I forgot about them. Being new maybe they did. After initial crit, they won't need it again.

I'll find out.

FIFY.

Plus long half life of most of the material means low decay rate and low dose rate.

This post does not advocate that arfcom play with their pu239 cores bare handed as was done under ww2 war time practice

These photos were a recreation by another scientist of the methods that were used, but without an active core. There were no photos of the actual experiment that killed the scientist.

Less in, more out.

I award you 100 internets for that response...very clever.  I got a good laugh out of it, thanks.

Oh fuggggg XDDDDDD

I need to change some things.

Yes

Nuclear Filson is like this jacket being radioactive.

Attached File

Little radiation is emitted from pure plutonium, other than alpha particles. Alpha particles are stopped within the material, or by the nickel plating on the outside of the ball.

"Dirtier" grades of plutonium have more of the isotope Pu240, which has a high rate of spontaneous fission, which increases the external radiation. Still nothing like a high-level radioactive element like Cobalt 60.

And yes, plutonium is a radiation hazard if you ingest/inhale it, so that it's in direct contact with internal body tissues, same as any alpha emitter. Polonium is the highest intensity alpha emitter and famously used as a poison by the Soviet Union and Russia.

Yes, and I can also spell it correctly.

Wow, I didn't know the last part that only heavy atoms can release net energy from fission.   That's cool, thanks for the summary.

That's what I thought too...    

Some people here may find it interesting that if you make liquid solutions of compounds containing fissile materials, that the liquid can go critical if you get too much of it in the same place.    

These liquids are prepared during the process of enrichment and manufacturing.    

Here is a tip:

If you were careless and accidentally caused a small criticality event by filling a specialty container to the wrong level for the concentration of solution you were using, DON'T try to hide your mistake by pouring the entire container down the floor drain, (which isn't designed to prevent criticality) and thus causing an even larger criticality event that drenched you in radioactive liquid.  

Yes, nuclear physics and fissile materials are very interesting!   Sometimes in the Chinese way.



Carpentry: Measure twice, cut once.

Fissile Liquids: Measure twice, pour once.

There are some atoms that are very large. So large that they spontaneously fly apart into smaller particles. In nuclear fusion we just help that process along more easily by shooting neutrons into them.  The difference in mass is released is energy.

There are some atoms that are very large. So large that they spontaneously fly apart into smaller particles. In nuclear fusion we just help that process along more easily by shooting neutrons into them.  The difference in mass is released is energy.

Wow. actually some good answers in this thread.....just a few amongst the yuk-yuk-hyuk boyz LOL.

Uranium ore needs to be processed to concentrate it before it's suitable for use as a nuclear fuel or in a weapon. Look up gaseous diffusion/centrifuge processing.
Uranium U235 and Plutonium U238 are different elements. U235 is commonly used to fuel nuclear reactors and is enriched (Processed as in above) to 20 percent or so. Weapons grade you need 90 percent. Or so. LOL.

The demon core story is a good read and is instructive. Mr Slotin's death provided information on contamination and exposure rates that actually saved lives down the road.

Nuclear reactors are controlled just so with the use of control rods that moderate or stop the fission process. The reactor generates heat, turning water pumped through it to steam. That runs turbines that generate electricity. Shazzam!

If the control rods are completely withdrawn, depending on the reactor design, the reactor will heat up beyond it's design specs and basically melt. Others more knowledgeable can speculate on a typical BWR going hiroshima. Another true story like the demon core that is worth a read is the SL-1 reactor story. Yeah. The three operators that were there when that reactor went critical are buried under tons of rock with the reactor when the site was cleaned up. Reactors typically melt because forming a critical mass, where the reaction is self sustaining and releases ALL of it's energy at once instead of "heating" is prevented by its design. Usually.

If you want to understand how nuclear weapons work, learn the story of Fatman and Littleboy first. Two main designs. Those are the original two basic fission weapons. The Little Boy is a gun-type weapon. Calculate a critical mass for the U235 you have. (like Mr Slotkin's experiment but without the POOF!!!) Divide that mass in a device far enough apart that they do not form a critical mass. To detonate the two cores are driven together with explosives. Portable Sunshine is created. The Fatman design is an implosion device. Create a hollow sphere of U235, or another shape, even a solid probably round mass that's not a critical mass until you crush it into a smaller symetrical shape that IS critical. To do this you use a high grade of explosives that have to be triggered in a specific way. Simply stuffing a bomb casing fulla dynomite around a core no-workee. It has to be a very precisely triggered IMPLOSION. Fusion is different. They pretty much all start with a fission explosion that triggers a second stage that creates a fusion explosion that releases even more energy.

