Thorium fuel cycle

The thorium fuel cycle is a

used nuclear fuel

and formed into new nuclear fuel.

The thorium fuel cycle has several potential advantages over a

molten salt reactor.^[3]^[4]^[5]

History

Concerns about the

limits of worldwide uranium resources motivated initial interest in the thorium fuel cycle.^[6] It was envisioned that as uranium reserves were depleted, thorium would supplement uranium as a fertile material. However, for most countries uranium was relatively abundant and research in thorium fuel cycles waned. A notable exception was India's three-stage nuclear power programme.^[7]

In the twenty-first century thorium's claimed potential for improving proliferation resistance and

rare earth element mining, it is much less abundant in seawater than uranium.^[11]

At

Alvin Weinberg was fired.^[12]

In 1993, Carlo Rubbia proposed the concept of an energy amplifier or "accelerator driven system" (ADS), which he saw as a novel and safe way to produce nuclear energy that exploited existing accelerator technologies. Rubbia's proposal offered the potential to incinerate high-activity nuclear waste and produce energy from natural thorium and depleted uranium.^[13]^[14]

Kirk Sorensen, former NASA scientist and Chief Technologist at Flibe Energy, has been a long-time promoter of thorium fuel cycle and particularly liquid fluoride thorium reactors (LFTRs). He first researched thorium reactors while working at NASA, while evaluating power plant designs suitable for lunar colonies. In 2006 Sorensen started "energyfromthorium.com" to promote and make information available about this technology.^[15]

A 2011 MIT study concluded that although there is little in the way of barriers to a thorium fuel cycle, with current or near term light-water reactor designs there is also little incentive for any significant market penetration to occur. As such they conclude there is little chance of thorium cycles replacing conventional uranium cycles in the current nuclear power market, despite the potential benefits.^[16]

Nuclear reactions with thorium

In the thorium cycle, fuel is formed when ²³²
Th

²³³
Pa

. This then emits another electron and anti-neutrino by a second
β⁻
decay to become ²³³
U
, the fuel:

{\ce {{\overset {neutron}{n}}+{^{232}_{90}Th}->{^{233}_{90}Th}->[\beta ^{-}]{^{233}_{91}Pa}->[\beta ^{-}]{\overset {fuel}{^{233}_{92}U}}}}

Fission product waste

light water reactor

of the same power. Other studies assume some actinide losses and find that actinide wastes dominate thorium cycle waste radioactivity at some future periods.^[18] Some fission products have been proposed for nuclear transmutation, which would further reduce the amount of nuclear waste and the duration during which it would have to be stored (whether in a deep geological repository or elsewhere). However, while the principal feasibility of some of those reactions has been demonstrated at laboratory scale, there is, as of 2024, no large scale deliberate transmutation of fission products anywhere in the world, and the upcoming MYRRHA research project into transmutation is mostly focused on transuranic waste. Furthermore, the cross section of some fission products is relatively low and others - such as caesium - are present as a mixture of stable, short lived and long lived isotopes in nuclear waste, making transmutation dependent on expensive isotope separation.

Actinide waste

In a reactor, when a neutron hits a fissile atom (such as certain isotopes of uranium), it either splits the nucleus or is captured and transmutes the atom. In the case of ²³³
U
, the transmutations tend to produce useful nuclear fuels rather than

transuranic

waste than in a reactor using the uranium-plutonium fuel cycle.


Transmutations in the thorium fuel cycle v t e
														²³⁷Np
														↑
		²³¹U	←	²³²U	↔	²³³U	↔	²³⁴U	↔	²³⁵U	↔	²³⁶U	→	²³⁷U
		↓		↑		↑		↑
		²³¹Pa	→	²³²Pa	←	²³³Pa	→	²³⁴Pa
		↑				↑
²³⁰Th	→	²³¹Th	←	²³²Th	→	²³³Th
Nuclides with a yellow background in italic have half-lives under 30 days Nuclides in bold have half-lives over 1,000,000 years Nuclides in red frames are fissile

²³⁴
U
, like most

²³⁷
Np
, ²³⁸
Pu
, and eventually fissile ²³⁹
Pu
and heavier isotopes of plutonium. The ²³⁷
Np
can be removed and stored as waste or retained and transmuted to plutonium, where more of it fissions, while the remainder becomes ²⁴²
Pu
, then americium and curium

, which in turn can be removed as waste or returned to reactors for further transmutation and fission.

