Optimal fuel loading Schemes for pressurized water reactors

A method was developed to determine optimum fuel loading patterns for pressurized water reactors (PWR). An optimal loading pattern is defined in which the local power peaking factor is lower than the maximum allowable value and the effective multiplication factor is maximized in order to extract the maximum energy 'low leakage (L.L.)'. The low leakage loading policy becomes the strategy adopted recently by most utilities. This policy is compared with the conventional out-in checkerboard loading scheme which is consisting with the most acceptable power distribution 'flat power'. The goal is performed without using burnable poisons inside fuel elements. This is desirable because the burnable poisons can not be totally depleted and therefore the residual burnable poisons will result in undesirable shortening of the cycle length. Also, the cost of the burnable poisons can be a significant contribution to the total fuel cycle cost. The developed program is based on a direct search method using an iterative approach in this search routine. A modified two-group two-dimensional coarse mesh diffusion theory method is used. The application of this method to the 2568 MW-t-h PWR results in: a) a significant increase in cycle length by about 10 compared with the conventional loading scheme, b) a reduction in pressure vessel embrittlement, due to decrease of the flux at the pressure vessel, by about 15% in comparison with the conventional loading scheme. The program has burnup capability which can be used to check power peaking throughout core life. 11 figs., 3 tabs