Evaluation of Commercial Production A533-B Steel Plates and Weld Deposits with Extra-Low Copper Content for Radiation Resistance

Abstract

A cooperative research program by the U.S. Nuclear Regulatory Commission (NRC), Combustion Engineering, Inc., (CE), and the Naval Research Laboratory (NRL) has explored trends in radiation effects for commercially produced ASTM A533-B steel plates, weld deposits, and weld heat-affected zones, depicting three levels of control over impurity copper content. The primary objective was to establish the trend of improved 288°C (550°F) radiation resistance with progressive reductions in allowable copper content. An overall objective was to develop information assisting the formulation of special specifications for steels for nuclear service and the delineation of associated embrittlement trends for reactor vessel design and operation. This report describes investigations on Series 3 materials, which represent optimum steelmaking practice, and a limitation on copper content of 0.06 percent copper maximum. Radiation resistance was assessed from Charpy-V (Cv) notch ductility changes with fluences of ∼5 to 7 × 1019 neutrons (n)/cm2 > 1 MeV. All Series 3 materials exhibited high resistance to radiation in terms of both transition temperature elevation and upper-shelf degradation. Typically, the postirradiation C v 41 J (30 ft-lb) transition temperature elevation was less than 56°C (100°F). An independent effect of nickel content on radiation resistance was not observed for weld metal containing a high nickel content (≈ 1 percent nickel) and an extra-low copper content (0.05 percent copper). Comparisons of Series 3 and Series 2 data trends revealed that the specification of an extra-low copper content (0.06 percent copper maximum) as opposed to a low copper content (0.10 percent copper maximum) does not provide a substantial increase in radiation resistance for A533-B materials for the fluence range investigated. Accordingly, the study has confirmed that new ASTM and American Welding Society (AWS) supplemental specifications on copper content for nuclear service are sufficiently restrictive to optimize 288°C (550°F) radiation resistance of A533 plates and weld deposits for most projected vessel fluence conditions.

Notch Ductility Degradation of Low Alloy Steels with Low-to-Intermediate Neutron Fluence Exposures.

“…The source of the scatter has not been established but may be due partially to the lack of a term for nickel content in the projection formula. That is, data are available which indicate that nickel content can cause a reenforcement of the primary copper content effect on radiation sensitivity [12,13] To summarize, the new data suggest that current penalties at low fluence could be reduced provided that reasons for inconsistencies in surveillance data become understood . The possibility for a reduced penalty appears to be greatest for upper shelf energy properties.…”