Today, the focus is on the Fukushima I Nuclear Power Plant, a complex with six BWR (boiling water reactor) reactors. Just minutes ago, BBC was reporting that the cooling for reactor #3 has completely failed.
I’ve been very confused by what’s happening at the plant over the last 36 hours. The confusion is because I did not understand some of the nuances in reactor design.
I knew from previous reports and from general knowledge that the reactors would have been SCRAMed immediately during the earthquake. That would lower the control rods into the reactor core, thus stopping the chain reaction. The rods control the amount of neutrons that are moving around the core. The rods are there to prevent the self-sustaining nuclear chain reaction, and thus lower the amount of power and heat generated.
So the problems at the plant were confusing. If the rods had been lowered, why was cooling still a problem?
Searching the web and wikipedia, I discovered that even if the reactor is shutdown (“subcritical”), there is still residual heat in the core that must be cooled. This is the cause of the problems in Fukushima. Although the chain reaction has stopped, there is still some spontaneous fission occurring, plus the heat that was in the core at the time of the SCRAM.
Something else bothers me about the first day of the crisis. On Friday, Secretary of State Hillary Clinton stated that “We just had our Air Force assets in Japan transport some really important coolant to one of the nuclear reactors.” She used the past-tense instead of future tense, meaning that it had already been done. The Reuters report about her statement was posted only 10h 19m after the quake; the White House web page does not have a timestamp. A video of her remarks is here: http://www.state.gov/video/?videoid=822710919001.
So far, I have not seen anyone in the press ask further questions about this. I have lots of questions.
1. What coolant was sent? Japan uses light water, which is basically normal water. It is different from heavy water used in other reactors; heavy water is where all of the hydrogen in the water molecules have an extra neutron to form deuterium. Is that what was sent?
2. Where did this coolant come from? Was it just sitting around on hand? Next to an air base?
3. How was it transported? In thousands of Evian bottles? What sort of container or containers? How much was delivered to the nuclear plant(s)?
4. How did the Air Force deliver the coolant? Was it a plane or a helicopter? The Secretary specifically said “so Air Force planes were able to deliver that”. If it was delivered by plane, then where did the planes land? Are there airstrips next to the nuclear plants? If the plants were hit by the tsunami, then any airstrip nearby would have also been hit and most likely useable. It is possible that it was a CV-22B Osprey, which can land vertically, but the Air Force only has 12 of them, none of them in Japan as far as I can tell. The Air Force also has two types of helicopters in inventory – the UH-1N Huey/Iroquois and the HH-60 Pave Hawk search and rescue helicopters. The HH-60 can sling about 8,000 pounds, and the UH-1 can sling about 5,000 pounds. That doesn’t seem like a lot of coolant capacity per helicopter, if that was actually the delivery mechanism. Another possibility is that Clinton said Air Force, but meant Marines, as they do have more inventory of helicopters and Osprey. I suppose to a politician, all planes are Air Force planes.
As I said, what Clinton said just seemed odd, although I cannot specifically tell what are the actual facts. Strangely, the Air Force web site makes no mention of this activity all. I would think that if they were involved in an important mission like trying to save a reactor, it would be all over the Air Force news web page.