<!--quoteo(post=1837797:date=Mar 18 2011, 04:53 PM:name=Tykjen)--><div class='quotetop'>QUOTE (Tykjen @ Mar 18 2011, 04:53 PM) <a href="index.php?act=findpost&pid=1837797"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->The western world making the nuke first was vital for the world we live in today. Saying anything otherwise is pretty lolbama
<a href="http://hypertextbook.com/eworld/einstein.shtml" target="_blank">http://hypertextbook.com/eworld/einstein.shtml</a><!--QuoteEnd--></div><!--QuoteEEnd--> What does that have to do with earthquakes or power plants? I don't understand where you're going with this. We're talking about earthquakes and power plants, you're talking about nuclear bombs and Hitler.
<!--quoteo(post=1837744:date=Mar 18 2011, 10:04 AM:name=Svenpa)--><div class='quotetop'>QUOTE (Svenpa @ Mar 18 2011, 10:04 AM) <a href="index.php?act=findpost&pid=1837744"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->What is it that actually explodes in a powerplant? I thought the material containing the radioactive matter only melted once it got too hot?<!--QuoteEnd--></div><!--QuoteEEnd--> Steam explosion. The reactor core is filled with water, which evaporates as it gets hotter, building up pressure. Steam explosions can be extraordinarily dangerous. The boiling point of a substance changes with pressure - as pressure increases, the boiling point increases. This means that as the pressure inside the boiler increases, the liquid water inside becomes far hotter than it could normally be under normal athmospheric pressure. When the boiler finally cracks, pressure drops dramatically, and large amounts of superheated water instantly flash into steam, adding to the violence of the explosion. When Chernobyl's reactor 4 blew, the 2000-ton "lid" was blown clear off the reactor core, and the roof was blown off the turbine hall. All of that damage was done by the steam explosion. The nuclear fission merely supplied the heat needed to do it.
<!--quoteo(post=1837800:date=Mar 18 2011, 05:09 PM:name=lolfighter)--><div class='quotetop'>QUOTE (lolfighter @ Mar 18 2011, 05:09 PM) <a href="index.php?act=findpost&pid=1837800"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->What does that have to do with earthquakes or power plants? I don't understand where you're going with this. We're talking about earthquakes and power plants, you're talking about nuclear bombs and Hitler.<!--QuoteEnd--></div><!--QuoteEEnd-->
Where did I mention Hitler? I mentioned the nazis because of all the anti-nuclear morons currently using the so called "nuclear apocalypse" in Japan as propaganda for their enviromentalist "green world" piss agenda. Thus overshadowing the importance of nuclear power and energy. Nobody could prepare for the quake and tsunami that followed in Japan..just a shame the western world and the mass media are mass panicing. Ofc you dont understand where Im going with this, I didnt expect you to.
It's quite hard to talk about nazism without thinking about its leader.
What isn't hard, however, is to talk about 'environmentalist "green world" piss agendas' without mentioning a political ideology founded on the principles of racial purity.
Saying that nuclear weaponry and nuclear power plants are the same thing is akin to blaming the petroleum industry for molotov cocktails, or trying to put a ban on the firework industry because gunpowder kills people.
<!--quoteo(post=1837812:date=Mar 18 2011, 06:51 PM:name=Cereal_KillR)--><div class='quotetop'>QUOTE (Cereal_KillR @ Mar 18 2011, 06:51 PM) <a href="index.php?act=findpost&pid=1837812"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->It's quite hard to talk about nazism without thinking about its leader.
What isn't hard, however, is to talk about 'environmentalist "green world" piss agendas' without mentioning a political ideology founded on the principles of racial purity.
Saying that nuclear weaponry and nuclear power plants are the same thing is akin to blaming the petroleum industry for molotov cocktails, or trying to put a ban on the firework industry because gunpowder kills people.<!--QuoteEnd--></div><!--QuoteEEnd-->
Glad I havent got your brains as well. Way to start talking about the final solution all of a sudden. I wont expect you to understand my point either; Comparing petroleum and gunpowder to nuclear power and nuclear weapons is as stupid as comparing nuclear power and nuclear weapons to.... petroleum and gunpowder.
I was "simply" saying that if the nazis had invented the nuke first, we wouldnt be discussing this right now :P But anti nuclear morons just dont get that simplicity.
