1. 3rd Meeting of the Norwegian Thorium Report Committee
Oslo, Norway – August 29, 2007
Thorium cycle and MSR
C. Renault
with major contributions from E. Merle-Lucotte (CNRS),
D. Grenèche (AREVA NC) and M. Delpech (CEA)
CEA, Nuclear Energy Division, France
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

2. About thorium cycle Why thorium ?
Th is a fertile material which generates a fissile isotope: 233U
232Th + n  233Th (22 min)  233Pa (27 days)  233U ( years)
comparable to :
238U + n  239U (23.5 min)  239Np (2.3 days)  239Pu ( years)
233U is rather unsensitive to neutron energy (a and h)
233U is the best fissile isotope in thermal range
There is a potential for breeding in thermal spectrum with the Th/U3 system
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

3. Some specific aspects of thorium cycle
About thorium cycle
Some specific aspects of thorium cycle
Production of isotopes with very energetic  emission (208Tl, 212Bi, 212Po), via 232U decay (~ 70 years)
 refabrication of 233U bearing fuels must be made in remote and shielded handling facilities
Formation of high concentration of 233Pa (27 days)
 management of 233Pa necessary to optimize 233U production
« delayed » reactivity increase after shutdown, due to 233U formation
Fissile 233U must be bred from 232Th, via 235U enriched fuel or recycled plutonium
 spent fuel reprocessing required (Thorex)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

4. Thorium cycle is efficient for the minimization of MA production
Thorium cycle and waste minimization
Thorium cycle is efficient for the minimization of MA production
MA production
0.5 kg/TWhe with 233U/Th (mainly Np)
3 kg/TWhe with 235U/U
12 kg/TWhe with MOX fuel
Less heavy and radiotoxic elements formed with thorium cycle (Th-U) until years
But production of highly radiotoxic actinides later (231Pa )
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

5. Thorium in nuclear reactors
India plans to use thorium in an extensive way in its future nuclear programme
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

6. Thorium in nuclear 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 in thermal spectrum 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)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

7. Thorium in nuclear reactors
Preliminary conclusions
Thorium cycle seems really attractive only if bred 233U can be recycled which implies the reprocessing of spent fuel
Past studies show that virtually every type of reactors can accomodate thorium-based fuels
Breeding conditions can be achieved in (conventional) thermal reactors with 233U/Th but technological tricks seem hard to be extrapolated at industrial scale (see Shippingport, BR~1.01)
Should FBRs be deployed
233U presents less good nuclear properties than Pu, and Th is much less fissile than 238U for fast neutrons
U resources would be sufficient to sustain the nuclear energy development
The incentive for implementation of thorium cycle in conventional reactors (T and F) at industrial scale may be questionable (+/-)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

8. The MSR is one of the 6 systems selected in Generation IV
MSR and thorium cycle
The MSR is one of the 6 systems selected in Generation IV
A REFERENCE CONCEPT: THE MOLTEN SALT BREEDER REACTOR (MSBR)
A set of unique characteristics: - A molten salt mixture acting both as coolant and fuel (actinides dissolved in molten salt) - The reactor coupled to a reprocessing plant (on-site reprocessing) - Specific and favourable safety characteristics (operation at low pressure, low source term, small residual heat, passive draining of liquid fuel,…)
OTHER CONCEPTS INVESTIGATED FOR BREEDING (AMSTER, TMSR) OR ACTINIDE BURNING (TIER, MOSART)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

9. MSR and thorium cycle n - 2(1+a)
MSR concepts provide a large flexibility for breeding, either in fast spectrum (U-Pu, Th-U) or in thermal spectrum (Th-U) = n -
2(1+a) N a
AVAILABLE NEUTRONS
WITHOUT LEAKAGE (CRITICAL REACTOR)
MSR in U-Pu cycle is breeder in fast neutron spectrum
MSR in Th-U3 cycle can be breeder in all type of neutron spectra
The use of liquid fuel (only graphite structure in the core) improves neutron balance for breeding in thermal spectrum
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

10. MSR and thorium cycle
Liquid fuel and on-site reprocessing allow flexible Pa management, minimize the contents of capturing FP and avoid fuel refabrication
Salt
Salt UF UF
Processed
Processed
salt
salt 6 6
purification
purification
reduction
reduction
Ln extraction (metal transfer) Th Th - - Li Li - - Bi Bi UF UF H H 3 3 6 6 2 2
Extractor
Extractor ( (
2.85 m
2.85 m /h /h ) )
Salt
Salt
containing
containing
rare
rare
earths
earths ( (
0.2 m
0.2 m 3 3 /h /h ) )
Uresidual+ Pa + TRU extraction Li Li - - Bi Bi
Extractor
Extractor Pa Pa
+TRU+
+TRU+ Zr Zr
LiCl
LiCl
Extractor
Extractor
extraction
extraction Li Li - - Bi Bi
(7.5 m
(7.5 m 3 3
/h)
/h)
Reactor
Reactor
Extractor
Extractor Li Li - - Bi Bi Pa Pa
Decay
Decay
Fluorination
Fluorination
Hydrofluor
Hydrofluor . .
Fluorination
Fluorination + +
Divalent
Divalent
rare
rare
earths
earths
U recovery F F F F HF HF 2 2 2 2 Li Li - - Bi Bi F F
Fluorination
Fluorination Bi Bi 2 2
Extractor
Extractor
Reductant
Reductant
Salt
Salt
addition
addition
Salt to
Salt to
Pa decay for residual U recovery
TRU to waste Li Li - - Bi Bi
Metal
Metal
waste
waste + +
Trivalents
Trivalents Li Li ( (
TRU+
TRU+ Zr Zr ) ) UF UF
rare
rare
earths
earths 6 6
MSBR FUEL PROCESSING FLOWSHEET
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

