[en] The presence of a natural gas transmission pipeline near a nuclear plant site introduces risks to the plant facilities and personnel. A sudden rupture of the transmission line releases large quantities of natural gas in short periods of time. The escaping gas disperses in the atmosphere, creating a gas/air mixture commonly referred to as a cloud. Under some meteorological conditions, the flammable region of the cloud can be relatively widespread and extend thousands of feet from the rupture. The analytical methods developed to provide quantitative estimates of the risks to nuclear power plants from hazards associated with pipeline system failures are described. The overall methodology used in the analysis is presented, followed by a description of the analytical models employed