The NRC is soliciting comment on draft interim staff guidance, Material Compatibility for non-Light-Water Reactors, DANU-ISG-2023-01 Revision 1, which assists the staff in reviewing applications for non-light water reactor designs including power and non-power reactors.

Interim staff guidance is how the agency tells its own reviewers what to look for before a formal regulatory guide exists. For a technology with little settled precedent, it is the operative standard.

The revision adds an appendix describing the information staff have generally used to review materials of construction and the performance of passive structures, systems and components. Written-down review practice is worth more to a supplier than the rule it implements, because it is what gets applied.

Non-light-water designs run coolants and temperatures that light water experience does not cover, which makes material compatibility one of the places a design review stalls.