[en] The purpose of present syudy is to establish the basis for evaluating system availability and potential accidents of nuclear power plants, and to perform probabilistic safety assessment reflecting localized parameters. The State-of-the-Art and their perspectives of the methodologies for reliability and risk analyses have been reviewed during 1981. Here, WASH-1400 methodology, risk-benefit approach, common mode failure analysis, the quantification of human errors, component reliability analysis, statistical inference, etc. have been included in order to indentify the potential studying fields for on-going project at KAERI. A computer-aided reliability analysis system has been constructed as the initial attempt using CAT and PREP/KITT codes in order to quantify engineered safety feature's availabilities. During the study, a computer code, CONINT, has also been developed for quantifying the uncertainties of fault tree analysis results. CAT-PREP/KITT is tested, just for constructing fault tree of AFWS given in WASH-1400. C0RRAL-2, IMPORTANCE, ALLCUTS, FRANTIC-NRC, etc. have also been collected and tested for later use. (Author)