Startup Valar Atomics said on Monday that it achieved criticality—an essential nuclear milestone—with the help of one of the country’s top nuclear laboratories. The El Segundo, California-based startup, which last week announced it had secured a $130 million funding round with backing from Palmer Luckey and Palantir CTO Shyam Sankar, claims that it is the first nuclear startup to create a critical fission reaction. The pilot program, which was formed following an executive order President Donald Trump signed in May, has upended US regulation of nuclear startups, allowing companies to reach new milestones like criticality at a rapid pace. “Zero power criticality is a reactor’s first heartbeat, proof the physics holds,” Valar founder Isaiah Taylor said in a statement. Enriched nuclear fuel releases neutrons, which hit other atoms, which then split apart; neutrons from that process then hit other atoms, and start the reaction over.