Thorium Fuel Cycles & Heavy Water Reactors AECL Experience Energy From Thorium Event – CNS – UOIT B. P. Bromley Advanced Reactor Systems Computational Reactor Physics AECL - Chalk River Laboratories March 22, 2013 UNRESTRICTED / ILLIMITÉ Opening Remarks • There’s nothing magical or mysterious about thorium except: –3 times abundant as uranium in the earth’s crust – a large resource. –U-233 (bred from Th-232) has a high 2.2, in both thermal and fast neutron energy spectrum; can be used for a breeder reactor. –Pu, Am, Cm, etc. production with Th-based fuels will much lower. • Any reactor (fast or thermal) can be adapted to use thorium. • Thermal reactors can operate with lower fissile wt%. • For thermal spectrum reactor, we want: –Minimal parasitic neutron absorption; maximum neutron economy. –Maximum burnup for Th-based fuel for a given fissile content. – OTT (Once Thru Thorium) Cycle – SSET (Self-sustaining Equilibrium Thorium) Cycle – Topping fuel cycles: Th (new + recycled) + (U/Pu) (new + recycled) UNRESTRICTED / ILLIMITÉ 2 Fundamental Advantage of Heavy Water • Heavy water has the highest moderating ratio (s/a). –Slows down neutrons with minimal absorption. – Better than H (in H2O), better than C (in graphite). –Can maximize neutron economy, in a thermal-spectrum reactor. – Save neutrons for fission and breeding new fuel. • HWR can run on natural uranium and achieve good burnup. – ~7,500 MWd/t in a CANDU PT-HWR UNRESTRICTED / ILLIMITÉ 3 Pressure Tube Heavy Water Reactors (PT-HWR) - Advantages • Pathway Canada Chose – AECL Pursued. • Excellent neutron economy. – High conversion ratios (C.R.>0.8). – Can operate on natural uranium (NU). – High fuel utilization; conservation of resources. • Continuous On-line refuelling. – Low excess reactivity. – Higher fuel burnup for a given enrichment. – 30% more burnup than 3-batch refuelling. – Maximize uranium utilization (kWh/kg-U-mined). – High capacity factors (0.8 to 0.95). – Flexibility in fuel loading – one or more fuel types can be used. • Modular construction. – Short, relatively simple fuel bundle design. – Pressure tubes; replaceable; reactor can be refurbished. – Local fabrication (do not need heavy forgings). UNRESTRICTED / ILLIMITÉ 4 PT-HWR • Operational Technology. • Future HWR variants. • Potential for further improvements. • Use R&D to find them. UNRESTRICTED / ILLIMITÉ 5 PT-HWR / CANDU Reactors • Designed to maximizes neutron economy. • Flexible in use of fuel types. • An existing, proven, and operational technology. • Supply chain in place. • Design naturally lends itself to implementation of Th-based fuels. –Thorium-based fuels have been tested in PT-HWR (NPD-2). –Thorium bundles have been used in India (in their PT-HWRs). – Power flattening for start-up cores; alternative to DU. • Practical implementation time should be relatively short. • AECL / CRL has helped develop and prove this technology, and is continually exploring technology improvements to facilitate implementation and expansion of thorium-based fuel cycles. – Emphasis on use of solid fuel forms. UNRESTRICTED / ILLIMITÉ 6 Overview of AECL Experience • AECL has over 50 years of extensive experience with Thoria-based fuels – Investments made in thorium fuel cycle R&D since the late 1950’s – First irradiation conducted in 1962 and the most recent in 2005 • Experience includes – Fuel Fabrication. – Irradiation testing. – Post Irradiation Examination. – Thorium fuel reprocessing. – Waste management. – Critical experiments. – Reactor physics. – Conceptual design studies. – Economic analyses. – System studies. UNRESTRICTED / ILLIMITÉ 7 Thorium in CANDU / PT-HWR Evolution PT-HWR Canadian SCWR With U-233 With U-233 Recycle Recycle Build U-233 resource U-233 + Pu U-233 + Once-through Pu Pu/Th Innovation Once-through Once-through LEU/Th Pu/Th Years AECL - OFFICIAL USE ONLY / À USAGE EXCLUSIF - EACL 8 Long-term Impact • Decay heat in spent fuel is a main parameter in determining the capacity of a long term disposal facility 1.6 Current global cycle, LWRs + HWRs 1.4 Transition to once-through thorium in CANDU Transition to fast reactors 1.2 Transition to Th with Once-through thorium gives the 1.0 same reduction as fast reactors U-233 recycle in 0.8 CANDU Once-through thorium gives 50% 0.6 reduction over current cycle 0.4 Decay heat (GW) heat Decay 0.2 0.0 0 200 400 600 800 1000 Years since end of scenario Thorium with U-233 gives a 75% reduction over the current cycle AECL - OFFICIAL USE ONLY / À