Since this stuff is declassed, unlike when I learned about it in 1970's Army, all of this info is out there and the YouTube videos alone are worth the watch.
Operation Castle
Upshot Knothole
Operation Plumbob to start.
It's far more instructive to do that and a lot more fun.

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There is no "reacting" in a reactor unless there is a critical mass.

"releasing all its energy at once" is a fast fission chain reaction which makes a bomb, which is not possible in a reactor for several reasons. No Chernobyl was not an atomic bomb.

Meltdowns happen because there is insufficient coolant to absorb the energy output. Lots of ways to get there, but that's the gist of it.

"You can't put too much water into the reactor."

Ed Asner

I believe popcorn is actually a really really tiny nuclear explosion.

U235 does not need to be enriched to 20% to fission in a light water reactor.  It can be enriched to much lower levels than that and still work in a light water reactor.  Natural uranium, meaning completely unenriched uranium can be used for fuel in CANDU reactors.

Commercial nuclear reactors can melt down and chemical or steam explosions can occur, but they can't have a nuclear bomb type explosion.

Reactors accidents can involve different mechanisms that don't involve uncontrolled fission.  At Idaho National Engineering Lab, there was an accident in an experimental reactor involving a control rod being manually pulled out way too far which made the reaction rate skyrocket.  So that one qualifies as uncontrolled fission.  Three Mile Island, was a loss of coolant accident, which resulted in a partial melt down.  Fukashima reactors were shut down and no longer having nuclear reactions.  The accident occurred because the coolant pumps could no longer be run since the on-site backup generation was inoperable and all other means of powering the coolant pumps were destroyed.  Since the coolant pumps were inoperable, the decay heat from the shut down reactor could not be removed and that decay heat was enough to cause all the subsequent accidents.  Decay heat of a commercial reactor like Fukashima is considerable.

Solar is safer.

US commercial reactors are enriched to no more than 5% U235.

US westinghouse PWRs run "all rods out" and use dissolved boron in the coolant to control reactivity. AP1000s are boron free but use some other type of rod in place of the "chemical shim."

No western designed reactor (or their copies) can "go Hiroshima."

@capn_rob or however it's spelled can

The plutonium ball on its own slowly emits small amounts of radiation.

The dome he was holding over the ball captures that small amount and reflects it back into the Plutonium.  The more completely it's covered the more gets reflected back and more fission events are triggered as a result.  Even a small gap is enough to keep the radiation at "safe" levels.  But if it were to get entirely covered the number of fission events would increase exponentially and quickly produce lethal doses of radiation.
The few seconds it was covered was enough to kill everyone in the room.

Also not all radiation is as dangerous as other types.
Light is radiation.  The heat you feel from a distant explosion... or the Sun... or a heat lamp... is radiation. When you get an X-ray... that's radiation. Then gama rays... All those are Light, only at different wavelengths and thus energies.
There's electron radiation... If you ever watched CRT TVs you were being shot with an Electron beam the whole time.
Then there's ionizing radiation... I might be combining types here I'm not too sure... As I understand it... Naked Protons and also Neutrons get ejected from the reaction at nearly the speed of light.  These "heavy" particles can strike other atoms such as those in your DNA and break things.  
Most deaths from radiation happen due to exposure to Ionizing radiation.

There were two criticality accidents with the core.  In the first accident, one dead in 25 days due to the radiation.  The other guy died at 61, 33 years later from leukemia.  (maybe due to the accident, maybe not, he got 8 rads).

In the second incident, one dead in 9 days due to radiation.  The others died much later.  You can look at the dose rates and see that many lived very long times and into advanced age and the causes of death is not a smoking gun for radiation.  Some died due to causes that weren't radiation, but if they lived longer, who knows.  

This is perfect. Especially the “not too fast” part.  Graphite for the win.  Or water if you’re in the west.

Watch Disney's Our Friend the Atom

Gasoline, Coal, diesl ect make 2.5-5ish units of energy per unit of coalC gas,
Diesel, input.
Fission breaks apart uranium  and makes say 1000000(I might be an order of magnitude Or 3 low)Units of energy per Unit of uranium.

Fusion makes energy by combing hydrogen atoms to make helium, it yields something like 10000000000000000 units per unit of hydrogen input.
Nukes are fission, the sun is fusion.

Strangely This summary is not inaccurate!

Thermonukes are fusion too.

@PlaysWithAtoms, yep, ops manager of V3 confirmed start up source.

Is that to get more even fuel burn, or what is the rationale for it?

Don't forget about turbidities.

Yes and even neutron flux distribution axially and radially.

Figures! It takes somebody from Australia to explain what nobody else here could try to do without mentioning "Mommy", "Daddy", "shit" or "fuck". He probably also didn't mug his teacher back in grade school.

