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

#121

Post by dkersten » Wed, Mar 16, 2011, 6:16 PM UTC

varjag wrote: post #113

dkersten wrote: post #90

Earlier quoted context omitted.

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

And in China they indeed burn even more coal. However, why build nuclear stations to displace coal, when it's possible to burn gas instead?

I imagine it has something to do with the quantity of power a nuclear power plant can generate compared to a gas based power station (given equivelent time/amounts of fuel)?? But I don't really know.

Having said that, though I don't remember the name/type ofdhand and am too lazy to look it up, there are new types of power plant in development/trials that 1) physically cannot meltdown, 2) produce much less (and less hazardous) waste and 3) use a plentiful form of nuclear fuel. If/when those nuclear power plants become production ready, then the choice between nuclear and fossil fuels is an easy one. For now, though, I agree with you and don't know the answer.

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

#122

Post by jellicle » Wed, Mar 16, 2011, 6:59 PM UTC

mchouza wrote: post #82

jellicle wrote: post #73

Earlier quoted context omitted.

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 unmoderat…

Chernobyl used UNENRICHED uranium, containing only .7% of U235, and went kablooey. Which you just said can't happen, so I suppose Chernobyl didn't actually happen. /thread

This thread has brought out the worst aspects of Hacker News - reasonably bright people who feel compelled to opine, in their usual arrogant "I am always right" manner, about subjects where they have no clue.

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

#123

Post by bioh42_2 » Wed, Mar 16, 2011, 7:05 PM UTC

lurch_mojoff wrote: post #75

timinman wrote: post #70

Earlier quoted context omitted.

Exactly, the bottom line is were playing with nuclear reactions and hoping everything goes as planned. It's arrogance.

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.

But a lot of people, especially those who know anything about planes are always crying out for more safety. Both in mechanical terms, more plane inspections, and in human terms, more rest for pilots.

And I don't think many people here are arguing for the abolishment of nuclear power. That is a straw man.

I think what we all want is the safest possible nuclear power.

And this argument is between the people who willing admit knowing little to nothing and think things can always get worse, versus the people who keep arguing things are peachy and there's no way they can get worse, even as the situation has continued to deteriorate.

I think this boils down to an argument of "Shit happens!" vs. "Nah uh, engineering is magic!"

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

#124

Post by icarus_drowning » Wed, Mar 16, 2011, 7:06 PM UTC

_delirium wrote: post #100

icarus_drowning wrote: post #66

Earlier quoted context omitted.

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…

I don't think all examination of qualifications constitutes a genetic fallacy. If anything it's closer to an argument from authority plus a closed-world assumption (i.e. I only accept arguments from authorities). But expertise and authority has a significant role in science, and not entirely an improper one imo. If I say that I prefer to hear expert analysis of nuclear reactors from someone with a PhD in nuclear phys…

I disagree. The logic of the post clearly states that the source of the information is a reason to reject it rather than a problem with the information itself. This is a common problem with a vast majority of the negative responses to the "why I am not worried" article.

Remember, the poster says that the origin of the facts makes those facts bullshit. Textbook genetic fallacy.

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

#125

Post by SamReidHughes » Wed, Mar 16, 2011, 7:08 PM UTC

timr wrote: post #119

yummyfajitas wrote: post #76

Earlier quoted context omitted.

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. Physics isn't biology/medicine. The laws of physics are not discovered by running experiments to enumerate every possible combination or permutation of configurations. You're assuming an intact core. Criticality is…

"Physics isn't biology/medicine. The laws of physics are not discovered by running experiments to enumerate every possible combination or permutation of configurations." Wanna bet? Guess how we know most of what we know about criticality and neutron cross-sections? People like Louis Slotkin, who spent hundreds of hours poking at piles of radioactive material in the lab, to derive those mathematical models that you're…

The physical principles behind criticality calculations are not fiendishly complicated. The computations are computationally intensive, yes (Slotin was around in a time where experiments were cheaper and easier than simulations), and (maybe -- I don't know) the exact nature of physical materials involved was not well known, and needed to be measured.

Prove it.

Why don't you prove it? It's not other people's job to do all the work for you. It is provable that a sphere is the optimal shape. If somebody on the internet suggests that you're wrong, you don't win the argument by saying it's their responsibility to do all the hard work of convincing you you're right. You're still the one who is wrong.

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

#126

Post by sliverstorm » Wed, Mar 16, 2011, 7:20 PM UTC

Duff wrote: post #84

sliverstorm wrote: post #32

Earlier quoted context omitted.

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…

Well, I imagine when people are dying. The quake and resulting waves killed a lot of people. This hasn't, yet. Excuse me for thinking the most about those.

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

#127

Post by timr » Wed, Mar 16, 2011, 7:22 PM UTC

SamReidHughes wrote: post #125

timr wrote: post #119

Earlier quoted context omitted.

"Physics isn't biology/medicine. The laws of physics are not discovered by running experiments to enumerate every possible combination or permutation of configurations." Wanna bet? Guess how we know most of what we know about criticality and neutron cross-sections? People like Louis Slotkin, who spent hundreds of hours poking at piles of radioactive material in the lab, to derive those mathematical models that you're…

The physical principles behind criticality calculations are not fiendishly complicated. The computations are computationally intensive, yes (Slotin was around in a time where experiments were cheaper and easier than simulations), and (maybe -- I don't know) the exact nature of physical materials involved was not well known, and needed to be measured. Prove it. Why don't you prove it? It's not other people's job to do…

"Why don't you prove it?"

Because I'm not the one making extraordinary claims. I'm also arguing that you can't 'prove' anything in this situation; there are too many unknowns.

