Here's two excerpts from yesterday's tele-conference of the Union of Concerned Scients. The first addresses the "salt-water question":

"Can you please comment on the New York Times story about the risk of salt build-up on the inside the reactors and what that might mean?

MR. LOCHBAUM: Yes, this is David Lochbaum, I'll take a first shot at. The salt water that's being used for both the spent fuel pools and the reactor cores will as that water evaporates leave the salt behind. If there's complete or near total evacuation of the water, then you have a lot of salt skewing left behind, and it could insulate the fuel and impede the heat transfer from the pellets inside the fuel through the cladding, through the salt layer, to the water, once water is restored.

So, they're, as quickly as they can, they're likely to want to stop injecting sea water, start injecting fresh water to dilute the salt concentration that's already in the spent fuel pools and in the reactors.

They were basically down to only the option of using sea water, so they were pretty much forced into using that for as long as they only had the one option.

It is complicating what they do, not only because of the effect that the salt could impede heat transfer and potentially block some of the cooling water flow paths, but it's also very corrosive and it will do damage to components in the plant. So that they need to, as quickly as they can, get out of using sea water, get it back out of the plant as quickly as they can. And again, they had no option, they had to use the only water they had available, given the baggage, even the baggage that it carried."

The second excerpt goes back to venting and the likely cause of the hydrogen explosions:

"REPORTER: Were they also venting, though, from the primary containment into the secondary containment? Were there relief valves that would have allowed the hydrogen to get out of the primary into the secondary?

MR. LOCHBAUM: You know, our understanding because of the periodic venting of the reactor vessel, they also had in turn to periodically vent the primary containment, because it would pressurize also. The normal way for venting the containment is through the reactor building inside piping that would discharge it through a stack outside of primary or secondary containment as well.

You've probably seen pictures where they have those stacks that are surrounded by scaffolding or supports to hold them. That should have been where the vented atmosphere from the primary containment went, was up through those stacks. For some reason, the hydrogen ended up in the reactor building itself.

We've posted something on our blog, allthingsnuclear.org, that suggests one pathway that it may have been that they waited to vent the containment too long, and the pressure built up, actually lifted the reactor vessel head off the flange enough to leak hydrogen into the reactor building.

Since they were following the same procedure, that would explain why it happened on Units 1, 2 and 3. They waited to the same pressure point, it was high enough to lift the reactor vessel head, not blow it off the top, but just enough to provide a small pathway for hydrogen to leak out.

The reason we provide that pathway, possible pathway, is that that did happen at the Brunswick Nuclear Plant, during its initial start-up testing, they pressurized the containment, the head lifted off of the flange and it wasn't hydrogen in those days, it was air that leaked out into the reactor building. So, we're saying since that happened once, it's possible that that same scenario explained what happened on Units 1, 2 and 3. The one difference between Unit 2 and the other two units is that the hydrogen seems to have exploded either in the torus or in the reactor building area just outside of the torus. We're not sure why there's a difference between that unit and the other two units in that regard. "

The current puzzle in my mind is why it is not Unit 2 which is in major trouble this morning. It's explosion was more internal and was thought to have breached the "torus" underlying the primary containment. But now officials are suggesting that there is a breach of primary containment in Unit 3.

All will be clear five years from now! The film release scheduled for next month may not get it quite right, except for the personal drama.

Charley Noble