COMPLETE DOCUMENT (1862 kb) - OECD Nuclear Energy Agency

2.2 Target and fuel fabrication technology
2.2.1 Fuels for homogeneous recycling
2.2.1.1 Fabrication of fuel including neptunium
237 Np and particularly its daughter 233 Pa have a considerable γemission requiring appropriate
shielding in the powder blending section of the fabrication plant. In the remainder of the fuel plant, the
effect is very small and can be neglected.
In principle, neptunium could be mixed with the standard UO 2 fuel of current PWR cores.
However, the reference 235 U enrichment should be significantly increased, which is seen as a major
penalty [54].
It is more advisable to mix NpO 2 with the usual MOX fuel (U, Pu)O 2 . This has been done
already for irradiation in fast reactors: first of all for the SUPERFACT experiment in Phénix, the fuel
of which was manufactured by ITU Karlsruhe, and more recently in view of the NACRE experiment in
Superphénix, the fuel of which was fabricated, with 2% Np, at the CFCA plant of Cogéma Cadarache.
In a MOX fuel factory, with respect to the pure PuO 2 reference case, the presence of NpO 2
does not affect the α and neutron emission but increases the γsource, due to 233 Pa (the daughter of
237 Np). The powder blending glove box should be protected by some 2 mm-thick Pb layers, to keep the
external dose rates unchanged [55].
In case of a multiple recycling of 237 Np, 238 Pu is progressively built-up, and this additional
source of neutrons (mostly from (α,n) reaction) and of heat affects further re-processing and
refabrication steps. Np should therefore be irradiated preferably in fast reactors with a lower capture to
fission ratio and consequently reduce 238 Pu yield from irradiation. On the other hand, a multiple recycle
of 237 Np in fast reactors also increases the tiny 236 Pu fraction, and the radioactive chain
236 Pu - 232 U - 208 Tl brings a further emission of high-energy γ-rays, so that the 2 mm-thick Pb layer
quoted above would become about 5 mm.
As a conclusion, Np recycling affects fuel refabrication in a UO 2 factory substantially but a
MOX factory to a limited extent, so that the present MOX plants can afford it without major
modification.
2.2.1.2 Fabrication of MOX fuel containing americium for LWR
For the implications of recycling, both plutonium and americium as MOX fuel in light water
reactors have been considered, with reference to the current (PuO 2 -UO 2 ) fabrication of MOX fuel.
Recycling of plutonium and americium simultaneously in LWRs
It is assumed that not only plutonium, but also americium can be recovered from spent fuel
reprocessing, and recycled in the form of MOX fuel (Pu+Am) in the same PWR under the same
conditions. A recovery yield of 99.5% for Pu and 98% for Am has been assumed.
141