Can Thorium Outperform Uranium in Energy Production Per Kilogram?

[DLHill]

In a reactor using Th232 as a fertile material to breed fissile U233, what is the amount of energy released per kg Th232 compared to a reactor using about 20% enriched uranium?

 

[Astronuc]

In a reactor using Th232 as a fertile material to breed fissile U233, what is the amount of energy released per kg Th232 compared to a reactor using about 20% enriched uranium?

The rate of energy release depends on two things: 1) energy per fission, and 2) fission rate.

The fission rate is carefully controlled such that the fuel state (e.g., temperature) remains within certain specified design limits, and would be constrained to certain limits if the system is upset.

20% enrichment would be rather high for a commercial (LWR) reactor, for which fuel is limited to 5%. Some small research reactors use highly enriched fuels since the core are small, and the fuel is not so optimized for the core size. Fast reactors, do use higher enrichments of 20% or more, and usually Pu-239 in the form of (U,Pu) ceramics (MO₂, MN or MC, where M = U, Pu).

The energy per fission is:

Isotope                         U-233   U-235   Pu-239 
Energy per fission   (MeV)      197.9   202.5    207.1
Energy in anti-neutrinos (MeV)    6.9     8.8      7.1
Recoverable energy    (MeV)     191.0   193.7    200.0

Another ~ 3 - 12 MeV can be recovered from capture gammas from the neutron capture (n, γ) reaction. The neutrons may be captured by fuel, but not cause fission, or they are captured by the coolant and structural (non-fuel) material, e.g., cladding.

Ref: http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html

In a thermal Th-breeder system, there would be some fissile species, e.g., U-233 or U-235, usually U-235 in the beginning and later U-233 as it becomes available.

In LWRs, about 8-10% of fissions are fast-neutron induced fissions in U-238, with the remaining fissions mostly due to thermal neutrons fissioning U-235 and Pu-239, as the Pu is produced in the reactor.

 

[raining Pete]

It is difficult to give an exact amount of energy released per kg of Th232 compared to enriched uranium, as there are many variables that can affect the efficiency and output of a reactor. However, in general, using Th232 as a fertile material can potentially yield more energy compared to enriched uranium.

This is because Th232 has a higher neutron capture cross section (meaning it is more likely to absorb neutrons and become fissile) and a longer half-life compared to enriched uranium. This allows for a longer fuel cycle and more efficient use of the material.

Furthermore, Th232 can be bred into U233, which is a highly fissile material that can release a large amount of energy. In contrast, enriched uranium only contains a small percentage of fissile U235, and most of the remaining material is non-fissile U238.

Overall, using Th232 as a fertile material has the potential to produce more energy per kg compared to enriched uranium. However, it is important to note that there are many other factors that can affect the overall efficiency and output of a reactor, so it is not a straightforward comparison.