Nutjobs, morons, nazis, piss agenda, nuclear apocalypse. Your choice of words is incendiary to say the least, and speaks of a lack of interest in constructive debate. It's true you never mentioned Hitler, my mistake. You said nazis, not Hitler. You are, however, the only one who's talking about a nuclear apocalypse. Pure hyperbole. I use words such as "disaster" and "incident." You shove words like "nuclear apocalypse" into my mouth in an attempt to make my position seem extremist and alarmist. This thread was civil until you got involved in it.
Oh you took my ranting on the morons personally? Get off your high horse. The austrian and german foreign ministers has actually called it a nuclear apocalypse and catastrophe. Truth is, there is alot "what we think is happening" in the western media, not many on this planet is actually inside the plant. Im just glad to see the Japanese acting all calm in the midst of it, which is what everyone should.
Kouji_SanSr. Hινε UÏкεεÏεг - EUPT DeputyThe NetherlandsJoin Date: 2003-05-13Member: 16271Members, NS2 Playtester, Squad Five Blue
The media in this day and age have been uninformed as a status quo, nothing you're saying is anything new though. You're kind of tooting the <i>horn of obvious</i> here...
<!--quoteo(post=1837744:date=Mar 18 2011, 10:04 AM:name=Svenpa)--><div class='quotetop'>QUOTE (Svenpa @ Mar 18 2011, 10:04 AM) <a href="index.php?act=findpost&pid=1837744"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->What is it that actually explodes in a powerplant? I thought the material containing the radioactive matter only melted once it got too hot?<!--QuoteEnd--></div><!--QuoteEEnd-->
Theres a reaction which occurs at high temperatures/pressures between the zircaloy sheaths used on the fuel rods and the cooling water - it effectively 'rusts' creating Zirconium Oxide and Hydrogen. The hydrogen eventually escapes out of the reactor and into the surrounding building, builds up and then something sets it off and theres your explosion. Thats the most likely cause of the explosions that are being reported.
On the one hand the explosion itself is mostly meaningless, it won't effect the reactor/core. On the other as long as hydrogen explosions keep happening it means the core is still way too hot then its should be.
Yes, using Zircalloy sheaths is a daft design and not used in modern reactors :P
NeonSpyder"Das est NTLDR?"Join Date: 2003-07-03Member: 17913Members
A good read on the nuclear situation in Japan and media reaction to it: <a href="http://www.cosmosmagazine.com/node/4149/full" target="_blank">Here</a>
Quote from the article: "These are just the headlines. The actual coverage has often been nonsensical, contradictory, overdramatic and occasionally hysterical. No wonder the public often react with fear when they see the word ‘nuclear’. "
<!--quoteo(post=1837815:date=Mar 18 2011, 07:02 PM:name=Tykjen)--><div class='quotetop'>QUOTE (Tykjen @ Mar 18 2011, 07:02 PM) <a href="index.php?act=findpost&pid=1837815"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->Glad I havent got your brains as well. Way to start talking about the final solution all of a sudden. I wont expect you to understand my point either; Comparing petroleum and gunpowder to nuclear power and nuclear weapons is as stupid as comparing nuclear power and nuclear weapons to.... petroleum and gunpowder.
I was "simply" saying that if the nazis had invented the nuke first, we wouldnt be discussing this right now :P But anti nuclear morons just dont get that simplicity.<!--QuoteEnd--></div><!--QuoteEEnd-->
Let's not mention my brain because there's no need to insult it.
I understand that if the nazis had invented the nuke first, the world wouldn't be as it is right now. But it just doesn't justify any argumentation, the world today is only the product of so many events. Of which the development of nuclear weaponry is only an example among many.
Back to my comparison then; petroleum, explosives, and nuclear reactions are all sources of energy. As a pro-nuclear, you understand (I hope) that this source of energy can be used for good and for bad. My point is that it is foolish argumentation to say "let's ban nuclear power, see what nukes can do". It is a statement, not a counter-argument. There is no link between nuclear power and nuclear weaponry (of course, barring the<i> intent </i>of developing weaponry, which power plant companies usually don't have). Mentioning nukes in a topic about a power plant crisis isn't pertinent to the subject at hand.
With all that being said, the only thing I'm saying here, is that there is no need to mention nazis, nukes or lolbama here. What might not really be obvious is that I am not anti-nuclear at all, far from it. I also believe that environmentalists don't understand at all what they're talking about, and it's frustrating to no end that, in a country like France where 80% of our power is nuclear-based, politicians are considering replacing our nuclear power plants with solar panels (laughable construction/recycling costs), dams (and they say that nuclear power destroys ecosystems) or wind turbines (We just need 40 thousand or so of them in optimal case scenarios). And just because it's good PR right now. But no need to rewrite history.
