Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thorium vs Uranium MJ/kg

  1. Feb 10, 2013 #1
    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?
  2. jcsd
  3. Feb 10, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    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:

    Code (Text):

    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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Thorium Uranium Date
Why isn't Thorium used for reactor fuel rods? May 12, 2016
Private Thorium reactors? Jan 18, 2016
Uranium,Thorium,what next? Jun 10, 2011
Move over uranium here comes Thorium Aug 9, 2010