NASA-Lewis in-pile high temperature reactor meltdown containment experiment

Abstract

The purpose of the in‐pile meltdown experiment was to demonstrate the feasibility of a proposed concept for preventing melt‐through of the containment vessel during and after the meltdown of a nuclear reactor. The concept was modeled and tested in the NASA Plum Brook Reactor Facility using fission heating to simulate fission product heating. In the concept a 38 mm (1.5 in) thick depleted UO2 pellet liner was placed on the inner surface of the stainless steel containment vessel. The high density, high melting point, and poor thermal conductivity of the UO2 pellet liner prevents molten materials from reaching the containment vessel walls. In turn, this results in a substantial increase in temperature of the molten pool. The high pool temperature causes the heat generating fission products to more quickly vaporize and condense throughout cooler regions within the containment volume. (At its melting point UO2 vaporizes at the rate of about 0.14 mm/s (0.006 in/s). Most fission products and their compounds vaporize even more rapidly.) The net effect is to reduce by orders of magnitude the heat flux through the containment vessel wall. A detailed physical description of the meltdown and containment process as derived from interpretation of the experimental measurements is presented. After meltdown, temperatures of the Mo‐UO2 core exceeded 3393 K (5647 °F), which surpassed the melting point of UO2 by 503 K (905 °F) and Mo by 313 K (563 °F). Temperatures at the midpoint of the depleted UO2 liner never exceeded 1300 K (1934 °F). No molten material penetrated as much as halfway through the UO2 barrier. The peak surface temperature of the stainless steel containment vessel never exceeded 928 K (1210 °F).