Mark-0

Overview

A full-scale, zero-power demonstration of the R1 core at Idaho National Laboratory's RACE facility, built under DOE's Reactor Pilot Program. It has no power conversion or heat-removal loop; the test validated reactor physics, control-drum behavior, and the DOE authorization pathway using BWXT-fabricated HALEU TRISO.

Achieved initial (zero-power) criticality on June 4, 2026. Not an electricity-producing plant. Antares plans to reuse the same INL facility and fuel batch for the Mark-1 electricity-producing reactor in 2027.

Key Specs

First criticality

June 4, 2026

Power level

Zero-power physics test (no electricity, no active heat removal)

Location

INL Reactor and Critical Experiment (RACE) facility, Idaho