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

The Back End of the Thorium Fuel Cycle
substance is dissolved in nitric acid and separated by solvent extraction. Thorium is considerably
less amenable than uranium to such processing.
Reprocessing difficulties are especially severe with HTR-type fuels of whatever composition, since
the particle coatings and graphite matrix are chemically resistant and troublesome to break down
mechanically.
6.3.1 The “Head-End” Operations
The aim of these operations is to obtain, after preliminary operations leading to dissolution, a
solution of U-Th nitrates together with a small quantity of minor actinides and fission products.
Extraction of U-233 from irradiated thorium rods was conducted extensively in the US from the
1950s until the 1970s. Almost 700 tonnes thorium were irradiated, delivering more than 1.5
tonnes of U-233. The separation operations were piloted at ORNL in the THOREX plant, and in
the Knolls Atomic Power Laboratory. The process was later adapted to the Great “canyon” plants
at Hanford and Savannah River (SRP), and the commercial direct maintenance plant of Nuclear
Fuel Services at West Valley near Buffalo, now being dismantled, which reprocessed the first core
of Indian Point 1 (95% ThO2, 5% U-235O2), but without recovering thorium (which was left in the
waste).
The processes are explained in an interesting paper [146], which is one of the early documents
giving details of the processes and of the adaptation of these large PUREX-type plants to the
THOREX processes (Figure 6.3).
Figure 6.3: Outline of the THOREX Process (Thorium Extraction).
Head-end operations for fertile fuels to extract U-233: Due to its great stability, dissolution of
thorium or ThO2 is not as straightforward as that of U, and especially of UO2. Strong nitric acid
with HF is required, and the process takes a rather long time, especially for high temperature
sintered compact ThO2. Dissolution can take up to 35 hours. To prevent corrosion of the
equipment by HF, aluminium nitrate was added as a buffer.
Similar processes have been used in India on a small scale for thorium and ThO2 rods and in
other countries (UK at Dounray, Canada at Whiteshell, Germany at Jülich and Karlsruhe). In
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