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1.1.1.1 Minor actinides
Americium and curium
Among the minor actinides, americium and curium, which are stable in valency III, are not
extracted by TBP and remain in the aqueous phase. They accordingly follow the path of the fission
products and are currently managed like the latter by conditioning in a glass matrix.
Neptunium
Another minor actinide, neptunium, whose stable oxidation state is V, is hence very slightly
extractable in this species by TBP. However, in the chemical conditions of the first cycle extraction
operation of the PUREX process (presence of nitrous acid), part of the Np(V) is oxidised to VI, and
accordingly extracted in the organic phase.
The operating results of the UP3 plant reveal that the majority of the Np is extracted by TBP,
follows the uranium stream, and is separated from the latter in the second uranium purification cycle.
The effluent containing neptunium is currently added to the high-level waste stream. Hence all the
neptunium is sent to vitrification apart from the proportion following the Pu product. The behaviour of
neptunium is independent of the type of fuel reprocessed.
1.1.1.2 Long-lived fission products
Among the fission products with long-lived isotopes, three elements (technetium, zirconium
and iodine) display specific behaviour in the PUREX process, which could be exploited for their
separation (see Figure II.1).
Technetium
During fuel dissolution, part of the technetium, probably in metallic or oxide form, does not
go into solution. This fraction, estimated at 10 to 20% of the total Tc for a UO 2 fuel, accompanies the
“insoluble residues” essentially consisting of noble metals (Ru, Rh, Pd). These insoluble residues are
currently incorporated in the vitrified or cemented wastes.
In nitric medium and in the absence of a reducing agent, the dissolved technetium is in its
highest valency (VII) which is the most stable. It occurs in anionic form in the state of pertechnetate ion,
TcO 4
−
. This species can be extracted by TBP at the same time as a metallic cation by substitution of a
pertechnetate group for a nitrate group in the neutral complex extracted.
The occurrence of this co-extraction was observed with the main metallic cations extracted by
TBP, and particularly with the cation ZrO 2+ (see below), which is present in large amounts in the feed
solution to the extraction cycle. This extraction of Tc proved to be a serious hindrance because of its
interference with the chemical mechanisms of the partitioning operation (U/Pu separation). The PUREX
process accordingly had to be adapted to limit the extraction of Tc.
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