In combination with a boiling water nuclear reactor core undergoing a reload, an improved core reload and process of reloading is disclosed. The core reload consists of fuel bundles having differing design margins to critical power and linear heat generation rate. Specifically, a first part of the core reload is selected from fuel bundles having relatively high critical power margin and relatively lower linear heat generation margin. A second part of the core reload is selected from fuel bundles having relatively high linear heat generation margin and relatively low critical power margin. Distribution of the reload fuel bundles throughout the reactor core occurs as a function of critical power margin and linear heat generation rate margin. Specifically, fuel bundles having the high critical power margin are placed in selected intervals to the central portion of the cylindrical core. Fuel bundles having high linear heat generation margin are placed in the peripheral region of the core. Preferably and on a diameter basis, the middle third of the core is interspersed with fuel bundle loading including the high critical power margin fuel bundles. The outer third of the core is interspersed with fuel bundle loading including the high linear heat generation rate margin. There results an overall core loading having overall power exceeding that power attainable by the prior art practice of utilizing one margin design uniformly distributed throughout the core.