Thoughts on the Fukushima Daiichi situation
(Note: this is taken from an FB post by Rick Boatright, one of the more science-oriented Barflies I know)
Remember that the Fukushima reactors took an earthquake shock with twice as much energy as their design provided for. Hold that idea in your mind while we work through the rest of this.
Then, the plant was swamped by a tsunami that took out the diesel generators, and contaminated the fuel supply for the diesels.
At the same time, the compressors and the electronic controls that are used to pneumatically open and close water valves inside the radioactive areas of the plant were taken out.
For about eight hours, the plant workers managed to keep the water running using battery power in at least SOME of the plants, but it has become clear that the sensors that measure things like water level and steam pressure inside various parts of the reactors were damaged. So, immediately, the team managing the reactors was handicapped because they didn't KNOW that they couldn't trust the data they were trying to run things by.
Sometime around the time that the batteries were dying, at least some replacement portable diesel generators were brought in. The frequently stated problem was "the plugs didn't fit." We can only speculate about what the real problem was, since in this sort of crisis someone could have ripped the plugs off and gotten electricity flowing. One of the things to think about tho is that it takes a LOT of electricity to manage a nuclear reactor. Among other things, imagine pumping water into a pressure cooker on your stove. You're pumping against the steam pressure, and the more water you push in, the more pressure you're fighting. It takes very powerful pumps. So, in order to allow more water in, they manually triggered a steam valve using an air line so that they could pump in more water. This happened over and over. in addition, because the core got SO HOT (because of the lack of water) the steam had reached a temperature where it split into Hydrogen and Oxygen. When that mixture came into the outer building around the containment, it triggered a BIG explosion of the H2 combing with the O and making water again. The buildings around the containments were blown to bits. Of course, that made working on the reactors that much harder, and sensor lines, control lines and water lines were damaged when the building blew up.
So far tho, it seemed that the situation was such that over the course of this week it would be brought under control. Pump more seawater into the cores, vent steam, pump more water, eventually things cool off.
This is where we were as of Monday night in the central US.
Then, something very odd happened. There was a hydrogen explosion in the building for reactor 4. That was odd because reactor four was SHUT DOWN. There wasn't any fuel in it. The thinking of everyone who thought at all about it was that reactor 4 was utterly safe. All the fuel had been removed. Why would we worry?
What happened? We have to guess. The guys inside the have been WAY to busy to talk to the media, and there's no remote sensing, and I suspect that no one really knows.
I'm going to try to separate my speculation from what we actually know.
We know that the spent fuel pool in the reactor 4 building had a LOT more fuel in it than normal. Reactor 4 had recently been de-fueled, and the rods in it are very hot, they just came out of the reactor.
Spent fuel pools lose water all on their own. The hot rods heat the water and it evaporates or, eventually boils off. Usually, that's not a big deal because the pools are filled to twelve to fifteen feet ABOVE the tops of the fuel rods. Boiling off twelve feet of water takes a LONG time.
But.... (speculation) it's certainly possible that some of the water spilled out in the earthquake. It's possible that during the earthquake the racks that hold the 14 foot long fuel rods cracked and shifted so that some rods came very close together, allowing the water between them to superheat and produce H2 and O2
However it happened, while everyone was paying attention to getting water into the 1,2, and3 reactors which had fuel in them, the spent-fuel pool at reactor 4 either boiled dry, or came close to boiling dry.
Now, this is a BIG pool. Several swimming pools. Filling it with a fire hose would be an hours long project even if it wasn't filled with nearly red-hot rods which flash the water to steam as soon as it hits them. You need big pipes, big powerful pumps and lots of electricity (which you don't have) and this is at the top of a building that has now been blown up, so you can't run new hoses and pipes up there.
Tepco is frantically running a power line into the plant from the nearest working electric supply, 50 miles away. They're patching and stitching existing hunks of line and new line and whatever, and hope to have electricity to the plant by tonight (wed the 16th us time) or some time tomorrow. If so, that will help a lot as they can use their big pumps, assuming those pumps are in working condition.
So, best-case worst-case.
Best case: Tepco gets an electric supply to the plant, there are enough working pumps to cool things, and they pump _a lot_ of seawater into reactors 1, 2, and 3 and into the cooling pools for those reactors and they pump a WHOLE LOT of seawater into the pool on top of reactor 4 and those rods get cooled off.
