Nuclear power/Thorium

Thorium-based fuels are appropriate both for pressurized-water reactors (top) and for high-temperature gas reactors (bottom). Credit: Barbara Aulicino.

Nuclear power is a phrase that refers to the use of a nuclear reactor as a provider of electrical power for commercial, public, or defense purposes.

Thorium is a fissionable element that can be used in a nuclear reactor.

"The use of thorium in power reactors has been considered since the birth of nuclear energy in the 1950s, in large part because thorium is considerably more abundant than uranium in the Earth's crust."

Pressurized-water reactors such as diagrammed at the top right in the image on the right "use ordinary water to transfer heat from the core and to slow the neutrons generated in the fission reactions".

High-temperature gas reactors, on the bottom of the image on the right, "use a gas such as helium to transfer heat and solid graphite to slow the neutrons".

Fuel cycles

"Unfortunately, thorium atoms cannot themselves be easily induced to split—the basic requirement of a fission reactor. But when a quantity of thorium-232 (the common isotope of that element) is placed within a nuclear reactor, it readily absorbs neutrons and transforms into uranium-233, which, like the uranium-235 typically used for generating nuclear power, supports fission chain reactions. Thorium is thus said to be "fertile" rather than fissile."

$\mathrm {n} +{}_{\ 90}^{232}\mathrm {Th} \rightarrow {}_{\ 90}^{233}\mathrm {Th} {\xrightarrow {\beta ^{-}}}{}_{\ 91}^{233}\mathrm {Pa} {\xrightarrow {\beta ^{-}}}{}_{\ 92}^{233}\mathrm {U}$

$\mathrm {n} +{}_{\ 90}^{232}\mathrm {Th} \rightarrow {}_{\ 90}^{233}\mathrm {Th} {\xrightarrow {\beta ^{-}}}{}_{\ 91}^{233}\mathrm {Pa} {\xrightarrow {\beta ^{-}}}{}_{\ 92}^{233}\mathrm {U} +\mathrm {n} \rightarrow {}_{\ 92}^{232}\mathrm {U} +2\mathrm {n}$

$\mathrm {n} +{}_{\ 90}^{232}\mathrm {Th} \rightarrow {}_{\ 90}^{233}\mathrm {Th} {\xrightarrow {\beta ^{-}}}{}_{\ 91}^{233}\mathrm {Pa} +\mathrm {n} \rightarrow {}_{\ 91}^{232}\mathrm {Pa} +2\mathrm {n} {\xrightarrow {\beta ^{-}}}{}_{\ 92}^{232}\mathrm {U}$

$\mathrm {n} +{}_{\ 90}^{232}\mathrm {Th} \rightarrow {}_{\ 90}^{231}\mathrm {Th} +2\mathrm {n} {\xrightarrow {\beta ^{-}}}{}_{\ 91}^{231}\mathrm {Pa} +\mathrm {n} \rightarrow {}_{\ 91}^{232}\mathrm {Pa} {\xrightarrow {\beta ^{-}}}{}_{\ 92}^{232}\mathrm {U}$

${}_{\ 92}^{232}\mathrm {U} {\xrightarrow {\ \alpha \ }}{}_{\ 90}^{228}\mathrm {Th} \ \mathrm {(68.9\ years)}$

${}_{\ 90}^{228}\mathrm {Th} {\xrightarrow {\ \alpha \ }}{}_{\ 88}^{224}\mathrm {Ra} \ \mathrm {(1.9\ year)}$

${}_{\ 88}^{224}\mathrm {Ra} {\xrightarrow {\ \alpha \ }}{}_{\ 86}^{220}\mathrm {Rn} \ \mathrm {(3.6\ day,\ 0.24\ MeV)}$

${}_{\ 86}^{220}\mathrm {Rn} {\xrightarrow {\ \alpha \ }}{}_{\ 84}^{216}\mathrm {Po} \ \mathrm {(55\ s,\ 0.54\ MeV)}$

${}_{\ 84}^{216}\mathrm {Po} {\xrightarrow {\ \alpha \ }}{}_{\ 82}^{212}\mathrm {Pb} \ \mathrm {(0.15\ s)}$

${}_{\ 82}^{212}\mathrm {Pb} {\xrightarrow {\beta ^{-}\ }}{}_{\ 83}^{212}\mathrm {Bi} \ \mathrm {(10.64\ h)}$

${}_{\ 83}^{212}\mathrm {Bi} {\xrightarrow {\ \alpha \ }}{}_{\ 81}^{208}\mathrm {Tl} \ \mathrm {(61\ m,\ 0.78\ MeV)}$

