Japanese reactor crisis - Page 2

dreadgeek · 03-14-2011, 11:45 AM

Okay, before I begin I want to make something clear. I'm NOT a nuclear engineer. I have never worked in a nuclear power plant. I considered being a nuclear power plant technician when I was contemplating joining the Navy and during that time I read everything I could get my hands on regarding nuke plants, how they work and various post-mortems on Three Mile Island. I have the understanding that, say, a decent science reporter might have. I understand the underlying physics pretty well and I'm following this unfolding event very closely.

My purpose in starting this thread and posting is NOT to show off. Rather, I know that *I* am concerned and I imagine other people are as well. To that end, I'm going to try to share what information and understanding I have. If you have a question, I will do my best to answer them.

It might be helpful to explain how nuclear power plants work and why TMI is the better model for what is happening than Chernobyl.

So...

Nuclear reactors are just very fancy and highly efficient ways of boiling water. As Einstein demonstrated a hundred years ago, E=MC^2 or energy is equivalent to the mass multiplied by the square of the speed of light (~186,000 mps in vacuum). The practical upshot of this equation is that very small objects contain a HUGE potential for energy. When certain substances are split, they release energy and certain kinds of metals--like uranium--actually have their atoms split rather easily. When an atom is split what happens is that a neutron hits the nucleus of an atom, causing it to be broken into smaller, sub-atomic components. As the protons and electrons are stripped from the atom that process releases energy. One by-product of this is yet *more* neutrons which hit yet *more* nuclei of U-235 (uranium with an atomic weight of 235) which causes a chain reaction. Another by-product of this is heat. The mass of the uranium-235 is being turned into energy in the form of heat and radiation. Radiation is simply high-energy parts of the electromagnetic spectrum.

So, the way this process works is that you have fuel rods that are filled with refined uranium-235 in pellets. Those rods are lowered into the core of the reactor where the nuclear reaction begins. To keep the temperature manageable most Western reactors (the Japanese use designs closer to Western designs than the old Soviet design--more on that below) cool the core by immersing the whole thing in water. As long as the water is kept at a sufficient level, the reactor will do its job of heating water, turning it into steam, the steam turns a turbine which has an electromagnet in which creates electricity. There are also control rods made of a material that will absorb neutrons without fissioning themselves. These control rods are lowered into the 'pile' (the fissionable material) to absorb neutrons thus slowing the reaction or removed to allow more reactions.

The problem facing the Japanese right now is that with the pumps down, they can't keep circulating water through the reactor. That means that any water covering the core will evaporate. This will turn into steam and with the plant shut down that steam has no place to go. It will build up in the containment building until the pressure is too great. KNOWING that this kind of thing could happen, designers of reactors build the containment buildings so that any explosion caused by a build up of hydrogen gas (this is NOT a hydrogen explosion as you would see in a nuclear bomb) will push *outward* away from the reactor itself so even if the building is damaged the reactor should maintain its structural integrity.

If the core is uncovered the rods will start to melt and can actually burst into flame. This should give you an idea of how hot (in the heat sense not the radioactive sense) the core of the reactor can get to that metal doesn't just melt it actually *burns*. This is the most immediate concern is that they will lose all control of the reactor, the reactor will become uncovered, the rods and the reactor housing itself will all melt into slag and then the we have to hope that the concrete floor of the containment building will stop it. That is, of course, the worst case scenario.

Whenever a problem happens at a reactor, it will either automatically shutdown or be shutdown by the human operators. This is called a 'SCRAM'.