Technically wrong though. Graphite helps neutrons be in the correct energy level but does not absorb neutrons. Adding more graphite to a pile increases available neutron flux and drives the reaction forward.

Username does not check out.

Since we're talking about fission chain reactions and not just fission, this point is important.

Uranium has two main isotopes in nature, U235 and U238. U238 is over 99% of natural uranium.

U238 tends to capture free neutrons that are zipping by. It has a "capture resonance" at the energy level that most neutron particles would be traveling at. U238 can be fissioned, if the neutrons are at a high energy, but that energy level is not possible from fission, so a chain reaction is not possible in U238.

However, if you slow the neutrons down to a slower speed, they're less likely to be captured by the U238, and may encounter a U235. That's when the magic happens... because if you add a neutron to U235, fission almost always happens.

You slow down neutrons by using a neutron moderator - some element or substance that the neutrons can bounce off of, and around in, to absorb their energy but that won't absorb the particles. Carbon is one such element, deuterium in heavy water is another.

Enrico Fermi joked that fission was discovered because he worked in Italy, and not in the US. One of the key steps in the discovery of fission was that the effect of neutrons on Uranium was significantly different if the experiment was performed on a marble top table vs a wood table. Wood is a neutron moderator, marble is not. Fermi noted that if he'd worked in the US, everything would have been done on a wood table so there would not have been a difference to notice.

You get a fission chain reaction when a neutron from one fissioning atom hits another atom and causes fission, and so on and so on.

Of course the fission chain reaction gets a lot easier if you increase the percentage of U235 in the uranium - enrichment.

If you increase the enrichment percentage high enough, you don't need the neutron moderator anymore as there is no U238 with its capture resonance. You can put a bunch of U235 together and it'll fission chain-react all by itself, a fast reactor. If you force a larger quantity of U235 together fast enough, it'll go through generations of chain reactions in millionths of a second, or what the Japanese call pika-don.

Just plain ol "light" water is a great moderator as well. That's why we went "cheap" in US by using light water while our northern neighbors went with expensive heavy water.

The resonance phenomenon you describe has a graph on page two of the thread (just saying for those that may not make the connection.)




Finally, all anyone really needs to know.

Keff = E  Lf p Lth f n

Ironically, Germany never got the bomb because of geography. Their coal had to much boron impurity, so they had to use heavy water, which came from Norway. That's a fascinating side bit to WWII and The Heavy Water War is a great watch.

Yes I can.

His username checks out. I'm getting a headache. But thanks for that.

Points 4 and 8, which are the entire essence of how nuclear fission works, were nearly completely wrong.

Reactors can use graphite to moderate neutrons.  Reactors can also use light water or heavy water to moderate neutrons.  Most reactors currently operating are moderated by light water, followed by graphite, followed by heavy water.  Moderation means to slow neutrons down to a speed where their chance of absorption into the nucleus of the nuclear fuel is greatly increased.  A slow moving neutron is more easily absorbed than a fast moving neutron and this neutron makes the nuclear fuel atom unstable.  The unstable nuclear fuel atom splits and releasing energy and enough neutrons to start a chain reaction if the reactor is properly designed.  Moderators must not absorb many neutrons or they would bring the chain reaction to a halt.  Control rods are made from materials that absorb neutrons.  They aren't made from graphite which moderates neutrons.  Control rods control the rate of reaction in the reactor by absorbing enough neutrons to maintain the desired heat production level.

So that post turned everything about how a reactor really works upside and backwards and you fell for it, hook, line, and sinker.

"Light" water is a moderator, but it absorbs too many neutrons to be able to maintain a chain reaction with natural uranium. You have to use enriched uranium to sustain a chain reaction with plain water as a moderator. IIRC you need like 2% U235 depending on the exact geometry etc. Graphite or heavy water, both at very high purity are IIRC the only moderators that have been successful with natural uranium.



Someone earlier in the thread I think mentioned the CANDU reactors that use heavy water, which is because they're designed to be able to use unenriched (natural) uranium. If you can run on natural uranium you don't need enrichment capability, which makes the industrial base needed significantly easier. We had enrichment, Canada didn't.

With no enrichment capability (or plutonium separation) you can't make a nuclear weapon either, so it's safer to give nuclear power technology to non-nuclear weapon countries if enrichment isn't required. If you have the capability to do enrichment, you can run it as long as you want to get to whatever percentage you want.

From the father of American theoretical nuclear physics John Atoms

Oh, well, yeah. Sorry I missed that you were making a point about natural uranium.

While CANDU reactors mean you don't have to enrich uranium, they are able to create plutonium and tritium.  Reactors specifically designed for making weapons grade plutonium are far more efficient at the job of making weapons grade plutonium.