Question

There is a lot of speculation currently about the element thorium as a way of producing nuclear energy at a much cheaper and safer level than can be done with uranium. Below are a few questions regarding this element. Answer them as best you can after doing a thorough literature search.

1. Thorium has been stated as being even more common than tin in the Earth’s crust. Can you substantiate this?

a. In terms of mass, is thorium more common than tin in the Earth’s crust?

b. In terms of moles, is thorium more common than tin in the Earth’s crust?

2. Is a nuclear reactor using thorium feasible? If so, how can it be constructed?

3. What are the advantages of thorium vs. uranium (if any—maybe uranium might be better)?

4. If there be disadvantages regarding thorium, what do you think that they would be?

Answer 1

Thorium in earth crust is almost 3 times more abundant than tin. Thorium in earth crust is around 6 ppm while tin is just 2.2 ppm. The total reserves of thorium in India amount to over 500,000 tons in the readily extractable form

b. Atomic mass of Thorium is 232.03806 u ± 0.00002 u

Atomic mass of Tin is 118.71 u

Since number of moles, n= Mass of the element/ Atomic mass

Ratio of no. of moles of Thorium to tin= (6 ppm/232.03806)/ (2.2/ 118.71 u)

                                                              =1.32

So, in terms of moles, thorium is more common than tin in the earth's crust

2. Nuclear reactor using thorium is feasible . Utilising Th in nuclear reactor involves 3 stages in which the first stage involves using Nat. Uranium to the pressurized heavy water reactor and the left over depleted uranium and formed Plutonium is fed to a Fast breeder reactor in stage 2 ,from where U-233 produced is further fed to a advanced reactor which uses thorium as a blanket in the third stage. It is so because Thorium itself is not a fissile material, and thus cannot undergo fission to produce energy therefore it is transmuted to uranium-233 in a reactor.

3. Advantages of thorium over uranium are: the possibility to breed fissile material in slow neutron systems is a unique feature for thorium-based fuels and is not possible with uranium fuels, its high abundance in india as the total reserves of thorium in India amounts to over 500,000 tons in the readily extractable form, while the known reserves of uranium are less than a tenth of this, its superior physical and nuclear fuel properties, , less transuranic elements in that waste, also, the use of thorium in most reactor types leads to extra safety margins and reduced nuclear waste production

4. The disadvantages of using Thorium in nuclear reactors are : the high start up cost of fuel fabrication and the cost of reprocessing to provide the fissile plutonium driver material. The high cost of fuel fabrication (for solid fuel) is due partly to the high level of radioactivity that builds up in U-233 chemically separated from the irradiated thorium fuel. Separated U-233 is always contaminated with traces of U-232 which decays (with a 69-year half-life) to daughter nuclides such as thallium-208 that are high-energy gamma emitters. Although this confers proliferation resistance to the fuel cycle by making U-233 hard to handle and easy to detect, it results in increased costs. There are similar problems in recycling thorium itself due to highly radioactive Th-228 (an alpha emitter with two-year half life) present