Uranium Conversion Facility

Evidently, throughout all these processes the isotopic composition of uranium remains in its natural abundance form, that is, containing 0.72% of U. Uranium of this composition is suitable for use as nuclear fuel in reactors that operate with heavy water (DjO) such as CANDU reactors or graphite (such as the old Magnox reactors) as the moderator for slowing neutrons. In this case, the UO2 is ground and sintered to form pellets that will be placed in fuel elements (see Chapter 2 for analytical procedures to characterize these pellets). As an example. Frame 1.4 describes the process used in India for production of UO2 powder, pellets, and fuel elements as an example of the processes in the UCF. 

FRAME 1.4 NUCLEAR FUEL PRODUCTION IN INDIA DESCRIPTION OF PROCESS 

The starting material for natural uranium oxide fuel used in the PHWR type of reactors is the indigenously available uranium concentrate mostly in the mineral belt of Jharkhand that is produced at the uranium mines of Uranium Corporation of India Ltd. (UCIL). 

The fuel assembly for the BWR type of reactors is made of low-enriched uranium (LEU), which is imported in the form of uranium hexafluoride. 

The conversion of uranium concentrate or UFg to nuclear grade UO2 involves various chemical process steps such as dissolution of uranium ore concentrate in nitric acid to dissolve uranium for the PHWR fuel or hydrolysis of LEU UFg, in case of BWR fuel production stream. 

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C26.08 C1188-91(1997)el Standard Guide for Establishing a Quality Assurance Program for Uranium Conversion Facilities... 

Reconstruction of pilot scale reprocessed uranium conversion facility was completed in June, 1994. 

In Chapter 2, we take a more detailed look at the analytical chemistry pertaining to key commercial activities, that is, uranium mining and its utilization in the nuclear fuel cycle (NFC) first, in the milling process, uranium-containing deposits are processed to form uranium ore concentrates (UOC) that are then shipped to uranium conversion facilities (UCF), where the uranium is transformed into high-purity nuclear grade compounds. These can serve as fuel for nuclear power plants or as feed material for isotope enrichment. Then we discuss the analytical aspects of compliance with the strict specifications of the materials used in enrichment plants and in fuel fabrication facilities. Finally, we deal with the analytical procedures to characterize irradiated fuel and waste disposal of spent fuel. 

The following section presents an overview of a generic uranium NFC (Figure 1.9) (IAEA 1613 2009) and a generic flow sheet of the chemical processes in a uranium conversion facility (UCF) where UOC is converted to UO2 (for nuclear fuel), U metal (for fuel or other metallurgical applications), or UFg (feed for enrichment plants) is shown in Eigure 1.10. 

FRAME 2.3 WHAT HAPPENS WHEN THINGS GO WRONG AT A URANIUM CONVERSION FACILITY ... 

Highlights Before shipping UOCs from the mill to the uranium conversion facility (UCF), an extensive series of tests is necessary, starting from proper sampling, continuing with dissolution procedures, and finally a suite of chemical, isotopic, and physical analyses must be carried out in order to produce the certificate that will... 

The main methods used for reprocessing of SNF flowsheet were reviewed in a 120 pages report by the Nuclear Energy Agency (NEA 2012). The three main processes are the so-called hydrometallurgy processes (PUREX and UREX), pyromet-allurgy processes and its variations, and the fluoride volatility process (quite like the method used at the uranium conversion facilities discussed in Chapter 1). The report reviewed in detail several of these processes that are deployed in different facilities for various types of spent fuel (NEA 2012). In this section, we shall try to briefly present an overview of the main points and the analytical aspects. 

In 1999, a serious accident happened at the JCO uranium conversion facility in Tokai-mura, Japan, resulting in a large release of uranium isotopes into the local environment. Yoshida et al. collected soil samples just after this accident from around the JCO factory and determined both the concentration of U and the 235 jy238 j j otope ratio in these samples. They reported that the isotope ratio in the soil around the JCO factory was elevated compared to the... 

At a conversion facility, uranium is first refined to uranium dioxide, which can be used as the fuel for those types of reactors that do not require enriched uranium. Most is then converted into uranium hexafluoride, ready for the enrichment plant. It is shipped in strong metal containers. The main hazard of this stage of the fuel cycle is the use of hydrogen fluoride. 

With regard to UO2 conversion supply, Cameco s plant is by far the largest supplier, with a licensed annual capacity of 2800 tU. In addition, smaller plants exist to meet the local needs in India, Argentina, and Romania. Cameco Corporation owns and operates ma-nium refinery and conversion facilities located respectively at Blind River and Port Hope. The Blind River plant refines natural uranium concentrates (U3O8) into uranium trioxide (UO3) and was commissioned in 1983. The intermediate product is shipped to the Port Hope plant (commissioned 1984) where further processing produces natural UFg. 

At a conversion facility, uranium trioxide is converted into a specific uranium end product according to the nuclear power reactor class. Actually, there are three uranium compounds used in nuclearpower reactors ... 

During the conversion process, the object is to create uranium hexafluoride (UF ), a highly corro-sh e substance that is gaseous at high temperatures, but is a white crystalline solid at lower temperatures. Uranium hexafluoride is easily transported in its ciystalline form to an enrichment facility (the step taken after conversion), but the gaseous form is well suited for the enrichment process, itself. First, the... 

Light water reactors (LWRs) require a process that involves transforming natural uranium concentrates into UFg. The UK s gas-cooled reactors (AGRs) also require UFs conversion. Ffeavy water reactors (HWRs), which are mainly of the CANDU design, require conversion from natural uranium concentrates directly to UO2. For the UK s Magnox gas-cooled reactors, conversion from natural uranium concentrates to uranium metal and fuel fabrication is handled domestically in dedicated facilities. 

Many of the secondary sources of uranium described above also displace demand for UFg conversion. These include inventories of UFgand low enriched uranium (LEU), Russian and US ex-military HEU and plutonium, uranium and plutonium recovered by civil spent fuel reprocessing, and UFg supply from the re-enrichment of tails. In addition, underfeeding of enrichment facilities can also affect the UFg market. 

The fuel fabrication process is shown schematically in Figure 12.4 from conversion of enriched uranium hexaflouride (UFg) gas to the final assembled product. The enriched material is received from an enrichment facility in the form of UFg. Figure 12.5 shows the original gaseous diffusion plant in Oak Ridge, Tennessee. This facility is no longer in... 

The operations and facilities include ore exploration (not included in NFCIS list), mining, ore processing, uranium recovery, chemical conversion to UO2, UO3, UF4, UFg, and uranium metal, isotope enrichment, reconversion of UF to UO2 (after enrichment), and fuel fabrication and assembly that are all part of the front end of the NFC. The central part of the NFC is the production of electric power in the nuclear reactor (fuel irradiation). The back end of the NFC includes facilities to deal with the spent nuclear fuel (SNF) after irradiation in a reactor and the disposal of the spent fuel (SF). The spent fuel first has to be stored for some period to allow decay of the short-lived fission products and activation products and then disposed at waste management facilities without, or after, reprocessing to separate the fission products from the useful actinides (uranium and plutonium). Note the relatively large number of facilities in Table 2.1 dedicated to dealing with the spent fuel. Also listed in Table 2.1 are related industrial activities that do not involve uranium, like heavy water (D2O) production, zirconium alloy manufacturing, and fabrication of fuel assembly components. 

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