Tensile and burst tests in support of the cadmium safety rod failure evaluation

Examination of cadmium safety rod thermal test specimens and failure mechanism evaluation

“…was 5.5%, Therefore a hoop strain of 6% and ramp time of 20 minutes were selected as bounding (0,06/20 = 3x10 -3 rain'1), Note that this strain rate is 2 orders of magnitude below the upper end of the LME susceptibility range (10 "2see"_= 0.6 min'l), and is just below the strain rate range employed in standard tensile tests (5x10 "3to 5x10 "2min'l). The "slow" strain rate (8x10 "5min "1)is intended to bound the lowest strain rate in the safety rod No reduction in ductility was observed for the tensile tests in Cd-Al liquid metal solution relative to the tests in air (Thomas 1992). Therefore, the results of the tensile tests are in J agreement with the conclusion reached above that neither CA nor Cd-Al mixtures embrittle SS304 under the conditions relevant to this evaluation.…”

“…Since failure strain is employed, the evaluation is independent of both the magnitude of the loads placed on the cladding and the loading mechanisms, The conclusions reached are therefore valid even if large amounts of water were present inside the safety rod prior to the tests, large amounts of hydrogen were generated during the tests, or if other loading mechanisms not discussed above were operative, In the absence of any cladding flaws or environmental degradation (e.g. interaction between the cladding and liquid metal solution), the cladding will fail when its hoop strain exceeds the failure strain (e.g, ductility exhaustion), conducted as part of this task (Thomas 1992) gave similar values (see Section 6,4.6).…”

“…In order to verify the high-temperatare multiaxial ductility of the safety rod cladding and demonstrate the nature of an overpressure failure with this material, a set of pressurized tube burst tests were conducted using safety rod cladding samples (Thomas 1992). These tests, conducted at the Westinghouse Science and Technology Center, were considered scoping in nature and were not carded out under an NRTSC technical procedure.…”

“…An immersion time of 1 hour was employed. The test conditions and results are summarized in Table 6-2 (Thomas 1992), The "fast" strain rate (3x10 3 min "1) is intended to bound the highest strain rate expected for the temperature ramp rates predicted for the gamma heating accident. Susceptibility to LME generally increases with increasing strain rate, as discussed in Section 6.4,2.…”