[jwalsh07]

Blaming operators? Hardly.

That's like blaming grunts for command decisions. Since I was a grunt I'm loathe to do either.

But it would seem that srubbing the steam and venting it to the atmosphere would be a better idea no?

Now my BS is in Electronic Engineering so I'm not pretending to be a Nuclear Design Engineer. And I hesitated commenting when the 1st building blew but since number 3 blew as well it became evident that the system was designed to vent steam into the building. If that isn't the case then my question does not obtain. If it is the case then the question stands and it has no bearing on the operators and techs at all. I salute all of them.

[SteveH]

But it would seem that srubbing the steam and venting it to the atmosphere would be a better idea no?

I am not certain what they did or did not do and whether they did or did not do whatever they did correctly.

To the extent that explosions of buildings are usually bad and all reasonable steps to prevent it at the design phase would be good whenever practical-- sure.

[raygun]

From what I can gather is that in a blackout situation, water is not circulating through the reactor core (which is quite warm). The coolant water in direct contact with the zironium tubes containing the uranium pellets boils and turns to steam. This steam is routed to a torus pool of stagnant water below the reactor core and is allowed to percolate throughout the cooler liquid water; heat from the reactor core is thereby exchanged from the reactor fuel elements; some of the percolating steam condenses, albeit the temperature of the torus pool rises (and pressure builds as uncondensed steam accumulates in the torus pool reservoir tank); eventually the torus pool itself boils. In order to maintain structural integrity of the primary core containement vessel - and to allow continued heat exchange from within the primary core - pressure within the torus pool tank is relieved by venting its steam into to the atmosphere.

If operators cannot pump additional water into the reactor vessel, the water level will begin to drop, uncovering the fuel rods. If the fuel remains uncovered for an extended period of time, fuel damage, possibly including melting of fuel, may occur. If there is fuel damage, and steam is being vented to the suppression pool, then to primary containment, then to secondary containment (in order to relieve pressure build-up on plant systems), small quantities of radioactive materials will escape to the environment.

The money sentances are here:

When exposed to very high temperatures, the zirconium reacts with water to form zirconium oxide and hydrogen. This appears to have happened at Fukushima Daiichi Unit 1 when a portion of the uranium fuel was uncovered. It is assumed that the hydrogen found its way into the reactor building, accumulated there, and ignited.

That is in extremely ignorant statement; its not that they don't know how the hydrogen got into the secondary containment vessel - which houses both primary reactor core containment and the secondary torus reservoir - its presence being putatively expected during emergencies of such magnitude as 'blackout' operation.

What they don't know is how to get water into the primary reactor core at thousands of PSIG in blackout condition. The system is designed such that the weight of the water in the secondary torus water reservoir acts as a cap against the explosive expansion of gas from within the primary reactor core; should that happen, the entire reactor core would not enjoy the heat sink properties of water and those in the vicinity of the nuclear plant will suddenly encounter a very bad day in an extremely short period of time.

Getting water into the secondary torus pool reservoir itself is not so much of an issue; cap the steam line from the reactor core and allow the secondary torus pool to fill via gravity feed. The problem is budgeting the mass of water contained in the primary loop such that sufficient heat can be exchanged from the reactor core.