1. Proliferation Safe Nuclear Power Does that exist ?
Y. KADI
CERN, AB Depart.
19 June 2008, JAI, Oxford
JAI June 19, 2008
Y. KADI, CERN

2. A new primary energy source
By 2050, the world’s 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 R&D effort, which is the only hope to solve the energy problem on the long term. This R&D 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.
JAI June 19, 2008
Y. KADI, CERN

3. JAI June 19, 2008
Y. KADI, CERN

4. World nuclear electricity production by scenarios (INPRO Phase-IA Report)
Schematic illustration of the four SRES storyline families (Source:IPCC)
Potential global market for nuclear electricity, hydrogen, heat and desalination for the A1T Scenario assuming aggressive nuclear cost improvements
JAI June 19, 2008
Y. KADI, CERN

5. 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?
The contribution of C. Rubbia has been to show that it is possible to optimize the system, and that the system is technically and economically feasible: choice of strategy and optimization of the parameters.
JAI June 19, 2008
Y. KADI, CERN

6. Uranium demand only slightly improved by MOX
typical new LWR (EPR):
10 years to build
60 years operation
China’s planned reactors : ≈ 2.5 Million tons of U
JAI June 19, 2008
Y. KADI, CERN

7. Yellow cake or yellow coal ?
Mining effort needed to produce 1 GWe x 30 years = 6.1 TWh
JAI June 19, 2008
Y. KADI, CERN

8. The problem of nuclear waste at very long lifetime
Warning: long-lived radio-toxicity of MOX waste 10 x larger
JAI June 19, 2008
Y. KADI, CERN

9. How many “Sellafield” for MOX ?
JAI June 19, 2008
Y. KADI, CERN

10. 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: x 108 = Sv [recommended ICRP max. dose to radiation workers 2.0 mSv/year]
Main concerns Leaks in the environment (biosphere)
Proliferation (Pu239): world’s waste stockpile about 5 ÷ 10 times the military Pu stockpile
 at end of present nuclear deployment: 600’000 critical Pu masses
JAI June 19, 2008
Y. KADI, CERN

11. 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!
2003: net nuclear electric generation: GWh per year => GWe
Typically 250kg of TRU and 830 kg of FF per GWe
JAI June 19, 2008
Y. KADI, CERN

12. Plutonium incineration in fast neutron reactors
CAPRA Core (CEA)
Plutonium incineration in fast neutron reactors
JAI June 19, 2008
Y. KADI, CERN

13. 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/(U+Pu) 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
JAI June 19, 2008
Y. KADI, CERN

14. Consequence on Core Safety Parameters
JAI June 19, 2008
Y. KADI, CERN

15. Proliferation Resistant Nuclear Fuel Cycle
Recommended topics of R&D 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
JAI June 19, 2008
Y. KADI, CERN

16. 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.
JAI June 19, 2008
Y. KADI, CERN

17. 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 10–4 in Th vs 12% in U.
JAI June 19, 2008
Y. KADI, CERN

18. Thorium as fuel in a system breeding 233U
Equilibrium concentrations are orders of magnitude lower than in a Uranium-plutonium based fuel
JAI June 19, 2008
Y. KADI, CERN

19. Thorium as fuel in a system breeding 233U
Pure Thorium does not fission, in practice, seeds are needed to start energy production:
==> 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)
JAI June 19, 2008
Y. KADI, CERN

20. Neutronic Properties
JAI June 19, 2008
Y. KADI, CERN

21. Neutronic Properties Th-232 capture probability
Th-232 fission probability
JAI June 19, 2008
Y. KADI, CERN

22. 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).
JAI June 19, 2008
Y. KADI, CERN

23. 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.
JAI June 19, 2008
Y. KADI, CERN

24. 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
JAI June 19, 2008
Y. KADI, CERN

25. Thorium use in Reactors
MSRE (MOLTEN SALT REACTOR EXPERIMENT)
EXPERIMENTAL REACTOR 8 MWth (ORNL)
3 FUEL TYPES: URANIUM ENRICHED 30% WITH 235U PURE 233U Pu
FUEL SALT 66%LiF-29%BeF2-5%ZrF4-0,2%UF4
OPERATED 5 YEARS (LOAD FACTOR 85%) WITHOUT ANY INCIDENT
MSRE OPERATED , SHUTDOWN IN 1969
JAI June 19, 2008
Y. KADI, CERN

26. Thorium use in Reactors
The use of thorium-based fuels in nuclear reactors has attractive features
Higher melting point of Th metal (1750°C) compared to U metal (1130°C) and of ThO2 (3300°C) compared to UO2 (2800°C)
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)
JAI June 19, 2008
Y. KADI, CERN

27. 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.
JAI June 19, 2008
Y. KADI, CERN

28. 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)
JAI June 19, 2008
Y. KADI, CERN

29. 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 < ksource
The parameters of the system can be chosen
so that k < 1 at all times.
JAI June 19, 2008
Y. KADI, CERN

30. Reactivity Insertions
There is a spectacular difference between a critical reactor and an EA (reactivity in $ = r/b; r = (k–1)/k) :
Figure extracted from C. Rubbia et al., CERN/AT/ (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10–3) of reactivity change corresponds to the sudden extraction of all control rods from the reactor.
JAI June 19, 2008
Y. KADI, CERN

31. A Th/Pu fueled ADS
JAI June 19, 2008
Y. KADI, CERN

32. 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;
Proliferation resistance (no separation of the TRUs);
And fuel fabrication and reprocessing at the reactor site
JAI June 19, 2008
Y. KADI, CERN

33. Evolution of the reactivity for ThPu fuel
JAI June 19, 2008
Y. KADI, CERN

34. Evolution of the reactivity for UPu fuel
JAI June 19, 2008
Y. KADI, CERN

35. A Th/Pu fuelled ADS
Application au cas de l’Espagne [C. Rubbia et al. CERN/LHC/97-01 (EET)], dans un AE spécialisé pour l’incinération de TRU.
Le taux d’élimination 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 l’Espagne, avec 5 EA il faudrait 37 ans pour éliminer les TRU tout en produisant 8% de la consommation d’énergie (100 Mtep/an)
JAI June 19, 2008
Y. KADI, CERN

36. 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
JAI June 19, 2008
Y. KADI, CERN

37. ROAD MAP FOR A DEMO Accelerator-driven nuclear waste burnerUO 2
+PuO 2+
PuO
High power accelerators technology
Technology of pyrochemical reprocessing of fuel
Technologies of fast reactors with lead-bismuth coolant
Liquid metal targets technology
Accelerator-driven nuclear waste burner
JAI June 19, 2008
Y. KADI, CERN

38. Phase 1 Phase 2 Phase 3 250 MeV*3 mA = 0.75 MWth 250 MeV*6 mA
Proton Driver Power
250 MeV*3 mA
= 0.75 MWth
250 MeV*6 mA
= 1.5 MWth
900 MeV*6 mA
= 5.4 MWth
Gain G0
0.75
2.5
Sub-criticality level, k
0.95
0.975
Gain=Go/(1-k) 15 30
100
Thermal Power Output
11.25 MWth
45 MWth
540 MWth
JAI June 19, 2008
Y. KADI, CERN

39. Global Parameters
JAI June 19, 2008
Y. KADI, CERN

40. 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).
JAI June 19, 2008
Y. KADI, CERN

41. 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 ?
JAI June 19, 2008
Y. KADI, CERN