Fracture mechanics assessment of cracks in the HDR reactor pressure vessel due to pressurized thermal shock loading

The feeding of cold water into the hot ring chamber of a LWR pressure vessel (RPV) during emergency core cooling is treated in this paper on the basis of a series of tests experimentally and analytically. The extensive works in this context have been performed and are under way at Oak Ridge National Laboratory (ORNL) and at University of Tokyo. The thermal shock cyclic loading test and the long term pressurized thermal shock loading test on HDR-RPVs have been carried out. The testing methods and the results of these tests are summarized. Accompanying the tests, the on-line and off-line measurements, the properties of the base metal and the cladding, the metallography and fractography of cracked material, the finite element stress calculation, the fatigue and crack growth in cyclic thermal loading and the long term thermal shocks on the nozzle and the cylinder wall were examined. A few hairline cracks appeared on the cylinder wall after 5000 cycles, and after 9500 cycles, a pronounced crack field was observed. The distribution of the J-integral as a function of time is shown for the cracks in the nozzle and the cylinder. (K.I.)