The government of India is promoting nuclear energy as a solution to the country’s future energy needs and is embarking on a massive nuclear energy expansion




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Part II: The Nuclear Fuel Cycle


The nuclear fission reaction that we have discussed above is only a small part of the entire complex process of generating electricity from uranium. The entire process is known as the nuclear fuel cycle. We now take a brief look at the various stages of this process (including the phase of uranium enrichment).

Mining: The nuclear fuel cycle starts with mining of uranium. Since 90% of the worldwide uranium ores have uranium content of less than 1%, and more than two-thirds have less than 0.1%, large amounts of ore have to be mined to obtain the amounts of uranium required.

Milling: The mined ore is then trucked to the mill to be processed to extract the uranium. Here, the ore is first ground into fine powder, and then treated with several chemicals to extract the uranium. The coarse powder thus obtained is called yellowcake. It contains 70-90% uranium oxide (U3O8).

Enrichment (not for Heavy Water Reactors): The uranium oxide in the yellowcake contains both the fissile U-235 and non-fissile U-238. The yellow cake is now taken to a processing facility. Here, the uranium oxide is converted to uranium hexafluoride (UF6), as this compound is gaseous at low temperatures and so is easier to work with. The UF6 is now enriched either through diffusion or centrifugation, meaning the proportion of fissile U-235 in it is increased from 0.7 percent to 3-5 percent. The process yields two types of UF6: one is enriched, and the other, which contains primarily U-238, is called depleted, so-called because most of the U-235 has been extracted from it.

Fuel element fabrication: The enriched uranium hexafluoride gas is now converted into solid uranium oxide fuel pellets, each the size of a cigarette filter. These pellets are packed into very thin tubes of an alloy of zirconium, and the tubes are then sealed. These tubes are called fuel rods. Each fuel rod is normally twelve feet long and half-an-inch thick. The finished fuel rods are bundled together to form the fuel assembly (or fuel bundle), which may have as many as 200 fuel rods. Several fuel assemblies are now placed in the reactor core of the nuclear power reactor—the number may go up to several dozen, depending upon the reactor design.

Nuclear reactor: The nuclear reactor is where the nuclear fuel is fissioned and the resulting chain reactions are controlled and sustained at a steady rate.



Decommissioning: Nuclear power plants are designed for an operating life of 30-60 years. When the reactor completes its working life, it is dismantled. Unlike conventional coal and gas power plants, the dismantling of a nuclear power plant is a very long-term, complicated and costly operation, because the entire nuclear power plant, including all its parts, has become radioactively contaminated. The long-term management and clean up of these closed reactors is known as decommissioning, which can take anywhere between 5 to 100 years, depending upon the type of decommissioning plan.

Disposal of radioactive nuclear fuel waste: Every year, one-third of the nuclear fuel rods must be removed from the reactor, because they are so contaminated with fission products that they hinder the efficiency of electricity production. The uranium fuel after being subjected to the fission reaction in the reactor core becomes one billion times more radioactive; a person standing near a single spent fuel rod can acquire a lethal dose within seconds. This spent nuclear fuel is going to be radioactive for tens of thousands of years. Therefore, it needs to be safely stored for centuries to come.

Generally, the spent fuel is first stored for many years in on-site storage ponds and continually cooled by air or water. If it is not continually cooled, the zirconium cladding of the rod could become so hot that it would spontaneously burn, releasing its radioactive inventory. The cooling period can be from a few years to decades. After cooling, there are two options for the waste—either it is reprocessed, or it is moved to dry cask storage.

In the latter case, the spent fuel rods are packed by remote control into highly specialised containers made of metal or concrete designed to shield the radiation. These casks must be stored for centuries to come; however, no country having nuclear plants has succeeded in building such a long-term nuclear waste dump site. Presently, in most countries having nuclear plants, these casks are ‘temporarily’ stored near the spent fuel cooling ponds.

Reprocessing spent fuel: Reprocessing is a chemical process to separate out the uranium and plutonium contained in the spent fuel, which can then be used as fuel for what are known as Fast Breeder Reactors. Reprocessing also segregates the waste into high-level, intermediate-level and low-level wastes.
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