(I'm going to close this post out and do another one on TMI and Chernobyl)

03-14-2011, 11:45 AM	#1
dreadgeek Power Femme How Do You Identify?: Cinnamon spiced, caramel colored, power-femme Preferred Pronoun?: She Relationship Status: Married to a wonderful horse girl Join Date: Oct 2009 Location: Lat: 45.60 Lon: -122.60 Posts: 1,733 My Photo Gallery Thanks: 1,132 Thanked 6,848 Times in 1,493 Posts Rep Power: 21474851	Japanese reactor crisis Okay, before I begin I want to make something clear. I'm NOT a nuclear engineer. I have never worked in a nuclear power plant. I considered being a nuclear power plant technician when I was contemplating joining the Navy and during that time I read everything I could get my hands on regarding nuke plants, how they work and various post-mortems on Three Mile Island. I have the understanding that, say, a decent science reporter might have. I understand the underlying physics pretty well and I'm following this unfolding event very closely. My purpose in starting this thread and posting is NOT to show off. Rather, I know that I am concerned and I imagine other people are as well. To that end, I'm going to try to share what information and understanding I have. If you have a question, I will do my best to answer them. It might be helpful to explain how nuclear power plants work and why TMI is the better model for what is happening than Chernobyl. So... Nuclear reactors are just very fancy and highly efficient ways of boiling water. As Einstein demonstrated a hundred years ago, E=MC^2 or energy is equivalent to the mass multiplied by the square of the speed of light (~186,000 mps in vacuum). The practical upshot of this equation is that very small objects contain a HUGE potential for energy. When certain substances are split, they release energy and certain kinds of metals--like uranium--actually have their atoms split rather easily. When an atom is split what happens is that a neutron hits the nucleus of an atom, causing it to be broken into smaller, sub-atomic components. As the protons and electrons are stripped from the atom that process releases energy. One by-product of this is yet more neutrons which hit yet more nuclei of U-235 (uranium with an atomic weight of 235) which causes a chain reaction. Another by-product of this is heat. The mass of the uranium-235 is being turned into energy in the form of heat and radiation. Radiation is simply high-energy parts of the electromagnetic spectrum. So, the way this process works is that you have fuel rods that are filled with refined uranium-235 in pellets. Those rods are lowered into the core of the reactor where the nuclear reaction begins. To keep the temperature manageable most Western reactors (the Japanese use designs closer to Western designs than the old Soviet design--more on that below) cool the core by immersing the whole thing in water. As long as the water is kept at a sufficient level, the reactor will do its job of heating water, turning it into steam, the steam turns a turbine which has an electromagnet in which creates electricity. There are also control rods made of a material that will absorb neutrons without fissioning themselves. These control rods are lowered into the 'pile' (the fissionable material) to absorb neutrons thus slowing the reaction or removed to allow more reactions. The problem facing the Japanese right now is that with the pumps down, they can't keep circulating water through the reactor. That means that any water covering the core will evaporate. This will turn into steam and with the plant shut down that steam has no place to go. It will build up in the containment building until the pressure is too great. KNOWING that this kind of thing could happen, designers of reactors build the containment buildings so that any explosion caused by a build up of hydrogen gas (this is NOT a hydrogen explosion as you would see in a nuclear bomb) will push outward away from the reactor itself so even if the building is damaged the reactor should maintain its structural integrity. If the core is uncovered the rods will start to melt and can actually burst into flame. This should give you an idea of how hot (in the heat sense not the radioactive sense) the core of the reactor can get to that metal doesn't just melt it actually burns. This is the most immediate concern is that they will lose all control of the reactor, the reactor will become uncovered, the rods and the reactor housing itself will all melt into slag and then the we have to hope that the concrete floor of the containment building will stop it. That is, of course, the worst case scenario. Whenever a problem happens at a reactor, it will either automatically shutdown or be shutdown by the human operators. This is called a 'SCRAM'. (I'm going to close this post out and do another one on TMI and Chernobyl) __________________ Proud member of the reality-based community. "People on the side of The People always ended up disappointed, in any case. They found that The People tended not to be grateful or appreciative or forward-thinking or obedient. The People tended to be small-minded and conservative and not very clever and were even distrustful of cleverness. And so, the children of the revolution were faced with the age-old problem: it wasn’t that you had the wrong kind of government, which was obvious, but that you had the wrong kind of people. As soon as you saw people as things to be measured, they didn’t measure up." (Terry Pratchett)