Method of determining nuclear reactor core design with reduced control blade density

An arrangement for determining a core design for a nuclear reactor, comprising:

• a memory for storing a plurality of fresh fuel bundles to be evaluated in a reference core design;
• an interface for receiving a set of limits applicable to the reference core design, and for selecting a unique subset of fresh fuel bundles from the bundles stored in memory to be evaluated in the reference core design, wherein the set of limits include a target hot excess reactivity constraint to be satisfied over a given core energy cycle and a given desired control blade definition for the reference core design that is set for the core energy cycle;
• and
• a processor arrangement for generating the reference core design based on the received limits, the reference core design including an initial loading pattern of current fresh fuel bundles arranged in a plurality of fuel locations within the reference core design and the given desired control blade definition;
• wherein the processor arrangement is configured to implement:
• a replacing function to replace, at each fuel location, at least one of the current fresh fuel bundles with at least one of the selected fresh fuel bundles;
• a simulating function to direct simulation of reactor operation on the reference core design to produce a plurality of outputs, each output corresponding to the reference core design containing one or more of the selected fresh fuel bundles;
• and
• a ranking function to rank the outputs based on the defined set of limits, the highest ranked output representing an accepted core design for the nuclear reactor that satisfies the target hot excess reactivity constraint with the set control blade definition.