Value stream map: a small modular reactor build
A small modular reactor is built mostly in factories and assembled on site. That moves the hard problems from the site into the supply chain: forgings, factory capacity, transport and the timing of deliveries against site readiness.
This map follows one reactor module from design release to first power. It shows each stage, the work waiting between stages, and how much of the lead time is working and how much is waiting.
Select any box for its analysis. Boxes marked “drill down” open the next level. Triangles are inventory: finished work waiting for the next stage. A red box is the constraint.
Three things to design for
- Most of the lead time is waiting, not working. In this example the module spends more time in queues, stores and hold points than being made, moved or installed. Waiting is cheaper to remove than working time, and it is where the programme is won or lost.
- The constraint moves. On the first unit, heavy forgings set the pace. In a series build the forging queue shortens and the factory’s qualified welders become the limit. The supply chain and the skills pipeline should be sized for the series constraint, not the first unit.
- Logistics is where finished work hides. Modules finished early wait in preserved storage, on the quay or on site laydown. Each week costs money, risks damage and needs re-inspection. The fix is a single delivery sequence pulled by site readiness, so the factory builds to the install order.
How the map is built
The top level is built from the drill-downs, so the two always agree. Each step has working time, waiting time inside the step and, where it matters, inventory waiting after it. Utilisation marks how close a shared resource is to its limit. Above 90% it is shown as the constraint.
Regulatory consents, site civils and people run in parallel with the main stream. They do not add to the module’s lead time, but each one can stop it. Their drill-downs show where.
We use the same method on live programmes, with contractor, supplier and outturn data in place of the placeholders. It shows where to spend effort and what a change is worth before it is made.