[etdgxcnc]

Apologies - I had skimmed the sentence immediately preceding the one I quoted, although it does contradict what you'd said. They wouldn't have welcomed it melting through the ground (just melting or otherwise) for the very reasons given by yourself.

There was no need for the rolling eyes smilie though. Why is everybody becoming so aggressive on this forum these days? Everybody seems to take offence at the slightest remark or be incapable of holding any kind of conversation without being prickly.

No worries, mate, I wasn't being a bit prickly, just drawing attention to it .
However, as I said " if it was a simple case of menting* it's way though the ground", I thought it was clear I was aware it wasn't viable and was referring to a simple "China Syndrome" scenario where it melted through towards the core. So no contradiction.

Down here I was very interested but having to rely on news reports, as one of the older European chaps, what do you remember of the disaster as it unfolded, and in the years that followed??

*Note, I left the typo in

[arriplify]

the big news was the cloud as it was tracked - no news out of soviet ukraine at the time (at all actually) , and welsh sheep dying as a result of being poisoned

[Twendypreency]

you dont actually need `weapons grade` material for a fissile reaction - all `weapons grade` or enriched uranium does is reduce the amount of material needed for criticality. also heavy water reactors use `unrefined` uranium , literally dug out of the ground and shoveled in (well not quite but you get the idea)

"Critical mass" implies 100% purity. In a chain reaction, the density of the fissile material greatly influences the actual mass needed. If you could compress the 235U with enough force from a conventional explosion, to reduce the volume in half, you'd need less than 1/2 the mass.

The relative abundance of fissile material 235U/238U in nuclear reactors precludes a nuclear explosion from occuring. It's not physically possible.

[Twendypreency]

Hundreds of people at the accident were exposed to far higher doses than the helicopter pilots but the total death toll after several weeks was around 30 - none of which were the pilots: they were actually safer than the ground workers once they stopped direct dumping. Of the people who died in later years, it's not possible to say with absolute certainty that the severe acute dose they received was responsible for their deaths.

Are you actually saying that the total death toll was 30? That's not even funny.

[etdgxcnc]

Are you actually saying that the total death toll was 30? That's not even funny.

It's not supposed to be funny!
So, what do you say it was, preferably with a few sources?
I've read a number of reports that also have around 30 fatalities, as Neeyik said - it's why I earlier talked about low numbers of workers dying.

[etdgxcnc]

"Critical mass" implies 100% purity. In a chain reaction, the density of the fissile material greatly influences the actual mass needed. If you could compress the 235U with enough force from a conventional explosion, to reduce the volume in half, you'd need less than 1/2 the mass.

The relative abundance of fissile material 235U/238U in nuclear reactors precludes a nuclear explosion from occuring. It's not physically possible.

I think you're getting two different things confused, 'critical mass' is that required for a sustained reaction, not always an explosion.
Explosives are used to bring the material fast enough together and, most important, hold it together long enough for the explosive reaction to occur. Getting the timing of all the charges to go off at virtually the same instant was one of their biggest problems as any variation would allow the pressure to 'squeeze out' and reduce the effectiveness of the explosion.

[phenterminediett]

A documentary I watched made it sound like more people died, and virtually all pilots were included in that.

Same here, although I'm not sure how specific it was about how soon everyone died afterwards either.

[etdgxcnc]

This says 30, this 56 and others, like Greenpeace [yawn] say the total toll will be up to a hundred thousand.

[Zhgpavye]

Allot of the deaths took weeks/months to happen.

[elton]

Are you actually saying that the total death toll was 30? That's not even funny.

He didn't say the total death toll was 30, he said the total death toll after several weeks was 30. I would have thought someone with your intellect would have better reading comprehension.

This says 30, this 56 and others, like Greenpeace [yawn] say the total toll will be up to a hundred thousand.

The first figure is talking about a few weeks after the accident, and the other two the death toll after that.

[Wachearex]

the sourse(s) i had were from a number of years ago - they simply said that (when translated from russian) the explosion was nuclear in nature , and it was the americans who were saying it was a steam explosion - the conditions within the core caused the overheat and poorly regulated nuclear reaction `ran away` causing a lowl level nuclear explosion.

Define "nuclear explosion" - one could argue that regards of the nature of the explosion it was nuclear-sourced, given that the heat generated was done through fission, but the typical definition is a fully uncontrolled thermonuclear detonation, which did not take place.

"Critical mass" implies 100% purity. In a chain reaction, the density of the fissile material greatly influences the actual mass needed. If you could compress the 235U with enough force from a conventional explosion, to reduce the volume in half, you'd need less than 1/2 the mass.

The relative abundance of fissile material 235U/238U in nuclear reactors precludes a nuclear explosion from occuring. It's not physically possible.

He said "criticality", not critical mass (and even then I don't think he implied 100% enrichment of U-235) but the point you raise about the amount of U-235 present is only part of the reason why reactor cores cannot undergo a nuclear explosion (it's also worth noting that at the end of the fuel cycle there are higher portions of fissile elements than U-235 present in the rods that also have much lower critical mass per unit area values). It's your other point on density that's a larger factor (reactor cores densities with respect to the mean free path of the neutrons is very low compared to the thermonuclear weapons) and there's also temperature to consider: as cores get very hot the amount of fission taking place begins to decrease because the mean neutron temperature falls more into the resonance region, even after moderation.

