थोरियम ईंधन चक्र

थोरियम ईंधन चक्र ( thorium fuel cycle) एक नाभिकीय ईंधन चक्र है जो थोरियम के समस्थानिक Th-232 का उपयोग उर्वर पदार्थ (फर्टाइल मैटेरियल) के रूप में करता है। रिएक्टर में Th-232 बदलकर यूरेनियम-२३३ बन जाता है जो नाभिकीय ईंधन है।

थोरियम के साथ नाभिकीय अभिक्रियाएँ

In the thorium cycle, fuel is formed when साँचा:SimpleNuclide2 captures a neutron (whether in a fast reactor or thermal reactor) to become साँचा:SimpleNuclide2. This normally emits an electron and an anti-neutrino (साँचा:SubatomicParticle) by [[beta decay|साँचा:SubatomicParticle decay]] to become साँचा:SimpleNuclide2. This then emits another electron and anti-neutrino by a second साँचा:SubatomicParticle decay to become साँचा:SimpleNuclide2, the fuel:

$\mathrm{n}+{}_{90}^{232}\mathrm{T}\mathrm{h}\to {}_{90}^{233}\mathrm{T}\mathrm{h}\stackrel{{\beta }^{-}}{\to }{}_{91}^{233}\mathrm{P}\mathrm{a}\stackrel{{\beta }^{-}}{\to }{}_{92}^{233}\mathrm{U}$

कचरा विखण्डन उत्पाद

Nuclear fission produces radioactive fission products which can have half-lives from days to greater than 200,000 years. According to some toxicity studies, the thorium cycle can fully recycle actinide wastes and only emit fission product wastes, and after a few hundred years, the waste from a thorium reactor can be less toxic than the uranium ore that would have been used to produce low enriched uranium fuel for a 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.

ऐक्टिनाइड कचरा

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 साँचा:SimpleNuclide2, the transmutations tend to produce useful nuclear fuels rather than transuranic wastes. When साँचा:SimpleNuclide2 absorbs a neutron, it either fissions or becomes साँचा:SimpleNuclide2. The chance of fissioning on absorption of a thermal neutron is about 92%; the capture-to-fission ratio of साँचा:SimpleNuclide2, therefore, is about 1:12 — which is better than the corresponding capture vs. fission ratios of साँचा:SimpleNuclide2 (about 1:6), or साँचा:SimpleNuclide2 or साँचा:SimpleNuclide2 (both about 1:3). The result is less transuranic waste than in a reactor using the uranium-plutonium fuel cycle. साँचा:Thorium Cycle Transmutation साँचा:SimpleNuclide2, like most actinides with an even number of neutrons, is not fissile, but neutron capture produces fissile साँचा:SimpleNuclide2. If the fissile isotope fails to fission on neutron capture, it produces साँचा:SimpleNuclide2, साँचा:SimpleNuclide2, साँचा:SimpleNuclide2, and eventually fissile साँचा:SimpleNuclide2 and heavier isotopes of plutonium. The साँचा:SimpleNuclide2 can be removed and stored as waste or retained and transmuted to plutonium, where more of it fissions, while the remainder becomes साँचा:SimpleNuclide2, then americium and curium, which in turn can be removed as waste or returned to reactors for further transmutation and fission.

However, the साँचा:SimpleNuclide2 (with a half-life of साँचा:Val) formed via (n,2n) reactions with साँचा:SimpleNuclide2 (yielding साँचा:SimpleNuclide2 that decays to साँचा:SimpleNuclide2), while not a transuranic waste, is a major contributor to the long-term radiotoxicity of spent nuclear fuel.

यूरेनियम-232 प्रदूषण

Uranium-232 is also formed in this process, via (n,2n) reactions between fast neutrons and साँचा:SimpleNuclide2, साँचा:SimpleNuclide2, and साँचा:SimpleNuclide2:

$\mathrm{n}+{}_{90}^{232}\mathrm{T}\mathrm{h}\to {}_{90}^{233}\mathrm{T}\mathrm{h}\stackrel{{\beta }^{-}}{\to }{}_{91}^{233}\mathrm{P}\mathrm{a}\stackrel{{\beta }^{-}}{\to }{}_{92}^{233}\mathrm{U}+\mathrm{n}\to {}_{92}^{232}\mathrm{U}+2\mathrm{n}$

$\mathrm{n}+{}_{90}^{232}\mathrm{T}\mathrm{h}\to {}_{90}^{233}\mathrm{T}\mathrm{h}\stackrel{{\beta }^{-}}{\to }{}_{91}^{233}\mathrm{P}\mathrm{a}+\mathrm{n}\to {}_{91}^{232}\mathrm{P}\mathrm{a}+2\mathrm{n}\stackrel{{\beta }^{-}}{\to }{}_{92}^{232}\mathrm{U}$

