Results and conclusions from the first pressurized-thermal-shock experiment. [Overcooling]

Pretest estimates of fracture toughness are reasonably close to the PTSE-1 values. Furthermore, the ASME Sect. XI toughness relationships are conservative relative to actual material characteristics. The experiment demonstrated that arrest toughness substantially above the 220 MPa...sqrt..m cutoff of Sect. XI could be realized. The arrest values in PTSE-1 also are consistent with arrest measurements made in wide-plate tests and reported by the Japan Welding Council. The highest PTSE-1 value of arrest occurred at a temperature approx. 30 K above the onset of the Charpy upper shelf. This is believed to be very close to the threshold temperature above which cleavage fracture cannot persist. This result also suggests that the methods of linear elastic fracture mechanics have an important role in fracture evaluation at high (upper-shelf) temperatures. The PTSE-1A and -1B transients were a demonstration that simple warm prestressing (K/sub I/ 0) prevailed during two periods of 40-s and 60-s duration without crack initiation, although K/sub I/ exceeded K/sub Ic/ by 30% to 50%. Clearly simple anti-warm prestressing is not a sufficient condition to alleviate the effects of warm prestressing. A narrow band of ductile tearing formed ahead of the initial cleavage fracture. The conclusions drawn from PTSE-1 suggest that procedures used for evaluating overcooling accidents in pressurized-water reactors should take into consideration realistically the fracture mechanisms that have been clearly demonstrated but not yet generally accepted.« less