Design changes during nuclear construction add delays & re-work

Engineering best practices encourage finalized designs before construction; nuclear cost overruns are sensitive to unplanned design changes that lead to delays and rework. Design changes may arise because

• Construction begins before designs are complete
• Regulatory changes impose new design changes

Beginning construction with an incomplete design

The scale and lead time of nuclear plant construction often results in builders being pushed to start construction before the design is complete. However, proceeding with an incomplete design inevitably results in design changes during the process of construction, causing delays and expensive on-site rework. Lower-cost plants have greater percentages of their design completed at the start of construction than higher-cost plants.

It often requires significant coordination effort just to figure out what work has been done (“Have you poured these foundations yet? Are the columns in yet?”), and what can and can’t be done in that situation. If a pipe needs to run through a beam, it’s easy to design the beam to accommodate that ahead of time. But if it’s a last-minute change, and the beam has already been fabricated, you might have to field cut a hole, or add reinforcing. Or maybe the beam can’t accommodate the hole at all, and you need to redesign the entire piping system (which will of course impact other in-progress work.) And while this expensive redesign is happening, everyone else might need to stop their work.

On a nuclear plant, which can employ up to 5,000 construction workers at a time (one source described planning the temporary construction facilities as equivalent to planning the utilities for a small city), we might expect these sorts of disruptions to be especially severe. A 1980 study of nuclear plant craft workers found that 11 hours per week were lost due to lack of material and tool availability, 8 hours a week were lost in coordination with other work crews or work area overcrowding, and 5.75 hours per week were lost redoing work. All together nearly 75% of working hours were lost or unproductively used.¹

Regulatory changes imposing new design changes

One issue with frequently changing regulations is that it’s often unclear to both builders and regulators how regulations should be interpreted. This creates expensive and time-consuming coordination failures, as builders and regulators gradually work their way to a mutual understanding²

Vectors for addressing the bottleneck

1. Build plants with mature designs

   “To minimize the likelihood of cost overrun, plants should be built using mature designs that don’t need to be changed during the construction process. In construction of the French reactor fleet, for instance, the CEO of the French utility company EDF noted that during plant construction “Whenever an engineer had an interesting or even genius [improvement] idea either in-house or at Framatome, we said: OK, put it on file, this will be for the next series, but right now, we change nothing.” By building multiple reactors using an unchanging design, the benefits of learning-by-doing can be unlocked. In the French reactor fleet, though costs increased whenever a new reactor type was introduced, later plants using a given reactor design tended to be cheaper than earlier plants. Similarly, the 4th unit built at the UAE’s Barakah plant was 50% cheaper than the 1st unit.”³

2. Stabilize the rate of regulatory changes

   ”A stable design is only possible if a plant can be permitted and built without needing to be changed to conform to updated regulatory requirements. Changing the design of a plant during its construction in response to regulatory changes inevitably results in increased costs and project delays. And because the updated design isn’t in the original project scope, the change designs often require the use of “cost-plus” contracts, which reduce incentives for contractors to complete the work under budget. Regulatory changes that inevitably do occur must be made predictable: it must be clear when they’ll be introduced, to what projects they’ll apply to when they are introduced, and exactly how the regulations will be translated to technical requirements. Plants under construction should be grandfathered in under earlier regulations.”³