[en] The NRC has historically required that the structural/mechanical responses due to various accident loads and loads caused by natural phenomena, (such as earthquakes) be combined when analyzing structures, systems, and components important to safety. Several approaches to account for the potential interaction of loads resulting from accidents and natural phenomena have been used. One approach, the so-called absolute or linear summation (ABS) method, linearly adds the peak structural responses due to the individual dynamic loads. In general, the ABS method has also reflected the staff's conservative preference for the combination of dynamic load responses. A second approach, referred to as SRSS, yields a combined response equal to the square root of the sum of the squares of the peak responses due to the individual dynamic loads. The lack of a physical relationship between some of the loads has raised questions as to the proper methodology to be used in the design of nuclear power plants. An NRR Working Group was constituted to examine load combination methodologies and to develop a recommendation concerning criteria or conditions for their application. Evaluations of and recommendations on the use of the ABS and SRSS methods are provided in the report