I'm not going to expand on the whole nazi thing because Godwin is watching us, but I suggest you to review a bit your history if you don't agree that the nazi party and racial identity go hand in hand (and note that final solution and racial purity are not the same)
Yeah. To clarify my earlier post, the steam explosion was Chernobyl, which Svenpa was asking about. At least I think so. The japanese reactors had completely different incidents.
Just read up on it a bit. We're both right, actually. There were two explosions: First the steam explosion that blew the reactor casing apart, then a nuclear excursion or criticality incident that blew the core itself apart and scattered it all over the surrounding area.
<!--quoteo(post=1837930:date=Mar 19 2011, 11:16 AM:name=lolfighter)--><div class='quotetop'>QUOTE (lolfighter @ Mar 19 2011, 11:16 AM) <a href="index.php?act=findpost&pid=1837930"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->Just read up on it a bit. We're both right, actually. There were two explosions: First the steam explosion that blew the reactor casing apart, then a nuclear excursion or criticality incident that blew the core itself apart and scattered it all over the surrounding area.<!--QuoteEnd--></div><!--QuoteEEnd--> In the case of Chernobyl, the first steam explosion was secondary to the initial supercriticality.
What do you mean by secondary? I doubt you're talking about the sequence of events, because every official report asserts that the steam explosion came first.
<!--quoteo(post=1837999:date=Mar 20 2011, 02:21 AM:name=lolfighter)--><div class='quotetop'>QUOTE (lolfighter @ Mar 20 2011, 02:21 AM) <a href="index.php?act=findpost&pid=1837999"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->the steam explosion came first<!--QuoteEnd--></div><!--QuoteEEnd--> While void played a role in the initial supercriticality, the 'steam explosion' that happened next was only because of the increased reactor power. Then following that was an even more rapid supercriticality, that you called the 'excursion'.
It is just more accurate to reserve the term 'steam explosion' for situations where the superheated coolant previously exists and then comes into contact with materials that cause it to flash. Otherwise it's like saying a fire is caused by the oxygen; combustion with oxygen makes more fire, but it's not the oxygen's fault... the fire was already started.
Hope that helps. I just think it's important to recognize the role of the reactor design in every step of a disaster. It's been a long time for me but I'm certain it is correct.
I think steam explosion is an accurate term for a boiler rupture that leads to explosive steam expansion. Like if the safety valve on your pressure cooker fails and it bursts. That's a steam explosion.
<!--quoteo(post=1838242:date=Mar 21 2011, 04:22 PM:name=lolfighter)--><div class='quotetop'>QUOTE (lolfighter @ Mar 21 2011, 04:22 PM) <a href="index.php?act=findpost&pid=1838242"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->I think steam explosion is an accurate term for a boiler rupture that leads to explosive steam expansion. Like if the safety valve on your pressure cooker fails and it bursts. That's a steam explosion.<!--QuoteEnd--></div><!--QuoteEEnd--> It's more like if you lit some TNT and put it in your pressure cooker; when it blows, the water flashes to steam and the safety valve fails. I'd say it was a TNT explosion rather than steam explosion.
Does anyone else find it deliciously ironic that the typical news media scare tactics used to gain viewers is causing people to poison themselves with potassium iodide in an effort to protect themselves from non-existent radiation threats?
<!--quoteo(post=1838285:date=Mar 22 2011, 04:01 AM:name=DiscoZombie)--><div class='quotetop'>QUOTE (DiscoZombie @ Mar 22 2011, 04:01 AM) <a href="index.php?act=findpost&pid=1838285"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->Does anyone else find it deliciously ironic that the typical news media scare tactics used to gain viewers is causing people to poison themselves with potassium iodide in an effort to protect themselves from non-existent radiation threats?<!--QuoteEnd--></div><!--QuoteEEnd-->
And yet I see nothing wrong with stupid people offing themselves.
