[en] A conceptual design study and accident analysis of small long-life nuclear power reactors used for remote or isolated area has been performed. Lead as well as lead-bismuth is employed as its coolant, and both metallic and nitride fuels are investigated. There are some severe requirements on these reactors for operability, maintainability, safety and proliferation resistance. Some important characteristics of the proposed designs (15OMWt) are: transportability between reactor factory and operation site; capability of long-life operation (12 years) without refueling or fuel shuffling while maintaining burnup reactivity swing less than 0.1%Δk; omission of intermediate heat exchanger; relatively large contribution of natural circulation; negative total core coolant void coefficient of reactivity over all burnup period. These two coolants require quite different operating temperature, and the lead-bismuth works in a wider range of operating temperature. The problem caused by ²¹⁰Po produced from-lead-bismuth is not significant, but may be even desirable from nuclear-proliferation resistance point. For the lead-bismuth coolant, the amount of resources as well as price may become problem. All of the reactors proposed in this study can survive the UTOP, ULOF, UTOP-ULOF and UTOP-ULOF-ULOHS accidents without any help of operator or active devices. All reactivity feedback components are negative for the above accidents. For the nitride fuel reactors, the Doppler effect plays important role during the unprotected accidents. On the other hands, for the metallic fuel reactors the axial fuel expansion plays important role. The radial core expansion is important for both metallic and nitride fuel reactors. The most severe criterion for the accidents is the maximum permissible temperature of cladding for metallic fuel. The margin of this temperature is small for the UTOP-ULOF-ULOHS accident. The lead-bismuth cooled reactors give better performance for the severe accidents compared to the lead cooled reactors due to their lower operating temperature. (author)