TY - GEN
T1 - Design stress evaluation based on strain-rate sensitivity analysis for nickel alloys used in the very-high temperature nuclear system
AU - Mo, Kun
AU - Tung, Hsiao Ming
AU - Chen, Xiang
AU - Zhao, Yang
AU - Stubbins, James F.
PY - 2012
Y1 - 2012
N2 - Both Alloy 617 and Alloy 230 have been considered the most promising structural materials for the Very High Temperature Reactor (VHTR). In this study, mechanical properties of both alloys were examined by performing tensile tests at three different strain rates and at temperatures up to 1000°C. This range covers time-dependent (plasticity) to time-independent (creep) deformations. Strain-rate sensitivity analysis for each alloy was conducted in order to approximate the long-term flow stresses. The strain-rate sensitivities for the 0.2% flow stress were found to be temperature independent (m ≈ 0) at temperatures ranging from room temperature to 700°C due to dynamic strain aging. At elevated temperatures (800-1000°C), the strain-rate sensitivity significantly increased (m > 0.1). Compared to Alloy 617, Alloy 230 displayed higher strain-rate sensitivities at high temperatures. This leads to a lower estimated long-term flow stresses. Results of this analysis were used to evaluate current American Society of Mechanical Engineers (ASME) allowable design limits. According to the comparison with the estimated flow stresses, the allowable design stresses in ASME B&PV Code for either alloy did not provide adequate degradation estimation for the possible long-term service life in VHTR. However, rupture stresses for Alloy 617, developed in ASME code case N-47-28, can generally satisfy the safety margin estimated in the study following the strain-rate sensitivity analysis. Nevertheless, additional material development studies might be required, since the design parameters for rupture stresses are constrained such that current VHTR conceptual designs cannot satisfy the limits.
AB - Both Alloy 617 and Alloy 230 have been considered the most promising structural materials for the Very High Temperature Reactor (VHTR). In this study, mechanical properties of both alloys were examined by performing tensile tests at three different strain rates and at temperatures up to 1000°C. This range covers time-dependent (plasticity) to time-independent (creep) deformations. Strain-rate sensitivity analysis for each alloy was conducted in order to approximate the long-term flow stresses. The strain-rate sensitivities for the 0.2% flow stress were found to be temperature independent (m ≈ 0) at temperatures ranging from room temperature to 700°C due to dynamic strain aging. At elevated temperatures (800-1000°C), the strain-rate sensitivity significantly increased (m > 0.1). Compared to Alloy 617, Alloy 230 displayed higher strain-rate sensitivities at high temperatures. This leads to a lower estimated long-term flow stresses. Results of this analysis were used to evaluate current American Society of Mechanical Engineers (ASME) allowable design limits. According to the comparison with the estimated flow stresses, the allowable design stresses in ASME B&PV Code for either alloy did not provide adequate degradation estimation for the possible long-term service life in VHTR. However, rupture stresses for Alloy 617, developed in ASME code case N-47-28, can generally satisfy the safety margin estimated in the study following the strain-rate sensitivity analysis. Nevertheless, additional material development studies might be required, since the design parameters for rupture stresses are constrained such that current VHTR conceptual designs cannot satisfy the limits.
KW - Alloy 230
KW - Alloy 617
KW - Design stress
KW - Strain-rate sensitive
KW - VHTR
UR - http://www.scopus.com/inward/record.url?scp=84870334051&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:84870334051
SN - 9781622763894
T3 - International Conference on the Physics of Reactors 2012, PHYSOR 2012: Advances in Reactor Physics
SP - 4244
EP - 4254
BT - International Conference on the Physics of Reactors 2012, PHYSOR 2012
T2 - International Conference on the Physics of Reactors 2012: Advances in Reactor Physics, PHYSOR 2012
Y2 - 15 April 2012 through 20 April 2012
ER -