SUMMARY

The high overnight capital cost (OCC), as well as the large delays and cost escalation during construction, make nuclear reactors unattractive for investors. The history of nuclear power plants construction in the US shows the necessity to properly estimate construction costs and cost contingency. Uncertainties during construction can be classified as "know unknowns" and "unknown unknowns". Project managers use tools to describe "know unknowns", while "unknown unknowns", due to their inherent nature, are not knowable. In this work, the cost trends in the various nuclear countries are analyzed, and the costs and the construction schedule of a four-loop PWR (PWR12) are described. A methodology to describe the construction of a nuclear power plant is then presented, and then applied to the Westinghouse SMR. The methodology is then extended to include stochastic analyses through Iman-Conover method to account for correlation between costs and activities. A probabilistic assessment is then performed for the construction of a fully-modularized SMR and a stick-built PWR12. The results show an improved prediction capability of TCIC uncertainty as correlations between variables are taken into account. The inputs of the model are then modified to be consistent with the cost history in the US for PWR12. The trend in the US before 1979 is used to adjust the model inputs to describe a stable nuclear era. The trend after 1979 is used to quantify, a posteriori, the impact of "unknown unknowns", representing regulatory changes during construction, resulting in an increase in cost and cost uncertainty. The analysis shows that the adoption of modular construction does not decrease OCC uncertainty with respect to stick construction, while it has a positive impact on the construction time uncertainty.