The. Biggest takeaway for me is that we have hard proof that any unusable waste products can be stabilized for at least a billion years! With processed SNF leaving waste that is around 300 years until equaling the mine they came from, I’d say that’s an acceptable safety factor!
There was no understanding of the existence of nuclear fission or radioactive decay in the 19th century or before. The view in the 19th century was that the Earth was simply radiating stored heat out of the planet's core. This prompted Lord Kelvin to calculate the age of the Earth as 20 million to 400 million years old, based on the rate of heat radiation out of the ground to atmosphere. Most of the earth's heat comes as we now know from the radioactive decay of uranium in the planet's liquid metal core. Lack of such radioactive decay is most of the reason why Mars does NOT have a liquid core and no seismic activity but is entirely a dead planet. Kelvin similarly argued that the Sun was simply radiating stored heat, and he argued for a lifespan of just a few hundred million years rather than the billions of years that we now know it to be.
William Thompson 1st Baron Kelvin, made many great contributions to science, particularly in the fields of thermodynamics and atmospheric physics. But his rejection of Rontgen's discovery of XRays, his rejection of the engineering of heavier-than-air flight, and his insistence that the Earth had only a 400 year supply of oxygen were proved very wrong within his lifetime. Ernest Rutherford's discovery of radiation and the basic structure of the atom would refute much of Kelvin's reliance on classical physics.
So what was discovered at Oklo was hard evidence that nuclear forces were indeed a very large part of our planet's formation and remain such today.
Not so. There is no possible fission reaction of uranium except in the presence of a moderator. There was a moderator at Oklo in the form of salt-saturated water. There is no moderator in our planet's core. Please do not confuse radioactive decay from nuclear fission; they are two entirely different processes.
What does exist is a huge mass of uranium, producing energy from radioactive decay. And given the enormous half-life of U-238, this source of radiation will continue long after the disappearance of all life on our planet about 400 million years from now.
You are right, I misspoke. Simple alpha-emission is enough. Still, any neutrons produced in the core will certainly slow down eventually, and I'll bet the odd slow neutron gets captured on the odd U-235 nucleus to cause extremely slow, extremely rare fission. (Lucky for us!)
There's a very old principle in nuclear physics. Stated simply: the rate of a reaction is directly dependent upon the proportion of fissile material there is in an object. U-235 and Pu-239 are fissile, U-238 is not fissile. For an object to fission very rapidly, (like a bomb), the proportion of fissile material must exceed 99% of the mass. Plutonium was used in Manhattan Project for Nagasaki (and ever since for all nuclear weapons), because Pu requires much less total mass than uranium. I believe the total mass of plutonium needed for a critical mass is about 4 kilograms.
This principle is why no nuclear power reactor can ever explode in a nuclear explosion. A nuclear power reactor's fuel has a maximum of 4- 5 % U-235 content. Natural concentration of U-235 is approximately 0.7%, so fuel enrichment means separating out a lot of U-238 and keeping the remainder at the fuel concentration you want.
A fast breeder reactor needed a fissile concentration of about 20%. Again, way below the 99% needed for a nuclear explosion.
The proportion of U-235 in all uranium everywhere at the time of the Oklo events was much higher than the current 0.7%, about 6 or 7%, meaning it was essentially a low-enriched fuel. Over a few thousand years, it produced lots of fission fragments, all of them absorbing neutrons, and ended the existence of the natural reactors at Oklo.
(a) Clearly there are no runaway chain reactions in the Earth's core; but U-238 also fissions under FAST neutron bombardment, and the neutrons it produces don't slow down very fast in scattering off the heavy elements there, so one can actually imagine the core as a very controlled reactor running on U-238. I wonder if that's so.
(b) There are a lot of other types of reactors besides the ones you mention, e.g. the CANDU reactor that runs of natural uranium, or the various designs that run on thorium.
CANDU indeed runs on natural uranium, but it requires a highly effective moderator in the form of heavy water. Thorium 232 is not a fissile material at all, but all thorium can be bred into U-233 (via neutron bombardment) which is fissile. Th-232 will be used as a nuclear fuel after all of the low cost uranium has been mined and used as fuel.
Never apologize for asking questions. PIcky are often important details which you may want to know.
As to fast neutron fission in the earth's core, not likely. The earth's core will include lots of other elements all of which will absorb neutrons.
You perhaps should have explained that U-235 has a relatively short half-life (700 million years), so natural uranium contained more readily fissionable uranium back when Oklo was active.
Thanks - very interesting.
