Thorium is a naturally occurring actinide,moderately abundant on the Earth like Iron and U-238. It’s density is 11.2 g per cc bringing it close to the well-known dense element Mercury. Enrichment of U-238 leads to the more ready fissile U-235 that India has been using to produce energy in its 20 nuclear reactors across the nation.
How it works?
Thorium-232, if bombarded with neutrons produces a readily fissile by-product in the form U-233, which upon further neutron bombardment undergoes nuclear fission. Each time Thorium undergoes fission, the next neutron that bombards the U-233 nucleus produces more energy than the primary fission. This way, it is possible to create a self-sustaining nuclear chain reaction to create more energy than provided to create the fission.
The Th-U cycle is more intriguing than the existing U-Pu cycle. We will read below how thorium-232 can be used as efficient fuel for energy below.
Pro’s of using Thorium:
1. Thorium is much more abundant on Earth than Uranium.
Almost 30% of the world reserves of Thorium are in the Eastern coast of Indian peninsula with maximum concentrations in the state of Andhra Pradesh, Tamil Nadu and Odisha. Naturally occurring Thorium exists in the form of Monazite – a rare phosphate of Thorium. But India somehow at the moments seems to be squandering the chances of a world monopoly like that of Crude oil in the middest by illegally exporting it.
2. End products of Thorium-Uranium cycle (Th-U) don’t release potentially dangerous elements like Plutonium, Curium and Americium etc. This means that over a period of approximately 10,000 years, Thorium as fuel is relatively safer than the existing Uranium-Plutonium cycle (U-Pu), although it is toxic nevertheless.
3. Breeding fuel might not be required. As the end product of the Th-U cycle produces U-233 which is readily fissable by a neutron. The energy produces is hence more than twice that of U-Pu cycle without breeding nuclear fuel as a second stage. This process happens naturally in the Th-U cycle.
4. Th-U end product such as U-233 cannot be as further used as weapons. Uranium-233 is fissile but cannot be chemically separated for the use in nuclear weapons. It may find uses in weapons if mass destruction, but not as readily as how Plutonium has been used in the manufacturing of Atomic bombs and further its usage to develop thermonuclear bombs.
Downsides of using Thorium for energy demands:
1. Preparation of Thorium is difficult as the element is naturally inert. It is difficult to chemically process Thorium with other elements and compounds. Furthermore, Thorium needs high temperatures to transform into liquid; about 550 degrees C more than Uranium.
2. Thorium if irradiated produces hazardous radioactive material with very high energy of the order of 2.6 MeV. Apart from the U-233, the irradiation of Thorium produces U-232 which fisses into hazardously radioactive substances like Thallium-208 (Tl-208). It is not easy to shield intense gamma radiation from this by-product.
3. Lack of experience of handling Thorium is seriously debilitating. So far, world economies have used and mastered the Uranium-235 fission process in reactors across the world. A lot more exercise is needed to understand the nuclear physics involved in using elemental Thorium for consumer use.
Physical Properties of Thorium:
Color – Silverish White
Density – 11.2 grams per cubic centimeter.
Melting point – 1842 degree C
Boiling point – 4788 degree C. Molten magma too cannot change the liquid thorium into its gaseous state.
Magnetism – Thorium is paramagnetic. Which means, Th can be magnetised in the presence of a magnetic field. However unlike ferromagnetic materials, Th cannot retain its magnetism after the magnetic field has been dissolved.
Solvabilty – Thorium gradually dissolves in water. However retains immunity towards most acids except hydrochloric acid (HCl). However it can dissolve in concentrated Nitric acid in the presence of fluoride ions.
Known Isotopes :
The lesser the half life value, the more radioactive an element is. Almost 27 such isotopes of Th have been discovered. Most others exists with known half-lives in the order between 10 minutes to 30 days.
Th-232 has a half-life of 14.05 billion years, it represents all but a trace of naturally occurring thorium.
Th-230 has a half-life of 75,380 years. Occurs as the by-product of U-238 decay.
Th-229 has a half-life of 7340 years. It has a nuclear isomer with a remarkably low excitation energy of 7.6 eV.
Th-228 has a half-life of 1.92 years.
Practical usage of Thorium as Nuclear fuel:
1. Heat of fission can be used to drive turbines to produce gigawatts of electricity. One large block of Thorium can produce enough energy to produces electricity for small towns.
2. Thorium reactors can produce new engines for conceptual automobiles much like hydrogen is tapped for fuel.
3. It can be used as a very effective energy/radiation shield.
4. Thorium powered propulsion system, using controlled explosions may be used in designs of rocket engines and missiles.