11. THE MSBR PROJECT (MOLTEN SALT BREEDER REACTOR) 2250 MWth – 1000 MWe
MSR and thorium cycle
THE MSBR PROJECT (MOLTEN SALT BREEDER REACTOR) MWth – 1000 MWe
MAIN CHARACTERISTICS :
FLUORIDE-BASED SALT
71%LiF-16%BeF2-12%ThF4-0.3%UF4
TWO ZONES CORE (“FISSILE” AND “FERTILE”)
GRAPHITE-MODERATED CORE (BREEDING IN THERMAL NEUTRON SPECTRUM, BR=1.06, IN 233U/Th FUEL CYCLE)
HIGH ENERGY CONVERSION EFFICIENCY (~45%)
PROJECT STOPPED IN 1976
SOME WEAK POINTS :
QUASI-CONTINUOUS FUEL SALT TREATMENT WITH HIGH PROCESSING RATE (PROCESS TIME ~ 10 DAYS) - FEEDBACK COEFFICIENT SLIGHTLY POSITIVE
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

12. MSRE OPERATED 1965-1969, SHUTDOWN IN 1969
MSR and thorium cycle
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
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

13. A reference breeder design optimized from the MSBR
The TMSR (Thorium Molten Salt Reactor)
A reference breeder design optimized from the MSBR
General parameters:
total power : 2500 MWth (1000 MWe)
salt composition :
78% LiF – 21.4% ThF4 – 0.6% UF4
average temperature : 630 °C
Geometrical parameters:
core radius : 1.6 m
hexagon size : 15 cm
channel radius: 8.5 cm
salt volume : 20 m3
fertile blanket : yes
core shape : cylindrical (H=D)
A systematic exploration of parameters and constraints with the objective to address MSBR weakpoints and set up an optimized design
Fuel salt process time ~ 6 months
Two salts (core, blanket)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

14. of optimization (epithermal)
The performances of TMSR (Thorium Molten Salt Reactor)
salt
15 cm
graphite
Performances according to salt channel radius
78%LiF–21.4%ThF4–0.6%UF4
Spectrum hardening improves temperature reactivity feedback
Breeding ratio > 1 in a broad range of salt channel radius
Graphite lifetime imposes a strong penalty (< 5 years in hardened spectrum)
Thermal spectrum minimizes initial fissile inventory (U3)
Attractive window
of optimization (epithermal)
(SOURCE CNRS, L. MATHIEU)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

15. The « Non-Moderated » TMSR
Another interesting option :
the non-moderated TMSR (no graphite in the active core)
Variation of x (mole Proportion of Heavy Nuclei) = Variation of the Moderation Ratio
x = [6% %]
Fuel Salt: 80%LiF, x%(HN)F4, (20-x)%BeF2
[for x≥20% (100- x)%LiF, x%(HN)F4]
Cf. Neutron Spectrum: Epithermal to Fast
233U Initial Inventory: 2500 to 6500 kg
Fuel Salt Volume: 20 m3
Operating Temperature: 630°C
Power: 2.5 GWth (1 GWél)
Core Internal Radius: 1.25 m
Core Height: 2.6 m
Fertile Blanket Salt: 72%LiF-28%ThF4
Parameters: Reprocessing, Initial Fissile Matter (233U, Pu), Fissile Inventory, Waste Management, Deployment Capabilities…
SOURCE CNRS, E. MERLE-LUCOTTE
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

16. The « Non-Moderated » TMSR
Breeding capability of non-moderated TMSR
for a reasonable salt processing rate (200 kgHN/d)
and limited 233U initial inventory (3-5 tons)
SOURCE CNRS, E. MERLE-LUCOTTE
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

17. The « Non-Moderated » TMSR
An increased intrinsic safety level among other “fast” neutron systems (voiding effect ?)
Reprocessing rate = 200 kgHN/d
Excellent (-10 pcm/K) to
Very Good (-5 pcm/K) Level of
Deterministic Safety
SOURCE CNRS, E. MERLE-LUCOTTE
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

18. The « Non-Moderated » TMSR
A transition scenario to pure 233U/Th cycle in TMSR
233U production and TMSR deployment
Reactor Doubling Time =
Operating time necessary to produce one initial fissile inventory
Optimized Reactor Doubling Time:
233U-started TMSR: ~ 45 years
(Pu+MA)-started TMSR: ~ 30 years
SOURCE CNRS, E. MERLE-LUCOTTE
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

