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

The Front End of the Thorium Fuel Cycle
Based in part on R&D pioneered by ORNL and other laboratories, private companies, especially
Du Pont at Savannah River and Battelle Pacific Northwest National Laboratory at Hanford,
Babcock and Wilcox, and others, under USAEC contracts, have installed pilot-to-industrial size
facilities to produce the different types of fuel used in the prototype reactors, BWR, PWR and
HTR. Fuel-based products could be obtained from National Lead, Mallinckrodt, Nuclear Fuels
Services, among others.
Complete fuel element fabrication on the 10 kg scale was available at Babcock and Wilcox [36],
and Allis-Chalmers had built a remotized fuel refabrication pilot facility at Rotondella, Italy, for
Elk-River BWR fuel [37].
The KILOROD Fuel Fabrication at Oak Ridge National Laboratory (ORNL) was operated in the
1960s on a 10 kg/day scale. The process scheme was based on the sol-gel process and vibratory
compaction of the powders into the pin cladding. 1280 kg of thoria were processed in an 8 months
campaign. The average radiation exposures in the KILOROD program were 0.19 mSv (milli
Sievert 2 ) per man per week for the sol-gel process and the rod fabrication. Considering the
accepted practical dose rates at the time (1968), which were of 20 - 50 mSv per year per operator,
it was concluded that direct fabrication is feasible with (Th,3%U-233)O2 fuels that contain less
than 20 ppm U-232. With shadow shielding, this limit can be increased to 200 ppm. With shadow
shielding and frequent cleaning and recycling, the limit is 600 ppm. Plants with larger capacities
will require shielding when operating permanently.
Similar results were obtained at a pilot fabrication plant of about 10 kg HM/batch operated from
1965 at Babcock and Wilcox on the same ORNL process. Its cost was 1 million dollars in 1965. It
consisted of a sol-gel preparation plant and a fuel fabrication plant. Both plants, like KILOROD,
were partly shielded only. In 1968, the total production at the plant was about 1150 kg. Up to
1968, 119 rods (232 kg of (Th,3%U-233)O2) were fabricated. The U-233 contained 42 ppm U-232.
The TURF ORNL Remote Fuel Fabrication Prototype Plant: As early as 1965, it was realised that
industrial-scale fabrication plants would have to be totally remotized. ORNL engineers designed
and built the TURF (Thorium-Uranium Recycle Facility) plant with remotely operated, manually
maintained equipment having production capacities from 60 to 3700 kg/day of heavy metal. The
TURF facility was intended to fabricate oxide (Th,U-233)O2 fuel for water-cooled reactors and
carbide fuel for HTGRs. The personnel radiation exposure is limited to 0.4 mSv/week. A shielding
of 10 cm steel was chosen as a practical limit for semi-remote fabrication, because of the difficulty
of working through a greater distance with gloved hands. A cost analysis based on these designs
showed that remote fabrication of oxide and carbide fuels would cost almost 1.5 to 2 times more,
respectively. The assumptions taken at the time do not now seem conservative, and heavier
shielding would be necessary (~ 1.2 m) and hence possibly a higher cost.
Although such a plant could be built and operated, the fuel fabrication step has been the main
roadblock to the development of the thorium fuel cycle to date. These technical complexities,
especially penalizing 30 years ago, and the added costs, combined with other factors, have led to a
provisory abandonment of this fuel cycle (except in India for strategic reasons).
The enormous technical progress accomplished since the 1960s, in mechanics, electrical motors,
materials, electronics and computers, and practical examples of remotized fuel fabrication
(MELOX in France) suggests that these fuel fabrication concepts be revisited so that their
advantages can be realised in the not-too-distant future.
2 The Effect of the Absorbed Dose: Equivalent or Effective Dose = Sievert (Sv)
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