Pressure Wave Generated in a Fissionable Gas by Neutron Irradiation

An experiment is proposed to study the nonsteady gasdynamic phenomena produced by neutron induced exothermic nuclear reactions in a gaseous medium. The problem is formulated in terms of a set of characteristic equations in a time dependent, spatially unidimensional system and solved by means of a simplified analysis leading to a system of two first order, nonlinear, ordinary differential equations that permit the attainment of a clearer understanding of the salient features of the problem than can be obtained from a more rigorous solution. The problem involves the generation of a pressure wave in a long tube filled with a boron trifluoride, fully enriched in the boron-10 isotope which undergoes the reaction: 10B(n, α) 7Li as a result of a 1000 MW neutron pulse of approximately 10 msec halfwidth directed along part of its length by irradiation from a TRIGA reactor. The analysis predicts that the gas residing initially in the core will be heated to approximately 3000°K and that a compression wave with a peak pressure ratio of approximately 3 will emanate from the reactor and coalesce into a shock of Mach number 1.8 at a distance of approximately 17 ft from the reactor core. Measurement of the pressure wave should provide information on the amount of reversible heating that can be obtained from a gaseous nuclear reaction. It should be considered therefore of particular value in gaining specific familiarity with fissionable gasdynamics.