THORIUM AS AN ENERGY SOURCE - Opportunities for Norway ...

5.3.1 Light Water Reactor (LWR)
Nuclear Reactors for Thorium
The Light Water Reactors (LWRs) utilize fuel based on uranium dioxide (UO2), plutonium dioxide
(PuO2) and/or thorium dioxide (ThO2) arranged in fuel rods. In the development of thoriumuranium
oxide fuels in LWRs, two types of arrangements have been explored:
1. Homogeneous mixed oxides of thorium and highly enriched uranium in uniform lattices (the
BORAX-IV, Indian Point I PWR, and Elk River BWR reactors).
2. Heterogeneous arrangements where the blanket contains less uranium and is responsible for
most of the in-core fissile generation (Shippingport PWR).
In the Shippingport Light Water Breeder Reactor (LWBR) program, the feasibility of net breeding
of fissile isotopes in the core was investigated. The results confirmed that the ratio of the fissile
content of the fuel at the end of operation to that at the beginning of operation was about 1.0139.
The effort also identified some shortcomings of the LWBR technology relative to the LWR
experience at that time, including a lower power density of the core (30 %), a need for high U-235
enrichments in the early stage of deployment, a more complicated design of a movable seed region
as well as a more complicated recycling of uranium and thorium including extra shielding needed
in the fabrication process compared to uranium and Pu recycling [45].
The main conclusions of the EPRI sponsored study on thorium cycle applications in the
Combustion Engineering System 80 PWRs can be summarized as follows:
• Use of thorium with recycling 3 can in the long run increase energy output per mined tonne of
uranium by about 85 % beyond the once-through 4 uranium cycle, and by 22 % beyond
plutonium recycle.
• Even with the above, the thorium cycle may not be economically attractive relative to cycles
with poor fuel conservation features because the early years' fuel demand is high, and savings
occur in later years.
• Comparison of the characteristics of uranium and thorium based cores indicates that thorium
fuelling is feasible, and modifications to a PWR designed to accommodate plutonium recycle do
not appear to be required.
• The introduction of a totally new system of advanced converters into the US would probably
require more effort and funding than can be justified.
In past attempts to improve LWR fuel cycle efficiency, it has been recognized [46], [47] that the
advanced converter concepts attain superior fuel utilization by elimination of major parasitic
reactivity control through one of three methods: adoption of on-line re-fuelling (CANDU, Molten
Salt and Pebble Bed), special geometry to capture leakage neutrons (seed-blanket), or moderation
control of neutron capture in fertile material (spectrum shift). At this stage only the CANDU
reactor has been successfully deployed worldwide. All these cores can have improved fuel
efficiencies when recycling the fissile material as well as with introduction of thorium in addition
to uranium in the fuel.
5.3.2 High Temperature Gas Cooled Reactor (HTGR)
KFA Jülich, Germany, has four decades of experience with thorium and its use as a nuclear fuel.
Thorium fuel with coated fuel particles (about 100 000) has been successfully tested in two High
3
Closed Fuel Cycle (the fuel is recycled): Reprocessing of spent fuel to extract the remining fissile material for further use.
4
Open Fuel Cycle (once-through cycle): The fuel is wasted after use (some fissile material left).
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