PERTURBATION ANALYSIS FOR DEMONSTRATION OF REACTIVITY IN CRITICALITY SAFETY ANALYSES

A fissile package assessment per TS-R-1 guidance must be performed assuming that a contents specification provides the maximum neutron multiplication (keff) consistent with the fuel bundle design and transport conditions. In ensuring demonstration of most reactive and realistic contents specification for licensing criticality safety analyses, a variation of parameters is applied to evaluate the effects on reactivity. Perturbation theory is useful in studying the relative worth of a desired parameter, as it allows determination of the sensitivity of the eigenvalues with respect to changes in the system. This sensitivity analysis results in a simplified contents specification that minimizes any potential, unnecessary restrictions that transport package requirements would impose on the fuel bundle design. The process of utilizing perturbation theory to determine the most reactive configuration defined by a set of realistic criteria is applicable to criticality safety contents and package evaluations. Through an optimization process, the parameter of effect is chosen, its function and impact investigated, and the relative worth of the parameter is evaluated by application of perturbation theory. Selection of the parameter value is determined by a set of realistic criteria specified by the application. These criteria add realism to the analysis, through basis on actual designs. By selecting the least worth or most reactive parameter value, the package contents can be specified in a manner that ensures maximum keff consistent with the transport condition. This perturbation technique is applied to a BWR shipping package criticality safety assessment, which assumes the presence of integral burnable neutron absorber (BA) fuel rods. The effectiveness of the BA rods as a neutron absorber varies with the location of the BA rod within the fuel bundle lattice, and the sensitivity was quantified by the largest present absorber. Package criticality evaluations were performed using the TSUNAMI-3D module in SCALE6 code package, which automates the process of sensitivity and uncertainty analysis. Results justify selection of least worth reactivity locations for BA rods in the BWR lattice, while ensuring a demonstration of most reactive and realistic contents configuration for package evaluations.