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Heavy water production
1) Heavy water, or deuterium oxide (D2O), is a form of water that contains hydrogen isotopes with an extra neutron. It is used as a moderator in CANDU nuclear reactors. 2) The document discusses various heavy water production processes including Girdler-Sulphide (G-S) and newer catalytic exchange processes like CECE and CIRCE that use hydrogen gas. 3) CECE and CIRCE processes are more environmentally friendly than G-S and allow for smaller, more efficient production facilities to be located near hydrogen production plants.
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Heavy water production
- 1. HEAVY WATER PRODUCTION Dr. GheorgheVASARU Aleea Tarnita, Nr 7, Apt. 11 CLUJ-NAPOCA, ROMANIA gvasaru@hotmail.com
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- 4. H2O and D2OMolecules
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- 6. Deuterium is a stablebut rare isotope of hydrogen containing one neutron and one proton in its nucleus (common hydrogen has only a proton). Chemically, this additional neutron changes things only slightly, but in nuclear terms the difference is significant. For instance, heavy water is about eight times worse than light water for slowing down ("moderating") neutrons, but its macroscopic absorption cross-section (i.e. probability of absorption) is over 600 times less, leading to a moderating ratio (the ratio of the two parameters, a useful measure of a moderator's quality) that is 80 times higher than that of light water.
- 7. Heavy Water (HW) HeavyWater is the common name for D2O, deuterium oxide. It is similar to light water (H2O) in many ways, except that the hydrogen atom in each water molecule is replaced by "heavy" hydrogen, or deuterium (discovered by American chemist Harold Urey in 1931, earning him the 1934 Nobel Prize in chemistry). The deuterium makes D2O about 10% heavier than ordinary water.
- 8. Heavy water or deuteriumoxide (D20) is a natural form of water used to lower the energy of neutrons in a reactor. It is heavier than normal water by about 10%, and occurs in minute quantities (about one part heavy water per 7,000 parts water). CANDU reactors use heavy water as both moderator and coolant. Heavy water is one of the most efficient moderators, and enables the CANDU design to use natural uranium fuel.
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- 18. HW Separation byThermal Diffusion
- 19. Heavy Water’s lowabsorption cross-section permits the use of natural uranium, which is low in fissile content and would not attain criticality in a light-water lattice. The lower slowing-down power of heavy water requires a much larger lattice than in light-water cores; however, the larger lattice allows space at the core endfaces for on-line refuelling, as well as space between channels for control rods, in-core detectors, and other non-fuel components.
- 20. In the pastall of the heavy water for domestic and export needs has been extracted from ordinary water, where deuterium occurs naturally at a concentration of about 150 ppm (deuterium-tohydrogen). For bulk commercial production, the primary extraction process to date, the "GirdlerSulphide (G-S)" process, exploits the temperaturedependence of the exchange of deuterium between water and hydrogen-sulphide gas (H2S). In a typical G-S heavy-water extraction tower, ordinary water is passed over perforated trays through which the gas is bubbled. In the "hot section" of each tower the deuterium will migrate to the hydrogen-sulphide gas, and in the "cold section" this deuterium migrates back into cold feedwater.
- 21. In a multistageprocess the water is passed through several extraction towers in series, ending with a vacuum distillation process that completes the enrichment to "reactor-grade" heavy water, nominally 99.75 wt% deuterium content.
- 22. During operation a CANDUplant will be required to periodically upgrade its inventory of heavy water (using again a vacuum distillation process), since a purity decrease of only 0.1 wt% can seriously affect the efficiency of the reactor's fuel utilization.
- 23. The GS process, whilecapable of supplying the massive CANDU build programme from the late 1960s to the late 1980s, is expensive and requires large quantities of toxic H2S gas. It is thus a poor match for current market and regulatory conditions, and the last G-S plant in Canada shut down in 1997.
- 24. AECL is currentlyworking on more efficient heavy-water production processes based on wet-proofed catalyst technology. CECE and CIRCE are based on electrolytic hydrogen and reformed hydrogen, respectively. CIRCE could be on the sidestream of a fertilizer or hydrogen-production plant, for example. AECL currently has a prototype CIRCE unit operating at a small hydrogen-production plant in Hamilton, Ontario. These catalyst technologies are more environmentally benign than the gas-extraction process they would replace. See "further reading" below for more details on the past and future of heavy-water production in Canada.
- 25. This process of"enriching" the moderator, rather than the fuel is expensive and is part of the reason for the slightly larger capital cost of CANDU reactors compared to light-water reactors (heavy water represents about 20% of the capital cost). However, since the fuelling cost of a CANDU reactor is much lower than that of light-water, enriched-uranium reactors, the lifetime-averaged costs are comparable. Nevertheless, future CANDU designs will use about a quarter the heavy-water inventory for the same power output (see related FAQ), thus making their capital (upfront) cost more competitive.
