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

CANDU PHWR

CANDU World Map

Reactor Types

Nuclear Fusion

NF

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.

http://www.nuclearfaq.ca/hvywtr.jpg

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.

http://www.nuclearfaq.ca/CIRCE_hamilton.jpg

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.

http://www.nuclearfaq.ca/#ngcandu

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

http://www.nuclearfaq.ca/cnf_sectionI.htm#gg3

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


1


2

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