1. A fueling plan evaluating system comprising: a fueling procedure formulating part configured to formulate fueling procedures of a nuclear reactor; an input setting part including: an input processing block to input and set values for calculations, a fueling procedure database configured to perform storage management of the fueling procedures formulated by said fueling procedure formulating part, a reactor-core-simulator-calculation nuclear-model database configured to store physics models for performing calculations through reactor core simulation, and a calculation condition database configured to store calculation conditions for performing at least one of control rod worth calculations and reactor shutdown margin calculations; a maximum worth control rod candidate selecting part including a control rod worth calculating unit configured to: input fuel loading and control rod patterns of each fueling procedure from said fueling procedure database, input a simpler second physics model, compared to a subdivided first physics model, the simpler second physics model to direct reactor shutdown margin calculations, from said reactor-core-simulator-calculation nuclear-model database, calculate, with said second physics model, from a difference between a degree of subcriticality of a reactor core in a state that all insertable control rods are inserted and a degree of subcriticality of the reactor core in a state that a focused single control rod or single pair of control rods is withdrawn, a control rod worth of said focused single control rod or single pair of control rods for each fueling procedure, calculate a control rod worth of a control rod or a control rod pair of each planned fueling procedure, and select a determined number of control rods or control rod pairs with large values of control rod worth as maximum worth control rod candidates; a reactor shutdown margin calculating part configured to: input the maximum worth control rod candidates selected by said control rod worth calculating unit, input a subdivided first physics model used for reactor shutdown margin calculations from said reactor-core-simulator-calculation nuclear-model database, and calculate, using said subdivided first physics model for reactor shutdown margin calculations, for each of the maximum worth control rod candidates, reactor shutdown margin in a case that, from the fuel loading and control rod patterns, a focused maximum worth control rod candidate is withdrawn; and an output part configured to accept the reactor shutdown margin calculated by said reactor shutdown margin calculating part, and configured to output or store said reactor shutdown margin as an evaluation of a fueling plan for a nuclear reactor.