Then, over the course of the next couple of months things cool down, and a team can be assembled and the painful slow process of de-commisioning the reactors and getting all the fuel rods out and into safe storage can proceed. A decade or so from now you'll have a brownfield site where there used to be a nuclear power plant at a cost probably of close to a trillion dollars.
Worst case: for whatever reason, Tepco is unable to get enough water into the pool at reactor 4. Perhaps the pool is cracked. Perhaps the lines are broken. Whatever, but that pool goes dry and stays dry for a long time. What happens then? Somewhere between 2200 degrees and 3000 degrees the zirconium-tin alloys over the uranium oxide fuel pellets melt. This is "bad." somewhere under 3000 degrees the zirconium, while not exactly boiling, starts to evaporate at high speeds. Zirconium metal is VERY willing to combine with oxygen, so it burns, adding more heat to the situation.
Needless to say, a pool of liquid metal at over 2000 degrees sitting in a concrete box is not going to stay there forever. Concrete is held together with cement that solidifies as it combines with water. Cook it, the water comes out and the concrete falls apart. Now, you have a stream of liquid radioactive metals burning as it falls through the air. Another explosion happens this time, but this time it scatters the Uranium oxide fuel pellets around the countryside, releases large amounts of Cesium and Iodine into the air, and contaminates the coast of japan for a long long time. That's a chernobyl level event. Ooops.
But wait, there's more. Now, you have no way to keep a team pumping water into reactors 1, 2, and 3, and over the next few days/weeks They over heat, blow up and contaminate the world too. The only good difference is, there are no giant blocks of graphite to burn carrying the radiation even further.
That's the worst case. An above-chernobyl level incident that makes a huge piece of Japan's northern coast uninhabitable for a long time.
No one saw that coming, because no one thought there was any CHANCE that the reactor 4 pool could boil dry this fast. Something's odd with that. Perhaps the earthquake made a crack. Perhaps the Tepco folks put WAY too much fuel in the one cooling pond. We won't know for a long time. Eventually, someone will fall on their swords over this, but not tonight. Tonight, lets pray for the brave sons of Martha who are in that plant trying to save what they can.
Remember that the Fukushima reactors took an earthquake shock with twice as much energy as their design provided for. Hold that idea in your mind while we work through the rest of this.
Then, the plant was swamped by a tsunami that took out the diesel generators, and contaminated the fuel supply for the diesels.
At the same time, the compressors and the electronic controls that are used to pneumatically open and close water valves inside the radioactive areas of the plant were taken out.
For about eight hours, the plant workers managed to keep the water running using battery power in at least SOME of the plants, but it has become clear that the sensors that measure things like water level and steam pressure inside various parts of the reactors were damaged. So, immediately, the team managing the reactors was handicapped because they didn't KNOW that they couldn't trust the data they were trying to run things by.
Sometime around the time that the batteries were dying, at least some replacement portable diesel generators were brought in. The frequently stated problem was "the plugs didn't fit." We can only speculate about what the real problem was, since in this sort of crisis someone could have ripped the plugs off and gotten electricity flowing. One of the things to think about tho is that it takes a LOT of electricity to manage a nuclear reactor. Among other things, imagine pumping water into a pressure cooker on your stove. You're pumping against the steam pressure, and the more water you push in, the more pressure you're fighting. It takes very powerful pumps. So, in order to allow more water in, they manually triggered a steam valve using an air line so that they could pump in more water. This happened over and over. in addition, because the core got SO HOT (because of the lack of water) the steam had reached a temperature where it split into Hydrogen and Oxygen. When that mixture came into the outer building around the containment, it triggered a BIG explosion of the H2 combing with the O and making water again. The buildings around the containments were blown to bits. Of course, that made working on the reactors that much harder, and sensor lines, control lines and water lines were damaged when the building blew up.
So far tho, it seemed that the situation was such that over the course of this week it would be brought under control. Pump more seawater into the cores, vent steam, pump more water, eventually things cool off.
This is where we were as of Monday night in the central US.
Then, something very odd happened. There was a hydrogen explosion in the building for reactor 4. That was odd because reactor four was SHUT DOWN. There wasn't any fuel in it. The thinking of everyone who thought at all about it was that reactor 4 was utterly safe. All the fuel had been removed. Why would we worry?
