Determination of safety limit minimum critical power ratio

A method for determining a safety limit minimum critical power ratio for a nuclear fuel core of a particular Boiling Water Reactor, comprising:

• determining, by a computer, a generic transient change-in-critical-power-ratio distribution of values based at least upon a pre-computed nominal change-in-critical-power-ratio bias value and a change-in-critical-power-ratio standard deviation;
• determining, by the computer, an initial critical power ratio for each of a plurality of fuel rods in the core;
• determining, by the computer, a plurality of transient minimum critical power ratios for the plurality of fuel rods in the core by applying the generic transient change-in-critical-power-ratio distribution of values to each determined initial critical power ratio;
• determining, by the computer, an operating limit minimum critical power ratio (OLMCPR) value by computing a mean number of fuel rods subject to a boiling transition corresponding to a histogram of the plurality of transient minimum critical power ratios and selecting an operating limit minimum critical power ratio value as a transient minimum critical power ratio which results in a corresponding mean number of fuel rods subject to a boiling transition value that is less than a cutoff value;
• and
• determining, by the computer, the safety limit minimum power ratio using the operating limit minimum power ratio, the nominal change-in-critical-power-ratio bias value, and the change-in-critical-power-ratio standard deviation.