Chernobyl's elephant's foot

[Shane Kennedy]

Has the possibility of retrieving material from the elephants foot been considered ? Could a robot with a core-drill extract material, replace it with graphite, and place the cores in lead containers for transport to a reprocessing facility ?

 

[jim hardy]

Why would anyone want to disturb it?
The fuel wrapped itself in sand that it turned into glass .
I've heard no reports that it's unstable, and if not unstable then it's best left alone .

 

[Shane Kennedy]

A wasted resource. A no-go area for a thousand years ?

 

[sandy stone]

A stark reminder of human fallibility?

 

[girts]

Well why would anyone want to take parts of or the whole "elephants foot" apart? That material cannot be used for anything anymore anyways, yes it was a still useful nuclear fuel 30+ years ago but that was when it was inside the core intact. Now it's mixed with sand and multiple other materials and decayed a bit and is pretty much a useless burden.

Well you can take small dust particles from it and add to your tea, if someone has a death wish and wants to die like the famous KGB officer Litvinenko. Ok, bad sarcasm.


It is simply unfeasible to transport such material from the reactor anywhere else, because that would require safety and storage and other stuff, since the reactor 4 is not like a normal intact reactor it also cannot be dismantled as normal reactors could be. So for now and for decades to come the reactor unit4 with the new ark over it will be basically the storage facility.
From what I have heard they have built in cranes and other equipment so that after sufficient time they could start to slowly remove and take apart the unit4 from inside the new ark without moisture, rain and wind affecting anything or posing a risk to the environment, that is also one of the reasons why the ark was made so big , to fully engulf the unit4. Mind you the RBMK reactor building is very high itself so the ark had to be so big.



By the way, why would you want to replace the drilled out material with graphite

 

[jim hardy]

A wasted resource.

Worth a lot less than the cost to recover it.

A no-go area for a thousand years ?

Byproduct of civilization. Humans make those here and there. That one's just a few acres.

Mother Nature doesn't abhor Uranium. You might enjoy this article about a natural reactor in Africa.
https://www.scientificamerican.com/article/ancient-nuclear-reactor/

I'm way more afraid of recently introduced pythons in the Everglades where i used to go camping as a kid. To me it's now a million acre "No Go Zone" .

 

[Bigjoemonger]

At this point nuclear fuel is not a very rare commodity. So it's much easier and cheaper to mine more than to reprocess the elephants foot. So there's no motivation to clean it up to use it.

Right now it's also much easier and safer to cover it and monitor it than it is to disturb in and try to move it. The ark was built so big because cleaning it up will eventually be on the to do list but at this point the damage is already done and if it's contained it's not causing further damage. If you move it you risk further exposure and contamination.

Also you can't simply drill into it because Radiation levels that high degrade electronics so the drill would likely break down and die.

 

[mfb]

I don't find radiation levels around the Elephant's Foot now. This old measurement says 10,000 röntgen/h, about 10000 rad/h or 100 Gy/h. 300 seconds would give a dose of ~8 Gy, that is roughly in the range where it is lethal - although the radiation is mainly alpha, so it depends a lot on your mask and how well you shower afterwards.
Everything should work for a few minutes, space-grade electronics should survive hours to days, and the most radiation tolerant components at particle accelerators can work there for months to years.
Increase all times a bit as the radiation levels today are lower than they were in the past.

 

[jim hardy]

Everything should work for a few minutes, space-grade electronics should survive hours to days, and the most radiation tolerant components at particle accelerators can work there for months to years.

We have to consider such effects when mounting electronics in the nuke plant.
i once tested an industrial pressure transducer . It was described as having "D-MOS" semiconductors.
I don't remember exactly what source we used, it was a few hundred R/hr gamma source that our health physics department kept for calibrating high range survey meters.

After 1000 R there was no noticeable effect.
After 10,000R its calibration shifted measurably .
At 20,000R it was no longer responsive.
So we declined to use that type for some locations.


I was told by an engineer at TI that NMOS is the most fragile type of structure and i should expect to start getting temporary NMOS computer memory errors at a couple thousand R and permanent damage as dose increased beyond that.
So i gave my TI-99 half that, a thousand R . It seemed not bothered at all.

So yes, radiation-wise the electronics is several times 'tougher' than humans.

old jim

 

[mfb]

Oxide layers in general tend to be problematic - they accumulate charges and then your gate voltages shift or you can’t turn the transistor off or on any more. For individual transistors, silicon carbide and gallium nitride are much more radiation tolerant. The chips are typically quite good, smaller transistors are less likely to break. Make sure you don’t rely too much on the memory. All these things are possible, but they need some attention, and the market for them is very small.

 

[girts]

Well considering the OP's question about drilling the elephant's foot I think such simple electronic gadgets like universal electric motors and AC induction motors would probably hold up to extreme radiation levels both neutron and EM type just fine because they are nothing more than a copper wire and soft steel combined with cast iron, so in terms of drilling a hole into a cooled down reactor fuel that has combined with sand and reinforced concrete I think the drill bit would be the one that suffers the most given the density of the materials in question.


