Nuclear Engineering Panel Technical Seminar
Thorium Reactors - Advantages and Challenges
Date: Wednesday 28 November 2012 Time: 5.30 pm for 6.00 pm Venue: Engineers Australia Harricks Auditorium,
Ground Floor, 8 Thomas St, Chatswood
Speaker: Dr John Harries, Australian Nuclear Association
Thorium is a little used nuclear energy source, in some ways perhaps cleaner and safer than uranium. The thorium fuel cycle has some advantages over uranium: thorium is more abundant than uranium, needs no enrichment, produces less long- lived radioactive waste and is a lower proliferation risk. But there are challenges: a thorium reactor needs much better neutron economy as each thorium atom requires two neutrons to fission and there are issues relating to fuel fabrication and management because of the high radiation dose from new fuel made from irradiated thorium. This talk will examine the history of thorium reactors; discuss reasons why there are so few thorium fuelled reactors today and look at new designs for thorium reactors proposed and prototypes now being built.
About the presenter: Dr John Harries is a physicist with extensive experience on the physics of nuclear reactors, radioactive waste management, the environmental effects of mining, environmental management and nuclear policy issues. He was a senior principal research scientist at the Australian Nuclear Science and Technology Organisation (ANSTO) and Acting Director of ANSTO Environment Division in 1998 and in 2003. At ANSTO, he worked on the physics of reactors, the management of radioactive waste and nuclear policy issues. He was leader of a project responsible for environmental management at the ANSTO nuclear research reactor site and of an R&D project investigating radioactivity in the environment. He is immediate Past President and currently Secretary of the Australian Nuclear Association and a consultant on nuclear issues.
Thorium Thorium –– Advantages and Advantages and
Challenges?Challenges? [& molten salt reactors][& molten salt reactors]
John Harries
28 November 2012
© John Harries © John Harries 20122012
New Age NuclearNew Age Nuclear Cosmos Magazine, Issue 8, April 2006
by Tim Dean
What if we could build a nuclear reactor that offered
no possibility of a meltdown, generated its power
inexpensively, created no weapons-grade by-
products, and burnt up existing high-level waste as
well as old nuclear weapon stockpiles? And what if
the waste produced by such a reactor was
radioactive for a mere few hundred years rather than
tens of thousands? … What makes this incredible
reactor different is its fuel source: thorium.
Could thorium help nuclear power clean Could thorium help nuclear power clean
up its act?up its act? Dan Warne
APC Magazine 20 Jan 2010
… growing worldwide interest in the use of an alternative
nuclear fuel promises a cleaner, more efficient method of
producing electricity without the toxic waste legacy of
today’s nuclear power plant
Uranium Is So Last Century Uranium Is So Last Century —— Enter Enter
Thorium, the New Green NukeThorium, the New Green Nuke
Richard Martin
Wired Magazine 21 Dec 2009
Published July 2012 Published May 2012
Factory-manufactured
LFTRs can produce
energy 40% cheaper
than coal, and
80% cheaper than wind
or solar energy.
… thorium …a low
risk nuclear energy
source to power our
planet.
Thorium Thorium –– What is it?What is it?
