The world is well aware that on March 11, 2011, Japan was shaken to its foundations by an earthquake of 9.0 magnitude. Following the earthquake, a tsunami battered the island. The loss of life has been beyond comprehension. Japan is home to several nuclear power generating plants; these plants were so damaged by the quake as to be irreparable. Even today workers are laboring to prevent further damage to the island and beyond, that may be caused by deadly radiation pouring from the ruins of the nuclear plants. The efforts to contain the hazardous clouds of smoke and gasses are hampered by radiation already omnipresent. The workers may be forced to give up the effort, because of the threat to their lives. Now, another concern has arisen.
Scientists tell us that in dealing with radioactive material, of the kind now bringing alarm to the population of Japan and to the world, at the nuclear power plant at Fukushima, Daiichi, there is a potential for a nuclear explosion which could engender far more impact than the radioactivity-escape dilemma already being encountered.
Nuclear rods, much discussed in recent days, are not solid rods at all. They are rather containers in the shape of long slender closed-end poles in the reactor, or in the spent rod holding area, for small pellets of fissionable material. Potentially these pellets could melt, if not contained by cooling water, and there is a possibility that the melted pellets could congeal into a single mass. Scientists tell us that such a mass, if it reaches or exceeds certain proportions may explode. Such an explosion would not be a mushroom cloud, nuclear bomb explosion of the type we have seen in tests, but rather would be similar to the detonation of a “dirty bomb.”
There are several million pounds of fissionable material at the Fukushima Daiichi nuclear plant. In some instances, thirty three pounds of uranium can produce a “critical mass”. Dirty bombs differ from more modern weapons in that they are often mixed with conventional explosives, which aid in spreading a radioactive cloud over a large area.
The nuclear weapons of the 1950s were inefficient. Of the destructive potential, only about 2% to 14% was in fact released. A dirty bomb is close in power to an ordinary explosive. The fear of contamination can cause widespread panic and terror. One difference between a weapon explosion and an accidental one rests in the fact that in bombs, reflectors are used to focus the fission toward the center of the fissionable material, achieving a much more disastrous blast.
There are three categories of mass involved in speaking of nuclear explosion; critical, sub-critical, and super-critical. In a critical, or super-critical mass explosion, there will be a steady chain reaction of neutrons flying about, rupturing, or splitting atoms, thus releasing more free neutrons. Collisions are called fissions. Each fission usually produces one more fission. Critical mass means that there is enough fissionable material involved to produce and sustain a chain reaction, which grows exponentially within a miniscule passage of time. This chain reaction is precisely what happens in nuclear weapons.
While first readings from American data-collection flights over the stricken Fukushima Daiichi nuclear plant show that the worst contamination has not spread beyond the 19-mile range, in the perhaps unlikely event of a critical mass explosion, that range, and the resultant danger could be far greater.