Thorium:

Natural thorium consists of one isotope, ²³²Th, within just trace quantities of another much more radioactive thorium isotope.   Just ore mineral of thorium, that is found in useful amounts is monazite.  The Monazite-bearing sands provide most commercial supplies. An extraction and purification of thorium is carried out in much the same manner as for uranium.  Thorium dioxide (ThO₂) is used as the fuel of some reactors.  A thorium dioxide can be prepared by heating thorium metal or a wide variety of other thorium compounds in air.  It happens typically as a fine white powder and is extremely refractory (hard to melt or work) and resistant to chemical attack.

The sole reason for using thorium in nuclear reactors is the fact that thorium (²³²Th) is not fissile, other than could be converted to uranium-233 (fissile) through neutron capture.  The Uranium-233 is an isotope of uranium that does not occur in nature.  While a thermal neutron is absorbed through this isotope, the number of neutrons generates is sufficiently larger than two, that allows breeding in a thermal nuclear reactor.  No other fuel could be used for thermal breeding applications.  It has the superior nuclear properties of the thorium fuel cycle while applied in thermal reactors which motivated the development of thorium-based fuels.  An establishment of the uranium fuel cycle preceded which of thorium since of the natural occurrence of a fissile isotope in natural uranium, uranium-235, that was capable of sustaining a nuclear chain reaction. At one  the  utilization  of  uranium dioxide  nuclear  fuels  had  been  build and  development  of  the  compound  thorium  dioxide logically followed.

As begin above, thorium dioxide is called to be one of the most refractory and chemically nonreactive solid substances available.  This material has several benefits over uranium dioxide. Its melting point is higher; it is between the highest measured.  It is not subject  to oxidation beyond  stoichiometric  (components  entering  into  and  resulting  from  combination)  ThO₂.  At comparable temperatures over most of the expected operating range its thermal conductivity is higher than that of UO₂.  One drawback is which the thorium cycle generates more fission gas per fission, while experience has shown which thorium dioxide is superior to uranium dioxide in retaining these gases.   Other drawback is the cost of recycling thoria-base fuels, or the "spiking" of initial-load fuels with ²³³U. That is harder since ²³³U always holds ²³²U as a contaminant.  ²³²U alpha decays to ²²⁸Th along with a 1.9 year half-life.  The decay chain of ²²⁸Th generates strong gamma and alpha emitters. All handling of like material must be completed under remote conditions along with containment.

Investigation and utilization of thorium dioxide and thorium dioxide-uranium dioxide (thoria-urania) solid solutions as nuclear fuel materials have been conducted at the Shipping port LWBR (Light Water Breeder Reactor). After a past of successful operation, the reactor was shut down on the year of 1982 of October 1. Another reactor experience along with ThO₂ and ThO₂-UO₂ fuels have been conducted at the Elk River (Minnesota) Reactor, and the High-temperature Gas-cooled Reactor (HTGR) at Peach Bottom, Pennsylvania or at Fort St. Vrain and a commercial HTGR in Colorado.