• A naturally occurring radioactive element
• Discovered in 1828 and named in honour of
Thor, the Norse god of thunder
• Found solely as thorium-232, half life 1.4x1010
years – a primordial isotope
- about 3 times age of earth
- about 3 to 5 times as abundant
as uranium
- thorium occurs as monazite
• Metal melting point 1750C
- Oxide melting point 3300C http://www.periodictable.com/Elements/090/index.html
Source: http://pubs.usgs.gov/of/2004/1050/thorium.htm
Tl-208 decays emit
2.6 MeV gamma
64 % 36 %
Estimated Thorium Resources 2007 Estimated Thorium Resources 2007 Country Tonnes % of total
Australia 489,000 19
USA 400,000 15
Turkey 344,000 13
India 319,000 12
Venezuela 300,000 12
Brazil 302,000 12
Norway 132,000 5
Egypt 100,000 4
Russia 75,000 3
Others 141,000 5
World total 2,610,000
(Reasonably assured and inferred resources recoverable at up to $80/kg Th)
Uranium 2007: Resources, Production and Demand, Nuclear Energy Agency (June 2008)
Estimated Thorium Resources 2011 Estimated Thorium Resources 2011
Country Tonnes % of Total
India 846,000 16
Turkey 744,000 14
Brazil 606,000 11
Australia 521,000 10
USA 434,000 8
Egypt 380,000 7
Norway 320,000 6
Venezuela 300,000 6
Canada 172,000 3
Other Countries 1,062,000 20
World Total 5,385,000
Uranium 2011: Resources, Production and Demand, OECD NEA & IAEA (Aug 2012)
Data quoted by World Nuclear Association (http://world-nuclear.org/info/inf62.html)
Thorium Fuel CycleThorium Fuel Cycle
- -
t½ = 22 m t½ = 27 d t½ = 1.6 x 105 y
fissile
Th-232 + n Th-233 Pa-233 U-233
U-233 +n fission products + neutrons
t½ = 1.4 x 1010 y
2.3 neutrons per neutron absorbed
at thermal energies
Thorium -232 is fertile, absorbs a neutron to produce
Uranium-233 which is fissile
Thorium-232 fission requires 2 neutrons to maintain chain reaction
then:
Uranium-233 production delayed with t½ = 27 days
Thorium Thorium –– Advantages (1)Advantages (1)
• Thorium is more abundant that uranium
- Th in crustal rocks is 3.6x more abundant than U
- energy content of known thorium reserves immense
• Thorium compounds are very stable
- very high burnup fuels can be manufactured
- suitable for high temperature reactors
• ThO2 more stable and has higher radiation
resistance than UO2
• fission product release from fuel lower
• ThO2 does not oxidise like UO2 (oxidises to U3O8)
• disposal simpler
Thorium Thorium -- Advantages (2)Advantages (2)
• Thorium-232 is a better fertile material than U-
238
- thermal neutron absorption almost 3x more likely than
U-238
• U-233 releases more neutrons per neutron
absorbed that U-235
- non-fissile absorption in U-233 less than for U-235
• hence less production of higher isotopes
thermal breeder possible
Neutron yield per neutron absorbed
U-233 η ~ 2.3
higher than U-
235 and Pu-239
At high energies
i.e fast reactors η for
Pu-239 much higher
than U-233
For breeding
η must be > 2
Thermal neutrons <1 eV Fast neutrons > 0.1 MeV
Thorium Thorium -- Advantages (3)Advantages (3)
• Only one naturally occurring isotope Th-232
- no enrichment needed
• Spent fuel from the thorium fuel cycle contains
much less long-lived actinides in waste than
U-235/U238 cycle
- Th-232 requires 7 neutrons to produce Pu-239,
whereas U238 requires only 1 neutron
- transuranic actinides (mainly Np-237 and Pu-238)
recycled in LFTR
- production of Pu in LFTR about 12x less than LWR
• U-233 from thorium fuel cycle is proliferation
resistant due to presence of U-232
Z
N
UraniumUranium--232232
• U-232 is a contaminant in the U-233 from a thorium
fuelled reactor
- produced by (n,2n) reaction on U-233, Pa-233 & Th-232
• U-232 (t½ = 72 y) has a 2.6 MeV gamma from
Tl-208 daughter product in the decay chain
- high gamma radiation from high-burnup fuel
- remote handling for even unirradiated fuel before it goes
in the reactor
• Advantage: provides proliferation resistance
• Disadvantage: extra cost to make and handle fuel
Thorium Thorium –– Challenges (1)Challenges (1)
• Thorium is fertile, not fissile
- needs to absorb a neutron to breed uranium-233,
hence required driver of U-235, Pu-239 or U-233
- reprocessing an integral part of thorium fuel cycle
• Protactinium-233 (t½ = 27 d) effect
