Analysis of the Technological Evolution of Materials Requirements Included in Reactor Pressure Vessel Manufacturing Codes

Abstract

The growth of green energy technologies within the frame of the 7th Sustainable Development Goal (SDG) along with the concern about climatic changes make nuclear energy an attractive choice for many countries to ensure energy security and sustainable development as well as to actively address environmental issues. Unlike nuclear equipment (immovable goods), which are often well-catalogued and analyzed, the design and manufacturing codes and their standardized materials specifications can be considered movable and intangible goods that have not been thoroughly studied based on a detailed evaluation of the scientific and technical literature on the reactor pressure vessel (RPV) materials behavior. The aim of this work is the analysis of historical advances in materials properties research and associated standardized design codes requirements. The analysis, based on the consolidated U.S. Nuclear Regulatory Commission (NRC) Regulatory Guide (RG) 1.99 Rev.2 model, enables determination of the best materials options, corresponding to some of the most widely used material specifications such as WWER 15Kh2MFAA (used from the 1970s and 1980s; already in operation), ASME SA-533 Grade B Cl.1 (used in pressurized water reactor-PWR 2nd–4th; already in operation), DIN 20MnMoNi55 and DIN 22NiMoCr37 (used in PWR 2nd–4th) as well as ASTM A-336 Grade F22V (current designs). Consequently, in view of the results obtained, it can be concluded that the best options correspond to recently developed or well-established specifications used in the design of pressurized water reactors. These assessments endorse the fact that nuclear technology is continually improving, with safety being its fundamental pillar. In the future, further research related to the technical heritage from the evolution of materials requirements for other clean and sustainable power generation technologies will be performed.

Multicriteria Analytical Model for Mechanical Integrity Prognostics of Reactor Pressure Vessels Manufactured from Forged and Rolled Steels

“…Nanoscale microstructures induced by irradiation obstruct the migration of dislocations, and this interaction prevents plastic deformation and induces steel embrittlement [27]. Neutron irradiation degrades the mechanical properties of RPV steels, and the extent of the degradation is determined by the type and structure of the steel and other factors such as neutron fluence, irradiation temperature, neutron fluence and chemical composition [8,26,27]. At the reactor operating temperature, the vessel material exhibits a ductile behavior.…”

“…The material, therefore, would be susceptible to experiencing brittle fracture when K r > 1, and it can suffer collapse if L r is greater than 1. The standardized requirements for chemical composition of materials [8] analyzed are shown in Table 2. They are necessary to obtain the potential ∆RT DBT based on materials' chemical requirements and the irradiation and temperature conditions using the calculation parameters indicated in Table 1.…”

“…RPVs are made up of a cylindrical body and a hemispherical bottom and lid. The body and hemispheres are made up of rings that, in turn, are made up of curved and vertically welded sheets, although in some of the more recently manufactured vessels, there has been an attempt to avoid welding, for which complete forging pieces are manufactured [8]. The RPV is made up of special ferritic steels internally cladded with stainless steel.…”

“…The surveillance capsules are periodically removed in order to test the specimens, which allows us to know in advance the state of the material that makes up the vessel. The capsules include tensile, Charpy impact and fracture toughness specimens, as well as the instrumentation necessary to monitor neutron fluence and temperature [8]. Traditional material research relies on a considerable amount of experimental trial designs, which are time-consuming and costly [39].…”

Evolution of Standardized Specifications on Materials, Manufacturing and In-Service Inspection of Nuclear Reactor Vessels

“…While all nuclear equipment (immovable goods) is often well catalogued and analyzed, manufacturing and in-service inspection codes and their standardized material specifications (movable and intangible goods) have not been thoroughly studied based on a detailed evaluation of the technical heritage made up of the scientific and technical literature on the behavior of RPV materials [19], comparing regulated criteria. The radiation degradation of nuclear design materials limits the operational lifetime of all nuclear installations or at least decreases its safety margin.…”