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

#128

Post by _delirium » Wed, Mar 16, 2011, 7:48 PM UTC

icarus_drowning wrote: post #124

_delirium wrote: post #100

Earlier quoted context omitted.

I don't think all examination of qualifications constitutes a genetic fallacy. If anything it's closer to an argument from authority plus a closed-world assumption (i.e. I only accept arguments from authorities). But expertise and authority has a significant role in science, and not entirely an improper one imo. If I say that I prefer to hear expert analysis of nuclear reactors from someone with a PhD in nuclear phys…

I disagree. The logic of the post clearly states that the source of the information is a reason to reject it rather than a problem with the information itself. This is a common problem with a vast majority of the negative responses to the "why I am not worried" article. Remember, the poster says that the origin of the facts makes those facts bullshit. Textbook genetic fallacy.

What I'm discussing is evidential weighting and critical source analysis, not logical inference (I do happen to research logic in my day job, so I'm familiar with what constitutes valid deduction).

Since this isn't a scientific paper that presents data sufficient to support its conclusions, we can't judge it purely objectively. It presents itself as an engineering safety analysis. The first step in judging an engineering safety analysis is usually: was it performed by someone qualified to perform such an analysis? We typically want them to be performed by people who are both domain experts (in this case, nuclear engineers), and specifically people who are experts in assessing the risks in that domain, as well as in the general science of risk analysis. If a safety analysis is done by someone who isn't such an expert, it's quite rational to give it lower weight, because we aren't confident that they're familiar with all the relevant science and possible risks.

I mean, would you argue it's also a genetic fallacy that I take articles in Nature more seriously than I take articles in the Daily Mail? That I believe what Richard Feyman's lectures have to say about physics more than I believe what some random person on Geocities has to say? It just seems like good sense to me; considering the source of a claim is a good first step when deciding how much weight to give it. Bayesians would agree! It's possible that the Daily Mail will publish an insightful new analysis of global warming, but it's not very likely, and I would probably want to hear confirmation from a more reliable source before I believed it. Same here; this analysis is interesting, but I'd have more confidence in an analysis performed by someone who's actually an expert in the field, so until I hear one of them say that it's correct, I treat it with skepticism.

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

#129

Post by yummyfajitas » Wed, Mar 16, 2011, 7:49 PM UTC

timr wrote: post #119

yummyfajitas wrote: post #76

Earlier quoted context omitted.

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. Physics isn't biology/medicine. The laws of physics are not discovered by running experiments to enumerate every possible combination or permutation of configurations. You're assuming an intact core. Criticality is…

"Physics isn't biology/medicine. The laws of physics are not discovered by running experiments to enumerate every possible combination or permutation of configurations." Wanna bet? Guess how we know most of what we know about criticality and neutron cross-sections? People like Louis Slotkin, who spent hundreds of hours poking at piles of radioactive material in the lab, to derive those mathematical models that you're…

So tell me again about the "laws of physics", and how they're not tested through pemutation.

Ok. You generally perform a sequence of experiments, construct a low entropy theory, and then apply that theory in the future. Kind of like what Louis Slotkin did.

He doesn't need to redo them on a train, a plane, in a car, at the bar. The fundamental principles discovered tend to be pretty solid.

Prove it.

Not that hard. Take a fixed volume, convolve it with the 1/r kernel of the neutron diffusion equation. If the volume of uranium is a sphere, you get the spot neutron density at the center is [(3V)^{2/3}]/2. If the volume is a disk of height dz, radius R, you find the the local density is 2(pi V dz)^{1/2}. The smaller dz gets, the smaller the local density of neutrons is, and the further from criticality you are.

(Computing the volume at someplace other than the center is left as an exercise for the reader. However, the maximum principle shows that it always goes down.)

Now plug this into the standard soliton machinery (i.e., use Duhamel's principle, L^p-L^q estimates, etc) and you'll always need a bigger source for a flat soliton than a spherical one.

Yes, I'm skipping a few steps. You can find them in Cazenave's book on solitons (that's where I learned it) and most likely any book on nuclear engineering (but with much less of a mathematical bent). No, it's not the "undergrad physics textbook" you seem to think I'm referring to.

It's pretty amazing how everyone wants to cite "physics" to prove that there's no problem with a meltdown (in the face of overwhelming empirical evidence to the contrary), but nobody is doing much more than hand-waving allusions toward their undergrad physics textbook in defense of their assertions.

What is the "overwhelming empirical evidence" that criticality will be achieved?

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

#130

Post by icarus_drowning » Wed, Mar 16, 2011, 7:59 PM UTC

_delirium wrote: post #128

icarus_drowning wrote: post #124

Earlier quoted context omitted.

I disagree. The logic of the post clearly states that the source of the information is a reason to reject it rather than a problem with the information itself. This is a common problem with a vast majority of the negative responses to the "why I am not worried" article. Remember, the poster says that the origin of the facts makes those facts bullshit. Textbook genetic fallacy.

What I'm discussing is evidential weighting and critical source analysis, not logical inference (I do happen to research logic in my day job, so I'm familiar with what constitutes valid deduction). Since this isn't a scientific paper that presents data sufficient to support its conclusions, we can't judge it purely objectively. It presents itself as an engineering safety analysis. The first step in judging an enginee…

I'm arguing about the original post that I responded to, which makes the argument "this is not from an engineer, but a lobbyist and is therefore bullshit". That is a genetic fallacy.

If he had made the entirely reasonable point that you did-- that this might not be as trustworthy a source compared to another, or engaged the actual evidence used, I wouldn't have taken the time to critique it.

In other words, my disagreement with you has nothing to do with the weighing of credible sources, but the fact that the original post didn't do that.

Note that I haven't even brought up the fact that the post he actually responded to was a revised version of the article by nuclear engineers, thus invalidating much of his claims about it anyway.