Yesterday I was conducting some research and came across this article published April 1, 2011 in Science: "Pool at Stricken Reactor #4 Holds Answers to Key Safety Questions" by Eli Kintisch
The article examines the dangers of zirconium fires:
[Excerpted] Lab experiments have shown that zirconium can burn either with steam or with oxygen. both reactions progress rapidly at roughly 800C; the former, crucially, releases hydrogen. The hydrogen explosion at reactor #4 points to the steam reaction, which releases less energy and therefore melts the fuel more slowly.... [end excerpt]
Majia here: This explanation makes sense and would explain why the spent fuel pool at unit 4 has seemingly "burned" more than once, at least, as evidenced by my observations of the Tepco webcam over the last year and a half (plus).
Webcam waters have seen strange lights on the top of unit 4 recently. The lights are red and blue and they are ephemeral. I was able to capture in a screen shot the red blur of light this morning. There is a red and blue halo over the orange protrusion from building4:
Perhaps the spent fuel rods in unit 4 - now covered by a steel plate - are periodically "steaming" and emitting radiation.
Perhaps the fuel is impossible to cool adequately when damaged and compressed. Arnie Gundersen has repeatedly emphasized that fuel rods are damaged at Daiichi, as illustrated here
That would mean the entire inventory at unit 4 could slowly steam away, over years. A slow, relentless assault against the DNA of all downwinders could be our fate.
The article notes that US spent nuclear fuel pools are more densely packed than those at Daiichi.
The article explains that the nuclear industry "balked at a 2008 recommendation by Jaczko - speaking in an onofficial capacity - to transfer US fuel older than 5 years to dry concrete casks...."
Majia here: Please explain why we allow a industry to "balk" at a basic safety provision that could prevent thousands if not more fatalities were a disaster to strike a US nuclear power plant in the event of flooding, fires, power outages, and other natural disasters.