Abstract: Improved closed-loop pyrochemical processes for the decomposition of water in which at least one reaction step in each process has a high energy requirement that may be expressed in standard Gibbs free energy change terms of more than 10 to 20 kcal/mole at 298.degree. K., .DELTA.G.sup.o.sub.f298. Such high energy steps are carried out in the central reaction chamber of a thermonuclear reactor wherein the energy of intense shock waves, hereinafter called the blast waves, caused by a pellet-by-pellet intermittent thermonuclear reaction provides an automatic drive for the process step kinetics. During the radial outward propagation of the blast wave reaction materials within the chamber are heated and compressed within the blast wave and entrained behind the blast wave. The product density immediately behind the blast wave remains directly proportional to the ambient density ahead of the wave.