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

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

“…Therefore a hoop strain of 6% and ramp time of 20 minutes were selected as bounding (0.06/20 = 3x10 -3 min-l). Note that this strain rate is 2 orders of magnitude below the upper end of the I.,ME susceptibility range, 0.6 rain -1 (Thomas et al 1992), and is just below the strain rate range employed in standard tensile tests, 5x10 "3to 5xi0 -2 min "l (ASTM Standards E21-79 and E8-88). Fast strain rate tests were conducted over a range of temperatures from 325 to 600°C.…”

“…As part of the failure evaluation, the potential for liquid metal embrittlement ([,ME) of the safety rod cladding by cadmium (Cd) -aluminum (Al) solutions was examined. (Thomas et al 1992) indicated that this system would not be susceptible to LME under these conditions.…”

“…The examination of failed specimens and failure evaluation are discussed in Thomas et al (1992). As part of the failure evaluation, the potential for liquid metal embrittlement ([,ME) of the safety rod cladding by cadmium (Cd) -aluminum (Al) solutions was examined.…”

“…The "fast" strain rate (3x10 -3 min -l) bounds 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 (Thomas et al 1992). The calculations performed to date for the gamma heating accident indicate that at least 30 minutes is required to reach peak safety rod temperatures less than 600°C (Cooper and Taylor 1991).…”

“…The calculations performed to date for the gamma heating accident indicate that at least 30 minutes is required to reach peak safety rod temperatures less than 600°C (Cooper and Taylor 1991). The highest measured hoop strain for specimens tested at or below 600°C was 5.5% (Thomas et al 1992). Therefore a hoop strain of 6% and ramp time of 20 minutes were selected as bounding (0.06/20 = 3x10 -3 min-l).…”