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."^[1]

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".^[1]

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".^[1]

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."^[1]

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

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

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

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

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

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

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

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

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

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

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

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

Thorium-fueled reactors

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."^[1]

"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."^[1]

Thorcon

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

See also

References