${}_{\ 81}^{208}\mathrm {Tl} {\xrightarrow {\beta ^{-}\ }}{}_{\ 82}^{208}\mathrm {Pb} \ \mathrm {(3\ m,\ 2.6\ MeV)}$

Transmutations in the thorium fuel cycle

230Th

→

231Th

←

232Th

→

233Th

(White actinides: t½<27d)

↓

↓

231Pa

→

232Pa

←

233Pa

→

234Pa

(Colored : t½>68y)

↑

↓

↓

↓

231U

←

232U

↔

233U

↔

234U

↔

235U

↔

236U

→

237U

↓

↓

↓

↓

(Fission products with t½<90y or t½>200ky)

237Np

Thorium-fueled reactors

Name	Country	Reactor type	Power	Fuel	Operation period
AVR	Germany	HTGR, experimental (pebble bed reactor)	015000 15 MW(e)	Th+235U Driver fuel, coated fuel particles, oxide & dicarbides	1967–1988
THTR-300	Germany	HTGR, power (pebble type)	300000 300 MW(e)	Th+235U, Driver fuel, coated fuel particles, oxide & dicarbides	1985–1989
Lingen	Germany	BWR irradiation-testing	060000 60 MW(e)	Test fuel (Th,Pu)O2 pellets	1968-1973
Dragon (OECD-Euratom)	UK (also Sweden, Norway & Switzerland)	HTGR, Experimental (pin-in-block design)	020000 20 MWt	Th+235U Driver fuel, coated fuel particles, oxide & dicarbides	1966–1973
Peach Bottom	USA	HTGR, Experimental (prismatic block)	040000 40 MW(e)	Th+235U Driver fuel, coated fuel particles, oxide & dicarbides	1966–1972
Fort St Vrain	USA	HTGR, Power (prismatic block)	330000 330 MW(e)	Th+235U
MSRE ORNL	USA	MSR	007500 7.5 MWt	233U molten fluorides	1964–1969
BORAX-IV & Elk River Station	USA	BWR (pin assemblies)	002400 2.4 MW(e); 24 MW(e)	Th+235U Driver fuel oxide pellets	1963 - 1968
Shippingport	USA	LWBR, PWR, (pin assemblies)	100000 100 MW(e)	Th+233U Driver fuel, oxide pellets	1977–1982
Indian Point 1	USA	LWBR, PWR, (pin assemblies)	285000 285 MW(e)	Th+233U Driver fuel, oxide pellets	1962–1980
SUSPOP/KSTR KEMA	Netherlands	Aqueous homogenous suspension (pin assemblies)	001000 1 MWt	Th+HEU, oxide pellets	1974–1977
NRX & NRU	Canada	MTR (pin assemblies)	020000 20MW; 200MW (see)	Th+235U, Test Fuel	1947 (NRX) + 1957 (NRU); Irradiation–testing of few fuel elements
CIRUS; DHRUVA; & KAMINI	India	MTR thermal	040000 40 MWt; 100 MWt; 30 kWt (low power, research)	Al+233U Driver fuel, ‘J’ rod of Th & ThO2, ‘J’ rod of ThO2	1960-2010 (CIRUS); others in operation
KAPS 1 &2; KGS 1 & 2; RAPS 2, 3 & 4	India	PHWR, (pin assemblies)	220000 220 MW(e)	ThO2 pellets (for neutron flux flattening of initial core after start-up)	1980 (RAPS 2) +; continuing in all new PHWRs
FBTR	India	LMFBR, (pin assemblies)	040000 40 MWt	ThO2 blanket	1985; in operation

India

"One country that has maintained interest is India, which began fueling some of its power reactors in the mid-1990s with bundles containing thorium. Although one of the reasons for employing thorium was simply to even out the distribution of power within the cores of these reactors, Indian engineers also took the opportunity to test how well thorium could function as a fuel source. The positive results they obtained motivated their current plans to use thorium-based fuels in more advanced reactors now under construction."

"India's attraction to thorium-based fuels stems, in part, from its large indigenous supply. (With estimated thorium reserves of some 290,000 tons, it ranks second only to Australia.) But that nation's pursuit of thorium, which helps bring it independence from overseas uranium sources, came about for a reason that has nothing to do with its balance of trade: India uses some of its reactors to make plutonium for atomic bombs. Thus India refuses to be constrained by the provisions that commercial uranium suppliers in countries such as Canada require: They demand that purchasers of their ore allow enough oversight to ensure that the fuel (or the plutonium spawned from it) is not used for nuclear weapons."

Thorcon

The subpage (linked in the subject header) covers a commercial thorium reactor effort.

See also

Wikipedia

• Wikipedia:Thorium-based nuclear power
• Wikipedia:Thorium fuel cycle