Further Experimental Verification of Warm Prestressing Effect Under Pressurized Thermal Shock (PTS)

Fracture tests for the verification of WPS (warm prestressing) effect were carried out by using large flat specimens with very low toughness. Tensile and bending loads and thermal shock were applied simultaneously to the specimens with the realistically postulated flaw and the two times larger one in order to make the maximum K{sub I} cross the lower bound of K{sub IC} data. During the tests, loading was controlled to simulate the shape of K{sub I} versus temperature curve for the postulated PTS transient. Both the specimens did not break within the scatter band of K{sub IC} when K{sub I} was decreased during cooling. K{sub I} values at fracture by reloading were beyond the upper bound of K{sub IC}. That is, the effectiveness of WPS was directly demonstrated for the PTS transients. Also, K{sup I} values at fracture can be predicted by Chell`s theory. As the test results, Japanese PWRs have sufficient temperature margin against PTS.