Question

Why didn’t Unit Reactor 2 explode at Fukushima Daiichi just like Units 1 & 3? How did Unit 2 contribute to regional radioactive contamination?

Answer 1

Unit Reactor 2 didn't explode at Fukushima Daiichi just like Units 1 & 3 because Unit Reactor 2 had  Reactor Core Isolation Cooling System((RCIC) instead of ICs. the explosion of unit 1 blew off the blowout panel of the reactor building of Unit 2 and allowed the hydrogen gas to be exhausted which contribute to the regional radioactive contamination. Also, the reactor pressure gradually started to rise approximately 2 h before the RCIC pump stopped and the containment vessel pressure started to drop. This shows the fact that the RCIC pump began to run abnormally, and the steam quantity consumed by the pump (for reactor heat removal) began to drop. As a consequence, the reactor pressure tends to rise, while the containment vessel pressure tends to drop due to the reduction of steam quantity entering the SC water.