Have they located the melted fuel at Fukushima?

a.ua.

Reactor RBMK has 2 turbines.

Kutt

You're right, having multiple smaller turbines is probably better than just one giant one for the reasons you stated.

Astronuc

Large equipment is transportable by road. That's usually how it gets to (of from) the plant. Each steam generator at San Onofre was about ~400 tons, ~65 feet in height and about 17 feet at maximum width.
http://www.ocregister.com/articles/s...enerators.html
http://www.huffingtonpost.com/2012/1...n_2077732.html
(turn down the volume and ignore that advertisements)

Two 600 MWe turbines still need specialized cranes/equipment, and each turbine rotor and the casings cannot be lifted by hand. Most people cannot lift and carry an object of their body weight very well. There are usually limits on what people lift, <25 kg.

jim hardy

Well,, our generator stator weighed about 392 tons.
It arrived in town by rail the first time, and a special hundred wheeled trailer was supposed to haul it the last ten miles.
But on that road out to the plant the earth beneath the pavement squished away and the generator tumbled into the swamp. So next time they barged it right to the plant.
Would a 200 ton generator on fifty wheels have squished the road? Anybody's guess...

It's really no more trouble to lift a 400 ton piece than a 200 ton piece just the crane is slightly bigger.

I think economy of scale applies - it's twice the complexity and twice the labor cost to build and maintain two half size machines instead of one full size one.
Dont forget the auxilliaries - a steam turbine needs a condenser, lubrication system, feedwater heaters, pipes, pumps , valves, etc.

Heed Thoreau - 'Simplify, Simplify"...

LabratSR

To the original question,

According to this report, TEPCO stuck a camera into the PCV "near" the pedestal room of Unit one but did not see anything that appeared to be corium.

From the summary of the report.

"Recently, within the October 2012 timeframe, TEPCO was able to insert a camera along with instrumentation through a penetration into the Unit 1 PCV [83]. Video within containment was obtained; however, the information has not been fully scrutinized and interpreted as of this report. The camera was able to view a small portion of the drywell floor [84] in a drywell location approximately 180 degrees opposite from the pedestal doorway. Core melt did not appear to be present in this view. Future analysis and data collection as to the debris location will provide insight into the accident progression."

I posted this in the big thread but it seems to fit here.

Enhanced Ex-Vessel Analysis for Fukushima Daiichi Unit 1:
Melt Spreading and Core-Concrete Interaction Analyses with MELTSPREAD and CORQUENCH

https://fukushima.inl.gov/PDF/MELTSP...%20Feb2013.pdf

I went back and looked and found these associated reports.

http://www.tepco.co.jp/en/nu/fukushi...21015_05-e.pdf

http://www.tepco.co.jp/en/nu/fukushi...21015_04-e.pdf

Kutt

Have they concluded whether or not the cores have burned their way through the concrete base of the reactor building and into the Earth beneath it?

zapperzero

There is no conclusion and there won't be for a long time. The modeling runs so far point to the fuel having eaten just a little into the basemat and stabilized there. Muon radiography is being considered

https://www.lanl.gov/newsroom/news-r...clear-scar.php

nikkkom

Thankfully, concrete base is about 10 meters thick.

Models so far say that corium almost reached the containment bottom (the light-bulb shaped thing), and if they are wrong, it may indeed reached it, but there are 7.5 more meters of concrete below it.

Attached Thumbnails

 

Kutt

How come giant containers at a steel mill which contain hundreds of tons worth of superheated white-hot molten steel do not have that molten mass burn through it's base? While a nuclear reactor pressure vessel cannot physically contain it's core if it melts?

russ_watters

Perhaps look up the melting temperature of steel vs the melting temperature of the container holding it?

Kutt

Why can't reactor vessels be made of a material that has a melting temperature greater than the temperature of molten corium?

nikkkom

Corium has no defined temperature. It heats up due to decay heat, and without sufficient cooling will become hotter and hotter until it melts the vessel.

Tougher vessels theoretically can be built (say, using vanadium, molybdenum alloys and such), but they will cost astronomical sums and still won't be 100% safe wrt meltdown.

Safety versus meltdown can be achieved only by designing in very robust emergency cooling systems. In my "armchair engineer" view, something like "reactor sitting in a stainless steel lined pit with no drains, and with a set of large tanks beside it which can be manually drained into the pit, no electricity needed" should work.

zapperzero

Large tanks of what, please?

nikkkom

Water.

jim hardy

You just described PWR "Acumulators".

Kutt

There should be robust "last resort" emergency cooling systems which can be manually operated by hand without electricity to supply the reactor with water. If such systems existed at Fukushima, the safety and stability of the reactors would have been ensured.

More water can be brought in via truck or helicopter if needed.

Speaking of, is it possible to bring in more diesel fuel to nuclear power plants by the truckload in case the emergency diesel generators run dry?

The roads leading to the Fukushima Daiichi NPP were blocked by debris from the Tsunami, making this impossible.

nikkkom

No. Accumulators are high pressure tanks (nitrogen pressurized) with water which are meant to inject this water into primary coolant loop.

They require RPV to be depressurized. As you know, in Fukushima depressurizing RPV and PCV proved difficult. Fail.

What I described are tanks which can, if all else fails, flood reactor pit and submerge the reactor, i.e. cool reactor from the outside.