- 26. Heavy water hasan alternate attraction for scientists seeking the elusive neutrino particle. In Canada's Sudbury Neutrino Observatory (SNO) Project, about 1000 tonnes of heavy water are used as an interaction medium in which to track the passage of neutrinos from the sun. The heavy water is held in a large acrylic container two kilometers deep in the Canadian Shield, surrounded by photomultiplier detectors
- 27. Old Technology andNew 1970s CIRCE technology H2 + H2O CECE 75 m of tower height finisher 2.5 m diam. for same scale 25 m high 0.15 m diam. for same scale Water G-S technology Distillation H2S + H2O finisher 300 m of total 85 m high tower height 7 m in diam. 0.4 m diam. 2000s
- 28. Old Technology andNew 1970s CIRCE technology H2 + H2O CECE 75 m of tower height finisher 2.5 m diam. for same scale 25 m high 0.15 m diam. for same scale Water G-S technology Distillation H2S + H2O finisher 300 m of total 85 m high tower height 7 m in diam. 0.4 m diam. 2000s
- 29. AECL’S Isotope SeparationTechnology for Heavy Water Production • Based on catalytic exchange of isotopes between hydrogen gas and liquid water using homogeneous mixture of hydrophobic catalyst and hydrophilic material • Processes are aided by a large separation factor among isotopes • Processes depend on deployment of high-activity, stable, tricklebed catalyst developed by AECL
- 30. CECE Detritiation Recombiner D2 +½ O2 → D2O Detritiated heavy water product D2O(liq) LPCE column D2O + DT → DTO + D2 Tritiated heavy water DTO(liq) Tritium packaging Ti + DT → TiDT DT D2O(liq) Electrolysis cell DTO →DT + ½ O2 Oxygen gas O2 + D2Ovap Oxygen Vapour Scrubber DTO(vap) + O2 Gas Phase Recombiner D2 + ½O2 →D2O
- 31. Combined Electrolysis andCatalytic Exchange (CECE) • Economical alternative for upgrading of D 2O − − − − Distillation: low separation factor (1.056 at 50°C), large diameter columns (0.1-1.3 m) CECE: high separation factor (2.73 at 60°C), smaller diameter columns (0.15-0.2 m), low emissions − − − − Upgrading: enrich deuterium concentrations from ~0.5% or higher to ≥ 99.8% (reactor grade) Detritiation: Reduce tritium concentrations by a factor of 1010 000 depending on design and requirements • Heavy water management for CANDU reactors
- 32. Combined Industrial Reformingand Catalytic Exchange (CIRCE) Steam-Methane Reforming CH4 + 2H2O ⇒ CO2 + 4H2 Catalytic Exchange HD + H2O ⇒ HDO + H2 H2O H2O 150 ppm D CH4 H2 125 ppm D SMR 100 ppm D Losses 150 ppm D H2 55 ppm D Cataly st Bed CO2 Product 6000 ppm D CH4 100 ppm D SMR CO2
- 33. CECE Detritiation Recombiner D2 +½ O2 → D2O Detritiated heavy water product D2O(liq) LPCE column D2O + DT → DTO + D2 Tritiated heavy water DTO(liq) Tritium packaging Ti + DT → TiDT DT D2O(liq) Electrolysis cell DTO →DT + ½ O2 Oxygen gas O2 + D2Ovap Oxygen Vapour Scrubber DTO(vap) + O2 Gas Phase Recombiner D2 + ½O2 →D2O
- 34. CECE Detritiation DemonstrationSummary • • • • • • • very high DFs achieved easily DF > 50 000 Model validated over a range of DFs from 100 – 50 000 low emissions High process availability and controllability demonstrated by long uninterrupted run CECE should be considered when selecting detritiation technologies (as front-end for CD or as stand-alone) results relevant to detritiation of light water
