Fuel enrichment zones

Enrichment = mass of fissile atoms/mass of fissile and fertile atoms (i. e. in U-based fuels + all Pu isotopes in U/Pu-based fuels) 

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At 20°C At operating temperature Width across flats Subassembly length Number of fuel enrichment zones... 

CORE AND BLANKET LAYOUT OR GEOMETRY (cont.) 2.9. Fuel enrichment zones ... 

The active core consists of 181 fuel subassemblies with two enrichment zones, of which 85 with 21% Pu02 content are in the inner enrichment zone and 96 with 28% Pu02 content are in the outer enrichment zone. Each fuel subassembly consists of 217 helium bonded pins of 6.6 mm outside diameter. Each pin has 1000 mm column of MOX, 300 mm each of upper and lower depleted UO2 blanket columns and lower fission gas plenum (fig. 1). 

The KALIMER core system is designed to generate 392 MWth of power. The reference core utilizes a homogeneous core configuration with two driver fuel enrichment (< 20% zones that can allow a compact core and fuel shuffling. The core, shown in Figure 3, consists... 

In SNEAK-2 (core hei t 60 cm), two concentric enrichment zones were first loaded entirely witti U1 and U2 later a 90 sector containing Pul and Pu2 was introduced. The size of this sector was increased by surrounding it widi a MASURCA-im-fueled buffer, to establish a better equilibrium spectrum in the experimental region. Since this core had a radial structure similar to the prototypes, the main interest was in the radial dependence of the parameters measured. 

Assembly 2 is a simulated aside-fueled core with two " enrichment zones of equal .vbl(ime, surrqunied Iqr a UQ2- sodium blanket and a steel reflector. The. Mre volume, fractions are 32% ojUde fuel eq vident, 4d%.So um,. 19%" steel, and 9% void. The inner, lower enrichment zone has a Single-drawer cell, with one column of Pu-U sdloy per drawer, and the miter zone has a tw-enrichment ratio, based on Pa4- Ri concentrations, is 1.51. 

The PRISM core has a heterogeneous layout of fuel, blanket, control, reflector, and shield assemblies. Three hundred and ninety-one core assemblies are broken down into 192 fuel assemblies in two TRU enrichment zones, 114 reflector assemblies, 66 shield assemblies, 6 GEMs, 9 control assemblies, and 3 ultimate shutdown assemblies. The baseline core configuration is shown in Figure 6.16. 

Given the small core size, neutron leakage and power peaking were significant. It was necessary to employ a central blanket incorporating two low-enrichment zones and three radial enrichment zones in the driver fuel to achieve satisfactory power peaking factors. 

Figure XXII-7 shows the SSTAR core map. The fuel lattice consists of cylindrical fuel rods arranged on a triangular pitch (the hexagonal geometry does not imply that the core is formed of individual hexagonal fuel assemblies or bundles it merely reflects the assumed nodalization used for neutronics modelling.) A central two low enrichment zones blanket, the three enrichment zones, and locations for shutdown and control rods are indicated in the figure.

The transuranic isotopic vector is assumed to be representative of fuel separated from used LWR fuel. The use of eliminates parasitic (n, p) reactions in and waste disposal problems that would be associated with " C production. In order to reduce the core peak-to-average power ratio, three TRU enrichment zones are employed. 

The power distribution over the core radius was flattened by the incorporation of a medium fuel enrichment (21%) zone between the existing core zones with "low" (17%) and "high" (26%) enrichment of fuel, resulting in a decrease of the fuel rod specific heat rating. 

A simpler application of under-sodium ultrasonics in which these difficulties can be avoided is the identification of components, particularly fuel subassemblies. A final check that the fuel has been loaded in the correct pattern can be made by identifying each subassembly positively as it is loaded. Such a system makes use of a series of marks machined into the top of each subassembly to form a code which identifies its type and, in particular, its enrichment. This code is read by an ultrasonic scanner as the subassembly is loaded, so that the correct assignment to core enrichment zones can be assured. 

Due to the large coolant temperature rise in the core, a cosine distribution may not be the ideal axial power distribution for the Super LWR. From the viewpoint of reducing the fuel temperature and effectively cooling the fuel rods, a bottom peak distribution may be more suitable than the cosine distribution. A bottom peak power distribution can be attained by dividing the fuel into two axial enrichment zones as shown in Fig. 2.76. Compared with the middle peak design (for the cosine power... 

The fuel enrichment in the seed assemblies is axially zoned to avoid excessive power peaking at the bottom part of the core where the coolant density is high. 

The seas are a source of aerosol (i.e. small particles), which transfer to the atmosphere. These will subsequently deposit, possibly after chemical modification, either back in the sea (the major part) or on land (the minor part). Marine aerosol comprises largely unfractionated seawater, but may also contain some abnormally enriched components. One example of abnormal enrichment occurs on the eastern coast of the Irish Sea. Liquid effluents from the Sellafield nuclear fuel reprocessing plant in west Cumbria are discharged into the Irish Sea by pipeline. At one time, permitted discharges were appreciable and as a result radioisotopes such as Cs and several isotopes of plutonium have accumulated in the waters and sediments of the Irish Sea. A small fraction of these radioisotopes were carried back inland in marine aerosol and deposited predominantly in the coastal zone. While the abundance of Cs in marine aerosol was refiective only of its abundance in seawater (an enrichment factor - see Chapter 4 - of close to unity), plutonium was abnormally enriched due to selective incorporation of small suspended sediment particles in the aerosol. This has manifested itself in enrichment of plutonium in soils on the west Cumbrian coast,shown as contours of 239+240p deposition (pCi cm ) to soil in Figure 3. 

Neutron multiplying parameters for large SP placement spacing had been studied using RITM reactor code, in which the neutron transfer equation is solved by the method of successive collisions. The composition of the canister (R=ll cm) fuel zone is represented by the uranium-zirconium SNF with enrichment of 56.7% by... 

The fuel elements in power reactor cores are distributed in zones of uranium enrichments, with the highest at the periphery to compensate for the lower neutron flux toward the periphery, and thereby achieve a flatter neutron-flux profile and higher power output. About once a year the fuel elements are discharged from the central zone of the core, and elements in the outer zones are moved inward. Fresh fuel elements are loaded... 

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