Are you actually saying that the total death toll was 30? That's not even funny. I said "the total death toll after several weeks was around 30" - after several years it was considerably higher and although we will almost certainly never know the true death toll from the accident to date, it must be well over several hundred.

[phenterminediett]

Define "nuclear explosion" - one could argue that regards of the nature of the explosion it was nuclear-sourced, given that the heat generated was done through fission, but the typical definition is a fully uncontrolled thermonuclear detonation, which did not take place.

--------

It's not. What you simply have is a reactor design that has a potentially unstable thermal output: reactor cores cannot undergo any kind of thermonuclear detonation.

This is basically what I meant earlier in the thread.

[arriplify]

at no time did i say it underwent a thermonuclear reaction - as a thermonuclear reaction is a fusion reaction , not an atomic reaction - the hiroshima bomb was an atomic or fission bomb , they split the atom like all nuclear reactors , a thermonuclear reaction is the fusing of duetirium and tritium , look at the JET project at culham,

the entire problem with the reactor in the is something uique - positive scram.

when the reactor is scrammed , because of the graphite tip on the control rods , you actually get an energy increase in the neutrons ,(as the graphire displaces the cooling water (also acting a moderator)) now coupled with the positive void coeffieicent , the large amount of steam and the presence of large amounts of high energy neutrons anyway - you have the recipe for something going very wrong - the positive scram effects the lowest part of the reactor first , as the thermocouples showed , the reaction climbed massively there first.


as i said above U238 is fertile rather than fissile - until they get a large of amount of high energy neutrons - so now we have U235/U238 and P239 in a high energy enviroment thats under high pressure.


which is why i believe the lowest part of the core did go `bang`.


criticality - is an accidently power excursion , or in the case of a nuclear reactor you can have a massive supercritical event which can lead to a runawy core;

enriched uranium - as said above , enrichement reduces the amount (mass) needed for critical mass , and comes in several `flavours`

SEU or slightly enriched uranium , which can be found naturally , is where the U235 content is above the `norma` of 0.7% but below 2% - this is for CANDU type heavy water reacotrs and better for waste managemnt


low enriched uranium - under 20% U235 , typically the LPWR or light pressurised water ractors use 5% U235 as fuel , higher concentrations are usually for research reactors converting for high enriched to low enriched.

and the `bombs` - HEU or highly enriched uranium , this is for U235 concentrations above 20% - and although useable as a weapon , it isnt weapons grade - that is for the highest enrichment - 85% or above.


BUT


stack enough uranium of any type into a big pile and it will go critical


http://ublib.buffalo.edu/libraries/p...tokaimura.html


600kg of 15% will go critical on its own , and i think if im right that it takes 300 tons of natural uranium to do the same.

[arriplify]

and a nuclear reactor can explode - windscale nearly did when the graphite core reached max temp , 1200 fuel rods collapsing downwards along with neutron sources - and they had no plan to put the fire out....

[phenterminediett]

http://www.youtube.com/watch?v=OwEIX...=33&playnext=6

[arriplify]

i think you dont get what i mean so some clarity:

can a nuclear reactor explose?

short answer - NO

long answer - NO unless its a russian RMBK design, then YES.

why yes?

unlike every western reactor , as neeyik said , when you turn off the coolant flow (and you get more voids or bubbles) the reactivity goes down a `negative void coefficent` till eventually it goes `out` , the RMBK is totally opposite - its had a very large - 4.7beta , positive void coefficient - the more bubbles , the more reactivity.

so , as in chernobyl , they turned off 4 of the 8 pumps - ergo , more bubbles.

next is containment - unlike western buildsings , the RMBK doesnt have a proper containment building.

and last - SCRAM or reator trip , the emergency method of shutting down a reactor undergoing a serious power excusrion (or problem) - it dropd the control rods and or reactor poison in an instant;

the RMBK scram cycle was 20 seconds - the control rods instead of being released to fall on there own weight , where attached to motors and driven down slowly into the core , and with the design of the control meaning 1 mete of its length was graphite - it was actually a positive scram (made it worse) on the lowest part of teh core , whilst the top was actually shutting down!



all of thsoe factors (and massive operator negligence - turning off the automatic safety systems) are why it went bag on a low level and why the wests reactors cant.

[Extipletape]

http://store.steampowered.com/agecheck/app/4500/

Steam.

[DailyRingtone]

I previously said, "molten core" which wasn't altogether untrue, as the core was indeed at melting point, about 2900*c and was actually in danger of reaching that point and melting down through the earth, until it reached the water table, where a secondary huge explosion would have occurred.

I originally read a page that described what I stated in my last post, that was written by the station manager at that time, Viktor Bryukhanov.
But I'm unable to find the same page that he described the whole incident and who died and when.

The Helicopter pilots did die, but years later apparently and not in the forthcoming weeks, so I was wrong about that bit.

If no ones posted it before, this is quite a good page on it.

http://www.guardian.co.uk/world/2006...nuclear.russia