The 'why I am not worried' article, edited by MIT nuclear scientists • Hacker News Board

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#81

Post by moe » Wed, Mar 16, 2011, 12:22 PM UTC

cperciva wrote: post #48

timr wrote: post #36

Earlier quoted context omitted.

"All good engineering works on the principle of defence in depth." That line is as much a sound-bite at this point as anything you'll hear on cable television. Yes, good engineering has many levels of fall-backs and redundancies. But when you've reached the point that you've evacuated the last fifty people from your site because it's no longer safe for them to be there , then you've exhausted your defenses. There's n…

Maybe the "wide concrete tray" will capture the waste. Maybe it won't. Maybe the laws of physics will change, but I'd be willing to bet that they won't. But in the meantime, you're hoping that there's not a secondary fire from the heat Concrete doesn't burn. or a steam explosion At the point when the nuclear fuel melts, all the water has boiled off 1000 degrees ago. or some other kind of explosion that flings radioac…

Concrete doesn't burn.

No. But concrete can crack during, say, an earthquake.

And I assume concrete can also lose integrity (melt? vaporize?) under very high temperatures.

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#82

Post by mchouza » Wed, Mar 16, 2011, 12:26 PM UTC

jellicle wrote: post #73

timr wrote: post #56

Earlier quoted context omitted.

"Maybe the laws of physics will change, but I'd be willing to bet that they won't." There's absolutely nothing about the "laws of physics" that guarantees that this particular reactor design is going to be able to contain a full meltdown, because it's never happened before . Nobody knows. "Concrete doesn't burn." No one said it did. There's plenty of other stuff around that does burn readily, which is why the plant i…

It's a shame that cperciva's nonsense is being modded up. > "Nuclear reactors don't hold enough fuel to form a critical mass." Come on. Each reactor core holds over 100 tons of uranium, of which about 3-5 tons is U-235. Critical mass under perfect conditions is 50 kilograms. Conditions are not perfect for forming a critical mass, but you've got 100 times as much U-235 as is strictly necessary, and there is no fucking…

Each reactor core holds over 100 tons of uranium, of which about 3-5 tons is U-235. Critical mass under perfect conditions is 50 kilograms.

Critical masses don't work that way: the additional U-238 absorbs neutrons making more difficult to achieve criticality. In fact, even an infinite amount of unmoderated natural uranium cannot sustain a chain reaction. See the figure 3.1 in [1] for more information about unmoderated critical masses for enriched uranium.

[1] http://www.ornl.gov/sci/radiation_transport_criticality/Hopp...

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#83

Post by Duff » Wed, Mar 16, 2011, 12:38 PM UTC

cperciva wrote: post #28

Duff wrote: post #23

I'm really kind of sick of listening to people talk about how everything is hunky-dory. I heard one supposed expert on CNN basically state that a nuclear meltdown is no big deal. The lesson to learn here is when a government tells you everything is ok regarding an event with potential regional impact, get the hell out of town. I'm assuming the reactors are melting down and are out of control. Pumping seawater in may…

I heard one supposed expert on CNN basically state that a nuclear meltdown is no big deal. He's right, in a sense. Modern nuclear reactors are designed so that if the fuel melts it will end up in a wide concrete tray which sits under the reactor, where -- thanks to the fact that the tray is very wide and not at all deep -- it will cool down to a safe temperature. All good engineering works on the principle of defence…

I respect your faith in good engineering, but I haven't seen alot of evidence of good engineering here.

There is no evidence to support your assertion that this is nothing like a "China syndrome" type issue. This facility is located a few miles from the eqicenter of the 4th largest earthquake in recorded history. None of the safety systems worked, and the power company and Japanese government has no clue about what to do.

So the future of (at a minimum) an entire region of Japan is dependent on a slab of concrete after a massive earthquake. It is a facility built in a known earthquake and flood hazard zone that requires continuous access to the utility grid.

Doesn't sound like good engineering by any standard to me.

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#84

Post by Duff » Wed, Mar 16, 2011, 12:46 PM UTC

sliverstorm wrote: post #32

cperciva wrote: post #28

Earlier quoted context omitted.

I heard one supposed expert on CNN basically state that a nuclear meltdown is no big deal. He's right, in a sense. Modern nuclear reactors are designed so that if the fuel melts it will end up in a wide concrete tray which sits under the reactor, where -- thanks to the fact that the tray is very wide and not at all deep -- it will cool down to a safe temperature. All good engineering works on the principle of defence…

I suspect your parent did not realize a nuclear meltdown simply means the melting of the fuel, and instead (like most people) simply directly associates the words with "huge disaster". (From that frame of reference of course- "a huge disaster would not be a big deal!"- it DOES sound ridiculous)

A few short days ago, we were told that everything was a-ok, no worries. Then the buildings started exploding -- still, everything is under control. On Monday we hear that fuel rods are fully exposed, but that is ok too.

Now we're talking about the staff evacuating the site to avoid acute radiation poisoning and dropping seawater from helicopters. At what point do you stop accepting the best-case scenario as the most likely one?

