Core fuel composition

If the damage increases, the core transfers to inadmissible condition, and the reactor installation running must be stopped. In such a case, fuel composition contacts directly with coolant that is evidenced by a-activity therein. 

Ductless fuel assemblies are used in the core. Each of three radial zones of the core consists of fuel pins with different diameters (9.1/9.6/10.4mm) with the same fuel composition and fuel pin pith small pins in central and big in outer zone. A rather large fuel pin to pin distance (13.6 mm) provides the large coolant flow cross section, suitable core hydraulic resistance. To reach core breeding ratio equal one, MOX fuel was replaced by U-Pu nitride. 

The reactor core is composed of fuel rods with square cross-section. At the comer there are fins that are spiral with respect to longitudinal axis of the fuel rod. Fuel composition is uranium-zirconium alloy with - 20 % enrichment by U235. Fuel cladding is made of zirconium alloy. Fuel rods are grouped in fuel assemblies (FA). Burnable rods placed in FAs and absorber rods moving outside fuel channels are used to compensate for reactivity change in the core. 

A lot of information has been accumulated on tested fuel. Results of tests of advanced nitride fuel core performed during almost 19 years are very important. Maximum burnup values achieved for different fuel compositions are as follows ... 

The largest efficiency of minor actinides burning can be reached by using core with fiiel without uradium 38 SVRE value as a function "of ma fi"action for different fuel compositions is shown in Table 5. 

The results to be quoted were all obtained by one of these methods. The calculated Doppler coefficients, which have been published for many fast breeder designs, are for systems that differ widely in size and shape of core and blanket, in fuel composition, core composition, etc. A comparison of many of them would not be meaningful, and so a few values will be selected which are suitable to demonstrate the major trends. 

The reactor core is built of fuel assemblies with the same fuel composition and fuel rod pitch. Radial equalization of the FA power and the coolant temperature gains relies on profiling of the fuel inventory and lead flow, with the former provided by using fuel rods of a smaller diameter in the central assemblies and those of a larger diameter in the peripheral ones. The equalized distributions are kept stable owing to the same fuel composition in all assemblies, subject to the condition of CBR s 1. 

Similar composition of the fuel unloaded from and loaded into the reactor core, requires no separation or addition of plutonium, with possible correction the fuel composition by adding to make up for its burnout. 

This fuel cycle is based upon FSV-type fuel, which operated from 1976 through 1989. Fuel composition consists again of two separate TRISO particles, 93% highly enriched uranium (HEU) particles and fertile Th-232 particles to achieve maximum U-233 conversion ratios and therefore limit the amount of plutonium produced. Although HEU-fueled reactors would not be considered for commercial use in the United States, the interest here is historical in nature. This design also uses a once-through fuel cycle, refueling half of the core at every reload interval. 

Finally, Ihe basic CANDU fuel bundle design lends itself to fuel-cycle flexibility because the fuel composition can be easily varied from ring to ring within the bundle. Because of the low sensitivity of neutron spectrum to details of the fuel design, new fuels can be accommodated within operating reactors without changes to the fuel bundle or reactor core geometry. 

Deeper knowledge is required on the properties of the fuel composition, the fuel pellet-cladding interaction (FPCI), which is the basis for the RBEC-M core performance. 

The LFR is compatible with a closed fuel cycle or an open fuel cycle. Fast reactors have been conceived for either fuel cycle scenario, and LFRs can be plutonium (Pu) breeders, Pu burners, or reactors with equilibrium fuel composition and long core life. 

The core design has demonstrated that it is possible to provide an adiabatic reactor concept with equilibrium fuel so that the fuel composition remains the same between two successive loadings, ensuring the fiiU recycling of all the actinides, with either NU or DU as only input and EPs as output. The equilibrium fuel composition is shown in Table 6.4 (Arteoli et al., 2010). 

Homogeneous fuel composition due to fast fuel circulation (in-core turbulence and multiple heat exchanger channels). This homogeneity allows for continuous fuel monitoring. 

The fuel composition is flexible. Core breeding for MOX fuel is facilitated by higher fuel volume fraction and increased fuel smeared density up to 9.2 g/cm. However, better physics parameters are provided for nitride cores, which are more compact and have higher breeding ratio and less excess reactivity. 

In PWR [2], most of the CEA use fingers (or pins or rods) fastened to a central cast spider assembly inserted from the top of the core in the fuel assemblies (Fig. 15.1). The number of fingers per CEA (about 20) and the number of CEA per core (about one for four fuel assemblies) depends on the core dimensions, fuel composition [due to neutron spectrum hardening, more control rods are required for mixed oxide fuel (MOX) fuels], and power. The neutron absorber materials are most often the Ag-In-Cd (AIC)... 

The plutonium fuel evaluation methodology is a multistep evaluation process designed to test and accept or reject a fuel composition based on its performance characteristics relative to a typical LWR fuel and core environment. The first step in the process is to establish mass loadings or volume fractions for a fixed reactivity level (k-infinity). The second step is to evaluate the fuel against the following performance characteristics ... 

The main components of the reactor in this experiment are the control rods. All four control rods are fuel bearing (with a fuel composition same as that of the core). The fine control rod (of 2.3-cm diameter) contains 3.6 g The two safety and coarse control rods are 4.7 cm in... 

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