USAGE EXCLUSIF - EACL 9 Fabrication • Generally, AECL has targeted a solid solution of Thoria and the fissile additive. • Many techniques are capable of achieving this and they fall into two main categories: 1. Solution blending – sol gel, co-precipitation – Mixing at the atomic level 2. Mechanical mixing – co-milling, high-intensity mixing – Often not a “perfect” solid solution – Must achieve mixing on the scale of individual particles UNRESTRICTED / ILLIMITÉ 10 Thorium Pellet Structure Granular Homogeneous UNRESTRICTED / ILLIMITÉ 11 Thoria Irradiation Experience at AECL • Thoria irradiations ongoing since early 1960s • Irradiations in NRX, NRU and WR-1 research reactors. • Irradiations in NPD-2 –~20 MWe prototype PT-HWR. • Pure ThO2, (U,Th)O2 , and (Pu,Th)O2 • NRU still operational. Irradiation # of experiments Irradiation Time Facility frame NPD 1 1976 NRX 20 1962-1992 NRU 28 1966-2005 WR1 18 1970-1980 UNRESTRICTED / ILLIMITÉ 12 NRX, NRU, WR-1, NPD • NPD-2 • WP-1 • NRU • NRX UNRESTRICTED / ILLIMITÉ 13 Critical Experiments • AECL: long history of critical experiments involving thorium-based fuels. • Three sets of experiments, dating back to the 1960’s – HEU/Th (1966-1968) – Pu/Th (1986) – U-233/Th (1990s) • Performed in the ZED-2 (Zero Energy Deuterium) critical facility at Chalk River Laboratories. –Reaction rate / foil data. –Reactivity changes due to X – X = coolant density, temperature, etc. –Verifies physics; validate computer codes. UNRESTRICTED / ILLIMITÉ 14 Alternative Fuel Bundle and Core Design Options Heterogeneous, Homogeneous 1.4 Mixed Bundle Bundle 1.2 1 NU 0.8 0.6 0.4 CANDU 0.2 Checkerboard Annular Seed- Blanket Seed-Blanket 0 Cores Cores 1 2 3 4 5 6 7 8 9 Row\Col 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Row\Col Row\Col 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Row\Col A 0 0 0 0 0 0 0 0 B B B B B B 0 0 0 0 0 0 0 0 A A 0 0 0 0 0 0 0 0 B B B B B B 0 0 0 0 0 0 0 0 A B 0 0 0 0 0 B B B S S S S S S B B B 0 0 0 0 0 B B 0 0 0 0 0 B B B S S S S S S B B B 0 0 0 0 0 B Checkerboard Core Designs C 0 0 0 0 B S S B S S B B S S B S S B 0 0 0 0 C C 0 0 0 0 B S S S S S S S S S S S S B 0 0 0 0 C D 0 0 0 B S S B B S S B B S S B B S S B 0 0 0 D D 0 0 0 B S S S S S S S S S S S S S S B 0 0 0 D Fissile Utilization, Relative to Natural Uranium Uranium Natural to Relative Fissile Utilization, E 0 0 B S S B S S B B S S B B S S B S S B 0 0 E E 0 0 B S S S S S S S S S S S S S S S S B 0 0 E Annular Core Designs F 0 0 B S B B S S B B S S B B S S B B S B 0 0 F F 0 0 B S S S S S S S S S S S S S S S S B 0 0 F G 0 B S B S S B B S S B B S S B B S S B S B 0 G G 0 B S S S S S S S S S S S S S S S S S S B 0 G H 0 B B B S S B B S S B B S S B B S S B B B 0 H H 0 B S S S S S S S S S S S S S S S S S S B 0 H J B S S S B B S S B B S S B B S S B B S S S B J J B S S S S S S S S S S S S S S S S S S S S B J K B S S S B B S S B B S S B B S S B B S S S B K K B S S S S S S S S S S S S S S S S S S S S B K L B S B B S S B B S S S S S S B B S S B B S B L L B S S S S S S S S S S S S S S S S S S S S B L M B S B B S S B B S S S S S S B B S S B B S B M M B S S S S S S S S S S S S S S S S S S S S B M Hafnium Tube N B S S S S S S S S S S S S S S S S S S S S B N 3.8% Pu N B S S S B B S S B B S S B B S S B B S S S B N 3 mm thick O B S S S B B S S B B S S B B S S B B S S S B O O B S S S S S S S S S S S S S S S S S S S S B O 96.2% Th P 0 B B B S S B B S S B B S S B B S S B B B 0 P P 0 B S S S S S S S S S S S S S S S S S S B 0 P Q 0 B S B S S B B S S B B S S B B S S B S B 0 Q Q 0 B S S S S S S S S S S S S S S S S S S B 0 Q PT R 0 0 B S B B S S B B S S B B S S B B S B 0 0 R R 0 0 B S S S S S S S S S S S S S S S S B 0 0 R Zr Rod S 0 0 B S S B S S B B S S B B S S B S S B 0 0 S S 0 0 B S S S S S S S S S S S S S S S S B 0 0 S T 0 0 0 B S S S S S S S S S S S S S S B 0 0 0 T CT T 0 0 0 B S S B B S S B B S S B B S S B 0 0 0 T U 0 0 0 0 B S S S S S S S S S S S S B 0 0 0 0 U U 0 0 0 0 B S S B S S B B S S B S S B 0 0 0 0 U V 0 0 0 0 0 B B B S S S S S S B B B 0 0 0 0 0 V V 0 0 0 0 0 B B B S S S S S S B B B 0 0 0 0 0 V W 0 0 0 0 0 0 0 0 B B B B B B 0 0 0 0 0 0 0 0 W W 0 0 0 0 0 0 0 0 B B B B B B 0 0 0 0 0 0 0 0 W Row\Col 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Row\Col Row\Col 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Row\Col Moderator AECL - OFFICIAL USE ONLY / À USAGE EXCLUSIF - EACL 15 Potential to Increase Utilization • Achieve ~ 20% to 100% higher utilization of fissile fuel than PT-HWR with NU fuel in an OTT cycle.