You know, I think that's a very good question! Somehow, uncontained neutron beams out in the wild don't really sound like a good thing, do they?
I've included the following Kyodo News from the following link at the end of my post:
http://english.kyodonews.jp/news/2011/03/80539.html
From that report it would seem that neutron beams are evidence that uranium or plutonium may have leaked and are fissioning a bit out in the open. If this is the case, since the uranium or plutonium were all originally contained in zirconium-clad fuel rods located either inside of the reactor pressure vessel itself or in external spent-fuel storage pools, then the fuel could only have leaked if the rods' cladding melted either in a storage pool lacking water or they melted in a compromised reactor pressure vessel that allowed the contents of the melted rods to spill into the environment. (BTW, is it even possible for a glob of melted uranium fuel out in the open to fission? And if so, how much would such a glob have to weigh?)
Quote from Kyoto News from March 23:
"Tokyo Electric Power Co. said Wednesday it has observed a neutron beam, a kind of radioactive ray, 13 times on the premises of the Fukushima Daiichi nuclear plant after it was crippled by the massive March 11 quake-tsunami disaster.
TEPCO, the operator of the nuclear plant, said the neutron beam measured about 1.5 kilometers southwest of the plant's No. 1 and 2 reactors over three days from March 13 and is equivalent to 0.01 to 0.02 microsieverts per hour and that this is not a dangerous level.
The utility firm said it will measure uranium and plutonium, which could emit a neutron beam, as well.
In the 1999 criticality accident at a nuclear fuel processing plant run by JCO Co. in Tokaimura, Ibaraki Prefecture, uranium broke apart continually in nuclear fission, causing a massive amount of neutron beams.
In the latest case at the Fukushima Daiichi nuclear plant, such a criticality accident has yet to happen.
But the measured neutron beam may be evidence that uranium and plutonium leaked from the plant's nuclear reactors and spent nuclear fuels have discharged a small amount of neutron beams through nuclear fission."
That was great...!
My understanding of Neutrons is limited but i understand the cause of beam like behaviour.