Fast Breeder Reactor – Advantages and Disadvantages
Fast Breeder Reactor – Nuclear Power Plant Reactor
Such reactors are designed to produce more fissile material (Plutonium) than they consume (Thorium Th-232). A fast breeder reactor is a small vessel in which the required quantity (corresponding to critical mass) of enriched uranium or plutonium is kept without a moderator. The fissionable fuel core is surrounded by a blanket of fertile material (U-238 or Th- 232).
The fertile material (U-238 or Th-232) absorbs neutrons produced by the fissioning of U-235 and produces fissile material Pu-239 or U-233 respectively. Two heat exchangers are used. The reactor core is cooled by liquid metal (sodium or potassium). In the second heat exchanger the coolant is again liquid sodium/potassium which transfers heat to feed water to generate steam.
This prevents the possibility of a sodium-water reaction with the radioactive sodium.
In fast breeder reactors neutron shielding is provided by using boron, light water, oil or graphite. Gamma-ray shielding is accomplished by lead, concrete with added magnetite or barium etc.
The core of a fast reactor needs high enrichment (above 10% of fissile material). To reduce the fuel cost effect, it is imperative to employ high ratings. The core consists of 30% fuel, 50% coolant and 20% canning and structural material by volume.
The power density in a fast breeder reactor is considerably higher than in normal reactors. Therefore, liquid sodium, which is an efficient coolant and does not moderate neutrons, is used to take away heat produced in the core. The efficiency obtained with liquid sodium is about 42%, whereas with other coolants it is about 28%.
An important advantage of FBR technology is that it can use Thorium (as fertile material) which gets converted to U-233, a fissile isotope. This holds great promise for India as we have one of the world’s largest deposit of Thorium—about 450,000 tons in form of sand dunes in Kerala and along Gopalpur Chattarpur coast of Orissa.
Typical power densities (MW/m) in fission reactor cores are – Gas cooled 0.53; High temperature gas cooled 7.75; Heavy water 18.0; Boiling water 29.0; Pressurized water 54.75 and Fast breeder reactor 760.0.
Comparison of Thermal and Fast Breeder Reactors:
Thermal reactors have the following advantages and disadvantages as compared to fast breeder reactors:
1. Heat developed per unit volume of core or per unit area of fuel surface is less.
2. Ease of control.
3. Greater inherent safety.
1. Severely limited choice of fuel from the point of view of neutron economy when fuel used is uranium.
2. Much larger size and weight of reactor per unit power.
3. More fissile material consumption than could be automatically replaced.
Fast breeder reactors can convert more fertile material to fissile material and therefore, net fuel consumption is much less. As a matter of fact more fissile material could be produced than would be consumed by it (fast breeder reactor).
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