Nitrogen Injection Begins to Prevent Re-Criticality and Hydrogen Buildup

To prevent recurrence of hydrogen explosions and the theoretical risk of re-criticality, TEPCO began injecting nitrogen gas into the reactor pressure vessels (RPVs) of Units 1, 2, and 3. Nitrogen injection displaced residual hydrogen and oxygen, creating an inert atmosphere. This was one of the first successful stabilization measures at the plant, demonstrating that while the cores were badly damaged, they could be managed.