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Thorium cycle and MSR

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

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Thorium cycle and MSR

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  1. 3rd Meeting of the Norwegian Thorium Report Committee Oslo, Norway – August 29, 2007 Thorium cycle and MSR C. Renault claude.renault@cea.fr 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 (1.5 105 years) comparable to : 238U + n  239U (23.5 min)  239Np (2.3 days)  239Pu (24 000 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. 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, via235U 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 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 10000 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 • 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 (+/-) Preliminary conclusions Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

  8. MSR and thorium cycle The MSR is one of the 6 systemsselected 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. = = = = = = N N N N N N n n n n n n - - - 2(1+a) 2(1+a) 2(1+a) a MSR concepts provide a large flexibility for breeding, either in fast spectrum (U-Pu, Th-U) or in thermal spectrum (Th-U) MSR and thorium cycle 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 Processed Processed salt salt Salt Salt UF UF 6 6 Ln extraction (metal transfer) purification purification reduction reduction Th Th - - Li Li - - Bi Bi 3 3 2.85 m 2.85 m /h /h ( ( ) ) UF UF H H Extractor Extractor 6 6 2 2 3 3 0.2 m 0.2 m /h /h Salt Salt containing containing rare rare earths earths ( ( ) ) Li Li - - Bi Bi Uresidual+ Pa + TRU extraction Extractor Extractor Pa Pa +TRU+ +TRU+ Zr Zr LiCl LiCl Extractor Extractor Li Li - - Bi Bi extraction extraction 3 3 (7.5 m (7.5 m /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 Li Li - - Bi Bi 2 2 F F Fluorination Fluorination Bi Bi 2 2 Extractor Extractor Reductant Reductant Salt Salt Salt to Salt to addition addition Li Li - - Bi Bi Pa decay for residual U recovery TRU to waste waste waste Metal Metal Trivalents Trivalents + + TRU+ TRU+ Zr Zr rare rare earths earths ( ( ) ) UF UF Li Li 6 6 MSBR FUEL PROCESSING FLOWSHEET Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

  11. MSR and thorium cycle THE MSBR PROJECT (MOLTEN SALT BREEDER REACTOR) 2250 MWth – 1000 MWe • 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%) MAIN CHARACTERISTICS : PROJECT STOPPEDIN 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. MSR and thorium cycle MSRE (MOLTEN SALT REACTOR EXPERIMENT) EXPERIMENTAL REACTOR 8 MWth (ORNL) 3 FUEL TYPES: URANIUM ENRICHED 30% WITH 235UPURE 233U239Pu FUEL SALT66%LiF-29%BeF2-5%ZrF4-0,2%UF4 OPERATED 5 YEARS(LOAD FACTOR 85%)WITHOUT ANY INCIDENT MSRE OPERATED 1965-1969, SHUTDOWN IN 1969 Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

  13. 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 Two salts(core, blanket) Fuel salt process time ~ 6 months Thorium cycle and MSR – Norwegian TRC, Oslo, August 29, 2007

  14. 15 cm salt graphite The performances of TMSR (Thorium Molten Salt Reactor) 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) • 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 Variation of x (mole Proportion of Heavy Nuclei) = Variation of the Moderation Ratio x = [6% - 27.5%] 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. An increased intrinsic safety level among other “fast” neutron systems (voiding effect ?) The « Non-Moderated » TMSR 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 2004 -2007 , 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, 2002-2004) Euratom 6th FP (LICORN, ALISIA) ISTC “Training in modern experimental and analytical methods for study of actinide-containing molten salts properties” in 2006-2007 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. MOLTEN SALT REACTOR SYSTEMS IN EUROPE THE ALISIA ACTION (SSA) IN THE 6TH FWP ASSESSMENT OF LIQUID SALTS FOR INNOVATIVE APPLICATIONS THE ALISIA CONSORTIUM : 15 PARTNERS (INCLUDING RRC-KI) 7 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 (2005-2007), 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 10000 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

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