Fuel cycles and envisioned roles of fast
neutron reactors and hybrids
M.Salvatores (CEA, Cadarache- France)
WORKSHOP ON
FUSION FOR NEUTRONS AND
SUB-CRITICAL NUCLEAR FISSION
FUNFI
Villa Monastero, Varenna, Italy
September 12 - 15, 2011
Nuclear Fuel Cycles
Many of the central issues associated with nuclear power are tied primarily to the
choice of fuel cycle. Resource limitations, non-proliferation, and waste management are
primarily fuel cycle issues.
The fuel cycle provides the mass flow infrastructure that connects the energy resources
of uranium and thorium ore through the nuclear power plants to the eventual waste
management of the nuclear energy enterprise.
Natural resources include fuels (uranium and thorium), materials of construction, and
renewable resources (such as water for cooling purposes). Wastes may include mill
tailings, depleted uranium, spent nuclear fuel (SNF) and high level (radioactive) waste
(HLW), other radioactive wastes, releases to the environment (air and water), and
nonnuclear wastes.
Multiple technical facilities are deployed in the fuel cycle. In a simplified fuel cycle
schematic, there are 7 major fuel cycle facilities.
3
2
4
5
6
1
1
1
7
The preferred choice or choices of fuel cycles and reactors depends
upon the
requirements for sustainability, safety, and economics
.
Four generic fuel cycles span the space of feasible conversion of ore resources to energy.
• Once through. The fuel is fabricated from uranium (and/or thorium), irradiated, and
stored to allow for reduction of heat, then directly disposed of as a waste. Light Water
Reactors (LWRs) in the United States currently use this fuel cycle.
• Partial recycle. Some fraction of the SNF is processed, and some fraction of the
actinide material is recovered from recycle, and new fuel is fabricated.
The fuel is returned to the reactor one-two times
• Full fissile recycle. All SNF is processed for recovery and recycle of plutonium (and/or
233U). The SNF is repeatedly processed and recycled. Minor actinides and fission products
are sent to the waste stream from the processing operation.
An example of this is the traditional Liquid Metal Fast Breeder Reactor (LMFBR) fuel cycle.
• Full-actinide recycle. All SNF is processed, and all actinides are multiply recycled.
An example of such a fuel cycle is a system of MOX-LWRs and dedicated burner reactors.
The MOX-LWRs produce power and the dedicated burner reactors (e.g. ADS, Hybrid
fission-fusion, critical fast reactors) are used to destroy higher actinides that would
otherwise be sent to the repository.
Another example is the full TRU multiple recycle in FRs, both to extend use of resources
and to reduce and stabilize wastes.
• Other fuel cycle options are envisaged according to e.g. waste management strategies
UOX-PWR
Repository
Irradiated fuel
Irradiated
fuel
FP and TRU losses
at
reprocessing
Reprocessing
Pu
Dedicated
Transmuter
Reprocessing
MA (+Pu)
Multi-recycling
Fuel Fabrication
Reprocessing
Pu
Multi-recycling
MOX-LWR
(or FR)
MA
MA(+Pu)
Fuel
Fabrication
Irradiated
fuel
Full-actinide recycle
(So-called “Double
Strata Fuel Cycle”)
Repository
UOX-LWR
Irradiated fuel
Reprocessing
Pu+MA
Fast Reactor:
homogeneous or
heterogeneous
recycle
Reprocessing
Multi-recycling
Pu+MA
Fuel/Target
Fabrication
Full-actinide recycle
(FR only)
Irradiated
fuel
 Fuel cycle simulation allows the calculation of the nuclei
evolution under irradiation and decay outside the reactor
(the Bateman equations)
 Once the nuclei evolution has been performed, it is
possible to evaluate all the derived quantities: nuclei
mass inventories, decay heat, neutron sources,
radiotoxicity, doses etc
Nuclei evolution under irradiation
The Uranium nuclei transmutation chain under neutron irradiation and the associated
Bateman equations can be represented as follows:
242 Cm
163d
241 Am
243 Cm
2.85y
237 Pu
87.8y
22.5h
236 Np
22.5h
238 Pu
237 Np
2.12d
238 Np
6.75d
239 Pu
2.35d
239 Np
240 Pu
242 Am
236 U
237 U
246 Cm
26m
243 Am
244 Am
4.96h
241 Pu
242 Pu
243 Pu
7.5m
240 Np

23.5m
n,
n,2n
235 U
245 Cm
17.9y
16h
14.7y
236 Pu
244 Cm
238 U
239 U

EC
dnj
dt
 n j   aj   j     jk   jk  nk
Bateman equations
k
where nj is the nuclide j density, σaj is the absorption cross section of isotope j, σjk is
the cross section corresponding to the production of isotope j from isotope k, λj is the
decay constant for isotope j, λjk is the decay constant for the decay of isotope k to
isotope j and, finally, Φ is the neutron flux.
