Is Nuclear Power "overunity"?

[DARK0717]

I was about to sleep last night, and i wondered, how much energy does it take to produce uranium needed vs the total energy production of nuclear power plants (regardless of energy used to construct the whole fascility ofc)

[Bufofrog]

The energy from a power plant is much more than the energy needed to produce usable uranium.  The same is true of coal.  

That doesn't mean overunity though.  We are simply utilizing the potential energy in the uranium or coal.

Edited April 5, 2020 by Bufofrog

[DARK0717]

4 hours ago, Bufofrog said:

The energy from a power plant is much more than the energy needed to produce usable uranium.  The same is true of coal.  

That doesn't mean overunity though.  We are simply utilizing the potential energy in the uranium or coal.

sooo, cant NukePlants make uranium and resupply itself or charge batteries to power equipment to gather uranium (i dunno how usable uranium is obtained)

also, why are the wiered magnet engines not considered as "utilizing potential energy in magnets" when that is actually the case?
I think its coz of the terms used in such devices, tho i cant agree that they break the laws of physics because energy from magnets cause motion and they basically act as (in the best conditions, long lasting batteries)

[swansont]

13 minutes ago, DARK0717 said:

sooo, cant NukePlants make uranium and resupply itself or charge batteries to power equipment to gather uranium (i dunno how usable uranium is obtained)

also, why are the wiered magnet engines not considered as "utilizing potential energy in magnets" when that is actually the case?
I think its coz of the terms used in such devices, tho i cant agree that they break the laws of physics because energy from magnets cause motion and they basically act as (in the best conditions, long lasting batteries)

!

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[Bufofrog]

18 minutes ago, DARK0717 said:

sooo, cant NukePlants make uranium and resupply itself or charge batteries to power equipment to gather uranium (i dunno how usable uranium is obtained)

Uranium U235 is mined.  Only a tiny amount of uranium is 235 is naturally occurring, the majority of the Uranium is you 238.  It is a very difficult procedure to isolate the uranium 235 from the uranium 238.

Breeder reactors can make fissile  material from the neutron capture of uranium 238 to form plutonium 239.  Only a small amount of plutonium 239 is produced, and it again is difficult to isolate it from Uranium 238.  It is not possible to construct a breeder reactor that produces more fuel than it consumes.

Edit to add:  U235 is a fissile material and U238 is not.

Edited April 5, 2020 by Bufofrog

[swansont]

21 minutes ago, Bufofrog said:

It is not possible to construct a breeder reactor that produces more fuel than it consumes.

What is the obstacle to doing this, in principle?

[Bufofrog]

39 minutes ago, swansont said:

What is the obstacle to doing this, in principle?

Now that I think about it you probably can, thank you for questioning that.  You of course cannot simply make more Plutonium than the Uranium in a breeder reactor and then have the reactor continue to run on the new Plutonium.  The core must be removed and the Plutonium must be extracted and then put into a new core to be used.

[swansont]

26 minutes ago, Bufofrog said:

Now that I think about it you probably can, thank you for questioning that.  You of course cannot simply make more Plutonium than the Uranium in a breeder reactor and then have the reactor continue to run on the new Plutonium.  The core must be removed and the Plutonium must be extracted and then put into a new core to be used.

Not seeing why a new core is necessary to “burn” the plutonium. It would be interspersed in the fuel just as the U-235 is.

[Bufofrog]

1 hour ago, swansont said:

Not seeing why a new core is necessary to “burn” the plutonium. It would be interspersed in the fuel just as the U-235 is.

I have never heard of anyone attempting anything like that and frankly doubt that it would be possible.  I have been out of nuclear power for 35 years, but I can't imagine something like that would be possible.  For instance part of the reason you replace the core is not to lack of fuel but due to fission products acting as a poison (absorbing neutrons).  

[swansont]

49 minutes ago, Bufofrog said:

I have never heard of anyone attempting anything like that and frankly doubt that it would be possible.  I have been out of nuclear power for 35 years, but I can't imagine something like that would be possible.  For instance part of the reason you replace the core is not to lack of fuel but due to fission products acting as a poison (absorbing neutrons).  

But the Pu is fissile. It doesn’t know not to undergo fission.

The core will reach an end of life and you can extract the remaining fissile material, just like any other core, but since you are creating more fuel, and also burning up the U-238, which is another poison, I would expect you could run longer before end-of-life.

[Bufofrog]

35 minutes ago, swansont said:

But the Pu is fissile. It doesn’t know not to undergo fission.

The core will reach an end of life and you can extract the remaining fissile material, just like any other core, but since you are creating more fuel, and also burning up the U-238, which is another poison, I would expect you could run longer before end-of-life.

Reading up on this a bit, I found that even commercial light water reactors do get an extended life from the formation of Plutonium.  It is still necessary to remove the breeder reactor core to extract the Plutonium and put it into a new core.  This reason primarily due to the poisoning of the core by fission products.

[OldChemE]

It is also possible to develop breeder reactors that convert Thorium.  This is less elegant, perhaps than plutonium plants, but it has been done commercially.  The US Navy nuclear program operated a demonstration plant in the Shippingport power plant something like 50 years ago.

[Ken Fabian]

At the end of all the energy production the mass of the fission waste products will be less than the mass of the nuclear fuel. That missing mass will equal all the energy produced, waste heat included, ie m= E/C2, aka E=mC2. There is no energy from nothing and fission is not over unity.

[DARK0717]

Soooooo, in essence, is it possible to make a NukePlant that makes its own fuel and using it, even doing removing the core or smth? disregard the energy it takes to build such a facility

[swansont]

1 hour ago, DARK0717 said:

Soooooo, in essence, is it possible to make a NukePlant that makes its own fuel and using it, even doing removing the core or smth? disregard the energy it takes to build such a facility

Thermal fission of U-235 produced an average of 2.43 neutrons. For the reactor to be critical, one of those neutrons must induce another fission. If you can get any of the other 1.43 neutrons to be absorbed in a nucleus that runs into fuel (e.g.U-238, forming U-239, which then undergoes two steps of beta decay to become Pu-239) then you have produced fuel. If you could arrange it so that more than one neutron per fission undergoes that reaction (not an easy task), you will have a net increase in the amount of fissile material.

[DARK0717]

18 hours ago, swansont said:

Thermal fission of U-235 produced an average of 2.43 neutrons. For the reactor to be critical, one of those neutrons must induce another fission. If you can get any of the other 1.43 neutrons to be absorbed in a nucleus that runs into fuel (e.g.U-238, forming U-239, which then undergoes two steps of beta decay to become Pu-239) then you have produced fuel. If you could arrange it so that more than one neutron per fission undergoes that reaction (not an easy task), you will have a net increase in the amount of fissile material.

i see