UPower (YC S14) Is Building Nuclear Batteries
I am one of the UPower founders.  The key takeaways here are that the main hindrances to novel nuclear are (1) meeting regulatory and safety necessities without huge testing costs, which also require a customer interested in purchasing, and (2) competing with the grid, (3) huge scientific/technical risks if not yet proven.UPower meets these by
(1) being small enough to build a very tough, full scale emulator for testing, never before done in nuclear.
(2) not competing on the grid, which gives immediate, in need customers which is also necessary for regulatory process to complete in (1).
(3) using technologies and materials with decades of experience, in a new way, eliminating the huge uncertainties of many startups you see in the news.