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• Potential role of FF hybrids
• Massimo Salvatores
• CEA-Cadarache- France
• Fusion-Fission Hybrids have a potential role (in
  principle and independently from any
  technological readiness consideration) for
  nuclear fuel breeding and as an option within
  radioactive waste management strategies in order
  to
• reduce the potential source of radiotoxicity, as
  a potential mitigation to the consequences of
  accidental scenarios (e.g. human intrusion) in
  the repository evolution with time,
• reduce the heat load in the repository and
• reduce the volume of the repository itself.
• This application can (should) be coupled (in
  principle) to electricity production.

Different objectives and policies can be gathered
into three broad categories and associated
scenarios
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Different objectives and policies can be gathered
into three broad categories and associated
scenarios
Scenario a) Sustainable development of nuclear
energy for electricity production and waste
minimization Scenario b) Reduction
(elimination) of MA inventory (pure waste
management objective) Scenario c) Reduction
(elimination) of TRU inventory as unloaded from
LWRs
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Scenario a) Sustainable development of nuclear
energy for electricity production and waste
minimization a1) Homogenous or heterogeneous
TRU recycling in a critical fast reactor. The
fuels are standard mixed oxide or dense fuels
(metal, nitride, carbide), with MA content of a
few percent (e.g. definitely lt 5-10). a2) Use
of a FFH, with similar fuel types and minor
actinide content in the fission blanket. In the
past, an ADS (or Energy Amplifier) has been
proposed. However the subcriticality is not an
issue (the effective delayed neutron fraction and
the Doppler effect can be kept as high as needed
since the MA content is lt10) and the economy was
found not to be attractive.
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a3) An alternative the LIFE concept
LIFE
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300 years after discharge 99.9 BU is
equivalent to multireprocessing of FR fuel with
99.9 recovery factor!
Provided by H. F. Shaw, LLNL
99.9 Recovery factor
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Another alternative the WISE concept
Use of  mobile  fuel, e.g. molten metals in a
critical reactor
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Scenario b) Reduction (elimination) of MA
inventory(pure waste management objective) The
objective is to reduce drastically the MA
inventories, while Pu is still considered a
resource. With respect to scenario a), the
implementation of advanced (e.g. fast) reactors
is somewhat delayed in time and a transition
scenario has to be envisaged, in order to avoid a
build up of MA. Need separation of Pu from MA,
to be kept together, or separation of Cm from Am,
and Cm storage. To implement this scenario
(double strata strategy) MA fuels could be
transmuted in external neutron source-driven
(like ADS or FFH). For ADS, the MA-loaded fuels
should contain some Pu (e.g. Pu/MA1) to keep
constant the reactivity of the sub-critical core
(i.e. the accelerator current constant during
the cycle, with both safety and economic
advantages). If Inert Matrix Fuel (IMF) is
envisaged, the conversion ratio of the
sub-critical core is CR0. However, a U-matrix
can be considered as alternative to U-free IMF
fuels. Critical burner FR with very low CR can
then be envisaged.
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Scenario c) Reduction (elimination) of TRU
inventory as unloaded from LWRs c1) reduction of
TRU stockpiles as a legacy of previous operation
of LWRs. The ratio MA/Pu is 0.1. As for
reprocessing, grouped TRU recovery without
separation of Pu from MA. To maximise
consumption, a U-free fuel (inert matrix) in a
fast neutron spectrum (i.e. an external neutron
source-driven system, ADS or FFH) with conversion
ratio CR0, can be envisaged. However, a
conversion ratio CR 0.5 or less, allows 75
(or more) of the maximum theoretical TRU
consumption, can also be envisaged in a
critical burner FR.
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c2) Reduction (elimination) of TRU inventory
within a continuous use of LWR-only nuclear
power The objective is to reduce the burden on
a deep geological storage, as an alternative to
direct storage of the spent fuel. Here again,
use of dedicated transmuters (e.g. ADS, FFH or
critical, low CR FR) As an option, it can be
envisaged to transmute at first the largest TRU
amount possible in a deep-burn reactor and to
send the leftovers to the dedicated transmuters
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How to compare a) performances with respect to
a) objective(s) and b) impact on the fuel cycle?

