RESULTS OF METALLOGRAPHIC EXAMINATIONS AND MECHANICAL TESTS OF PRESSURE-VESSEL SAMPLES FROM THE TMI-2 LOWER HEAD

Fifteen prism-shaped steel samples were removed from the lower head of the damaged Three Mile Island Nuclear Station Unit 2 (TMI-2) reactor pressure vessel to assess the effects of approximately 19 metric tons of molten core debris that had relocated there during the 1979 loss-of -coolant accident. Metallographic examinations of the samples revealed that inside-surface temperatures of 800 to 1100 degrees C were attain ed during the accident in an elliptical ''hot spot'' approximately 1 x 0.8 m. Tensile, creep, and Charpy V-notch specimens were cut from the samples to assess the mechanical properties of the lower-head materia l at temperatures up to the peak accident temperature. These propertie s were used in a margin-to-failure analysis of the lower head.