The. Biggest takeaway for me is that we have hard proof that any unusable waste products can be stabilized for at least a billion years! With processed SNF leaving waste that is around 300 years until equaling the mine they came from, I’d say that’s an acceptable safety factor!
Great story. “Never does nature say one thing and wisdom another.” - Juvenal
There was no understanding of the existence of nuclear fission or radioactive decay in the 19th century or before. The view in the 19th century was that the Earth was simply radiating stored heat out of the planet's core. This prompted Lord Kelvin to calculate the age of the Earth as 20 million to 400 million years old, based on the rate of heat radiation out of the ground to atmosphere. Most of the earth's heat comes as we now know from the radioactive decay of uranium in the planet's liquid metal core. Lack of such radioactive decay is most of the reason why Mars does NOT have a liquid core and no seismic activity but is entirely a dead planet. Kelvin similarly argued that the Sun was simply radiating stored heat, and he argued for a lifespan of just a few hundred million years rather than the billions of years that we now know it to be.
William Thompson 1st Baron Kelvin, made many great contributions to science, particularly in the fields of thermodynamics and atmospheric physics. But his rejection of Rontgen's discovery of XRays, his rejection of the engineering of heavier-than-air flight, and his insistence that the Earth had only a 400 year supply of oxygen were proved very wrong within his lifetime. Ernest Rutherford's discovery of radiation and the basic structure of the atom would refute much of Kelvin's reliance on classical physics.
So what was discovered at Oklo was hard evidence that nuclear forces were indeed a very large part of our planet's formation and remain such today.
Note: Geothermal power also comes from nuclear fission. The Earth is a huge reactor whose containment is the Earth's crust.
Not so. There is no possible fission reaction of uranium except in the presence of a moderator. There was a moderator at Oklo in the form of salt-saturated water. There is no moderator in our planet's core. Please do not confuse radioactive decay from nuclear fission; they are two entirely different processes.
What does exist is a huge mass of uranium, producing energy from radioactive decay. And given the enormous half-life of U-238, this source of radiation will continue long after the disappearance of all life on our planet about 400 million years from now.
You are right, I misspoke. Simple alpha-emission is enough. Still, any neutrons produced in the core will certainly slow down eventually, and I'll bet the odd slow neutron gets captured on the odd U-235 nucleus to cause extremely slow, extremely rare fission. (Lucky for us!)
There's a very old principle in nuclear physics. Stated simply: the rate of a reaction is directly dependent upon the proportion of fissile material there is in an object. U-235 and Pu-239 are fissile, U-238 is not fissile. For an object to fission very rapidly, (like a bomb), the proportion of fissile material must exceed 99% of the mass. Plutonium was used in Manhattan Project for Nagasaki (and ever since for all nuclear weapons), because Pu requires much less total mass than uranium. I believe the total mass of plutonium needed for a critical mass is about 4 kilograms.
This principle is why no nuclear power reactor can ever explode in a nuclear explosion. A nuclear power reactor's fuel has a maximum of 4- 5 % U-235 content. Natural concentration of U-235 is approximately 0.7%, so fuel enrichment means separating out a lot of U-238 and keeping the remainder at the fuel concentration you want.
A fast breeder reactor needed a fissile concentration of about 20%. Again, way below the 99% needed for a nuclear explosion.
The proportion of U-235 in all uranium everywhere at the time of the Oklo events was much higher than the current 0.7%, about 6 or 7%, meaning it was essentially a low-enriched fuel. Over a few thousand years, it produced lots of fission fragments, all of them absorbing neutrons, and ended the existence of the natural reactors at Oklo.
(a) Clearly there are no runaway chain reactions in the Earth's core; but U-238 also fissions under FAST neutron bombardment, and the neutrons it produces don't slow down very fast in scattering off the heavy elements there, so one can actually imagine the core as a very controlled reactor running on U-238. I wonder if that's so.
(b) There are a lot of other types of reactors besides the ones you mention, e.g. the CANDU reactor that runs of natural uranium, or the various designs that run on thorium.
Just being picky, sorry! -- Jess
CANDU indeed runs on natural uranium, but it requires a highly effective moderator in the form of heavy water. Thorium 232 is not a fissile material at all, but all thorium can be bred into U-233 (via neutron bombardment) which is fissile. Th-232 will be used as a nuclear fuel after all of the low cost uranium has been mined and used as fuel.
Never apologize for asking questions. PIcky are often important details which you may want to know.
As to fast neutron fission in the earth's core, not likely. The earth's core will include lots of other elements all of which will absorb neutrons.
You perhaps should have explained that U-235 has a relatively short half-life (700 million years), so natural uranium contained more readily fissionable uranium back when Oklo was active.