Download - Heavy water production
HEAVY WATER PRODUCTION
Dr. Gheorghe VASARUAleea Tarnita, Nr 7, Apt. 11
CLUJ-NAPOCA, [email protected]
Hydrogen Isotopes
HI
Water Molecule
WM
H2O and D2O Molecules
Tritium Atom
Deuterium is a stable but 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.
Heavy Water (HW)
Heavy Water 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.
Heavy water or deuterium oxide (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.
Nuclear Fission Process in HW
PHWR
PHWR
HWR
CANDU PHWR
CANDU World Map
Reactor Types
Nuclear Fusion
NF
ITER
HW Separation by Thermal Diffusion
Heavy Water’s low absorption
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.
In the past all 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-to-hydrogen). For bulk commercial production, the primary extraction process to date, the "Girdler-Sulphide (G-S)" process, exploits the temperature-dependence 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.
In a multistage process
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.
During operation
a CANDU plant 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.
The GS process,
while capable 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.
AECL is currently working 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.
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 (up-front) cost more competitive.
Heavy water has an 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
Old Technology and New
WaterDistillation
finisher85 m high
0.4 m diam.
G-S technologyH2S + H2O
300 m of total tower height7 m in diam.
CECEfinisher25 m high
0.15 m diam.
for samescale
1970s CIRCE technologyH2 + H2O
75 m of tower height2.5 m diam. for same scale
2000s
Old Technology and New
Water Distillation
finisher 85 m high
0.4 m diam.
G-S technology H2S + H2O
300 m of total tower height 7 m in diam.
CECE finisher 25 m high
0.15 m diam.
for same scale
1970s CIRCE technology H2 + H2O
75 m of tower height 2.5 m diam. for same scale
2000s
AECL’S Isotope Separation Technology 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, trickle-bed catalyst developed by AECL
CECE Detritiation
Electrolysis cell DTO DT + ½ O2
Recombiner D2 + ½ O2 D2O
Detritiated heavy water product
Tritiated heavy water
Oxygen gas
LPCE column D2O + DT DTO + D2
Tritium packaging Ti + DT TiDT
O2 + D2Ovap
DTO(vap) + O2
Oxygen Vapour Scrubber
D2O(liq)
D2O(liq)
DT DTO(liq)
Gas Phase Recombiner D2 + ½O2 D2O
Combined Electrolysis and Catalytic Exchange (CECE) Economical alternative for upgrading of D2O
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
Heavy water management for CANDU reactors Upgrading: enrich deuterium concentrations from ~0.5% or higher to 99.8% (reactor grade) Detritiation: Reduce tritium concentrations by a factor of 10- 10 000 depending on design and requirements
Combined Industrial Reforming and Catalytic Exchange (CIRCE)
SMR
SMR
Catalyst
Bed
CO2
CO2
Losses
CH4
CH4
H2O H2
H2O H2
100 ppm D
125 ppm D
150 ppm D
100 ppm D
150 ppm D
55 ppm D
Product 6000 ppm D
Catalytic Exchange HD + H2O HDO + H2
Steam-Methane Reforming CH4 + 2H2O CO2 + 4H2
CECE Detritiation
Electrolysis cellDTO DT + ½ O2
RecombinerD2 + ½ O2 D2O
Detritiatedheavy water product
Tritiatedheavy water
Oxygen gas
LPCE columnD2O + DT DTO + D2
TritiumpackagingTi + DT TiDT
O2 + D2Ovap
DTO(vap) + O2
OxygenVapourScrubber
D2O(liq)
D2O(liq)
DTDTO(liq)
Gas PhaseRecombinerD2 + ½O2 D2O
CECE Detritiation Demonstration Summary
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
Prototype CIRCE Plant (PCP)PSA
2
Purifier
City waterVent H2
D2OProduct
H2
Product
CORemoval
H2
Pre-enrichLPCE
LPCE1
ColdLPCE
2
HotLPCE
2
Blower
LPCE3
E-cell
OVS
H2O
Vent O2
STAGE 1 STAGE 2 STAGE 3
H2O
SMR&
ModsNatural
Gas
CO2
H2O
H2
H2O
H2
H2
Bypass
H2O
Combined Industrial Reforming and Catalytic Exchange (CIRCE)
SMR
SMR
CatalystBed
CO2
CO2
Losses
CH4
CH4
H2O H2
H2O H2
100 ppm D
125 ppm D150 ppm D
100 ppm D
150 ppm D 55 ppm D
Product6000 ppm D
Catalytic Exchange
HD + H2O HDO + H2
Steam-Methane Reforming
CH4 + 2H2O CO2 + 4H2
Process Model ValidationDF = 46,000
0.001
0.01
0.1
1
10
100
1000
10000
0 10 20 30 40Catalyst Bed Height (m from bottom)
Liq
uid
Tri
tiu
m C
on
cen
trat
ion
GB
q/k
g
MeasuredSimulationFeed
Comparison of G-S vs 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 0C) Disadvantage: • Slow Reaction Kinetics - requires Pt-based catalyst - catalyst needs to be wetproofed
D2O Production and Processing Technologies based on Hydrogen/Water CECE - Combined Electrolysis and Catalytic Exchange - synergistic with production of H2 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 H2 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
Effect of Losses on D2O (99.8%) Production
30
35
40
45
50
55
60
0 0.5 1 1.5 2 2.5
Loss of hydrogen species as % of Feed Water Flow
Hea
vy W
ater
(99
.8%
D2O
) P
rod
uct
ion
, Mg
/a100 million scfd Hydrogen plant2.8 million m3/day Hydrogen Plant
Hydrogen Isotope Separation Applications
•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
Hydrogen-Water Isotope Exchange Reaction 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
Modifications to SMR Plant for CIRCE Adaptation
H2 product
Desul- furizer
Reformer Low Temp Shift
PSA #1
Recycle Compressor
CIRCE HWP
Purifier Feed water
Fuel
D2O product Flue-gas
Vent CO2
CO Removal
H2
O
H2
CO2 Ads
CO2
Des
HWP Components
SMR Modifications
Baseline SMR Components
PSA #2
Offgas Compressor
CH4, CO, H2, H2O
H2 N2
H2
CH4
High Temp Shift
N2
H2
B/D Recove
ry
Boiler
Drain
Overview of the SMR-PCP at Hamilton,Ont.