However, the

neutron absorption

, its neutron absorption cross section is relatively low, making this rather difficult and possibly uneconomic.

Uranium-232 contamination

²³³
Pa

, and ²³²
Th
:

{\begin{aligned}{}\\{\ce {{^{232}_{90}Th}->[+n]{^{233}_{90}Th}->[\beta ^{-}]{^{233}_{91}Pa}{\text{ }}->[\beta ^{-}]{^{233}_{92}U}->[+n-2n]{^{232}_{92}U}}}\\{\ce {{^{232}_{90}Th}->[+n]{^{233}_{90}Th}->[\beta ^{-}]{^{233}_{91}Pa}{\text{ }}->[+n-2n]{^{232}_{91}Pa}->[\beta ^{-}]{^{232}_{92}U}}}\\{\ce {{^{232}_{90}Th}->[+n-2n]{^{231}_{90}Th}->[\beta ^{-}]{^{231}_{91}Pa}{\text{ }}->[+n]{^{232}_{91}Pa}->[\beta ^{-}]{^{232}_{92}U}}}\\{}\end{aligned}}

Unlike most even numbered heavy isotopes, ²³²
U
is also a

full decay chain

, along with half-lives and relevant gamma energies, is:

decay chain of ²³²
Th

{\begin{aligned}{}\\{\ce {^{232}_{92}U ->[\alpha] ^{228}_{90}Th}}\ &\mathrm {(68.9\ years)} \\{\ce {^{228}_{90}Th ->[\alpha] ^{224}_{88}Ra}}\ &\mathrm {(1.9\ year)} \\{\ce {^{224}_{88}Ra ->[\alpha] ^{220}_{86}Rn}}\ &\mathrm {(3.6\ day,\ 0.24\ MeV)} \\{\ce {^{220}_{86}Rn ->[\alpha] ^{216}_{84}Po}}\ &\mathrm {(55\ s,\ 0.54\ MeV)} \\{\ce {^{216}_{84}Po ->[\alpha] ^{212}_{82}Pb}}\ &\mathrm {(0.15\ s)} \\{\ce {^{212}_{82}Pb ->[\beta^-] ^{212}_{83}Bi}}\ &\mathrm {(10.64\ h)} \\{\ce {^{212}_{83}Bi ->[\alpha] ^{208}_{81}Tl}}\ &\mathrm {(61\ m,\ 0.78\ MeV)} \\{\ce {^{208}_{81}Tl ->[\beta^-] ^{208}_{82}Pb}}\ &\mathrm {(3\ m,\ 2.6\ MeV)} \\{}\end{aligned}}

Thorium-cycle fuels produce hard

used nuclear fuel; however, chemical separation of thorium from uranium removes the decay product ²²⁸
Th
and the radiation from the rest of the decay chain, which gradually build up as ²²⁸
Th
reaccumulates. The contamination could also be avoided by using a molten-salt breeder reactor and separating the ²³³
Pa
before it decays into ²³³
U
.^[3]

The hard gamma emissions also create a radiological hazard which requires remote handling during reprocessing.

Nuclear fuel

As a fertile material thorium is similar to ²³⁸
U
, the major part of natural and depleted uranium. The thermal neutron absorption

resonance integral

(average of neutron cross sections over intermediate neutron energies) for ²³²
Th
are about three and one third times those of the respective values for ²³⁸
U
.

Advantages

The primary physical advantage of thorium fuel is that it uniquely makes possible a breeder reactor that runs with slow neutrons, otherwise known as a thermal breeder reactor.^[6] These reactors are often considered simpler than the more traditional fast-neutron breeders. Although the thermal neutron fission cross section (σ_f) of the resulting ²³³
U
is comparable to ²³⁵
U
and ²³⁹
Pu
, it has a much lower capture cross section (σ_γ) than the latter two fissile isotopes, providing fewer non-fissile neutron absorptions and improved neutron economy. The ratio of neutrons released per neutron absorbed (η) in ²³³
U
is greater than two over a wide range of energies, including the thermal spectrum. A breeding reactor in the uranium–plutonium cycle needs to use fast neutrons, because in the thermal spectrum one neutron absorbed by ²³⁹
Pu
on average leads to less than two neutrons.

