On the basis of equal health hazard risk, economic assessment of Nuclear is compared with that of coal for expansion planning of electric power generation in the year 2000. In comparison of health risk, the risk on coal was roughly one order of magnitude higher than the risk of nuclear according to various objective thesis about energy system risk assessment. The zero risk condition can never be achieved. Therefore, only excess relative health risk of coal over nuclear was considered for cost. The health risk cost was estimated by calculation of mortality and morbidity cost. Mortality cost was 250,000 US$ and morbidity cost was 90,000 US$ in the year 2000. Through cost/benefit analysis, the optimal emission standard of coal-fired power generation was predicted. This was obtained at the point of least social cost for power generation. In the year 2000, the optimal emission standard of SOx was 165ppm for coal power plants in Korea. From these assessment, economic comparison of nuclear and coal in the year 2000 is shown to be that nuclear is more economical than coal, whereas uncertainty of future power generation cost of nuclear is more than that of coal.