19. MSR AND LIQUID SALTS : INTERNATIONAL FRAMEWORK
International projects are underway and interlinked
IAEA CRP on “Studies of Advanced Reactor Technology Options for Effective Incineration of Radioactive Waste” in , Domain VI MOSART
(RRC-KI, CEA, FZK, NRG, SCK-CEN, Polito Univ, NRI)
National programmes (CNRS, EDF, CEA)
ISTC#1606
Foreign collaborators:
CEA, CNRS, EdF, FZK, IAEA, KTH, NRI
Euratom 5th FP (MOST project, )
Euratom 6th FP (LICORN, ALISIA)
ISTC “Training in modern experimental and analytical methods for study of actinide-containing molten salts properties” in
I-NERI Action (DOE-CEA)
(Hydrogen Process to High Temperature Heat Source Coupling Technology)
GENERATION IV
US Liquid Salt R&D activity ORNL, UC–Berkeley, SNL, INL, U. Wisconsin
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

20. MSR – R&D issues and key-points
The major role of chemistry in the viability demonstration has been recognized and emphasized
- Liquid salt properties and salt control (redox, purification, homogeneity)
- Chemical interaction with structural materials
Compatibility of liquid salts with sodium, water, air (considered good, to be confirmed)
Viability of the « on line » pyrochemical reprocessing
The impact of physico-chemistry on safety
R&D issues
A rethinking of the safety approach is needed (fuel in liquid form and chemistry-controlled phenomena)
The development of adequate simulation tools coupling neutronics, thermal-hydraulics and chemistry (design and safety) together with basic models (physico-chemistry) is a high priority task
Experimental (analytical and integral) infrastructures are needed at mid term (liquid salt loops)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

21. ASSESSMENT OF LIQUID SALTS FOR INNOVATIVE APPLICATIONS
MOLTEN SALT REACTOR SYSTEMS IN EUROPE
THE ALISIA ACTION (SSA) IN THE 6TH FWP
ASSESSMENT OF LIQUID SALTS FOR INNOVATIVE APPLICATIONS
THE ALISIA CONSORTIUM : PARTNERS (INCLUDING RRC-KI) EC COUNTRIES + EURATOM + RUSSIA
5 WORK PACKAGES : WP1 FUEL SALT CHEMISTRY (JRC-ITU) WP2 MATERIALS – MECHANICS (SKODA, EVM) WP3 REACTOR PHYSICS (CNRS, EDF) WP4 FUEL SALT CLEAN-UP (NRI) WP5 DESIGN AND SAFETY (CEA)
ALISIA STARTED FEBRUARY 2007 FOR ONE YEAR DURATION
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

22. ISTC-1606 programme & liquid salts loops in Russia
The availability of experimental R&D means is rather limited in Europe.There is strong potential with existing facilities in Russia
SOURCE KI, V. IGNATIEV
A lot of data acquired in the frame of ISTC-1606 ( ), to be continued in ISTC-3749 ( 2008)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

23. Conclusions : thorium cycle
Thorium cycles have been widely investigated in the past. These studies show that virtually every type of reactors can accomodate thorium-based fuels.
The use of Th in « conventional » reactors has several advantages (very high melting point of ThO2, good neutronic properties of 233U, potential for high conversion ratios, etc.) but presents some drawbacks (high concentration of 233Pa). Breeding in thermal neutron spectrum cores is very difficult to achieve
Radiotoxic inventory of ultimate waste from thorium cycles is less than the one of U/Pu cycles until years, there is a penalty lfor longer term
Thorium cycle implementation has a strong impact on dose rates (g-emitting isotopes) in fuel cycle facilities
Thorium cycle has a good potential, but its deployment at short-mid term should be motivated by a very specific local or regional context. It can be useful to devote some R&D efforts on this cycle to better assess its assets and to seek technical solutions able to improve the conditions of its implementation in the longer term
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

24. Conclusions : MSR and thorium cycle
MSR offers very attractive specific characteristics among other 4th generation systems. However MSR is often considered more innovative and less mature than other systems, thus requiring long term R&D effort for viability demonstration
MSR concepts (TMSR) offer alternative options for breeding and waste reduction with the added value of liquid fuel (intrinsic safety features, fuel cycle flexibility, fuel refabrication not required)
MSR is specially well fitted to thorium cycle. MSR opens wider the perspectives of thorium cycle development, by addressing some of the drawbacks of solid fuel reactors in thorium cycle (Pa management, tight neutron balance, time for deployment, safety concerns, fuel refabrication ?)
The potential of MSR concepts is mainly substantiated by theoretical studies, to be confirmed. Some critical key-points must be addressed because of complex and rather poorly known behaviour of liquid salts as working fluids (chemistry control, pyrochemical fuel salt treatment, materials interactions,…). The scenarios for the production of initial 233U load must be be assessed.
The R&D effort at international level (Euratom, Generation IV) is well coordinated. However, the available funding is rather limited today and should be increased to develop the experimental infrastructures (analytical and integral salt loops) required for qualification of liquid salt technologies (thermal-hydraulics and chemistry)
Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007