Application
Composition of Spent Nuclear Fuel (Standard PWR 33GW/t, 10 yr. cooling)
1 tonne of SNF contains:
955.4 kg U
8,5 kg Pu
Minor Actinides (MAs)
0,5 kg 237Np
0,6 kg Am
0,02 kg Cm
Most of the hazard stems from Pu, MA and some
LLFP when released into the environment, and
their disposal requires isolation in stable deep
geological formations.
Long-Lived fission
Products (LLFPs)
0,2 kg 129I
0,8 kg 99Tc
0,7 kg 93Zr
0,3 kg 135Cs
A measure of the hazard is provided by the
radiotoxicity arising from their radioactive
nature.
Short-Lived fission
products (SLFPs)
1 kg 137Cs
0,7 kg 90Sr
Stable Isotopes
10,1 kg Lanthanides
21,8 kg other stable
Most of the derived quantities are of the type:
where ni is the nuclei i density and hi are coefficients, specific for each
application
Example: the Radiotoxicity R of nuclei i is given by:
Ri(Sievert)= Fi(Sv/Bq)xAi(Bq)
where F is a Dose Factor (ingestion or inhalation) and A is activity in Bq
Total activity A: number of decays an object undergoes per second.
Decay constant λ: the inverse of the mean lifetime.
One has:
Finally:
Ri(Sievert)= Fi(Sv/Bq)xAi(Bq) =Fi xniλi
Derived quantities: the radiotoxicity
Evolution of the radiotoxic inventory, expressed in sievert per tonne of initial heavy
metal (uranium) (Sv/ihmt) of UOX spent fuel unloaded at 60 GW d/t, versus time (years).
1.00E+07
Total
Radiotoxicity (Sv/MT Natural Uranium)
1.00E+06
Minor Actinides & Decay Products
1.00E+05
"Uranium Ore"
1.00E+04
Plutonium & Decay Products
Fission Products
Radiotoxicity of Natural Uranium
and Decay Products
1.00E+03
Uranium & Decay Products
1.00E+02
1.00E+02
1.00E+03
1.00E+04
Years after Spent Fuel Discharge
1.00E+05
1.00E+06
Derived quantities: the decay heat, one of the most
demanding parameters of the fuel cycle
Decay Heat
Components
Fuel Cycle Modelling
Decay heat: relative role of FPs and Actinides for standard
LWR fuel
Actinides
FP
Long cooling times
Short cooling times
Decay heat: FPs and Actinides components for standard LWR fuel
100
Decay Heat, Watts/GWd of Energy Produced
FP
Total
TRU
PU238
PU239
Am-241
10
PU240
PU241
Pu-238
AM241
AM243
CM242
CM243
1
CM244
Actinides
SR
Y
CS
0.1
BA
EU
Fission Products
Total
0.01
10
100
1000
Time after Discharge, Years
10000
Derived quantities and the impact of different fuel cycle
scenarios
 The full TRU recycle, as indicated previously, allows a
significant reduction of the radiotoxicity and of the decay
heat of residual wastes to be sent to the repository.
 This reduction can have a favorable impact in the
assessment of future fuel cycles
 This result is true within both scenarios for full TRU
recycle indicated above.
Example: Impact of the actinides management strategy on the
radiotoxicity of ultimate waste
MA +
FP
Plutonium
recycling
Pu +
MA +
FP
Spent Fuel
Direct disposal
Uranium Ore (mine)
P&T of MA
FP
Time (years)
Recycle of all actinides from spent LWR fuel in fast reactors provides a
significant reduction in the time required for radiotoxicity to decrease to that of
the original natural uranium ore used for the LWR fuel:
From 250,000 years down to about 400 years, if 0.1% TRU loss to wastes during
reprocessing.