- the U-233 continues to be produced long after
shutdown causing a positive reactivity change
- requires longer cooling time of at least a year to
complete decay of Pa-233 to U-233
• Data and experience with thorium fuels and
thorium fuel cycle limited
Thorium Thorium –– Challenges (2)Challenges (2)
• Presence of Uranium-232 in spent fuel
- decay chain emits hard 2.6 MeV gammas
- U-233 fuel production requires remote handling
• In reprocessing solid thorium fuel, ThO2
dissolution is harder than UO2
- ThO2 melting point 3350 C verses 2800C for UO2
- not a factor in molten salt fuelled reactors
Reactors suitable for ThoriumReactors suitable for Thorium
• Heavy Water Reactors (PHWRs)
- thermal neutrons, very good neutron economy
• High Temperature Gas-Cooled Reactors (HTR)
- thermal neutrons, thorium stable at high temps
• Molten Salt and Molten Salt Cooled reactors
- thermal neutrons, good neutron economy, high temps
• Fast Reactors
- Th can be used as fuel to produce U233, but U238 is
better fuel in fast reactors
Historic Use of Thorium FuelHistoric Use of Thorium Fuel
• Molten Salt Reactor
- 1965-69 MSRE (7.4 MWth) USA
• High Temperature Gas Cooled Reactors (HTGRs)
- 1966-75 Dragon (20 MWth) UK
- 1967-74 Peach Bottom (40 MWe) USA
- 1968 AVR (15 MWe) Germany
- 1976 Fort St Vrain (330 MWe) USA
- 1985 THTR (300 MWe) Germany
• Pressurised Water Reactors (PWR
- 1977-82 Shippingport ( 60 MWe) USA
- 1970s Commercial PWRs USA
Molten Salt Reactor ExperimentMolten Salt Reactor Experiment
• Operated at Oak Ridge, USA, 1965-69
- 7.4 MW, graphite moderated, core diameter 1.4 m
• Fuel: fluorides of lithium-7,
beryllium, zirconium and U
- melting temp 434C
- secondary coolant:
fluorides of lithium-7
and beryllium (FLiBe)
• Jun 1965 critical on U-235
• Oct 1968 critical on U-233
- first reactor to operate on
U-233 Haubenreich & Engel 1970
1. Reactor Vessel
2. Heat Exchanger
3. Fuel Pump
4. Freeze Flange
5. Thermal Shield
6. Coolant Pump
7. Radiator
8. Coolant Drain Tank
9. Fans
10.Fuel Drain Tanks
11.Flush Tank
12.Containment Vessel
13.Freeze Valve
Molten Salt Reactor Experiment ORNL
1964-1969
A top down view of the Molten Salt Reactor ExperimentA top down view of the Molten Salt Reactor Experiment
http://energyfromthorium.com/2011/10/04/flibe-uk-4/
http://upload.wikimedia.org/wikipedia/commons/a/ae/FLiBeSolidandMelted.gif
Molten Salt Reactor ExperimentMolten Salt Reactor Experiment
• Demonstrated molten salt reactor was viable.
- operated for equivalent of 1.5 years full power
- fuel salt was immune to radiation damage, and graphite
not attacked by fuel salt
- only single fluid reactor, heat released from radiators
- no thorium and no breeding
• Issues identified: radiation hardening, tritium
production and tiny cracks inside the piping were
identified as requiring further development
- solutions subsequently found
Conceptual Molten Salt BreederConceptual Molten Salt Breeder
• 1000 MWe reactor conceptual design developed at
Oak Ridge National Laboratory 1970-76
- technology based on successful MSRE project
• MSR development cancelled in 1976
- heavy commitment to liquid metal fast breeder reactor
• Clinch River Breeder Reactor, which was designed
and sited but never built
- molten salt technology waste considered a backup
competing technology
- also political and technical support too thin
geographically
Historic Use of Thorium FuelHistoric Use of Thorium Fuel
• Molten Salt Reactor
- 1965-69 MSRE (7.4 MWth) USA
• High Temperature Gas Cooled Reactors (HTGRs)
- 1966-75 Dragon (20 MWth) UK
- 1967-74 Peach Bottom (40 MWe) USA
- 1968 AVR (15 MWe) Germany
- 1976 Fort St Vrain (330 MWe) USA
- 1985 THTR (300 MWe) Germany
• Pressurised Water Reactors (PWR
- 1977-82 Shippingport ( 60 MWe) USA
- 1970s Commercial PWRs USA
Thorium in Thorium in HTGRsHTGRs
• High Temperature Gas Cooled Reactors
- graphite moderated, helium coolant
- fuel in small coated microspheres (<1 mm diam)
• microspheres then in graphite blocks (prismatic)
or in billiard ball size spheres
(pebble bed)
• Thorium used as fuel the early
HTGRs
- BUT always with highly
enriched Uranium (HEU)
Peach Bottom HTR, 40 MWe, 1967-1974
Experimental helium-
cooled, graphite-
moderated reactor.
