Fuel irradiated, structure

Fast Breeder Test Reactor (FBTR) is a 40 MWt/ 13.2 MWe sodium cooled, mixed carbide fuelled, loop type reactor. It has two primary and secondary sodium loops and a common steam water circuit, which supplies high pressure, high temperature superheated steam to turbine generator (TG). Heat is rejected in cooling tower (Fig 1). A 100% capacity dump condenser is provided for reactor operation even when the TG is not in service. The mmn aim of the reactor is to generate experience in the design, construction and operation of sodium cooled fast reactors and to serve as an irradiation facility for the development of fuels and structural material for fast reactors. It achieved first criticality in Oct 85 with Mark I core... 

Baldev Raj et al - Post irradiation examination of mixed (Pu, U) C fuel irradiated in the fast breeder reactor, IAEA - TEC DOC - 1039 on Influence of high dose irradiation on core structural and fuel materials in advanced reactors, 16-19 June 97, Obninsk, Russian Federation. 

In addition to the nuclear fuel rods with the cladding as discussed above, the reactor core also contains structural materials such as spacers, springs, bolts etc., as well as the fuel assembly upper and lower end structures, in which radionuclides are also produced by neutron activation reactions. Quite in contrast with the fuel itself, no generally valid data on the activity inventories of these structural materials can be established. The main reason for this are the differences in composition of the materials used by different manufacturers, in particular as regards impurities such as cobalt (which is the source element of Co which is frequently the predominant radionuclide in irradiated structural materials). Another important fact is that the standard codes for activity calculations such as Origen, Korigen or Anisn usually are quite accurate for the active zone of the reactor core, whereas in the outer regions (where the fuel assembly end pieces are located) only approximate values can be obtained, due to the steep axial decrease in neutron flux. 

The design of the PFBR calls for complete understanding of unique fuel and structural material behavior under high temperature, sodium, and irradiation environments as well as the science and technology aspects in the domains of sodium chemistry, aerosol behavior, sodium fire and sodium water reactions, special sensors for sodium... 

SINTER BMI, Pacific Northwest Laboratory Temperature and fuel structure changes as a function of fuel irradiation time 11,68... 

Properties. Most of the alloys developed to date were intended for service as fuel cladding and other structural components in liquid-metal-cooled fast-breeder reactors. Alloy selection was based primarily on the following criteria corrosion resistance in liquid metals, including lithium, sodium, and NaK, and a mixture of sodium and potassium strength ductility, including fabricabiUty and neutron considerations, including low absorption of fast neutrons as well as irradiation embrittlement and dimensional-variation effects. Alloys of greatest interest include V 80, Cr 15, Ti 5... 

The problem of UO2 pellet densification under irradiation causes contraction and leads to collapse of the cladding in axial gaps in sections of the fuel columns. The solution is to control the manufacturing process to ensure the production of pellets with higher density and stabilized pore structures (pore size and grain size). Prepressurizing the fuel rod with helium also avoids clad flattening,... 

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. 

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