Preferred Chemical Exchange Processes
Factor Girdler-Sulphide (Employe
d at Bruce)
Ammonia-Hydrogen
Water-Hydrogen
Relative Cost
x3 x2 x1
Safety Very toxic
Toxic Harmless
Catalyst Does not require catalyst
Requires catalyst
Requires special
hydrophobic catalyst
Deployment
Large-scale(400 Mg/a)
Middle-scale
(50 Mg/a)
Middle-scale
(50 Mg/a)
Existing plants
India, Romania
Argentina (mothballed
)India
None
CECE-UD Upgrading Demonstration
Upgrading demonstration 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
Prototype/Full-Size Comparison
Comparison of Full-Scale and Prototype Plant Parameters
60 10 H2O inventory in SMR, Mg
<0.5% ~1.0% Losses as % of feed water
4 3 Number of Stages
55 1 D2O production, Mg/a
2 800 62 H2 production, (x1000, m3/d)
Full-scale Prototype
Modifications to SMR Plant for CIRCE Adaptation
H2 product
Desul-furizer
Reformer Low TempShift
PSA#1
RecycleCompressor
CIRCEHWP
PurifierFeed water
Fuel
D2O productFlue-gas
Vent CO2
CORemoval
H2O
H2
CO2
Ads
CO2
Des
HWP Components
SMR Modifications
Baseline SMR Components
PSA#2
OffgasCompressor
CH4, CO, H2, H2O
H2
N2
H2
CH4
HighTempShift
N2
H2
B/DRecovery
Boiler
Drain
CECE Upgrading
Downgradedheavy water
Reactor-gradeheavy water
O2
H2 to vent(D < background)
Electrolysis cellD2O D2 + ½O2
LPCE column
HDO + D2 D2O + HD
Light waterO2 to vent
Oxygen VapourScrubber
Gas-PhaseRecombiner
Plus D2O, D2 impurities
Light water
HDO Returnto Process
H2O + HD HDO + H2
D2
(D2 + ½O2 D2O)
Prototype CIRCE Plant SchemePSA
2
Purifier
City waterVent H2
D2OProduct
H2
Product
CORemoval
H2
Pre-enrichLPCE
LPCE1
ColdLPCE
2
HotLPCE
2
Blower
LPCE3
E-cell
OVS
H2O
Vent O2
STAGE 1 STAGE 2 STAGE 3
H2O
SMR&
ModsNatural
Gas
CO2
H2O
H2
H2O
H2
H2
Bypass
H2O
Prototype CIRCE Plant
1 Mg/a D2O – 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
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 D2O 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
Summary of CIRCE Demonstration
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
SUMMARY
AECL has developed lowest 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
Technical Highlights of PCP – 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 Validation 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
HW Ice Cubes
HW Storage Tank
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 British-trained Norwegian commandos succeeded in a second attempt at destroying the production facility, one of the most important acts of sabotage of the war.
HWP Vermork, Rjukan, NORWAY
HW Factory, Rjukan, NORWAY
HWP Rjukan, Norway
Rjukane
HWP - ARGENTINA
NH3-H2, Argentina
HWP Arroyito, BRASIL
3
HWP Arroyito, BRASIL
1
HWP Arroyito, BRASIL
2
HWP Arroyito, BRASIL
GS HW-Towers
CIRCE, Hamilton, CANADA
Bruce 3, CANADA
INDIA - Nuclear
HWP, INDIA
IRAN Nuclear Plan
IRAN Fuel Cycle
IRAN, Natanz
IRAN - Esfahan
HWP Arak, IRAN
29 02 2004
HWP Arak, IRAN
17 02 2005
HWP Arak, IRAN
27 02 2005
HWP Khushab, PAKISTAN
1
HWP Khushab, PAKISTAN
2
RAAN, ROMANIA
D20+H2S <> H2O+D2S
HWP Halanga, ROMANIA
1
HWP Halanga,ROMANIA
2
Vawe
Val