From the paper today, first page, in reference to the PULSTAR reactor:

"I know if it blows up, it wouldn't take out too much."

It reminds me of public speaking when I was talking about Yucca Mtn. One person noted "If it blows up, I don't know if it would take out the whole Earth, but at least a good part of it".


Just... exactly how many of you think like that?

11/2/2005 12:05:42 PM

Could you rephrase your question? I just want to make sure I know your possition before I lash out in an irrational rage.

11/2/2005 1:37:57 PM

I don't think like that--it's not possible for a nuclear reactor to "blow up." Steam explosions are possible at a nuclear power plant (as with any pressurized plant, regardless of the heat source), but I don't believe NCSU's reactor is pressurized. So if the shit went down, I wouldn't expect a whole lot more than a lot of steam.

11/2/2005 2:09:30 PM

I disagree with using y'all on the internet.

11/2/2005 3:07:38 PM

Yeah, there is not nearly enough fuel in the reactor to make critical mass for a nuclear bomb-type explosion. Face it, folks are uninformed about a lot of things.

11/2/2005 6:06:34 PM

Quote :

"but I don't believe NCSU's reactor is pressurized."

If, by "pressurized," you mean "not at normal atmospheric pressure," you'd be wrong. It's actually in about 20 feet of water, so rho-g-h it and you'll get the pressure it is at.

I will tell you that it operates at around 100F.



[Edited on November 2, 2005 at 6:10 PM. Reason : editing]

11/2/2005 6:09:55 PM

Quote :

"Could you rephrase your question? I just want to make sure I know your possition before I lash out in an irrational rage."

Ok, are you concerned that the reactor will literally explode due to an operating error or attack of some kind? If you look at my major you can about guess what my position is.

My point is that there are people living in this country who actually think that an explosion of the same nature as a nuclear bomb can occur due to problems with nuclear reactors.

11/2/2005 7:23:11 PM

OMF 1KW OF THERMAL ENERGY.

IT'LL BE THREE MILE ISLAND ALL OVER AGAIN.

11/2/2005 7:26:51 PM

No matter how big the reactor is, a nuclear reactor will NEVER explode like a nuclear bomb. It is physically impossible for that to happen; a nuclear reactor is not built like a bomb.

By pressurized, I mean that the reactor is not contained in a closed vessel. If there were some sort of over power casualty, the water would just boil like a pot of water on your stove. This, as opposed to something like Chernobyl were there was an over power condition, the water heated up, eventually flashing to steam and resulting in an over pressurized closed system which failed catastrophically: a steam explosion.

[Edited on November 2, 2005 at 8:28 PM. Reason : I forgot that you're a nuke, kdawg. What I mean is that it's not a pressurized water reactor.]

11/2/2005 8:24:41 PM

I know what you meant, Tanz. I was just giving you crap.

11/2/2005 8:36:22 PM

Ah, OK. Somebody let you out of the box and now you're getting all smart-ass.

11/2/2005 8:41:46 PM

a chernobyl-like incident will never occur in a US nuclear reactor facility

it's just not possible

11/2/2005 9:13:18 PM

Haha, well, the same company that built Chernobyl built the Three Mile Island reactor complex. That didn't turn out too well, but admittedly it was no Chernobyl.

11/2/2005 10:21:34 PM

I can't wait to see what salisburyboy thinks of this.

11/2/2005 10:32:17 PM

Quote :

"the same company that built Chernobyl built the Three Mile Island reactor complex."

Where the hell did you come up with that? Your ass?

11/2/2005 10:54:20 PM

Ah damn they didn't build it.

I remember hearing somewhere (on TV or something, I used to leave the history channel running whenever I did anything near a television) that there was a company connected to both three mile island and chernobyl, connected in how the reactors (or some component thereof) were designed. Hell if I can find it now.

11/2/2005 11:17:27 PM

I've never heard that. I'd be inclined to doubt it since both reactors were built during the Cold War.

11/3/2005 6:36:09 AM

Quote :

"No matter how big the reactor is, a nuclear reactor will NEVER explode like a nuclear bomb. It is physically impossible for that to happen; a nuclear reactor is not built like a bomb."

ummm, thats not exactly true. if you get the factors wrong, then you have the propensity for an explosion (large release of energy). Of course, mose reactors in the US are built to avoid a combination of those factors, especially after TMI (retrofitting, duh), but still. Crazy shit can still happen.

If, however, you mean "explode" as in "release the same energy at the same rate as a nuclear bomb," then yes, US probably can't do that.

11/3/2005 8:25:40 AM

In case you missed the news flash, Chernobyl was mainly because of operator error.

11/3/2005 8:34:35 AM

You could also blow up a coal, oil, or natural gas power plant and do tremendous damage to the surrounding community.

I remember in St. Louis, there was an accident at a propane storage site. Exploding propane tanks were launched up to a mile in all directions, raining down fireballs on the neighborhoods below.

