub-drains should take care of it (or at least part of it) and collect it into the sub-drain pits - which later could be emptied.

NUCENG

Sorry, I should have linked my post to Robinson's post instead of Zapperzero. I was replying to his thought that normal plants were not anywhere near 1 Sv/hr.

During a submarine refueling I witnessed a dribble of water fall onto the floor of the refueling shack while removing a spent fuel assembly into a transfer cask. A Health physicist took a swipe of the spill using a small paper swipe. When he checked the reading it overranged a frisker and so he checked it with another high range detector. It was 75 R/hr or about 0.75 Sv on contact. Apparently that dribble contained a bit of highly activated CRUD. That little piece of paper was a walking high radiation area. It doesn't take much volume to make a lot of radiation depending on the isotope and its half life.

Astronuc

I suspect that the analysis might have been very conservative, and perhaps considered adiabatic conditions, i.e., no heat removal from the fuel. I would like to see Allison's report.

See also - http://www.world-nuclear-news.org/RS...3_2605111.html


Meanwhile, Westinghouse is responding to the event by introducing a mobile emergency SFP cooling system.
http://www.world-nuclear-news.org/RS...l-2605117.html

Jorge Stolfi

AFAIK it is not necessary for the moderator to penetrate the fuel; just surrounding the fuel with moderator should be enough.

To have fission one needs to have a significant fraction of the emitted neutrons slowed down and scattered back to the fissile material. If the fuel is immersed in a large amount of moderator, and there is no absorption, every neutron that leaves it will eventually be scattered back to it, by "drunkard's walk" statistics. (This is the same effect that makes sunlit clouds look white.)

The half-life of a free neutron's is 15 minutes, so decay should not be a significant factor.

I suppose that neutron absorption is the main factor preventing re-criticality. TEPCO has been using boron in the emergency cooling water; the effect should be like that of soot particles making smoke clouds black instead of white. Also the corium itself may (or may not) include neutron-absorbing material from the control rods.

Is this correct?

havemercy

Hello to all. I'am very sorry if this question has already been asked, but it is quite difficult to read all the posts to check.

Is it possible that the corium, we know TEPCO said has been in the bottom of the reactor vessel, has leaked out in a porous soil, and, with contact with the water in such soil, resulted in a low blast that everybody has interpreted as a replica of 5.6 on Richter scale ?

(Sorry for the english)

Many thanks in advance.

SteveElbows

When do you think this may have happened?

SteveElbows

This subject seems to keep coming up every day for several days in a row now. Is someone posting scare stories about this data elsewhere on the internet, or is it just that lots of people have been using that atmc website graphs all along and are now wondering why its showing scary stuff?

In any case, this subject has been addressed here multiple times in recent days. Main summary of points:

The atmc website makes some bad errors with what data it uses sometimes, so it is not a good idea to use it as main source. Use TEPCO data instead, which shows 2 x drywell CAMS and 2 x suppression chamber CAMS readings for all reactors.

Main data site index page: http://www.tepco.co.jp/en/nu/fukushima-np/index-e.html

The CAMS readings are part of the pressure & temperature data sheet, so for reactor 1 it is:

http://www.tepco.co.jp/en/nu/fukushi..._data_1u-e.pdf

So yes, one of the sensors is sometimes showing values of 200 or higher. But the other sensor shows much lower values, and TEPCO think the sensor(s) may be damaged because they dont agree with eachother, and one of them fluctuates a lot.

Other thing to note is that this is not a new thing, only reason its suddenly being noticed is because TEPCO only started publishing the data for this sensor again recently (around may 17th), after not bothering for many weeks, probably because the readings seemed unreliable.

In conclusion, there are too many unknowns about this data to make any conclusions, and if there is a problem its not a new event, it happened quite a long time ago. I do not think the CAMS data is good enough to be able to use it to reach interesting and firm conclusions about how much of the core fell into the drywell, so there is no point getting excited about the big numbers. All it really tells us is that fuel got damaged, and we know that already.

havemercy

On April 22 :
http://mysouth.su/2011/04/in-fukushi...magnitude-5-6/

elektrownik

The problem is that second sensor which show low value cant be correct if any amount of corium is in drywell, this hight value can be corect if corium hit drywell cams sensor... Chernobyl was >300Sv around core, at this time we know on 99% that unit 1 core melted from rpv and damaged drywell

mscharisma

Does this fall into the good or the bad news category? No leak into groundwater is surely good, but there wasn't supposed to be any kind of leak, I assume? What, if anything, does it tell that also the wastewater facility leaks somehow?

Borek

No idea why you think these things are in any way related. Epicenter was 22 km from the plant, not under reactor building. Besides, there were many quakes in the area since the big one, why this particular one caught your attention?