Y. KADI

1
Proliferation Safe Nuclear Power Does that exist
?

• Y. KADI
• CERN, AB Depart.
• 19 June 2008, JAI, Oxford

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A new primary energy source

• By 2050, the worlds consumption ( 2/y) should
  reach 34 TW, of which 20 TW should come from new
  energy sources? A major innovation is needed in
  order to replace the expected decay of the
  traditional energy sources!
• This implies a strong RD effort, which is the
  only hope to solve the energy problem on the long
  term. This RD should not exclude any direction a
  priori!
• Renewables
• Nuclear (fission and fusion)
• Use of hydrogen
• Can nuclear energy play a major role?
• Nuclear energy has the potential to satisfy the
  demand for a long time (at least 15 centuries for
  fission, essentially infinite for fusion), and is
  obviously appealing from the point of view of
  atmospheric emissions.

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World nuclear electricity production by scenarios
(INPRO Phase-IA Report)
Schematic illustration of the four SRES storyline
families (SourceIPCC)
Potential global market for nuclear electricity,
hydrogen, heat and desalination for the A1T
Scenario assuming aggressive nuclear cost
improvements
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Which type of nuclear energy?

• Nuclear fusion energy not yet proven to be
  practical. Conceptual level not reached (magnetic
  or inertial confinement?). ITER a step, hopefully
  in the right direction.
• Nuclear fission energy well understood, and the
  technology exists, with a long ( 50 years)
  experience, however, present scheme has its own
  problems
• Military proliferation (production and extraction
  of plutonium)
• Possibility of accidents (Chernobyl 1986 Three
  Mile island 1979)
• Waste management.
• However, it is not given by Nature, that the way
  we use nuclear fission energy today is the only
  and best way to do it. One should rather ask the
  question
• Could nuclear fission be exploited in a way that
  is acceptable to Society?

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Uranium demand only slightly improved by MOX

• typical new LWR (EPR)
• 10 years to build
• 60 years operation

Chinas planned reactors 2.5 Million tons of U
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Yellow cake or yellow coal ?
Mining effort needed to produce 1 GWe x 30 years
6.1 TWh
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The problem of nuclear waste at very long lifetime
Warning long-lived radio-toxicity of MOX waste
10 x larger
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How many Sellafield for MOX ?
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Radioactive Waste from LWRs

• ? at end of present nuclear deployment 1.8
  Million ton
• How radio-active? 108 Sv/ton ?105 times the
  initial Uranium used. It decays back to radio
  toxicity of initial Uranium only after 106
  years (geologic times)
• ? at end of present nuclear deployment 1.8 106
  x 108 1.8 1014 Sv recommended ICRP max. dose
  to radiation workers 2.0 mSv/year
• Main concerns ?Leaks in the environment
  (biosphere)
• ?Proliferation (Pu239) worlds waste
  stockpile about 5 10 times the military Pu
  stockpile
• ? at end of present nuclear deployment 600000
  critical Pu masses

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Evolution of radiotoxicity of nuclear waste

• TRU constitute by far the main waste problem
  long lifetime reactivity. The system should
  be optimized to destroy TRU. Same as optimizing
  for a system that minimises TRU production.
  Interesting for energy production!

Typically 250kg of TRU and 830 kg of FF per GWe
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CAPRA Core (CEA)

• Plutonium incineration in fast neutron reactors

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Consequence on Core Safety Parameters

• Successive recycles in reactors with a thermal
  neutron spectrum continuously lower the isotopic
  grade of the Pu, leading to the necessity to
  increase the total Pu/(UPu) ratio. Consequently,
  the void coefficient in a PWR may no longer be
  negative in all circumstances.
• The recycling of Pu MA in conventional Fast
  Reactors (FRs) brings about several adverse
  effects
• on cycle operations (heat and dose rate at
  fabrication, reprocessing, transportation)
• on global core performance and safety (Sodium
  void, Doppler effect, etc.)
• This limits the Pu MA content and consequently
  the transmutation capacity of the core, resulting
  in a higher proportion of FRs in the park.
• If MAs are directly mixed with the fuel
  (homogeneous recycling), the worsening of safety
  parameters such as coolant void or Doppler effect
  sets stringent limitation on MA content
  typically 2.5 wt in large FRs. The variation
  is almost linear with MA concentration.
  Heterogeneous recycling (subassemblies at core
  periphery) brings about lesser penalties on core
  parameters allowing higher contents of MAs, but
  still limited to 30 to 40 in mass due to high
  He release

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Consequence on Core Safety Parameters
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Proliferation Resistant Nuclear Fuel Cycle