Thorium is estimated to be about three to four times more abundant than uranium in Earth's crust,

rare-earth extraction from monazite sands. Notably, there is very little thorium dissolved in seawater, so seawater extraction

is not viable, as it is with uranium. Using breeder reactors, known thorium and uranium resources can both generate world-scale energy for thousands of years.

Thorium-based fuels also display favorable physical and chemical properties that improve reactor and

oxidize.^[6]

Because the ²³³
U
produced in thorium fuels is significantly contaminated with ²³²
U
in proposed power reactor designs, thorium-based

detection

of such materials.

The long-term (on the order of roughly 10³ to 10⁶ years) radiological hazard of conventional uranium-based used nuclear fuel is dominated by plutonium and other

transuranic elements, whereas five captures are generally necessary to do so from ²³²
Th
. 98–99% of thorium-cycle fuel nuclei would fission at either ²³³
U
or ²³⁵
U
, so fewer long-lived transuranics are produced. Because of this, thorium is a potentially attractive alternative to uranium in mixed oxide (MOX) fuels to minimize the generation of transuranics and maximize the destruction of plutonium.^[22]

Disadvantages

There are several challenges to the application of thorium as a nuclear fuel, particularly for solid fuel reactors:

In contrast to uranium, naturally occurring thorium is effectively

molten salt reactor

from 1964 to 1969, which was expected to be easier to process and separate from contaminants that slow or stop the chain reaction.

In an

light water reactors

(LWR), which compose the vast majority of existing power reactors.

In a once-through thorium fuel cycle, thorium-based fuels produce far less long-lived

transuranics

than uranium-based fuels, some long-lived actinide products constitute a long-term radiological impact, especially ²³¹
Pa
and ²³³
U
.^[17] On a closed cycle,²³³
U
and ²³¹
Pa
can be reprocessed. ²³¹
Pa
is also considered an excellent burnable poison absorber in light water reactors.^[23]

Another challenge associated with the thorium fuel cycle is the comparatively long interval over which ²³²
Th
breeds to ²³³
U
. The

transuranic

production.

Alternatively, if solid thorium is used in a

decay products of ²³²
U
. This is also true of recycled thorium because of the presence of ²²⁸
Th
, which is part of the ²³²
U
decay sequence. Further, unlike proven uranium fuel recycling technology (e.g. PUREX

), recycling technology for thorium (e.g. THOREX) is only under development.

Although the presence of ²³²
U
complicates matters, there are public documents showing that ²³³
U
has been used once in a nuclear weapon test. The United States tested a composite ²³³
U
-plutonium bomb core in the MET (Military Effects Test) blast during Operation Teapot in 1955, though with much lower yield than expected.^[24]

Advocates for liquid core and

molten salt reactors such as LFTRs claim that these technologies negate thorium's disadvantages present in solid fuelled reactors. As only two liquid-core fluoride salt reactors have been built (the ORNL ARE and MSRE) and neither have used thorium, it is hard to validate the exact benefits.^[6]

Thorium-fueled reactors

Thorium fuels have fueled several different reactor types, including

molten salt reactors.^[25]

List of thorium-fueled reactors

It has been suggested that this section be split out into another article titled List of thorium-fueled reactors. (Discuss) (August 2020)

This article needs to be updated. Please help update this article to reflect recent events or newly available information. (August 2020)

From IAEA TECDOC-1450 "Thorium Fuel Cycle – Potential Benefits and Challenges", Table 1: Thorium utilization in different experimental and power reactors.[6] Additionally from Energy Information Administration, "Spent Nuclear Fuel Discharges from U. S. Reactors", Table B4: Dresden 1 Assembly Class.^[26]

