perhaps a simplistic thought but why didn't they design these Nukes so that

[JohnWxy]

the heated water would flow out of the reactor at the top, go through a system of radiators to cool the water which after being cooled would then flow into the bottom of the reactor to replace the hot water leaving at the top. I guess it's impossible to design a cooling system that operates on heat differentials alone driven by the heat created by the reactor and not requiring electrically powered pumps to move the water through the system.

[liberal N proud]

1. That is old fashioned silly

Cars have been doing that for years.

:sarcasm:

[FBaggins]

2. Small reactors can do essentially that (run on convection)

The larger ones pretty much need a pump.

[JohnWxy]

4. I guess because convection beyond a certain size of core could not be counted on to keep cooling

uniform across the entire core. Thus you would get plutonium rods in middle over-heating while those on the outside of the core would be better cooled.

Of course, my next question would be then, why not make larger reactors collections of smaller cores where convection would work? Probably boils (no pun intended) down to cost and 'efficiency'.

[FBaggins]

5. They are working on smaller reactors, but they've come up with a better idea for this.

They just make passive cooling systems that don't require pumps or electricity.

In the case of the most popular new design, it's just a great big tank of water above the containment building that uses gravity.

[Nederland]

3. New designs do exactly that

They are designed to provide enough cooling to avoid a meltdown using gravity and convection alone. I believe the AP1000 design can provide passive cooling for up to 72 hours with no intervention at all. Beyond that time period, cooling can be maintained without power indefinitely, provided you have a means of topping off the emergency coolant tank.

[FBaggins]

6. And "topping it off" should be far easier.

They have to introduce new water into the containment structures (in Japan), which means that you can't just run a hose to the oceam with a P250. You have to somehow connect to the existing network of cooling options.

If there's a big tank above the containment (as with the AP 1,000) you could presumably just top off that tank. Bring a pumper truck or two with you and you should be fine.

[SpoonFed]

7. Current situation

Don't worry, in theory the new designs can't suffer from these sorts of silly little problems that we're seeing here, in reality, at present. That fact alone makes me feel so much better about this whole thing.

I say we give the industry (in Japan or even world wide) an honest chance to implement some new designs so that we can test whether they are truly safer than these old (but currently in operation) reactor designs we're seeing here in Japan and elsewhere during this current crisis.

It's the reasonable thing to do.
This latest set back was just bad luck.

[JohnWxy]

8. though I was asking why wasn't gravity feed and convection that used the heat generated by the core

to circulate water with no power inputs needed, used, that does not mean that I think we should keep experimenting with nukes.

Seems like there is no end to the somethings that nobody thought of. And since the possible aftermaths can be horrendous...and possibly everlasting (I figure 100 to several thousand years counts as everlasting) I think gambling with this technology is insane.

..I just thought shouldn't it be kindof obvious to not rely on generated power to make a critical system such as cooling to work. The default position should be that the core is always adequately supplied with water.

[SpoonFed]

11. Oh

I wasn't suggesting you held such a position. I was suggesting that the pro-nuke
proponents around here believe such things.

It sounds from your clarification that we agree that it's insane to continue
gamble with this technology. Reports are coming in as I write this that 3 reactors
are now officially melting down.

[madokie]

9. Thats the way the model T was cooled

no pump involved, Heat goes up cold goes down, pretty simple.

I done an experiment years ago to see how much water flow there is and how much heat a person can get from the sun on a cold day by taking a 60 foot of soft 1/2 inch copper tubing laying on a sheet of metal, 16 gauge steel, crudely fastened to it and all painted black. I then took a piece of garden hose and connected it to the center of the flat circle I had the copper in and ran it up to the top of a 5 gallon bucket. the other end of the copper pipe I ran to the bottom of that 5 gallon bucket. On a 45 degree day with a 5 mph or so wind blowing on my crude collector I was able to warm the water from 52 degrees to 140 degrees in three minutes. The water flow out of the hot side that was going to the top of the bucket was a full 1/2 inch stream going out at about a 6 maybe 8 inch radius. I failed to measure the flow cause I wanted to see for myself how much heat could be obtained from a solar heater. I was impressed how fast it brought the water temperature up by 90 degrees. I'm still surprised I don't have a solar hot water heater today but I don't.

[kristopher]

10. They *are* designed to use convection for circulation

It is their final cooling "fail-safe". It just isn't effective enough, especially when water levels are falling for an unexplained reason.