Irradiated oxide reactor fuel

Irradiated Oxide Reactor Fuel Composition and Chemical State.391... 

Eindlay, J.R. 1974. The composition and chemical state of irradiated oxide reactor fuel material. 

Thermal oxide reprocessing plant, 6, 885 Thermal reactor fuels, 6,926 dissolution, 6,927 irradiated... 

Fast breeder reactor fuel rods consist of stainless-steel-clad mixed oxide (U,Pu)02 fuel however, more stable alloys for cladding and in-core structural materials, with resistance to swelling and embrittlement under fast neutron irradiation, and more efficient fuels (carbide see 17.3.12.1.2) or nitride (see 17.3.12.3)] are needed h The mechanical, metallurgical, and chemical processes in fuel element irradiation are depicted in Figure 1. Figure 2 shows the PFR (U.K.) fast breeder fuel element, and Figures 3 and 4 illustrate the Fast Flux Test Facility (FFTF) fuel system. 

Mixed oxide (MOX) fuel, 21.0-wt% Pu in 18.0-wt% enriched uranium, was irradiated from the 16 to 35 cycle at the 3" row in the experimental fast reactor JOYO. Tire effective full power days were 1019.33, and the peak bumup was 143.8 GWd/t. Atotal of 1560 days have passed from the reactor shut down to analysis. 

There are two breeder reactor fuel cycles. One involves the irradiation of U/ Pu oxide fuel with fast neutrons and is at the prototype stage of development. The other involves the irradiation of Th/ U oxide fuel with thermal neutrons and is at the experimental stage. Fuel from the U/ Pu cycle may be reprocessed using Purex technology adapted to accommodate the significant proportion of plutonium present in the fuel. Increased americium and neptunium levels will also arise compared with thermal reactor fuel. The Th/ U fuel may also be reprocessed using solvent extraction with TBP in the Thorex (Thorium Recovery by Extraction) process. In this case the extraction chemistry must also take account of the presence of Pa arising as shown in Scheme 2. 

JOYO is a sodium cooled fast reactor with mixed oxide (MOX) fuel. The main reactor parameters of the MK-II irradiation bed core are shown in Table 1, which compares the MK-II with the future MK-III core. 

UsuaUy, such double oxides are highly temperature-resistent and it can be expected that these fission products will show virtually no thermal-induced migration in the fuel matrix. This assumption has been confirmed by numerous measurements that show a distribution dependent on the bumup profile of the fuel. Most of the information in this area has been gained by examining fast breeder reactor fuels (Kley-kamp, 1985), i. e. materials which had been irradiated at distinctly higher fuel temperatures than LWR fuels. For this reason, thermal-induced migration of the polyvalent fission products in LWR fuels, with their distinctly lower temperatures during reactor operation, can be ruled out. 

Despite the limited solubility of BaO in UO2 (quite in contrast to SrO, which is highly soluble), barium seems to be homogeneously distributed in the irradiated fuel matrix, presumably as Ba(II) in the UO2 lattice. Barium can also be incorporated into the perovskite-type grey phase which was detected predominantly in high-burnup fast breeder reactor fuels however, the significance of this phase in irradiated LWR fuels seems to be questionable. The chemical state of fission product barium in the oxide fuel apparently depends strongly on the stoichiometry of... 

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