Th-HEU fuel
microspheres
embedded in graphite
First HTGR to
produce electricity
Fort Saint Vrain High Temperature Gas Cooled (HTGR) Reactor, 330 MWe
https://netfiles.uiuc.edu/
Operated 1977-1992, Colorado USA
Primary coolant helium, fuel a combination of
fissile uranium and fertile thorium
microspheres dispersed within a prismatic
graphite matrix
Very high burnup: Th-232 converted to U-233
for fission without removal from core
Pebble bed reactor: TRISO
microspheres in 6 cm pebbles
.
Over half the 674,000 pebbles
contained Th-HEU fuel particles
(the rest graphite moderator and
some neutron absorbers).
Pebbles continuously moved
through core, each pebble passed
through core about six times.
THTR was closed down due to
technical difficulties with flow of
pebbles and radioactive dust after
only three years
Thorium High Temperature Reactor (THTR), 300 MWe,1983-1989 Hamm, Germany
Historic Use of Thorium FuelHistoric Use of Thorium Fuel
• Molten Salt Reactor
- 1965-69 MSRE (7.4 MWth) USA
• High Temperature Gas Cooled Reactors (HTGRs)
- 1966-75 Dragon (20 MWth) UK
- 1967-74 Peach Bottom (40 MWe) USA
- 1968 AVR (15 MWe) Germany
- 1976 Fort St Vrain (330 MWe) USA
- 1985 THTR (300 MWe) Germany
• Pressurised Water Reactors (PWR)
- 1977-82 Shippingport ( 60 MWe) USA
- 1970s Commercial PWRs USA
Shippingport Atomic Power Station
60 MWe Light Water Reactor, 1957- 1982
“First full scale nuclear power plant devoted exclusively to peace time uses”
Third core (1977-1982) an experimental thermal breeder reactor
Third core:
fuel pellets thorium dioxide and
U-233 oxide.
initial 5.6% in U233 in seed
region, 1.5-3% in the blanket
and none in reflector.
When core removed after five
years it contained nearly 1.4%
more fissile material than when
it was installed.
Thorium in USA LWR ReactorsThorium in USA LWR Reactors
• Shippingport LWR
- Demonstrated the light water breeder reactor concept
• used Th and U-233 in seed/blanket configuration
• In 1970s thorium used in a number of
commercial reactors in USA for production of
U-233.
- U-233 manufactured in Indian Point I reactor N.Y. and
at reactors in Colorado, Illinois and Pennsylvania
UU--233 Stockpile in USA233 Stockpile in USA
• USA stockpile of U-233 produced from Th-232
- 805 kg in separated form of which 607 kg is high
isotopic purity (ORNL-6952, Sept 1999)
- 904 kg in spent nuclear fuel and targets
- U-233 was investigated for use in nuclear weapons
and as a reactor fuel; however, it was never deployed
in nuclear weapons or used commercially as a
nuclear fuel
• October 2012, US Dept Energy announced
proposed disposal of U233 stockpile at cost of
US$473 million
Molten Salt Reactors (MSR)Molten Salt Reactors (MSR)
• MSR concept now being updated
• MSR don’t have to be breeders, or be limited to a
thorium cycle.
- without fuel processing, MSRs can run as simple
converters with excellent uranium utilization even on a
once-through cycle.
