Muitiobjective pressurized water reactor reload core design by nondominated genetic algorithm search

The design of pressurized water reactor reload cores is not only a formidable optimization problem but also, in many instances, a multiobjective problem. A genetic algorithm (GA) designed to perform true multiobjective optimization on such problems is described. Genetic algorithms simulate natural evolution. They differ from most optimization techniques by searching from one group of solutions to another, rather than from one solution to another. New solutions are generated by breeding from existing solutions. By selecting better (in a multiobjective sense) solutions as parents more often, the population can be evolved to reveal the trade-off surface between the competing objectives. An example illustrating the effectiveness of this novel method is presented and analyzed. It is found that in solving a reload design problem the algorithm evaluates a similar number of loading patterns to other state-of-the-art methods, but in the process reveals much more information about the nature of the problem being solved. The actual computational cost incurred depends: on the core simulator used; the GA itself is code independent.

Appraisal of PD6493:1991 fracture assessment procedures

PD6493:1991 fracture assessment have been performed for a range of large-scale fracture mechanics tests conducted at TWI in the past. These tests cover several material groups, including pressure vessel steels, pipeline steels, stainless steels and aluminium alloys, including parent material and weldments. Ninety-two wide plate and pressure vessel tests have been assessed, following Levels 1, 2 and 3 PD6493:1991 procedures. In total, over 400 assessments have been performed, examining many features of the fracture assessment procedure including toughness input, proof testing, residual stress assumptions and stress state (tension, bending and biaxial). In all cases the large scale tests have been assessed as one would actual structures: i.e., based on lower bound toughness values obtained from small scale fracture toughness specimens.