{"id":27312,"date":"2020-06-13T11:03:50","date_gmt":"2020-06-13T11:03:50","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=27312"},"modified":"2023-08-01T10:46:07","modified_gmt":"2023-08-01T10:46:07","slug":"uranium-enrichment","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-fuel\/nuclear-fuel-cycle\/uranium-enrichment\/","title":{"rendered":"Uranium Enrichment"},"content":{"rendered":"
Uranium enrichment<\/strong> is a process in which the percent composition of uranium-235 is increased through the process of isotope separation. The level of enrichment required depends on the specific reactor design (e.g., \u00a0PWRs and BWRs require 3% \u2013 5% of 235U) and specific requirements of the nuclear power plant operator (e.g., cycle length).<\/div><\/div>\n

Since natural uranium<\/strong><\/a> contains only 0.71% of fissile isotope 235<\/sup>U and most current power reactors require enriched uranium<\/a>, this natural uranium must be enriched. Only uranium 235 is a fissile material (i.e., it can undergo nuclear fission only after capturing a thermal neutron<\/a><\/strong>). Still, as it only accounts for 0.7% of the makeup of natural uranium, it is not present in sufficient proportions to be used in LWR-type nuclear power plants. The level of enrichment required depends on the specific reactor design (e.g., \u00a0PWRs and BWRs require 3% \u2013 5% of 235U) and specific requirements of the nuclear power plant operator (e.g., cycle length). Without required enrichment, these reactors cannot initiate and sustain a nuclear chain reaction for as long as 12 months (or more).<\/p>\n

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Nuclear Fuel Cycle. Source: Nuclear Regulatory Commission from the US. License: CC BY 2.0<\/figcaption><\/figure>\n

Enrichment<\/strong> is accomplished using any of several methods of isotope separation. Most commercial uranium enrichment<\/strong> processes (ga搜索引擎优化us diffusion and the gas centrifuge method) require the uranium to be in a ga搜索引擎优化us form. Therefore, the uranium oxide concentrate must first be converted to uranium hexafluoride, a gas at relatively low temperatures. Therefore the input material in this process is uranium hexafluoride, also known as “hex.” In the enrichment process, ga搜索引擎优化us uranium hexafluoride<\/a> is separated into two streams, one being enriched to the required level and known as low-enriched uranium; the other stream is progressively depleted in uranium-235 and is called ‘tails,’ or simply depleted uranium<\/strong><\/a>. The product of this stage of the nuclear fuel cycle is enriched uranium hexafluoride, which is reconverted to produce enriched uranium oxide. From a non-proliferation standpoint, uranium enrichment is a sensitive technology needing to be subject to tight international control.<\/p>\n

Before enrichment, natural uranium<\/strong> consists primarily of isotope 238<\/sup>U<\/a> (99.28%). Therefore the atomic mass of the uranium element is close to the atomic mass of the 238<\/sup>U isotope (238.03u). Natural uranium also consists of two other isotopes: 235<\/sup>U<\/a> (0.71%) and 234<\/sup>U<\/a> (0.0054%). The abundance of isotopes in nature is caused by differences in the half-lives. All three naturally-occurring isotopes of uranium (238<\/sup>U, 235<\/sup>U, and 234<\/sup>U) \u00a0are unstable<\/a>. On the other hand, these isotopes (except 234<\/sup>U) belong to primordial nuclides<\/a>\u00a0because their half-life is comparable to the age of the Earth (~4.5\u00d7109<\/sup>years for 238<\/sup>U).<\/p>\n

About 10 kg of natural uranium is required with a byproduct of about 9 kg of depleted uranium to produce 1 kg of enriched uranium with 5% of 235<\/sup>U. Therefore annual natural uranium consumption<\/strong> of a 3000 MWth reactor is about 250 tonnes of <\/strong>natural uranium<\/strong><\/a> (to produce about 25 tonnes of enriched uranium).<\/p>\n

Consumption of a 3000MWth (~1000MWe) pressurized water reactor (12-month fuel cycle)<\/strong><\/p>\n

It is an illustrative example, and the following data do not<\/strong> correspond to any reactor design.<\/em><\/p>\n