6. 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.
7. 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.
8. 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.
19. 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.
20. 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-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 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.
22. 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.
23. 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.
24. 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.
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 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
27. Old Technology and New
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 and New
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 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, 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 and Catalytic 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 Reforming and
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 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
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
and Catalytic 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-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 0°C)
Disadvantage:
• Slow Reaction Kinetics
- requires Pt-based catalyst
- catalyst needs to be wetproofed
39. D2O Production and Processing 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 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
•
•
•
•
•
43. Modifications to SMR Plant 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
46. 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
47. Prototype/Full-Size Comparison
Comparison of Full-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 SMR Plant 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
O2 to 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 Plant Scheme
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/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
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 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
54. 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
55. 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 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
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.
