[en] As one example of decommissioning studies of low power research reactors, RANDEC studied the decommissioning case of a 100kW TRIGA II type research reactor. Immediate dismantling (one year after shutdown) and deferred dismantling after several safestore terms were selected as decommissioning modes, and decommissioning schedules, dismantling methods, costs etc. were studied for these selected modes. The following results were obtained; - generated radwaste exceeding clearance level was approx. 87tons in the case of immediate dismantling, and approx. 27 tons in the case of deferred dismantling after a 50-year-safestore. - as the index of 100 for dismantling costs of the reactor without dismantling of the concrete biological shielding, the estimated index is 1,090 (except the reactor building dismantling) in the immediate dismantling mode. For the deferred dismantling modes after a 5-year, 10-year, 20-year, and a 50-year-safestore, the indexes are 1,300, 1,500, 1,700, and 2,300 respectively. As described above, the decommissioning cost was estimated that the longer safestore resulted in the cost increase, because more management costs were needed for the care during the longer safestore. (author)