For those of you who recognize me from the LAB over its history, you may remember my infrequent discussions of nuclear energy. From those discussions it is generally clear that I am a proponent of nuclear energy, and, with important qualifications, remain so.
The rest of this post is not going to read like something that would be written by a proponent of nuclear power, but I hope it will be a reasonable, if sobering, explanation of what I think should be expected from Japan over the coming weeks. As long as the water keeps flowing, and the fires are put out, they should get out of this with a IAEA Level 6 accident.
1. This situation is extremely serious, but not Chernobyl bad
2. The GE BWR reactor with Mark 1 containment is essentially the worst design in the western world for this circumstance:
3. The GE BWR Mark 1 is inferior because of its suppression design:
4. All three operating reactors likely have experienced melting of the fuel rods, if not the internal uranium oxide:
5. As long as they keep successfully filling the three reactor cores with water, the spent nuclear fuel is a bigger problem moving forward:
6. All operating reactors are somewhat susceptible to what is befalling Japan at the moment:
7. Future reactor systems, with passive cooling, would be much better in this situation, but the industry needs to upgrade the scope of their accident consideration:
8. There needs to be a worldwide uniform "dire emergency" system for cases like this:
I truly hope this doesn't get much worse, but it might. I simply hope that people can read this and understand more deeply what could happen, and some steps to make actionable from it.
The rest of this post is not going to read like something that would be written by a proponent of nuclear power, but I hope it will be a reasonable, if sobering, explanation of what I think should be expected from Japan over the coming weeks. As long as the water keeps flowing, and the fires are put out, they should get out of this with a IAEA Level 6 accident.
1. This situation is extremely serious, but not Chernobyl bad
Chernobyl was a graphite moderated reactor running at beyond full power when the reactor incident occurred. Chernobyl had no containment structure to speak of. Chernobyl had a massive graphite fire that burned for nearly three weeks, all the while chimney-stacking radionuclides into the air. The russians literally dumped thousands of tons of lead, boron, and other ceramics directly into the open core of the reactor in an attempt to reign in the fire. Japan's situation should never progress to the point of that in Chernobyl, but unfortunately that is more a commentary about the severity of Chernobyl than of the situation in Japan
2. The GE BWR reactor with Mark 1 containment is essentially the worst design in the western world for this circumstance:
The reactors Japan installed at this facility are known to be the weakest in the face extreme circumstances of all western designs. Now, the Russian RBMK reactor (Chernobyl design) remains the world's most dangerous operating reactor, and all off them need to be shuttered, but the GE Mark 1 needs to be at the top of the list of Western designs to be decomissioned. By all accounts the Mark 1 is inferior to all other western designs (and the Russian VVER PWR).
3. The GE BWR Mark 1 is inferior because of its suppression design:
The GE BWR Mark 1 has its suppression pool located outside of the primary containment structure. All reactor designs have a "drywell" and a "wetwell." The drywell routes any steam leakage from the reactor vessel into the wetwell. The wetwell is a very large thermal mass of water that condenses the leaking steam into water, and moderates the pressure inside the pressure vessel (keeping the pressure vessel from failing from the inside out. The GE mark 1 has this suppression pool outside of the primary containment, in the secondary containment, which is the section of the building which was damaged by the hydrogen explosions. The explosion damaged structure is now what we depend on to protect the environment from the core leakage. GE BWR Mark 2 and Mark 3 contain the drywell and wetwell inside the primary containment vessel.
4. All three operating reactors likely have experienced melting of the fuel rods, if not the internal uranium oxide:
Nuclear reactors with the control rods inserted still have latent heat up to about 8% of their "at power" thermal energy generating capacity. This is at least several tens of megawatts, and requires thousands of gallons of water per minute to cool effectively. With water not added to the pressure vessel for multiple hours in several cases, fuel cladding melting has almost assuredly occurred in all three reactors. Expect the cleanup of the reactors to take 20 years if the situation does not worsen.
5. As long as they keep successfully filling the three reactor cores with water, the spent nuclear fuel is a bigger problem moving forward:
Nuclear fuel generates residual heat from the decay of the radionuclide reaction products that build up inside the cladding during the "burn up" period of the fuel. These are what generate the residual heat of the shut down core, and need cooled for an extended period of time (3 years to cask storage). If the spent nuclear fuel overheats, it can release the same nuclear materials as the fuel inside reactor, only without the extensive protection of the pressure vessel and reactor containment. This would be far worse for the environment than what might happen inside the reactor containment.
6. All operating reactors are somewhat susceptible to what is befalling Japan at the moment:
All existing reactor systems need active cooling (ie pumps and motors) of the core after a shutdown for a period of several days to weeks. All reactors rely on grid power and/or diesel backups. All diesel generators would get swamped if hit with a tall enough tsunami. Now, many existing operating reactors would behave more gracefully than the GE BWR Mk1 is currently, but everybody would have the same basic problems. I'm surprised the Japanese ever built the GE Mark 1 reactor, it does not strike me as being up to the task for a country in Japan's seismic circumstances.
7. Future reactor systems, with passive cooling, would be much better in this situation, but the industry needs to upgrade the scope of their accident consideration:
The new Westinghouse AP1000 would, for instance, be able to cool its innards for three days using water stored on site, above the reactor, relying only on gravity. This gives you three days to figure out your next move. If this resevoir is refilled, it continues to provide cooling indefinitely. 1000 year events like this quake an tsunami need to be considered in all reactor designs, as do calamities such as a tsunami produced by a meteor hitting earth. Reactors designs that are "passively safe" should be given priority above all else.
8. There needs to be a worldwide uniform "dire emergency" system for cases like this:
High pressure/volume pumps, and power to run them, need stockpiled globally. Uniform connections for these fixtures to all existing reactors need established. Global stockpiles of important repair systems also need to be established. Almost every US reactor is different, so we would probably be one of the biggest complications to such a scheme. I fear most nations are too proud for this sort of thing. I was surprised the Japanese waited so long for international help. If I was in Japan's shoes, I'd want both Russian and American nuclear people on site as soon as possible.
I truly hope this doesn't get much worse, but it might. I simply hope that people can read this and understand more deeply what could happen, and some steps to make actionable from it.