• Define
• objective(s)
• corresponding scenario caracteristics
• caracteristics of the different systems involved
  (critical FR, external source driven systems etc)
• isotopic compositions and fuel forms
• caracteristics of the fuel cycle installations
  (reprocessing, fuel fabrication etc)
• parameters of interest for the overall fuel
  cycle (e.g. mass flows, radiotoxicity, decay
  heat, neutron sources etc.)
• Then, run a scenario code in a dynamic mode (i.e.
  to account for transition phase towards
  equilibrium)

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An example a regional (European) scenario with
ADS The scenario considered two groups of
countries Group A is in a stagnant or phase-out
scenario for nuclear energy and has to manage his
spent fuel, and especially the Plutonium and the
minor actinides (MA). Group B is in a
continuation scenario for the nuclear energy and
has to optimize the use of his resources in
Plutonium for the future deployment of fast
reactors. The deployment of Fast reactors is
delayed and there is need to manage MA inventory
increase.

• The Scenario PT within a double strata approach
• deployment of a number of ADS shared by the two
  groups of countries.
• The ADS will use the Plutonium of the Group A
  and will transmute the minor actinides of the two
  groups.
• The Plutonium of the Group B is continuously
  recycled in PWRs.
•  
• The main objective of this scenario is to
  decrease the stock of spent fuel of countries of
  Group A down to 0 at the end of the century, and
  to stabilize both Pu and MA inventories of Group
  B.

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Scenario lay-out (Double strata)
Countries Group A
Spent Fuel A
Regional Facilities
Pu
MA
ADS Fuel Fabrication
Reprocessing A
ADS
Pu
MA
MA
Spent Fuel ADS
Reprocessing B
ADS Fuel Reprocessing
Pu
Countries Group B
MOX Fabrication
PWR MOX
Spent Fuel B
UOX Fabrication
PWR UOX
Enriched U
Actual data (e.g. spent fuel inventories) have
been provided from Belgium, Czech Republic,
France, Germany, Spain, Sweden and Switzerland
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Examples of results
The required number of ADS  (400 MWth) was
determined to be 27 units
A total reprocessing capacity of 3300 tonnes is
needed 850 t/y for ADS reprocessing plant, 850
t/y for Group A spent fuel legacy, and 1600 t/y
for Group B.
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At present, for the same scenario ADS and
critical, low conversion ratio FR are
compared We are investigating how to
enlarge this type of studies to FFH. First
discussion to include SABR (GA-Tech). Data from
an external source driven system are easily
implemented in the scenario code (COSI), widely
used in Europe and a reference for most
international studies.
?m Kg/TWh ADS (k0.97) Low CR (0.58) Critical FR
Pu -3.8 -9.5
Np -1.4 -4.8
Am -47.8 -24.4
Cm 10.5 4.7
Total -42.0 -33.0
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A crucial issue the impact on the fuel cycle
parameters
Impact on some fuel cycle parameters of different
transmutation strategies.
Mostly a Cf-252 effect
Cm-244, Cm-246 effect
Cm-244, Am-241, Pu-238 effect
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Summary

• Within different scenarios and according to
  different objectives, there is a potential role
  for FFH to be investigated.
• However, to judge of the realism and
  cost/benefits of each option, a detailed in-depth
  comparative analysis (that should include the
  full fuel cycle) is needed.
• The experience of the past for similar cases has
  shown that qualitative statements do not help the
  credibility of a particular concept.
• Comparative analysis and collaborative
  initiatives can be set-up now, independently from
  the equally needed assessment of technological
  readiness and implementation horizon of the
  different options.

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• Summary of typical results
• The spent fuel stock of Group A can be
  decreased, as required, down to 0 by 2100 all
  the fuel was reprocessed by that date.
• In order to stabilize the MAs production from
  Group B, the required number of ADS  (400 MWth)
  was determined to be 27 units
• The plutonium inventory of Group B is stabilized
  starting from 2100 at ca. 100 tonnes
• As for the Regional facilities
• A total reprocessing capacity of 3300 tonnes is
  needed 850 t/y for ADS reprocessing plant, 850
  t/y for Group A spent fuel legacy, and 1600 t/y
  for Group B.
• The needed fabrication capacity is 690 t/y
  for UOX, 390 for MOX, and 40 for ADS.

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ADS electric power production vs. time
Spent fuel cumulative inventory (in tonnes) in
Group A spent fuel interim storage
Minor Actinides total mass (in tonnes) in all
facilities
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