11/3/2005 10:30:03 AM

Quote :

"ummm, thats not exactly true."

Ummm, it's exactly true. Unless you build a nuclear reactor like a nuclear bomb (in which case it would be a bomb, not a reactor) then it can not and will not explode like a nuclear bomb. At both TMI and Chernobyl, there was zero chance that there would be a nuclear explosion. A nuclear reactor, US or not, will never come close to releasing energy at the same rate as a bomb.

Quote :

"Crazy shit can still happen."

So what factors, retrofitting, and crazy shit did you have in mind?

^^ Yes, but the situation was exacerbated by extremely poor design.

[Edited on November 3, 2005 at 8:10 PM. Reason : add to bigun20]

11/3/2005 8:09:37 PM

If NC State's reactor blew up, the Nuke dept would be pissed.

Thats about the extent of it.

11/3/2005 9:55:31 PM

Quote :

"Unless you build a nuclear reactor like a nuclear bomb (in which case it would be a bomb, not a reactor) then it can not and will not explode like a nuclear bomb."

Thus the reason that I effectively said that it depends on what you mean by "nuclear explosion." There really is no such thing as a "nuclear explosion." The only thing that sets apart a nuclear explosion from a conventional explosion is that the nuclear explosion is caused by the changing of nuclei of the reactants. Thus, a nuclear explosion is just an explosion caused by changing nuclei. At the bare minimum, then, Chernobyl had an explosion, which was directly caused by changing nuclei. Thus, the Chernobyl explosion was "nuclear." TMI, had the hydrogen bubble exploded, would thus also have been caused by the changing of nuclei (far more indirectly, though), and thus also fit the definition of nuclear.

Quote :

"So what factors, retrofitting, and crazy shit did you have in mind?"

The factors? Pretty damned simple, the factors in the five-factor equation which effectively governs the rate of fission in the reactors. In a fission bomb (atomic-bomb), the factors are arranged (by materials used, shape, etc) so as to increase the rate of fission enormously so, i believe exponentially. In a reactor, however the factors are arranged to maximize control of the reaction. However, if you lose control of the reaction and do not compensate quickly enough (on the order of seconds at the most), the factors align to that of a nuclear bomb (non-fusion, of course), thus yielding similar energy release rates. I didn't get into reactor design, so I can't say what retrofitting and "crazy shit" would actually change all of the factors, but I can speak for a few, especially with respect to Chernobyl and TMI and their critical differences.

In reactor design, there is a medium known as a "moderator." The moderator usually serves to slow the rate of the reaction. There are also more than one type of moderator. One type is an explicit type: it sucks up neutrons, thus killing the neutrons' ability to split more atoms. The other type is a more implicit type, which depends on the design of the reactor and the arrangement of the five factors. This implicit moderator uses the reactor's design itself to help dictate the rate of the reaction. The design of the reactor is such that if you remove the implicit moderator, the reaction rate slows. Re-introduce the implicit moderator, reaction rate increases. In this way, an implicit moderator is kind of the opposite of an explicit one, where adding the explicit moderator decreases the reaction rate.

In US designs, including TMI, there are examples of both types. The explicit moderator are carbon graphite rods. You stick in the rods, the reaction slows down, end of story. The implicit moderator is water. Neutrons need to be at a certain velocity to continue the fission reaction in US reactors (a result of the ordering of the five factors). However, neutrons which emitted from the fission of uranium are much faster than this velocity. The graphite rods serve only to suck up neutrons. It doesn't slow many down. The water, itself when a liquid, slows down neutrons but doesn't suck them up. As well, the factors were arranged such that if a neutron gets away from the fuel assembly, it will not likely be reflected back into the reactor vessel, or, if it is, it will be reflected at still above the velocity needed in order to induce fission in uranium. Thus, if you drain the liquid water from the reactor, the reaction shuts down instantly, because there are not enough neutrons of the correct speed.

The Chernobyl design, was quite different. In that design, the moderator was aluminum, I believe, or maybe an aluminum-carbon alloy. Thus, it didn't suck up a lot of neutrons. However, the design of the reactor was such that neutrons that escaped the fuel assembly were quite likely to remain in the reactor vessel, and thus were able to slow down to a speed at which they could induce uranium fission. Water was kind of an explicit moderator as well. Thus, if you drained all the liquid water from Chernobyl, the reaction rate would increase and there would be little you could do to stop it.