<!--quoteo(post=1838280:date=Mar 22 2011, 03:43 AM:name=juice)--><div class='quotetop'>QUOTE (juice @ Mar 22 2011, 03:43 AM) <a href="index.php?act=findpost&pid=1838280"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->It's more like if you lit some TNT and put it in your pressure cooker; when it blows, the water flashes to steam and the safety valve fails. I'd say it was a TNT explosion rather than steam explosion.<!--QuoteEnd--></div><!--QuoteEEnd--> It is a TNT explosion, but not for the reason you say. The TNT will blow the pressure cooker apart long before the steam has a chance to - steam doesn't even play a factor in the explosion at this point. The expansion of gasses from a TNT explosion is so much faster than that of steam. And the thermal output of TNT isn't all that significant. That isn't what happened in Chernobyl. The reactor spiked to a thermal output of ten times what it was rated for, causing water to flash into steam, leading to massive overpressure, rupture of pipes and eventually the entire reactor casing splitting apart. The nuclear excursion came into play seconds later, possibly due to the almost total loss of coolant and moderator combined with the reactor type's positive void coefficient (which means that gaps or voids in the moderator (which the coolant in the reactor also served as) cause the reactor to increase in output, unlike safer reactor designs with negative void coefficients that cause a decrease in reactor output in such a situation).
If we want a more accurate pressure cooker analogy, imagine that you put a very powerful heating element (capable or reaching temperatures in excess of the melting point of steel, for argument's sake) inside an empty pressure cooker: The entire thing will become red hot, until eventually overpressure will combine with structural weakening from the overheating to cause it to burst. The overpressure inside will be relatively low, because while athmospheric air does increase in volume as you heat it up, the effect isn't all that pronounced. The main reason it pops is because the metal is slowly approaching a liquid state. The overpressure will quickly equalise and the pot will just melt into slag.
However, if you fill the pressure cooker with water, then once the water reaches boiling point, some of it turns to steam. Steam has a much higher volume than the equivalent mass of water (if I remember correctly we're talking about three orders of magnitude), so pressure inside the pot will increase drastically. The effect is far more pronounced than simple thermal expansion. As pressure inside the pot increases, the boiling point of water increases as well, so the water in the pot becomes superheated, i.e. heated beyond its boiling point at normal athmospheric pressure. At some point, the cooker can't handle the pressure anymore. We're nowhere near the temperature we reached in the previous experiment, so structural integrity isn't yet affected, but the pressure is simply too much for the cooker to handle, and it cracks somewhere. The outrush of steam causes pressure in the cooker to fall drastically, meaning that all the superheated water suddenly finds itself at normal athmospheric pressure, causing much of it to flash into steam. The cooker splits apart spraying shrapnel and boiling water all over the kitchen. And THEN the heating element explodes, because it turns out that this is the kind of heating element that explodes once there's no water around it anymore.
Kouji_SanSr. Hινε UÏкεεÏεг - EUPT DeputyThe NetherlandsJoin Date: 2003-05-13Member: 16271Members, NS2 Playtester, Squad Five Blue
edited March 2011
<!--quoteo(post=1838360:date=Mar 22 2011, 04:58 PM:name=Temphage)--><div class='quotetop'>QUOTE (Temphage @ Mar 22 2011, 04:58 PM) <a href="index.php?act=findpost&pid=1838360"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->And yet I see nothing wrong with stupid people offing themselves.<!--QuoteEnd--></div><!--QuoteEEnd--> Isn't that what we call Natural Selection :P
Comments
<a href="http://hypertextbook.com/eworld/einstein.shtml" target="_blank">http://hypertextbook.com/eworld/einstein.shtml</a>
<a href="http://www.cosmosmagazine.com/news/1341/green-nuclear-power-coming-norway" target="_blank">http://www.cosmosmagazine.com/news/1341/gr...r-coming-norway</a>
<a href="http://hypertextbook.com/eworld/einstein.shtml" target="_blank">http://hypertextbook.com/eworld/einstein.shtml</a><!--QuoteEnd--></div><!--QuoteEEnd-->
What does that have to do with earthquakes or power plants? I don't understand where you're going with this. We're talking about earthquakes and power plants, you're talking about nuclear bombs and Hitler.
<!--quoteo(post=1837744:date=Mar 18 2011, 10:04 AM:name=Svenpa)--><div class='quotetop'>QUOTE (Svenpa @ Mar 18 2011, 10:04 AM) <a href="index.php?act=findpost&pid=1837744"><{POST_SNAPBACK}></a></div><div class='quotemain'><!--quotec-->What is it that actually explodes in a powerplant? I thought the material containing the radioactive matter only melted once it got too hot?<!--QuoteEnd--></div><!--QuoteEEnd-->
Steam explosion. The reactor core is filled with water, which evaporates as it gets hotter, building up pressure.
Steam explosions can be extraordinarily dangerous. The boiling point of a substance changes with pressure - as pressure increases, the boiling point increases. This means that as the pressure inside the boiler increases, the liquid water inside becomes far hotter than it could normally be under normal athmospheric pressure. When the boiler finally cracks, pressure drops dramatically, and large amounts of superheated water instantly flash into steam, adding to the violence of the explosion.
