ASME NTB-4-2021 pdf download

ASME NTB-4-2021 pdf download.Background Information for Addressing Adequacy or Optimization of ASME BPVC Section III, Division 5 Rules for Nonmetallic Core Components.
The general requirements under BPVC subsection HAB complement the technical rules, as subsection HAB details the rules for classifying graphite core components (HAB-2000), the responsibilities and duties during the design and construction process (HAB-3000), the quality assurance aspects (HAB-4000), the Authorized Inspection requirements (HAB-5000), the applicable standards (HAB-7000), and the required certificates and reports (HAB-8000). It also provides a glossary of highlighted terms (HAB-9000). It specifically states the limitations of the rules in HAB-1130 [2]: The rules of this Subpart and Subsection HH, Subpart A provide requirements for new construction and include consideration of mechanical and thermal stresses due to cyclic operation. They include consideration of deterioration that may occur in service as a result of radiation effects and oxidation. At the outset, several materials issues were considered when drafting the code: · Differences between nuclear graphite and traditional ferrous core construction metals · The manufacture of graphite · The effect of the reactor environment on nuclear graphite
ASME NTB-4-2021: BACKGROUND INFORMATION FOR ADDRESSING ADEQUACY OR OPTIMIZATION OF ASME BPVC SEC. III, DIV. 5 RULES FOR NONMETALLIC CORE COMPONENTS 3 One unique aspect of the behavior of graphite is the material’s temperature response. Graphite, unlike other materials, increases in strength with increasing temperature. Tensile strength increases of ~50% are typical, with the strength increasing with temperature until the onset of plasticity at approximately 2000°C. This behavior requires the exclusion of oxidizing gases, such as air, to prevent gasification of the graphite. Several consequences of the manufacture of graphite must be considered in formulating a design code. Although graphite has been in production for over 100 years, there are no standardized graphite grades. Polycrystalline graphite is produced from specifically sized carbonaceous fillers bonded with a carbon-rich binder; this plastic mix is formed into the desired shape and heat treated to carbonize the binder (~1000°C) and heat treated again at ~2500–3000°C to graphitize the material [3]. When this process is coupled to the desire to control the chemical purity, it can be understood why each graphite grade has a unique distribution of pore sizes and shapes. These differences lead to a unique set of properties and a somewhat unique response to reactor environmental conditions. An extensive review of graphite materials as they relate to application, selection, and qualification; the available graphite grades and properties; and operational considerations was conducted for the Next Generation Nuclear Plant project [1], which provides details and a comprehensive background and overview.
This section provides the basis for the code and a typical design sequence for a graphite core component. Because there is not a standardized graphite grade for nuclear applications, the code places the responsibility for determining the design properties of the graphite used on the core designer. The approved properties for the selected graphite grade are then determined through material testing and listed in the form of a materials data sheet [4]-[6], which is used to justify the design. Previous studies [7], [8] determined that variations of the Weibull distribution best describe the graphite reliability curve. HHA-II-3000 [9] describes how to statistically characterize graphite material based on specimen test results so that a material reliability curve can be derived. The approach is supported by many other studies [10]-[17]. To perform a stress-based analysis, the rules derive an equivalent stress state (from a multiaxial stress analysis) to determine the peak equivalent stress for a component for a given load condition. In general, parts are designed by comparing calculated stresses to strength limits based on specimen test results and adequate design margins. But in the case of graphite, fixed design margins do not ensure uniform reliability because of the variability in the material. The stochastic strength (large random fluctuations from the population mean) and the nonlinear stress-strain response (quasi-brittle) of graphite [18], as well as billet-to-billet variation [19], require that the material be statistically characterized. That characterization is then used to determine the design margin [20], [21]. The identified modes of failure for graphite are brittle fracture, fatigue, excessive deformation (including both elastic instability and irradiation-induced dimensional changes) and environmental effects such as irradiation and chemical attack.