RESULTS OF EXAMINATIONS OF PRESSURE-VESSEL SAMPLES AND INSTRUMENT NOZZLES FROM THE TMI-2 LOWER HEAD

15 prism-shaped steel samples were removed from the lower head of the damaged Three Mile Island Unit 2 (TMI-2) nuclear reactor pressure vess el to assess the effects of approximately 19 tonne of molten core debr is that had relocated there during the 1979 loss-of-coolant accident. Metallographic examinations of the samples revealed that inside-surfac e temperatures of 800-1100 degrees C were attained during the accident , in an elliptical 'hot spot' with dimensions of about 1 m x 0.8 m. Te nsile, creep and Charpy V-notch specimens were cut from the samples to assess the mechanical properties of the lower head material at temper atures up to the peak accident temperature. These properties were used in a margin-to-failure analysis of the lower head. Examinations of in strument nozzles removed from the lower head region assisted in defini ng the relocation scenario of the molten core debris and showed that t he lower head was largely protected from catastrophic failure by a sol idified layer below the molten core debris that acted as a partial the rmal insulator. (C) 1997 Elsevier Science S.A.