Genesis wrote..

I'm very curious as to why they're doing that if they allegedly have external power of any sort, as if they have working high-pressure pumps and a Hx I'd expect them to cool the unit using the usual path.

I strongly suspect that at some point they developed an unisolable loss of coolant causality and haven't disclosed it yet.

Granted we don't know exactly what has been damaged in each plant from the earthquake and tsunami but there's no obvious reason unit 1 should be in so much worse shape than the others. In addition, flooding the reactor container is normally only something you do as a last resort when the reactor vessel can no longer hold water.

CNN reported that they are pumping boron in with the sea water.

Also, japanese government handing out iodine tablets.

I think you're probably right, as that's the only rational explanation for flooding the containment in this fashion - there's a failure inside the containment building and beyond the last valve they can close.

What also bothers me, however, is the statements that they're feeding boron into there. If the unit is subcritical what purpose does that serve? That's a neutron poison but what does it add to the picture in terms of stability of the unit is subcritical?

Something smells here.

Asimov wrote..

CNN reported that they are pumping boron in with the sea water.

That's necessary due to the temperature of the water. If you cool one of those reactors down to ambient temperature they need boron because the control rods are insufficient to keep the reactor shut down at those temperatures.

The US Navy spends a fortune on halfnium to make sure their reactors stay shut down even if the most reactive rod is removed under the worst cases of reactivity and temperature.

Commercial power plants do not do this - they require chemical shutdown if you cool the plants down too far below normal operating temperature.

Reposting from main thread:

Quote:

Tokyo Electric Power Co. said Sunday another reactor of its quake-hit Fukushima nuclear power plants had lost its cooling functions, while at least 15 people at a nearby hospital were found to have been exposed to radioactivity.

The utility supplier notified the government early Sunday morning that the No. 3 reactor at the No. 1 Fukushima plant had lost the ability to cool the reactor core. The reactor is now in the process of releasing radioactive steam, according to top government spokesman Yukio Edano.

It was the sixth reactor overall at the Fukushima No. 1 and No. 2 plants to undergo cooling failure since the massive earthquake and ensuing tsunami struck Japan on Friday.

The disaster raised fears over radioactive leaks from the plants after cooling systems there were hampered, most seriously at the No. 1 reactor.

An explosion Saturday at the No. 1 plant blew away the roof and the walls of the building housing the No. 1 reactor's container.

The government and nuclear authorities said there was no damage to the steel container housing the troubled No. 1 reactor, noting that the blast occurred as vapor from the container turned into hydrogen and mixed with outside oxygen.

Tokyo Electric Power has begun new cooling operations to fill the reactor with sea water and pour in boric acid to prevent an occurrence of criticality. Chief Cabinet Secretary Edano said in a press conference Sunday morning that there had been no major changes in the results of monitoring radioactivity near the No. 1 reactor.

Following the explosion, the authorities expanded from 10 kilometers to 20 km the radius of the evacuation area for residents living in the vicinity of the Fukushima plants.

The Fukushima prefectural government said Saturday that three people had their clothes contaminated with radioactive substances while fleeing from the No. 1 nuclear plant.

The Fire and Disaster Management Agency said Sunday that 15 people were found to have been contaminated at a hospital located within 10 km from the No. 1 reactor. Edano said there was a possibility that nine people who fled on a bus had been exposed to radioactivity.

http://english.kyodonews.jp/news/2011/03....

Ab: Yea, I know. Just the first "official" mention of it I've heard. (And confirmed by kyoto news above.)

Part of the reason for the evacuations is so that they can do more steam dumping without worrying about the short-lived radiation affecting the civilian population.

Abn: How do you load the thing then without it starting up on you? You've got a higher criticality available with fresh fuel than used.....

I know that PWRs have an initial boron load and then dilute it. There are also ways of heating up the primary without operating the reactor. I'm not exactly sure what procedure BWRs use.

From what I can find doing quick searching it looks like BWRs don't need chemical shims like PWRs use so then their rods should be enough to keep the core shutdown by themselves.

However the reactor that recorded a problem with a control rod was at the other site.

Perhaps this precaution could be related to the extra moderating effect of having water outside the reactor vessel as well as inside as well as the fact that if you've had fuel element failure you can no longer be certain of your core geometry and thus the adequacy of your cold shutdown margin.

Karl,

Re: Seawater..

it could be that the generators were damaged.. and/or they ran out of fuel to keep the pumps running.

i think in a singular event.. they could have controlled this easily.