$\mathrm{n}+{}_{90}^{232}\mathrm{T}\mathrm{h}\to {}_{90}^{231}\mathrm{T}\mathrm{h}+2\mathrm{n}\stackrel{{\beta }^{-}}{\to }{}_{91}^{231}\mathrm{P}\mathrm{a}+\mathrm{n}\to {}_{91}^{232}\mathrm{P}\mathrm{a}\stackrel{{\beta }^{-}}{\to }{}_{92}^{232}\mathrm{U}$

Uranium-232 has a relatively short half-life (साँचा:Val), and some decay products emit high energy gamma radiation, such as साँचा:SimpleNuclide2, साँचा:SimpleNuclide2 and particularly साँचा:SimpleNuclide2. The full decay chain, along with half-lives and relevant gamma energies, is:

साँचा:SimpleNuclide2 decays to साँचा:SimpleNuclide2 where it joins the [[thorium series|decay chain of साँचा:SimpleNuclide2]]

${}_{92}^{232}\mathrm{U}\stackrel{\alpha }{\to }{}_{90}^{228}\mathrm{T}\mathrm{h}\mathrm{(}\mathrm{6}\mathrm{8}\mathrm{.}\mathrm{9}\mathrm{y}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{s}\mathrm{)}$

${}_{90}^{228}\mathrm{T}\mathrm{h}\stackrel{\alpha }{\to }{}_{88}^{224}\mathrm{R}\mathrm{a}\mathrm{(}\mathrm{1}\mathrm{.}\mathrm{9}\mathrm{y}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{)}$

${}_{88}^{224}\mathrm{R}\mathrm{a}\stackrel{\alpha }{\to }{}_{86}^{220}\mathrm{R}\mathrm{n}\mathrm{(}\mathrm{3}\mathrm{.}\mathrm{6}\mathrm{d}\mathrm{a}\mathrm{y},\mathrm{0}\mathrm{.}\mathrm{2}\mathrm{4}\mathrm{M}\mathrm{e}\mathrm{V}\mathrm{)}$

${}_{86}^{220}\mathrm{R}\mathrm{n}\stackrel{\alpha }{\to }{}_{84}^{216}\mathrm{P}\mathrm{o}\mathrm{(}\mathrm{5}\mathrm{5}\mathrm{s},\mathrm{0}\mathrm{.}\mathrm{5}\mathrm{4}\mathrm{M}\mathrm{e}\mathrm{V}\mathrm{)}$

${}_{84}^{216}\mathrm{P}\mathrm{o}\stackrel{\alpha }{\to }{}_{82}^{212}\mathrm{P}\mathrm{b}\mathrm{(}\mathrm{0}\mathrm{.}\mathrm{1}\mathrm{5}\mathrm{s}\mathrm{)}$

${}_{82}^{212}\mathrm{P}\mathrm{b}\stackrel{{\beta }^{-}}{\to }{}_{83}^{212}\mathrm{B}\mathrm{i}\mathrm{(}\mathrm{1}\mathrm{0}\mathrm{.}\mathrm{6}\mathrm{4}\mathrm{h}\mathrm{)}$

${}_{83}^{212}\mathrm{B}\mathrm{i}\stackrel{\alpha }{\to }{}_{81}^{208}\mathrm{T}\mathrm{l}\mathrm{(}\mathrm{6}\mathrm{1}\mathrm{m},\mathrm{0}\mathrm{.}\mathrm{7}\mathrm{8}\mathrm{M}\mathrm{e}\mathrm{V}\mathrm{)}$

${}_{81}^{208}\mathrm{T}\mathrm{l}\stackrel{{\beta }^{-}}{\to }{}_{82}^{208}\mathrm{P}\mathrm{b}\mathrm{(}\mathrm{3}\mathrm{m},\mathrm{2}\mathrm{.}\mathrm{6}\mathrm{M}\mathrm{e}\mathrm{V}\mathrm{)}$

Thorium-cycle fuels produce hard gamma emissions, which damage electronics, limiting their use in military bomb triggers. साँचा:SimpleNuclide2 cannot be chemically separated from साँचा:SimpleNuclide2 from used nuclear fuel; however, chemical separation of thorium from uranium removes the decay product साँचा:SimpleNuclide2 and the radiation from the rest of the decay chain, which gradually build up as साँचा:SimpleNuclide2 reaccumulates. The hard gamma emissions also create a radiological hazard which requires remote handling during reprocessing.

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