What happened? We have to guess. The guys inside the have been WAY to busy to talk to the media, and there's no remote sensing, and I suspect that no one really knows.
I'm going to try to separate my speculation from what we actually know.
We know that the spent fuel pool in the reactor 4 building had a LOT more fuel in it than normal. Reactor 4 had recently been de-fueled, and the rods in it are very hot, they just came out of the reactor.
Spent fuel pools lose water all on their own. The hot rods heat the water and it evaporates or, eventually boils off. Usually, that's not a big deal because the pools are filled to twelve to fifteen feet ABOVE the tops of the fuel rods. Boiling off twelve feet of water takes a LONG time.
But.... (speculation) it's certainly possible that some of the water spilled out in the earthquake. It's possible that during the earthquake the racks that hold the 14 foot long fuel rods cracked and shifted so that some rods came very close together, allowing the water between them to superheat and produce H2 and O2
However it happened, while everyone was paying attention to getting water into the 1,2, and3 reactors which had fuel in them, the spent-fuel pool at reactor 4 either boiled dry, or came close to boiling dry.
Now, this is a BIG pool. Several swimming pools. Filling it with a fire hose would be an hours long project even if it wasn't filled with nearly red-hot rods which flash the water to steam as soon as it hits them. You need big pipes, big powerful pumps and lots of electricity (which you don't have) and this is at the top of a building that has now been blown up, so you can't run new hoses and pipes up there.
Tepco is frantically running a power line into the plant from the nearest working electric supply, 50 miles away. They're patching and stitching existing hunks of line and new line and whatever, and hope to have electricity to the plant by tonight (wed the 16th us time) or some time tomorrow. If so, that will help a lot as they can use their big pumps, assuming those pumps are in working condition.
So, best-case worst-case.
Best case: Tepco gets an electric supply to the plant, there are enough working pumps to cool things, and they pump _a lot_ of seawater into reactors 1, 2, and 3 and into the cooling pools for those reactors and they pump a WHOLE LOT of seawater into the pool on top of reactor 4 and those rods get cooled off.
Then, over the course of the next couple of months things cool down, and a team can be assembled and the painful slow process of de-commisioning the reactors and getting all the fuel rods out and into safe storage can proceed. A decade or so from now you'll have a brownfield site where there used to be a nuclear power plant at a cost probably of close to a trillion dollars.
Worst case: for whatever reason, Tepco is unable to get enough water into the pool at reactor 4. Perhaps the pool is cracked. Perhaps the lines are broken. Whatever, but that pool goes dry and stays dry for a long time. What happens then? Somewhere between 2200 degrees and 3000 degrees the zirconium-tin alloys over the uranium oxide fuel pellets melt. This is "bad." somewhere under 3000 degrees the zirconium, while not exactly boiling, starts to evaporate at high speeds. Zirconium metal is VERY willing to combine with oxygen, so it burns, adding more heat to the situation.
Needless to say, a pool of liquid metal at over 2000 degrees sitting in a concrete box is not going to stay there forever. Concrete is held together with cement that solidifies as it combines with water. Cook it, the water comes out and the concrete falls apart. Now, you have a stream of liquid radioactive metals burning as it falls through the air. Another explosion happens this time, but this time it scatters the Uranium oxide fuel pellets around the countryside, releases large amounts of Cesium and Iodine into the air, and contaminates the coast of japan for a long long time. That's a chernobyl level event. Ooops.
But wait, there's more. Now, you have no way to keep a team pumping water into reactors 1, 2, and 3, and over the next few days/weeks They over heat, blow up and contaminate the world too. The only good difference is, there are no giant blocks of graphite to burn carrying the radiation even further.
That's the worst case. An above-chernobyl level incident that makes a huge piece of Japan's northern coast uninhabitable for a long time.
No one saw that coming, because no one thought there was any CHANCE that the reactor 4 pool could boil dry this fast. Something's odd with that. Perhaps the earthquake made a crack. Perhaps the Tepco folks put WAY too much fuel in the one cooling pond. We won't know for a long time. Eventually, someone will fall on their swords over this, but not tonight. Tonight, lets pray for the brave sons of Martha who are in that plant trying to save what they can.