Interactions Between Molten Sodium and Standard Pipe Insulation

Abstract

Safety system design and implementation are critical to the operation of any nuclear plant. For sodium-cooled nuclear reactors, hazards external to the reactor core are present in the form of molten sodium that leaks through degraded piping structures. These structures are often clad in high-temperature insulation to preserve the heat needed to keep the sodium molten in the piping. While large sodium leaks are quite noticeable and often result in hazardous fire situations, small leaks of molten sodium are often masked by the shroud of insulation until a large pool of material has collected outside of the failed pipe. This study concentrated on the physical and chemical interactions between molten sodium and standard fiberglass insulation in temperatures ranging from 100 °C to 500 °C. The degradation of the insulation material begins with the volatilization of the organic binder around 250 °C, thereafter the insulation deteriorates at an advanced rate in areas that are in direct contact with the sodium. Chemical profile data were collected for a variety of sample locations that were in contact with the molten sodium, with only a slight increase in the amount of sodium present that can be attributed to the external sodium source. In this way, the molten sodium chemically reacts with the insulation, which accelerates the degradation of the insulation in locations where the sodium is in direct contact with the insulation. These reactions are enhanced by the temperature of the sodium.