• Molten salt fuelled and molten salt cooled reactors
enthusiastically proposed for thorium
Advantages of Molten Salt ReactorsAdvantages of Molten Salt Reactors
• Advantages:
- low pressure, high temperatures
- large negative temp and void reactivity coefficients
- no large and expensive pressure vessel
- suitable alloys allow operation to 700 C
• Challenges
- design to avoid coolant freezing “freezing event”
- higher temperatures desirable but materials for higher
temperatures not yet validated
- no experience with production scale reactors
- controlling corrosion in molten salt fuelled systems
Molten Salt Reactors Molten Salt Reactors
• Molten Salt Reactor based on ORNL prototype
- fuel fluorides in the molten salt (e.g FLiBe)
- lithium must be enriched in Li-7 (99.995% Li-7)
- tritium must be continually removed
- corrosion issues from U and fission products in salt
- fissile materials must not separate on cooling
• Molten Salt Cooled Reactors, also known as Fluoride-
salt-cooled High-temperature Reactors (FHR)
- molten salt coolant (FLiBe) but solid fuel (pebbles or
prismatic
- “clean molten salt” so corrosion very low
Molten Salt Reactors with ThoriumMolten Salt Reactors with Thorium
• Liquid Fluoride Thorium Reactor (LFTR)
- based on ORNL prototype
- two fluid reactor
• high-neutron-density core that burns U-233 from
the thorium fuel cycle
• separate blanket of thorium salt absorbs the
neutrons and eventually is transmuted to U-233
fuel
• Doubling times typically 40-60 years
- after start up phase using Pu and minor actinides
Current & Proposed Thorium ReactorsCurrent & Proposed Thorium Reactors
• India
- long-term three stage program for thorium fuel cycle
• China
- 2 MW experimental molten salt reactor to be built in
Shanghai
- assessing use of Th fuels in CANDU 6 reactors
- demonstration high temperature pebble bed reactor
210 MWe being built in Shandong
• USA
- studies of molten salt reactors
Indian Nuclear Power ProgramIndian Nuclear Power Program
The three stages:
1. Natural uranium fuelled Pressurised Heavy Water
Reactors (PHWRs)
• 18 PHWR in operation and 2 BWR
• produces plutonium
2 Fast Breeder Reactors (FBRs) using Pu fuel
• 500 MWe prototype fast breeder under construction
at Kalpakkam with Th and U blanket
• to produce U-233
3 Advanced Heavy Water Breeder Reactors under
development using U-233 and Th to breed U-233
http://defenceforumindia.com/forum/strategic-forces/207-indias-fast-breeder-reactor-thorium-tritium-heavy-water-program-13.html
Current use of Thorium in IndiaCurrent use of Thorium in India
• PHWRs in India
- use thorium-bearing fuel bundles for power flattening
• Research reactor Kamini (Kalpakkam, India)
- 30 MWth using U-233 (600 g) in Al plates since 1996
- The only U-233 fuelled reactor in world
- U-233 produced in adjacent Fast Breeder Test Reactor
• Fast Breeder Test Reactor (FBTR), Kalpakkam
- 30 MWth operating since 1985
- uses plutonium/uranium mixed carbide fuel and sodium
coolant
• Prototype Fast Breeder Reactor 500 MWe
- expected to be commissioned in 2013
Indian Fast Breeder Reactor 500 MWe under construction at Kalpakkam, near Chennai, India
Main Vessel being installed Dec 2009
Thorium/UThorium/U--233 Cycle233 Cycle
• Doubling time for breeding U-233 is 50-100 y
- thorium reactors need to be started with U-235 or Pu
- thorium reactors can be self sustaining once started with
sufficient U233
• Indian program requires fast reactors to generate
enough plutonium to start thorium reactors
- full deployment of thorium reactors not until 2050
Current & Proposed Thorium ReactorsCurrent & Proposed Thorium Reactors
• India
- long-term three stage program for thorium fuel cycle
• China
- 2 MW experimental molten salt reactor to be built in
Shanghai
- assessing use of Th fuels in CANDU 6 reactors
- demonstration high temperature pebble bed reactor
210 MWe being built in Shandong
• USA
