Construction schedule and cost risk for large and small light water reactors

•Uncertainty of cost and schedule for nuclear energy is modeled.•This uncertainty was applied to leading large/small GenIII + designs.•In tight labor markets, single unit SMRs have the least risk.•Reduced cost from Economy of Scale outweighs increased risk in most cases.•Design changes and human errors were the largest drivers for risk. Capital cost and construction schedule estimates for nuclear projects often under-estimate the realized costs upon project completion. Uncertainty quantification of nuclear construction project cost estimates have seldom been used in open-literature and have not shown to effectively bound the realized schedules and costs. Building on recent studies of advanced light water reactor costs and construction schedules, this paper explored the risk of different construction delay drivers and the implication on total installed cost. Using data from previous nuclear projects, as well as other megaprojects and analyses, we modeled the impact of supply chain delays, human error, change orders, and productivity on four different reactor architectures: a large passively safe PWR, a large modular BWR, small modular BWR, and a multi-module PWR. The probability and impact of supply chain delays and change orders were modeled based on the AP1000 construction experience at Vogtle Units 3 & 4, while the human error and productivity models came from non-nuclear sources. The estimated risk to cost overrun and schedule delays were found to be significant. The multi-module plant was the most susceptible to construction delays, and the small modular BWR was the least susceptible. However, the risk mitigation by a small reactor only offset the lost economy of scale in a few scenarios relative to the large reactors, because there was still significant onsite work despite modularization. Access to large labor markets mitigated the upper bound cost and schedule risks significantly for all reactor types. Finally, design changes and the resulting productivity hits were the largest driver of construction delays, and human error was the second largest driver, but supply chain delays only accounted for a small fraction of the delays for the assessed water-cooled concepts.