The NGNP, which is an advanced HTGR concept with emphasis on both electricity and hydrogen production, involves helium as the coolant and a closed-cycle gas turbine for power generation with a core outlet/gas turbine inlet temperature of 900-1000°C. In the indirect cycle system, an intermediate heat exchanger is used to transfer the heat from primary helium from the core to the secondary fluid, which can be helium, nitrogen/helium mixture, or a molten salt. The system concept for the VHTR can be a reactor based on the prismatic block of the GT-MHR developed by a consortium led by General Atomics in the U.S. or based on the PBMR design developed by ESKOM of South Africa and British Nuclear Fuels of U.K.This report has reviewed the available information on candidate materials for the construction of RPV and has made a preliminary assessment of several relevant factors to make a judicious selection of the material for the RPV. Some of the factors addressed in this report are availability of commercial alloys for RPV application, their status in ASME Codes for nuclear service, ASME code compliance during steady state and depressurized conduction cooling conditions, baseline mechanical properties, effects of thermal aging on mechanical properties and code compliance over long term, fabrication and welding issues, global assessment of availability/capability of vendors for RPV procurement, and technology gaps in our knowledge base to address some of the technical issues. The assessment included three primary candidate alloys namely, low alloy steel SA508 (UNS K12042), Fe-2.25Cr-1Mo-0.25V steel (UNS K31835), and modified 9Cr-1Mo steel (UNS K90901) for the RPV. Several conclusions were drawn from this assessment:Baseline Mechanical Properties: There is sufficient database available for the mechanical properties of SA-508 steel. There is limited data available on the thermal aging effects on the mechanical properties and additional information needs development on the long-term aging effects. The steel is approved for use up to 371°C (700°F) under the ASME Code. At present no data is available on the effects of impure helium on the long-term corrosion and mechanical properties of the material.There is adequate tensile data on the Fe-2.25Cr-1Mo-0.25V in the temperature range of interest in NGNP RPV. There is only limited creep data available for the steel and additional data are needed, especially at elevated temperatures that encompass depressurized conduction cooldown conditions. However, substantial data on the creep fatigue properties, thermal aging affects on the mechanical properties, performance characteristics in impure helium, and properties of thick section material are needed prior to its selection for NGNP RPV. Furthermore, the steel is approved under ASME Code Section VIII (for non nuclear applications) and is not approved under Section III for use in nuclear systems.Substantial database on the baseline mechanical properties is currently available for the Modified 9Cr-1Mo steel. Sufficient data are also avail...

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