In both incidents, liquid water drained from the reactor vessel. At chernobyl, the reaction increased, causing an explosion. At TMI, the reaction ceased. The problem at TMI was different, though. At TMI, they couldn't get the reactor to cool down, because there was not enough liquid water in the core. The water that was in the core was undergoing hydrolysis (IIRC), and creating a hydrogen bubble at the top of the reactor vessel. Hydrogen is bad ju-ju. Unfortunately, everything the operators saw told them that there was only liquid water in the core. When they finally figured out that there wasn't enough liquid water in the core, they didn't have enough water in the primary coolant system to actually fix the problem. Thus, they couldn't cool the core down quickly enough to stop the hydrolysis. I forget how they actually solved the problem at TMI itself. However, I believe that a partial "meltdown" did actually occur at TMI, thus they had to discontinue its use. Or maybe the hydrogen bubble warped the reactor vessel so much that it was unusable, but radioactivity levels made it impossible to remove the vessel.

What the gov't did after TMI was do some retrofitting of all other reactors to ensure that all reactor designs were such that water draining from the core would conclusively stop the reaction. Also, they fixed the problem in the instruments of the reactors that caused the operators to think that they still had water in the reactor vessel. IIRC, they also added some other backup systems which would also help avoid that same problem again.

Thus, similar things (water emptying from the reactor vessel and even "meltdown") happened at chernobyl and TMI, but reactor design played the critical role in determining the outcome (huge explosion, lots of dead people vs. big scare but no explosion or dead people). Ironically, TMI occurred before Chernobyl, so the Russians should have seen the advantage of the implicit moderator.

BTW, I made up the terms "implicit moderator" and "explicit moderator," so none of you nukies have a fit on me, OK?

11/3/2005 11:09:14 PM

Both incidents were caused by mechanical failure and human error.

11/3/2005 11:13:01 PM

I have slightly more respect for aaronburro now.

11/4/2005 1:37:53 AM

First of all, let's get your terms right.

A moderator is used to thermalize neutrons. That's it--nothing more, nothing less. True, the material that's used for a moderator may also serve other functions, such as being a coolant or reflector, and it may even absorb neutrons (as all moderators do, to a lesser or greater extent, depending on the material you use). Regardless, a moderator's purpose is to thermalize neutrons--not to "slow the rate of fission in the reactors." Chernobyl used graphite as a moderator, TMI used water.

A poison "sucks up neutrons" through capture/absorption reactions. Common poisons include boron, hafnium, cadmium, xenon and samarium. Carbon is not used as a poison; carbon has an absorption cross-section of 0.004b. Compare that to the poisons listed above which have cross-sections of 755, 105, 2450, 35, and 5600 b. Control rods are typically made of hafnium.

Where in the hell are you getting this implicit/explicit crap?

As for Chernobyl. Again, the moderator at Chernobyl was graphite. The use of graphite did lead to a design/control problem but, based on your previous post, I'm guessing you're not familiar with positive temperature coefficients of reactivity. Anyway, aluminum came into play as fuel cladding, which is supposed to contain fission products (the 'baddies'). Normally it works fine, however aluminum does have a relatively low melting point. When things went south at Chernobyl and things heated up, the aluminum cladding failed, releasing fission products. These, of course, eventually made their way into the environment.

You are right in that the design of Chernobyl was such that water acted as a poison. However, water draining from the reactor did not cause the accident. As has been pointed out already, operator error and abnormal operating conditions were the direct causes. The whole situation was worsened by poor design. Don't get me wrong--water certainly did have a role, but it had more to do with design deficiencies and nothing to do with draining water from the plant.

At TMI, there was a loss of coolant casualty, which led to uncovering the core, hydrogen production, etc... By "Hydrogen is bad ju-ju" I assume you meant that hydrogen is flammable. Several hours into the casualty, the hydrogen did ignite and there was a minor hydrogen exlposion (I say minor because the pressure transient did not exceed the design pressure of the reactor vessel--the explosion was completely contained). The core did partially meltdown, which is why it was no longer usable. Also, I'm pretty sure that particular unit (TMI-2) has since been decommisioned and the core removed. The other nuclear reactors at the TMI site have continued to operate.

Explosions.
Dictionary.com defines explosions as a "release of mechanical, chemical, or nuclear energy in a sudden and often violent manner..." So, I would say that a nuclear explosion would directly involve the release of nuclear energy, either from fission or fusion. At TMI, there was a chemical explosion (hydrogen combustion). At Chernobyl there was a steam explosion: water flashed to steam, causing the vessel to rupture by rapidly exceeding design pressure. I'm not sure whether you would classify that as chemical or mechanical. Probably chemical since it involves a change in state. Regardless, neither TMI or Chernobyl was a nuclear explosion.

Again, a nuclear reactor absolutely CANNOT explode like a nuclear weapon. There are fundamental differences in design such that physics prevents a nuclear reactor from behaving like a nuclear bomb and vice versa; a bomb cannot be operated as a reactor. Also, weapon grade uranium is generally considered to have U-235 enrichment of 94%, compared to an enrichment of 3.5% for reactor grade uranium. TMI had an enrichment of 2-4% and Chernobyl had about 2%.

[Edited on November 4, 2005 at 12:23 PM. Reason : ]

11/4/2005 12:17:33 PM