Containment of fast breeder reactors — Present status—Remaining problems

Abstract

This presentation of fast reactor containment analysis is limited to sodium-cooled fast breeder reactors. The excursion phenomenon that may need containment in a hypothetical accident could initiate at the core for variety of reasons and usually, but not always, propagates inside the primary system, first as a shock wave, second as a sodium momentum, and third as an expanding gas bubble. Primary containment pertains to the absorption and dissipation of explosive effects in the primary system. The primary containment analyses and codes already developed and currently under development at Argonne National Laboratory combine the equations of hydrodynamics with the equations of state. They start with an energy input in the core in the form of temperatures, pressures and internal energy. This is the neutronic input leading to core disassembly. This energy is propagated through the primary system and components (blankets, reflector, grid, reactor vessel, plug, etc.) in a manner so as to provide a constant inventory of the position and deformation of these components at any one time after the start of the excursion. More specifically, the codes' output is in the form of displacements (strains), pressures, velocities, accelerations, densities, and internal energies. Recently work has started to include in the energy input, the continuing effects of fuel-coolant interactions. The subject analyses and computer codes are two-dimensional. The next development step will attempt to modify these codes to provide engineering solutions for three-dimensional (asymmetric) cases. The treatment of the primary system response terminates with the possible dislocation of the reactor plug. The subject codes ultimately will provide, along with plug displacement, an inventory of sodium spillage into the secondary containment. Secondary containment pertains to the confinement of radioactive gases and aerosols which may have escaped the primary reactor system. Secondary containment must be capable of retaining its gas tightness under the pressures and temperatures resulting from sodium spillage fires.