Chain Explosion

Figure 2.1 The lower and upper limits of an explosive chain reaction as a function of temperature and pressure.

Chain Explosions and Chain Reactions. See Vol 2, p C146-L and in this section under Detonation (and Explosion), Chain Reactions... 

Detonation (and Explosion) by Priming and Boostering. These are means of building up a detonation from an initiating shock (Ref 2, p 294). The detonator, the first element in an explosive train or "explosive chain , may have three parts. 

It is remarkable that in the neighbourhood just to the right of G we have a state of affairs where the rate of reaction decreases with decreasing pressure, and yet if the pressure be reduced a point will be reached at which the mixture explodes this illustrates the difference between the explosive chain and the thermal explosion, which at some high enough pressure terminates the curve CD. 

The limit at C is almost independent of the surface of the vessel thus in accordance with the considerations of the earlier section on critical limits, it represents the point at which some deactivation process in the gas phase becomes marked enough to prevent branching chains from developing explosively. It is suggested that the deactivation process in question is the mutual destruction of H202 molecules, which between B and C are the centres from which explosive chains develop, e. g. 

The ideas from the dissertation were then further developed in a paper with Kramers whose intimate knowledge of the theories of Bohr concerning atomic structure contributed essentially to the correct representation of the theory. In this paper inter alia the possible occurrence of explosive chain reactions, i.e., chain reactions in which no steady state concentrations of the intermediates is obtainable, was mentioned. The surprising results by Moureau and Dufraisse (17) concerning antioxidants were explained as being due to autoxidation proceeding as a chain reaction, the chains being broken by the antioxidant. 

Safe separation studies were conducted to achieve increased production and cost effectiveness with improved safety. A typical ammunition production line flow diagram (in this case for the manufacture of 105 mm projectile) consists of several work areas as shown in Fig 8. ( (l) Receiving and storage, (2) Box open and inspect (3) Melt Pour (U) Cool (5) Hold (6) Funnel Pull and (T) Riser Preparation.) Explosive material is transferred by automatic conveyor between these work areas. The requirement was to establish safe separation between explosive boxes, pallets with and without funnels, buckets, and to determine critical height of continuous feed flake Comp B and TNT. The objective of these tests was to establish minimum nonpropagation distances between these items so that an explosion chain reaction will be prevented. 

In the case of the reaction between hydrogen and oxygen, the first gaseous reaction to be studied88 where stable and measurable chains occurred, the mechanism has been found to be influenced markedly by pressure. Thus, within certain limits explosive chains are set up from active centers of hydrogen peroxide ... 

Arts. Neutron-induced fission reactions of the heavy elements have as their products two or more neutrons of high energy. This multiplies the eifect of the initiating neutron, and can lead to an explosive chain reaction. 

Not long from Nazi Germany, Frisch found his argument against a violently explosive chain reaction reassuring. It was backed by the work of no less a theoretician than Niels Bohr. With satisfaction he published it. 

Sometime in February 1940 he looked again. There had always been four possible mechanisms for an explosive chain reaction in uranium ... 

If Frisch now glimpsed an opening into those depths he did so because he had looked carefully at isotope separation and had decided it could be accomplished even with so fugitive an isotope as U235. He was therefore prepared to consider the behavior of the pure substance unalloyed with U238, as Bohr, Fermi and even Szilard had not yet been. I wondered— assuming that my Clusius separation tube worked well—if one could use a number of such tubes to produce enough uranium-235 to make a truly explosive chain reaction possible, not dependent on slow neutrons. How much of the isotope would be needed ... 

These experiments gave direct evidence of an explosive chain reaction. They gave an energy production of up to twenty million watts, with a temperature rise in the hydride up to 2 C per millisecond. The strongest burst obtained produced 10 neutrons. The dragon is of historical importance. It was the first controlled nuclear reaction which was supercritical with prompt neutrons alone. 

The disadvantage of the BDD is that it only represents the structural elements of the system, here the interrupted explosive chain and not the connections between them. To overcome that challenge one has to model the connections between the blocks in a different kind of diagram. The internal block diagram (see Figure 4) can be used for this task. 

---