Nuclear Situation In Japan
June 2, 2012 5:14pm CST
OK so I'll explain some of what I've seen so far on NHK, CNN, etc. My husband's company is installed at a few nuke facilities, only some of TEPCO, but the GE reactor design that was shown on NYT is similar to one that I've seen in South Korea at two of my clients. The explosion at Fukushima Dai'ichi Reactor 1 was a hydrogen blast that sheered the roof of the containment building. There are conflicting reports about the state of the reactor vessel but the detection of cesium isotopes outside the plant indicate that there must have been a breach or blackflow. If you saw the tsunami washing over the power station, you can imagine how messed-up the cooling system must have been with a huge wall of seawater pounding the plant and flooding motor rooms for the cooling pumps. The hydrogen blast basically goes like this: - Reactor overheats - Overheated steam or hot air (exposed fuel) gives nothing to stop neutrons, increasing fission - The hot metal softens and corrodes the fuel casing. The casing used on the fuel rods when exposed to hot steam will generate hydrogen and increase pressure in the reactor vessel, which also causes an increase in temperature - When this pressurized hydrogen is released, as H2, it will interact with oxygen in the air. If it is too concentrated (in the reactor building) the rapid oxidaztion reaction will generate an explosion. The explosion actually solves one (of many) problems the engineers have on their hands in trying to cool the fuel in the reactor to prevent an uncontrolled meltdown, it greatly lowered the pressure in Reactor Unit 1 and gave room to release more pressure and inject more sea water. If the reactor fuel loses its geometry due to excessive heat, then you lose control over all mechanical means to control the reactor core. So flooding the core with boric-acid treated seawater is being used to overmoderate the core, which is hoped to cool the reactor and "kill the melt" from progressing. This will be a long process if there was melt going on. The boric acid is a substitute to the boron control rods that would have been used to moderate the nuclear reaction. Seawater is another clue that there was a Three Mile Island-type of partial meltdown inside the reactor. Water on its own is a neutron moderater, so one has to be EXTREMELY careful how its applied in the core. You don't want to slow neutrons down to the point where criticality increases again. So the reactor will remain fairly hot for probably days as they try to kill the melt. Reactor number 3 at the Fukushima plant has a similar reactor design but uses a blended fuel type that includes uranium and plutonium. The Pu part makes managing the cooling emergency extremely dangerous. Pu when it is split throws off neutrons at a faster rate, so it is a more "ferocious" fuel. When the cooling system failed they probably already had plenty of time to jam in all the control rods but they have a residual heat problem they have to get rid of. If they do not get rid of this heat, they could have fuel degredation that could damage the geometry of the control rods which has the potential to bring the reactor back to a semi supercritical state. It appears that this is already happened because now there is talk of preparation of a 2nd hydrogen explosion at Unit 3, so it's clear to me that this has escalated to a containment issue. Lastly, cesium aerosol was detected outside Reactor Unit 1. That is a VERY telltale sign that fuel was damaged and melted inside the reactor. Cesium is a byproduct of PWR and BWR reactor types and all isotypes of cesium are quite heavy. In a reactor it exists in liquid form swimming around the fuel rods and partially as a gas. To have cesium being expelled dozens of meters away from a nuclear plant indicates a serious containment problem. Normally when a cooling vent release occurs at a BWR nuclear plant you'll have krypton and iodides... they naturally exist as gases, but heavy strontium and cesium metals would normally not make it as an aerosol unless the core was excited because the cooling system has malfunctioned.