Peer review of the Three Mile Island Unit 2 Vessel Investigation Project metallurgical examinations

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Fifteen samples recovered from the lower head of the Three Mile Island (TMI) Unit 2 nuclear reactor pressure vessel were subjected to detailed metallurgical examinations by the Idaho National Engineering Laboratory (INEL), with supporting work carried out by Argonne National Laboratory (ANL) and several of the European participants. These examinations determined that a portion of the lower head, a so-called elliptical ``hot spot`` measuring {approx}0.8 {times} 1 m, reached temperatures as high as 1100{degrees}C during the accident and cooled from these temperatures at {approx}10--100{degrees}C/min. The remainder of the lower head was found to have remained below the ferrite-toaustenite transformation temperature of 727{degrees}C during the accident. Because of the significance of these results and their importance to the overall analysis of the TMI accident, a panel of three outside peer reviewers, Dr. Robert W. Bohl, Mr. Richard G. Gaydos, and Mr. George F. Vander Voort, was formed to conduct an independent review of the metallurgical analyses. After a thorough review of the previous analyses and examination of photo-micrographs and actual lower head specimens, the panel determined that the conclusions resulting from the INEL study were fundamentally correct. In particular, the panel reaffirmed that four lower head samples attained temperatures as highmore » as 1100{degrees}C, and perhaps as high as 1150--1200{degrees}C in one case, during the accident. They concluded that these samples subsequently cooled at a rate of {approx}50--125{degrees}C/min in the temperature range of 600--400{degrees}C, in good agreement with the original analysis. The reviewers also agreed that the remainder of the lower head samples had not exceeded the ferrite-to-austenite transformation temperature during the accident and suggested several refinements and alternative procedures that could have been employed in the original analysis.« less