- 35. Prototype CIRCE Plant(PCP) H2 Product PSA 2 H2 H2O H2O Purifier Vent H 2 City water H2 Bypass Vent O2 Cold LPCE 2 LPCE 1 OVS H2O H2O LPCE 3 Pre-enrich LPCE CO2 H2 CO Removal Hot LPCE 2 H2 H2O Blower Natural Gas SMR & Mods STAGE 1 STAGE 2 E-cell STAGE 3 D2O Product
- 36. Combined Industrial Reforming andCatalytic Exchange (CIRCE) Steam-Methane Reforming Catalytic Exchange CH4 + 2H2O ⇒ CO2 + 4H2 HD + H2O ⇒ HDO + H2 H2O H2 150 ppm D CH4 100 ppm D H2O 150 ppm D H2 55 ppm D 125 ppm D SMR Losses Catalyst Bed CO2 Product 6000 ppm D CH4 100 ppm D SMR CO2
- 37. Process Model Validation DF= 46,000 10000 Liquid Tritium Concentration GBq/kg 1000 Measured Simulation Feed 100 10 1 0.1 0.01 0.001 0 10 20 30 Catalyst Bed Height (m from bottom) 40
- 38. Comparison of G-Svs H2/H2O Processes Girdler - Sulphide (GS): HDO + H2S H2O + HDS Disadvantages: • Highly Toxic and Corrosive • Low D-recovery (< 20%) - thermodynamic and phase limitations • High Energy Requirements (10 kg steam/g of D2O) - phase limitation Advantages: • Relatively Fast Kinetics (No Catalyst Needed) Hydrogen/Water Exchange: HD + H2O H2 + HDO Advantages: • Non Toxic and Non Corrosive • High D-recovery (50-60%) - favourable thermodynamics • No Phase Limitation (except 0°C) Disadvantage: • Slow Reaction Kinetics - requires Pt-based catalyst - catalyst needs to be wetproofed
- 39. D2O Production andProcessing Technologies based on Hydrogen/Water CECE - Combined Electrolysis and Catalytic Exchange - synergistic with production of H 2 by electrolysis - 175 MW plant ⇒ 20 Mg/a D2O - also suitable for heavy water upgrading and detritiation CIRCE - Combined Industrial Reforming and Catalytic Exchange - synergistic with production of H 2 by steam reforming - 2.8 million m3/d H2 or 1500 Mg/d NH3 plants ⇒ - 50-60 Mg/a D2O BHW - Bithermal Hydrogen-Water - stand-alone production - 1500 Mg/h water/steam ⇒ 400 Mg/a
- 40. Heavy Water (99.8%D 2O) Production, Mg/a Effect of Losses on D2O (99.8%) Production 60 2.8 millionmillion Hydrogen Plant 100 m3/day scfd Hydrogen plant 55 50 45 40 35 30 0 0.5 1 1.5 2 Loss of hydrogen species as % of Feed Water Flow 2.5
- 41. Hydrogen Isotope SeparationApplications •Low concentrations – (natural abundance D ~ 1.5x10-4, T ~ 10-17 mole fractions) – large separative work Production of heavy water (>99.8% D2O) for Pressurized Heavy Water Reactors – a new CANDU-6 requires ~ 470 Mg Upgrading of reclaimed heavy water contaminated with light water (0.2 to 99 mol%) to reactor grade (>99.8 mol%) Removal of tritium from contaminated ground water Removal of tritium from the moderator Production of pure tritium gas • • • • •
- 42. Hydrogen-Water Isotope ExchangeReaction Overall Reaction: HD + H2O liq H2 + HDO liq Two-Step Reaction: Catalytic Kinetic Step (requires hydrophobic catalyst): HD + H2O vap HDO vap + H2 Mass Transfer Step (requires hydrophilic surface): HDO vap + H2O liq H2O vap + HDO liq
- 43. Modifications to SMRPlant for CIRCE Adaptation H2 product Feed water PSA #2 H Purifier 2 CIRCE HWP 2 CO Removal H 2 Offgas Compressor H 2 H H2 O Drain B/D Recove ry CH4 Boiler Desulfurizer N 2 N D2O product Flue-gas 2 Vent CO2 Reformer High Temp Shift Low Temp Shift CO CO2 Ads 2 Des PSA #1 Fuel CH4, CO, H2, H2O Baseline SMR Components Recycle Compressor SMR Modifications HWP Components
- 44. Overview of theSMR-PCP at Hamilton,Ont.
