Fukushima Daiichi No. 5 and 6

Due to suspicion of hydrogen gas emission at No. 5 and No. 6 plants, coupled with the slow heatup over time of the spent fuel pool at No. 5, TEPCO has created three holes in the roof of each of the reactor buildings -- No. 5 and No. 6 -- to absolutely prevent any hydrogen gas buildup. TEPCO is now all too well aware of the consequences of this and appears to have decided that any risk due to openings in the roof is worth the payoff with no hydrogen explosion risk. That's a wise policy.

Normally you'd be able to detect hydrogen levels in the buildings, ventilate the buildings through HEPA filters and even in some plants you would have hydrogen burners to recombine hydrogen before it reaches combustible (4% by mass) or even approaches explosive (19% by mass) concentrations in air.

6:55 PM Eastern Saturday 3/19
ATOMIC POWER REVIEW