Startup Valar Atomics said it has achieved cold criticality – an essential nuclear milestone – with the help of one of the country’s top nuclear laboratories.

The California-based company, which recently announced it had secured a $130m (€112m) funding round, claims that it is the first nuclear startup to create a critical fission reaction.

Valar Atomics said approach-to-criticality operations began at Los Alamos National Laboratory’s National Criticality Experiments Research Center at the Nevada National Security Site on 12 November and zero-power criticality was achieved at 11:45 local time on 17 November.