Boron core size

Calculations show that using a uranium dioxide fuel with 60% enrichment on with a zirconium hydride moderator makes it possible to obtain a core size of no more than 25 cm. The reactor is controlled by rotary steel drums with insertion from boron carbide, all drums are located in the reflector. The reactor shielding has a total thickness of 2 m, consisting of two layers light (1.6m) and heavy (0.4m) concrete. 

The material reviewed in this Chapter hitherto has focused on metallacarboranes in which the metal atom is a vertex in an icosahedral cage framework. Until recently, monocarbollide metal compounds with core structures other than 12 vertexes were very rare since suitable carborane precursors were not readily available." However, Brellochs recent development of the reaction of decaborane with aldehydes to give 10-vertex monocarboranes permits a considerable expansion in this area of boron cluster chemistry. As a consequence, several intermediate-sized monocarboranes are now easily accessible and we have recently begun to exploit the opportunities that these present. In particular, we have focused thus far on complexes derived from the C-phenyl-substituted species [6-Ph- zJo-6-CBgHii] It is clear from these initial studies that a wealth of new chemistry remains to be discovered in this area, not only from among the metal derivatives of PhCBg car-boranes such as those discussed in this section, but also in the metal complexes of other newly available carboranes. 

Figure 14 Estimates of mixed-layer pH and atmospheric CO2 derived from boron isotope analyses of planktonic foraminifera recovered from drill cores taken in the western equatorial Pacific. Results are replotted from Pearson and Palmer (2000). Note that uncertainty associated with both pH and CO2 estimates amphfies in the Early Cenozoic. This reflects the intrinsic insensitivity of the boron isotope pH proxy at low pH (see Eigure 12). Atmospheric CO2 estimates require additional assumptions about the size of the DIC pool in surface waters.

The furnace is usually cooled externally to limit the toss of volatile materials and hence the outer mantle stays unreacted. The core contains blocky boron carbide of relatively high purity (total metallic impurities <0.5 mass-%), reproducible stoichiometry (B/C ratio = 4.3) [50], and several percent of residual graphite. The chunks are crushed and milled to the final grain size. 

In order to avoid huge losses of volatile boron oxide compounds, the furnace is cooled externally such that the outer shell remains unreacted. The core contains low-impurity boron carbide blocks (total metal impurities <0.5 wt%) with a stoichiometry of B/C = 4.3 and residual carbon [25]. The blocks are crushed, milled to the desired final grain size, and purified by chemical leaching. 

The core consists of 151 hexagonal fuel assemblies (FAs) (size across flats is 234 mm) with fuel elements and fuel lattice parameters analogous to those in VVER-1000. Each FA contains boron carbide rods which are combined in a cluster to form a control device. The control devices of 135 FAs are connected to drives of the electromechanical control and protection system (CPS). The core height is 3.53m, its equivalent diameter is 3.05m at average power density of 69.4 kW/1. 

Within the constraints imposed by the requirements of symmetry and simplicity, and by the ZPR-9 facility, FTR-3 was intended to apprcndmate the design of the FTR. The core he ight was 91.6. cm. The radii of the timer core zone, outer core zone, and radial reflector were 37.6, 60.3, and 85.4 cm, respectively, hi addition, a 12-cm-thick stainless steel and sodium shield surrounded the radial reflector. The axial reflector thickness was 31.4 cm. The total volume of the Inner and outer core zones was 1045 liters. The U peripheral boron control zones of the FTR-3 were approximately evenly spaced around the outer edge of the outer core. Each control zone was 11.2 liters in volume, extended the full height of the core, and were similar in size and composition to the peripheral boron control rods in the FTR design. 

The reactor module components are contained within three steel pressure vessels the reactor vessel, a steam generator vessel, and connecting cross-vessel. The uninsulated steel reactor pressure vessel is approximately the same size as that of a large boiling water reactor (BWR) and contains the core, reflector, and associated supports. The annular reactor core and the surrounding graphite reflectors are supported on a steel core support plate at the lower end of the reactor vessel. Top-mounted penetrations house the control-rod drive mechanisms and the hoppers containing boron carbide pellets for reserve shutdown. 

Addition of boron after shutdown compensates for die increase in reactivity due to die reduction in the reactor coolant temperature as the core has a negative moderator reactivity coefficient. The boron concentration within the core make-up tanks is at 3400 ppm and sufficient to maintain the reactor at sub-critical conditions. The core make-up tank size and injection capability are selected to provide adequate reactor coolant system boration and safety injection for the limiting Design Basis initiating event. 

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