This study aims at development of the best-estimate system analysis code, which shall be applied generally to performance analysis, guide for operating procedures, accident management, and Non-LOCA analysis. In this year, both examination of the characteristics of TASS1.0 and its verification/validation on the design basis accidents have been carried out. One-dimensional kinetics model has been developed for core reactivity and a steam generator model has been also developed using a moving boundary between boiling and subcooled zone in the riser. The calculational results of TASS1.0 comparing with those of RELAP5/MOD3 have shown unrealistic behaviors of pressurizer and break flow. Inconsistancy among governing equations in the SG model also have been found. In next year, the development of TASS2.0 should take into account of improvements on the identified problems. (Author).