In the early years of nuclear power development, the first small-scale boiling water reactor exploded catastrophically, claiming the lives of three engineering technicians. This nuclear accident occurred in January of 1961 at the U.S. National Reactor Testing Station near Idaho Falls, Idaho, and is the only nuclear accident resulting in the loss of life ever to occur in the United States. The accident, called a "prompt criticality," resulted from a variety of factors, including inadequate design, inadequate materials testing, and poor procedures and training.