TRS435_web

neptunium can be stored as an oxide; however, safeguards control is necessary,
since it is in principle a fissile material.
Conditioning of separated neptunium for long term storage can be
achieved by transforming it into, for example, a Synroc type of compound (a
mixture of zirconolite, hollandite and perowskite), which is much more
insoluble than glass forms. Long term surface storage or retrievable disposal in
underground facilities are options to be studied.
Target fabrication for future transmutation is another alternative. For
example, mixing of NpO 2 with aluminium powder and transformation into
uranium/plutonium/neptunium subassemblies makes it suitable for irradiation
in thermal and fast neutron flux reactors or in ADS facilities.
Irradiation by thermal neutrons [9] produces large inventories of 238 Pu,
while irradiation in FRs or in fast spectrum ADSs reduces this formation but
does not eliminate it. Multiple recycling in dedicated FR or ADS facilities has
to be considered to achieve complete incineration. Hot refabrication of 237 Np–
238 Pu targets is a technology that needs development in order to ensure a high
decontamination factor (DF) from the ingrown actinides ( 239 Pu, 240 Pu).
The following industrial facilities and processes will be necessary to
produce and process the irradiation targets resulting from a reactor system of
100 GW(e) [1]:
(a)
(b)
(c)
(d)
(e)
(f)
(g)
A neptunium chemical purification plant with a capacity of ~1.6 t/a;
A neptunium target fabrication facility of an equivalent capacity;
Interim safeguarded (or underground retrievable) storage of fresh
neptunium targets;
A dedicated chemical processing rig for irradiated targets;
A hot refabrication plant for recycling of 237 Np– 238 Pu targets;
An HLW connection with an LWR UO 2 vitrification plant;
A medium level alpha waste treatment plant for effluent processing.
Long term storage or disposal of ~1.6 t of 238 Pu and fission products (880
and 190 kW(th), respectively) will be necessary, depending on the fission rate
and the cooling period.
A dedicated FR or ADS transmutation facility should be erected in the
immediate vicinity. This complex ought to be associated with one of the big
industrial reprocessing plants, in order to avoid unnecessary transfers and
transport on public roads.
The real benefit of this development for waste management is the
reduction of the neptunium inventory and of the very long term radiological
risk associated with the migration of 237 Np into the biosphere. However, it has
to be remembered that quantitative transmutation of industrial quantities of
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