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#85

Post by anigbrowl » Wed, Mar 16, 2011, 12:52 PM UTC

icarus_drowning wrote: post #66

kitsune_ wrote: post #50

This is BULLSHIT, the guy (Oehmen) is a mechanical engineer with a management focus. He worked at my alma mater (ETHZ). His field of experties is supply chain risk management. Look up his papers, he isn't a nuclear physicist. I'd say he's about as qualified to make a comment on the situation as I am. The "essay" by Oehmen was first published by a notorious nuclear lobbyist, Jason Morgan. Look at this: http://nuclearf…

Lets see: genetic fallacy[1], circumstantial ad hominem[2], appeal to spite[3], and well-poisoning[4]. All in all, a very good compendium of logical fallacies, but as such, not a terribly good argument against the assertions made. 1: http://www.nizkor.org/features/fallacies/genetic-fallacy.htm... 2: http://www.nizkor.org/features/fallacies/circumstantial-ad-h... 3: http://www.nizkor.org/features/fallacies/appeal-to-s…

To be fair, the unworried proponents of this piece used equally fallacious rhetorical tricks, and did so with the intent to deceive.

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#86

Post by NickPollard » Wed, Mar 16, 2011, 12:52 PM UTC

moe wrote: post #80

lurch_mojoff wrote: post #75

Earlier quoted context omitted.

As is every technological and scientific achievement humankind has ever reached and is relying upon. Replace nuclear reactions with, say, human flight and your statement remains just as valid. I don't see many people crying out for abolishment of planes, though.

I don't see many people crying out for abolishment of planes, though. I think there's a tiny difference between a plane falling out of the sky and a nuclear reactor melting down. I'm sure you can spot it, too, if you think long and hard.

The plane falling happens a lot more often?

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#87

Post by bdonlan » Wed, Mar 16, 2011, 1:14 PM UTC

dexen wrote: post #59

cperciva wrote: post #28

Earlier quoted context omitted.

I heard one supposed expert on CNN basically state that a nuclear meltdown is no big deal. He's right, in a sense. Modern nuclear reactors are designed so that if the fuel melts it will end up in a wide concrete tray which sits under the reactor, where -- thanks to the fact that the tray is very wide and not at all deep -- it will cool down to a safe temperature. All good engineering works on the principle of defence…

EDIT: nvm, found the answer by re-reading the article. In short, even without chain reaction, substantial (7% of normal output early after shutdown) heat is produced, so some cooling is needed. -- The original post: Why are (or were) they pumping water in anyway? Wasn't the whole point of reactors moderated by water that once the moderating water escapes (evaporates or flows out), the unmoderated neutrons don't susta…

There's already no chain reaction - the control rods, plus the boron in the water they're pumping in absorb too many neutrons to sustain a reaction. The heat is not from uranium fission, but rather from the fission products made while the reactor was running undergoing spontaneous decay. This process cannot be stopped; you can only wait for it to slow down and cool to a reasonable level.

The reason they want to keep it cool is to prevent the fuel rods from melting. While melting won't immediately mean a release, it would mean the loss of two of the five barriers to a radioactive release, as well as quite a lot of heat for the remaining barriers. It would also significantly complicate later cleanup. As such, it is preferable that the fuel rods remain intact if at all possible, and this means attempting to cool them.

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#88

Post by bdonlan » Wed, Mar 16, 2011, 1:16 PM UTC

wtracy wrote: post #3

Idle speculation from someone who is not a nuclear or a chemical engineer: I'm suddenly wondering if the pressure relief valves for the primary coolant system could be designed with ignition circuits. The idea would be to burn off any hydrogen in a controlled fashion as it exits the coolant system, rather than giving it a chance to accumulate and later detonate. It would be similar to the way oil rigs burn off unwant…

By the point you're producing hydrogen, you're already well beyond your design limits...

Moreover, they've already lost primary, secondary, and tertiary power, so what exactly is going to run those ignition circuits? A gas flame near the reactor is just trading one source of explosion for another. And if they _did_ have power, they'd be running the primary (or secondary) coolant loops, and wouldn't have any hydrogen gas generation.

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#89

Post by dkersten » Wed, Mar 16, 2011, 1:21 PM UTC

moe wrote: post #79

brazzy wrote: post #68

Earlier quoted context omitted.

total number of causalities of 35, all in Chernobyl Wrong, according to http://en.wikipedia.org/wiki/Chernobyl_disaster - 31 dead from acute radiation poisoning within months - 216 non-cancer deaths until 1998 - Between 9,000 (official government report) and 60,000 (TORCH report) cancer deaths overall

60,000 (TORCH report) cancer deaths overall Thanks for pointing that out one more time. I'm not an anti-nuclear zealot but I'm getting extremely tired of supposedly intelligent people citing the "35 deaths" bullshit-figure on HN in each japan-thread. If there had been only 35 or 4000 deaths then Chernobyl would not be considered a catastrophic event up to this day. Instead it would be considered a testament to the sa…

I was watching a documentary about Chernobyl a while ago and some of the birth defects are extremely severe.

Re: The 'why I am not worried' article, edited by MIT nuclear scientists

#90

Post by dkersten » Wed, Mar 16, 2011, 1:23 PM UTC

varjag wrote: post #77

rimantas wrote: post #53

Earlier quoted context omitted.

> In short: FUD by nuclear energy lobbyists. So mechanical engineer cannot possibly say anything truthful about nuclear energy? The fact still remains: nuclear energy is the safest and cleanest we have for now. So far we had what, three serious incidents with total number of causalities of 35, all in Chernobyl. Sure it affected much more people but still: the single incident at Sayano-Sushenskoye hydroelectric power…

> The fact still remains: nuclear energy is the safest and cleanest we have for now. Burning natural gas is both cleaner is safer, and it is a power source for much of Europe. I wonder why all nuclear advocates always bring in coal into the comparison.

I imagine this is why: http://upload.wikimedia.org/wikipedia/en/8/83/2008_US_electr...