exotic nuclei structure and reaction noyaux exotiques ... - IPN - IN2P3

nides. A global comparison can be performed, in
the same conditions of reactor operation (power,
oxide fuels, burn-up, breeding rate) and cycle process
(chemical losses, cooling down and refabrication
times). Figure 2 summarizes the radiotoxicity
comparison.
Fig. 2. Comparison of total radiotoxicity for reference U/Pu
SFR (pink), for Th/U SFR w/o reprocessing (green), for homogeneous
MA reprocessing U/Pu SFR (red), and for homogeneous
MA reprocessing Th/U SFR (dark green).
This shows that the transmutation of minor actinides
leads to a reduction by a factor 10 to 100 of
the radiotoxicity of waste, from 300 years after discharge
up to 1 million of years. When minor actinides
are not reprocessed, the thorium cycle offers
a reduction by a factor 10 of the waste radiotoxicity
only during a few century. After 3000 years both U
and Th cycles are similar.
With homogeneous reprocessing, there is a clear
advantage of Th/U over U/Pu SFR between 300
years and 100,000 years. Then, due to the 233 U
contribution, the radiotoxicity of U/Pu SFR is lower.
The thorium cycle, coupled with minor actinides
reprocessing, leads to a reduction by factor 100 or
1000 of the waste radiotoxicity during 10000 years,
as compared to the reference U cycle without MA
transmutation.
SFR with a thermal
power of 3600 MWth.
Fissile zone is split into
two enrichment zones.
The evolution is performed
over 250 years
with refuelling. The equilibrium
is reached after
200 years. The core is
divided in 5 radial zones
and 1 axial zone. The
reference configuration
consists on a fuel made of depleted uranium and
plutonium at equilibrium. In this case, minor actinides
are not reprocessed.
The management of the core assemblies depends
on 3 parameters: the “cycle length”, the “cooling
time” of used assemblies before the reprocessing
and the “refabrication time” to make fresh assemblies.
At each irradiation time, the inner fuel assembly
zone is removed from the core. Assemblies
are moved sequentially from the exterior to the
interior of the core (Fig. 1). The fresh assemblies
are put in the outer zone. The fresh assemblies are
made using the recycled U/Pu from previous depleted
ones (after “the cooling time”) and a “fresh
fuel” (which is depleted Uranium oxide since the
reactor is breeder). This refabrication process
takes a “refabrication time”. In this study, the irradiation
time is 1 year for core assemblies (thus, on
average 1/5 of the core is changed each year), the
cooling time is 5 years and the refabrication time is
2 years for core assemblies.
Fig. 1. Fuel management in the core, cooling-down, reprocessing
and fabrication process.
When the transmutation strategy is considered, the
reprocessed minor actinides are Neptunium, Americium,
Curium, Berkelium and Californium. When
recycling, the efficiency of Plutonium, Uranium and
MA separation is 99.9%, leading to 0.1% of losses
that are sent to waste storage with all fission products.
This methodology is used to compare the waste
radiotoxicity induced by Uranium and Throium cycle,
with or without transmutation of minor acti-
It has to be noticed that the same calculations can
be made for the residual heat, which is the key
parameter for the dimensioning of the waste storage.
The difference between cycles and reprocessing
strategies are very similar to the radiotoxicities
conclusions.
Waste and inventories
In order to compare very precisely the different
reprocessing strategies, one must take into account
the waste produced, but also the total mass
of materials involved in the cycle. This inventory
becomes a waste only when the nuclear fleet shut
down, and this makes the global comparison quite
difficult. Thus, we propose to study the global gain
in terms of waste generation, as a function of the
time at which the nuclear fleet will shut down.
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