Name	Operation period	Country	Reactor type	Power	Fuel
NRU	1947 (NRX) + 1957 (NRU); Irradiation–testing of few fuel elements	Canada	MTR (pin assemblies)	020000 20 MW; 200 MW ( see )	Th+²³⁵ U , Test Fuel
Dresden Unit 1	1960–1978	United States	BWR	300000 197 MW(e)	ThO₂ corner rods, UO₂ clad in Zircaloy-2 tube
CIRUS; DHRUVA; & KAMINI	1960–2010 (CIRUS); others in operation	India	MTR thermal	040000 40 MWt; 100 MWt; 30 kWt (low power, research)	Al+²³³ U Driver fuel, ‘J’ rod of Th & ThO2, ‘J’ rod of ThO₂
Indian Point 1	1962–1965^[27]	United States	PWR , (pin assemblies)	285000 285 MW(e)	Th+²³³ U Driver fuel, oxide pellets
BORAX-IV & Elk River Station	1963–1968	United States	BWR (pin assemblies)	002400 2.4 MW(e); 24 MW(e)	Th+²³⁵ U Driver fuel oxide pellets
ORNL	1964–1969	United States	MSR	007500 7.5 MWt	²³³ U molten fluorides
Peach Bottom	1966–1972	United States	HTGR, Experimental (prismatic block)	040000 40 MW(e)	Th+²³⁵ U Driver fuel, coated fuel particles, oxide & dicarbides
Dragon (OECD-Euratom)	1966–1973	UK (also Sweden, Norway and Switzerland)	HTGR, Experimental (pin-in-block design)	020000 20 MWt	Th+²³⁵ U Driver fuel, coated fuel particles, oxide & dicarbides
AVR	1967–1988	Germany (West)	pebble bed reactor )	015000 15 MW(e)	Th+²³⁵ U Driver fuel, coated fuel particles, oxide & dicarbides
Lingen	1968–1973	Germany (West)	BWR irradiation-testing	060000 60 MW(e)	Test fuel (Th,Pu)O₂ pellets
SUSPOP/KSTR KEMA	1974–1977	Netherlands	Aqueous homogeneous suspension (pin assemblies)	001000 1 MWt	Th+HEU, oxide pellets
Fort St Vrain	1976–1989	United States	HTGR, Power (prismatic block)	330000 330 MW(e)	Th+²³⁵ U Driver fuel, coated fuel particles, Dicarbide
Shippingport	1977–1982	United States	PWR , (pin assemblies)	100000 100 MW(e)	Th+²³³ U Driver fuel, oxide pellets
RAPS 2, 3 & 4	1980 (RAPS 2) +; continuing in all new PHWRs	India	PHWR , (pin assemblies)	220000 220 MW(e)	ThO₂ pellets (for neutron flux flattening of initial core after start-up)
FBTR	1985; in operation	India	LMFBR , (pin assemblies)	040000 40 MWt	ThO₂ blanket
THTR-300	1985–1989	Germany (West)	pebble type )	300000 300 MW(e)	Th+²³⁵ U Driver fuel, coated fuel particles, oxide & dicarbides
TMSR-LF1	2023; operating license issued	China	Liquid fuel thorium-based molten salt experimental reactor	002000 2 MWt	Thorium-based molten salt
Petten	2024; planned	Netherlands	High Flux Reactor thorium molten salt experiment	060000 45 MW(e)	?

References

^ ^a ^b Robert Hargraves; Ralph Moir (January 2011). "Liquid Fuel Nuclear Reactors". American Physical Society Forum on Physics & Society. Retrieved 31 May 2012.
^ Sublette, Carey (20 February 1999). "Nuclear Materials FAQ". nuclearweaponarchive.org. Retrieved October 23, 2019.
^
S2CID 8033110. "Archived copy" (PDF). Archived from the original (PDF) on 2014-12-03. Retrieved 2015-03-02.{{cite web}}: CS1 maint: archived copy as title (link
)

^ ""Superfuel" Thorium a Proliferation Risk?". 5 December 2012.
S2CID 4414368
. We are concerned, however, that other processes, which might be conducted in smaller facilities, could be used to convert 232Th into 233U while minimizing contamination by 232U, thus posing a proliferation threat. Notably, the chemical separation of an intermediate isotope — protactinium-233 — that decays into 233U is a cause for concern. ... The International Atomic Energy Agency (IAEA) considers 8 kilograms of 233U to be enough to construct a nuclear weapon1. Thus, 233U poses proliferation risks.

^ ^a ^b ^c ^d ^e ^f ^g "IAEA-TECDOC-1450 Thorium Fuel Cycle – Potential Benefits and Challenges" (PDF). International Atomic Energy Agency. May 2005. Retrieved 2009-03-23.

^ Ganesan Venkataraman (1994). Bhabha and his magnificent obsessions. Universities Press. p. 157.

^ "IAEA-TECDOC-1349 Potential of thorium-based fuel cycles to constrain plutonium and to reduce the long-lived waste toxicity" (PDF). International Atomic Energy Agency. 2002. Retrieved 2009-03-24.

