The BWRX-300, explained

The BWRX-300 is GE Vernova Hitachi Nuclear Energy's 300 MWe boiling-water small modular reactor — the design that turned the SMR conversation from slideware into a construction schedule. It is the tenth evolution of GE's boiling-water reactor line, deliberately boring by design: proven fuel, proven water chemistry, and a licensing story regulators already know how to read.

Key facts

• 300 MWe boiling-water reactor, derived from the NRC-licensed ESBWR and using standard GNF2 fuel already in commercial use
• Four units approved at OPG's Darlington site in Ontario, totalling 1,200 MW; unit 1 is under construction
• Excavation of unit 1's reactor building shaft has passed 80 per cent completion, with the reactor pressure vessel in manufacturing
• Poland's Orlen Synthos Green Energy is seeking state financing for 14 BWRX-300 units across three sites

How it works

A boiling-water reactor makes steam directly in the reactor vessel — no separate steam generators, which removes a whole class of components, piping, and failure modes. The BWRX-300 pushes the simplification further with natural-circulation cooling (no primary recirculation pumps) and passive safety systems designed to keep the core cooled for days without operator action or external power. GE Vernova Hitachi's pitch is economic as much as technical: the design targets substantially lower capital cost per MW than previous water-cooled SMR concepts by shrinking the building volume around the reactor.

Where it stands

Darlington is the reference project. Ontario and OPG approved a four-unit program, unit 1 construction is well underway, and OPG has already applied for a 20-year operating licence — the step that would make it the first operating SMR in a G7 country, targeted for completion by the end of the decade. Every utility considering the design watches the same three numbers at Darlington: schedule, budget, and the licensing clock.

The order book is the other story. Poland's proposed 14-unit program would be Europe's first serial SMR fleet if its Contract-for-Difference financing lands, and GE Vernova and Hitachi are marketing the design in the US, UK, and Southeast Asia. Serial orders are precisely what the SMR economic model needs — see the SMR guide for why repetition is the whole game.

Common misconceptions

"It's a new, unproven reactor type." The opposite: it is the most conservative of the leading SMRs — a smaller, simplified configuration of technology that has run commercially for six decades, burning fuel that is already in reactors today.

"SMR means factory-built and shipped whole." Not here. The BWRX-300's heavy components are factory-made, but the plant is still constructed on site — the modularity is in standardized components and repeatable construction, not a reactor on a truck.

Current state (July 2026)

Unit 1 at Darlington is in full construction with major excavation nearly complete and long-lead components in fabrication. The operating licence application is before the CNSC with a public hearing to be scheduled. Poland's CfD request is with the energy ministry. For how the design stacks up against its nearest rivals, see BWRX-300 vs AP300 vs Natrium.