• Recommended topics of RD for methods to
  accelerate reduction of current stockpile of
  separated plutonium
• LWR fuel cycle with extended fuel burnup
• Ultra-long lived fuel for high conversion
  reactors with ten years or longer lifetime
• Thorium-uranium oxide fuel
• HTGR with Th fuel design
• Fast spectrum reactors which would breed and burn
  material without reprocessing

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Proliferation Resistant Nuclear Fuel Cycle

• Pu burning with Th is more proliferation
  resistant than with uranium
• No production of additional Pu from U
• The proliferation risk of Pu burning with Th in
  Fast Neutron Reactor (FNR) or Accelerated Driven
  System (ADS) is mainly due to 233U. The amount
  produced of 233U is about one third that of the
  Pu incinerated in Pu/Th MOX fuel. An intrinsic
  barrier to proliferation with 233U is provided by
  the gamma emission from 232U.
• PWR with Th and medium enriched U (20 enriched)
  is proliferation resistant. This is because U
  amount in a fresh fuel assembly (130kg) is
  remarkably smaller than the bare critical mass
  (750kg of 20 enriched U). At the end of the fuel
  irradiation, however, plutonium is produced,
  which could be used for weapon purposes.

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Thorium as fuel in a system breeding 233U
It is the presence of the accelerator which makes
it possible to choose the optimum fuel. Low
equilibrium concentration of TRU makes the system
favourable for their elimination Pu 104 in Th
vs 12 in U.
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Thorium as fuel in a system breeding 233U

• Equilibrium concentrations are orders of
  magnitude lower than in a Uranium-plutonium based
  fuel

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Thorium as fuel in a system breeding 233U

• Pure Thorium does not fission, in practice, seeds
  are needed to start energy production
• gt Any fissionable material can be used
  (233U, 235U, 239Pu or TRU)
• TRU's are destroyed by fission, a process which
  produces energy and makes the method economically
  attractive (TRU's still represent 40 of the
  energy delivered by the reactor which produced
  them)

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Neutronic Properties
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Neutronic Properties
Th-232 capture probability
Th-232 fission probability
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Thorium use in Reactors
ThC and ThO2 have been used with great success in
high temperature reactors operated until now in
different countries AVR and THTR in
Germany Peach Bottom and Fort St. Vrain in
USA Dragon-reactor in Great Britain as a
European project. In heavy water reactors the
use of Thorium partly is common practice, too
PHWR (Pressurised heavy water reactors) in
India Fast breeder system with Th to breed U
233 in India Light water reactors have been
tested with Thorium containing fuel elements in
the past insertion of some Th-elements in the
reactor Shippingport (USA) insertion of
Th-containing fuel elements in Lingen and
Obrigheim (D).
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Thorium use in Reactors
For the future application there is much work
preparing the use of Thorium in different types
of reactors use of Thorium to convert weapon
grade Plutonium in a HTR-gasturbine-project
(common activity of USA and Russia) potential
future application of Thorium in the pebble bed
HTR (South Africa, China) use of the potential
for a application of MOX-fuel in LWR-plants in
operating commercial reactors in different
countries (PuO2/ThO2-mixtures) use of Thorium
in molten salt reactor-concepts insertion of
Thorium containing fuel elements in AHWR
(Advanced Heavy Water Reactors) CANDU-reactors
in Canada are planned to use Plutonium and
Thorium in ADS-concepts (Accelerator Driven
Systems) Thorium can be applied in a subcritical
blanket. New fuel U 233 can be bred and actinides
can be destroyed.
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Thorium use in Reactors
Concept of the HTR-Module (200 MWth) for
Plutonium conversion a) Vertical section through
the reactor b) Data of the core
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Thorium use in Reactors
MSRE (MOLTEN SALT REACTOR EXPERIMENT)
EXPERIMENTAL REACTOR 8 MWth (ORNL)
3 FUEL TYPES URANIUM ENRICHED 30 WITH 235U
PURE 233U 239Pu
FUEL SALT66LiF-29BeF2-5ZrF4-0,2UF4
OPERATED 5 YEARS(LOAD FACTOR 85)WITHOUT ANY
INCIDENT
MSRE OPERATED 1965-1969, SHUTDOWN IN 1969
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Thorium use in Reactors
The use of thorium-based fuels in nuclear
reactors has attractive features

• Higher melting point of Th metal (1750C)
  compared to U metal (1130C) and of ThO2 (3300C)
  compared to UO2 (2800C)
• Thermal conductivity of Th is better than U
• Both of these thermal properties allows higher
  margins for the design and for the operation of
  reactor cores
• Less long-lived minor actinide production
• 233U is a good fissile material both in fast and
  thermal neutron spectra
• There is a potential for breeding with 233U/Th
  cycle

