Hexagonal fuel assemblies

The initial SNL analysis used the core model depicted in Fig. 3.1. ° A 2.54-cm-diam fuel compact was surrounded by six 0.8-cm-diam coolant channels in a hexagonal array with a 3. 41-cm pitch. The fuel and coolant channels were contained in an annular core region (i.e., the individual hexagonal fuel assemblies were not modeled explicitly). This yielded a 10% coolant voliune fraction and a 50% fuel-compact volume fraction. The computed void coefficients for total core voiding are given in Table 3.1 for several candidate salts. For salts containing Li, it was assumed that the lithiiun contained no °Li isotope. 

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. 

The reactor core consists of 199 hexagonal fuel assemblies. Each fuel assembly consists of325 fixel rods with burnable poison similar to that of well established PWRs. The dimensions and composition of the fuel rod are the same as those of the existing PWR. The average power density is designed relatively low, 65 MW/m. ... 

The reactor core contains 349 hexagonal fuel assemblies, each of them consisting of 129 fuel rods with a diameter of 9.1 mm and a length of 3.21 m the fuel rods are kept in position by 15 honeycomb-type spacer grids which are fixed on a central channel. Seventy-three of the fuel assemblies contain movable control assemblies with boron steel as an effective material in the V213 fuel assemblies, six of the fuel rods are replaced by fixed burnable poison rods. 

Fuel assembly Hexagonal fuel assemblies with ducts... 

The core consists of 121 hexagonal fuel assemblies with ducts placed in a regular triangular lattice with a pitch of 100 mm. The fuel assembly height is 1800 mm the flat-to-flat size is 97 mm. 

Reactor core Effective cylinder contains 151 hexagonal fuel assemblies the effective diameter is 3.0 m the core height is 3.7 m... 

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.

Core Cylindrical, made up of 313 hexagonal fuel assemblies, equivalent diameter -3.16m, height of active part of the fuel assemblies -2.42 m... 

The reactor core is located in the lower part of the vessel-vault and is composed of 91 hexagonal fuel assemblies with fuel rods of the WER-440 type containing uranium dioxide fuel in a zirconium cladding. The structural material of the fuel assemblies is zirconium alloy. Fuel assemblies are placed in a triangular lattice with the pitch of 147 mm and form a regular and symmetrical system. The reactor core height is 1400 mm the equivalent diameter of the core is 1420 mm. 

Core Cylindrical, made of hexagonal fuel assemblies (FA) with a pitch of 100 mm, effective diameter - 1.5-2 m, height of FA active part - 1.0 m, heterogeneous. Can be surrounded by side and end breeding screens. ... 

To create a RBEC-M cylindrical core with an effective diameter of 4.24 m, hexagonal fuel assemblies without shrouds are used, with a 1.0 m height of the active fuel assembly part. 

An integral primary system layout is employed (Fig. 12.4), ie, reactor core, variable frequency submersible coolant pumps, intermediate heat exchanges, safety system heat exchangers, and cold trap filters. The reactor vessel is enclosed in a guard vessel. There are no auxiliary sodium systems in the primary circuit. The reactor core consists of fuel assemblies, boron shield assemblies, and absorber rods. The central part of the core consists of wrap-spaced hexagonal fuel assemblies and cells with absorber rods. The spent fuel is stored in the reactor vessel for up to 2 years, which facilitates spent fuel cooling and eliminates the need for spent fuel storage casks. Assemblies with boron carbide are placed behind the spent fuel to protect the reactor vessel. 

The R-Z two-dimensional core calculation model, as described by Fig. 2.30, may be a good first approximatiOTi to calculate a fast reactor core with a relatively simple loading pattern of hexagonal fuel assemblies (a tight fuel lattice). In such a configuration, the spatial dependence of the fast neutron flux is small and the rough estimation by the R-Z two-dimensional model may be applicable. 

Fig. 2.33 Hexagonal fuel assembly. (Taken from doctoral thesis of K. Dobashi, the University of Tokyo (1998) [18])...

The hexagonal fuel assembly design also needs to be revised to improve the neutron economy. The neutron moderation provided by the water rods is not sufficient and the core designed with this fuel assembly is under-moderated. 

The square fuel assembly shown in Fig. 2.35 [9] is designed to overcome the problems encountered with the hexagonal fuel assembly. The design is intended to flatten the coolant outlet temperature distribution at the outlet of the assembly by using uniform subchannels and a lower local power peaking. The area of the water rods is also increased from the hexagonal fuel assembly to gain neutron moderations. 

---