NOTE: The Title suggests that Chernobyl is no longer a problem, however if you read the whole story you will discover that there is still one reactor that will be operational at Chernobyl at the Roll over..... ______________________________________________________

Ukraine orders Chernobyl reactor shut down

Copyright ) 1999 Nando Media Copyright ) 1999 Associated Press

KIEV, Ukraine (March 16, 1999 3:53 p.m. EST http://www.nandotimes.com) - Ukraine's government has ordered an idle reactor at the Chernobyl nuclear power plant permanently shut down to comply with an earlier pledge to fully close the station.

In a resolution approved Monday, the Cabinet ordered the gradual closure of Chernobyl's reactor No. 2, the Interfax news agency said. No deadlines were set for the shutdown.

Reactor No. 2 has remained in standby mode since 1991, when it was damaged in a fire.

The government had considered restarting it, but dropped the plan, saying it could not raise the $100 million needed to put the reactor back on line.

In 1986, the plant's reactor No. 4 exploded, spewing radiation over much of Europe in the world's worst nuclear accident.

Ukraine has promised to close all of Chernobyl's four reactors by 2000 and already has shut down the plant's No. 1 reactor in compliance with the pledge. Only reactor No. 3 is operational, and was restarted two weeks ago after months of repairs.

Ukraine's leaders have repeatedly said Chernobyl would continue operating after 2000 unless Western countries provide financial aid to complete two new nuclear reactors to compensate for Chernobyl's closure.

-- helium (heliumavid@yahoo.com), March 16, 1999

Answers

Didn't someone post in a previous thread about nukes that there's no chance of them exploding!!

-- A (nuketh@exploded.com), March 16, 1999.

I was in Germany when Chernobyl blew. We all had to avoid fresh produce, stay off the grass, and drink milk packaged before it happened. Luckily the Germans drink boxed milk with long unrefrigerated shelf life. Just a little reminiscing...

-- Shimrod (shimrod@lycosmail.com), March 16, 1999.

A - I believe it was more of a big fire than an explosion. At any rate, it was not a nuclear explosion. Also had no containment building like our reactors do. <:)=

-- Sysman (y2kboard@yahoo.com), March 16, 1999.

Disclaimer: I am NOT a nuclear engineer or scientist, just well read:

It is my understanding that nuclear reactors used for power generation cannot explode in the nuclear sense of the word - the concentration of fissile material is insufficient for a "super- critical mass" to form, thus a "runnaway" chain-reaction cannot happen. The concentration of U235 in the fuel rods ensures that a runnaway chain-reaction cannot happen because there are insufficient neutrons of the right type (slow vs. fast) released to sustain the reaction. Reactors which are used commercially use uranium "enriched" to about 3% of the '235 variety (U238 comprises most naturally occuring uranium; U235, it's more nuclear-reacting isotope, is what reactors and bombs need and it is very rare, 0.7%, in nature. Enriched or "weapons grade" uranium is, I think, something over 80% U235.) Plutonium, used chiefly in weapons, is NOT used in commercial reactors.

Now, you can have steam explosions (from the extreme pressure of super-heated steam) or traditional chemical explosions from flammable materials. One scary way for steam explosions to occur is for the reactor to be deprived of coolant. Even an idle reactor will then melt itself from the heat of the naturally occuring radioactive decay. Super-hot metal will explode water into steam on contact (think of a reactor core melting into a pool a water). That's what the 'China Syndrome' was about (self-melting reactor core melting into the ground until it reaches China). This is similar to what happened with Chernobyl - the reactor exploded because it could not dissipate its waste heat (yes, there were other factors, but it got way too hot too fast - that's my point). This is why nukes have backup power, so they can run pumps to cool the reactor core.

Any explosion in a reacter vessel could potentially release radioactive dust which is not healthy to be around (that's why most reactors have some kind of containment vessel surrounding the reactor vessel).

As for (plutonium) breeder reactors and fuel reprocessing facilities, these sites DO deal with highly enriched fissile material (that's why they exist). Obviously they try to keep this in sub-critical masses, otherwise they go very boom (and while it would not be an *efficient* nuclear explosion, lots of people would never care--again). BTW this stuff has to be kept cool too.

Hope this helps (if I'm slighly off, or you think my writing style is not up to par, have mercy and don't flame me).

-- Brett Blatchley (bblatchl@inmar-inc.com), March 18, 1999.

OOPS, Correction: While neutrons (slow ones) are crucially important in a fission reaction, it's the high concentration of U235 that makes for a bomb. (I think this is because U235 splits much more readily than U238). As for neutrons, the reaction won't start, sustain, or runnaway without sufficient numbers of the proper type.

-- Brett Blatchley (bblatchl@inmar-inc.com), March 18, 1999.