Uranium cycle

Uranium Purification. Subsequent uranium cycles provide additional separation from residual plutonium and fission products, particularly zirconium— niobium and mthenium (30). This is accompHshed by repeating the extraction/stripping cycle. Decontamination factors greater than 10 at losses of less than 0.1 wt % are routinely attainable. However, mthenium can exist in several valence states simultaneously and can form several nitrosyl—nitrate complexes, some for which are extracted readily by TBP. Under certain conditions, the nitrates of zirconium and niobium form soluble compounds or hydrous coUoids that compHcate the Hquid—Hquid extraction. SiUca-gel adsorption or one of the similar Hquid—soHd techniques may also be used to further purify the product streams. 

Contaminant Thorium Uranium Third uranium cycle... 

Neutron energy (thermal vs. fast) The sodium-moderated reactor operates with fast neutrons to breed using the uranium cycle. The water and graphite reactors operate with thermalized neutrons to more effectively burn the fissile material. 

Two engineering system demonstrations were performed to reduce the uranium-from-ore requirements of LWRs recycle of the plutonium and conversion to the thorium-uranium cycle to achieve thermal breeding. The demonstration phase of the plutonium recycle development was carried out in seven power reactors. Several LWRs originally were started up on the thorium-uranium cycle, and a light... 

Uranium cycle U is extracted from U2M HNO3 into the organic phase and back-extracted into as 0.01 M HNO3. The organic phase is refined and recycled. 

Baturin (1973b) examined the uranium cycle in the Black Sea and Azov Sea and found most transport to be in solution as a uranyl carbonate complex. The Azov Sea is a shallow-water basin in which sediments are often disturbed by storms bottom sediments have a fairly uniform and low (0.3— 2.3 pgg" ) content of uranium. The Black Sea, by contrast, is deep, with H2S-rich bottom waters of low Eh. The bottom water is strongly depleted in uranium, while the sediment is of variable, sometimes high (0.2—23.0 pg g" ) uranium content. The Black Sea sediments are said to receive up to 400 Mg of ur2mium from the water. The residence time of uranium in Azov Sea waters is only 14.5 y, but in Black Sea water, is of the order of 3000—4000... 

Uranium in the IBU solvent stream was transferred to the aqueous phase in the uranium-stripping column 1C by back-extraction with 0.01 M HNO3 and left this section of the plant as crude uranium product ICU. Thorium was removed from this crude uranium in the second and third uranium cycles (not shown) and was returned to IBXF feed in the 2BW and 3BW streams. 

Table 10.19 Decontamination factors observed by Kiichler in hot-cell run with two-stage Thorex process followed by thM uranium cycle...

Hanfoid [D3]. Nitrite concentration in feed to the HA column of a standard Purex plant was adjusted to route most of the neptunium in inadiated natural uranium into the extract from the HS scrubbing column. Sufficient ferrous sulfamate was used in the partitioning column to reduce neptunium to Np(IV), which followed uranium. This neptunium was separated from uranium by fractional extraction with TBP in the second uranium cycle. The dilute neptunium product was recycled to HA column feed, to build up its concentration. Periodically, irradiated uranium feed was replaced by unirradiated uranium, which flushed plutonium and fission products from the system. The impure neptunium remaining was concentrated and purified by solvent extraction and ion exchange. 

Nuclear energy cannot be produced by a self-sustained chain reaction in thorium alone because natural thorium contains no Bssile isotopes. Hoice the thorium-uranium cycle must be started by using enriched uranium, by irradiation of thorium in a uranium- or plutonium-fueled reactor or by using a strong external neutron source, e.g. an accelerator driven spallation source. 

The evaluated concepts foresee partly different fuel cycles. Rssion reactors can be operated in principle on the basis of eittier a Uranium-Plutonium-cycle or a Thorium-Uranium-cycle, while combinations of these cycles among them or with other reactor concepts than proposed are possible. With t(xja/s nuclear park (comprising mainly LWRs), the world-wide plutonium excess increases annually by about 1001. Besides strategies based on reprocessing like... 

In spite of these considerations, studies (5i) have shown that the use of the low-enrichment uranium cycle in the HTGR may be attractive under some conditions. Of greater importance, perhaps, are the results (53) showing that recycle operation of the HTGR reusing bred from the thorium fertile material and making use of plutonium instead of as a makeup fuel is an attractive possibility. 

The supercritical-water-cooled reactor (SCWR) ( Fig. 58.21) system features two fuel cycle options the first is an open cycle with a thermal neutron spectrum reactor the second is a closed cycle with a fast-neutron spectmm reactor and full actinide recycle. Both options use a high-temperature, high-pressure, water-cooled reactor that operates above the thermodynamic critical point of water (22.1 MPa, 374°C) to achieve a thermal efficiency approaching 44%. The fuel cycle for the thermal option is a once-through uranium cycle. The fast-spectrum option uses central fuel cycle facilities based on advanced aqueous processing for actinide recycle. The fast-spectrum option depends upon the materials R D success to support a fast-spectrum reactor. 

Ac and U are produced by the neutron irradiation of uranium-cycle by-products such Pa. 

Comparison of thorium and uranium cycles for high bumup. 

VII-4] RADKOWSKY A., et al.. Optimization of once-through uranium cycle for pressurized light water reactors. Nuclear Science and Engineering, 75 (1985), p.265-264. 

Thorium irradiated to 3500 grams of mass-233 per ton, two complete cycles for both uranium and thorium, one additional uranium cycle for material decayed only 30 days. 

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