UPDATE HERE: March 24, BBC: Neutrons are emitted during a “nuclear chain reaction” — March 20, Kyodo: “Nuclear chain reaction” feared at spent fuel pool

Smoke disrupts nuke plant restoration work, radiation fears reach Tokyo, Kyodo, March 24, 2011 at 1:03 pm EDT:

… TEPCO said, meanwhile, it had observed neutron beams, a kind of radioactive ray, 13 times on the premises of the Fukushima plant over the three days from March 13, but they were not at a dangerous level.

The detection of the beams suggests the possibility that uranium and plutonium have leaked from rods in the plant’s reactors or spent nuclear fuel pools and have undergone nuclear fission. …

Read the report here.