As Jim and mfb said, it's mostly semiconductors that are vulnerable to high radiation, for example vacuum tubes and relays and other older or electromechanical devices are so much more robust in terms of radioactivity.
maybe someone has some info about the maximum field a vacuum tube could operate? I assume it could work under extreme radiation as long as the cathode and grid metal structure physically holds up?

 

[mfb]

A vacuum-tube controlled robot?

Vacuum tubes should be fine as long as the induced charge from radioactivity is small, but you’ll struggle getting more than extremely basic functions that way. Better keep the robot attached to a long cable and feed commands from a more friendly place. Even remote cameras with bundles of glass fibers exist.

 

[krater]

Don't forget that even simple machines like AC motors have needs as well. Air cooling is a common theme with most drills. It's not easy designing a ventilated system with potential to generate dust that doesn't have a problem with aspirating said dust in its own fan. Water cooling can help, both to isolate the motor as well as keep dust to a minimum when attempting to drill a very hard aggregate for example. But this can get scarily out of control fast when things like leaks, sprays, and spills occur.

Magnify these difficulties several fold in an especially radioactive environment. Also consider that it can be a challenge trying to obtain modern human-operable drilling tools that are entirely free of any microprocessor or semiconductor mediated power control.

in terms of drilling a hole into a cooled down reactor fuel that has combined with sand and reinforced concrete I think the drill bit would be the one that suffers the most

Radioactive slurry, potential electrocution hazards, or handling of a metal case filled with microscopic active particles? It seems to me any human involved with this operation would fare much worse than any equipment.

 

[nikkkom]

You can imagine the type of problems to be expected and possible approaches to solve them if you read how TMI-2 cleanup effort was dealing with corium (they were removing it from ruined reactor's inside). Here is the report:

http://svcf.jp/pdf/Three_Mile_Iland2NP-6931.PDF

Section 8.

 

[jim hardy]

Here is the report .... section 8:

Section 8 starts on pdf page253 of 382.

 

[Rive]

I've heard no reports that it's unstable, and if not unstable then it's best left alone .

As I recall I've seen something about the slowly deteriorating surface of the stuff. If needed I might try to find a source.

Also you can't simply drill into it because Radiation levels that high degrade electronics so the drill would likely break down and die.

Only fine electronics is affected, drills are not. The most problematic part is to keep an eye on the operation - even rad hardened cameras has a limited lifetime in such environment.

 

[jim hardy]

As I recall I've seen something about the slowly deteriorating surface of the stuff.

Drilling makes lots of radioactive chips and dust that have to be caught and handled. High potential for making a real mess.
Some stubborn surface contamination can be immobilized with a coat of good quality paint. If indeed it's spalling and the objective is to keep it stable that's the simplest approach.

Let sleeping isotopes lie.

old jim

 

[Rive]

Let sleeping isotopes lie.

old jim

I do agree with you - if they start on anything there then that should be the rubble pile in the place of the reactor cavity, not the basement.
I've just added my part in general.

 

[jim hardy]

I've just added my part in general.

Yes, i figured you were correcting possible misconception that big industrial drills are sensitive electronic devices. It needed to be pointed out.

We've not heard from OP in a while ?

old jim

 

[HowlerMonkey]

Anyone have temperature data on it?

 

[franklyamazed]

They DID, they took samples from the "Elephant's Foot". The first samples were most likely taken during the 'Complex Expedition" that took place between December 1986 and early 1987, I think they blasted some samples off it with rounds from a Kalashnikov assault rifle, after attempts to chip some away with a hammer and an axe failed.

The 'Corium' from Chernobyl is known to have formed into six distinct masses below the level of the reactor's base plate, the 'Elephant's Foot' is just the most famous of these, and is black lava. There may be a mass of corium above the base plate, but I believe that is an unknown as this point, and it is possible that this does not exist! Three of these masses are black lavas, one is brown lava on a molten steel base, and the other two are brown lava covered by a porous ceramic material.

A lot of samples have been taken and analysed, (most after 1990 when it was discovered that the mechanical (physical) strength of the 'Corium' had weakened through radioactive deterioration. Many of these samples are held at the "V.G. Khlopin Radium Institute", where many scientific studies have had interesting results. Hydrofluoric Acid was used to dissolve some samples, this acid is known for it's ability to dissolve glass.

The coriums masses are different depending upon what the fuel melted and combined with, and studies suggest the fuel reached above 2,600 °C BEFORE the explosion, and fuel at these temperatures melted into the Zirconium alloy fuel cladding and combined with steel from the pressure tubes and the sand from the outer circumference barrier (which formed into a strange glass ceramic). Accident mitigation measures also dropped boron carbide, sand, lead, clay, and dolomite into the open reactor, and I do not know if any of these additives contributed to the corium's constitution.

It appears that the reaction was ONLY really stopped when Liquid Nitrogen started to be introduced into the reactor space on May 5th, this had a significant thermal cooling effect within 24 hours, the nitrogen acted as an oxygen blocker too, and May 6th showed a sharp reduction in the release of radionuclides. It took 9 days to really bring the runaway reaction under control.