Pu +
MA +
FP
Spent fuel
direct disposal
One
PuMOX
recycling in PWR
Mono
10000
Multiple
Pu recycling
in PWR
Recyclage
Pu en
REP
Example:
Impact
of the
Pu
and Am recycling
in PWR
Cmaudisposed
Recyclage
Pu+Am en
REP –
Cm
CSDV
actinides
management
Pu
recycling Pu
in FNR
Recyclage
en
RNR
Pu
and MA recycling
Recyclage
Pu+Np+Am+Cm
RNR
strategy
onin FNR
theendecay
Once
cycle
cyclethrough
ouvertultimate
heat
of
waste
w/Twhé
1000
Pu,
Am recycling
in PWR
– Cm
stored
Recyclage
Pu+Am
en REP
Cm
entreposé
100
10
1
0.1
10
MA partitioning and
transmutation
FP
100
1000
10000
years
années
100000
1000000
Pu recycling
no MA partitioning
MA +
FP
An Example of Scenario Study
Hypotheses and assumptions
In the selected scenario study two groups of nations are
considered:
• the first one with a stagnant or phasing-out nuclear policy (Group A)
• the second with an ongoing nuclear power development (Group B)
The final goals of the scenario are:
- to reduce Group A TRU inventory down to zero till the end of the century;
- to stabilize Group B MA inventory and to save reprocessed Pu in order to
allow a later introduction of fast reactors for nuclear power generation.
In the fuel cycle transmuters first use MA coming from their closed cycle
(in order to completely transmute heavy nuclides), then those of Group A,
and finally those of Group B.
-Three types of transmuters have been compared:
- The SABR fusion-fission hybrid concept is a sodium
cooled sub-critical fast reactor driven by a D-T fusion
neutron source;
-ADS-EFIT is Pb cooled and the external neutron source is
provided by Pb-proton (800 MeV) spallation reaction on a
Pb windowless target;
-LCFR is a Na cooled critical fast reactor with a conversion
ratio ~0.5
-The scenario is of the “Double Strata” type, as described
previuosly
Scenario Flow Sheet
Group A: Belgium, Czech
Republic, Germany,
Spain, Sweden and
Switzerland
Group B: France
Regional (i.e. shared)
facilities (i.e.
transmuters, fuel
fabrication,
reprocessing facilities
and stocks) operation
start-up is assumed to
be in 2045.
Required Transmuters Energy Production
- Comparison is
presented per energy
produced
- The corresponding
number of units are 13
(X384 MWth) ADS-EFITs, 9
(X1000 MWth) LCFRs, and
2 (X3000 MWth) SABRs
- As expected, more
critical low conversion
ratio transmuters are
needed since they achieve
~70% of the max
theoretical burning rate
(i.e. when no U in the fuel)
MA Stocks Comparison
- MA stock of Group A goes
to zero before the end of
the century (in all cases)
- MA stock of Group B is
stabilized before the end of
present century (in all
cases)
Fuel Cycle
Impacts
Radiotoxicity and
heat load in a
repository are
reduced by two
orders of
magnitude with
respect to the
direct disposal
scenario
• Uranium and thorium mills. Uranium and thorium ores are mined and then milled to extract
uranium and thorium. This process generates the highest volume waste stream in the fuel cycle: mill
tailings. Also, purification and conversion facilities.
• Uranium enrichment. The uranium is isotopically separated into a stream enriched in the fissile
isotope 235U and a stream depleted in the fissile isotope 235U. The enriched stream is used for fuel in
most reactors. The depleted uranium may be stored for (1) further recovery of 235U in the future or (2)
use in fast neutron reactors. Alternatively, it may become a waste.
• Fuel fabrication. Reactor fuel is fabricated from natural uranium, enriched uranium, plutonium
reclaimed from processing discharged fuel, or uranium-233, depleted uranium, and thorium.
• Reactor. The reactor produces energy and SNF.
• Spent Nuclear Fuel Storage. The SNF is stored to allow its radioactivity and heat release rate
to decrease. After storage, the SNF may be (1) considered a waste for disposal or (2) processed to
recover fissile materials from the SNF for recycle back to the reactor as new fuel.
• Processing. If the SNF is recycled, the recovered fissile materials can be
used to produce new fuel.
• Waste disposal. SNF direct disposal or vitrification of residues from reprocessing