A methodology is presented that can be used to determine if a proposed fusion power plant design modification, directed at improving plant safety, is cost-effective. Both normal and accident conditions can be handled. An approach for evaluating the maximum justified spending on safety is outlined. The incremental costs involved with a dose reduction measure are identified, and models for their assessment are given. By comparing the spending on the design modification to the justified expenditure ceiling, the cost-effectiveness of the design can be assessed. The utility of this approach is illustrated through two examples. For normal plant conditions, the cost-effectiveness of replacing the steel alloy PCA by low-activation silicon carbide (SiC) in the STARFIRE design is assessed. Based on a specified set of assumptions, it was determined that if the installed cost of SiC components is less than $110/kg, then the low-activation design is cost-effective. The second example illustrates the applicability of the methodology to accident situations. Four emergency detritiation options for the International Tokamak Reactor, using zero, one, two, or three cleanup units, are evaluated. The assessment was based on the release of 25 g of tritium into the reactor building and on several specified assumptions. The analysis indicated that if the probability of the accident occurring exceeds 3.59 × 10−2, the most cost-effective option would be the use of one detritiation unit. For lower probabilities, the use of any cleanup system would not be justified.