Abstract
In early 1950s USAEC launched the strategic step of R&D named “Power Reactor Demonstration Program” in the nuclear power reactors development. The purpose of the program was to enlist private resources to demonstrate the technical and economic feasibility of power reactors. In this program, the light water reactors established a basic design concept in a short development period, but it was economically unsuccessful. After that, reactor manufacturers were able to make light water reactors successful products by pursuing economic efficiency by means of increasing the scale and the power density of reactors, though these reactors were technologically unmature. Such procedure of the development led to weakness of the reactors in safety, that is, core melting due to loss of cooling function.
