thorium reactors
TRANSCRIPT
Thorium Reactors
An alternative to the Uranium fuel cycle
The Thorium Fuel Cycle
Th-232Neutron
captureTh-233 β
−decay
Pa-233β−
decayU-233Fission
Fission
Neutrons
Advantages of Thorium
Uranium Thorium
Known Reserves [1] 5,902,500 tonnes 6,355,000 tonnes
Abundance in the Earth’s Crust [2] 2.8 ppm 10.7 ppm
Isotopic abundance U-235 – 0.72% U-238 – 99.27% [3] Th-232 – 100%
Relative Abundance
Advantages of Thorium
Nuclear Properties
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
100000
1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08
σ/
barn
s
Energy / eV
Fission and Neutron absorption cross sections of U-233 and U-235 U-233(N,G) U-233(N,F) U-235(N,G) U-235(N,F)
Data from the NNDC’s ENDF
Advantages of Thorium
Nuclear Properties
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08
σ/
barn
s
Energy / eV
Neutron absorption cross sections of Th-232 and U-238 Th-232(N,G) U-238(N,G)
Data from the NNDC’s ENDF
Advantages of Thorium
Nuclear Properties
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
100000
1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08
σ/
barn
s
Energy / eV
Fission and Neutron absorption cross sections of U-233 and Pu-239 U-233(N,G) U-233(N,F) Pu-239(N,G) Pu-239(N,F)
Data from the NNDC’s ENDF
Advantages of Thorium
U-233 U-235 Pu-239
Thermal Fast Thermal Fast Thermal Fast
ν 2.5 2.6 2.4 2.5 2.9 3.0
α 0.1 0.1 0.2 0.25 0.4 0.2
η-1 1.28 1.32 1.06 1.01 1.12 1.40
Nuclear Properties
ν = mean number of neutrons per fissionα = σc
f / σf - the capture to fission ratioη = number of neutrons produced per neutron absorbed in the fuel.
Advantages of Thorium
Material Properties of Th02 vs U02
• More chemically stable – preferred 4+ valence state vs 6+
• Higher melting point and thermal conductivity
• Lower thermal expansion
• Higher radiation damage resistance [4]
Advantages of Thorium
Non Proliferation
• Production of U-233 also creates U-232
• Decays to Th-228 and enters the Th-232 decay chain
• Daughter product Th-208 produces 2.6 MeV γ-ray
• Shielding problem and easily detectable
Disadvantages of Thorium
• Higher melting point – more difficult to sinter
• More chemically stable – does not dissolve easily in nitric acid
• Presence of U-232
• Pa-233 has a half-life of ~27 days vs. 2.35 days for Np-239
• Industrial chemical process and nuclear data do not exist yet
Thorium Reactors
• Pebble bed and prismatic fuel design
• Graphite moderated
• Helium cooled
Decommissioned - HTGR
Thorium Reactors
• KEMA Suspension Test Reactor
• Light water moderated and cooled
• Uranium and Thorium oxide particles in suspension - 10µm diameter [5]
Decommissioned - KSTR
Thorium Reactors
• Shippingport and BORAX-IV
• Uranium and Thorium oxide pellets in blanket and seed rods
• Shippingport - Used 5% U-233 seed
• 20MW thermal capacity – designed to test heat affects and fuel rod failure
Decommissioned – LWBR and BWBR
Thorium Reactors
• Molten Salt Reactor
• Graphite moderated
• 65% Li7F, 29.1% BeF4, 5% ZrF4, 0.9% ThF4/UF4 fuel [6], with U-233, U-235 and Pu-239
• Fuel outlet temperature – 663°C
• Cladding - Hastelloy-N (68% Ni, 17% Mo, 7% Cr, 5% Fe)
Decommissioned - MSRE
Thorium Reactors
• CANDU type reactors in India
• Heavy water moderated and cooled
• Natural UO2 pellets as main fuel ThO2 fuel rods used for flux flattening
• Testing of bundle arrangements for AHWR
Running - PHWR
Thorium Reactors
• Lead Cooled Fast Reactor
• Advanced Heavy Water Reactor
• Thorium Molten Salt Breeder Reactor• AMSTER
• TMSR-SF – TRISO fuel
• TMSR-LF – molten salt fuel
Future and Gen IV
Summary
• Greater abundance
• Lends itself to a closed loop fuel cycle
• Efficient thermal breeding
• Less long lived waste activity
• Possibly safer reactor designs
Further Reading
IAEA - Thorium fuel cycle — Potential benefits and challenges
http://www-pub.iaea.org/mtcd/publications/pdf/te_1450_web.pdf
The Thorium Fuel Cycle - An independent assessment by the UK National Nuclear Laboratory
http://www.nnl.co.uk/media/1050/nnl__1314092891_thorium_cycle_position_paper.pdf
References
[1] OECD NEA & IAEA, (2014) Uranium 2014: Resources, Production and Demand ("Red Book")
[2] Taylor SR, McLennan SM (1985) The continental crust: its composition and evolution, Blackwell
Scientific Publication, Carlton, p.312
[3] Buerger S. et. Al (2010) The range of variation of uranium isotope ratios in natural uranium samples and potential application to nuclear safeguards
[4] IAEA, VIENNA (2005) Thorium fuel cycle — Potential benefits and challenges
[5] Went J.J. (1960) INSTRUMENTATION FOR A SUBCRITICAL HOMOGENEOUS SUSPENSION REACTOR. I. REASONS BEHIND THE CHOICE OF A HOMOGENEOUS SUSPENSION REACTOR
[6] Rosenthal M.W. (2010) An Account of Oak Ridge National Laboratory’s Thirteen Nuclear Reactors