When Chernobyl's reactor 4 blew, the 2000-ton "lid" was blown clear off the reactor core, and the roof was blown off the turbine hall. All of that damage was done by the steam explosion. The nuclear fission merely supplied the heat needed to do it.
Where did I mention Hitler? I mentioned the nazis because of all the anti-nuclear morons currently using the so called "nuclear apocalypse" in Japan as propaganda for their enviromentalist "green world" piss agenda. Thus overshadowing the importance of nuclear power and energy. Nobody could prepare for the quake and tsunami that followed in Japan..just a shame the western world and the mass media are mass panicing. Ofc you dont understand where Im going with this, I didnt expect you to.
What isn't hard, however, is to talk about 'environmentalist "green world" piss agendas' without mentioning a political ideology founded on the principles of racial purity.
Saying that nuclear weaponry and nuclear power plants are the same thing is akin to blaming the petroleum industry for molotov cocktails, or trying to put a ban on the firework industry because gunpowder kills people.
What isn't hard, however, is to talk about 'environmentalist "green world" piss agendas' without mentioning a political ideology founded on the principles of racial purity.
Saying that nuclear weaponry and nuclear power plants are the same thing is akin to blaming the petroleum industry for molotov cocktails, or trying to put a ban on the firework industry because gunpowder kills people.<!--QuoteEnd--></div><!--QuoteEEnd-->
Glad I havent got your brains as well. Way to start talking about the final solution all of a sudden. I wont expect you to understand my point either; Comparing petroleum and gunpowder to nuclear power and nuclear weapons is as stupid as comparing nuclear power and nuclear weapons to.... petroleum and gunpowder.
I was "simply" saying that if the nazis had invented the nuke first, we wouldnt be discussing this right now :P
But anti nuclear morons just dont get that simplicity.
It's true you never mentioned Hitler, my mistake. You said nazis, not Hitler. You are, however, the only one who's talking about a nuclear apocalypse. Pure hyperbole. I use words such as "disaster" and "incident." You shove words like "nuclear apocalypse" into my mouth in an attempt to make my position seem extremist and alarmist. This thread was civil until you got involved in it.
Theres a reaction which occurs at high temperatures/pressures between the zircaloy sheaths used on the fuel rods and the cooling water - it effectively 'rusts' creating Zirconium Oxide and Hydrogen. The hydrogen eventually escapes out of the reactor and into the surrounding building, builds up and then something sets it off and theres your explosion. Thats the most likely cause of the explosions that are being reported.
On the one hand the explosion itself is mostly meaningless, it won't effect the reactor/core. On the other as long as hydrogen explosions keep happening it means the core is still way too hot then its should be.
Yes, using Zircalloy sheaths is a daft design and not used in modern reactors :P
Quote from the article: "These are just the headlines. The actual coverage has often been nonsensical, contradictory, overdramatic and occasionally hysterical. No wonder the public often react with fear when they see the word ‘nuclear’. "
I was "simply" saying that if the nazis had invented the nuke first, we wouldnt be discussing this right now :P
But anti nuclear morons just dont get that simplicity.<!--QuoteEnd--></div><!--QuoteEEnd-->
Let's not mention my brain because there's no need to insult it.
I understand that if the nazis had invented the nuke first, the world wouldn't be as it is right now. But it just doesn't justify any argumentation, the world today is only the product of so many events. Of which the development of nuclear weaponry is only an example among many.
Back to my comparison then; petroleum, explosives, and nuclear reactions are all sources of energy. As a pro-nuclear, you understand (I hope) that this source of energy can be used for good and for bad. My point is that it is foolish argumentation to say "let's ban nuclear power, see what nukes can do". It is a statement, not a counter-argument. There is no link between nuclear power and nuclear weaponry (of course, barring the<i> intent </i>of developing weaponry, which power plant companies usually don't have). Mentioning nukes in a topic about a power plant crisis isn't pertinent to the subject at hand.
With all that being said, the only thing I'm saying here, is that there is no need to mention nazis, nukes or lolbama here. What might not really be obvious is that I am not anti-nuclear at all, far from it. I also believe that environmentalists don't understand at all what they're talking about, and it's frustrating to no end that, in a country like France where 80% of our power is nuclear-based, politicians are considering replacing our nuclear power plants with solar panels (laughable construction/recycling costs), dams (and they say that nuclear power destroys ecosystems) or wind turbines (We just need 40 thousand or so of them in optimal case scenarios). And just because it's good PR right now.
