Reply #19: The eventual goal would be a 99% reduction in nuclear waste.

[Statistical]

In a traditional reactor spent fuel is only about 3% fissioned when it is "spent".

The reason it is spent is some of these long lived isotopes are massive neutron blockers. Their large neutron cross section blocks thermal nuetrons. As the amount of long lived isotopes build up this interferes with the fission of uranium (and generation of heat and thus electricity) in the reactor.

So when fuel is "spent" it simply means the % of neutron blockers is so high it becomes difficult to sustain nuclear fission at levels that can produce power.

Future reactors will likely not used fixed fuel. Something like a molten salt reactor will have nuclear fuel mixed with salt which is liquified by the heat of nuclear fission.

The liquified salt could pass out of reaction chamber into a refining chamber. Think of it like oil filter on your car but one that seperates out long lived fission products.

Those long lived isotopes then could undergo fast neutron bombardment to transmute them into isotopes which decay much faster.

The combination of using greater percentage of original fuel and transmuting long lived isotopes could massive reduce the length of time before waste decays to harmless elements as well as the amount of waste.

Current U-235 fission products via thermal neutrons

Half life length % Yield
<1 year
Less than 1 year ~65%
1 to 100 years ~15%
200K to 300K yrs ~6%
1.5mil+ years ~13%

Transmuting Tc99 would eliminate 6% of the long lived isotopes.
Leaving a relatively tiny amount of waste which is very long lived
Cs-135, Pd-107, I-129 these isotopes despite having very long halflives are actually relatively harmless. They can be sealed in glass and are "inmobile" = tends not to move in air,water, earth.

So isotope separation, transmutation, and future reactor designes (like molten salt Gen 4 reactor) could substantially simplify the waste disposal question.