“On 20 May, two workers at unit 1 of the Fukushima Daiichi plant made their way to the basement of the reactor building to assess flooding there. The workers reported that the water in the basement was some 4.2 metres deep. This was slightly higher than the level measured over a week ago, when plant owner Tokyo Electric Power Company (Tepco) first confirmed the existence of water…

The increase in the level of the water in the basement of the reactor building suggests that water being pumped into the reactor to keep it cool is indeed leaking through both the reactor vessel and containment vessel.

Tepco continues to empty water from the cabling trench at unit 2 and from the turbine building of unit 3. This water is being pumped to the central waste treatment facility on the plant site. By 20 May, some 7932 tonnes of water had been removed from the trench at unit 2, while 852 tonnes had been pumped from unit 3’s turbine building…

Tepco has now reported that the presence of highly radioactive debris around unit 3. The company said that it had found debris releasing 1000 millisieverts per hour in an area south the unit’s reactor building – the highest level of radiation so far discovered in debris on the Fukushima Daiichi site.”

“Since the rods in the spent fuel pool are apparently intact the hydrogen must have come from somewhere else.”

That statement isn’t accurate. Hydrogen is formed continuously under normal conditions (intact rods) by radiolysis of water. That’s why spent fuel pools are vented and monitored for hydrogen.

If cooling to a pool were interrupted, the rods could heat up enough to accelerate hydrogen production via oxidation of the zirconium cladding. The rods could still remain intact and never rupture depending on the specific conditions of a particular pool.

Previously the assumption was the only way hydrogen could have built up in unit 4 was from exposed fuel rods in the spent fuel pool.

Since the rods in the spent fuel pool are apparently intact the hydrogen must have come from somewhere else. That’s good because we really don’t want those rods, which are outside any sort of containment, getting hot enough to start melting.

Mike.