^ Evans, Brett (April 14, 2006). "Scientist urges switch to thorium". ABC News. Archived from the original on 2010-03-28. Retrieved 2011-09-17.

^ Martin, Richard (December 21, 2009). "Uranium Is So Last Century – Enter Thorium, the New Green Nuke". Wired. Retrieved 2010-06-19.

ISSN 0012-821X
.

^ Miller, Daniel (March 2011). "Nuclear community snubbed reactor safety message: expert". ABC News. Retrieved 2012-03-25.

Cosmos
. Retrieved 2010-06-19.

^ MacKay, David J. C. (February 20, 2009). Sustainable Energy – without the hot air. UIT Cambridge Ltd. p. 166. Retrieved 2010-06-19.

^ "Flibe Energy". Flibe Energy. Retrieved 2012-06-12.

^ The Future of the Nuclear Fuel Cycle (PDF) (Report). MIT. 2011. p. 181.

^ ^a ^b Le Brun, C.; L. Mathieu; D. Heuer; A. Nuttin. "Impact of the MSBR concept technology on long-lived radio-toxicity and proliferation resistance" (PDF). Technical Meeting on Fissile Material Management Strategies for Sustainable Nuclear Energy, Vienna 2005. Retrieved 2010-06-20.

^ Brissot R.; Heuer D.; Huffer E.; Le Brun, C.; Loiseaux, J-M; Nifenecker H.; Nuttin A. (July 2001). "Nuclear Energy With (Almost) No Radioactive Waste?". Laboratoire de Physique Subatomique et de Cosmologie (LPSC). Archived from the original on 2011-05-25. according to computer simulations done at ISN, this Protactinium dominates the residual toxicity of losses at 10000 years

^ "Interactive Chart of Nuclides". Brookhaven National Laboratory. Archived from the original on 21 July 2011. Retrieved 2 March 2015. Thermal neutron cross sections in barns (isotope, capture:fission, f/f+c, f/c) 233U 45.26:531.3 92.15% 11.74; 235U 98.69:585.0 85.57% 5.928; 239Pu 270.7:747.9 73.42% 2.763; 241Pu 363.0:1012 73.60% 2.788.

^ "9219.endfb7.1". atom.kaeri.re.kr.

^ "The Use of Thorium as Nuclear Fuel" (PDF). American Nuclear Society. November 2006. Retrieved 2009-03-24.

^ "Thorium test begins". World Nuclear News. 21 June 2013. Retrieved 21 July 2013.

^ "Protactinium-231 –New burnable neutron absorber". 11 November 2017.

^ "Operation Teapot". 11 November 2017. Retrieved 11 November 2017.

^ "IAEA-TECDOC-1319 Thorium Fuel Utilization: Options and trends" (PDF). International Atomic Energy Agency. November 2002. Retrieved 2009-03-24.

ISBN 978-0-7881-2070-1. Retrieved 11 June 2012. They were manufactured by General Electric (assembly code XDR07G) and later sent to the Savannah River Site
for reprocessing.

^ "Indian Readied for New Uranium". Mount Vernon Argus. White Plains, New York. March 16, 1966. p. 17. Retrieved March 21, 2023.

Further reading

Kasten, P. R. (1998). "Review of the Radkowsky Thorium reactor concept" Science & Global Security, 7(3), 237–269.

Duncan Clark (9 September 2011), "Thorium advocates launch pressure group. Huge optimism for thorium nuclear energy at the launch of the Weinberg Foundation", The Guardian

Nelson, A. T. (2012). "Thorium: Not a near-term commercial nuclear fuel". Bulletin of the Atomic Scientists. 68 (5): 33–44.
S2CID 144725888
.

B.D. Kuz'minov, V.N. Manokhin, (1998) "Status of nuclear data for the thorium fuel cycle", IAEA translation from the Russian journal Yadernye Konstanty (Nuclear Constants) Issue No. 3–4, 1997

Thorium and uranium fuel cycles comparison by the UK National Nuclear Laboratory

Fact sheet on thorium Archived 2013-02-16 at the Wayback Machine at the World Nuclear Association.

Annotated bibliography for the thorium fuel cycle Archived 2010-10-07 at the Wayback Machine from the Alsos Digital Library for Nuclear Issues

External links

International Thorium Energy Committee

Retrieved from "https://en.wikipedia.org/w/index.php?title=Thorium_fuel_cycle&oldid=1220532546"

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