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The Radiation Surveillance Program for Combustion Engineering (C-E) Reactor Vessel Materials is designed to provide the operating utility with the capability of determining the radiation-induced changes in the mechanical and fracture toughness properties of the materials in the region of the reactor vessel encompassing the core. The term “materials” is used to collectively describe the metallurgical characteristics of base metal, deposited weld metal, and the heat-affected-zone (HAZ) metal. By conducting such determinations periodically, the neutron-induced changes in the initial reference temperature (RTNDT) can be assessed by direct measurement and the conservatism in the planned adjustments to plant operating parameters to compensate for the RTNDT changes can be verified.

Within the scope of this research, a new short-time procedure designated as StressLifeHCF was developed. Through a combination of classic fatigue testing and non-destructive monitoring of the material response due to cyclic loading, a process-oriented fatigue life determination can be carried out. A total of two load increases and two constant amplitude tests are required for this procedure. By using data from non-destructive measurements, the parameters of the elastic approach according to Basquin and the plastic approach according to Manson–Coffin were determined and combined within the StressLifeHCF calculation. Furthermore, two additional variations of the StressLifeHCF method were developed in order to be able to accurately describe the S-N curve over a wider range. The main focus of this research was 20MnMoNi5-5 steel, which is a ferritic-bainitic steel (1.6310). This steel is widely used for spraylines in German nuclear power plants. In order to validate the findings, tests were also performed on an SAE 1045 steel (1.1191).

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.