But in the context of what has happened in Japan, it may not be possible to avert a worst case scenario.

You happen to know how long it must reamin cooled after SCRAM until it essentially cools on it's own?

I think you can blame the tsunami for the generators going offline.

It's discouraging to realize they could build this thing in a tsunami plane to begin with, but to not have safeguards in to keep the diesels about of harms way from a tsunami (like on top of the buildings) and enough fuel to operate for LONG periods of time is unthinkable.

Ofcourse, there could be other reasons, such as actual damage from continued aftershocks screwed up other things. But it seems "power failure" is what we continually hear.

Quote:

I don't understand why, given the presence of lots of steam (that you don't want) during such an event there isn't a system in place to use it to pump feedwater at high pressure.

This I cannot fully understand either.

Why shut down the circulation of the steam into the turbines if that process cools the core and provides power? -The Facility still need both just to maintain integrity of the core reactor systems themselves.

"I don't understand why, given the presence of lots of steam (that you don't want) during such an event there isn't a system in place to use it to pump feedwater at high pressure."

Because that would require power.

I think they do not have a direct line of power to this site.

Normally, the back up power for pumps and systems like you described would come from multiple generators made to take over in such an event.

I think it's obvious that the generators have been rendered useless. Otherwise, they wouldn't be trying to pump seawater into the thing.

Fall out map

http://www.youtube.com/watch?v=QfKawRWSk....

There's another possibility - they have a plumbing failure they're not admitting to, and thus can't get feedwater into the reactor despite the systems.

The production of steam is the basis for the production of the power the plant produces.

The reactors were taken offline.
Granted: earthquake, tsunami; there should definitely be a rigorous and comprehensive examination.

But, the reactors are still producing steam; and being offline the steam is not being piped to the turbines which generate electricity so they are not producing power.

The reactors need power to cool down; basically a very similar process to what the plants are designed to do for providing power is now required just to keep them from melting down.

This seems idiotic.

IF these is enough steam to warrant a pressure release then there is enough steam to shunt off to the usual turbine systems even if the aim is simply to leech heat off the reactors.

How can anything actually be made any worse by dissipating the heat via the usual heat-transfer turbine systems used by the reactors to provide power?

You don't know if the plumbing or turbines are any good ex-event. They may not be.

That's true.

There could be plumbing collapses from the earthquake. The delivery system itself may have been destroyed.

Quote:

You don't know if the plumbing or turbines are any good ex-event. They may not be.

ALL of it FUBAR at every single reactor?

-Well that would be pretty ****ing desperately sad.

Well, they have to be able to pump coolant/water back to the core (you don't want exposed fuel rods). First they lost grid power to run the pumps, then the tsunami hit the diesel generators and then went to batteries. I think that was consistent for all running reactors at Daini and Daiichi sites.

Personally, I don't think they have a plumbing problem.

Beyond generators, there is battery backup for pumps. But that only lasts so long. I would guess that the problems with pumping may stem from damage to the intake structure (clogged, damaged, whatever).

The boron dumping is a last resort for a BWR in this situation. Boron would permanently foul the fuel rods if used in a last resort manor. I assume that they're hoping to get power back soon, and don't want to kill their reactors until it's absolutely necessary.

It's also unfortunate that they don't have steam driven pumps as a fail-safe. Hindsight 20/20 and all.

That they pump boron smells fishy to me too. First that means that the reactor vessel is essentially open, otherwise the boron could not reach the place to do any good. That in turn might indicate that the control rods may not all be in the place they should be.

The reported cooling problems with all 6 plants with 13 diesels out of service is very troublesome. The only reason I can think of that you can not get them to run anymore after a Tsunami flood is that they where all operating during the flood and all did suck water into the intake. That kills the engine beyond repair.

Seems there has to be something else. I would think they could helicopter generators in within hours. Ofcourse if the electric feed lines were destroyed by the tsunami that would be another problem, but not huge if they were just the feeder lines.

I said quite some time ago I wondered about additional damage from the after shocks to plumbing, etc being the problem.

Quote:

It's also unfortunate that they don't have steam driven pumps as a fail-safe. Hindsight 20/20 and all.

Deeply unfortunate.

They need ONE ****ing turbine or array of turbines to spin -and they would have power right there to cool the rest of the reactors at the site.

There would be some damn scary distribution to be undertaken; -but, it could be done if there were no other choice than to permanently kill the reactors and destroy billions of dollars of power infrastructure...