No abstract

Fracture mechanics evaluations were performed for three w~lds in the LOFT blowdown,system and one weld in the LOFT primary coolant system. Beca~se the applied stress is not known, a sensitivity analysis was run. The a~sumed initial defect size was one tha~ had a small probability of being missed; applied stresses of 68.9,•, i37.8, 206.7, and 344.8 MPa were used. It was found that at the lowest stress (68.9 MPa or 10 ksi} the. number of cycles from the initial size to: rupture was over 6 x 10 6 . The current calculations indicate that with the worst crack configura~ibn--depth-to-length ratio (a/ 2 } of O.io--about c .1000 cycles with a peak stress of 227.5 MPa (33 ksi} wjll be needed to. propagate the 0.5 x 5.1 em (0.2 x 2.0 in.) crack to failure.

But, it only required a single cycle 'to grow the through-the-thickness defect to a length (19.3 em or 7.59 in.) required to cause catastrophic failure. The circumferentially oriertted defect of crack depth (a) = 1.3 em (0.50 in.) would result in failure occurring before the defect penetrated the wall thickness, although, it would require 334 cycles to grow the potential defect (a= 1.3 em or 0.50 in.) to a critical size (14.1 em or 5.57 in. long).

No abstract