Thorium Reactors - Advantages and Challenges

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



- 1965-69 MSRE (7.4 MWth) USA







• Pressurised Water Reactors (PWR



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



- 1965-69 MSRE (7.4 MWth) USA







• Pressurised Water Reactors (PWR)



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

Documents

Thorium Reactors - Advantages and Challenges