Thorium nuclear energy – just a dream or our future
Imagine a cheap, plentiful source of energy that could provide safe, emissions-free power for hundreds of years without refueling and without any risk of nuclear proliferation. The fuel is thorium, and it has been trumpeted by proponents as a superfuel that eludes many of the pitfalls of today’s nuclear energy.
Interest in thorium has been growing in recent years. After the recent nuclear disaster in Fukushima, some see it as a safer alternative to nuclear reactors powered by uranium. Some scientists are proposing the use of liquid thorium fuel in high-temperature molten salt reactors. That combination would allow for small reactors that are safer than existing technology and yield far less nuclear waste.
Father of the hydrogen bomb, Edward Teller argued for a reactor that, when buried underground, could operate safely for 200 years without refueling. Such a reactor would eliminate the possibility of meltdown.
In the thorium fuel cycle, fuel is formed when Th-232 captures a neutron to become Th-233. This normally emits an electron and an anti-neutrino (ν) by β− decay to become Pa-233 (Protactinium). This then emits another electron and anti-neutrino by a second β− decay to become U-233, as shown on picture below.
Advantages of thorium as nuclear fuel:
- Abudance – thorium is four ties abudant as uranium
- Safety – Thorium radioactivity is significantly lower than uranium so it is more safer and cleaner fuel; no meltdown risk during the work under atmosphere pressure
- No nuclear weapons – Thorium reactor’s plutonium production rate would be less than 2 percent of that of a standard reactor
- Waste – hazardous waste will be a thousand times less than with uranium
- Costs – all natural thorium can be used as a fuel, and the fuel is in the form of a molten salt instead of solid fuel rods; reactor construction does not need the expensive high-pressure reactor vessel for the core of light water reactors
Disadvantages of thorium use:
- No fissile isotopes – thorium is not itself fissile so it is not directly usable in a thermal neutron reactor and generally, U-233 of U-235 or Pu-239 have to be added to start a chain reactions.
- Open fuel cycle – higher burnup is necessary to achieve a favorable neutron economy
- Closed fuel cycle – in which U-233 is recycled and remote handling is necessary for fuel fabrication because of the high radiation levels resulting from the decay products of U-232
- Long timed fuel cycle – a very long interval over which Th-232 breeds to U-233. The half-life of Pa-233 is about 27 days, which is an order of magnitude longer than the half-life of Np-239. As a result, substantial Pa-233 develops in thorium-based fuels. Pa-233 is a significant neutron absorber and although it eventually breeds into fissile U-235, this requires two more neutron absorptions, which degrades neutron economy and increases the likelihood of transuranic production (transuranic elements are the chemical elements with atomic numbers greater than 92)
History of Thorium and some properties
Thoriumhas been discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, who named it after Thor, the Norse god of thunder. It is slightly radioactive metal that exists in nature in a single isotopic form Th-232 which decays very slowly.
In nature, virtually all thorium is found as thorium-232 (Th-232) which undergoes alpha decay with a half-life of about 14.05 billion years. Thorium is estimated to be about three to four times more abundant than uranium in the Earth’s crust, and is chiefly refined from monazite sands as a by-product of extracting rare earth metals. Pure thorium is a silvery-white metal which is air-stable and retains its luster for several months. When contaminated with the oxide (has highest melting point of 3300 °C of all oxides), thorium slowly tarnishes in air, becoming gray and finally black.
There are seven types of reactor into which thorium can be introduced as a nuclear fuel. The five of these have all entered into operational service at some point and the two are still conceptual.
Research into the use of thorium as a nuclear fuel has been taking place for over 40 years, though with much less intensity than that for uranium or uranium-plutonium fuels. With huge resources of easily-accessible thorium and relatively little uranium, India has made utilization of thorium for large-scale energy production a major goal in its nuclear power programme, utilising a three-stage concept. First fuelled by natural uranium and producing plutonium; second using plutonium-based fuel to breed U-233 from thorium and in the last one burning the U-233 and this plutonium with thorium, getting about 75% of their power from the thorium.
According to the 2007 IAEA-NEA publication Uranium 2007: Resources, Production and Demand (often referred to as the ‘Red Book’) India, Turkey, Brazil and Australia have more than 50 percent of world’s thorium deposits.
Question is now, is Thorium our future fuel, would it be leaving uranium behind as cleaner and safer nuclear fuel or some other energy source or sources would prevail?
- Nuclear drought
- Developing nuclear power as alternative energy
- Japan’s new energy plan
- Pursuing Alternative Forms of Energy
- Fossil fuels depletion in future