10.40. A “scoping” analysis is carried out in the first phase of the pre­liminary design effort to develop long-term strategy considerations and to estimate average characteristics of a fuel batch. For such purposes, a point reactor model that provides a minimum level of geometric representation is usually adequate.

10.41. An example of a modern, fast-running, but sophisticated scoping code is BRACC, which can be run on a microcomputer [9]. Fuel batch reactivity is approximated as a linear function of burnup. Although zero dimensionality (point reactor model) is used, the code accounts for neutron leakage, burnable poison effects, and coupling between assemblies of dif­ferent batches, by various functions and submodels.

10.42. Methods used in conjunction with reload assembly pattern de­velopment are generally based on two — or three-dimensional nodal models. For some years, the Electric Power Research Institute (EPRI) has sup­ported the development of a family of codes to provide a standard core analysis capability for electric utility in-house core management applica­tions. This effort has been known as the Advanced Recycle Methodology Program (ARMP). EPRI-NODE-P was a preliminary design code devel­oped for PWRs. More recently, codes of the SIMULATE family have been developed under the auspices of EPRI for both preliminary and final design [8].

10.43. A two-dimensional version for preliminary design purposes uses the cross-section code CASMO [10] and a four-node per assembly repre­sentation in the model. A number of features are provided, including the ability to analyze core response to control rod insertion. The ARMP pack­age includes SIMULATE-E, a three-dimensional version suitable for final design for which the two-dimensional diffusion theory code, PDQ-7 [11], has traditionally been used. Such three-dimensional analysis is also useful for the evaluation of certain accident possibilities as control rod ejection (§12.75).