But no need to rewrite history.
I'm not going to expand on the whole nazi thing because Godwin is watching us, but I suggest you to review a bit your history if you don't agree that the nazi party and racial identity go hand in hand (and note that final solution and racial purity are not the same)
Thx dude, you got it right.
It is true though, steam explosions are also possible.
To the question, what is it exactly that explodes in a nuclear reactor? Well, it depends what caused the explosion that time :D :D
In the case of Chernobyl, the first steam explosion was secondary to the initial supercriticality.
<center><object width="450" height="356"><param name="movie" value="http://www.youtube.com/v/5La0MQfz8Vo"></param><embed src="http://www.youtube.com/v/5La0MQfz8Vo" type="application/x-shockwave-flash" width="450" height="356"></embed></object></center>
bah, embedding disabled.
<a href="http://www.youtube.com/watch?v=5La0MQfz8Vo" target="_blank">http://www.youtube.com/watch?v=5La0MQfz8Vo</a>
Racist against the Brits :<
While void played a role in the initial supercriticality, the 'steam explosion' that happened next was only because of the increased reactor power. Then following that was an even more rapid supercriticality, that you called the 'excursion'.
It is just more accurate to reserve the term 'steam explosion' for situations where the superheated coolant previously exists and then comes into contact with materials that cause it to flash. Otherwise it's like saying a fire is caused by the oxygen; combustion with oxygen makes more fire, but it's not the oxygen's fault... the fire was already started.
Hope that helps. I just think it's important to recognize the role of the reactor design in every step of a disaster. It's been a long time for me but I'm certain it is correct.
It's more like if you lit some TNT and put it in your pressure cooker; when it blows, the water flashes to steam and the safety valve fails. I'd say it was a TNT explosion rather than steam explosion.
<img src="http://imgs.xkcd.com/blag/radiation.png" border="0" class="linked-image" />
And yet I see nothing wrong with stupid people offing themselves.
It is a TNT explosion, but not for the reason you say. The TNT will blow the pressure cooker apart long before the steam has a chance to - steam doesn't even play a factor in the explosion at this point. The expansion of gasses from a TNT explosion is so much faster than that of steam. And the thermal output of TNT isn't all that significant.
That isn't what happened in Chernobyl. The reactor spiked to a thermal output of ten times what it was rated for, causing water to flash into steam, leading to massive overpressure, rupture of pipes and eventually the entire reactor casing splitting apart. The nuclear excursion came into play seconds later, possibly due to the almost total loss of coolant and moderator combined with the reactor type's positive void coefficient (which means that gaps or voids in the moderator (which the coolant in the reactor also served as) cause the reactor to increase in output, unlike safer reactor designs with negative void coefficients that cause a decrease in reactor output in such a situation).
If we want a more accurate pressure cooker analogy, imagine that you put a very powerful heating element (capable or reaching temperatures in excess of the melting point of steel, for argument's sake) inside an empty pressure cooker: The entire thing will become red hot, until eventually overpressure will combine with structural weakening from the overheating to cause it to burst. The overpressure inside will be relatively low, because while athmospheric air does increase in volume as you heat it up, the effect isn't all that pronounced. The main reason it pops is because the metal is slowly approaching a liquid state. The overpressure will quickly equalise and the pot will just melt into slag.
However, if you fill the pressure cooker with water, then once the water reaches boiling point, some of it turns to steam. Steam has a much higher volume than the equivalent mass of water (if I remember correctly we're talking about three orders of magnitude), so pressure inside the pot will increase drastically. The effect is far more pronounced than simple thermal expansion. As pressure inside the pot increases, the boiling point of water increases as well, so the water in the pot becomes superheated, i.e. heated beyond its boiling point at normal athmospheric pressure.
At some point, the cooker can't handle the pressure anymore. We're nowhere near the temperature we reached in the previous experiment, so structural integrity isn't yet affected, but the pressure is simply too much for the cooker to handle, and it cracks somewhere. The outrush of steam causes pressure in the cooker to fall drastically, meaning that all the superheated water suddenly finds itself at normal athmospheric pressure, causing much of it to flash into steam. The cooker splits apart spraying shrapnel and boiling water all over the kitchen.
And THEN the heating element explodes, because it turns out that this is the kind of heating element that explodes once there's no water around it anymore.
Isn't that what we call Natural Selection :P