Evidence Of Recriticality?

Radiation levels are rising in waste water samples taken from reactors #1 and #2 at Fukushima I.

TEPCO collected wastewater samples from the No.1 and No.2 reactors on Wednesday, and found that radioactivity levels had increased dramatically during the past week.

According to TEPCO, 400 becquerels of iodine-131 and 53 becquerels of cesium-134 per cubic centimeter were detected in the wastewater of the No.1 reactor. These levels are 6 times and 38 times higher than a week ago respectively. In the No.2 reactor, 610 becquerels of iodine-131 and 7.9 becquerels of cesium-134 per cubic centimeter were detected. These levels are 17 times and 8 times higher than a week ago respectively.

I see two main possibilities. Either they have cut water injection by at least a factor of 6 (actually 12 which I will explain in a bit) or those two reactors are sporadically critical.

The half life of Iodine 131 is 8 days. So if the water injection is constant you would expect to see 1/2 as much in the water after a week (not exactly but close enough). So the number reported is not just an increase of six times over the previous week but a factor of twelve over the expected number.

Of course this is an accident and there are a LOT of variables to consider - like maybe salt encrustations dissolved making more radioactives available to be dissolved in the water. Or maybe an earth temblor reconfigured the junk. Or maybe the junk has gone sporadically critical.

If they were giving out neutron measurements or Iodine 134 measurements or measurements of some other short lived fission fragment we would know a lot more. They are awfully sparse on details that would allow a definitive determination of what is going on. At this point I think the lack of critical (heh) details is intentional.