10.48. Advances in both computing methods and core modeling during recent years have led to automation of many of the iterative steps in the design process. Although the development of optimization procedures has received much attention at universities, the parameters that affect the “best” strategy tend to change over the long planning periods required. Therefore, electric utilities and fuel vendors tend to concentrate on the development of fast and efficient procedures that allow a wide range of loading scenarios to be explored to take advantage of changing economic and regulatory conditions.

The Haling Principle

10.49. In connection with both automation and optimization proce­dures, the Haling principle has proven to be a useful concept [13]. It was shown that if a power shape (power distribution) could be maintained constant throughout the operating cycle by proper management of soluble poison, solid absorbers, and movable control rods, the peak-to-average power value will be at a minimum. Although in practice it may be difficult to achieve such a goal, which would require matching control rod with­drawal with burnup effects, the concept is useful as a reference.

10.50. The Haling principle has been used in some fuel management schemes to separate the multicycle management problem from that of an individual cycle. However, the 1988 revision of regulatory emergency core cooling system modeling methods had the effect of increasing allowable core peaking factors (§12.132). Therefore, there has been a shift in design practice from attempting to achieve minimum core peaking to an emphasis on minimum fuel cycle costs. Such methods do not make use of the Haling principle.