- studies of molten salt reactors
Molten Salt Reactor Project in ChinaMolten Salt Reactor Project in China
• Chinese Academy of Sciences (CAS) launched
“Advanced Fission Energy Program” in Jan 2011
- TMSR R&D at Shanghai Institute of Applied Physics
- 2 MW pebble-bed fluoride salt cooled reactor (with
thorium-uranium alternate once through fuel cycle ~2017)
- 2 MW Molten Salt Reactor (with thorium-uranium
modified open fuel cycle (~2020)
• thorium molten salt reactor (TMSR)
• largest national program on LFTR
- $350m committed for 5 years
- TMSR staff to double from 334 to 750 by 2015
Use of Thorium in Use of Thorium in CanduCandu ReactorsReactors
• Candu Energy signed agreement with China
National Nuclear Corp in July 2009 to
- to jointly develop and demonstrate the use of thorium
fuel, and
- to study the commercial and technical feasibility of its
full-scale use in Candu units
- AECL has developed and irradiated Th fuels
• Two 728 MWe Candu 6 units are in operation at
the Qinshan Phase III plant
Fuji Molten Salt Reactor, JapanFuji Molten Salt Reactor, Japan
• Design for molten-salt-fuelled thorium fuel
cycle thermal breeder reactor
- technology similar to ORNL molten salt reactor
- consortium between Japanese company International
Thorium Energy & Molten-Salt Technology (IThEMS),
together with partners from the Czech Republic
• Doubling time
- too long in fission reactors (~20 years at best)
- proposed an associated spallation accelerator system
to breed the U-233
• Consortium was seeking $300m for 10 MWe
MiniFUJI
US Department of EnergyUS Department of Energy
• University Integrated Research Project from DOE
- US$7.5 million 3-year project to develop a path forward
to a commercially viable FHR
- MIT, U California , U Wisconsin
- Westinghouse advisory role
• FHR
- coated-particle fuel
- high temperature reactor
- primary system in secondary tank filled with salt
- air Brayton cycle
- test materials in MIT research reactor
Other Molten Salt ResearchOther Molten Salt Research
• United States and Czech Republic announce
Bilateral Nuclear Energy Research and
Development Efforts (Sept 29, 2011)
- Molten Salt Reactor Coolant Salt Reactivity
Experiments one of 5 areas of cooperation
- USDOE gives salt coolant from earlier MSRE for use
in molten salt test loop at Řež Nuclear Research
Institute, Czech Republic
Other Thorium & MSR Other Thorium & MSR InitiativesInitiatives
• MSR one of 6 options for Gen IV reactors
• Flibe Energy in USA
- proposes 40 MWe MSR pilot plant for US Army
• Kirk Sorensen Energy from Thorium blog
• Thorium Energy Generation Pty. Limited (TEG)
- Australian company supporting accelerator driven sub-
critical (ADS) systems for thorium and waste elimination
- consortium with Czech companies
• Grenoble, France – investigation of MSFR
• Norway, Thor Energy – thorium MOX fuel tests
Thorium a wonder fuel?
Liquid Fluoride Thorium Reactor (LFTR)
potential advantages
over existing uranium power reactors
similar to 1965-69 MSRE reactor at ORNL
a Gen IV reactor type
fertile not fissile,
hence used to breed
uranium-233
historically
1960-70s
thorium fuel cycle lost out to uranium reactors and U/Pu breeders
India pursuing a thorium fuel cycle
program because lack of uranium
much less long lived
actinides in waste
very stable
no enrichment
Molten Salt Reactor
Experiment (1965-69)
7.4 MWth reactor, ORNL
Th used usually with
HEU driver
recent renewed interest in
thorium fuel cycle
ConclusionConclusion
• Thorium is a large and unused source of energy
- low cost of U still a disincentive to Thorium use
• New strong interest in Th/U-233 cycle
• Also renewed interest in Molten Salt Reactors
- potential to breed U-233 from Th
- China to build a MSR experimental reactor
- Gen IV program includes study of MSR
• Only current use of Th in heavy water reactors
• Much work needed before commercial power using
thorium/U233 fuel cycle becomes a reality