Determination of operating limit minimum critical power ratio

A method for determining an operating margin for a nuclear fuel core of a particular Boiling Water Reactor (BWR), wherein fuel design or core configuration are contingent upon an operating margin for the reactor, said operating margin being determined by a process for evaluating an operating limit minimum critical power ratio (OLMCPR), comprising:

• a) determining a generic transient change-in-critical-power-ratio (ΔCPR/ICPR) distribution of values, wherein said generic transient ΔCPR/ICPR distribution is based at least upon a pre-computed nominal ΔCPR/ICPR bias value and an ΔCPR/ICPR uncertainty;
• b) determining initial critical power ratios (ICPRs) for each fuel rod in the core corresponding to a particular BWR plant;
• c) determining a plurality of transient Minimum CPRs (MCPRs) for all fuel rods in the fuel core by applying the generic transient ΔCPR/ICPR distribution to each ICPR determined in (b);
• and
• d) effecting said Boiling Water Reactor operation by applying a selected OLMCPR as an operational control parameter, said OLMCPR selected for the particular BWR by computing a mean NRSBT (number of fuel rods subject to boiling transition) corresponding to a histogram of said plurality of transient Minimum CPRS and selecting an OLMCPR value as a transient Minimum CPR which results in a corresponding mean NRSBT value that is less than a predetermined cutoff value.