- 45. Preferred Chemical Exchange Processes Factor Relative Cost Safety Catalyst Deployment GirdlerSulphide (Employed atBruce) x3 AmmoniaHydrogen WaterHydrogen x2 x1 Very toxic Does not require catalyst Toxic Requires catalyst Largescale Harmless Requires special hydrophobic catalyst Middle-scale Middlescale
- 46. CECE-UD Upgrading Demonstration • Upgradingdemonstration successfully completed >11 Mg of water processed • Feed water containing 1, 10, 50, 90 mol% D2O upgraded to >99.9 mol% D2O • Dual feeds of 97 and 50 mol% D2O and 97 and 10 mol% D2O Upgraded to >99.9% • Deuterium content of overhead product routinely below natural concentrations (≤140 ppm) • Deuterium profiles match model predictions validating design methodology • Catalyst activity maintained over test duration of 18 months
- 47. Prototype/Full-Size Comparison Comparison ofFull-Scale and Prototype Plant Parameters Prototype Full-scale H2 production, (x1000, m3/d) D2O production, Mg/a Number of Stages Losses as % of feed water H2O inventory in SMR, Mg 62 1 3 ~1.0% 10 2 800 55 4 <0.5% 60
- 48. Modifications to SMRPlant for CIRCE Adaptation H2 product Feed water PSA #2 H2 Purifier CIRCE HWP CO Removal Offgas Compressor H2 H2 N2 H2O B/D Recovery Boiler N2 H2 D2O product Flue-gas Vent CO2 Drain CH4 Desulfurizer Reformer High Temp Shift Low Temp Shift CO2 Ads CO2 Des PSA #1 Fuel CH4, CO, H2, H2O Baseline SMR Components Recycle Compressor SMR Modifications HWP Components
- 49. CECE Upgrading Light water O2to vent H2 to vent (D < background) Light water Oxygen Vapour Scrubber H2O + HD →HDO + H2 Downgraded heavy water LPCE column HDO + D2 →D2O + HD Reactor-grade heavy water D2 HDO Return to Process Gas-Phase Recombiner (D2 + ½O2 →D2O) O2 Electrolysis cell D2O → D2 + ½O2 Plus D2O, D2 impurities
- 50. Prototype CIRCE PlantScheme H2 Product PSA 2 H2 H2O H2O Purifier Vent H 2 City water H2 Bypass Vent O2 Cold LPCE 2 LPCE 1 OVS H2O H2O LPCE 3 Pre-enrich LPCE CO2 H2 CO Removal Hot LPCE 2 H2 H2O Blower Natural Gas SMR & Mods STAGE 1 STAGE 2 E-cell STAGE 3 D2O Product
- 51. Prototype CIRCE Plant 1 Mg/aD2O – With 62 000 m3/d SMR – Stage 3 (CECE) enriches to 99.8% D2O – Stage 2 (BHW) to ~8% D2O – Stage 1 enriches from 150 ppm to 6600 ppm
- 52. Prototype CIRCE Plant(PCP) •built in collaboration with Air Liquide Canada in Hamilton •integrated with a new, small 62 000 m3/day PSA-based steam reformer •to operate for at least 2 years (2000-2002) •to be capable of producing ~1 Mg/a of D 2O Primary Goals: •to demonstrate all CIRCE-related technologies and interfaces with the reformer •to confirm robustness of AECL’s proprietary catalyst in an industrial reformed-hydrogen setting
- 53. Summary of CIRCEDemonstration • Industrial demonstration of first-time technology − − − − − CIRCE demonstration highly successful No major problems Integration of SMR and CIRCE problem-free SMR operation never compromised by CIRCE Catalyst proved stable in industrial environments • Next generation technology for D2O production established − Flexible process that is economic on small scale (~ 50 Mg/a D2O) − Costs depend on: • SMR type and design; and • whether new or existing
- 54. SUMMARY • AECL has developedlowest cost, thermodynamically most favourable, hydrogen isotope separation technologies based on catalytic hydrogen/water exchange • AECL’s proprietary wetproofed catalyst has been successfully demonstrated • CIRCE process successfully demonstrated for heavy water production in prototype CIRCE plant • CECE technology successfully demonstrated for upgrading and detritiation in CECE-UD facility and in prototype CIRCE plant
- 55. Technical Highlights ofPCP – contd. • Operability − − − − − Effective control of multiple columns in each of the three stages Demonstrated integration of the bithermal intermediate stage for deuterium enrichment Effective control of L/G ratio using on-line densitometer − − − − − Model validated using plant operation data Accurate prediction of production of full-scale CIRCE plants Reduced design margin for future plants Dynamic model also validated for predicting process transients • Model Validation
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- 58. Norsk Hydro In 1934,Norsk Hydro built the first commercial heavy water plant with a capacity of 12 tons per year at Vemork. During World War II, the Allies decided to destroy the heavy water plant in order to inhibit the Nazi development of nuclear weapons. In late 1942, a raid by British paratroopers failed when the gliders crashed and all the raiders were killed in the crash or shot by the Gestapo . In 1943, a team of Britishtrained Norwegian commandos succeeded in a second attempt at destroying the production facility, one of the most important acts of sabotage of the war.
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- 77. HWP Arak, IRAN 2902 2004
- 78. HWP Arak, IRAN 1702 2005
- 79. HWP Arak, IRAN 2702 2005
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