But

• Neutron balance is very tight for breeding in
  thermal spectrum (? strict FP and Pa management)
• Thorium cycle has a penalty for long term waste
  radiotoxicity (231Pa)
• Some aspects of thorium cycle require specific
  design and operation features for the reactor and
  fuel cycle facilities (reactor operation, fuel
  processing, fuel refabrication)

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Basic Principle of Energy Amplifier Systems

• One way to obtain intense neutron sources is to
  use a hybrid sub-critical reactor-accelerator
  system called Accelerator-Driven System

? The accelerator bombards a target with
high-energy protons which produces a very
intense neutron source through the
spallation process.
? These neutrons can consequently be
multiplied (fission and n,xn) in the sub-critical
core which surrounds the spallation target.
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General Features of Energy Amplifier Systems

• Subcritical system driven by a proton
  accelerator
• Fast neutrons (to fission all transuranic
  elements)
• Fuel cycle based on thorium (minimisation of
  nuclear waste)
• Lead as target to produce neutrons through
  spallation, as neutron moderator and as heat
  carrier
• Deterministic safety with passive safety
  elements (protection against core melt down and
  beam window failure)

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Safety margin from prompt criticality

• For a critical system, it is measured by the
  fraction of delayed neutrons. For the Energy
  Amplifier, it is an intrinsic property, and can
  be chosen.
• Subcriticality implies strong damping of reaction
  to reactivity insertion, making the system very
  stable (presence of higher modes in neutron flux).

Keff lt ksource The parameters of the system can
be chosen so that k lt 1 at all times.
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Reactivity Insertions
There is a spectacular difference between a
critical reactor and an EA (reactivity in
r/b r (k1)/k)

• Figure extracted from C. Rubbia et al.,
  CERN/AT/95-53 9 (ET) showing the effect of a
  rapid reactivity insertion in the Energy
  Amplifier for two values of subcriticality (0.98
  and 0.96), compared with a Fast Breeder Critical
  Reactor.
• 2.5 (Dk/k 6.5?103) of reactivity change
  corresponds to the sudden extraction of all
  control rods from the reactor.

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A Th/Pu fueled ADS
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Reprocessing
In the case of the ADS (Energy Amplifier
project), pyroprocessing is regarded as a key
technology in many aspects. In comparison the
acqueous reprocessing, it promises Compactness
and simplicity Less secondary wastes Proliferati
on resistance (no separation of the TRUs) And
fuel fabrication and reprocessing at the reactor
site
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Evolution of the reactivity for ThPu fuel
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Evolution of the reactivity for UPu fuel
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A Th/Pu fuelled ADS

• Application au cas de lEspagne C. Rubbia et al.
  CERN/LHC/97-01 (EET), dans un AE spécialisé pour
  lincinération de TRU.
• Le taux délimination des TRU de 402 kg/an
  correspond à 30,6 kg/TW.hth à comparer au taux de
  production de TRU par un REP de 14 kg/TW.hth
• Dans le cas de lEspagne, avec 5 EA il faudrait
  37 ans pour éliminer les TRU tout en produisant
  8 de la consommation dénergie (100 Mtep/an)

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Radiotoxicity

• The radiotoxicity of spent fuel reaches the level
  of coal ashes after only 500 years, and is
  similar to what is predicted for future
  hypothetical fusion systems

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ROAD MAP FOR A DEMO
Technology of pyrochemical reprocessing of fuel
High power accelerators technology
Technologies of fast reactors with lead-bismuth
coolant
Liquid metal targets technology
Accelerator-driven nuclear waste burner
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Global Parameters
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Transmutation Rates
Plutonium incineration in ThPu based fuel is more
efficient and settles to approximately 43 kg/TWh,
namely 4 times what is produced by a standard PWR
(per unit energy). The minor actinide production
is very limited in this case. Long-
Lived Fission products incineration is made
possible in a very efficient way through the use
of the Adiabatic Resonance Crossing Method. Such
a machine could in principle incinerate up to 4
times what is produced by a standard PWR (per
unit energy).
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Conclusions

• Can atomic power be green ? Physics suggests it
  can !!
• Accelerator-driven systems have additional safety
  margins, which give operational flexibility to
  future systems for safe and clean energy
  production and/or waste transmutation (including
  nuclear weapons)
• Present accelerator technology offers the
  possibility for applying a closed thorium cycle,
  but also for an open once-through cycle using
  thorium oxide with some topping fuel and a very
  high fuel burnup. The Energy Amplifier is one of
  the examples with high potential
• Next step DEMO ? when ? where ?