The fuel loading weight per unit core volume is determined by considering the moderator-to-fuel volume ratio (Vm/Vj) (which is discussed in the next section) and fuel density. Then the total core volume is calculated from the weight per volume and the total fuel loading weight W determined by Eq. (3.23). Core height and equivalent diameter are determined according to the following conditions.

(i) Equivalent core diameter should be suitable for reactor vessel design and manufacture.

(ii) Core height and equivalent diameter should be as close to each other in value as possible to reduce neutron leakage to the core outside from the viewpoint of neutron economy.

(iii) The number of fuel assemblies should be a multiple of four + one; quarter-symmetry fuel loading pattern and one rod cluster control assem­bly located in the core center.

Current plants have small variations regarding the second condition which was considered in the early core designs. In the process of sizing up the core, a large equivalent diameter has come to be used since fuel active height was standardized (namely, the core height was fixed).

An example of core configuration with fuel assemblies can be seen in Fig. 3.30. The core is a four-loop core with 193 fuel assemblies.